How to Use HTRI for Shell & Tube Exchanger Design

How To Use HTRI For Shell & Tube Exchanger Design

Frank Shan May 18, 2005

Contents What Can HTRI Do General Procedures Example: Liquid-Liquid Exchanger Design Result Evaluation

What Can HTRI Do? Air Cooler

HTRI - Heat Transfer Research Inc.

Fire Heater

Hairpin Exchange r

S&T Exchanger

HTRI Xchanger Suite

Jacket Pipe Plate-Frame Exchanger Exchanger

Tube Layout

Vibration Analysis

General Procedure

Data Sheet

Case Mode Rating, Simulation, Design

Shell & Tube Geometry

Process Inlet/Outlet Fluid (Cold/Hot) Properties

Result Analysis

End

Other Input

Example: Liquid-Liquid S&T Exchanger Standard Data Sheet

1. Create an empty case: select File > New Shell and Tube Exchanger

1.1 Xist Main Window Click for help

Required Input is highlighted in red

Navigation Tree Click + to expand

2. Setting Unit: select Edit > Data Units, or click button

3. Select Case Mode

Rating (Default) You define exchanger geometry and enough process conditions for Xist to calculate the required heat duty. Simulation You define exchanger geometry and fewer process conditions for Xist to calculate the required heat duty. Design You define most exchanger geometry and enough process conditions for Xist to calculate the required heat duty.

4. Input Shell Side Geometry

HTRI allows shell diameter up to 1000 in

Shell and Tube Exchanger Selection

Shell Selection depends on available ∆P, the E-type is the least expensive shell.

(Courtesy of TEMA)

Shell and Tube Exchanger Selection

(Courtesy of GPSA)

5. Input Tube Side Geometry

Tube Geometry

Tube Dia.:

3/4 ~ 1 in are more compact and more economical. 1 inch tube are normally used when fouling is expected, or low ∆P is required.

Tube Length: In general, the greater the ratio of tube length to shell diameter, the more economical the exchanger. Practically, 16 ft or 20 ft facilitate reasonable plot space and maintenance for horizontal exchanger. Tube Pitch Ratio: 1.25, 1.333 are most common For kettle reboiler operating at low pressure, 1.5 pitch ratio has been proved effective

Tube layout

A 30-degree layout (default) is most common. Triangular tube-layouts result in better shellside coefficients and provide more surface area in a given shell diameter, whereas square pitch or rotated-square pitch layout are used when mechanical cleaning of tube outside is required

6. Input Baffles Geometry

Baffle Type

Cut range: 1 – 49%

Cut range: 5 – 30% For TEMA E Shell, No.Crosspass = No.Baffle+1

Double-segmental Baffle

Cut range: 5 – 30% Baffle cut (100*h/D): 17% to 35% of shell diameter A 22% cut is the optimum (HTRI) Baffle spacing:

20% to 100% of shell diameter (HTRI recommends 40% of shell dia. as start point)

7. Input Shellside Nozzle Location

8. Input Optional Data

DT: only for printout DP: to calculate tubesheet thickness & bundle-to-shell clearance for pull-through floating head bundle

9. Input Process Data

10. Input Hot Fluid Properties. 10.1 Select Physical Property Input Method

The component-by-component option is recommended for single-phase-only fluids for which the variation in fluid properties is not large.

10.2 Use User Define Properties

10.3 Input Liquid Properties

11. Input Cold Fluid Properties. (Same Procedure as Hot Fluid)

Alternate Input Methods (Process condition & properties)

Import Case: (need simulator installed) File>Import Case>change file type >select simulation file>select exchanger> generate properties

Property Generator... Hot/Cold Fluid Properties>Property Generator>select Property package – HYSYS >simulation file>select exchanger>select fluid>generate properties

HTRIFileGen - developed by Hyprotech to transfer data from simulation HYSYS extension – allow you to develop and run the process simulator while using the HTRI proprietary methods.

12. Run Case Click or File>Run Case or Ctrl+F5

Indicate incomplete input

Result Drawing

13. Analyze Final Results Consider the following, and think of the possibility of a better design. Program message

Overdesign factor

Main design dimensions

∆P

Velocities

Heat transfer coefficients

Distribution of thermal resistances

Flow regime distribution

Terminal process conditions

Baffle design

EMTD and temp profile

Vibration analysis

13.1 Program Messages

Fatal: Problems lead to incorrect results Warning: Unusual, limiting need your attention Informative: Unusual data

13.2 Velocity:

High enough to suppress fouling Low enough to prevent erosion higher velocity gives better heat transfer and suppresses fouling, thus provides a longer run length. But too high a velocity will cause tube erosion, and/or vibration. For heavy oil services, consider 4 feet per second on the tubeside as the “design” number. Faster is better until you reach 10-12 fps for water or (density) x velocity^2 of 10,000 to 12,000 (English units). Shellside velocities are more difficult but anything less than 3 fps will definitely foul when in heavy oil service. (Advised by Tom Kemp)

13.3 Thermal Resistances Check thermal resistances for shellside, tubeside, fouling, and tube metal. Check dominant value. Shellside Heat Transfer Limited

Action

Result

Watch For

Change shell type (F,G)

Increase shellside velocity, MDMT, and heat transfer coefficient

Design requirement

Reduce tube pitch

Increase shellside velocity

Bypassing and leaking

Decrease tube dia.

Slight increase in heat transfer coefficient

Tubeside ∆P increase

Consider finned tubes

Smaller exchanger

Use sealing strips

Reduce E stream with decreased baffle-to-shell clearance

Tubeside Heat Transfer Limited Action

Result

Change tube length

Improve tubeside performance

Decrease tube dia.

Increase tubeside h, velocity at given shell size

Switch tube/shell side

More efficient design

Increase tube pitch

Increase tubeside velocity at given shell size because of fewer tubes

Watch For

Increased tubeside ∆P

13.4 Overdesign Factor Overdesign = (Qcalc – Qreq’d) / Qreq’d x 100 = (Ucalc – Ureq’d) / Ureq’d x 100

13.5 Shellside Flow Distribution

B stream: C and F stream:

normally at least 60% of total flow for turbulent flow and 40% for laminar flow Normally should not exceed 10%

13.6 Pressure Drop It is highly undesirable if the exchanger is limited by ∆P, exchangers are larger than necessary to accommodate allowable ∆P rather than to satisfy heat transfer demands. For critical exchangers (condenser, reboiler), try to meet the required ∆P. For heavy streams, “no fouling” is the first concern over ∆P. Shellside ∆P Limited Action

Result

Watch For

Change shell type

∆P reduced greatly (TEMA E to J decrease by up to factor of 8)

Investigate multisegmental bundles

Double-segmental baffle ∆P reduced to about 1/3 of that for segmental baffle with same central spacing

Tube vibration is possible

Investigate NTIW bundles

∆P reduced to 1/4 if window area large enough

Extreme caution: inefficient heat transfer may result

Increase baffle cut

∆P reduced by large cut

Increase nozzle sizes

∆P reduced

Tubeside ∆P Limited Action

Result

Increase tube dia.

∆P reduced sharply, ∆P~f(d^5)

Decrease tube pitch

Larger tubeside flow area (more tubes fit into shell)

Check singletubepass design

∆P is 1/8 of that of 2tubepass design

Decrease tube length

∆P reduced sharply

Increase nozzle sizes

∆P reduced

Watch For

Reduces heat transfer surface and shellside flow area.

14. Finishing

Re-adjust the parameters if necessary

Re-run the case Not satisfied

Evaluation

Satisfied

Finish

Thanks !