Heat Transfer Equipment

Some Industrial Applications

Teo Chee Seng17 Feb 2015

Types of Heat Exchangers Typical Applications in Oil refinery Cryogenic applications in LNG industry Design Operations Vendors Practical aspects

Agenda

HXs can be broadly divided by the following applications◦ Heat exchange eg. Cold crude oil versus hot

column residue◦ Boilers eg. Steam reboilers, distillation column

reboilers◦ Cooler eg. Water coolers, air fin coolers◦ Chillers eg. Chilled water coolers◦ Cryogenic eg. Propane refrigeration coolers, air

separation HXs

Types of HXs

Shell and Tube (S&T) HXs are the majority Water coolers – trim coolers or rundown

coolers Air cooled HXs – distillation column

condensers Steam heaters – reboilers or preheater Hot oil heaters – closed loop process

heating

Typical Applications in oil refinery

Preheat Train – Simplified Flow Scheme in CDU

Crude Pre-heat network

Preheat Train

Heat transfer through S&T HXs Design of heat exchange network is

optimised by matching temperature level consideringo application of pinch technology in designo spiral heat inserts; special baffles

Efficiency of network has an impact on unit throughput and fuel consumptiono application of online chemical cleaningo optimization of cleaning schedule

Plate exchangers in LNG plants, air separation units

Spool wound heat exchangers in LNG liquefaction plants

Printed circuit exchangers in offshore platforms Propane “kettles” characterized by narrow

temperature approaches In LNG terminals, LNG is vaporised into natural

gas using vaporisers (ORVs or SCVs)◦ ORV – Open Rack Vaporisers◦ SCV – Submerged Combustion Vaporisers

Cryogenic Applications eg. LNG

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LNG TanksVaporisers

HP Pumps

BOG Compressor

Second Metering Station etc.

Metering Station

BTU adjustment / odorisation

Recondenser

LNG Carrier

Flare / Vent

In-tank Pumps

Utilities

Typical LNG Receiving Terminal Flow Scheme

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Open Rack Vaporizer

                                          

ORV conceptional flow

Open Rack Vaporizer

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Submerged Combustion Vaporizer – Ext View

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Submerged Combustion Vaporizer – Int View

Banks of Air Cooled Heat Exchangers are used as condensers in baseload LNG liquefaction plants

http://www.gea-heatexchangers.com/products/finned-tube-heat-exchangers/air-fin-coolers-for-oil-and-gas/

ACHEs

Aluminium HX for enhanced heat transfer

Very specialised equipment for Air/NG liquefaction

Spool Wound HX

Service – fouling / corrosive? Temperature difference / approach Allowable/available pressure drop O&M philosophy Applicable codes and regulations CAPEX / OPEX

Design : General Considerations

Overall Heat Transfer Coefficients

Note the lower

OHTC for gas-gas

HX

HX TEMA classification

Design Codes

Fixed Tubesheet (TEMA type BEM)◦ Cheap and easy

construction◦ Tubes fixed on

both ends; tube external not accessible for cleaning

U tube (TEMA type BEU)◦ Good for large

differential Ts◦ Limited internal

tube cleaning

Common S&T

Floating Head (TEMA type BES)◦ Allow access to shell &

tube external for cleaning

◦ Good for large dTs◦ Expensive

Kettle Reboiler◦ Meant for vaporising

medium either heating eg. Distillation column bottom reboilers or chilling like propane refrigerant

◦ Vapour space allows liquid and gas separation

Common S&T

A) PCHE B) Plate Fin type Often applied for narrow

temperature differences and clean services like air, N2, natural gas etc

Plate type HEA B

Typical “task” for process engineer is to monitor the effectiveness of heat exchange network

WHY?◦ Lower efficiency means increased firing in furnaces leading to more

burning more fuel and higher costs◦ Efficiency reduces with time due to “fouling”

How to monitor?◦ Trending the overall heat transfer coefficient of individual HXs or groups

of HXs◦ There is no OHTC meter! OHTC has to be back calculated based on

temperatures and flowrates◦ An alternative is to monitor the fouling factors – essentially the same

principle as OHTC◦ “normalisation” to the right flowrates and temperature is important as

differernt flowrates and temperature can have significant effect on OHTC calculations

Decide when to clean and what to clean!

Operations : Process Monitoring (I)

Example : Preheat Train

Key process parameters to monitor areo Furnace Inlet Temperatureo Individual exchanger heat transfer coefficient

trendso Individual exchanger delta P

Pix showing tube internal cleaning of the tube bundle

For water coolers and air coolers, there are often no flowmeters and temperature meters on the air/water side

Monitoring is often by setting a “baseline” eg after a maintenance shutdown when equipment is clean

Troubleshooting is often via hand held meters like an IR meter to gauge the temperature of the process / portable ultrasonic flowmeters for water flow measurement

Comparison against design values often give good clues to current performance – process models on rating mode is very useful

Operations : Process Monitoring (II)

S&T HXs equipment are no longer considered specialized equipment and there are many vendors in the world

Brazed aluminum plate exchangers are more “specials” – Chart industries/Linde are two of the leading vendors

Printed circuit HX is a special small form factor compact HX offered by Heatric

SWHE – specialised HX offered by APCI/Linde for cryogenic applications

Vendors

Heat exchangers are crucial pieces of equipment in maintaining unit throughput and optimizing fuel efficiency

O&M know how and considerations like space requirements, cleaning schedule, valving arrangements, flushing, fouling etc need to be considered in the initial design

Relevant experience is important in choice of HX to be applied

Trend is towards more online cleaning, non-intrusive monitoring and process monitoring via simulation

Practical Aspects

Movie on heat exchanger incident at the Tesoro refinery

https://www.htri.net/ http://www.tema.org/ Prices

Some links