Some Industrial Applications

Teo Chee Seng

17 Feb 2015

Types of Heat Exchangers

Typical Applications in Oil refinery

Cryogenic applications in LNG industry

Design

Operations

Vendors

Practical aspects

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

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

Heat transfer through S&T HXs

Design of heat exchange network is optimised by matching temperature level considering

o application of pinch technology in design

o spiral heat inserts; special baffles

Efficiency of network has an impact on unit throughput and fuel consumption

o application of online chemical cleaning

o 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

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LNG Tanks Vaporisers

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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ORV conceptional flow

Open Rack Vaporizer

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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/

Aluminium HX for enhanced heat transfer

Very specialised equipment for Air/NG liquefaction

Service – fouling / corrosive?

Temperature difference / approach

Allowable/available pressure drop

O&M philosophy

Applicable codes and regulations

CAPEX / OPEX

Note the lower

OHTC for gas-gas

HX

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

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

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

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

A 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!

Key process parameters to monitor are o Furnace Inlet Temperature o Individual exchanger heat transfer coefficient

trends o 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

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

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

Movie on heat exchanger incident at the Tesoro refinery

https://www.htri.net/

http://www.tema.org/

Prices