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How to Use HTRI for Shell & Tube Exchanger Design

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How To Use HTRI For Shell & Tube Exchanger Design

Frank Shan

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What Can HTRI Do

General Procedures

Example: Liquid-Liquid Exchanger Design

Result Evaluation

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HTRI Xchanger Suite

Air Cooler Fire Heater

Hairpin Exchange r S&T Exchanger Jacket Pipe Exchanger Plate-Frame Exchanger

Tube Layout Vibration Analysis

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Shell & Tube Geometry Fluid (Cold/Hot) PropertiesProcess Inlet/Outlet Data Sheet

Case Mode

Rating, Simulation, Design

Result Analysis

Other Input

End

General Procedure

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Example:

Liquid-Liquid S&T Exchanger

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1.1 Xist Main Window Required Input is highlighted in red Navigation Tree Click + to expand

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Simulation

Design

Rating (Default)

You define exchanger geometry and enough process

conditions for Xist to calculate the required heat duty.

You define exchanger geometry and fewer process

conditions for Xist to calculate the required heat duty.

You define most exchanger geometry and enough

process conditions for Xist to calculate the required

heat duty.

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4. Input Shell Side Geometry

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Shell and Tube Exchanger Selection (Courtesy of TEMA) Shell Selection depends on available P, the E-type is the least expensive shell.

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(Courtesy of GPSA)

Shell and Tube Exchanger

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Tube Geometry

3/4 ~ 1 in are more compact and more economical.

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.

1 inch tube are normally used when fouling is

expected, or low

P is required.

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 Length:

Tube Dia.:

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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

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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) Cut range: 5 – 30% Cut range: 1 – 49%

Cut range: 5 – 30% Double-segmental Baffle Baffle Type

For TEMA E Shell,

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8. Input Optional Data

DT: only for printout

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

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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.

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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.

Alternate Input Methods

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12. Run Case Click or File>Run Case or Ctrl+F5 Indicate incomplete input

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13. Analyze Final Results

Vibration analysis EMTD and temp profile

Baffle design Terminal process

conditions

Flow regime distribution Distribution of thermal

resistances

Heat transfer coefficients Velocities

P Main design dimensions

Overdesign factor Program message

Consider the following, and think of the possibility of a better design.

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13.1 Program Messages

Fatal: Problems lead to incorrect results

Warning: Unusual, limiting need your attention Informative: Unusual data

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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.

13.2 Velocity:

(Advised by Tom Kemp)

High enough to suppress fouling

Low enough to prevent erosion

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Check thermal resistances for shellside, tubeside, fouling, and tube metal. Check dominant value.

13.3 Thermal Resistances

Reduce E stream with decreased baffle-to-shell clearance

Use sealing strips

Smaller exchanger Consider finned

tubes

Tubeside P increase

Slight increase in heat transfer coefficient

Decrease tube dia.

Bypassing and leaking

Increase shellside velocity Reduce tube pitch

Design requirement Increase shellside velocity,

MDMT, and heat transfer coefficient

Change shell type (F,G)

Watch For Result

Action

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Increase tubeside velocity at given shell size because of fewer tubes

Increase tube pitch

More efficient design Switch tube/shell

side

Increased tubeside

P Increase tubeside h, velocity

at given shell size Decrease tube dia.

Improve tubeside performance

Change tube length

Watch For Result

Action

Tubeside Heat Transfer Limited

13.4 Overdesign Factor

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

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13.5 Shellside Flow Distribution

normally at least 60% of total flow for turbulent flow and 40% for laminar flow

B stream:

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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.

13.6 Pressure Drop

P reduced Increase nozzle sizes

P reduced by large cut Increase baffle cut

Extreme caution: inefficient heat transfer may result

P reduced to 1/4 if window area large enough

Investigate NTIW bundles

Tube vibration is possible

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

Investigate multi-segmental bundles

P reduced greatly (TEMA E to J decrease by up to

factor of 8) Change shell type

Watch For Result

Action

Shellside P Limited

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Reduces heat transfer surface and shellside flow area.P reduced sharply Decrease tube lengthP reduced Increase nozzle sizesP is 1/8 of that of 2-tubepass design Check single-tubepass design

Larger tubeside flow area (more tubes fit into shell) Decrease tube pitch

P reduced sharply,

P~f(d^5) Increase tube dia.

Watch For Result

Action

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Re-adjust the parameters if necessary

Re-run the case

Satisfied Evaluation Not satisfied

Finish

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References

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