[Glitsch] - Ballast Tray - Bullettin 4900

The Separations Company'"

Sixth Edition

To those using this manual""

@

This manual is a design procedure for Glitsch Ballast Trays. Certain aspects of tower design are important if maximum capacity is desired and potential bottlenecks are to be circumvented. In the initial phase of tower design, the following points should considered when spacings are 1. Extra tray spacing usually is required at transition trays, i.e., where a change in the number of

passes is contemplated. A spacing of 4'-0" is preferred, particularly in large towers. 2. Extra space is required if the feed is vaporized. 3. Extra space should be provided for internal liquid feed pipes if tower loadings are high at the

feed point. Internal piping preferably is located at a point just below trusses of the next higher tray.

A column may Hood prematurely for reasons other than tray design. The following are examples: 1. The liquid line to the reb oiler is too small, becomes plugged with debris, or the reboiler vapor

line is too small or otherwise restricted. Any of these may cause liquid to back up in the bottom of the column above the reboiler vapor line. 2. The reboiler vapor jet stream impinges on the seal pan overflow, resulting in excessive entrain-

ment to the bottom tray. 3. A restriction to liquid flow through a downcomer exists due to incorrect tray installation or the

of 4. Reboiler or feed vapor improperly introduced. ,5. Excessive foaming or vaporization of liquid in downcomer. 6. Internal loads are appreciably higher than design loads due to an incorrect latent heat of vaporization, a change in operating pressure, or not having made a proper heat and material balance.

phase. An occasional slug of methanol has been used to alleviate hydrate problems, 8. The system pressure is too close to the critical pressure.

The design procedure given herein is intended to be neither conservative nor optimistic. As design procedures for some valve type trays frequently indicate a "calculated" capacity which is higher than calculated by this design manual, it should be understood that Glitsch Ballast trays are guaranteed to have a capacity equal to, or greater than, any other conventional trays on the market.

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Ballast® Tray Features \Vebster has defined ballast for usc in reference to "that which needs to be held down because it is

too light, too buoyant, or the like; it implies the addition of something heavy or solid enough to insure stability." Durmg an early phasc in research and development of Ballast trays, it was found that valves that wcre permitted to seat Hush had a tendency to be unstablc; i.e., at low vapor rates, the vapor would channel through a few wide-open valves in a small aerated zone located at some indeterminate position. The remaining valves would be completely closed. With flush seatcd units, liquid can bypass around the aerated zone on single pass trays; and on two pass trays, one side of the tray can be completely inactive, or the activity can switch back and forth from one side to the other. Glitsch has climinated the problem of instability with various types of Ballast trays. The Glitsch A-I Ballast tray has a thrcc-piece unit consisting of an orifice CO\'er, Ballast plate and a travcl stop. At extremely low \'apor rates, the orificc cover rise is limited by thc wcight of the Ballast plate. \Vhen only thc orifice co\'ers arc open, the slot area is relatively low which causes a larger portion of the capped area to hc actiw'. At highcr \'apor rates, thc Ballast plate rises until it contacts the travel stop. The A-I Ballast tray is vcry resistant to leakage and is highly recommended when the liquid rates are extremely low, or if the absolute maximum Hexibility is required. It is a valve type tray somewhat similar to the "rivet" tray first used in 1922. It differs from other vah'e type trays in three major respects. First, the V-I unit has a two-stage slot opening rather than the single-stage conventionally used. This permits a flow of vapor through all of the valves at low \'apor rates and results in a wide range of stable operating conditions. Second, the of the valve

provided with a 5h

is sloped d

at the

portion of the lip. The sharp edge accentuates turbulence at the position where vapor enters the liquid and generates additional \'Clpor-liquid interfacial area to give a high tray effiCiency. Third, a heavy weight unit is normally used except in vacuum towers. The heavy unit increases the pressure drop and thereby increases tray efficiency in the operating region where the valves are not fully open.

Advantages of Ballast trays may be summarized as follows: 1. Maximum efficiency at low loads insures a minimum quantity of off.·specification products during start-up. The high degree of flexibility makes it possible to operate with a minimum utility expense over a \vide range of feed rates. 2. High efficiency at conditions 5 to 10 per cent below incipient Hooding results in an increase in usable capacity. This permits more effective utilization of the column and auxiliary equipment. 3. High efficiency at intermediate load conditions can be utilized to improve product quality; to reduce the reHux ratio, resulting in a savings in utilities; or, to reduce the number of trays.

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4. The combination of low pressure drop and high efficiency for vacuum systems means a lower tower pressure drop. The V-4 Ballast tray has been used to separate the ethylbenzene-styrene system in a single column. 5. The mechanical design of the tabs are such as virtually to eliminate sticking problems. No sticking problem.s bave occurred in approximately 4000 pro·cess nnits and 30,000 columns of V-type trays. Shutdown time is decreased, due to rapid draining. Maintenance is simplified and worker comfort is improved because the top of the disc is smooth and flat. There are no sharp projections above the tray deck. At zero to relatively low vapor rates, the V-type unit is seated on three tabs which hold the disc above the deck by a distance of approximately 0.1". The 0.1" height is an optimum distance. A higher initial rise results in too much slot area for operation at low loads and a lower initial rise results in tray instability. The line of contact of the tab with the deck is a 90 0 edge which is provided in order to help prevent sticking from mst and corrosion. For special conditions, it may be desirable to permit selected Ballast units to seat completely. The tabs are omitted to accomplish this. At high vapor rates, the unit rises vertically to a maximum clearance above the deck of approximately 0.32". At intermediate vapor rates, some units will be completely open and the others will be resting on the deck. Ballast trays may be used in any clean service, and have been used in many services subject to severe fouling with excellent success. By experience in commercial columns where cleaning may be necessary, it has been found that Ballast trays stay on stream for much longer periods of time than do other trays in the same service. services use customers prefer stainless for nmy use tray components not touching the valve. Carbon steel or monel must be used in service where HF is present. Carbon steel decks have been used in approximately 60 per cent of all installations to date. Carbon steel Glitsch Ballast units are only occasionally used for reasons of economy. They are not normally recommended because the sharp edge on the lip will be lost due to rusting prior to the initial start-up or at shutdowns. The sharp edge is worth 5 to 10 per cent in added tray efficiency. . . . . , ... ' five users in the selection of the Glitsch equipment best suited to their needs. All technical data contained herein teere deueloped under carefully controlled conditions tehich may not duplicate the user's actual process conditions. Therefore, nothing in this manual is to be deemed a warranty. Glitsch will be pleased to give appropriate warranties in its quotation and which tcill be incorporated into the user's purchase order.

Glitsch reserves the right to modify or improve these products without notice.

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I

•

FIGURE 1

Ballast®Unit Types Nomenclature used: X: Flushoseating B: Blanked H: Heavy

Vol, V-4

, A-2X, A-5X

V-lX, V-4X

..0.-2, ..0.-5

(Flat Orifice)

V-4 TYPE ~ (Extruded Orifice)

V-2X

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Description of Ballast® Units The various types of Ballast units are shown on the facing page. A description of each unit follows:

V-o A non-moving unit similar in appearance to the V-I in a fully open position. It is used in services where only moderate flexibility is required and minimum cost is desired. V-I A general purpose standard size unit, used in all services. The legs are formed integrally with

the valve for deck thicknesses up to

%".

V-2 The V-2 unit is similar to the V-I unit except the legs are welded-on in order to create a more

leak-resistant umt. The welded legs permit fabrication of Ballast units for any deck thickness or size. Large size units are frequently used for replacement of bubble caps. V·3 A general purpose unit similar to the V-2 unit except the leg is radial from the cap center. V-4 This signifies a venturi-shaped orifice opening in the tray floor which is designed to reduce sub-

stantially the parasitic pressure drop at the entry and reversal areas. A standard Ballast unit is used in this opening normally, although a V-2 or V-3 unit can be used for special services. The maximum deck thickness permissible with this opening is 10 gage. V-5 A combination of

v-o and V-I units. It normally

is used where moderate flexibility is required

and a low cost is essential. A-I The original Ballast tray with a lightweight orifice cover which can close completely. It has a

separate Ballast plate to give the two-stage effect plate and orifice cover in proper relationship.

a cage or

stop to

A·2 The same as A-I, except the orifice cover is omitted. A-4 An A-I unit combined with a venturi-shaped orifice opening in order to reduce the pressure

drop.

The diameter of the standard size of the V-series of Ballast units is 1%". The V-2 and V-3 units are available in sizes up to 6". Photographs of several Ballast trays are shown on page 8 and 9.

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FIGURE 2

Vol BALLAST TRAY, 9'06" DIA.

Vol BALLAST TRAY (with Recessed Inlet Sump) 10'-0" DIA.

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FIGURE 3

V-I BALLAST TRAY, 5'-6" DlA.

V-I BALLAST TRAY,

V-6 BALLAST TRAY 6" DIA. PILOT COLUMN

15'-0" DIA.

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Process Design Data Sheet

Item No. or Service .............. I I : - - - - - - - - - - - , r - - - - - - - - - - r - - - - - - - - - - - , - - - - - - - \ I Tower diameter, LD .............. \ t - - - - - - - - - \ - - - - - - - - \ - - - - - - - - l - - - - - - - - - - i I Tray spacing, inches .............. \t---------\--------\---------l------~ Total trays in section .............. D---------\----------i--------l-------~ Max./.:;, P, mm Hg ................ 1 - - - - - - - - \ - - - - - - - + - - - - - - - + - - - - - - - - 1 Conditions at Tray No ............. I - - - - - - - j - - - - - - - j f - - - - - - - - t - - - - - - - f Vapor to tray, of ................. Pressure, ............ Compressibility .............. "Density, lb./ cu. ft. ............ "Rate, lb./hr. ................. cu. fUsec. (cfs) .............. cfs V D,·I (DL-D,,) ............

1--------t---------1----.-----I--------II I-------t--------j-------t-------f II:----------il--------I-------.--\---------\I

I--------!--------\---------I-------------I 11---------+--------[--------1---------11 11---------+--------[-------1--------11 II--------f--------II---------f------

Liquid from tray, of .............. I J - - - - - - - f - - - - - - - - - j - - - - - - - - - I - - - - - - - - J I Surface tension ............... 1 1 : - - - - - - - 1 - - - - - - - - 1 - - - - - - - - - - 1 - - - - - - - \ 1 Viscosity, cp ................. I J - - - - - - - - - - - , f - - - - - - - - - j - - - - - - - - - - I - - - - - - - J I "Density, lb./ cu. ft. ............ 1 I : - - - - - - - - I I - - - - - - - - - I - - - - - - - - - I - - - - - - - - - i I "Rate, lb./hr. ................. D--------+--------ff---------+------~ GPM hot liquid .............. ~_ _ _ _ _"b.,,_ _ _ _ _"""-_ _ _ _ _"""""_ _ _ _ __!I Foaming tendency............ None ____ Moderatc ____High _ _ _ _ Severe ____ _ "These "alues are required in this form for direct computer input. NOTES:

6. 7. S. 9.

various in one tower, rnay sections loading cases. Use additional sheets if necessary. Is maximum capacity at constant vapor-liquid ratio desircd?_ _ _ _ _ _ __ Minimum rate as % of design rate: % Allowable downcomer velocity (if specified): ftl sec Number of flow paths or passes: Glitsch Choice; _ _ _ _ _ _ _ _ _ _ _ _ _ __ Bottom tray downcomer: Total draw ; Other ______________ Trays numbered: top to bottom ; bottom to top _ _ _ _ _ _ _ _ _ _ _ _ _ __ Enclose tray and tower drawings for existing columns. ~lanhole size, inches. Manways removable: top ; bottom _ _ _ __ top & bottom _ _ _ _ _ _ _ _ _ __

12. 13. 14. 15. 16. 17.

AdjllstahI6 weirs required: ycs _ _ _ _ _ _ _ _ _ _ _ _ _ __ Packing material if reqnired ____._,______,___________________ , _______ ,__ ; not required _ _ __ Tray material and thickness _ _ _ _ _ _ _ _ _ _ ._ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ Valve material _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ Ultimate user _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ Plant location _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ Other _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __

1 J .•

2. 3. 4. 5.

Form No. PE-S

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Tray Design Information Required

Although it is possible to design valve trays based on only the internal vapor and liquid rates and densities, a more thorough design frequently can be obtained with complete information shown on the Process Design Data Sheet PE-8 (facing page). It is not necessary to provide all the information requested unless the system has properties different from those of conventional refinery and chemical separations.

Howeve1', a design which is m01'e likely to give the desi1'ed sepamtion, capacity, p1'essure drop and flexibility will be obtained if complete information is given. The amount of time 1'equired to fill in the form is negligible when the importance of complete information is 1'ecognized. It is important to have internal liquid and vapor loads at several tray locations if the loads vary appreciably from tray to tray. If the column is to bc used in several different services, the loadings for each case should be calculated. An indication of minimum anticipated loads is also important. Minimum loads may be expressed as a percentage of design loads. The type of service involvcd, or variety of services, should be given. Glycol dehydrators and amine absorbers are not designed by the same procedure as other service having identical densities and flow rates. If the system is frothy or has some other peculiar characteristic, the property should be described. Surface tension is an important physical property which should be given if available.

The allowable pressure drop, if specified, should not be made more 1'estrictive than necessary. Ballast trays can be designed for a very low pressure drop; lwweve1', an unnecessarily restrictive pressure drop limitation )nay reduce the number of trays to a point where the desired separation cannot be obtained without going to two

01'

more towers in series.

Frequently, an existing or specified tower diameter is larger than required. If a future increase in capacity is not contemplated, a less expensive design can be obtained by using larger downcomers than necessary, or by reducing the number of Ballast units. Many customers wish to utilize potential excess capacity. In order to obtain maximum capacity at constant vapor-liquid ratio, the ratio of downcomel' area to active area is maintained for design conditions. This provides both adequate downcomer area and the proper active area for future increased loads. In most instances, the ultimate user will prefer

Adjustable weirs are not required for a majority of services. They will not be used unless specified by the customer or required by process conditions. Packing is not ordinarily required except in sumps and at the ends of trusses. The packing material is important for unusual services.

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Design Procedure Ballast trays arc designed by a simple procedure. A diameter and tray spacing are estimated. The capacity, pressure drop and flexibility of a modular layout in that diameter are compared to customer specifications. A change in diameter, down comer dimensions, cap spacing or tray spacing can then be made to meet specifications, to obtain a minimum cost design, or to obtain an optimum design, i.e., a design having maximum capacity and maximum efficiency.

Design Basis Although it may be feasible to operate columns at near flood conditions, it is not possible to design them with a small safety factor and rely on them to always have the desired capacity and efficiency, whether guaranteed or not. It has been a common practice of the industry to derate the calculated flood capacity for particular

systems. For example, high pressure deethanizers have been known from experience to flood at say 60 per cent of the rate which might be obtained from an atmospheric column. Similarly, amine absorbers and glycol contactors might "carry-owl''' at say 70 per cent of calculated flood rates by some procedure. The capacity procedure given in this manual accounts for the effect of high vapor density and foaming and no additional derating is necessary. In other words, a calculated per cent of flood of 100% means the tower can be expected to flood at design rates. By older methods, a calculated per cent of flood of say 60(/~), for a deethanizer as an example, might be equi\'alent to 100% of flood by the method given herein.

We recommend that new columns be sized so that design rates are no more than 82 per cent of flood rates. Some customers prefer a more liberal design in order to provide a contingency for process uncertainties. For example, a customer may specify that a column be capable of operating at 125 per cent of design rates. This implies a design at .82/1.2.5, or 66 per cent of flood as a maximum. An alternative would be to increase rates by a factor of 1.25 to obtain a new design basis.

mally used for vacuum towers and a value of not more than .82 is used for other services. These values are intended to give not more than approximately lOc;7o entrainment. Higher flood factors may result in excessive entrainment andlor a column sized too small for effective operation.

A flood factor of .6.5 to .7.5 should be used for column diameters under 36".

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Downcomer Design Velocity, VDdsg Velocities used by various companies for sizing downcomers vary by a factor of more than two. Some companies use a residence time approach and others use a "maximum allowable velocity." Columns can be operated with a liquid velocity in the downcomer as high as 3 ft/sec provided the vapor rate is sufficiently low. This is about five times as high as the "maximum allowable" by most methods. Hence, the term "maximum allowable" can be misleading. The procedure used in the manual for establishing downcomer area is based on a "design" velocity given by Figure 4 or Equation l. The smallest value from Equation la, Ib or lc is used. The "system factor" used in Equation I makes an allowance for foaming. If the designer knows that a particular system has a foaming tendency, an appropriate system factor should be applied. Factors for several typical services are shown in Table 1. VDdog

=

250 x System Factor

( Ia)

VDc10g = 41 x VDL - Dv x System Factor VDdsg

=

(Ib)

7-.5 x ,ITS x VDL - D" x System Factor

(Ie)

where VDdsg = Design velocity, gpm/sq. ft. TS

=

Tray spacing, inches TABLE la

Downcomer SystelTI Factors System Factor

Non foaming, regular systems ................................. . 1.00 Fluorine systems, e.g., BFs, Freon ............................. . .90 Moderate foaming, e.g., oil.absorbers, amine and glycol regenerators .85 foaming, amine and glycol absorbers . , , .. , .. , ... , .. , . .73 Severe foaming, e.g., MEK units ............................... , .60 Foam-stable systems, e.g., caustic regenerators .................. . .30 FIGURE 4

Downcomer Design Velocity VD dsg

= (VD dsg ';')

(System Factor)

VDdsg *

20

30

50

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Vapor Capacity Factor, CAF Figure 5 shows the vapor capacity factor of Ballast trays. The value of CAF 0 from Figure 5 is multiplied by a "system factor" given in Table 1b to obtain a value corrected for foaming. CAF = CAF 0 x System Factor

(2a)

The system factor used in Equation 2a is given below.

TABLE Ib

System Factors System Factor

Sen"ice

Non-foaming, regular systems .................................. 1.00 Fluorine systems, e.g., BF3, Freon . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. .90 Moderate foaming, e.g., oil absorbers, amine and glycol regenerators .S5 Heavy foaming, e.g., amine and glycol absorbcrs ........ . . . . . . . .. .73 Severe foaming, e.g., l\IEK units ............................... .60 Foam-stable systems, e.g., caustic regenerators ................ .30-.60 The capacity of Ballast trays increases with increasing tray spacing up to a limiting value. For practical purposes, the limit occurs at 4S/I for vapor densities below 4 lb / cu ft. Very high vapor density systems reach a limit at a tray spacing below 48/1. For example, a system having a vapor density of 7 lb / cu It would have a capacity factor of 0.33 for any tray spacing above lS/I. Since a 24" tray spacing is generally selected for mechanical accessibility, this spacing could be used rather than 30/1 which might otherwise be considered. The amount of energy dissipated by vapor flowing through a tray and the quantity of entrainment generated thereby increase with decreasing vapor density. In vacuum columns the amount of entrainment generated causes a reduction in the capacity factor from that which can be obtained with higher vapor densities. This effect is given by the equation shown as step 3 on Figure 5a. Figure 5b is a coordinate plot showing the same relation given on Figure 5a. The limit point shown on Figure 5b can be exceeded at very high vapor densities for systems such as high pressure absorbers, values

i~;'liquic1"densities ul~der

Cll

35 lbl c~[ ft. (2b)

Vload = CFS /Dd (DL - D\ ) where CFS = vapor rate, actual

approximately

ft/sec

This term is used for sizing a column and for calculating per cent of flood for a given column diameter.

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5.5

.55

FIGURE 5a

5.0

FLOOD CAPACITY OF BALLAST TRAYS 4.5

.5

t!.

Lim it point

4.0

oI 3.5

.45

3.0

.4

2.5

D (1J

0

-I

2.0

U

....

4-

2

.35

:::J 0



0'

15

-.J

>

~

Q...

G 1500

10

1000

500

o

o

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Approximation of Column Diameter Flow Path Length, FPL. An approximate flow path length is useful for establishing the minimum tower diameter. Figure 6 is used to obtain an approximation of tower diameter from which the flow path length can be estimated. FPL = 9 x DT/NP

(3)

where FPL = Flow path length, inches DT = Tower diameter, feet NP = Number of flow paths or passes

Active Area, AAM. The minimum active area is a function of vapor and liquid loads, system properties, flood factor and flow path length. Visual inspection of tray loadings usually will determine that tray which will give the largest active area. AAM = Vload -I-

GP~1 X FPL/13000 CAF X FF

(4)

where Vload = Vapor load for any tray in the section GPM = Liquid load for the same tray AAl\1 = l\Iinimum active area, sq. ft. CAF = Capacity factor from Equation 2a FF = Flood factor or design per cent of flood, fractional

Downcomer Area, ADM. The minimum downcomer area is a fun9tion of liquid rate, downcomer design velocity and flood factor. A visual inspection of liquid loads usually is sufficient to determine which tray requires the most downcomer area. The tray having the maximum liquid load is not nccessarily the same one requiring the most active area. ADM

= GPl\II(VDclsg

(5)

X FF)

where VDdsg = Downcomer velocity for design purposes, gpm/sq ft =-= :'IIinimum dowlleomer area, sq ft

If the downcomer area calculated by Equation 5 is less than 11 % of the active area, use the smaller of the following: ADM = 11% of the active area, or AD:\f = Double that by Equation 5

Column Area. The approximate column cross sectional area is calculated by Equation 6a or 6b. The for more detailed calculations. Further design calculations may result in a change in tower diameter. =

or ATM

=

Vload .78 X CAF X FF

=

1/ ATM/.7854

DT

where ATl\f

AAM

+2

ATM

=

X ADM

(6a) (6b) (7)

Minimum column cross sectional area, sq ft

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Allocation of Areas for a Fixed Column Diameter The diameter of a column may be estimated by Equation 7, or it may be some other value; e.g., an existing column diameter or one specified by the customer may be used. In any event, the actual cross sectional area of the diameter which is to be used is not likely to be the same as the approximate minimllm by Equation 6.

If the actual tower cross sectional area is less than the calculated minimum area, a design for maximum capacity should be used; if it is greater than the calculated minimum, a design for either minimum cost or maximum capacity may be used. Minimum Cost Design is obtained by making the active area equal to the minimum active area. The remaining tower area is devoted to downcomer area and downcomer seal area. For existing columns, it may be possible to reuse the existing downcomers at a savings, provided neither the downcomer area nor the active area is too small. Maximum Capacity Design, one also giving maximum efficiency, is obtained by proportioning the active area and downcomer area so that the per cent of flood for vapor load is equal to the per cent of flood for liquid load. This type design is usually desired by the ultimate user; and, in the absence of specifications to the contrary, maximum capacity design is used by Glitsch for new columns. For maximum capacity design, the total down comer area is calculated as follows:

(8)

AD = AT X ADM/ATM where AD = Total downcomer area, sq ft AT = Actual tower area, sq ft ADM "" i\Iinimum down comer area

Equation 5

ATM = rdinimum tower area by Equation 6 The down comer area generally should not be less than 10% of the column area. However, if the liquid rate is unusually low, a downcomer area smaller than 10r;'o of the column area may be used provided it is at least double the calculated minimum downcomer .area.

Having established the tower diameter arid down comer area, a sketch of the tray is useful to establish other dimensions. Figure 7 shows typical sketches for one to five pass trays.

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H,

I

J.I

FPL I

~r

H,

I I

I

1

SINGLE PASS

TWO PASS

FOUR PASS

FIGURE 7

TRAY SKETCHES

I 1 ~

FIVE PASS

J

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Downcomer Widths, H The terms H" Hl, Ho and H, are used to designate the width in inches of the side, center, off-center and off-side downcomers, respectively. Corresponding areas at the top of downcomers are designated A" Al, As and A" respectively. Refer to Figure 7. The total downcomer area should be divided between the downcomers of multipass trays in proportion to the liquid rate received and the active area served. For large diameter towers having three or more flow paths, the active area in each flow path should be equal and the weir lengths adjusted so that the liquid rate to each weir is the same. This may require the use of sweptback side down comer weirs or sweptback side downcomers. Sweptback downcomers of the circular and segmental circular type are shown on page 34. Table 2 is useful for allocating downcomer area in accordance with this concept. For example, each of the side downcomers of a four-pass tray would have an area of approximately 25% of the total down comer area. TABLE 2

Allocation of Downcomer Area & Downcomer Width Factors Passes

AD,

2

.50 ea.

3

.34

4

.25 ea. .20

p

;:)

Fraction of Total Downcomer Area AD, AD"

Width Factors, WF AD,

l.00 .50

~

~-

~

12.0

.66 .50 ea. .40

6.0 .40

8.63 6.78 ea. 5.66

5.5

The width of side downcomers can be obtained from Table 4. An accurate estimate of the width of other than a side downcomer can be obtained by substituting width factors from Table 2 in Equation 9. H, = WF X AD/DT \vhere Hi = \Yidth of individual downcomer, inches AD = Total downcomer area, sq. ft.

(9)

rro

lower

WF = Width factor from Table 2 Downcomer widths are usually adjusted to give a modular flow path length. For preliminary purposes, the flow path length can be made equal to 8.5" plus a multiple of 1.5". The flow path length is calculated by Equation 10 and then downcomer widths may be adjusted to give a modular FPL. FPL = 12 X DT- (2Hl

+ Hl + 2H. + 2H,) NP

(10 )

A flow path length of less than Z6" is not feasible if internal manways are required. Some services haw such a high liquid load relative to the vapor load that the flow path length minimum of 16" may make it necessary to use a larger tower diameter than that calculated by Equation 7. For this condition, the minimum required downcomer area and the minimum flow path length establish the least cost design.

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Downcomer Area, AD With downcomer widths adjusted to modular dimensions, or established by other considerations, actual downcomer areas can be calculated exactly by use of Table 4. Alternately, the area of the center, off-center or off-side downcomers can be calculated with sufficient accuracy for preliminary purposes by use of the following equation: ADi = Hi X SF X DTIl2

(11 )

where ADi = Area of individual downcomer, sq ft Hi = Width of individual downcomer, inches SF = Span factor, fractional DT = Tower diameter, ft The span factor used in the above equation is the wall-to-wall distance at the mid-point of a downcomer, expressed as a fraction of tower diameter. Table 3 gives span factors. This table is also useful for estimating weir lengths and for checking exact methods for both downcomer area and weir length. TABLE 3

Approximate Downcomer Span Factors, SF Fraction of Tower Diameters Passes

2 3 4 5

~

.l:!L 1.0

.95 .885 .98

1.0

.88

The downcomer area of even-numbered trays may be somewhat different from that of odd-numbered trays for two or four passes. An average value may be used as the total downcomer area for fur-

ther

Active Area, AA Active area is the area available for Ballast units between inlet and outlet edges of the tray. Either of the following two equations apply for straight downcorhers or sloped downcomers with recessed inlets. AA

=

AT - (2ADl + AD3

+ 2AD5 +

2AD7)

AA = AT - 2 X (ADa\g)

(12a) (12b)

downcomers normally are used only with recessed inlet areas or draw sumps. The width and area of recessed inlets are usually the same as that at the top of the downcomers. Sloped downcomers with flat seal areas at the bottom are used when it is necessary to obtain additional Ballast units for decreasing the pressure drop. The additional active area which can be obtained by this type of downcomer design usually is not more than 50% of the downcomer area.

-22-

TABLE 4

SEGMENTAL FUNCTIONS

= TOWER DIAMETER = CHORD HEIGHT L = CHORD LENGTH

D

H

An AT

D

>1/0 FROM .0 TC

H/O

L/O

AO/ AT

.0000 .0005 .0010 .0015 .0020

.0000 .0447 .0632 .0774 .0894

.0000 .0000 .0001 .0001 .0002

.0200 .0205 .0210 .0215 .0220

.2800 .2834 .2868 .2901 .293 11

.0048 .0050 .0051 .0053 .0055

.0400 .0405 .0410 .0415 .0420

.0025 .0030 .0035 .0040 .0045

.0999 .1094 .1181 .1262 .1339

.0002 .0003 .0004 .0004 .0005

.0225 .0230 .0235 .0240 .0245

.2966 .2998 .3030 .3061 .3092

.0057 .0059 .006.1 .0063 .0065

.0050 .0055 .0060 ,0065 .0070

.1411 .1479 . i 545 .1607 . 1667

.0006 .0007 .0008 .0009 .0010

.0250 .0255 .0260 .0265 . 0270

.3122 .3153 .3183 .3212 . 3242

.00 0 .0085 .0090 .0095

.00~5

.1726 .1782 .1836 .1889 .1940

,0011 .0012 . 0013 .0014 .0016

.02 0 .0285 .0290 .0295

.02~5

.3271 .3299 .3328 .3356 .3384

.0100 .0105 .0110 .0115

.1990 .2039 .2086 .2132

.0,017 ,0018 .0020 .0021

.0300 .0305 .0310 .0315

.3412 .3439 .3466 .3493

.~'2~1 ';'0024

TOWER AREA

.1

AO/ AT

i/O

L/O

Ar:/AT

H/O

L/O

AO/AT

.3919 .3943 .3966 .3989 .4012

.0134 .0137 .0139 .0142 .0144

.0600 .0605 .0610 .0615 .0620

.4750 .4768 .4787 .4805 .4823

.0245 .0248 .0251 .0254 .0257

.0800 .0805 .0810 .0815 .0820

.5426 .5441 .5457 .5472 .5/187

.0375 .0378 .0382 .0385 .0389

.0 1125 .0430 .0435 .0440 .0445

.4035 .4057 .4080 .4102 .4124

.0147 .0149 .0152 .0155 .0157

.0625 .0630 .0635 .0640 .0645

.4841 .4859 .4877 .4895 .4913

.0260 .0263 .0266 .02]0 .0273

.0825 .0830 .0835 .0840 .0845

.5502 .5518 .5533 .5548 .5563

.0392 .0396 .0399 .0403 .0406

.0067 .0069 . 0071 .0073 • 0075

.0450 .0455 .0460 .0465 .0470

.4 PI6 .4168 ,4190 ,4211 , 4233

.0160 .0162 .0165 .0168 . 0171

.0650 .0655 .0660 .0665 .0670

.4931 .4948 .4966 .4ge3 .5000

.0276 .0279 .0282 .0285 .0288

.0850 .0855 .0860 .0865 .0870

.5578 .5592 .5607 .5622 ,5637

.0410 .0413 .0417 . 0421 . 0424

.0077

.00 1 .0083 .0085

.0475 .0480 .0485 .0490 .0495

.4254 .4275 .4296 .4317 .4338

.0173 .0176 .0179 .0181 .0184

.0675 .0680 .0685 .0690 .0695

.5018 .5035 .5052 .5069 .5086

.0292 .0295 .0298 .0301 .0304

.0875 .0880 .0885 .0890 .0895

.5651 .5666 .5680 .5695 .5709

.0428 .0431 .0435 .0439 ,0442

.0087 .0090 .0092 .0094

.0500 .0505 .0510 .0515

.4359 .4379 .4400 .4420

.0187 .0190 .0193 .0195

.0700 .0705 .0710 .0715

.5103 .5120 .5136 .5153

.0308 .0311 .0314 .0318

.0900 .0905 .0910 .0915

.5724 .5738 .5752 .5766

.0446 .0449 .0453 .0457

:63is .0330

:j~'4"g ',OO':,ltl ' '.0525 ; 41;l)1

:o~or

.0204 ,0207 .0210 .0212

,012$ .0730 .0735 .0740 .0745

:5

.5203 .5219 .5235 .5252

.&H'l, .0327 .0331 .0334 .0337

.0925 .0930 .0935 .0940 .0945

H/O

L/O

AO/AT

.00~9

):~;~-:""

1/0

L/O

,:/,' >"",;

.,

.2265 .2308 .2350 .2391

.0025 .0027 .0028 .0030

.3573 .0335 .3599 .0340 .3625 .0345 .3650

.0101 .0103 .0105 .0108

.0530 .0535 .0540 .0545

.4481 ,4501 .4520 .4540

.0150 .0155 .0160 .0165 .0170

.2431 .2471 .2510 .2548 .2585

.0031 .0033 .0034 .0036 .0037

.0350 .0355 .0360 .0365 .0370

.3676 .3701 .3726 .3751 .3775

.0110 .0112 .0115 .0117 .0119

.0550 .0555 .0560 .OS65 .0570

.4560 .4579 .4598 .4618 .4637

.0215 .0218 .0221 .0224 .0227

.0750 .0755 .0760 .0765 .0770

.5268 .5284 .5300 .5316 .5332

.0341 .0344 .0347 .0351 .0354

.01~5

.2622 .2659 .2695 .2730 .2765

.0039 .0041 .0042 .0044 .0046

.0375 .0380 .0385 .0390 .0395

.3800 .3824 .3848 .3872 .3896

.0122 .0124 .0127 .0129 .0132

.0575 .0580 .05es .0590 .0595

.4656 .4675 .4694 .4712 .4731

.0230 .0233 .0236 .0239 .0242

.0775 .0780 .0785 .0790 .0795

.5348 .5363 .5379 .5395 .S410

.0358 .0361 .0364 .0368 .0371

.01 0 .0185 .0190 .0195

CHOHD AREA

=

-23-

~'5j~5 .,>6464' .5809 .5823 .5837 .5850

.0468· .0472 .0475 .0479

.0950 .0955 .0960 .0965 .0970

.5864 .5878 .5892 .5906 .5919

.0483 .0486 .0490 .0494 .0498

.0975 .0980 .0985 .0990 .0995

.5933 .5946 .5960 .5973 .5987

.0501 .0505 .OS09 .0513 .0517

H/O ,,10M .1

H/D

L/D

"0/ AT

H/U

L/D

Au/AT

~/J

.1000 .1005 .1010 .1015 .1020

.6000 .6013 .6027 .6040 .6053

.0520 .0524 .0528 .0532 .0536

.1200 · 1205 .1210 .1215 · 1220

.6499 . 65 11 .6523 .6534 .6546

.0680 . 0684 .0688 .0692 .0696

.1400 .1405 .1410 · 1415 .1420

.6066 .6079 .6092 .6105 lOltS ,hllB

.0540 .0544 .0547 .0551 .0555

.1225 .6557 .0701 .1230 .6569 .0705 .1235.6580.0709 · 1240 .6592 .0713 ,1245 .6603 .0717

· 1425 .1430 .1435 .1440

.6991 .7001 .7012 .7022 .1 1,1'5 .7032

.1025 .1030 .1035 .1040 ~

L/U

TC; .2

\/A r

• H/e .1600 .1605 .1610 .1615 .1620

H/D

L/D

Au/ AT

.7332 .1033 .7341.1037 .7351.1042 .7360 . 1047 .7369 . 1051

.1800 .1805 .1810 .1815 · 1820

.7684 .7692 .7700 .7709 . 771 7

.1224 .1229 .1234 .1239 . 1244

.0873 .0878 .0882 .0886 .0891

.1625 · 1630 · 1635 .1640 .1645

.7378 .7387 .7396 .7406 ,7415

.1056 .1061 .1066 .1070 · !OJ5

· 1825 .1830 .1835 .le40 .184,

.7725 .7733 .7742 .7750 .7758

.1249 · 1253 .1258 .1263

Au/AT

.6940 .0851 .6950 .0855 .6960 .0860 .6971 .0864 .6981,.0869

L/J

.1268

.1050 .1055 .1060 .1065 .1070

.6131 .6144 .6157 .6170 .6182

.0559 .0563 .0567 .0571 .0575

.1250 · 1255 .1260 .1265 .1270

.0721 .0726 .0730 .0734 .0738

.1450 .1455 .1460 .1465 .1470

.7042 .7052 .7062 .7072 .7082

.0895 .0900 .0904 .0909 .0913

.1650 .1655 .1660 .1665 .1670

.7424 .7433 .7442 .7451 .7460

.1080 .1084 .1089 .1094 .1099

.1850 .1855 .1860 .1865 .1870

.7766 .7774 .7782 .7790 .7798

.1273 .1278 .1283 .1288 .1293

.1075 .1080 .1085 .1090 .1095

.6195 .6208 .6220 .6233 .6245

.0579 .0583 .0587 .0591 .0595

.1275 .6671 .0743 .1280 .6682 .0747 .1285 .6693 .0751 • 1290 .6704 .0755 .1295 .6715 .0760

.1475 .1480 .1485 .1490 .1495

.7092 .7102 .7112 .7122 .7132

.0918 .0922 .0927 .0932 .0936

.1675 .1680 .1685 .1690 · 1695

.7468 .7477 .7486 .7495 .7504

.1103 .1108 · 1113 .1118 · 1122

.1875 .1880 .1885 .1890 .1895

.7806 .7814 .7822 .7830 .7838

.1298 .1303 .1308 · 1313 .1318

.1100 .1105 .1110 .1115 .1120

.6258 .6270 .6283 .6295 .6307

.0598 .0602 .0606 .0610 .06111

.1300 .1305 .1310 .1315 .1320

.6726 .6737 .6748 .6759 .6770

.0764 .0768 .0773 .0777 .0781

.1500 .1505 .1510 .1515 .1520

.7141 .7151 .7161 .7171 .7180

.0941 .0945 .0950 .0954 .0959

.1700 .1705 .1710 .1715 .1720

.7513 .7521 .7530 .7539 .7548

.1127 .1132 .1137 .1142 .1146

.1900 .1905 .1910 .1915 .1920

.7846 .7854 .7862 .7870 .7877

· 1323 · 1328 · 1333 .1338 .1343

.1125 .1130 .1135 .1140 .1145

.6320 .6332 .631r4 .6356 .6368

.0619 .0623 .0627 .0631 .0635

.1325 .1330 · 1335 .1340 .1345

.6781 .6791 .6802 .6813 .6824

.0785 .0790 .0791, .0798 .0803

· 1525 .1530 · 1535 .1540 .1545

.7190 .7200 .7209 .7219 .7229

.0963 .0968 .0973 .0977 .0982

.1725 .1730 .1735 .1740 .1745

.7556 .7565 .7574 .7582 .7591

.1151 .1156 .1161 .1166 .1171

.1925 .1930 .1935 .1940 .1945

.7885 .7893 .7901 .7909 .7916

.1348 .1353 .1358 .1363 .1368

.1150 .1155 .1160 .1165 .1170

.6380 .6392 .61r04 .6416 .6428

.0639 .0643 .0647 .0651 .0655

· 1350 .1355 .1360 .1365 .1370

.6834 .6845 .6856 .6866 .6877

.0807 .0811 .0816 .0820

.0825

.1550 .1555 .1560 .1565 .1570

.7238 .7248 .7257 .7267 .7276

.0986 .0991 .0996 .1000 .1005

.1750 • 1755 .1760 .1765 .1770

.7599 .7608 .7616 .7625 .7633

.1175 .1180 .1185 .1190 .1195

.1950 .1955 .1960 .1965 .1970

.7924 .7932 .7939 .7947 .7955

.1373 .1378 .1383 .1388 .1393

.1175 .1180 .1185 .1190 .1195

.6440 .6452 .6464 .6476 .6488

.0659 .0663 .0667 .0671 .0676

.1375 .6887 .0829 .1380 .6898 .0833 .1385 .6908 .0838 .1390 .6919 .0842 .1395 .6929 .0847

.1575 .1580 .1585 .1590 .1595

.7285 .7295 .7304 .7314 .7323

.1009 .1014 .1019 .1023 .1028

.1775 .1780 .1785 .1790 .1795

.7642 .7650 .7659 .7667 .7675

.1200 .1204 .1209 .1214 .1219

.1975 .1980 .1985 .1990 .1995

.7962 .7970 .7977 .7985 .7992

.1398 .1403 .1409 .1414 .1419

H/D

L/D

AD/ AT

.2000 .2005 .2010 .2015 .2020

.8000 .8007 .8015 .8022 .8030

. tl,24 .1429 .1434 .1439 .1444

.6614 .6626 .6637 .6648 .6659

H/D rRO~ .2 TO .3 H/D

L/D

"0/ AT

H/O

L/D

H/D

L/D

AD/AT

H/D

L/D

AD/ AT

.2200 .8285 .1631 .2205 .8292 .1636

.2210 .8298 .1642 .2215 .8305 .1647 .2220 .8312 .1652

.2400 • 21,05 .2410 .2415 .2420

.8542 .85 1,8 .8554 .8560

.1845 . 1851 .1856 .1862 .8566 .1867

.2600 .2605 .2610 .2615 .2620

.8773 .8778 .8784 .8789 .8794

.2066 .2072 .2077 .2083 .2088

.2800 .2805 .2810 .2815 .2820

.8980 .8985 .8990 .8995 .8999

.2292 .2298 .2304 .2309 .2315

.2025 .8037 .1449 .2030 .8045 .1454 .2035 .8052 .1460 • 2040 .8059 • 1465 .2045 .8067 .1470

.2225 .2230 .2235 .2240 .2245

.8319 .8325 .8332 .8338 .8345

.1658 .1663 .1668 .1674 .1679

.2425.8572 .1873 .2430 .8578 .1878 ,2435 .8584 .1884 .2440 .8590 .1889 .2445 .8596.1895

.2625 .2630 .2635 .2640 . 2645

.8800 .8805 .8811 .8816 .8821

.2094 .2100 .2105 .2111 .2116

.2835 .9014 .2332

.2840 .9019 .2338 .2845 .9024 .2344

.2050 .2055 .2060 .2065 .2070

.8074 .8081 .8089 .8096 .8103

.1475 .1480 .1485 .1490 .1496

.2250 .2255 .2260 .2265 .2270

.8352 .8358 .8365 .8371 .8378

.1684 . 1689 .1695 ,1700 .1705

.2450 .2455 .2460 .2465 .2470

.8602 .8608 .8614 .8619 .8625

.1900 .1906 .1911 .1917 .1922

.2650 .2655 .2660 .2665 .2670

.8827 .8832 .8837 .8843 .8848

.2122 .2128 .2133 .2139 .2145

.2850 .2855 .2860 .2865 .2870

.9028 .9033 .9038 .9043 .9047

.2349 .2355 .2361 .2367 .2372

• 2075 .2080 .2085 .2090 .2095

.8110 .8118 .8125 .8132 .8139

• 1501 .1506 .1511 .1516 .1521

.2275.8384.1711 .2280 .8391 .1716 .2285 .8397 .1721 .2290 .8404 .1727 .2295.81>10.1732

.2475 .2480 .2485 .2490 .2495

.8631 .8637 .8643 .8649

.1927 .1933 .1938 .1944 .8654 .1949

.2675 .2680 .2685 .2690 .2695

.8853 .8858 .8864 .8869 .8874

.2150 .2156 .2161 .2167 .2173

.2875 .2880 · 2885 .2890 .2895

.9052 .9057 .9061 .9066 .9071

.2378 .2384 . 2390 .2395 .2401

.2125 .2130 .2135 .2140 .2145

.8182 .8189 .8196 .8203 .8210

.1553 . 1558 .1563 .1568 .1573

.2325 .2330 .2335 .2340 .2345

.2525 .2530 .2535 .2540 .2545

.8689 .8695 .8700 .8706 .8712

.1983 .1988 .1994 .1999 .2005

.2725 .2730 .2735 .2740 .2745

.8905 .8910 .8915 .8920 .8925

.2207 .2212 .2218 .2224 .2229

.2925 .2930 .2935 .2940 .2945

.9098 .9103 .9107 .9112 .9116

.2436 .2442 .2448 .2453 .2459

.8449 .1764 .6455 . 1770 .8461.1775 .8467 .1781 .8474 .1786

AD/ AT

.2825 .9004 .2321 .2830 .9009 .2326

.2150.8216 .1579 .2155 .8223 .1584 .2160 .8230 .1589 .2165.8237.1594 .2170 .8244 .1600

.2350 .8480 .2355 .8486 .2360 .8492 .2365 .8499 .2370.8505

.1791 .1797 .1802 .1808 .1813

.2550 .2555 .2560 .2565 .2570

.8717 .8723 .8728 .8734 .8740

.2010 .2016 .2021 .2027 .2033

2750 .2755 .2760 .2765 .2770

.8930 .8935 .8940 .8945 .8950

.2235 .2241 .2246 .2252 .2258

.2950 .2955 .2960 .2965 .2970

.9121 .9125 .9130 .9134 .9139

.2465 .2471 .2477 .2482 .2488

.2175 .8251 .2180 .8258 .2185 .8265 .2190.8271 .2195 .8278

.2375 .2380 .2385 .2390 .2395

.8511 .8517 .8523 .8529 .8536

.1818 .1824 .1829 .1835 .1840

.2575 .2580 .2585 .2590 .2595

.8745 .8751 .8756 .8762 .8767

.2038 .2044 .2049 .2055 .2060

.2775 .2780 .2785 .2790 .2795

.8955 .8960 .8965 .8970 .8975

.2264 .2269 .2275 .2281 .2286

.2975 .2980 .2985 .2990 .2995

.9143 .9148 .9152 .9156 .9161

.2494 .2500 .2506 .2511 .2517

.1605 .1610 .1615 .1621 .1626

-24-

HID FROM .3 TO .4 HID LID ADIAT

HID

LID

Aol AT

HID

LID

ADIAT

HID

LID

ADIAT

HID

LID

VAT

.3000 .3005 .3010 .3015 .3020

.9165 .9170 .9174 .917B .91B3

.2523 .2529 .2535 .2541 .2547

.3200 .3205 .3210 .3215 .3220

.9330 .9333 .9337 .9341 .9345

.2759 .2765 .2771 .2777 .2782

.3400 .3405 .3410 .3415 .3420

.9474 .9478 .94Bl .94B4 .94B8

.2998 .3004 .3010 .3016 .3022

.3600 .3605 .3610 .3615 .3620

.9600 .9603 .9606 .9609 .9612

.3241 .3247 .3253 .3259 .3265

.3BOO .3805 .3810 .3B15 .3820

.970B .9710 .9713 .9715 .971B

.3487 .3493 .3499 .3505 .3512

.3025 .3030 .3035 .3040 .3045

.9187 .9191 .9195 .9200 .9204

.2552 .2558 .2564 .2570 .2576

.3225 .3230 .3235 .3240 . 321f5

.9349 .9352 .9356 .9360 .9364

.2788 .2794 .2800 .2806 .2B12

.3425 . 31+}0 .3435 .3440 .3445

.9491 .9494 .9498 .9501 .9504

.3028 .3034 .3040 .3046 .3053

.3625 .3630 .3635 .3640 .3645

.9614 .9617 .9620 .9623 .9626

.3272 .3278 .32B4 .3290 .3296

.3B25 .3830 .3835 .3840 .3845

.9720 .9722 .9725 .9727 .9730

.3518 .3524 .3530 .3536 .3543

.3050 .3055 .3060 .3065 .3070

.9212 .9217 .9221 .9225

.9208 .2582

.2588 .2593 .2599 .2605

.3250 .3255 .3260 .3265 .3270

.9367 .9371 .9375 .9379 .9382

.28 f8 .2824 .2830 .2836 .2842

.3450 .3 1'55 .3460 .3465 .3470

.9507 .9511 .9514 .9517 .9520

.3065 .3071 .3077 .3083

.3059

.3650 .3655 .3660 .3665 .3670

.9629 .9631 .9634 .9637 .9640

.3308 .3315 .3321 .3327

.3855 .3B60 .3865 .3870

.9734 .9737 .9739 .9741

.3555 .3561 .3567 .3574

.3075 .3080 .30B5 .3090 .3095

.9229 .9233 .9237 .9242 .9246

.2611 .2617 .2623 .2629 .2635

.3275 .3280 .3285 .3290 .3295

.9386 .9390 .9393 .9397 .9401

.2848 .2854 .2860 .2866 .2872

.3475 .34BO .34B5 .3490 . 31f95

.9524 .9527 .9530 .9533 .9536

.3089 .3095 .3101 .3107 .3113

.3675 .36BO .3685 .3690 .3695

.9642 .9645 .9648 .9651 .9653

.3333 .3339 .3345 .3351 .3357

.3875 .3880 .3885 .3B90 .3895

.9744 .9746 .9748 .9750 .9753

.3580 .3586 .3592 .3598 .3605

.3100 .3105 .3110 .3115 .3120

.9250 .9254 .9258 .9262 .9266

.2640 .2646 .2652 .2658 .2664

.3300 .3305 .3310 .3315 .3320

.9404 .9408 .9411 .9415 .9419

.287B .2884 .2890 .2896 .2902

.3500 .3505 .3510 .3515 .3520

.9539 .9543 .9546 .9549 .9552

.3119 .3125 .3131 .3137 .3143

.3700 .3705 .3710 .3715 .3720

.9656 .9659 .9661 .9664 .9667

.3364 .3370 .3376 .3382 .3388

.3900 .3905 .3910 .3915 .3920

.9755 .9757 .9759 .9762 .9764

.3611 .3617 .3623 .3629 .3636

.3125 .3130 .3135 .3140 .3145

.9270 .9274 .9278 .9282 .9286

.2670 .2676 .2682 .2688 .2693

.3325 .3330 .3335 .3340 .3345

.9422 .9426 .9429 .9433 .9436

.290B .2914 .2920 .2926 .2932

.3525 .3530 .3535 .3540 .3545

.9555 .9558 .9561 .9564 .9567

.3150 .3156 .3162 .3168 .'3174

.3725 .9669 .3394 .3730 .9672 .3401 .3735 .9675 .3407 .3740 .9677 .3413 .3745 .9680 .3419

.3925 .3930 .3935 .3940 .3945

.9766 .9768 .9771 .9773 .9775

.3642 .3648 .3654 .3661 .3667

.3150 .3155 .3160 .3165 .3170

.9290 .9294 .9298 .9302 .9306

.2699 .2705 .2711 .2717 .2723

.3350 .3355 .3360 .3365 .3370

.9440 .9443 .9447 .9450 .9454

.2938 .2944 .2950 .2956 .2962

.3550 .3555 .3560 .3565 .3570

.9570 .9573 .9576 .9579 .9582

.3180 .3186 .3192 .3198 .3204

.3750 .3755 .3760 .3765 .3770

.9682 .9685 .968B .9690 .9693

.3425 .3431 .3438 .3444 .3450

.3950 .3955 .3960 .3965 .3970

.9777 .9779 .9781 .9783 .9786

.3673 .3679 .3685 .3692 .3698

.3175 .3180 .3185 .3190 .3195

.9310 .9314 .9318 .9322 .9326

.2729 .2735 .2741 .2747 .2753

.3375 .3380 .3385 .3390 .3395

.9457 .9461 .9464 .9467 .9471

.2968 .2974 .2980 .2986 .2992

.3575 .35BO .3585 .3590 .3595

.9585 .9588 .9591 .9594 .9597

.3211 .3217 .3223 .3229 .3235

.3775 .3780 .3785 .3790 .3795

.9695 .9698 .9700 .9703 .9705

.3456 .3462 .3468 .3475 .3481

.3975 .3980 .3985 .3990 .3995

.9788 .9790 .9792 .9794 .9796

.3704 .3710 .3717 .3723 .3729

HID

LID

ADIAT

HID

LID

Aol AT

HID

LID

Ao/AT

HID

LID

Ao/AT

.4000 .4005 .4010 .4015 .4020

.9798 .9800 .9802 .9804 .9806

.3735 .3742 .3748 .3754 .3760

.4200 .4205 .4210 .4215 .4220

.9871 .9873 .9874 .9876 .9878

.3986 .3992 .3998 .4005 .4011

.4400 .4405 .4410 .4415 .4420

.9928 .9929 .9930 .9931 .9932

.4238 .4244 .4251 .4257 .4263

.4600 .4605 .4610 .4615 .1,620

.9968 .9969 .9970 .9970 .9971

.4491 .44,,8 .4504 .4510 .4517

.4800 .4805 .4810 .4815 .4820

.9992 .9992 .9993 .9993 .9994

.4745 .4752 .4758 .4765 .4771

.4025 ,1,030 .1,035 .4040 .4045

.9808 9810 .9812 .9814 ,9816

.3767

.4017 ,4073 .4030 .4036

.9934 ,9935 .9936 .9937 ,9938

.4270 ,4276 .4282 .4288 ,4295

.4625 .9972 .1,630 .9973 .1,635 ,9973 .4640 .9974 ,1,645 ,9975

,4529 ,4536

4042

.4425 ,L,1130 ,if43, .1,440 ,1,445

.4523

.3779 .3785 .3791

.4225 .9879 ,4230 ,9881 .4235 .9882 .4240 .9884

.4542 ,1'548

.4825 ,4830 .4835 .4840 ,4845

.9994 ,9991, ,9995 .9995 ,9995

.4777 ,4784 .4790 .4796 .4803

.4050 .4055 .4060 .4065 .4070

.9818 .9820 .9822 .9B24 .9825

.3798 .3804 .3810 .3B16 .3823

.4250 .4255 .4260 .4265 .4270

.9887 .9B88 .9890 .9891 .9893

.4049 .4055 .4061 .4068 .4074

.4450 .4455 .4460 .4465 .4470

.9939 .9940 .9942 .9943 .9944

.4301 .4307 .4314 .4320 .4326

.4650 .4655 .4660 .4665 .4670

.9975 .9976 .9977 .9978 .9978

.4555 .4561 .4567 .4574 .4580

.4850 .4855 .4860 .4B65 .4B70

.9995 .9996 .9996 .9996 .9997

.4809 .4815 .4B22 .4B28 .4834

.4075 .4080 .4085 .4090 .4095

.9827 .9829 .9831 .9833 .9B35

.3829 .3835 .3842 .3848 .3854

.42 0 .4285 .4290 .4295

.42~5

.9B94 .9896 .9897 .9899 .9900

.4080 .4086 .4093 .4099 .4105

.4475 . 44BO .44B5 .4490 .4495

.9945 .9946 .9947 .9948 .9949

.4333 .4339 .4345 .4352 .4358

.4675 .4680 .46B5 .4690 .4695

.9979 .9979 .9980 .9981 .9981

.4586 .4593 .4599 .4606 .4612

.4875 .4880 .4B85 .4890 .4895

.9997 .9997 .9997 .9998 .9998

.4B41 .4847 .4854 .4B60 .4866

,3773

,4245 ,9885

HID FRDH .4 TO .5 HID LID ADIAT

:3301

.3850 .9731 .3949

.4900 .9998 .4873 .4905 .9998 .4879 .4910 .9998 .4B85

.4100 .9837 .3860 .4105 .9B38 .3B67 .4110 .9840 .3B73

.4300 .9902 .4112 .4305 .9903 .4118 .4310 .9904 .4124

.4500 .9950 .4364 .4505 ,9951 .4371 .4510 .9952 .4377

.4700 .9982 .4618 .4705 .9983 .4625 .4]10 .998 .4631

.4125 ,4130 .4135 .4140 .4145

.9846 .9B47 .9849 .9851 .9853

.3892 .3898 .3904 .3910 .3917

.4325 .4330 .4335 .4340 .4345

.9908 .9910 .9911 .9912 .9914

.4143 ,4149 .4156 .4162 .416B

.4525 .4530 .4535 .4540 .4545

.9955 .9956 .9957 .9958 .9959

.4396 ,4402 .4409 .4415 .4421

.4725 .4730 .4735 .4740 .4745

.9985 .99!l5 .9986 .9986 .9987

.4650 .4656 .4663 .4669 .4675

.4925 .4930 .4935 .4940 .4945

.9999 .9999 .9999 .9999 .9999

.4150 .4155 .4160 .4165 .4170

.9854 .9856 .9858 .9860 .9861

.3923 .3929 .3936 .3942 .394B

.4350 .4355 .4360 .4365 .4370

.9915 .9916 .9918 .9919 .9920

.4175 .4181 .4187 .4194 .4200

.4550 .4555 .4560 .4565 .4570

.9959 .9960 .9961 .9962 .9963

.4428 .4434 .4440 .4447 .4453

.4750 .4755 .4760 .4765 .4770

.9987 .9988 .9988 .9989 .9989

.4682 .4688 .4695 .4701 .4707

.4950 .4955 .4960 .4965 .4970

1.0000 1.0000 1.0000 1.0000 1. 0000

.4175 .4180 .4185 .4190 .4195

.9863 .9865 .9866 .9868 .9870

.3954 .3961 .3967 .3973 .3979

.4375 .4380 .4385 .4390 .4395

.9922 .9923 .9924 .9925 .9927

.4206 .4213 .4219 .4225 .4232

.4575 .4580 .4585 .4590 .4595

.9964 .9965 .9965 .9966 .9967

.4460 .4466 .4472 .4479 .44B5

.4775 .4780 .4785 .4790 .4795

.9990 .9990 .9991 .9991 .9992

.4714 .4720 .4726 .4733 .4739

.4975 .4980 .4985 .4990 .4995 .5000

1. 0000 .4968 1. 0000 .49~5

-25-

1.0000 1.0000 1.0000 1.0000

.4905 .4911 .4917 .4924 .4930 .4936 .4943 .4949 .4955 .4962 .49 1 .4987 .4994 .5000

Percent of Flood at Constant V /L Ratio 'Pith various areas established, the "percent of flood," i.e., design Vload expressed as a percent of the flood Vload, may be calculated by Equation 13.

%

Vload

Flood 100

+ GPM

----~AA

NOTE,

X FPL/1.3000 X CAF

(15),

(1

(13)

are

riO

have valid application. The capacity of Ballast trays is also a function of the dry tray pressure drop. Columns with a short flow path length, small diameter columns, or columns with obstructions in the active area 'vill have fewer Ballast units per square foot of active area than do columns not having these limitations. The number of Ballast units used on a tray may also be reduced from the maximum potential number to obtain a minimum cost design or for process reasons, i.e., to obtain efficient operation at substantially reduced rates. The following equation covers this criterion:

[

L,PclJ

J flood

= TS

X .2

( 17)

where TS = tray spacing, inches L,PcI" = dry tray pressure drop from page 27 based on V-I units

Flood Vload The flood Vload at constant vapor to liquid ratio is the design (Vload) (100) divided by the percent of flood.

Major beams (lattice type) supporting four levels of trays. -26-

Pressure Drop The pressure drop of Ballast trays is a function of vapor and liquid rates; number, type, metal density, and thickness of the valve; weir height and weir length. At low to moderate vapor rates, when the valves are not all fully open, the dry tray pressure drop is proportional to the valve weight and is essentially independent of the vapor rate. At vapor rates sufficiently high to open the valves fully, the dry tray pressure vapor

Dry Tray Pl'essme Drop. The dry tray pressure drop of the V-I and V-4 Ballast trays most frequently used is obtained from Figure 8. This nomogram is based on a valve metal density of 510 1b cu ft. The following two equations may be used for conditions not covered by the nomogram. The larger value is correct. (18a) (18b) where L:i.Pdry = inches liquid tm = valve thickness, inches Dm = valve metal density, Ib/ cu ft K" Ke = pressure drop coefficients VH = hole velocity, ftl sec Values of K, and K2 are given below together with the thickness corresponding to several gages and densities of commonly used metals. PRESSUBE DROP COEFFICIENTS K, for cleck thickness of

T\pe Unit ~---

K,

.0~'4"

.104"

.1:34"

0.1117"

0.250"

.20 .10

1.18 .68

.9,5

.86 .68

.67

.61

.68

n.a.

n.a.

..- - " - -

V-I V-4

Valve l\!aterial Gage

20 18 16 14

Thickness till, inches

.037 .050 .060 .074

l\fetal

Density lb/cu ft

Metal

Density lb/cu ft

490 500 553 550

Hastelloy Aluminum Copper Lead

560 168 560 708

C.S . S.S. Nickel ~Ionel

H ole Area. The area used to calculate hole velocity in Equation 18 is as follows:

AI-! = NU178.5

(19 )

where NU = total number of Ballast units AH = hole area, sq ft See page 31 for an estimate of the number of units. -27 -

Total Tray Presstl1'e Drop, L,P. Total tray pressure drop is calculated from the following equation: L,P = L,Pctry

+ .4(gpm/Lwi)2/3 + .4 H"

(20)

where L,P = total pressure drop, inches liquid Hw = weir height, inches Lw i = weii' length, inches Pressure drop in inches of liquid can be converted to pounds per square inch or mm Hg by the following equations: L,P, Ibl sq in = (L,P, inch liq) (DL) 11728 L,P,mmHg

(21a)

= (L,P,inchliq)(DL)/33.3

(21b)

Downcomer Backup The downcomer backup should not exceed 40% of the tray spacing for high vapor density systems (approximately 3.0 Ibsl cu.ft. ), 50% for medium vapor densities and 60% for vapor densities under 1.0 Ibsl cu. ft. Otherwise, flooding may occur prior to the rate calculated by the jet flood equations. Downcomer backup, Hdc, in inches of liquid is calculated as follows:

Hd, Hud

H" + .4 (gpm/L,;)2/3 + [~Ptra) + H ud]

=

= .65 (Vud)2

where Hud = Vud = Hdc = DCCL = DCE =

or = 0.06

(~;~

.... +

{{-

....

-+ -+

-+

+

-+

+

-+

...

-+

...

...

-+

+

....

...

-+

+++++

-+

...

:!C

...

::

++

m

In

.,;

25 x 1.50' 37.50

11.25

4.25

FIGURE 9

TYPICAL 5'-0" SINGLE PASS BALLAST TRAY

-30-

T

Flow Path Width, WFP The width of flow path is defined as the active area in square inches divided by the flow path length. This term is used to estimate the number of Ballast units. (26)

WFP = AA X 144/FPL

ApproximateN"umber of Ballast"U nits The number of Ballast units which will fit within the active area is the number of rows of units multiplied by the average number of units per row, with corrections for tray manway loss. This can be estimated as follows: 1. With truss lines parallel to liquid How,

Rows = [FPL - 8.5 .5 X Base

+ l][NPJ

WFP Units/Row = - - - - 5.75 X NP

(27)

(.8) (No. Major Beams

+ 1)

(28)

2. With truss lines perpendicular to liquid flow, Rows = [FPl! - 1.75 X

~~. Trusses -

WFP Units/Row =, - - - - Base X NP

J[ NP J

(29)

6.0

(2) (No. MaJ'or Beams

where FPL = Flow path length, inches WFP = Width of How path, inches NP = ~llmber of passes Base c-c Base spacing of units, usually 3,0,

4.0,

+ 1)

(30)

or 6.0 inches

There will be approximately 12 to 14 units per square foot of active area using a base of 3 inches. Fewer units can be obtained by omitting rows or changing the base to use one of the other standard dimensions. Truss lines are usually parallel to liquid flow in columns not having a major beam, but are usually perpendicular to liquid flow in columns having a major beam. Swept-back weirs will result in a loss of Ballast

A typical tray layout is shO\vn on Figure 9.

-31-

FIGURE 10

PICKET FENCE WEIR

Anti-Jump Baffles for Multipass Trays Operation at high rates require that anti-jump baffles be added at the center and/ or off-center downcomers of multipass trays. A discussion of the function, conditions which require such baffles, and mechanical design follows. These comments apply to all types of trays; bubble cap, sieve, etc. Anti-jump baffles consist of a metal plate suspended vertically above the center and off-center downcomersof multipass trays.

bottonl of

is

at

sm:nc

P~t""·,,.rt

the overflow weir. The top of the baffle is 11" to 20" above the tray floor. The baffle is essentially equal in length to the weir length but does not require sealing at joints or the tower shelL It is normally made in three pieces; the center piece being a manway. These baffles haw been tested thoroughly in a three foot wide x six foot long air-water simulator and are in successful service in owr 2000 columns. By observation, vapor expansion at the outlet weir pumps the liquid over the weir. At a sufficiently high "apor rate, the trajectory carries the liquid completely O\'er the dowllcomer and onto the opposite side of the tray. The tray then floods prematurely due to increased liquid holdup, caused by cycling of the liquid across one side of the tray and back to the other. Anti-jump baffles deflect the liquid into the downcomer, as does the tower shell when the flow is towards the side downcomers. Baffles are recommended if the operating Vload/ AA exceeds the limiting Vload AA: \\'here limiting Vload AA = 0.336 - 0.0192 (CF:l\1 i WFP) There are other factors which could cause baffles to be required.

Picket Fence Weirs Picket Fence Weirs are normally recommended if the GPM/Lwi is less than 0.25-0.30. These are shown on the opposite page. For verv lo\\' liq Llid rates splash baffks are recomlTlended. These are solid to

1S

overflow

to,

Well'.

Number of Passes Usually, a smaller tower diameter can be obtained by using multipass trays to hold liquid rates below 8 CPl\1/\\'FP. The number of Ballast units which can be placed on a tray decreases as the number of passes increases; and, both pressure drop and downcomer backup may increase. Tray efficiency will decrease with increasing number of passes due to the smaller flow path length. The minimum practical

0; o.

Passes

Diameter, Ft.

5

Two Three Four Five

8

10 13

6 9 12

15

l\lany customers prefer to use trays ha\'ing no more than two passes. If the number of passes is restricted, either by cllstomer preference or by tower diameter limitations, liquid rates up to 20 CPM/WFP can be and have been used. -33-

Downcomer Types

FIGURE 11

L_

AJNLET AREA

]V.ERTICAL. APRON DOWNCOMER

L_

L_

r

"(

RECESSED

I

C

INLET AREA

1SLOPED APRON DOWNCOMER

L

STEPPED APRON DOWNCOMER

-gJ-

L~

I

I

EJ

j-

ENVELOPE DOWNCOMER

P~PE

DOWNCOMER

SWEPT-BACK SIDE WEIR SEGMENTAL CIRCULAR DOWNCOMER

L_

[ EXTENDED DOWNCOMER SEAL PAN CIRCULAR DOWNCOMER

CENTER BOXED DOWNCOMER FROM CENTER SUMP

-34-

SIDE BOXED DOWNCOMER FROM CENTER SUMP

Weir Length \Veir lengths may be obtained from Table 4. An average weir length for even-numbered and odd·· numbered trays of two and four pass trays is used for calculating pressure drop. A swept-back weir on the side downcomers can be used to increase the weir length for purposes of reducing pressure drop. A swept-back weir does not significantly change either the active area or the effective downcomer area, or the capacity of the trays.

Weir Height A weir height of 2" is used in most services. Exceptions are those having a low pressure drop specifition. A weir height as low as 1/2" has been used in vacuum columns but a %e" minimum weir height is normally recommended. A weir height up to 6/1 can be used where a high liquid residence time is necessary, for example where a chemical reaction is involved. If the weir height is greater than 15% of the tray spacing, the effective tray spacing for purposes of calculating percent of flood should be reduced by the excess of the weir height over 15% of the tray spacing.

Inlet Weirs Inlet weirs ordinarily are not used with Ballast trays except to distribute reflux to the top tray or to insure a positive seal at high vapor rates and low liquid rates.

Inlet Sumps Hecessed inlet sumps used in conjunction with slo1,)ed or stepped downcomers have the following ad\'antages as a method for introducing liquid to the tray. 1. A positive seal is provided under all operating conditions. 2. Liquid enters the tray' with a vertical component rather than with only a horizontal movement. This results in better aeration at the inlet edge of the tray and increases both tray efficiency and capacity. 3. Decreases downcomer backup. Inlet sumps are slightly more expensive than flat seal areas. However, the added cost is small compared with value received.

Area

~Under

Downcomer, AUD

The term AUD is used to designate the most restricted area at the bottom of the downcomer. This area is usually established at Y2 to lis that at the top of the downcomer. A velocity of 1.5' /sec is not unusual. Foamy systems' require a lower velocity.

Downcomer Types Various types of downcomers are shown on Figure 11.

-35-

Example Design Problem A two pass tray design with a 20 inch tray spacing 'will be illustrated. Design loads together with a summary of design calculations are shown on the facing page. The method of determining the proper downcomer area for maximum capacity is shown below. The column will be designed for not more than 70~J of customer flood is .70. The is nonfoarfling, and the system factor is 1.0. Eq. lc

VDd'~ =

Eq. 2a

CAF

Fig. 6

Approximate DT

Eq. 3

Approximate FPL

Eq.4

AAM

=

(8.86

Eq. 5

ADM

=

noo/ (170

Eq. 6b

ATM

=

42.5 + 2 X 9.25

Eq. 7

DT = V61.0/.7854 = 8.8 ft. Use 9'-0" or 108" 2 AT = .785 X 9.0 = 63.62 sq ft

Eq. 8

AD = 63.62 X 9.25/61.0 = 9.9 sq ft AD is more than 10% of column area. OK

Eq. 9

H3

=

=

7.5 X (20 X (29.33 - 2.75 X 1.0 .395 X 1.0

=

=

170 gpm/sq ft

.395 ft/sec

7'-6/1 (based on 24" TS & 80% Flood)

=

9 X 7.5/2

=

=

33.7 inches

+ noo X 33.7/13000)/(.395 X .70)

12 X 9.9/9.0

=

X .70) = 9.25 sq ft

=

=

61.0 sq ft

13,2 inches

AD, = 9.9/2 = 4.95 AD,/ AT = 4.95/63.62 = .0777 H,/D = .1315 from Table 4 H, = .1315 X 108 = 14.2 inches Eq. 10

FPL = (12 X 9 - (2 X 14.2 + 13.2) )/2 = 33.2 inches Modular FPL = 32.5 or 34 inches, use 32.5 Use H, = 14.5, H3 = 14/1 AD, = 5.09 sq ft each 2 X AD, = 10.18

Eg. 12a AA = 63,62 - 20.68 = 42.94 sq ft

Eq. 13

% Flood

=

(100) (8.86

+ noo

X 32.5113000) =

42.94 X .395

Eq. 14

o

_

100 (8.86)

10 Flood - 63.62 X .395 X .78

45.2

Since Eq. 13 gives greater value than Eq. 14, use Eq. 13

-36-

68 6 .

42.5 sq ft

GLiTSCH, INC.

Ballast Tray Design Customer User _ _ _ _ _ _ _ _ _.

Glitsch Job No. __.__._ _ _ _ Date ______ Sheet of _ _ _ _ Rev. _ _ _ __

Inq. No. _ _ __

Vessel No.~3 I Service CJ S,d/ti6R I DT, Tower· Dia, __.q~~_~~__ c _____ c_.. _._~~L~L._,__._.__ ,inches AT, Tower Area 6S 6.:2 sq ft AA, Active Area "I~. 91' sq ft 10.34;/ sq ft AD, Downcomer Area NP, No. of flow paths ,;). FPL, flow path length 3.;1· .sinches WFP, flow path width 190 inches L'i, weir length: /U 7 ineh; swept~ Hw, weir height: d inch; adj. 4/0 Anti-jump baffles on trays £1'*':41:4= It?t?ds Draw pans on Feed to . vaporized_._ __ Manholes on trays I.D._.-_ __ MtllThk: Valve_~1 1ft,tI,i?,.; Decks (!s / /C)(;;;dI,. Packing; Tray D Sumps D Truss Ends 8 None D Loadings at Tray No. No. Trays in Section Tray Spacing, inches System (foam) Factor Rate, 1bs/hr Rate, cfs, cu ftl sec 'Dv, lblcu ft Vload. cfsvDv/(DL - Dv) CAF Hate. Ib/hr

:I +..'

DP, inches liquid DP, mm Hg or psi Vloadl Ah dsgn Aud, sq ft HU