How To Use HTRI For Shell & Tube Exchanger Design
Frank Shan
What Can HTRI Do
General Procedures
Example: Liquid-Liquid Exchanger Design
Result Evaluation
HTRI Xchanger Suite
Air Cooler Fire Heater
Hairpin Exchange r S&T Exchanger Jacket Pipe Exchanger Plate-Frame Exchanger
Tube Layout Vibration Analysis
Shell & Tube Geometry Fluid (Cold/Hot) PropertiesProcess Inlet/Outlet Data Sheet
Case Mode
Rating, Simulation, Design
Result Analysis
Other Input
End
General Procedure
Example:
Liquid-Liquid S&T Exchanger
1.1 Xist Main Window Required Input is highlighted in red Navigation Tree Click + to expand
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.
4. Input Shell Side Geometry
Shell and Tube Exchanger Selection (Courtesy of TEMA) Shell Selection depends on available ∆P, the E-type is the least expensive shell.
(Courtesy of GPSA)
Shell and Tube Exchanger
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.:
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
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,
8. Input Optional Data
DT: only for printout
DP: to calculate tubesheet thickness & bundle-to-shell clearance for pull-through floating head bundle
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.
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
12. Run Case Click or File>Run Case or Ctrl+F5 Indicate incomplete input
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.
13.1 Program Messages
Fatal: Problems lead to incorrect results
Warning: Unusual, limiting need your attention Informative: Unusual data
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
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
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
13.5 Shellside Flow Distribution
normally at least 60% of total flow for turbulent flow and 40% for laminar flow
B stream:
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
Reduces heat transfer surface and shellside flow area. ∆P reduced sharply Decrease tube length ∆P reduced Increase nozzle sizes ∆P 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
Re-adjust the parameters if necessary
Re-run the case
Satisfied Evaluation Not satisfied
Finish