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 !
