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Chemical Process Technology

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Sunday, July 11, 2010

Main Cryogenic heat exchanger (MCHE) is one of key equipment in natural gas liquefaction (LNG) plant. MCHE used in liquefaction of natural gas having some special characteristic :
  • Intensive/excessive heat exchange (230 - 400 kW / ton LNG)
  • Complex heat transfer - Heat transfer from one (or several) very high pressure natural gas stream to one or several low pressure refrigerant streams
  • Thermal stress/shock - Very large temperature difference between inlet (40 degC) and outlet temperature (-162 degC)
  • Operate at very low temperature (-162 degC)
  • High heat transfer efficiency - Very low temperature approach (2-3 degC) to maximize heat transfer per unit area
  • Involve phase change and risk of phase separation and proper distribution
  • High risk of leakage and safety related issue
  • High risk of blockage/plugging
  • Lightweight & easy transportation

Two type of compact MCHE widely used in LNG plant. There are Plate-Fin Heat Exchanger and Coil (Spiral) Wound Heat Exchanger. Below images are typical CWHE and PFHE.


CWHE is coils/tubes wound in spiral around a mandrel and all coils / tubes are contains within a pressure vessel. Multiple coils/tube in bundle can be flew simultaneously within the pressure vessel.


PFHE is corrugated or serrated plate stacking on each and others to creates cross and/or counter flow paths to allow heat transfer of multiple fluids.

Although both type of HE have been widely used, CWHE and PFHE have their own special features and advantages. Below are simple comparison between both CWHE and PFHE.

FeaturesCoil Wound Heat Exchanger (CWHE) Plate-Fin Heat Exchanger (PFHE)
CompactnessCompact Extremely compact
Heat Transfer area (m²/m³) 20 - 300300 - 1400
Flow type in heat transferCross-CounterCross and/or Counter
Flow patternSingle and/or two phasesSingle and/or two phases
Flow streamsSingle or MultipleSingle or Multiple
ConfigurationSingle or multiple coil-in-vessel unitMultiple plate-fin units
Flow path8-12mm tube1-2 mm flow channel
Risk of contaminant built-upLess (smooth tube surface)More (multiple channels / cores increase crevices)
Risk of PluggingLowerHigher
Thermal Stress ResistanceHigher (tube robustness & flexibility)Lower (plate fin inflexible)
Risk of Thermal StressLowerHigher
Gas/Liquid distributionLess mal-distribution (single flow channel)Higher mal-distribution (multiple unit in parallel)
Risk of Thermal ShockLowerHigher (mal-distribution lead to imbalance heat transfer)
SafetyLower (tube contains within pressurized vessel - natural gas leaks to vessel)Higher (natural gas leaks to atmosphere)
AvailabilityHigher (production continue with some tube leaks until next shutdown)Lower (immediate production shutdown when leaks occur)
TransportationReasonable easy (with multiple bundles)Easy (Multiple units)
MaterialAluminum / Stainless Steel / Carbon Steel / Others AlloyAluminum

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posted by Webworm, 3:08 AM | link | 0 Comments |
Recommended :

It is often found necessary to transfer heat form hot to cold fluids by means of heat exchangers. there is wide variety of equipment available for this purpose, although in this Engineering Design Guide discussion is restricted to the more common types (other heat exchangers being mentioned only in passing). The very important aspect of removing heat from a primary source, such as a fired heater or the fuel elements of a nuclear reactor, also falls outside the scope of this guide. Although sufficient information is provided to enable the reader to understand and deal with simple heat transfer problems, this text to a large extend serve as an introduction to the more specialized books to which reference is made...

This FREE HEAT TRANSFER ebook discusses on several topics related to heat transfer and heat exchange. It content cover the general problem of heat exchange, analysis of heat conduction, convective heat transfer, thermal radiation heat transfer, mass transfer, etc

Source : http://www.hts.org.uk/
Thanks to D. Butterworth

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posted by Webworm, 3:07 AM | link | 0 Comments |
Recommended :

Some of you may not received your FREE Chemical Engineering Digital magazine for past two months. If you still complete the subscription form in recent update, you may still possible to access latest issue of Chemical Engineering of that particular month. The changes would lead to more visit to Chemical Engineering website and potentially increase sales to CE. However, it could be less favorable to most of you. But you may still obtain FREE Chemical Engineering continuously. The only differences is you need to login to Chemical Engineering website.

To access free monthly CE contents of the month :
  1. Login to Chemical Engineering Website
  2. Click "Current Issue"
Let's try click here

Some  interesting articles of CE July 2010.
  • Piping Design for Hazardous Fluid Service
  • Containing Fugitive Emissions
  • Distillation Tray Design 
  • Propelling distillation research
  • Process cooling: Just Cool It! 
  • Focus on Computer Modeling 
  • Decoding Pressure Vessel Design

If you are subscriber, you may access previous digital releases. Learn more in "How to Access Previous Chemical Engineering Digital Issue".

If you yet to be subscriber of Chemical Engineering, requested your FREE subscription via this link (click HERE). Prior to fill-up the form, read "Tips on Succession in FREE Subscription".

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posted by Webworm, 3:07 AM | link | 0 Comments |
FREE Hydrocarbon Processing for JULY 2010 is available now...

Select Articles from the July 2010 Issue 

Liquefied natural gas and North American shale gas: Room for both?
Let's take a look at the drivers affecting these commodities

Materials market update: Opportunities in a challenging economy
As companies emerge from the downturn, new capital project models will
be vital

Dynamic simulation of liquefied natural gas processes
Here's how to improve the process design and operation of your facility

Perfecting liquefied natural gas analysis techniques and methods
Following these procedures will improve measurement accuracy and reliability

Liquefied natural gas terminal with low environmental impact
Implement these steps to mitigate performance risks

Finetune boil-off gas generation from refrigeration storage facilities
Improved estimation methods accurately calculate vaporized product for liquefied natural gas transfer systems

If you yet to be subscriber of Hydrocarbon Processing, requested your FREE subscription via this link (click HERE). Prior to fill-up the form, read "Tips on Succession in FREE Subscription".

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posted by Webworm, 3:06 AM | link | 0 Comments |