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ExxonMobil Research and Engineering Company – Fairfax, VA
FRACTIONATING TOWERS
VALVE TRAYS EXXON ENGINEERING
DESIGN PRACTICES Section
Page
III-E
1 of 69
Date PROPRIETARY INFORMATION - For Authorized Company Use Only
December, 1998 Changes shown by ç
CONTENTS Section
Page
SCOPE ............................................................................................................................................................ 4 REFERENCES ................................................................................................................................................ 4 INTERNATIONAL PRACTICE ................................................................................................................ 4 OTHER LITERATURE ............................................................................................................................ 4 BACKGROUND .............................................................................................................................................. 4 DEFINITIONS / EQUATIONS.......................................................................................................................... 4 APPLICATION ................................................................................................................................................ 4 CARTRIDGE TRAYS .............................................................................................................................. 6 BASIC DESIGN CONSIDERATIONS ............................................................................................................. 6 VAPOR CAPACITY LIMITATIONS ......................................................................................................... 6 LIQUID CAPACITY LIMITATIONS.......................................................................................................... 8 Downcomer Design Considerations ..................................................................................................... 8 OTHER BASIC DESIGN CONSIDERATIONS ...................................................................................... 10 DETAILED DESIGN PROCEDURE .............................................................................................................. 11 VAPOR AND LIQUID LOADINGS (STEP 1) ......................................................................................... 11 TRIAL TRAY SPACING, SIZE AND LAYOUT (STEP 2)....................................................................... 11 FINAL TRAY SPACING, SIZE AND LAYOUT (STEP 3)....................................................................... 13 OPEN AREA, PRESSURE DROP AND TURNDOWN (STEP 4).......................................................... 13 Drawing Notes.................................................................................................................................... 16 TRAY HYDRAULICS AND DOWNCOMER FILLING (STEP 5) ............................................................ 16 CHECKING PROCESS LIMITATIONS (STEP 6).................................................................................. 17 TRAY EFFICIENCY (STEP 7)............................................................................................................... 17 BALANCED DESIGN (STEP 8) ............................................................................................................ 17 TOWER CHECKLIST (STEP 9) ............................................................................................................ 17 NOMENCLATURE ........................................................................................................................................ 18 COMPUTER PROGRAMS ............................................................................................................................ 20 AVAILABLE PROGRAMS ............................................................................................................................ 20 VALVE TRAY CALCULATION FORM (CUSTOMARY) ............................................................................... 47 VALVE TRAY CALCULATION FORM (METRIC)......................................................................................... 59
EXXON RESEARCH AND ENGINEERING COMPANY - FLORHAM PARK, N.J.
DESIGN PRACTICES Section
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III-E
FRACTIONATING TOWERS
VALVE TRAYS
2 of 69
Date December, 1998
PROPRIETARY INFORMATION - For Authorized Company Use Only
EXXON ENGINEERING
CONTENTS (Cont) Section TABLES Table 1 Table 2 Table 3A Table 3B Table 3C Table 4A Table 4B FIGURES Figure 1A Figure 1B Figure 1C Figure 1D Figure 2 Figure 3 Figure 4A Figure 4B Figure 5A Figure 5B Figure 6 Figure 7 Figure 8A Figure 8B Figure 8C Figure 8D Figure 8E Figure 8F Figure 8G Figure 8H Figure 9A Figure 9B Figure 9C Figure 10 Figure 11
Page
Valve Tray Design Principles (Metric Values Shown in Parentheses) ........................... 21 Design Criteria for Specific Towers................................................................................ 24 Common Valve Types Offered by Major U.S. Vendors.................................................. 25 Koch-Glitsch Valves – Dimensions and Open Area ....................................................... 26 Dry Tray Pressure Drop Coefficients for Valve Trays .................................................... 27 Standard Nutter Package Tray Data (Customary Units) ................................................ 28 Standard Nutter Package Tray Data (Metric Units)........................................................ 29
KHL Factors for Jet Flood Equations Hydrocarbon Systems (Customary Units) ............ 30 KHL Factors for Jet Flood Equations Aqueous Systems (Customary Units)................... 30 KHL Factors for Jet Flood Equations Hydrocarbon Systems (Metric Units).................... 31 KHL Factors for Jet Flood Equations Aqueous Systems (Metric Units) .......................... 31 Standard Surface Tension, σSTD (Same for Customary and Metric Units)..................... 32 Kσµ Factor for Jet Flood Correlation (Same for Customary and Metric Units) ............... 33 Allowable Downcomer Inlet Velocity (Customary Units) ................................................ 33 Allowable Downcomer Inlet Velocity (Metric Units) ........................................................ 34 Allowable Downcomer Filling for Valve Trays All Systems Not Covered in Table 2 (Customary Units) .......................................................................................................... 35 Allowable Downcomer Filling for Valve Trays All Systems Not Covered in Table 2 (Metric Units).................................................................................................................. 35 Sieve and Valve Tray Efficiency Comparison (Tray Efficiency vs. Vapor Rate at Total Reflux)................................................................................................................... 36 Valve Tray Turndown Diagram (For Tray With Two Different Valve Weights) ............... 37 Vapor Energy Parameter PVE (Customary Units)........................................................... 38 KVE Factor (Customary Units)........................................................................................ 38 Vapor Energy Parameter PVE (Metric Units) .................................................................. 39 KVE Factor (Metric Units) ............................................................................................... 39 KW Factor (Customary Units)......................................................................................... 40 Froth Density (Ψ) (Customary Units).............................................................................. 40 KW Factor (Metric Units) ................................................................................................ 41 Froth Density (Ψ) (Metric Units) ..................................................................................... 41 Valve Hole Variations..................................................................................................... 42 Koch-Glitsch Valves....................................................................................................... 43 Norton Valves ................................................................................................................ 44 Nutter Movable Valves – Dimensions and Open Area ................................................... 45 Nutter Fixed Valves – Dimensions and Open Area........................................................ 46
EXXON RESEARCH AND ENGINEERING COMPANY - FLORHAM PARK, N.J.
FRACTIONATING TOWERS
VALVE TRAYS EXXON ENGINEERING
DESIGN PRACTICES Section
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December, 1998
CONTENTS (Cont) Revision Memo 12/98
Highlights of this revision are: 1. Updated references. 2. Recommended using the sieve tray correlations for spray/froth transition, entrainment, and weeping to check valve tray performance. 3. Information on the various types of valve trays from the leading vendors has been included, i.e., description, dimensions, open area. 4. Operating limits for valve trays have been added. 5. New guidelines for low liquid rate tray design have been added. 6. The methods for calculating valve tray open area have been updated. 7. The section on computer programs has been updated. 8. Corrected 8 gage thickness. 9. Updated dry tray pressure drop coefficients. 10. Mentioned other vendors as possible valve tray suppliers. 11. Revised design drawing notes. 12. Indicated V-Grid valves on Nutter Package trays are SVG valves. 13. Included design criteria for ACN extractive distillation systems.
EXXON RESEARCH AND ENGINEERING COMPANY - FLORHAM PARK, N.J.
DESIGN PRACTICES Section
VALVE TRAYS
Page
III-E
FRACTIONATING TOWERS
4 of 69
Date PROPRIETARY INFORMATION - For Authorized Company Use Only
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EXXON ENGINEERING
SCOPE This section covers the techniques for specifying or rating the process design features of valve trays for new designs or revamps. It is assumed that the designer has already read Section III-A (Device Selection and Basic Concepts) and determined that valve trays are the best choice for the design. Detailed mechanical design as well as beam and valve layout are normally handled by the tray fabricator. A calculation form, showing the step-by-step calculation procedure, is given at the end of this section. Computer Programs 1134 and 1143 are available to perform these calculations rapidly (see discussion under Computer Programs later in this section). A list of FRACTIONATION SPECIALISTS to contact for help is provided at the beginning of Section III. For the design of tray-related tower internals, such as nozzles, drawoff boxes and reboiler connections, refer to Section III-H, Tower Internals. For the design of heat transfer trays, see Section III-F. To calculate tray efficiency, see Section III-I.
REFERENCES Some of the following literature has been used in the preparation of this section. The rest is listed for convenient reference. ç
INTERNATIONAL PRACTICE IP 5-2-1,
Internals for Towers, Drums, and Fixed Bed Reactors
OTHER LITERATURE ç ç ç
1. 2. 3. 4. 5.
Becker, P. W., Sieve Tray Capacity Correlations Have Been Improved, Report No. EE.76E.72, June, 1972. Bell, A. M., Nutter V-Grid Trays, 93CET211 (August 13, 1993). Kokoska, R. J. and Perry, D., Downcomer Capacity Correlations Have Been Improved, Report No. EE.49E.80 June, 1980. Niedzwiecki, J. L., Computer Program Update, Sieve Tray Design Program #1133, CPEE-0009, January, 1990. Niedzwiecki, J. L., Computer Program Update, Valve Tray Rating/Design Program #1134, CPEE-0013, October, 1990.
BACKGROUND ç
The equations given in this section for predicting valve tray capacity, downcomer limitations and clear liquid height are identical to those used for sieve trays. The turndown and dry tray pressure drop equations, however, are specific to valve trays. They have been derived largely from Fractionation Research, Inc., (FRI) data, supplemented by data from simulator and commercial tests. These equations represent the data far more accurately than do the correlations prepared by FRI, various vendors, or those available in the literature. Sieve tray correlations for entrainment, spray/froth transition, and weeping should be used to check valve tray performance until similar correlations for valve trays are available.
DEFINITIONS / EQUATIONS For a discussion of such concepts as jet flooding, efficiency, flexibility, etc., see Section III-A, Device Selection and Basic Concepts. See the Nomenclature section for symbol definitions. All equations in the text of this section are numbered in the same way as they appear on the Valve Tray Calculation Forms. Those equations not discussed in the text are shown in the appropriate section of the Valve Tray Calculation Forms. Wherever possible both the customary and the metric equations are shown in the text, the latter shown with an “M.” However, if the equation is complex, the metric version has been omitted in the text for clarity but can be found on the Valve Tray Calculation Form (Metric).
APPLICATION For most towers, sieve trays with 2/1 or 3/1 flexibility are normally adequate and should be used. If greater flexibility is required, valve trays can be specified. Several examples of services requiring wide flexibility are: •
When vapor rates change appreciably (and often unpredictably) over a given section of a tower.
•
When a tower is utilized in blocked operation at varying rates and/or feed compositions.
•
When seasonal fluctuations in feed rate, customer demand, etc., necessitate operating a tower at very low rates (less than 30% of design).
•
When servicing of auxiliary equipment necessitates operating the entire unit at low rates.
EXXON RESEARCH AND ENGINEERING COMPANY - FLORHAM PARK, N.J.
DESIGN PRACTICES
FRACTIONATING TOWERS
VALVE TRAYS EXXON ENGINEERING
Section
Page
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December, 1998
APPLICATION (Cont) ç
ç
ç
ç
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Valve trays contain proprietary devices. Exxon has commercial and/or FRI experience with certain valves manufactured by Koch-Glitsch Inc., Norton, and Nutter Engineering. The valve size, shape, weight and other parameters vary from vendor to vendor (see Tables 3A and 3B and Figures 9A, 9B, 9C, 10 and 11). For design purposes the capacity and peak efficiency of valve trays recommended in this section are assumed to be about equal to that of a sieve tray, but their cost is roughly 10% higher. At times the cost difference between valve trays and sieve trays is negligible and valve trays would be preferred to maximize flexibility. There are various other vendors who make trays with proprietary valve units (e.g., Metawa (Sulzer) and Baretti). If valve trays from these vendors are being considered consult your FRACTIONATION SPECIALIST for Exxon commercial experience. Fixed valve trays can best be described as valve trays whose valve units are fixed in the fully open position (e.g., Glitsch V-O, Nutter V-Grid). The flexibility or turndown of such devices is generally better than that of a sieve tray, e.g., fixed valve trays have a turndown ratio of 3/1, but not as good as that of a movable valve tray. Also, fixed valve trays are generally less expensive than movable valve trays. Nutter Engineering's Small V-Grid (SVG) trays on triangular pitch are considered to be an alternative to sieve trays and generally have somewhat better turndown ratio (20% higher). Fixed valve trays may be useful for extending run lengths in some fouling services (but not where sticky material is entrained from below). Nutter Engineering's Larger V-Grid (LVG) and fixed valve trays on square pitch have lower capacity and should only be used upon consultation with a FRACTIONATION SPECIALIST. The Nutter Mini V-Grid (MVG) tray contains fixed mini-valves (Figure 11). At pressures under 50 psia (345 kPa), a well designed Nutter MVG tray has less liquid entrainment and possibly 10 - 15% jet flood capacity advantage when compared to a conventional sieve tray with approximately the same efficiency. Contact your FRACTIONATION SPECIALIST for more details if an application of fixed mini-valve trays is being considered. If Nutter valve or V-Grid trays are used, only small valve (BDH), small V-Grid (SVG), or MVG units on triangular pitch are acceptable. When revamping Nutter trays having large valve (BDP) or V-Grid (LVG) units, or if the units are on rectangular pitch, consult your FRACTIONATION SPECIALIST since these configurations may have less capacity than recommended designs. Valve trays are not recommended for fouling, corrosive, or coking service, such as steam cracker light ends debutanizers, visbreaker fractionators, and for these services, sieve trays are preferred. If severe coking is anticipated, shed baffles or disc and donuts should be used. Figure 6 illustrates the effect of vapor rate on the efficiency of typical valve trays and compares this behavior with that of similar sieve trays with the same downcomer sizes, tray spacing, and outlet weir heights. As can be seen from this figure, the valve tray usually maintains high efficiency over a much wider range of vapor rates than does the sieve tray. However, details of the sieve and valve tray designs and the operating pressure can affect the efficiency, capacity and turndown of the tray. The table below, which is based on operating experience, lists the lower and upper operating limits for most valve tray designs. If your case does not fall within these limits, contact your FRACTIONATION SPECIALIST to see what, if any, problems may exist. VARIABLE
LOWER LIMIT
UPPER LIMIT
Pressure, psia (kPa)
3 (21)
450 (3100) distillation 900 (6200) absorption
Temperature, °F (°C)
-130 (-90)
800 (430)
Diameter, ft (mm)
1.0 (300)
45 (13,700)
1 (1) 0.05 (.05) 0.005 (.08) 20 (320)
75 (75) 10 (10) 5 (80) 80 (1300)
12 (300)
36 (910)
Physical properties surface tension, dyne/cm (mN/m) liquid viscosity, cP (mPa•s) vapor density, lb/ft3 (kg/m3) liquid density, lb/ft3 (kg/m3) Tray spacing, in. (mm) Open Area as % of Ab
5%
18%
DC Clearance, in. (mm)
1 (25)
3.5 (90)
DC Inlet area as % of As
7%
40% sloped; 25% straight
Number of Passes Weir Height, in. (mm) Hole/slot size, in. (mm) Flow Path Length, in. (mm)
1
4
0 (0)
4 (100)
0.25 (6.4)
1.53 (39)
16 (410) for access
15 ft (4600 mm)
EXXON RESEARCH AND ENGINEERING COMPANY - FLORHAM PARK, N.J.
DESIGN PRACTICES Section
FRACTIONATING TOWERS
VALVE TRAYS
Page
III-E
6 of 69
Date December, 1998
PROPRIETARY INFORMATION - For Authorized Company Use Only
EXXON ENGINEERING
APPLICATION (Cont) CARTRIDGE TRAYS
ç
For small diameter towers [less than about 2.5 ft (750 mm) in diameter] it is frequently more convenient to have sets of trays prefabricated so they can be inserted into the shell. This eliminates the need for welding tray support rings in a tight area and facilitates maintenance. Several vendors offer these cartridge type trays; but Exxon’s experience shows that Nutter cartridge trays are superior to their competitor’s trays. This is because Nutter cartridge trays have metal piston-type seal rings, which provide a much better circumferential seal than other devices marketed. Cartridge trays require more diameter than conventional trays due to waste area. Also, cartridge trays need a round tower with no interior welds/nozzles and a crane to properly install in a vessel. Standard Nutter cartridge trays are available for tower inside diameters ranging from 12.0 to 30.5 in. (305 to 775 mm). The tray panels may be equipped with Nutter BDH valves or Nutter SVG V-Grid units on triangular pitch. Sieve holes may also be used. Tables 4A and 4B give the vital information for each of Nutter’s standard cartridge tray packages. Note that the designer has the option of specifying any weir height, downcomer clearance, and tray spacing needed. The designer may also specify the number of BDH valves or V-Grid units per tray, as long as it is less than the maximum number listed in Table 4A or 4B. Note that Program 1134 cannot be used directly to design cartridge trays, since cartridge trays have waste area and frequently have unconventional (non-chordal) downcomers. The bubble area, downcomer area, and weir length (which is also the length under the downcomer except for the two sloped downcomer designs) listed in Table 4A or 4B should be used in the calculation form at the end of this section. The waste area should be calculated per Note 5 of Table 4A or 4B.
BASIC DESIGN CONSIDERATIONS The design procedure outlined later in this section requires either: a) the selection of a trial diameter and tray layout for new designs, or b) tray hardware details for revamps. The design is then checked against critical performance limitations including jet flooding, ultimate capacity, downcomer limitations, etc. These limitations, which are common to all types of trays, are discussed fully in Section III-A. Only those items requiring further explanation are discussed below.
VAPOR CAPACITY LIMITATIONS Jet Flooding - Occurs when the vapor rate is sufficiently high to “jet” liquid from a given tray to the tray above. It is the primary cause of tower flooding. It is a strong function of diameter and tray spacing and a lesser function of the number of liquid passes used. These relationships are discussed below. •
Tray Spacing - The optimum combination of diameter, tray spacing, and number of liquid passes is the one which minimizes total investment, subject to the limitations outlined under Detailed Design Procedure discussed later in this section. The optimum spacing usually lies between 18-24 in. (450-600 mm). While the 1134 program selects tray spacings at 3 in. (75 mm) intervals for convenience, the designer is free to use any tray spacing desired as long as it’s within the acceptable range (see Table 1).
•
Number of Liquid Passes - The vapor handling capacity of towers with high liquid rates can usually be increased by the use of multipass trays. Since multipass trays are more expensive than single pass trays, they can be justified only if their use reduces the overall tower cost. Generally, this means that a capacity advantage of at least 5 to 10% for multipass trays is required. However, each case must be studied on its own merits, since overall tower cost depends on many factors, including height, diameter, operating pressure and materials of construction. If the liquid rate is greater than 14 gpm/in. of weir/pass (35 dm3/s/m of weir/pass), the FRACTIONATION SPECIALIST should be consulted because of the lack of reliable design data above this liquid rate. More detailed selection criteria are given in Table 1. Specific guidelines for 3 and 4 pass trays are given in Table 5 of Section III-B. If the tower is limited by downcomer filling which cannot be reduced by other hardware changes, the use of multipass trays should also be considered.
•
Tower Diameter - The tower diameter must provide enough cross-sectional area to avoid both downcomer and jet flooding limitations. Downcomer sizing will be discussed later. The equations for jet flooding are given below. (The equation numbers are the same as those used on the Valve Tray Calculation Forms.)
EXXON RESEARCH AND ENGINEERING COMPANY - FLORHAM PARK, N.J.
DESIGN PRACTICES
FRACTIONATING TOWERS
VALVE TRAYS EXXON ENGINEERING
Section
Page
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Date PROPRIETARY INFORMATION - For Authorized Company Use Only
December, 1998
BASIC DESIGN CONSIDERATIONS (Cont) •
Jet Flooding Equations. For hydrocarbon systems: VL A f Allow
=
0.296 KHL Kσµ
(Customary)
Eq. (3c4)
=
0.090 KHL Kσµ
(Metric)
Eq. (3c4)M
=
0.204 KHL Kσµ
(Customary)
Eq. (3c5)
=
0.0622 KHL Kσµ
(Metric)
Eq. (3c5)M
For aqueous systems: VL A f Allow
where: VL
=
Af
=
KHL =
ρv Vapor load, ft3/s (m3/s) at conditions = qv ρL − ρv
0.5
.
Average free area, ft2 (m2). See Section III-A, Figure 13. For two pass trays, both passes must be checked. Tray spacing - liquid rate factor, dimensionless [Figure 1A for Eq. (3c4) and Figure 1C for Eq. (3c4)M, Figures 1B for Eq. (3c5) and Figure 1D for Eq. (3c5)M]. When checking a two pass tray with inboard downcomers, the liquid rate, L, should be based on the inboard weir length I* . The outboard pass should be based on I . o
o
Kσµ qv ρv ρL
= = = =
Surface tension - viscosity factor, dimensionless (Figures 2 and 3). Volumetric vapor rate, ft3/s (dm3/s) at conditions. Vapor density at conditions, lb/ft3 (kg/m3). Liquid density at conditions, lb/ft3 (kg/m3).
Equation (3c4) should be used for all hydrocarbon systems and for other systems when the surface tension is equal to or less then 40 dynes/cm (mN/m). Equation (3c5) should be used for aqueous systems and whenever surface tension is greater than 40 dynes/cm (mNm). If a predominantly aqueous system has a surface tension equal to or less than 40 dynes/cm (mN/m) (e.g., alcohol/water), Equation (3c4) should be used. The following list outlines which equation to use for various systems. Any systems known to foam should be designed for 60% of the allowable jet flood velocity for that system. However, if the system is listed in Part 3 of Table 2, use that value. If in doubt, contact your FRACTIONATION SPECIALIST. EQUATION (3c4)
EQUATION (3c5)
All hydrocarbon light ends towers
Absorption of HCI, H2SO4, etc. in water
All sidestream and bottoms strippers
Amine and FLEXSORB scrubbers and regenerators
Aqueous systems containing alcohols, ketones, aldehydes, etc., if surface tension < 40 dynes/cm (mN/m)
Ammonia fractionators
Other non-aqueous chemical plant towers (i.e., oxo-alcohols, butyl rerun, etc.)
Catacarb absorbers and regenerators
Aromatics separations
Caustic scrubbers
Atmospheric and vacuum pipestills
Sour water strippers
Cat, steam cracker, coker, FLEXICOKER, and HYDROCRACKER primary fractionators above the bottom pumparound
Water wash sections
Hydrocarbon absorbers
Foaming aqueous systems
Prefractionators and outboard flash towers
Other aqueous liquid/steam stripped towers
EXXON RESEARCH AND ENGINEERING COMPANY - FLORHAM PARK, N.J.
DESIGN PRACTICES Section
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VALVE TRAYS
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EXXON ENGINEERING
BASIC DESIGN CONSIDERATIONS (Cont) In addition, the above equations must be used in conjunction with the appropriate percentage of the jet flood velocity permitted by Table 2. Ultimate Capacity. The ratio of design vapor load (VL) to the vapor load for ultimate capacity VL(Ult) Eq. (6a1) must be kept below 90%. If necessary, the tower diameter must be increased, even though Equation (3c4) or (3c5) has already been satisfied for jet flooding. However, the diameter calculation from Equation (3c4) or (3c5) usually provides sufficient free area to satisfy the ultimate capacity limitation. VL(Ult )
0.25
β σL = 0.62 A f 1 + β ρL − ρv
ρ − ρv where: β = 1.4 L ρv
(Customary)
Eq. (6a1)
0.5
For the metric equation Eq. (6a1)M, use a coefficient of 0.378 vs. the 0.62 shown above.
LIQUID CAPACITY LIMITATIONS Downcomer Design Considerations 1.
Downcomer Sizing - The required downcomer inlet area is set by froth disengaging limitations. This calculated velocity is a function of the froth density ( ψ ) and the physical properties of the system and therefore varies from system to system. Figures 4A & 4B or Table 2 provide the maximum allowable downcomer entrance velocity for most systems. However, if the ratio of ρV / ρL is greater than 0.03 then a velocity should be calculated from Eq. (6c1) below. The same equation is valid for customary or metric units. The designer should compare this value versus that obtained from Figure 4A, 4B or Table 2 and use the lower velocity.
Vdi =
Ψ VL(Ult ) 1 − Ψ ρv Af ρL − ρv
where: Ψ
=
0.5
Eq. (6c1)
Froth density, fraction of froth volume occupied by liquid, dimensionless. For two pass trays, use the smaller value of Af.
For foaming systems a velocity of 0.2 ft/s (0.06 m/s) should be used. However, if the foam is very stable, even a very low velocity still may not prevent tower flooding. If the designer expects to face this situation, then a. Process changes should be considered to eliminate the source of the foaming (removal of entrained hydrocarbons into aqueous systems, elimination of suspended solids, etc.) b. Consider using packing and consult your FRACTIONATION SPECIALIST. c. If the foam source can’t be eliminated, then an anti-foam agent may be required. This is usually an expensive solution to the problem since anti-foam must be added continuously. Downcomer inlet sizing should also be checked for a possible choking limitation. The choking criterion is defined as a limiting froth height to downcomer inlet rise ratio as shown below: •
For outboard downcomers hf − h wo must be ≤ 1.0 1.3r
•
Eq. (6d1)
For inboard downcomers hf − h wo must be ≤ 1.0 1.6 (r / 2)
If the above ratio > 1.0, the downcomer rise should be increased.
EXXON RESEARCH AND ENGINEERING COMPANY - FLORHAM PARK, N.J.
Eq. (6d2)
FRACTIONATING TOWERS
VALVE TRAYS EXXON ENGINEERING
DESIGN PRACTICES Section
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BASIC DESIGN CONSIDERATIONS (Cont)
2.
3.
When the liquid velocity entering the downcomer is greater than the velocity of the bubbles rising through it, vapor recycling occurs. The vapor cannot disengage and this results in vapor being swept through the downcomer and recycled onto the tray below. Thus, vapor recycling will cause an increase in the vapor load leaving a tray and will adversely affect both tray capacity and efficiency. Therefore, for both new designs and revamps, the downcomer size should be increased to avoid vapor recycle. See Section III-A for more background on vapor recycling. Downcomer sloping criteria are discussed under Detailed Design Procedure - Step 2 - Downcomer Area. Areas and lengths of chords are given in Section III-K. Downcomer Filling - Downcomer filling as a percentage of tray spacing, should not exceed the values in Figure 5A or 5B. For hydrocarbon and aqueous systems that are known to foam, use 80% of the value given in Figure 5A or 5B. In addition, special downcomer filling criteria for specific aqueous towers are listed in Table 2. If these criteria cannot be met by reducing the weir height, increasing the downcomer clearance, etc., the tray spacing, and/or the number of liquid passes should be increased. Downcomer Clearance - Downcomer clearance (c) is the vertical distance between the bottom edge of the downcomer and the tray deck. This clearance should be no smaller than 1 in. (25 mm) and is based on a normal head loss (hud) of 0.5 to 1.5 in. (13 to 38 mm) of hot liquid, according to the submerged weir formula given below. This range was chosen to avoid excessive liquid velocity at the tray inlet. hud
hud
1000 QL = 160 c Np lud
where: QL Np lud
4.
2
Q L = 0.06 c Np lud
= = =
(Customary)
2
(Metric)
Eq. (5d1)M
Liquid rate, gpm (dm3/s) at conditions Number of liquid passes Length of bottom edge of downcomer, in. (mm)
In those cases where high liquid rates would require use of either a large downcomer clearance [over 3 in. (75 mm)] or a deep recessed inlet box, a shaped downcomer lip may be used instead (see figures in Section III-A). For these shaped lip downcomers, the coefficient in Equation (5d1) is reduced from 0.06 to 0.02 (160 to 53 for metric equation). However, a shaped downcomer lip must not be used when either a recessed inlet box or an inlet weir has been specified. This is because the obstruction presented by the vertical face of the recessed inlet box, or by the inlet weir, would cause turbulence and defeat the purpose of the shaped downcomer lip. The clearance with a shaped lip should also be set so as not to exceed 1.5 in. (38 mm) of head loss. For two pass trays, a shaped lip is usually used on both inboard and outboard passes. Downcomer Sealing - To prevent some of the vapor from bypassing a tray by traveling up the downcomer, the downcomer must be sealed at minimum rates by the liquid on the tray below. Therefore, it is necessary to check the sum of the clear liquid height at the inlet to the tray or tray inlet head (hi) and the head loss under the downcomer (hud) at the minimum liquid flow rate. This sum plus 1/4 in. (6 mm) must be at least equal to the downcomer clearance. If a seal is not obtained, consider: •
Increasing the outlet weir height.
•
Reducing the clearance to 1 in. (25 mm) provided the downcomer filling is not exceeded at design rates.
•
Using a shaped downcomer lip if a wide range of rates must be handled. Do not use if a recessed box or inlet weir has already been specified.
•
Adding an inlet weir.
•
5.
Eq. (5d1)
Using a recessed inlet box provided the liquid rate is below 11 gpm/in. of diameter/pass (28 dm3/s/m of diameter/pass). Note that designing near the high end of the head loss range may unnecessarily increase downcomer filling if a higher clearance will still seal the downcomer. Therefore, there is no justification for setting downcomer clearance any lower than that required for downcomer sealing. See discussion and figures in Section III-A for more background. Anti-jump Baffles - Must be provided on all inboard downcomer(s) of multipass trays if the liquid rate exceeds 4.2 gpm/in. of diameter/pass (10 dm3/sec/m of diameter/pass). This is to prevent liquid from jumping across (choking) the downcomer and causing premature flooding (see Section III-A for further background information on downcomer choking).
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BASIC DESIGN CONSIDERATIONS (Cont) OTHER BASIC DESIGN CONSIDERATIONS Tray Layout, Hole Area, and Valve Layout - Two important features of the tray layout are the bubble area Ab and the free area Af (see Figures 12 and 13 in Section III-A). These, in turn, depend on the liquid handling areas (downcomers) and waste area Aw, defined as any unperforated area farther than 3 in. (75 mm) from the edge of the nearest perforation. Normally, there is no waste area on a valve tray unless a very low hole area is required (part of the tray is left unperforated). However, due to their unique construction, cartridge trays have a significant amount of waste area. For these trays, refer to Tables 4A or 4B for the method to calculate Aw. Methods of specifying open area or valve area on a tray are discussed under Detailed Design Procedure, Step 4. For new designs, the designer need not concern himself with valve layout, since the vendor normally handles this detail. However, for Nutter trays, be sure that only small valve or V-Grid units are used and that they are on triangular pitch.
ç
ç
In general, low open area trays have higher pressure drops, somewhat higher efficiencies, and greater flexibility. A good first guess at open area would be 12% Ao / Ab. If downcomer filling becomes excessive, tray spacing should be increased in preference to using a higher open area tray. If further measures are required to lower tray pressure drop or downcomer filling, then higher open areas may be used (up to 18%). However, it should be recognized that flexibility will be reduced. The valve tray vendor should be told to check the final layout for a “blowing limitation.” Glitsch’s blowing criteria are described under Detailed Design Procedure, Step 4. Tray Hydraulics - The final dry tray pressure drop will generally fall in the range of 1 to 4 in. (25 to 100 mm) of hot liquid. The effect of increasing dry tray pressure drop (reducing open area) on tray hydraulics and downcomer filling can be calculated from Eq. (4a1) or (4a2) on the calculation form. Downcomer filling, as a percent of tray spacing, should not exceed the values given as a function of pressure in Figure 5A or 5B. In addition, special downcomer filling criteria for aqueous towers are given in Table 2. If downcomer filling is excessive, the tray spacing and/or the tower diameter should be increased. Tray Turndown - Turndown is the ratio of the maximum to minimum vapor loadings between which good tray efficiency is maintained. It is limited by jet flooding (excessive entrainment) at high vapor rates and by excessive weeping at very low vapor rates. The maximum turndown ratio for fixed valve trays is typically 3/1. A turndown ratio of between 3/1 and 4/1 is usually achievable with movable valve trays. If a very large turndown is required (about 5 to 1), more expensive two-stage opening valves are typically required. Turndown requirements are dictated by combining two effects. The first is operating turndown and the second is the inherent variation in the loading profile over a tower section. If this loading variation is significant and the trays cannot meet the required turndown, consider breaking the original tower section into two (or more) smaller sections. If this reduces the loadings range to an acceptable level, develop a tray design for each of the new smaller sections. Tray Mass-Transfer Efficiency and Heat Transfer - The designer should recognize that efficiency calculations are necessary for each section in a fractionation tower. In addition, the trays selected to check hydraulics are sometimes not suited for efficiency calculations due to concentration profile reversals or for other reasons. See Sections III-I and F for more information on tray mass-transfer efficiency and heat transfer respectively. Low Liquid Rate Tray Design - When designing a tray to operate at a low liquid rate, it may become necessary to modify the tray design in order to decrease the excessive entrainment that often occurs under low liquid loads. On valve trays, entrainment can be reduced by increasing the valve area. Since a valve tray also provides good low-loading flexibility, turndown ratios of 2 to 1 or more can usually be maintained for low liquid rates. This compares favorably to the sieve tray where turndown is severely restricted at low liquid rate. If the liquid rate, L, lies between 0.25 to 1.5 gpm/in. of weir/pass (0.6 to 3.7 dm3/s/m of weir/pass) the dry tray pressure drop, hed, at design rates should be equal or less than 2.25 in (57 mm). If L is less than 0.25 (0.6), contact your FRACTIONATION SPECIALIST since picket fence weirs and inlet weirs may be required. (See Section III-A and its discussion on the “Operating Window” for more background.) If the design liquid rate is ≤ 1.5 gpm/in. (3.7 dm3/s/m) of weir/pass at pressures under 50 psia (345 kPa), spray/froth transition, entrainment, and weeping may be a problem. Checks need to be done using the Sieve Tray Design Program #1133 since correlations for valve trays are not yet available. A hole size of 0.5 in. (13 mm) should be specified with an open area that gives a dry (sieve) tray pressure drop comparable to the valve tray prediction. If entrainment, spray/froth transition, or weeping exceed the recommended limits, consult with a FRACTIONATION SPECIALIST. The tray vendors may be able to provide guidance on valve tray weeping and entrainment predictions.
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BASIC DESIGN CONSIDERATIONS (Cont) Startup Considerations - At very low vapor velocities (such as during startup), even valve trays may weep, with the result that insufficient liquid is maintained on the tray feeding the reboiler drawoff box. Hence, when thermosyphon reboilers are used on valve tray towers, special provisions may be necessary to ensure that the reboiler will have liquid feed during startup. This can be done by either: •
Installing a jumpover line from the tower bottoms drawoff line to the reboiler inlet. The jumpover line must have a valve, so that it can be closed when the reboiler is generating enough vapor to support the liquid on the drawoff tray or
•
By providing a chimney tray as the drawoff tray. For the design of chimney trays, drawoffs and other tower internals, see Section III-H.
DETAILED DESIGN PROCEDURE The step-by-step procedure for designing or revamping a valve tray is given on the Valve Tray Calculation Form. A computer program (#1134) is available to perform these calculations. See discussion under Computer Programs later in this section. For new designs, the procedure involves assuming a trial design with the help of the principles given above, checking it against various potential operating limitations, and then modifying it as required to arrive at the optimum tray design. For revamps, all of the tower hardware is given. It must be checked against the various potential operating limits and modified as required. Deciding how to modify the various hardware parameters will require judgment and application of the basic design considerations already discussed as well as those contained in Table 1. If help is needed, contact your FRACTIONATION SPECIALIST. The calculation step numbers used below correspond to those used on the calculation form.
VAPOR AND LIQUID LOADINGS (STEP 1) This information is normally calculated as part of the heat and material balance(s) for the tower and usually comes from a computer program like PRO/II or PROVISION. If minimum liquid and vapor loadings have not been specified, assume 33% of the design loadings. Vapor loadings are to the tray in question; liquid loadings are from the tray in question since these are nearly always the maximum values for the tray in question. However, the designer should be aware that loadings will occasionally increase significantly across a given theoretical tray. If this is the case and the overall efficiency is less than about 70%, the vapor loading from the tray in question may be higher. The designer must then prorate loadings between the loadings to and from the theoretical tray in question. In the case of bottoms and sidestream strippers for pipestills, guidelines are presented in Section III-I, Tray Efficiency, for 4 and 6 tray strippers. In the design of heavy hydrocarbon/steam strippers (e.g., pipestill sidestream and bottoms strippers), the tray hydraulics are normally checked for an assumed vapor rate to the top tray equal to the stripping steam rate plus 60 mole percent (for 4-tray strippers) of the total hydrocarbon vapor stripped out. Once the top tray is designed, lower trays may require modified designs due to the large decrease in vapor rate. The optimum design of trays for these strippers is detailed in Section III-I, Tray Efficiency.
TRIAL TRAY SPACING, SIZE AND LAYOUT (STEP 2) Tray Spacing - A low tray spacing between 18 and 24 in. (450 to 600 mm) is often the most economical. For the first trial, a tray spacing of 18 in. (450 mm) or that shown below (whichever is larger) should be used. The values given are the minima for most applications, as determined by maintenance considerations and support beam depth. In special cases, however, even smaller spacings may be justified (especially if the required number of trays can be contained in one shell vs. two), but this makes maintenance more difficult. On the other hand, downcomer filling requirements may require the use of tray spacings larger than the minimum. Spacings up to 36 in. (900 mm) may be used to permit a higher superficial vapor velocity.
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DETAILED DESIGN PROCEDURE (Cont) CLEAN SERVICE
FOULING SERVICE 1-pass
Tower Diameter, ft (mm) 5 or less (≤ 1500)
in. 12 V
mm 300 V
in. 18 V
mm 450 V
2 or more passes in. mm -----
> 5 to 8 (> 1500 to 2400)
12 V
300 V
21 V
525 V
18 V
450 V
> 8 to 10 (> 2400 to 3000)
15 V
375 V
24
600
21 V
525 V
> 10 to 20 (> 3000 to 6000)
18 V
450 V
27
675
24
600
greater than 20 (> 6000) V V
21 V
525 V
30
750
27
675
V
If there is no manhead between trays. Minimum tray spacing with a manhead present is 24 in. or 6 in. (600 mm or 150 mm) more than the manhead diameter, whichever is greater.
VV
For towers larger than 20 ft (> 6000 mm) in diameter, “lattice” type trusses must be used to facilitate maintenance and permit good vapor distribution. (See Section III-H for a picture of lattice truss.)
Trial Tower Diameter. The trial diameter (Dtr) is calculated from Eq. (2a4) on the calculation sheet. It may need to be adjusted either upward or downward when the trial design is checked against various performance limitations. Eq. (2a4) is a sieve tray capacity equation which has been verified with FRI and commercial valve tray data. It is the same equation used in Section III-B as Eq. (2a4). Number of Liquid Passes - The number of passes should be selected on the basis of the criteria given in Table 1. The number is not likely to change when the trial design is finalized, unless the tower diameter is changed substantially. The calculation sheet is designed to handle one and two pass trays. For three and four pass trays, refer to Table 5 in Section III-B and Program 1143. Note: Program 1143 will require some hand calculations since it is designed for use with sieve trays. Downcomer Areas - The maximum velocity of the liquid entering the downcomer(s) should be determined from Figures 4A & 4B, Eq. (6c1) or Table 2, whichever gives the lower value. For known foaming systems, a very low downcomer inlet velocity (about 0.2 ft/s; 0.06 m/s) should be used. There is no lower limit on the downcomer inlet velocity. However, if long liquid residence time in the downcomer promotes fouling, consider either the use of modified arc downcomers or sloping to reduce downcomer volume. When revamping vendor designed trays with swept back outlet weirs, the unperforated area between the weir and the downcomer should be considered as additional disengaging area for downcomer inlet velocity calculations. Consult your FRACTIONATION SPECIALIST should any questions arise on these rarely used trays. For a sloped or stepped downcomer, the downcomer outlet area is based on the following table: MAXIMUM Vdi
MAXIMUM Vdo
ft/s
m/s
< 0.3
< 0.09
> 0.3 and < 0.6
> 0.09 and < 0.18
> 0.6
> 0.18
ft/s
m/s
2 times maximum entrance velocity 0.6
0.18
Equal to Vdi (downcomers are straight)
As a general rule, a sloped or stepped downcomer should be used if Adi is greater than 12% of As. To ensure good liquid distribution to the tray below, however, the downcomer outlet area also must be at least 6.8% of As. This applies to all single pass trays and the outboard downcomer of multipass trays. This assures that the chord length is at least 65% of the tower diameter for chordal downcomers. If the tower diameter exceeds 6 ft (1800 mm) and the liquid rate requires a downcomer area much less than 6.8% of As, consider the use of a segmental downcomer (modified arc). If a segmental downcomer is used, it must be at least 6 in. (150 mm) wide. (See Section III-K, Figure 3, for sizing modified arc downcomers.) If the sum of Adi + Ado exceeds 60% of As, the tower diameter should be increased and both KHL and Af corrected. Remember that KHL is based on the liquid rate per in. (m) of weir length and will change if the diameter changes. In addition, for modified arc downcomers, use the projected weir length, not the total weir length. (See discussion in Section III-A on downcomers for more details.) This sets the downcomer areas to be used for the first trial. However, any changes in tower diameter made during the remainder of the design procedure could also necessitate changes in downcomer sizing. Outlet Weirs and Downcomer Clearances - Criteria for selecting outlet weir heights and downcomer clearances are given in Table 1. For tray geometry relationships, see Section III-K.
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DETAILED DESIGN PROCEDURE (Cont) FINAL TRAY SPACING, SIZE AND LAYOUT (STEP 3) Tower Area - To permit the trial design to be checked against the jet flooding and ultimate capacity limitations, the quantities listed under Step 3a on the calculation form must first be calculated, based on the trial design. Ultimate Capacity - The vapor load factor corresponding to ultimate capacity is calculated from Equation (6a1). The ratio of design to the ultimate capacity vapor rate must be kept below 90%. Jet Flooding - The allowable vapor load for jet flooding is calculated from Equations (3c4) and (3c5). The ratio of the design vapor load to that for jet flooding should not exceed the percentages recommended in Table 2. For systems not covered by Table 2, your FRACTIONATION SPECIALIST should be consulted for the proper value. Trays With Drawoff Sumps - A drawoff box generally creates waste area (Aw) on the tray and may also obstruct the flow of vapor from the tray below. This dictates a conservative design approach. The design criteria for such trays are outlined in Section III-H, Tower Internals.
OPEN AREA, PRESSURE DROP AND TURNDOWN (STEP 4) Open Area and Layout - The valve tray vendor should be told to check the final tray design for blowing. (Glitsch uses the criteria that blowing occurs when the dry tray pressure drop, in in. (mm) of hot liquid, exceeds 20% of the tray spacing.) Nutter proposals should be checked to ensure that only small valve or V-Grid units have been provided and that they are on triangular pitch. Turndown Requirements - There are many ways that valve tray vendors have to achieve the turndown ratio desired. The more important ones include: •
Using movable valves.
•
Using valves that have different thicknesses (weights). That is, have light and heavy valves in different rows or in some alternating pattern within the same row.
•
Using various ratios of light to heavy valves (i.e., 25% light; 75% heavy; 50/50, etc.).
•
Varying the number of valves per unit of contacting area or using valves with longer legs - thereby providing more slot area.
•
Placing a light and a heavy valve in the same retaining cage - like the Glitsch A-1. This produces a staged opening effect at each valve location. Such valves are, however, more expensive. It is important to recognize that each vendor has their own unique way of designing valve trays for a given turndown ratio. Thus, for new jobs where competitive bidding is used, the final tray design isn’t known until bidding completion. At this point, the vendor then prepares the detailed tray and valve layout. Only then can the designer check the turndown expected for the tray in question. Therefore, for new designs it is important that the designer tell the vendors in the Design Specification what turndown ratio is required and what maximum dry tray pressure drop is acceptable. By specifying the dry tray pressure drop, the designer will know that the downcomer filling is within acceptable design limits for the tray spacing used. To permit these calculations, the vendor must be given a table of maximum and minimum tray loadings. When supplying these loadings, the tower should be split into sections (“sectioned”) such that the vapor turndown in each section is preferably not more than 3 or 4 to 1. Also, see subsequent material under Information Required By Valve Tray Vendor. For revamps, the more detailed calculation procedure outlined below can be used for movable valves where the tray details are known. This procedure is based on the fact that most valve tray vendors use both light and heavy valves on their trays when the turndown ratio exceeds 2/1. The rationale for this procedure is discussed in the next paragraph and is best understood by referring to Figure 7. Each valve contains several “dimples” around its periphery that prevent the valve from completely shutting off. Thus, a uniform bubbling action is maintained across the tray even at very low vapor rates. As the vapor rate is increased, the light valves begin to open (Region 1, Figure 7). As the vapor rate is increased further (Region 2), pressure drop increases until the heavy valves begin to open (Region 3). Once the heavy valves are fully open (Region 4), the resulting pressure drop follows the standard orifice pressure drop line. These various regions are defined by transition velocities (i.e., Vo(T1), etc.) which are calculated from the equations shown below and on the Calculation Form. When rating a valve tray that contains only ONE VALVE WEIGHT (a rare case), calculate Vo(T3) from Eq. (4a3). If the actual Vo is less than Vo(T3), calculate Hed from Eq. (4b6). If the actual Vo is greater than Vo(T3) calculate hed from Eq. (4b7). Calculate the fraction of valves open from Eq. (4b5) by setting A1 = 0 and A2 = Ao. Trays with only one valve weight should be checked carefully, since they are more prone to valve pulsation and thus may experience shortened valve life due to excessive valve wear.
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DETAILED DESIGN PROCEDURE (Cont) Transition velocity at which the lighter valves are fully open, Vo(T1)
Vo( T1)
ρm 1.35 t1 ρv = K2 − K1 2 (A1 / A o )
where: A1 A2 Ao K1 K2 qv t1 t2 ρL ρm ρv Vo
= = = = = = = = = = = =
0.5
(Customary and Metric)
Eq. (4a1)
Open area of lighter valves, ft2 (m2) Open area of heavier valves, ft2 (m2) Total valve open area, ft2 (m2) (Ao = A1 + A2) Dry tray pressure drop coefficient (from Table 3C) Dry tray pressure drop coefficient (from Table 3C) Vapor rate at conditions, ft3/s (m3/s) Thickness of lighter valves, in. (mm) (from Table 3C) Thickness of heavier valves, in. (mm) (from Table 3C) Liquid density at conditions, lb/ft3 (kg/m3) Metal density, lb/ft3 (kg/m3) (from Table 3C) Vapor density at conditions, lb/ft3 (kg/m3) Average hole velocity (qv / Ao), ft/s (m/s)
Transition velocity where heavier valves begin to open, Vo(T2)
Vo ( T 2)
ρm 1.35 t 2 ρv = K2 − K1 2 (A1 / A o )
0.5
(Customary and Metric)
Eq. (4a2)
Transition velocity where heavier valves are fully open, Vo(T3)
Vo ( T 3 )
ρm 1.35 t 2 ρ v = K 2 − K1
0.5
(Customary and Metric)
Eq. (4a3)
Once the transition velocities have been calculated, it is then possible to calculate the fraction of valves open (f1, f2, etc.) as well as the dry tray pressure drop, hed1, hed2, etc. in each region. This can be done using the equations below. Reminder: it is only necessary to do the calculations below for the region(s) of interest. REGION 1 — Where the average hole velocity (Vo) is less than Vo(T1) and f2 = 0. K2 (A1 / A o ) 2 f1 = 1.35 t1 ρm K1 + Vo2 ρv where: f1 f2 f hed
= = = =
0.5
(Customary and Metric)
Fraction of lighter valves open Fraction of heavier valves open Fraction of total valves open, (f1 + f2) Dry tray pressure drop, in. (mm) of hot liquid
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Eq. (4b1)
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DETAILED DESIGN PROCEDURE (Cont) A A f = f1 1 + f2 2 A o Ao hed1 = 1.35 t1
(Customary and Metric)
ρm ρ + K1 Vo2 v (Customary and Metric) ρL ρL
Eq. (4b2)
Eq. (4b3)
REGION 2 — Where the average hole velocity (Vo) is > Vo(T1), but < Vo(T2) Then, f1 = 1 and f2 = 0. Calculate f from Eq. (4b2) above. hed2
Vo = K2 A1 / A o
2
ρv ρL
(Customary and Metric)
Eq. (4b4)
REGION 3 — Where the average hole velocity (Vo) is > Vo(T2) but < Vo(T3) and f1 = 1. Vo K2 f2 = ρ A 2 / A o 1.35 t 2 m + K1 Vo2 ρv
0.5
−
A1 (Customary and Metric) A2
Eq. (4b5)
f, calculate from Eq. (4b2) above hed3 = 1.35 t2
ρm ρ + K 1 Vo2 v (Customary and Metric) ρL ρL
Eq. (4b6)
REGION 4 — Where the average hole velocity (Vo) > Vo(T3) f1 = 1.0 (all the valves are fully open) hed4 = ç
K 2 Vo2 ρv ρL
(Customary and Metric)
Eq. (4b7)
Vendors have indicated that valve trays work well only when a certain minimum fraction of the valves are open at design rates and at turndown. The turndown of valve trays may be restricted by channeling (poor vapor distribution) or by pulsation at low vapor rates. Vapor channeling induces non-uniform weeping and a reduction in tray efficiency. To minimize vapor channeling, valve trays should be designed to exceed a minimum f ratio. The following minimum values of f are recommended at turndown conditions. Trays which meet or exceed these ratios are acceptable. If these ratios cannot be met, selected valves should be blanked, the valve density should be reduced, or the ratio of light to heavy valves should be increased. 1-pass trays f = 0.35 2-pass trays f = 0.50 3 or 4-pass trays f = 0.70 Note that if the desired turndown cannot be achieved with standard valve trays, vendors can design trays with special valves (e.g., two-stage opening as provided by Glitsch’s A-1 valve tray). If a very large turndown is required (about 5 to 1), the more expensive two-stage opening valves must be specified. In addition, all valve tray specifications should include a note stating that “valve tray layout should be designed so that valve pulsation will not occur at minimum vapor rates.” This is to insure maximum valve life. Vendors can achieve this by blanking, punching fewer openings, using varying valve weights, etc. Calculating Open Area From Given Valve Tray Dimensions - The open area for the various types of valves can be determined from Table 3B, Figure 10, and Figure 11. Note that the open area for some valves is based on the hole area punched in the tray deck. Whereas, the open area for other valves is based on the peripheral escape or slot area. Information Required by Valve Tray Vendor - A typical design specification for a valve tray will include the specification of all tray geometry (weir heights, downcomer clearances, downcomer rises, etc.), but will not include the number or type of valves used on the tray. Instead, a table consisting of the maximum and minimum tray liquid and vapor loadings and densities for each section of the tower should be supplied. In addition, the following notes should be included with the tray drawings.
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DETAILED DESIGN PROCEDURE (Cont) Drawing Notes 1.
2. ç
3.
ç
4. 5.
ç
ç ç
The number of valves on a given tray in each tower section should be designed so that the dry tray pressure drop at the maximum vapor rate is close to (i.e., within + 10%) but does not exceed the following values in in. (mm) of hot liquid: TRAY #
MAX. DRY TRAY ∆P
To be specified by designer
To be specified by designer
Valve layout should be designed so that valve pulsation will not occur at the minimum vapor rate in each section. This is to insure maximum valve life. All valve tray drawings shall be submitted for approval by the Owner’s Engineer before approval for fabrication is granted. Vendor's "For Approval" drawings shall show number, lift, and size of each valve type; the valve layout on tray deck, including distance from valves to downcomers, tray support rings, and tray panel edges; and typical valve pitch. Valve units must be of dimpled obstruction, unless otherwise specified. If carbon steel tray decks are used, the valve units must be alloy. Valves shall incorporate an anti-rotation feature that will prevent spinning of the element. Mechanical design of trays and material selection shall be in accordance with Exxon International Practices IP 5-2-1.
6.
Vendor shall check layout for “blowing” limitation and confirm that weeping will not be more than 10% of the liquid rate at the minimum vapor rate. 7. Nutter quotations are to be based on trays having only small valve (BDH) or small V-Grid (SVG) units on triangular pitch. Large valves (BDP) or large V-Grid (LVG) units are not acceptable. The use of rectangular pitch with any size unit is also unacceptable. 8. Valve layout should include alternate pairs of rows of light and heavy valve if multi-weight valves are used. The first two rows and last two rows should be light valves to maximize bubble area. 9. Tray vendor shall provide a minimum open area to bubble area ratio of 5%. Blanking - For revamps, the ways to reduce valve area are to use blanking strips or replace the tray deck panels with ones having a smaller number of valves. For valves contained in a “cage,” contact the vendors for their proprietary blanking devices. The valves must be removed prior to blanking. If blanking 50% or less of the hole area, blank single rows or pairs of rows of holes. Leave at least two consecutive rows unblanked. For large amounts of blanking: •
Use a combination of items mentioned above plus waste area.
•
Consider adding vertical baffles to restrict flow path width. (See Figure C in Section III-I under How Can Trays Be Improved.)
•
Check adverse impact on tray efficiency (if any) because of the added waste area. Consider running parametric cases on Program 1134 with varying amounts of inputted waste area.
TRAY HYDRAULICS AND DOWNCOMER FILLING (STEP 5) This part of the calculation form permits calculation of the various components of tray pressure drop and downcomer filling. Recommended values for downcomer filling as a percentage of the tray spacing for specific services are given in Table 2. For all other services, use the value obtained from Figure 5A or 5B. Figures 8A through 8H are used to calculate the tray clear liquid height and froth density. Their use is restricted to towers between 4 and 20 ft (1200 to 6000 mm) in diameter. For designs falling outside this range, the more rigorous trial-and-error procedure presented in Tables 3A or 3B of Section III-B must be used. A deviation of ± 10% between the rigorous and short cut methods is both normal and acceptable. While the rigorous correlation was developed for sieve trays, it can be easily adapted to valve trays by using a hole diameter (do) of 0.5 in. (13 mm) in the rigorous equations for all types of valve trays. The clear liquid height (hc) on the tray must be checked at the minimum liquid flow rates to make sure that the downcomer is sealed (see earlier discussion under Downcomer Sealing). If a seal is not obtained, consider the use of a higher outlet weir, a smaller downcomer clearance, a shaped downcomer lip, or a recessed inlet box. The dry tray pressure (hed) should not exceed 2.25 in. (57 mm) for foaming systems and 4.5 in. (114 mm) for non-foaming systems.
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DETAILED DESIGN PROCEDURE (Cont) CHECKING PROCESS LIMITATIONS (STEP 6) After the tray design has been established, be sure that the ultimate capacity and the downcomer entrance velocity for highpressure systems have been met. If any of these criteria have been violated, the trial tray design must be modified. If all of the criteria cannot be met simultaneously, consult your FRACTIONATION SPECIALIST.
TRAY EFFICIENCY (STEP 7) The tray efficiency should be calculated by the modified procedure given in Section III-I for valve trays. The number of actual trays required is then calculated by dividing the number of theoretical trays (which are developed during the process simulation stage of the design) by the efficiency expressed as a fraction.
BALANCED DESIGN (STEP 8) Even when a new tray design or revamp meets all the above criteria, the designer should check to see if the design is as “balanced” as possible. That is, the “ideal” balanced design would have the jet flood velocity, the downcomer entrance velocity and downcomer filling all at approximately the same percentage of their respective limits (e.g., say 85% of maximum jet flood, 85% of the allowable downcomer entrance velocity, and 85% of the allowable downcomer filling limits respectively). This prevents building a potential bottleneck into a tower and permits the unit to be pushed to its maximum by plant personnel. The designer should consider running parametric computer cases to balance a design rather than carrying out several lengthy calculations by hand. Likewise, the designer should try to get all sections of the tower as balanced as possible (i.e., above the feed vs. below the feed, etc.).
TOWER CHECKLIST (STEP 9) Table 7 of Section III-A contains a detailed tower checklist that should be reviewed for all new designs as well as revamps.
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EXXON ENGINEERING
NOMENCLATURE ft2
(m2)
Ab
=
Bubble Area
Adi Ado Af
= = =
Total downcomer inlet area, ft2 (m2) Total downcomer outlet area, ft2 (m2) Average tower free area, ft2 (m2) (superficial area minus arithmetic average of inlet and outlet area of downcomer(s) above the tray minus the waste area); for multipass trays, use the tray having the smallest value of Af. (See Figure 13 in Section III-A.)
(see Figure 12 in Section III-A)
Ao A1 A2 As Aw c
= = = = = =
Total valve open area, ft2 (m2) (ALSO, Ao = A1 + A2) Open area of lighter valves, ft2 (m2) Open area of heavier valves, ft2 (m2) Superficial (total) tower area, ft2 (m2) Waste area, ft2 (m2) (normally zero for valve trays) Clearance between tray and downcomer apron at tray inlet, in. (mm) (see Figure 6 in Section III-A)
Cs do Dt Dtr EO f
= = = = = =
Capacity factor based on cross-sectional area, VL / As, ft/s (m/s) Hole diameter, in. (mm) (Used only in rigorous clear liquid height calculations) Tower diameter, ft (mm) Trial tower diameter, ft (mm) Overall efficiency, % (see Section III-I) Fraction of total valves open
f1 f2 H hc hd hed
= = = = = =
Fraction of lighter valves open Fraction of heavier valves open Tray spacing, in. (mm) Clear liquid height on tray, in. (mm) of hot liquid Downcomer filling, in. (mm) of hot liquid Effective dry tray pressure drop, in. (mm) of hot liquid. With subscripts 1, 2, 3 and 4 added, it refers to the pressure drop in Regions 1, 2, 3 and 4 of Figure 7, respectively.
hf hi ht hud hwi hwo KHL
= = = = = = =
Tray froth height, in. (mm) of hot liquid Tray inlet head, in. (mm) of hot liquid Total tray pressure drop, in. (mm) of hot liquid Head loss under downcomer or splash baffle, in. (mm) of hot liquid Inlet weir height, in. (mm) (see Figure 11, Section III-A) Outlet weir height, in. (mm) (see Figure 6, Section III-A) Tray spacing - liquid rate factor, dimensionless (see Figures 1A through 1D)
Kn Kσµ KVE Kw K1 K2 L L'
= = = = = = = =
Constant for calculating open area for Nutter rectangular valves Surface tension-viscosity factor, dimensionless (see Figure 3) Factor for graphical solution of clear liquid height (see Figures 8B and 8D) Factor for graphical solution of clear liquid height (see Figures 8E and 8G) Dry tray pressure drop coefficient (see Table 3C) Dry tray pressure drop coefficient (see Table 3C) Liquid rate, gpm/in. of weir/pass, (dm3/s/m of weir/pass) Liquid rate, gpm/in. of diameter/pass (dm3/s/m of diameter/pass)
LL LL(Min) li
= = =
Liquid load, ft3/s (dm3/s) at conditions Minimum liquid load, ft3/s (dm3/s) at conditions Inlet weir length, in. (mm)
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NOMENCLATURE (Cont) lo
=
Outlet weir length, in. (mm) (see Figures 9 and 12 in Section III-A)
I*
o
=
Outlet weir length on inboard tray, in. (mm) (see Figure 12 in Section III-A)
lud
=
Length of bottom edge of outboard downcomer, in. (mm) (see Figure 12 in Section III-A)
I*
ud
=
Length of bottom edge of inboard downcomer, in. (mm)
NA Np NT PVE
= = = =
Number of actual trays Number of liquid passes Number of theoretical trays Vapor energy parameter (see Figures 8A and 8C)
QL qv r ro
= = = =
Liquid rate, gpm (dm3/s) at conditions Volumetric vapor rate, ft3/s (m3/s) at conditions Downcomer inlet rise for chordal downcomers or downcomer inlet width for inboard downcomers, in. (mm) Inboard downcomer rise (width) at bottom of downcomer, in. (mm)
t1 t2 tm Vdi Vdo Vf
= = = = = =
Thickness of lighter valves, in. (mm) Thickness of heavier valves, in. (mm) Valve metal thickness, in. (mm) Velocity of clear liquid entering downcomer, ft/s (m/s) Downcomer outlet velocity, ft/s (m/s) Vapor velocity based on tower free area, ft/s (m/s)
VL
=
ρv Design vapor load = qv ρL − ρv
VL(Min)
=
Minimum vapor load. See appropriate Calculation Form. Eq. (1a4) for definition, ft3/s (m3/s)
VL(Ult) Vo
= =
wL wv
= =
Ultimate capacity vapor load dependent on system properties, ft3/s (m3/s) at conditions Vapor velocity through the total valve (punched) area, ft/s (m/s) for round movable valves. For round fixed and Nutter valves it is the peripheral area between the tray deck and the fully open valve element. Liquid mass flow rate, klb/hr (kg/s) Vapor mass flow rate, kib/hr (kg/s)
β
=
ρ − ρv Factor in ultimate capacity equation, 1.4 L ρv
µL
=
Liquid viscosity at conditions, cP (mPa•s)
µv
=
Vapor viscosity at conditions, cP (mPa•s)
ρL
=
Liquid density at conditions, lb/ft3 (kg/m3)
ρm
=
Valve metal density, lb/ft3 (kg/m3)
ρv
=
Vapor density at conditions, lb/ft3 (kg/m3)
σL
=
Liquid surface tension at conditions, dynes/cm (mN/m)
σSTD
=
Standard liquid surface tension, dynes/cm (mN/m) (see Figure 2)
Ψ
=
Froth density, fraction of froth volume occupied by liquid, dimensionless
0.5
at conditions ft3/s (m3/s)
0.5
(Customary and Metric)
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EXXON ENGINEERING
COMPUTER PROGRAMS ç
For up-to-date information on available programs and how to use them, affiliate personnel should contact their FRACTIONATION SPECIALIST. A site's TECHNICAL COMPUTING CONTACT can also provide help on accessing available programs. The valve tray programs can be accessed through three sources.
AVAILABLE PROGRAMS SOURCE
PROGRAM NAME OR NUMBER
VERSION NUMBER
PEGASYS
Fractionating Towers, Valve Tray
2.3
PRO/II
Valve Tray Program
2.3
Stand Alone
#1134
2.3
The Valve Tray programs utilize the design equations contained in this section, Table 1, and the equations on the Valve Tray Calculation Form. They can be used for both designing new towers or trays, and rating existing trays. Existing tray designs can be rated by specifying some or all of the tray hardware dimensions. The programs also include an option to calculate valve tray efficiency (see Section III-I).
ç
ç
An input form for the stand-alone program (1134) is available in Computer Program Update, Valve Tray Rating Design Program #1134, CPEE-0013, October, 1990. This memorandum contains a detailed description of the program, output sheets, and a step-by-step procedure illustrating how various cases are arranged. The program's input and output can be in either customary or metric units. When rating fixed valve trays, the K1 coefficient is not used to calculate the dry tray pressure drop. Specify a low valve thickness (0.037 in., 0.91 mm) and check that all valves are fully open at design and minimum rates when using the valve tray programs. For valve tray spray/froth transition, weeping, and entrainment estimates the Sieve Tray Design Program (#1133) should be used. A hole size of 0.5 in. (13 mm) should be specified with an open area that gives a dry (sieve) tray pressure drop comparable to the valve tray prediction. There is no multipass (3 or 4 pass) design program for valve trays. However, since many of the design equations for sieve trays are also common to valve trays, the sieve tray Multipass Design Program (#1143) can be used as a starting point for multipass valve tray design. The FRACTIONATION SPECIALIST should always be contacted for guidance in determining what supplemental hand calculations are required.
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TABLE 1 VALVE TRAY DESIGN PRINCIPLES (METRIC VALUES SHOWN IN PARENTHESES) VALUES SUGGESTED
ALLOWABLE RANGE
1. Tray Spacing
12 to 30 in. (300 to 750 mm)
8 to 36 in. (200 to 900 mm)
It is generally economical to use minimum values, as limited by downcomer filling or maintenance considerations. Use of variable spacings to accommodate loading changes from section to section should be considered to minimize lower height.
2. Number of Liquid Passes
1 or 2
1 to 4
For diameters 5 ft (1500 mm) and less, use single pass. For diameters over 5 ft (1500 mm), try 2 passes if the liquid rate exceeds 7 gpm/in. of diameter (17 dm3/s/m of diameter). Try 1 pass if the liquid rate is equal to or less than 7 gpm/in. of diameter (17 dm3/s/m of diameter). For the final design, choose the number of passes which minimizes the total tower cost (i.e., tower height and diameter). If the liquid rate exceeds 14 gpm/in. of weir/pass (35 dm3/s/m of weir/pass) consult your FRACTIONATION SPECIALIST. The minimum diameter for 3-pass trays is 8 ft (2400 mm); for 4 pass it is 12 ft (3600 mm).
DESIGN FEATURE
COMMENTS
3. Downcomers and Weirs a) Allowable downcomer inlet velocity, ft/s (m/s)
Calculate per Figure 4A or 4B, read from Table 2, or calculate per Eq. (6c1).
b) Type of downcomer
Chord
c)
Inboard downcomer width (inlet and outlet) and antijump baffles
___
Downcomer inlet velocity should be below that determined from Figure 4A or 4B, that given in Table 2, and that calculated from Eq. (6c1). As the vapor density approaches the liquid density, vapor disengaging becomes more difficult and a larger downcomer area (lower downcomer inlet velocity) must be used. This is especially critical for light hydrocarbon distillation towers operating at pressures over 200 psig (1400 kPa gage). For foaming systems, use very low downcomer inlet velocities (about 0.2 ft/s; 0.06 m/s). Segmental [with 6 in. (150 mm) minimum rise]
Inlet and outlet chord length must be at least 65% of the tower diameter for good liquid distribution. Sloped downcomers can be used when downcomer inlet velocities are at or below 0.6 ft/s (0.18 m/s). The maximum outlet velocity for sloped downcomers should be twice the inlet velocity or 0.6 ft/s (0.18 m/s), whichever is less, if the allowable inlet velocity exceeds 0.6 ft/s (0.18 m/s) the downcomer must be straight.
Inlet width:
Whenever the liquid rate exceeds 4.2 gpm/in. of diameter (10 dm3/s/m of diameter/pass), use a 14 to 16 in. (350 to 400 mm) high anti-jump baffle, suspended lengthwise in the center of the inboard downcomer and extending the length of the downcomer. This will prevent froth from choking the downcomer as it converges from opposite sides. The base of the antijump baffle should be level with the top of the outlet weirs or the tray deck if no weirs are present. (See Figure 14 in Section III-A.)
8 in. (200 mm) minimum
Outlet width: 6 in. (150 mm) minimum d)
Outlet weir height
2 in. (50 mm)
0 to 4 in. (0 to 100 mm)
The optimum weir height is the one which maximizes tray efficiency without creating downcomer sealing or filling problems. This optimum usually occurs at a height of 2 in. ± 1 in. (50 mm ± 25 mm). See Section III-I, Tray Efficiency, for more details or run parametric cases on the 1134 program.
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TABLE 1 VALVE TRAY DESIGN PRINCIPLES (Cont) (METRIC VALUES SHOWN IN PARENTHESES) VALUES SUGGESTED
DESIGN FEATURE 3. e) Clearance under the downcomer
1.5 in. (38 mm)
ALLOWABLE RANGE 1 in. (25 mm) and up
1.5 in. (38 mm) and up in fouling services
f) Downcomer seal
Operating or process seal (See Section III-A, pg. 14)
Inlet weir or recessed inlet box Inlet weir should be avoided in fouling services
g) Downcomer filling, % of tray spacing
COMMENTS Set the clearance to give a head loss of approximately 1 in. (25 mm). Higher values of head loss can be used if necessary to assure sealing of the downcomer. If high liquid rates occur, consider use of a shaped downcomer to reduce the head loss. (See Section III-A, Figure 11) However, do not use a shaped downcomer with a recessed box, an inlet weir, or a seal pan. The head loss with a shaped downcomer must not exceed 1.5 in. (38 mm), to prevent excessive liquid velocity on the inlet side of the tray. In most cases, the liquid level on the inlet side of the tray can be made high enough to seal the downcomer through the use of the outlet weir (operating seal). However, if the sum of the clear liquid height at the inlet to the tray (hi) and the head loss under the downcomer (hud) plus 0.25 in. (6 mm) is less than the downcomer clearance at minimum rates, the downcomer will not be sealed. Should this occur, consider decreasing the clearance, increasing the outlet weir height or using an inlet weir or recessed inlet box. Inlet weirs add to downcomer filling; in some cases they may be desirable for 3-pass or 4-pass trays to insure equal liquid distribution. Recessed inlet boxes are more expensive but may be necessary in cases where an operating seal would require an excessively high outlet weir. See Figure 5A or 5B for hydrocarbon systems and criteria in Table 2 for aqueous systems.
See Comments
See Comments
a) Valve size and pitch
__
__
Set by the vendor.
b) Valve distribution
__
__
Open area should be uniformly distributed within the bubble area. Do not have valves closer than 2 in. (50 mm) to a downcomer. For further details see IP 5-2-1.
4. Hole Size and Layout
ç
c) Ratio of hole area to bubble area (Ao / Ab), percent
10 to 15
d) Dry tray pressure drop, hed, in. of hot liquid
3 in. (75 mm)
5 to 15 (Nutter) 5 to 18 (KochGlitsch and Norton)
In general, the lower the open area, the higher the efficiency and the lower the capacity. A tray with 12% open area gives good efficiency and flexibility without a capacity debit for a wide range of liquid rates. Open area need not be specified by the designer. Instead, a table of loadings and a maximum allowable dry tray pressure drop can be specified, and the tray vendor will choose the proper number and type of valves required. (See discussion of dry tray pressure drop below.)
1 to 4.5 in.
As discussed in the text, the required maximum dry tray pressure drop is a function of the required turndown and is limited by the downcomer filling constraint. For new designs a pressure drop of 3 in. (75 mm) of hot liquid should be used. Lower dry tray pressure drops can be achieved, if special valves or valve layouts are used by the vendors. For low liquid rate cases, if L lies between 0.25 to 1.5 gpm/in. of weir/pass (0.6 to 3.7 dm3/s/m of weir/pass), hed should be < 2.25 in (57 mm). If L < 0.25 (0.6), contact your FRACTIONATION SPECIALIST.
(25 - 113 mm)
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TABLE 1 VALVE TRAY DESIGN PRINCIPLES (Cont) (METRIC VALUES SHOWN IN PARENTHESES) VALUES SUGGESTED
DESIGN FEATURE
ç
4. e) Bubble area, Ab
55 to 90% of As
f) Hole blanking
___
5. Tray Efficiency
Calculate per Section III-I
ALLOWABLE RANGE 40 to 90% of As
___
Calculate per Section III-I
COMMENTS Ab / As ratios below 40% or above 90% must not be used, because they are outside the range of available data. For trays having a significant amount of waste area, the Ab / As ratio is based on dividing Ab by (As − Aw). Blanking is not generally required unless the tower is being sized for future service at much higher rates or if some trays have much lower vapor loadings than the rest of the tower (e.g., upper trays of absorber de-ethanizers and lower trays of heavy hydrocarbon/steam strippers. To maintain best efficiency, blank uniformity within the bubble area. See IP 5-2-1 for more details on tray blanking. The efficiency for valve trays should be calculated by the procedure given in Section III-I, Tray Efficiency.
6. Foaming Design Criteria a) Percent of jet flood
60% of Allowable
___
Design for 60% of the allowable percent of jet flood given by Eq. (3c4) or (3c5) if not covered in Part 3 of Table 2. However, do not downrate the values given in Part 3 of Table 2.
b) Maximum downcomer filling
80% of Fig. 4A or 4B
___
Design for 80% of the allowable downcomer filling given by Figure 4A or 4B or the value given in Part 3 of Table 2, whichever is lower.
c) Downcomer inlet velocity
0.2 ft/s (0.06 m/s)
___
Design for 0.2 ft/s (0.06 m/s) unless operating data from the same system permits higher velocities. However, if ρv / ρL > 0.03, calculate a velocity from Eq. (6c1) and use this velocity if < 0.2 ft/s (0.06 m/s).
d) Maximum dry tray pressure drop
2.25 in. (57 mm)
___
Design for a dry tray pressure drop of 2.25 in. (57 mm) or less.
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TABLE 2 DESIGN CRITERIA FOR SPECIFIC TOWERS 1.
Light Hydrocarbon Towers and Other Non-Aqueous Systems
% of Jet Flood [Eq. (3c4)]
Downcomer Inlet Velocity
Maximum % Downcomer Filling
ft/s Demethanizers (and systems where σL < 2.0) Deethanizers Absorber - deethanizers; absorber – depropanizers Ethylene/ethane splitters: < 325 psia (2240 kPa) 325-375 psia (2240-2586 kPa) Depropanizers; C3 / C4 splitters Propylene/propane splitters Hydrocarbon absorbers: [P ≥ 500 psig (3450 kPa gage)] [P < 500 psig (3450 kPa gage)] Other hydrocarbon systems Foaming hydrocarbon systems Xylenes splitters Non-hydrocarbon systems [σL < 40 dynes/cm (mN/m)] Non-hydrocarbon systems [σL ≥ 40 dynes/cm (mN/m)]
2.
3.
ç
Heavy Hydrocarbon Towers Atmospheric pipestills; sidestream strippers for atmospheric and vacuum pipestills Cat, coker, FLEXICOKER, HYDROCRACKER, and steam cracker primary fractionators above the bottom pumparound Prefractionators; outboard flash towers Vacuum pipestills All heavy hydrocarbon "bottoms" strippers Aqueous Systems
m/s
70 85 70
(1)
40
(1) 0.3(3)
0.09(3)
40 40
90 90 85 100
(1) (1) (1) (1)
45 42 (2) (2)
80 85 90 60 100 90
(1) (1) (1)
(2) (2) (2) 80% of Fig. 5A or 5B (2) (2)
0.2(3)
0.06(3) (1) (1)
Use correlation for aqueous systems, where appropriate, or consult your FRACTIONATION SPECIALIST Percent of Jet Flood [Eq. (3c4)] Fractionation Fractionation Downcomer Inlet Maximum % Critical Not Critical Velocity Downcomer Filling 100 (1) (2) 95
95
100
(1)
(2)
90
95
(1)
(2)
80 to 85 50
(1) (1)
(2) (2)
≤ 80 50 % of Jet Flood [Eq. (3c5)]
Downcomer Inlet Velocity(3)
Maximum % Downcomer Filling(5)
ft/s m/s 0.30 0.09 40 Amine, FLEXSORB and caustic 60 scrubbers 0.25 0.075 50 Amine and FLEXSORB regenerators 75 Catacarb absorbers: Lean 60 0.25 0.075 40 40 40 0.35 0.10 Bulk 0.075 50 Catacarb regenerators: Lean 70 0.25 50 Bulk 60 0.35 0.10 0.35 0.10 40 Sour water strippers 75 0.40 0.12 50 Water wash sections 75 Other aqueous liquid/steam strippers 80 0.40 0.12 50 Fig. 5A or 5B (4) Other aqueous systems 90 (4) 0.06 Foaming aqueous systems 60 0.20 80% of Fig. 5A or 5B 64 0.26 0.079 ACN extractive distillation 37 Notes: (1) Use Figure 4A or 4B, or Eq. (6c1), whichever is less. Remember: Calculate Eq. (6c1) only if ρv / ρL > 0.03. (2) Use Figure 5A or 5B. (3) Use the velocity given by Figure 4A or 4B or Eq. (6c1) if lower than those tabulated. Remember: Calculate Eq. (6c1) only if ρv / ρL > 0.03. (4) Contact your FRACTIONATION SPECIALIST for help. (5) Use values from Figure 5A or 5B if lower than the values tabulated below.
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TABLE 3A COMMON VALVE TYPES OFFERED BY MAJOR U.S. VENDORS(10)
ç
TRAY VENDOR KOCH - GLITSCH GLITSCH(6)(7)
KOCH(3)
NORTON
NUTTER
Standard
V-1
Au
L, MR2L(2)(9)
BDH(1)
Low Pressure(5)
V-4
(2)
(2)
Not Available
Standard
A-2, A-1(11)
Tu
G(2), MR2 Cage(2)(9)
Not Available
Low Pressure(5)
A-5, A-4(11)
Tou
SG(2), MR7 Cage(2)(9)
Not Available
V-0
(2)
(2)
SVG(1)
Movable
MV-1(2)
Not Available
Not Available
Not Available
Fixed
VG-0(2)
(2)
(2)
MVG(12)
VALVE TYPE Movable
Caged(8)
Fixed High Capacity Mini-valves (4)
Notes: (1)
Nutter's BDH and SVG valves are preferred to Nutter's BDP and LVG valves due to lower entrainment.
(2)
Limited data were available to ER&E at the time of this writing. Consult your FRACTIONATION SPECIALIST for any recent capacity or efficiency data.
(3)
For Koch valves, the "o" designation refers to a venturi orifice in the tray deck. The "u" designation refers to a dimpled construction on the valves to prevent flush seating.
(4)
See Section III-A, Table 4A for specific applications.
(5)
Valves designated as "low pressure" have a venturi-shaped orifice opening in order to reduce the pressure drop in vacuum applications; however, weeping will increase and turndown will decrease.
(6)
An "X" designation for Glitsch valves refers to the valve being flush-seating and is not recommended and therefore is not included in Table 3A. The float element should be crimped to prevent full peripheral contact of the element with the tray deck.
(7)
The diameter of the standard size Glitsch V-series round valves is 1-7/8 in. (48 mm).
(8)
Caged valves are more robust than movable valves without the cage, however, caged valves are typically more expensive. Caged or fixed valves are preferred if leg wear or loss of valves has been experienced.
(9)
Valve types manufactured in Europe.
(10)
See Table 3B and Figures 9A, 9B, 9C, 10 and 11 for more geometry details on the various types of valves.
(11)
The original Ballast valve with a light weight orifice cover to give a two-stage effect; used for high turndown ratios.
(12)
Fractionation Research, Inc. has recently obtained high quality mass-transfer efficiency and capacity data on these trays at 5 and 24 psia (34 and 165 kPa). However, these data were not available at the time of this writing. Contact your FRACTIONATION SPECIALIST for up-to-date advice.
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TABLE 3B KOCH-GLITSCH VALVES – DIMENSIONS AND OPEN AREA
ç
(CUSTOMARY UNITS) TRAY TYPE
DECK THICKNESS (in.)
NET LEG LIFT (in.)
OPEN AREA/VALVE (ft2)
Glitsch Type MV-1(3)
0.074, 0.104, 0.134
0.00479(1)
Glitsch Type V-0(5) (fixed)
0.074, 0.104, 0.134
0.25
0.00835(2)
Glitsch Type V-1(5)
0.074, 0.104, 0.134
0.0128(1)
Glitsch Type VG-0(4) (fixed)
0.074, 0.104, 0.134
0.25
0.00628(2)
Koch Type A(5)
0.074, 0.104, 0.134
0.0128(1)
Koch Type Tu(5)
0.074, 0.104, 0.134
0.0128(1)
Koch Type Tou(5)
0.074, 0.104, 0.134
0.0128(1)
(METRIC UNITS)
TRAY TYPE
DECK THICKNESS (mm)
NET LEG LIFT (mm)
OPEN AREA/VALVE (m2)
Glitsch Type MV-1(3)
2.0, 2.8, 3.5
0.000445(1)
Glitsch Type V-0(5) (fixed)
2.0, 2.8, 3.5
6.35
0.000776(2)
Glitsch Type V-1(5)
2.0, 2.8, 3.5
0.00119(1)
Glitsch Type VG-0(4) (fixed)
2.0, 2.8, 3.5
6.35
0.000583(2)
Koch Type A(5)
2.0, 2.8, 3.5
0.00119(1)
Koch Type Tu(5)
2.0, 2.8, 3.5
0.00119(1)
Koch Type Tou(5)
2.0, 2.8, 3.5
0.00119(1)
Notes: (1)
The open area for the round movable valves is based on the punched hole diameter in the tray deck.
(2)
The open area for Glitsch V-0 and VG-0 fixed valves is based on the peripheral escape or slot area.
(3)
The hole size in the tray deck for the Glitsch MV-1 valve is 15/16 in. (24 mm).
(4)
The hole size in the tray deck for the Glitsch VG-0 valve is 1-1/8 in. (29 mm).
(5)
The hole size in the tray deck for these valve types is 1-17/32 in. (39 mm).
EXXON RESEARCH AND ENGINEERING COMPANY - FLORHAM PARK, N.J.
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Date PROPRIETARY INFORMATION - For Authorized Company Use Only
December, 1998
TABLE 3C DRY TRAY PRESSURE DROP COEFFICIENTS FOR VALVE TRAYS(3)(4)(6)(7)
ç
K1 Deck Thickness(2) Vendor Valve Type Koch-Glitsch MV-1
0.074 in. (2.0 mm)
0.104 in. (2.8 mm)
0.134 in. (3.5 mm)
N.A.
Note (1) N.A.
0.60 (164) 0.37 (101) 0.96 (264) 0.50 (137) 0.70 (191) N.A.
0.74 (201) 0.37 (101) 0.91 (250) 0.50 (137) 0.53 (145) 0.92 (251) 0.92 (251) 0.76 (207) N.A. 0.44 (120) 0.44 (120) 0.44 (120) 0.40 (109) 0.44 (120)
Koch-Glitsch
V-4 (lower pressure drop) VG-0(8) (fixed) A
Koch-Glitsch
Tu
N.A.
N.A.
Koch-Glitsch
N.A.
N.A.
Norton
Tou (lower pressure drop) L(5)
N.A.
N.A.
0.64 (174) 0.37 (101) 0.95 (260) 0.50 (137) 0.56 (153) 0.95 (260) 0.95 (260) 0.76 (207) N.A.
Nutter
BDH(8)
Nutter
BDP(8)
0.14 (38) 0.10 (27)
Nutter
LVG(8) (fixed) MVG(8) (fixed) SVG(8) (fixed)
0.44 (120) 0.44 (120) 0.44 (120) 0.40 (109) 0.44 (120)
0.44 (120) 0.44 (120) 0.44 (120) 0.40 (109) 0.44 (120)
Koch-Glitsch Koch-Glitsch Koch-Glitsch Koch-Glitsch
Nutter Nutter
V-0(8) (fixed) V-1
Note (1) 0.20 (55) 0.10 (27)
Note (1) Note (1) Note (1)
VALVE THICKNESS (tm)
VALVE METAL DENSITIES (ρ m) Metal
lb/ft3
kg/m3
0.91
C.S.
480
7,700
1.22
S.S.
510
8,200
0.060
1.5
Monel
550
8,800
14
0.074
2.0
Titanium
283
4,500
12
0.104
2.8
Hastelloy
560
9,000
10
0.134
3.5
Aluminum
168
2,700
8
0.164
4.2
Gage
ç
K2
—
in.
mm
20
0.037
18
0.050
16
Notes: (1) The K1 coefficient is not used for calculating the dry tray pressure drop of fixed valve trays since valves are fully open. For the valve tray program #1134, use a K1 of 0.1, a low valve thickness [0.037 in. (0.91 mm)], a fraction light valves of 1.0, valve density as low as 16 lb/ft3 (260 kg/m3), the K2 and open area for the specific fixed valve, and check that all the valves are fully open at design and turndown rates. (2) Tray deck thickness should be obtained from IP 5-2-1 based on the corrosion allowance and tray service life required. (3) For explanation of symbols, refer to Nomenclature. (4) For open area and dimensions of Koch-Glitsch valves, see Table 3B and Figure 9B. For open areas and dimensions of Nutter valves, see Figures 10 and 11. (5) For screening purposes, assume Norton Type L valve has same open area and pressure drop coefficients as Glitsch V-1 valve. (6) N.A. = Information not available. Use K1 and K2 values for Glitsch V-1 (for standard valves) or V-4 (for lower pressure drop valves). (7) For valve trays not listed, consult with your FRACTIONATION SPECIALIST. (8) The K2 coefficients for these valves are based on the peripheral escape or slot area.
EXXON RESEARCH AND ENGINEERING COMPANY - FLORHAM PARK, N.J.
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FRACTIONATING TOWERS
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Date PROPRIETARY INFORMATION - For Authorized Company Use Only
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TABLE 4A STANDARD NUTTER PACKAGE TRAY DATA (CUSTOMARY UNITS)(5)
Adc(1)
MAXIMUM BDH VALVES
MAXIMUM NUMBER OF SVG UNITS
0.366
0.070
5
4
9.75
13.0
12.0
0.437
0.168
6
5
14.25
15.5
14.5
3
0.565
0.140
6
5
12.625
15.5
14.5
4
0.667
0.107
10
8
11.75
15.5
14.5
5
0.725
0.081
10
8
11.25
15.5
14.5
6
0.814
0.053
10
8
10.125
15.5
14.5
7
0.610
0.230
7
6
15.00
17.5
16.5
8
0.708
0.199
12
10
14.25
17.5
16.5
9
0.856
0.158
12
10
14.25
17.75
16.75
10
0.940
0.131
12
10
13.125
17.75
16.75
11
1.118
0.095
16
14
12.125
17.75
16.75
12
0.932
0.297
12
12
16.375
19.5
18.5
13
1.112
0.226
14
12
15.50
19.5
18.5
14
1.283
0.160
19
16
14.375
19.5
18.5
15
1.444
0.101
19
17
12.875
19.5
18.5
16
1.569
0.058
24
20
11.25
19.5
18.5
17
1.783
0.152
32
28
15.00
22.5
21.5
18
0.831
0.576
9
8
21.625
23.75
22.75
19
1.047
0.481(3)
18
16
21.625(4)
23.75
22.75
20
1.452
0.395
18
16
20.25
23.75
22.75
21
1.618
0.328(3)
25
21
20.25(4)
23.75
22.75
22
1.743
0.305
27
24
19.125
23.75
22.75
23
1.915
0.260
27
24
17.50
23.75
22.75
24
2.049
0.205
32
28
16.50
23.75
22.75
25
2.179
0.170
32
28
15.50
23.75
22.75
26
3.11
0.231
52
47
18.375
29
28
27
3.64
0.127
58
52
15.75
29
28
28
2.320
0.587
44
40
23.75
29.5
28.5
29
2.455
0.556
44
40
23.125
29.5
28.5
30
2.560
0.485
44
40
22.375
29.5
28.5
31
2.790
0.420
44
40
21.625
29.5
28.5
32
2.950
0.352
52
47
20.75
29.5
28.5
33
3.110
0.290
52
47
19.75
29.5
28.5
34
3.240
0.232
52
47
18.625
29.5
28.5
35
3.420
0.177
60
54
17.375
29.5
28.5
36
3.540
0.128
60
54
15.875
29.5
28.5
37
2.960
0.424
56
51
21.75
30
29
38
3.625
0.240
52
47
19.375
30.5
30.25
INDEX NO.
Ab(1)
1 2
WEIR LENGTH(2)
MAXIMUM TOWER DIAM.(2)
Notes: (1) All areas in ft2. (2) All linear dimensions in in. (3) Average downcomer area with sloped downcomer design. (4) For Index No. 19; length under downcomer is about 17.625 in.; for No. 21 it is about 17.75 in. (5) The waste area, Aw, for cartridge trays can be calculated from Aw = As − 2 (Adc) − Ab. Reprinted with permission of Nutter Engineering.
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MINIMUM TOWER DIAM.(2)
DESIGN PRACTICES
FRACTIONATING TOWERS
VALVE TRAYS
Section
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TABLE 4B STANDARD NUTTER PACKAGE TRAY DATA (METRIC UNITS)(5)
Adc(1)
MAXIMUM BDH VALVES
MAXIMUM NUMBER OF SVG UNITS
WEIR LENGTH(2)
MAXIMUM TOWER DIAM.(2)
MINIMUM TOWER DIAM.(2)
0.0340
0.0065
5
4
248
330
305
0.0406
0.0156
6
5
362
395
370
3
0.0525
0.0130
6
5
321
395
370
4
0.0620
0.0099
10
8
298
395
370
5
0.0674
0.0075
10
8
286
395
370
6
0.0756
0.0049
10
8
257
395
370
7
0.0567
0.0214
7
6
381
445
420
8
0.0658
0.0185
12
10
362
445
420
9
0.0795
0.0147
12
10
362
450
425
10
0.0873
0.0122
12
10
333
450
425
11
0.1039
0.0088
16
14
308
450
425
12
0.0866
0.0276
12
12
416
495
470
13
0.1033
0.0210
14
12
394
495
470
14
0.1192
0.0149
19
16
365
495
470
15
0.1342
0.0094
19
17
327
495
470
16
0.1458
0.0054
24
20
286
495
470
17
0.1657
0.0141
32
28
381
570
545
18
0.0772
0.0535
9
8
549
605
580
19
0.0973
0.0447(3)
18
16
549(4)
605
580
20
0.1349
0.0367
18
16
514
605
580
21
0.1503
0.0305(3)
25
21
514(4)
605
580
22
0.1619
0.0283
27
24
486
605
580
23
0.1779
0.0242
27
24
445
605
580
24
0.1904
0.0190
32
28
419
605
580
25
0.2024
0.0158
32
28
394
605
580
26
0.2889
0.0215
52
47
467
735
710
27
0.3382
0.0118
58
52
400
735
710
28
0.2155
0.0545
44
40
603
750
725
29
0.2281
0.0517
44
40
587
750
725
30
0.2378
0.0451
44
40
568
750
725
31
0.2592
0.0391
44
40
549
750
725
32
0.2741
0.0327
52
47
527
750
725
33
0.2889
0.0269
52
47
502
750
725
34
0.3010
0.0216
52
47
473
750
725
35
0.3177
0.0164
60
54
441
750
725
36
0.3289
0.0119
60
54
403
750
725
37
0.2750
0.0394
56
51
552
760
735
38
0.3368
0.0223
52
47
492
775
770
INDEX NO.
Ab(1)
1 2
Notes: (1) All areas in m2. (2) All linear dimensions in mm. (3) Average downcomer area with sloped downcomer design. (4) For Index No. 19; length under downcomer is about 448 mm; for No. 21 it is about 451 mm. (5) The waste area, Aw, for cartridge trays can be calculated from Aw = As − 2 (Adc) − Ab. Reprinted with permission of Nutter Engineering.
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FIGURE 1A KHL FACTORS FOR JET FLOOD EQUATIONS HYDROCARBON SYSTEMS (CUSTOMARY UNITS) 2.0 1.8 1.6 Tray Spacing, Inches
1.4 1.2
30 27 24
1.0
33
36
21 KHL
0.8
18
0.7 15
0.6 0.5
12
0.4
(0.47 + 0.122L)
0.3
H 12 KHL =
e 0.072L (0.43 + 0.63 H/12)
0.2 0
2
4
6
8
10
12
14
16
18
20
L, gpm/inch of weir/pass
DP3EF01a
FIGURE 1B KHL FACTORS FOR JET FLOOD EQUATIONS AQUEOUS SYSTEMS (CUSTOMARY UNITS) 2.0 1.8
Tray Spacing, Inches
1.6
36
KHL
1.4
30 24
1.2
18 1.0 12 0.8 H 12
KHL =
– L/210
0.5
10
0.6 0 DP3EF01b
2
4
6
8
10
12
14
16
L, gpm/inch of weir/pass
EXXON RESEARCH AND ENGINEERING COMPANY - FLORHAM PARK, N.J.
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20
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FRACTIONATING TOWERS
VALVE TRAYS
Section
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FIGURE 1C KHL FACTORS FOR JET FLOOD EQUATIONS HYDROCARBON SYSTEMS (METRIC UNITS) 2.0 1.8 1.6 Tray Spacing, mm
1.4 1.2
900
800 700 600
1.0 0.9
KHL
0.8
500
0.7
400
0.6 0.5
300
0.4
0.3
H 304.8 KHL =
(0.47 + 0.0493L)
e L(0.0125 + H/16,700)
0.2 0
10
20
30
40
50
L, dm3/s per meter of weir/pass
DP3EF01c
FIGURE 1D KHL FACTORS FOR JET FLOOD EQUATIONS AQUEOUS SYSTEMS (METRIC UNITS) 2.0 1.8
Tray Spacing, mm
1.6
900 800 700 600 500
KHL
1.4 1.2 1.0
400
0.9
300
0.8 KHL = 0.0573H 0.5 (10) – 0.00191L
0.7 0.6 0 DP3EF01d
10
20
30
40
L, dm3/s per meter of weir/pass
EXXON RESEARCH AND ENGINEERING COMPANY - FLORHAM PARK, N.J.
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FRACTIONATING TOWERS
VALVE TRAYS
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December, 1998
FIGURE 2 STANDARD SURFACE TENSION, σSTD (SAME FOR CUSTOMARY AND METRIC UNITS)
100 80 60
σ STD = 10a a = 1.68 –
σ STD,dyne/cm (mN/m)
40
0.244
µ L0.55
20
10 8 6 4
2
1 0.03 DP3EF02
.05
.07
0.1
0.2
0.3
0.4
0.6 0.8
1
2
3
Viscosity, cP or mPa•s
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5
10
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FRACTIONATING TOWERS
VALVE TRAYS
Section
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Date PROPRIETARY INFORMATION - For Authorized Company Use Only
December, 1998
FIGURE 3 Kσµ FACTOR FOR JET FLOOD CORRELATION (SAME FOR CUSTOMARY AND METRIC UNITS) 2.0
Kσµ
1.5
1.0 0.9 0.8 0.7 0.6 0.5 0.2
0.3
0.4
0.5
0.8
1
2
3
4
Actual / Standard Surface Tension Ratio, ( σ L / σ STD)
K
σµ
=
σL σ STD
0.317
for
σL < 1.0 σ STD
K
σµ
= 1.0 for
σL ≥ 1.0 σ STD
DP3EF03
FIGURE 4A ALLOWABLE DOWNCOMER INLET VELOCITY (CUSTOMARY UNITS) 1.0 0.9 0.8 0.7 0.6 0.5
Vdi, ft/s
0.4 0.3
0.2
Vdi = 0.82
σ L (ρ L – ρ V)
0.1
0.311
ρ L2
0.08 0.01 DP3EF04a
.02
.03
.04
.06
.08
0.1
0.2
0.3
0.4
σ L(ρ L – ρ V) / ρ L2
EXXON RESEARCH AND ENGINEERING COMPANY - FLORHAM PARK, N.J.
0.6
0.8
1
DESIGN PRACTICES Section
FRACTIONATING TOWERS
VALVE TRAYS
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FIGURE 4B ALLOWABLE DOWNCOMER INLET VELOCITY (METRIC UNITS) 0.4
0.3
Vdi, m/s
0.2
0.1 .09 .08 .07
Vdi = 0.59
σ L (ρ L – ρ V)
.06 0.05 0.001 DP3EF04b
.002
.004
.006
0.01
0.02
0.311
ρ L2
0.03 0.04
σ L(ρ L – ρ V) / ρ L2
EXXON RESEARCH AND ENGINEERING COMPANY - FLORHAM PARK, N.J.
0.06
0.08 0.1
DESIGN PRACTICES
FRACTIONATING TOWERS
VALVE TRAYS
Section
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Date PROPRIETARY INFORMATION - For Authorized Company Use Only
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FIGURE 5A ALLOWABLE DOWNCOMER FILLING FOR VALVE TRAYS ALL SYSTEMS NOT COVERED IN TABLE 2 (CUSTOMARY UNITS)
60 DCF = 50 for p ≤ 90 psia = 50 – 0.0545 (P – 90) for p > 90 and < 365 psia = 35 for p ≥ 365 psia Where: DCF = Allowable % Downcomer Filling p = Tower Pressure, psia
Allowable % Downcomer Filling
55
50
45
40
35
30 0
50
100
150
200
250
300
350
400
Tower Pressure, psia
DP3EF05a
FIGURE 5B ALLOWABLE DOWNCOMER FILLING FOR VALVE TRAYS ALL SYSTEMS NOT COVERED IN TABLE 2 (METRIC UNITS) 60 DCF = 50 for p ≤ 600 kPa = 50 – 0.0079 (P – 600) for p > 600 and < 2500 kPa = 35 for p ≥ 2500 kPa Where: DCF = Allowable % Downcomer Filling p = Tower Pressure, kPa
Allowable % Downcomer Filling
55
50
45
40
35
30 0 DP3EF05b
500
1000
1500
2000
2500
Tower Pressure, kPa
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3000
Overall Tray Efficiency (%)
0.05
8.4% Sieve Tray (4 psia)
EXXON RESEARCH AND ENGINEERING COMPANY - FLORHAM PARK, N.J.
0.10
0.20
0.25
Capacity Factor, Cs (ft/s)
0.15
14% Sieve Tray
0.30
0.30
0.35
System O/P-xylene 100 mmHg
0.35
0.40
0.40
40
50
60
70
80
90
100
110
120
130
140
0.00
0 0.00
10
20
0.05
0.05
0.10
0.10
0.20
0.25
0.20
0.25 Capacity Factor, Cs (ft/s)
0.15
FRI Type 2(Norton L Valve)
0.30
0.30
10.3% Sieve Tray
Capacity Factor, Cs (ft/s)
0.15
0.35
System iC4 / nC4 165 psia
0.35
System C6 / C7 24 psia
0.40
0.40
PROPRIETARY INFORMATION - For Authorized Company Use Only
DP3Ef6a
0.05
0.25
14% Sieve Tray
Date
0.00
FRI Type 1(Norton L Valve)
0.20
Capacity Factor, Cs (ft/s)
0.15
30
40
36 of 69
0
10
20
30
40
50
60
70
80
90
0.10
System C6 / C7 5 & 4 psia
50
Page
100
0 0.00
10
20
14% Sieve Tray
8.4% Sieve Tray
December, 1998
30
60
70
80
FRI Type 1(Norton L Valve)
ç
40
50
60
90
70
110
120
100
FRI Type 1(Norton L Valve)
80
90
100
Overall Tray Efficiency (%)
III-E
Overall Tray Efficiency (%)
Section
Overall Tray Efficiency (%)
DESIGN PRACTICES FRACTIONATING TOWERS
VALVE TRAYS EXXON ENGINEERING
FIGURE 6 SIEVE AND VALVE TRAY EFFICIENCY COMPARISON (TRAY EFFICIENCY VS. VAPOR RATE AT TOTAL REFLUX)
DESIGN PRACTICES
FRACTIONATING TOWERS
VALVE TRAYS EXXON ENGINEERING
Section
Page
III-E PROPRIETARY INFORMATION - For Authorized Company Use Only
December, 1998
hed, Dry Tray Pressure Drop
FIGURE 7 VALVE TRAY TURNDOWN DIAGRAM (FOR TRAY WITH TWO DIFFERENT VALVE WEIGHTS)
REGION 1
REGION 2
REGION 3
REGION 4
Light Valves Partially Open
Light Valves Fully Open
Light Valves Fully Open
All Valves Fully Open
Heavy Valves Closed
Heavy Valves Closed
Heavy Valves Partially Open
Vo (T1) DP3EF07
37 of 69
Date
Vo (T2)
Vo (T3)
Vo, Average Valve Velocity
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FRACTIONATING TOWERS
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Date PROPRIETARY INFORMATION - For Authorized Company Use Only
December, 1998
FIGURE 8A VAPOR ENERGY PARAMETER PVE (CUSTOMARY UNITS) 10
Vapor Energy Parameter PVE
8 6 /ρ L
ρV
=
.2
.1 5 .0
4
2 .0 1 .0 05 .0
2
02 .0 01 .0
Ao Ab , %
Multiply PVE By
3 4 5 6 7 8 9 10 11 12 13 14 15
1.28 1.19 1.13 1.08 1.04 1.00 0.97 0.95 0.92 0.91 0.89 0.87 0.86
5 00 .0
6.3 Vb0.82 PVE =
1 .3
.4
.5
.8
1.0
2
4
6
8
ρv ρL
0.36
(Ao / Ab) 0.25
10
Vapor Velocity Vb, ft/s
DP3EF08a
FIGURE 8B KVE FACTOR (CUSTOMARY UNITS) 20
For hwo = 1-4 inches KVE = 2.64 PVE0.72 L0.23
15 5 =1
QL L=
KVE
10
Nρ
lo
For hwo < 1 inches
10
KVE = 2.27 PVE0.83 L0.23
6 4
8
2 Single pass or Outboard 2 pass 1
6
hf = hwo + KVE KW
.5 where KW is from Fig 8e
.25
Inboard 2 pass
4 hwo = 1 to 4 inches
hf = hwo + (PVE L)0.53
hwo < 1 inches 3 1 DP3EF08b
2
3
4
5
6
8
10
(use lo to obtain L for this case also).
Vapor Energy Parameter PVE
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FIGURE 8C VAPOR ENERGY PARAMETER PVE (METRIC UNITS) 10 Ao
Vapor Energy Parameter PVE
8
,%
Ab
6 = /ρ L
ρV
.1 5 .0 2 .0 1 .0 05 .0 02 .0
2
1.28 1.19 1.13 1.08 1.04 1.00 0.97 0.95 0.92 0.91 0.89 0.87 0.86
3 4 5 6 7 8 9 10 11 12 13 14 15
.2
4
01 .0
5 00 .0
16.7 Vb0.82 PVE =
1 0.1
0.2
0.4
Multiply PVE By
0.6
0.8
1
ρv ρL
0.36
(Ao/Ab) 0.25
2
Vapor Velocity Vb, m/s
DP3EF08c
FIGURE 8D KVE FACTOR (METRIC UNITS) 20
For hwo = 25-100 mm KVE = 2.14 PVE0.72 L0.23
15 3
0 x1
lo QL Nρ = L
10
30
For hwo < 25 mm 20
KVE = 1.84 PVE0.83 L0.23
10
9 KVE
=
5
8
Single pass or Outboard 2 pass
7
2
6
hf = hwo + 25.4 KVE KW
1
5
where KW is from Fig 8g
0.5
Inboard 2 pass
4
hwo = 25 to 100 mm hwo < 25 mm
3
1
DP3EF08d
1.5
2
2.5
3
4
5
6
7
8
9 10
hf = hwo + 15.7(PVE L)0.53 (use lo to obtain L for this case also).
Vapor Energy Parameter PVE
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FIGURE 8E KW FACTOR (CUSTOMARY UNITS) 1.0
.9
Kw
.8
.7
.6
h wo
4 To =1
h wo
.5
To =0
in. in. .99
.4 0
.1
.2
.3
.4
.5
.6
.7
.8
PVE / r 2 3 P P P For h wo = 1 − 4 in., K w = exp − 4.35 VE + 8.8 VE − 5.06 VE r r r 2 3 P P P For hwo < 1.0 in., K w = 0.925 exp − 4.7 VE + 9.36 VE − 5.39 VE r r r DP3EF8e
FIGURE 8F FROTH DENSITY (Ψ) (CUSTOMARY UNITS) 0.7
0.6
Froth Density, ψ
0.5
ψ = 0.411 – 0.293 In (PVE / hf 0.41)
0.4
0.3 Note: To Calculate Clear Liquid Height hc = ψ hf
0.2
0.1
0.0 0.4 DP3EF08f
0.6
0.8
1
1.5
2
2.5
PVE / hf 0.41
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FIGURE 8G KW FACTOR (METRIC UNITS) 1.0
.9
Kw
.8
.7
.6
h wo .5
=2
h wo
5T
=0
0 o1
2 To
0m
4.9
m
mm
.4 0
0.01
0.02
0.03
PVE / r 2 3 P P P For h wo = 25 − 100 mm, K w = exp − 110.5 VE + 5677 VE − 82920 VE r r r 2 3 P P P For h wo < 25 mm, K w = 0.925 exp − 119.4 VE + 6039 VE − 88330 VE r r r DP3EF8g
FIGURE 8H FROTH DENSITY (Ψ) (METRIC UNITS) 0.7
0.6
Froth Density, ψ
0.5
ψ = 0.022 – 0.293 In (PVE / hf0.41)
0.4
0.3 Note: To Calculate Clear Liquid Height hc = ψ hf
0.2
0.1
0.0 0.1 DP3EF08h
0.15
0.2
0.3
0.4
0.5
0.6 0.7 0.8 0.9 1
PVE / hf0.41
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FIGURE 9A VALVE HOLE VARIATIONS
1.53 in.
1.53 in.
1.53 in.
(39 mm)
(39 mm)
(39 mm)
Standard Valve Hole
DP3Ef09a
Anti-Spin Valve Hole (European standard 1 tab only)
Venturi Valve Hole (lower pressure drop)
Reprinted with permission of Norton Chemical Process Products Corporation.
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FIGURE 9B KOCH-GLITSCH VALVES KOCH
GLITSCH
Standard Valve Type
V-1, V-4
Type "A U"
Caged Valves
A-1, A-4 Type "TOU" (Venturi Hole in Tray Deck)
A-2, A-5
Type "TU"
Fixed Valves
V-0
Note: (1)
For Koch valves, the "o" designation refers to the venturi orifice in the tray deck. The "u" designation refers to the dimpled construction on the valve.
Reprinted with permission of Koch-Glitsch, Inc.
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FIGURE 9C NORTON VALVES
Standard Valves
L Valve
M Valve
MR2L Valve
MR2 Valve
Caged Valves
G Valve (Venturi version is SG)
MR2 Cage Valve
MR7 Cage Valve
Reprinted with permission of Norton Chemical Process Products Corporation.
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FIGURE 10 NUTTER MOVABLE VALVES – DIMENSIONS AND OPEN AREA
Liqu id Fl ow
Dimple B
C
A
Net Leg Lift DP3Ef10
FLOAT VALVE TYPE Dimensions, in. (mm)
BDH
BDP
2 1/2 (63.5)
5 (127) *
0.3125, 0.375, 0.4375, 0.5 (7.94, 9.52, 11.1, 12.7)
0.3125, 0.375, 0.4375, 0.5 (7.94, 9.52, 11.1, 12.7)
7/8 (22.2)
7/8 (22.2)
Length (A) Gross Valve Lift (B) Width (C)
* The BDP valve has a 1/4 in. (6.35 mm) strip of material in the middle of the deck piece separating two slots, each 2 3/8 in. (60.3 mm) long.
Slot peripheral open area is calculated as: Ao =
(Number of valves ) (Net leg lift ) (K n ) , ft 2 144
(Customary)
or Ao =
(Number of valves ) (Net leg lift ) (K n ) 10 6
where: Net leg lift = Kn = Kn =
, m2
(Metric)
Gross leg lift - Tray deck thickness, in. (mm) (also see Table 3C, Note 2) 4.575 (116) for BDH valves 9.660 (245) for BDP valves
The gross leg lift is generally defined by a number following the valve type. For example: GROSS LEG LIFT Identification Number
in.
mm
313
0.3125
7.94
375
0.3750
9.52
438
0.4375
11.1
500
0.5000
12.7
Reprinted with permission of Nutter Engineering.
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FIGURE 11 NUTTER FIXED VALVES – DIMENSIONS AND OPEN AREA Wide Side or Upstream Side of Liquid Flow
Top Length (B)
V-Grid Nutter Element D
E Net Lift (A)
Liquid Flow
Base Length (C) DP3Ef11
V-GRID DIMENSIONS (CUSTOMARY UNITS) (A) VALVE TYPE
LIFT in.
(B) TOP LENGTH in.
LVG LVG LVG LVG LVG SVG SVG SVG SVG SVG MVG MVG
0.2500 0.3125 0.3750 0.4375 0.5000 0.2500 0.3125 0.3750 0.4375 0.5000 0.2500 0.3125
3.63 3.63 3.63 3.63 3.63 1.00 1.00 1.00 1.00 1.00 0.70 0.70
(C) BASE LENGTH in.
(D) WIDE END WIDTH in.
(E) NARROW END WIDTH in.
OPEN AREA PER VALVE ft2(1)
4.31 4.49 4.66 4.83 5.00 1.69 1.86 2.03 2.20 2.38 1.39 1.56
1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.25 0.75 0.75
0.75 0.75 0.75 0.75 0.75 1.00 1.00 1.00 1.00 1.00 0.55 0.55
0.0138 0.0176 0.0216 0.0257 0.0300 0.00466 0.00621 0.00790 0.00974 0.0117 0.00363 0.00490
V-GRID DIMENSIONS (METRIC UNITS) (A) VALVE TYPE
LIFT mm
(B) TOP LENGTH mm
LVG LVG LVG LVG LVG SVG SVG SVG SVG SVG MVG MVG
6.35 7.94 9.50 11.10 12.70 6.35 7.94 9.53 11.11 12.70 6.35 7.94
92.08 92.08 92.08 92.08 92.08 25.40 25.40 25.40 25.40 25.40 17.78 17.78
(C) BASE LENGTH mm
(D) WIDE END WIDTH mm
(E) NARROW END WIDTH mm
OPEN AREA PER VALVE m2(1)
109.56 114.09 118.21 122.64 127.04 42.88 47.25 51.62 55.99 60.36 35.26 39.63
31.75 31.75 31.75 31.75 31.75 31.75 31.75 31.75 31.75 31.75 19.05 19.05
19.05 19.05 19.05 19.05 19.05 25.40 25.40 25.40 25.40 25.40 13.97 13.97
0.00128 0.00165 0.00200 0.00238 0.00278 0.000434 0.000577 0.000734 0.000904 0.001089 0.000337 0.000456
Reprinted with permission of Nutter Engineering. Note: (1)
The open area for Nutter fixed valves is based on the peripheral escape or slot area.
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VALVE TRAY CALCULATION FORM (CUSTOMARY) SHEET 1 OF 12 (1) Location & Project_________________________________________________ Date _______________________________ Tower Number ___________________________________________________ By _________________________________ Service _________________________________________________________ Tower Section (Top, Bottom, etc.) ______________________ Tray Number(s) Covered by this Design ______________________ Design Based on Tray Number ______________________ 1.
Vapor and Liquid Loadings at Conditions (a) Vapor to or from tray (use maximum value) Temperature, °F Pressure, psia Density, ρv, lb/ft3 Vapor rate, wv, k lb/hr qv, volumetric vapor rate, ft3/s =
1000 w v 3600 ρv
ρv wv
______________________ ______________________ ______________________ ______________________
Eq. (1a1)
qv
______________________
Eq. (1a2)
VL
______________________
Vapor load, VL, ft3/s 0.5
ρ v VL = qv ρL − ρv Minimum vapor rate, wv(min), k lb/hr Density at minimum rates, ρv(min) lb/ft3 Minimum vapor rate qv(min), ft3/s qv(min) =
1000 w v(min)
______________________ ______________________
Eq. (1a3)
qv(min)
______________________
Eq. (1a4)
VL(min)
______________________
µL σL wL ρL
______________________ ______________________ ______________________ ______________________ ______________________
Eq. (1b1)
LL
______________________
3600 ρv (min)
Minimum vapor load, VL(min), ft3/s ρv (min) VL(min) = qv(min) ρL(min) − ρv(min)
0.5
(b) Liquid to or from tray (use maximum value) Temperature, °F Viscosity µL, cP Surface tension σL, dynes/cm Liquid rate, wL, klb/hr Density ρL, lb/ft3 1000 w L LL liquid rate, ft3/s = 3600 ρL
(1)
QL, liquid rate, gpm = LL(448.9) Minimum liquid rate, wL(min), k lb/hr Density at minimum rates, ρL(min) lb/ft3 1000 WL(min) LL(min), minimum liquid rate = 3600 ρL(min)
Eq. (1b2)
QL wL(min) ρL(min)
______________________ ______________________ ______________________
Eq. (1b3)
LL(min)
______________________
QL(min), minimum liquid rate, gpm = LL(min) (448.9)
Eq. (1b4)
QL(min)
______________________
If an equation is not given on this calculation form for a given variable, it can be found on the pertinent figure.
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VALVE TRAY CALCULATION FORM (CUSTOMARY) SHEET 2 OF 12
2.
Tray number(s)
______________________
σSTD
______________________
Trial Tray Spacing, Size and Layout (For rating case, use actual tower dimensions and modify as needed.) (a) Trial tray size Standard surface tension σSTD, from Figure 2 or from: σSTD = 10a where a = 1.68 - 0.244 / µL0.55
Eq. (2a1)
σL σSTD
______________________
Kσµ = from Figure 3 or from: σ Kσµ = L σSTD
0.317
for
σL < 1.0 σSTD
Eq. (2a2)
Kσµ
______________________
Eq. (2a3)
Kσµ
______________________
H
______________________
Dtr
______________________
As
______________________
L'
______________________
Np
______________________
OR Kσµ = 1.0 for
σL ≥ 1.0 σSTD
For rating cases, skip to Step 2b. Tray spacing H, in. (Select from table in Detailed Design Procedure - Step 2 or use 18 in. for first trial) Trial diameter Dtr, ft: Dtr = 3.25LL +
12.4 VL H 2 12 K σµ
[
0.5
]
Eq. (2a4)
Superficial area As, ft2: As =
π D2tr 4
For first trial, assume Np = 1 L' = gpm/in. of diameter/pass =
QL 12 Dtr (Np )
If L' < 7 or Dtr < 5 ft, Np = 1
Eq. (2a5)
If L' > 7, set Np = 2. If L' > 14 using final value of Np, consult your FRACTIONATION SPECIALIST.
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VALVE TRAY CALCULATION FORM (CUSTOMARY) SHEET 3 OF 12 Tray number(s)
______________________ Inboard* Outboard
Vdi
______________________
(b) Downcomer Sizing Vdi = Allowable downcomer inlet velocity, ft/s, from either Figure 4A and its corresponding equation [Eq. (2b1)] below, or from Table 2. Use the lower value. For foaming systems, use Vdi ≈ 0.2 ft/s σ ( ρ − ρ ) Vdi = 0.82 L L 2 V ρL
0.311
Eq. (2b1)
Note: If the ratio of ρv / ρL > 0.03 a lower velocity may be required by Eq. (6c1). Eq. (6c1) cannot be calculated yet because several of the required variables are not calculated until Steps 5 and 6. However, if Figure 4A or Eq. (2b1) yields a velocity > 0.3 ft/s, set Vdi = 0.3 for the first trial. Minimum TOTAL downcomer inlet area Adi, ft2 Adi (min) =
Eq. (2b2)
LL Vdi
______________________ Vdi
______________________
Adi(min)
__________ ___________
Vdo
______________________
Ado(min)
__________ ___________
For single pass trays, Adi must be ≥ 0.068 As. For outboard downcomers of two pass trays, Adi / 2 must be ≥ 0.068 As. For inboard downcomers, their width must be at least 8 in. Vdo = Allowable downcomer outlet velocity, ft/s = 2 (Vdi) or 0.6 ft/s, whichever is less provided Vdi ≤ 0.6 ft/s For Vdi > 0.6 ft/s make Vdo = Vdi Also, if straight downcomers are desired, set Vdo = Vdi Minimum total downcomer outlet area Ado, ft2 Ado (min) =
LL
Eq. (2b3)
Vdo
However, Ado must be ≥ 0.068 As for single pass trays and outboard downcomers of multipass trays. For inboard downcomers, their width at the bottom must be at least 6 in. If the sum of Adi + Ado exceeds 60% of As, the tower diameter must be increased and a new KHL and Af calculated. *For 2-pass trays.
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EXXON ENGINEERING
VALVE TRAY CALCULATION FORM (CUSTOMARY) SHEET 4 OF 12
3.
Tray number(s)
______________________ Inboard* Outboard
Dt H As Aw Ab Af Ao/Ab
______________________ ______________________ ______________________ __________ ___________ __________ ___________ __________ ___________ ______________________
Ao
__________ ___________
Final Tray Spacing, Size and Layout (a) Tower areas Tower diameter Dt, ft Tray Spacing H, in. Superficial area, As, ft2 Waste area AW (if any), ft2 Bubble area Ab, ft2 (see Figure 12 in Section III-A) Free area, Af, ft2 (see Figure 13 in Section III-A) Fraction hole area Ao / Ab [Select value from Table 1 to start with 0.12 (12%)] Actual hole area Ao, ft2 (Ab x Ao / Ab) Note: For 2-pass trays, try to keep the Ao the same for each pass. If required, revise the Ao / Ab ratio above. (b) Downcomers and weirs** Downcomer rises/widths, r, in.
(Inlet) (Outlet)
r ro
__________ __________
__________ __________
TOTAL Downcomer inlet area Adi, ft2 [from Eq. (2b2)] TOTAL Downcomer outlet area Ado, ft2 [from Eq. (2b3)]
Adi Ado
__________ __________
__________ __________
Outlet weir height hwo, in. (from Table 1 or 2 in. for first trial) Outlet weir length, lo and lo*, in. Inlet weir height hwi, in (use only if needed for sealing the downcomer) Inlet weir length li, in. (Reminder: li ≠ lud) Length of bottom edge of downcomer, lud, in.
hwo
__________
__________
lo* hwi
__________ lo__________ __________ __________
li lud*
__________ __________ __________ lud__________
l *o
__________ lo __________
(c) Jet Flooding Outlet weir length lo and lo*, in. (from Step 3b) For segmental downcomers, use length of a chord joining the ends of the segmental downcomer (projected weir length). L = gpm/in. of weir/pass For 2-pass trays, calculate a value for each pass, i.e., for
Eq. (3c1)
L
lo and l*o KHL, tray spacing-liquid rate factor. (Use Figure 1A for hydrocarbon systems, Figure 1B for aqueous systems OR the equations below.) For 2-pass trays, calculate a value for each pass.
*For 2-pass trays. **See Section III-K for chord length and area tables.
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VALVE TRAY CALCULATION FORM (CUSTOMARY) SHEET 5 OF 12 Tray number(s)
______________________ Inboard* Outboard
3. Final Tray Spacing, Size and Layout (Cont) For hydrocarbon systems (from Figure 1A or)
KHL =
H 12
( 0.47 + 0.122L )
e(0.072L )( 0.43 + 0.63 H / 12 )
Eq. (3c2)
KHL
__________
__________
Eq. (3c3)
KHL
__________
__________
Kσµ
______________________
For aqueous system (from Figure 1B or) H KHL = 12
0.5
(10)(-L/210)
Kσµ (from Step 2a) Jet flooding for hydrocarbon systems: VL = 0.296 Kσµ KHL A f Allowable Jet flooding for aqueous systems VL = 0.204 Kσµ KHL A f Allowable
Eq. (3c4)
__________
__________
Eq. (3c5)
__________
__________
__________
__________
__________
__________
VL (from Steps 1a and 3a) A f Design Design/Allowable jet flood velocity, expressed as %. Compare calculated value(s) with criteria in Table 1 for foaming systems and Table 2 for all other systems. If these criteria are not satisfied, change lower diameter and/or tray spacing and repeat Step 3.
% Jet Flood
4. Turndown and Dry Tray Pressure Drop (a)
For NEW designs, assume a dry tray pressure drop, hed based on discussion in text and Table 1 and proceed to Step 5a.
hed
______________________
Vo t1 t2 K1 K2 A1
__________ __________ ______________________ ______________________ ______________________ ______________________ __________ __________
For REVAMPS, follow the procedure outlined below.** Calculate the various transition velocities (see Figure 7) and compare with the average hole velocity, Vo. This will determine the Region (Figure 7) your tray is operating in. Do for both the design and the turndown operation. Vo t1 t2 K1 K2 A1
= = = = = =
q v / Ao Thickness of lighter valves, in. Thickness of heavier valves, in. Dry tray pressure drop coefficient (Table 3C) Dry tray pressure drop coefficient (Table 3C) Open area of lighter valves, ft2
*For 2-pass trays. **For trays with only one valve weight, see Design Procedure, Step 4 in the text for guidance.
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VALVE TRAY CALCULATION FORM (CUSTOMARY) SHEET 6 OF 12 Tray number(s) 4.
______________________ Inboard* Outboard
Turndown and Dry Tray Pressure Drop (Cont) A2 = Open area of heavier valves, ft2 Ao = Total valve open area, ft2 (A1 + A2) Reminder: Ao is based on the punched area for round movable valves and the peripheral area for round fixed and Nutter valves.
A2 Ao
__________ __________
__________ __________
Eq. (4a1)
Vo(T1)
__________
__________
Eq. (4a2)
Vo(T2)
__________
__________
Eq. (4a3)
Vo(T3)
__________
__________
Eq. (4b1)
f1
__________
__________
Transition velocity where lighter valves are fully open, Vo(T1), ft/s
Vo(T1)
ρm 1.35 t1 ρ v = K2 − K 1 2 (A1 / A o )
0.5
Transition velocity where heavier valves begin to open, Vo(T2), ft/s
Vo(T2)
ρm 1.35 t 2 ρv = K2 − K1 2 ( A1 / A o )
0.5
Transition velocity when all valves are fully open, Vo(T3), ft/s
Vo(T3)
ρm 1.35 t 2 ρ v = K 2 − K1
0.5
(b) Calculation of fraction of valves open and the dry tray pressure drop for each Region (Figure 7). REGION 1 If the average hole velocity (Vo) is less than Vo(T1), then the fraction of light valves open, f1 is K2 (A1 / A o )2 f1 = 1.35 t1 ρm K1 + Vo2 ρv
0.5
*For 2-pass trays.
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VALVE TRAY CALCULATION FORM (CUSTOMARY) SHEET 7 OF 12 Tray number(s) 4.
______________________ Inboard* Outboard
Turndown and Dry Tray Pressure Drop (Cont) And the fraction of the total valves open, f, is A A f = f1 1 + f2 2 A o Ao Where f2 = 0 by definition And the dry tray pressure drop, hed1, in in. of hot liquid is ρ ρ hed1 = 1.35 t1 m + K 1 Vo2 v ρL ρL REGION 2 If the average hole velocity, Vo is > V0(T1) and < Vo(T2), calculate the fraction of total valves open from A A f = f1 1 + f2 2 A o Ao Where f1 = 1.0 and f2 = 0 (by definition) And the dry tray pressure drop, hed2, in in. of hot liquid is Vo hed2 = K2 (A / A ) 1 o
2
ρv ρL
Eq. (4b2)
f
__________
__________
Eq. (4b3)
hed1
__________
__________
Eq. (4b2)
f
__________
__________
Eq. (4b4)
hed2
__________
__________
Eq. (4b5)
f2
__________
__________
Eq. (4b2)
f
__________
__________
Eq. (4b6)
hed3
__________
__________
REGION 3 If the average hole velocity, Vo, > Vo(T2) and < Vo(T3) then the fraction of heavy valves open, f2, is
Vo f = 2 A 2 / Ao
1.35 t 2
K2 ρm + ρv
0.5 2 K1 Vo
−
A 1 A 2
And the fraction of total valves open, f, is A A f = f1 1 + f2 2 A o Ao And the dry tray pressure drop, hed3, in in. of hot liquid is ρ ρ hed3 = 1.35 t 2 m + K1 Vo2 v ρ ρL L
*For 2-pass trays.
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______________________ Inboard* Outboard
REGION 4 If the average hole velocity, Vo, > Vo(T3) f = 1.0 (by definition) And the dry tray pressure drop, hed4, in in. of hot liquid is hed4 =
K 2 Vo2 ρv ρL
Eq. (4b2)
f
__________
__________
Eq. (4b7)
hed4
__________
__________
hed
__________
__________
hed
__________
__________
PVE
__________
__________
Vb
__________
__________
(c) hed = Effective dry tray pressure drop, in. of hot liquid obtained from the appropriate REGION above. (hed should not exceed 2.25 in. for foaming systems and 4.5 in. for all other systems.) Reminder for low liquid rate cases: If L lies between 0.25 to 1.5, hed should be ≤ 2.25 in. If L < 0.25, contact your FRACTIONATION SPECIALIST. If f equals or exceeds: 0.35 for 1-pass 0.50 for 2-pass
0.70 for 3 & 4-pass, then design is acceptable.
If f is less than the value given above, see your FRACTIONATION SPECIALIST. Remember: It is presumed that the tower has already been “sectioned” to reduce turndown requirements. 5.
Tray Hydraulics and Downcomer Filling (a) Effective dry tray pressure drop hed (obtain from Step 4b). (b) Clear liquid height, hc The shortcut clear liquid height calculation procedure is outlined below (a rigorous trial and error procedure is presented in Table 3A of Section III-B). Determine vapor energy parameter. PVE from Figure 8A or calculate from:
PVE =
6 .3
ρ v Vb0.82 ρL
Ao Ab
0.36
Eq. (5b1)
0.25
where Vb is the vapor velocity through the bubble area, ft/s (i.e., qv / Ab)
*For 2-pass trays.
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VALVE TRAY CALCULATION FORM (CUSTOMARY) SHEET 9 OF 12 Tray number(s) 5.
______________________ Inboard* Outboard
Tray Hydraulics and Downcomer Filling (Cont) L [from Eq. (3c1)] For single pass trays, and outboard downcomers on 2-pass trays, calculate froth height, hf via hf = hwo + KVE KW
L
__________
__________
Eq. (5b2)
hf
XXX
__________
Eq. (5b3)
hf
__________
XXX
Eq. (5b4)
ψ
__________
__________
Eq. (5b5)
hc
__________
__________
Eq. (5c1)
ht
__________
__________
Eq. (5d1)
hud
__________
__________
Eq. (5d2)
c
__________
__________
Eq. (5e1)
hi
__________
__________
where: hwo from Step 3b KVE from Figure 8B or from Eq. on that figure KW from Figure 8E or from Eq. on that figure For inboard downcomers on 2-pass trays, calculate hf from
[
hf = h wo + PVE L
]0.53
Determine froth density, ψ from Figure 8F or from P Ψ = 0.411 − 0.293 ln 0VE .41 ) (hf Calculate clear liquid height hc from hc = ψ hf (c) Total tray pressure drop ht ht = hc + hed (d) Head loss under downcomer hud hud
QL = 0.06 c Np Iud
2
Assume c = 1.5 in. or use actual clearance for a rating case. If hud > > 1.0, set hud = 1.5 in. and calculate c from: c=
0.25 QL
[ ]0.5
Np Iud hud
Note: For shaped downcomers use a coefficient of 0.02 in place of 0.06, in Eq. (5d1) (e) Inlet head hi For tray with an inlet weir: Q hi = 0.5 L Np li
2/3
+ h wi
*For 2-pass trays
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VALVE TRAY CALCULATION FORM (CUSTOMARY) SHEET 10 OF 12 Tray number(s) 5.
______________________ Inboard* Outboard
Tray Hydraulics and Downcomer Filling (Cont) For tray without an inlet weir: hi = hc [from Step 5b, Eq. (5b5)] (f)
Eq. (5e2)
hi
__________
__________
Eq. (5f1)
hd
__________
__________
hd (calculated) as a % of tray spacing
__________
__________
hd (allowable) as % of tray spacing (see Table 2 and Figure 5A for non-foaming systems and Table 1 for foaming systems).
______________________
Downcomer filling hd With 2-pass trays for inboard hd, use value of hi on the outboard tray and vice versa. See Figure 14 of Section III-B for further explanation. ρL hd = (ht + hud ) + h i + 1.0, in. ρL − ρv Note: For a tray with a recessed inlet box or an inlet weir, substitute 2 hud in place of hud, in the above equation.
If hd (calculated) exceeds hd (allowable) reduce hed, hc, hud, hi, or increase tray spacing. (g) Downcomer Sealing Calculate [hi + hud] at minimum rates. Repeat calculations in Steps 5d and 5e using QL(min) and qv(min).
Eq. (5g1)
__________
__________
If at minimum rates, (hi + hud + 0.25 in.) is less than c, consider using a lower value of c (possibly with a shaped downcomer lip), increasing the outlet weir height, adding an inlet weir, or using a recessed inlet box, in that order of preference. If sealing is still a problem, consult your FRACTIONATION SPECIALIST. 6.
Checking Process Limitations (a) Ultimate capacity Free area Af, ft2 from Step 3(a). For 2-pass trays, use the smallest value. β VL(Ult) = 0.62 A f 1 + β
σL ρL − ρv
ρ − ρv where : β = 1.4 L ρv
______________________
0.25
Eq. (6a1)
VL(Ult)
______________________
0.5
Design vapor load, VL [from Eq. (1a2)] VL / VL (Ult) as % must be < 90%; otherwise repeat Step 3 with a larger value of Dt.
Eq. (6a2)
______________________
% Ult
*For 2-pass trays
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VALVE TRAY CALCULATION FORM (CUSTOMARY) SHEET 11 OF 12 Tray number(s) 6. ç
______________________ Inboard* Outboard
Checking Process Limitations (Cont) (b) Liquid load L [from Eq. (3c1)]
__________
__________
If L is < 1.5, run the sieve tray program #1133 using 0.5 in. diameter holes and an open area that gives the same dry tray pressure drop as the valve tray. Consult your FRACTIONATION SPECIALIST if any warning messages are generated. If L is < 0.25 or > 14, consult your FRACTIONATION SPECIALIST. (c) Downcomer entrance velocity for high pressure towers If ρv / ρL > 0.03, the designer must calculate the downcomer inlet velocity based on Eq. (6c1). If Eq. (6c1) gives a lower velocity than that calculated from Eq. (2b1), recalculate all steps after Eq. (2b1) using this lower value. If Eq. (6c1) gives a higher value than that calculated from Eq. (2b1), use the Eq. (2b1) value and repeat all calculations following Eq. (2b1). ψ 0.5 ρv Af ρL − ρ v
VL(Ult)
Vdi =
ψ
1 −
Eq. (6c1)
______________________
For 2-pass trays, use the smaller value of Af and its corresponding value of ψ in Eq. (6c1). (d) Downcomer Inlet Choking For outboard downcomers: h − hwo Determine whether f > 1.0 1 .3 r
Eq. (6d1)
XXX
__________
If it is, increase downcomer size by increasing r until the ratio ≤ 1.0. Repeat all calculations from Step 2b onward. For inboard downcomers: h − h wo Determine whether f > 1.0 1.6 (r / 2)
Eq. (6d2)
If it is, increase downcomer size by increasing r until the ratio ≤ 1.0 Repeat all calculations from Step 2b onward.
*For 2-pass trays
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VALVE TRAY CALCULATION FORM (CUSTOMARY) SHEET 12 OF 12 Tray number(s)
______________________ Inboard* Outboard
EO NT
______________________ ______________________ ______________________ ______________________
(e) Vapor Recycle Check If the downcomer inlet velocity exceeds the allowable inlet velocity, some vapor recycle will occur. New designs and revamps - avoid vapor recycle by enlarging the downcomer inlet area. 7.
Tray Efficiency Overall efficiency, EO (From Section III-I) Number of theoretical trays required (NT) Number of actual trays required (NT /EO) Number of actual trays specified or available (for revamps)
8.
NA
Balanced Design Review paragraph in text entitled Balanced Design (Step 8) to ensure that the final tray design is as “balanced” as possible.
9.
Tower Checklist See Table 7 in Section III-A for Tower Design Checklist (Trays).
*For 2-pass trays
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VALVE TRAY CALCULATION FORM (METRIC) SHEET 1 OF 11 (1) Location & Project ____________________________________________ Date ____________________________________ Tower Number _______________________________________________ By _____________________________________ Service _____________________________________________________ Tower Section (Top, Bottom, etc.) Tray Number(s) Covered by this Design Design Based on Tray Number 1.
______________________ ______________________ ______________________
Vapor and Liquid Loadings at Conditions (a) Vapor to or from tray (use maximum value) Temperature, °C Pressure, kPa abs Density, ρv, kg/m3 Vapor rate, wv, kg/s qv, volumetric vapor rate, m3/s =
wv ρv
ρv wv
______________________ ______________________ ______________________ ______________________
Eq. (1a1)M
qv
______________________
Eq. (1a2)M
VL
______________________
Vapor load, VL, m3/s ρ v VL = qv ρ − ρv L
0.5
______________________ ______________________
Minimum vapor rate, wv(min) kg/s Density at minimum rates, ρv(min) kg/m3 Minimum vapor rate, qv(min), m3/s qv(min) =
w v(min) ρv(min)
Eq. (1a3)M
qv(min)
______________________
Eq. (1a4)M
VL(min)
______________________
µL σL wL ρL
______________________ ______________________ ______________________ ______________________ ______________________
LL, QL
______________________
wL(min) ρL(min)
______________________ ______________________
QL(min)
______________________
Minimum vapor load, VL(min), m3/s ρv(min) VL(min) = qv(min) ρL(min) − ρv(min)
0.5
(b) Liquid to or from tray (use maximum value) Temperature, °C Viscosity µL, mPa•s Surface tension σL, mN/m Liquid rate, wL, kg/s Density ρL, kg/m3 LL = QL , liquid rate, dm3 / s =
Eq. (1b2)M
1000 w L ρL
Minimum liquid rate, wL(min), kg/s Density at minimum rates, ρL(min) kg/m3 QL(min) , minimum liquid rate, dm3 /s =
1000 w L(min) ρL(min)
Eq. (1b4)M
(1) If an equation is not given on this calculation form for a given variable, it can be found on the pertinent figure.
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VALVE TRAY CALCULATION FORM (METRIC) SHEET 2 OF 11
2.
Tray number(s)
______________________
σSTD
______________________
Trial Tray Spacing, Size, and Layout (For rating case, use actual tower dimensions and modify as needed.) (a)
Trial tray size Standard surface tension σSTD, from Figure 2 or from: σSTD = 10a where a = 1.68 - 0.244 / µL0.55 σL σSTD Kσµ from Figure 3 or from: σ K σµ = L σSTD
0.317
for
σL < 1 .0 σSTD
Eq. (2a1)M
______________________
Eq. (2a2)M
Kσµ
______________________
Eq. (2a3)M
Kσµ
______________________
Eq. (2a4)M
Dtr
______________________
As
______________________
L'
______________________
Np
______________________
OR K σµ = 1.0 for
σL ≥ 1.0 σSTD
For rating cases, skip to Step 2b. Tray spacing H, mm (select from table in Detailed Design Procedure - Step 2 or use 450 mm for first trial). Trial diameter Dtr, mm: 134 VL Dtr = 305 0.115 LL + H K σµ 1000
[
]
2
0.5
Superficial area As, m2: As =
π D2tr X 10- 6 4
For first trial, assume Np = 1 L' = dm3 / s / m of diameter / pass =
1000 QL Dtr (Np )
If L' ≤ 17 or Dtr ≤ 1500 mm, Np = 1
Eq. (2a5)M
If L' > 17, set Np = 2. If L' > 35 using final value of Np, consult your FRACTIONATION SPECIALIST.
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VALVE TRAY CALCULATION FORM (METRIC) SHEET 3 OF 11
2.
Tray number(s)
______________________ Inboard* Outboard
Vdi
______________________
Trial Tray Spacing, Size, and Layout (Cont) (For rating case, use actual tower dimensions and modify as needed.) (b) Downcomer Sizing Vdi = Allowable downcomer inlet velocity, m/s, from either Figure 4B and its corresponding equation (Eq. 2b1)M below, or from Table 2. Use the lower value. For foaming systems, use Vdi ≈ 0.06 m/s. σL (ρL − ρv ) Vdi = 0.59 ρL 2
0.311
Eq. (2b1)M
Note If the ratio of ρv / ρL > 0.03 a lower velocity may be required by Eq. (6c1)M. Eq. (6c1)M cannot be calculated yet because several of the required variables are not calculated until Steps 5 and 6. However, if Figure 4B or Eq. (2b1)M yields a velocity > 0.09 m/s, set Vdi = 0.09 for the first trial.
______________________
Vdi
______________________
Minimum TOTAL downcomer inlet area Adi, m2 A di(min) =
Eq. (2b2)M
QL 1000 Vdi
Adi (min)
__________
__________
For single pass trays, Adi must be ≥ 0.068 As. For outboard downcomers of two pass trays, Adi/2 must be ≥ 0.068 As. For inboard downcomers, their width must be at least 200 mm. Vdo = Allowable downcomer outlet velocity, m/s = 2 (Vdi) or 0.18 m/s, whichever is less provided Vdi ≤ 0.18 m/s. For Vdi > 0.18 m/s make Vdo = Vdi Also, if straight downcomers are desired, set Vdo = Vdi. Minimum total downcomer outlet area Ado, m2 A do (min) =
QL 1000 Vdo
Vdo Eq. (2b3)M
Ado(min)
However, Ado (min) must be ≥ 0.068 As for single pass trays and outboard downcomers of multipass trays. For inboard downcomers, their width at the bottom must be at least 150 mm. If the sum of Adi + Ado exceeds 60% of As, the tower diameter must be increased and a new KHL and Af calculated.
*For 2-pass trays.
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VALVE TRAY CALCULATION FORM (METRIC) SHEET 4 OF 11
3.
Tray number(s)
______________________ Inboard* Outboard
Dt H As Aw Ab Af Ao / Ab
______________________ ______________________ ______________________ __________ __________ __________ __________ __________ __________ ______________________
Final Tray Spacing, Size and Layout (a) Tower areas Tower diameter Dt, mm Tray spacing H, mm Superficial area, As, m2 Waste area Aw (if any), m2 Bubble area Ab, m2 (See Figure 12 in Section III-A) Free area, Af, m2 (See Figure 13 in Section III-A) Fraction hole area Ao / Ab [Select value from Table 1 or start with 0.12 (12%)] Actual hole area Ao, m2 (Ab • Ao / Ab)
Ao
__________
__________
r ro
__________ __________
__________ __________
TOTAL Downcomer inlet area Adi, m2 [from Eq. (2b2)M] TOTAL Downcomer outlet area Ado, m2 [from Eq. (2b3)M] Outlet weir height hwo, mm (from Table 1 or 50 mm for first trail)
Adi Ado hwo
__________ __________ __________
__________ __________ __________
Outlet weir length, lo and l*o , mm.
lo* hwi
__________ lo_________ __________ __________
li lud*
__________ __________
__________ lud________
lo*
__________
lo_________
Eq. (3c1)M
L
__________
__________
Eq. (3c2)M
KHL
Note: For 2 pass trays, try to keep the Ao the same for each pass. If required, revise the Ao / Ab ratio above. (b) Downcomers and weirs** Downcomer rises/widths, r, mm.
(Inlet) (Outlet)
Inlet weir length hwi, mm (use only if needed for sealing the downcomer) Inlet weir length li, mm. (Reminder: Ii ≠ lud) Length of bottom edge of downcomer, lud, mm. (c) Jet flooding Outlet weir length lo and lo*, mm (from Step 3b) For segmental downcomers, use length of a chord joining the ends of the segmental downcomer (projected weir length). L = dm3/s/meter of weir/pass For 2-pass trays, calculate a value for each pass, i.e., for lo and l*o . KHL, tray spacing-liquid rate factor. (Use Figure 1C for hydrocarbon systems, Figure 1D for aqueous systems OR the equations below). For 2-pass trays, calculate a value for each pass. For hydrocarbon systems (from Figure 1C or) (0.47 + 0.0493 L )
KHL
H 304.8 = L(0.0125 + H / 16,700 ) e
__________
*For 2-pass trays. **See Section III-K for chord length and area tables.
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VALVE TRAY CALCULATION FORM (METRIC) SHEET 5 OF 11 Tray number(s) 3.
______________________ Inboard* Outboard
Final Tray Spacing, Size, and Layout (Cont) For aqueous systems (from Figure 1D or) KHL = 0.0573 (H)0.5 (10)−0.00191L
Eq. (3c3)M
K σµ (from Step 2a)
KHL
__________
__________
Kσµ
______________________
Jet flooding for hydrocarbon systems: VL = 0.090 K σµ KHL A f Allowable
Eq. (3c4)M
__________
__________
Eq. (3c5)M
__________
__________
__________
__________
Jet flooding for aqueous systems: VL = 0.0622 K σµ KHL A f Allowable VL A f Design
= (from Steps 1a and 3a)
Design/Allowable jet flood velocity, expressed as %. Compare calculated value(s) with criteria in Table 1 for foaming systems and Table 2 for all other systems. If these criteria are not satisfied, change tower diameter and/or tray spacing and repeat Step 3. 4.
% Jet Flood
Turndown and Dry Tray Pressure Drop (a) For NEW designs, assume a dry tray pressure drop, hed based on discussion in text and Table 1 and proceed to Step 5a.
hed
______________________
Vo t1 t2 K1 K2 A1 A2 Ao
__________ __________ ______________________ ______________________ ______________________ ______________________ __________ __________ __________ __________ __________ __________
For REVAMPS, follow the procedure outlined below.** Calculate the various transition velocities (see Figure 7) and compare with the average hole velocity, Vo. This will determine the Region (Figure 7) your tray is operating in. Do for both the design and the turndown operation. Vo t1 t2 K1 K2 A1 A2 Ao
= = = = = = = =
q v / Ao Thickness of lighter valves, mm Thickness of heavier valves, mm Dry tray pressure drop coefficient (Table 3C) Dry tray pressure drop coefficient (Table 3C) Open area of lighter valves, m2 Open area of heavier valves, m2 Total valve open area, m2 (A1 + A2) Reminder: Ao is based on the punched area for round movable valves and the peripheral area for round fixed and Nutter valves.
*For 2-pass trays. **For trays with only one valve weight, see Design Procedure, Step 4 in the text for guidance.
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VALVE TRAY CALCULATION FORM (METRIC) SHEET 6 OF 11 Tray number(s) 4.
______________________ Inboard* Outboard
Turndown and Dry Tray Pressure Drop (Cont) Transition velocity where lighter valves are fully open, Vo(T1), m/s
Vo( T1)
ρm 1.35 t1 ρv = K2 − K 1 2 ( A / A ) 1 o
0.5
Eq. (4a1)M
Vo(T1)
__________
__________
Eq. (4a2)M
Vo(T2)
__________
__________
Eq. (4a3)M
Vo(T3)
__________
__________
Eq. (4b1)M
f1
__________
__________
Eq. (4b2)M
f
__________
__________
Transition velocity where heavier valves begin to open, Vo(T2), m/s
Vo( T 2 )
ρm 1.35 t 2 ρv = K2 − K1 2 ( A / A ) 1 o
0.5
Transition velocity when all valves are fully open, Vo(T3), m/s
Vo( T 3 )
ρm 1.35 t 2 ρ v = K 2 − K1
0.5
(b) Calculation of fraction of valves open and the dry tray pressure drop for each Region (Figure 7) REGION 1 If the average hole velocity (Vo) is less than Vo(T1), then the fraction of light valves open, f1, is K2 ( A1 / A o )2 f1 = 1.35 t1 ρm K1 + Vo2 ρv
0.5
And the fraction of the total valves open, f, is A2 A f = f1 1 + f2 Ao Ao
*For 2-pass trays.
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VALVE TRAY CALCULATION FORM (METRIC) SHEET 7 OF 11 Tray number(s) 4.
______________________ Inboard* Outboard
Turndown and Dry Tray Pressure Drop (Cont) Where f2 = 0 by definition And the dry tray pressure drop, hed1, in mm of hot liquid is hed1 = 1.35 t1
ρm ρ + K1 Vo2 V ρL ρL
Eq. (4b3)M
hed1
__________
__________
Eq. (4b2)M
f
__________
__________
Eq. (4b4)M
hed2
__________
__________
Eq. (4b5)M
f2
__________
__________
Eq. (4b2)M
f
__________
__________
Eq. (4b6)M
hed3
__________
__________
Eq. (4b2)M
f
__________
__________
Eq. (4b7)M
hed4
__________
__________
REGION 2 If the average hole velocity, Vo is > Vo(T1) and < Vo(T2), calculate the fraction of total valves open from A A f = f1 1 + f2 2 Ao Ao Where f1 = 1.0 and f2 = 0 (by definition) And the dry tray pressure drop, hed2, in mm of hot liquid is 2
Vo ρv hed2 = K 2 (A / A ) 1 o ρL REGION 3 If the average hole velocity, Vo, > Vo(T2) and < Vo(T3) then the fraction of heavy valves open, f2, is Vo K 2 f2 = A 2 / A o 1.35 t 2 ρm + K1 Vo2 ρv
0.5
A − 1 A2
And the fraction of total valves open, f, is A A f = f1 1 + f2 2 Ao Ao And the dry tray pressure drop, hed3, in mm of hot liquid is hed3 = 1.35 t 2
ρm ρ + K1 Vo2 v ρL ρL
REGION 4 If the average hole velocity, Vo, > Vo(T3) f = 1.0 (by definition) And the dry tray pressure drop, hed4, in mm of hot liquid is hed4 =
K 2 Vo2 ρv ρL
*For 2-pass trays.
EXXON RESEARCH AND ENGINEERING COMPANY - FLORHAM PARK, N.J.
DESIGN PRACTICES Section
FRACTIONATING TOWERS
VALVE TRAYS
Page
III-E
EXXON ENGINEERING
66 of 69
Date PROPRIETARY INFORMATION - For Authorized Company Use Only
December, 1998
VALVE TRAY CALCULATION FORM (METRIC) SHEET 8 OF 11 Tray number(s) 4.
______________________ Inboard* Outboard
Turndown and Dry Tray Pressure Drop (Cont) (c) hed = Effective dry tray pressure drop, mm of hot liquid obtained from the appropriate REGION above. (hed should not exceed 56 mm for foaming systems and 113 mm for all other systems.)
hed
__________
__________
hed
__________
__________
PVE
__________
__________
Vb
__________
__________
L
__________
__________
Eq. (5b2)M
hf
XXX
__________
Eq. (5b3)M
hf
Reminder for low liquid rate cases: If L lies between 0.6 to 3.7, hed should be ≤ 57 mm. If L < 0.6, contact your FRACTIONATION SPECIALIST. If f equals or exceeds: 0.35 for 1-pass 0.50 for 2-pass
0.70 for 3 & 4-pass, then design is acceptable.
If f is less than the value given above, see your FRACTIONATION SPECIALIST. Reminder: It is presumed that the tower has already been “sectioned” to reduce turndown requirements. 5.
Tray Hydraulics and Downcomer Filling (a) Effective dry tray pressure drop, hed (Obtain from Step 4b). (b) Clear liquid height, hc The shortcut clear liquid height calculation procedure is outlined below (a rigorous trial and error procedure is presented in Table 3B of Section III-B). Determine vapor energy parameter, PVE from Figure 8C or calculate from:
PVE
ρ 16.7 Vb0.82 v ρL = 0.25 Ao Ab
0.36
Eq. (5b1)M
where Vb is the vapor velocity through the bubble area, m/s (i.e., qv / Ab) L [from Eq. (3c1)M] For single pass trays, and outboard downcomers on 2-pass trays, calculate froth height, hf via hf = hwo + 25.4 KVE KW where: hwo from Step 3b KVE from Figure 8D or from Eq. on that figure KW from Figure 8G or from Eq. on that figure For inboard downcomers on 2-pass trays, calculate hf from hf = h wo + 15.7 [ PVE L ]0.53 Determine froth density, ψ from Figure 8H or from *For 2-pass trays.
EXXON RESEARCH AND ENGINEERING COMPANY - FLORHAM PARK, N.J.
__________
XXX
DESIGN PRACTICES
FRACTIONATING TOWERS
VALVE TRAYS EXXON ENGINEERING
Section
Page
III-E
67 of 69
Date PROPRIETARY INFORMATION - For Authorized Company Use Only
December, 1998
VALVE TRAY CALCULATION FORM (METRIC) SHEET 9 OF 11 Tray number(s) 5.
______________________ Inboard* Outboard
Tray Hydraulics and Downcomer Filling (Cont) P ψ = 0.022 − 0.293 In VE 0.41 (hf )
Eq. (5b4)M
ψ
__________
__________
Calculate clear liquid height hc from hc = ψ hf
Eq. (5b5)M
hc
__________
__________
Eq. (5c1)M
ht
__________
__________
Eq. (5d1)M
hud
__________
__________
Eq. (5d2)M
c
__________
__________
Eq. (5e1)M
hi
__________
__________
Eq. (5e2)M
hi
__________
__________
Eq. (5f1)M
hd
__________
__________
hd (calculated) as a % of tray spacing
__________
__________
hd (allowable) as % of tray spacing (see Table 2 and Figure 5B for non-foaming systems and Table 1 for foaming systems).
__________
__________
(c) Total tray pressure drop ht ht = hc + hed (d) Head loss under downcomer hud hud
1000 Q L = 160 c Np Iud
2
Assume c = 38 mm or use actual clearance for a rating case. If hud >> 25 mm, set hud = 38 mm and calculate c from: c=
1.29 × 10 4 QL Np Iud (hud ) 0.5
Note: For shaped downcomers use a coefficient of 53 in place of 160, in Eq. (5d1)M. (e) Inlet head hi For tray with an inlet weir: 1000 QL hi = 6.93 Np Ii
2/3
+ h wi
For tray without an inlet weir: hi = hc [from Step 5b, Eq. (5b5)M] (f)
Downcomer filling hd With 2-pass trays for inboard hd, use value of hi on the outboard tray and vice versa. See Figure 14 of Section III-B for further explanation. ρL hd = (ht + hud ) + hi + 25, mm ρL − ρv Note: For a tray with a recessed inlet box or an inlet weir, substitute 2 hud in place of hud, in the above equation.
If hd (calculated) exceeds hd (allowable) reduce hed, hc, hud, hi, or increase tray spacing. *For 2-pass trays.
EXXON RESEARCH AND ENGINEERING COMPANY - FLORHAM PARK, N.J.
DESIGN PRACTICES Section
FRACTIONATING TOWERS
VALVE TRAYS
Page
III-E
68 of 69
Date PROPRIETARY INFORMATION - For Authorized Company Use Only
December, 1998
EXXON ENGINEERING
VALVE TRAY CALCULATION FORM (METRIC) SHEET 10 OF 11 Tray number(s) 5.
______________________ Inboard* Outboard
Tray Hydraulics and Downcomer Filling (Cont) (g) Downcomer Sealing Calculate [hi + hud] at minimum rates. Repeat calculations in Steps 5d and 5e using QL(min) and qv(min).
Eq. (5g1)M
__________
__________
If at minimum rates, (hi + hud + 6 mm) is less than c, consider using a lower value of c (possibly with a shaped downcomer lip), increasing the outlet weir height, adding an inlet weir, or using a recessed inlet box, in that order of preference. If sealing is still a problem, consult your FRACTIONATION SPECIALIST. 6.
Checking Process Limitations (a) Ultimate capacity ______________________
Free area Af, m2 from Step 3(a). For 2-pass trays, use the smallest value. β VL(Ult ) = 0.378 A f 1 + β
σL ρL − ρv
ρ − ρv where : β = 1.4 L ρv
0.25
VL(Ult)
______________________
0.5
Design vapor load, VL [from Eq. (1a2)M] VL / VL(Ult) as % (must be < 90%; otherwise repeat Step 3 with a larger value of Dt). ç
Eq. (6a1)M
Eq. (6a2)M
______________________
% Ult
______________________ ______________________
(b) Liquid load L [from Eq. (3c1)M] If L < 3.7, run the sieve tray program #1133 using 13 mm diameter sieve holes and an open area that gives the same dry tray pressure drop as the valve tray. Consult your FRACTIONATION SPECIALIST if any warning messages are generated. If L is < 0.6 or > 35, consult your FRACTIONATION SPECIALIST. (c) Downcomer entrance velocity for high pressure towers If ρv / ρL > 0.03, the designer must calculate the downcomer inlet velocity based on Eq. (6c1)M. If Eq. (6c1) gives a lower velocity than that calculated from Eq. (2b1)M, recalculate all steps after Eq. (2b1)M using this lower value. If Eq. (6c1)M gives a higher value than that calculated from Eq. (2b1)M, use the Eq. (2b1)M value and repeat all calculations following Eq. (2b1)M.
*For 2-pass trays.
EXXON RESEARCH AND ENGINEERING COMPANY - FLORHAM PARK, N.J.
__________
__________
DESIGN PRACTICES
FRACTIONATING TOWERS
VALVE TRAYS EXXON ENGINEERING
Section
Page
III-E
69 of 69
Date PROPRIETARY INFORMATION - For Authorized Company Use Only
December, 1998
VALVE TRAY CALCULATION FORM (METRIC) SHEET 11 OF 11 Tray number(s) 6.
______________________ Inboard* Outboard
Checking Process Limitations (Cont)
Vdi
ψ VL(Ult) 1 - ψ = 0.5 ρv Af ρL − ρv
Eq. (6c1)M
______________________
For 2-pass trays, use the smaller value of Af and its corresponding value of ψ in Eq. (6c1)M. (d) Downcomer Inlet Choking For outboard downcomers: h − hwo Determine whether f > 1 .0 1 .3 r
Eq. (6d1)M
XXX
__________
If it is, increase downcomer size by increasing r until the ratio ≤ 1.0. Repeat all calculations from Step 2b onward. For inboard downcomers: h − h wo Determine whether f > 1 .0 1.6 (r / 2)
Eq. (6d2)M
__________
XXX
If it is, increase downcomer size by increasing r until the ratio ≤ 1.0. Repeat all calculations from Step 2b onward. (e) Vapor Recycle Check If the downcomer inlet velocity exceeds the allowable inlet velocity, some vapor recycle will occur. New designs and revamps - avoid vapor recycle by enlarging the downcomer inlet area. 7.
Tray Efficiency Overall efficiency, EO (From Section III-I) Number of theoretical trays required (NT) Number of actual trays required (NT/EO) Number of actual trays specified or available (for revamps)
8.
EO NT NA
Balanced Design Review paragraph in text entitled Balanced Design (Step 8) to ensure that the final tray design is as “balanced” as possible.
9.
Tower Checklist See Table 7 in Section III-A for Tower Design Checklist (Trays).
*For 2-pass trays.
EXXON RESEARCH AND ENGINEERING COMPANY - FLORHAM PARK, N.J.
______________________ ______________________ ______________________ ______________________
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