Heat Transfer Equipment Some Industrial Applications Teo Chee Seng 17 Feb 2015

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

Types of HXs 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

Typical Applications in oil refinery 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

Preheat Train – Simplified Flow Scheme in CDU Circled parts showing a simplified view. One exchanger representing banks of exchangers

Crude Pre-heat network

Preheat Train Heat transfer through S&T HXs Design of heat exchange network is optimised by matching temperature level considering application of pinch technology in design spiral heat inserts; special baffles Efficiency of network has an impact on unit throughput and fuel consumption application of online chemical cleaning optimization of cleaning schedule

Cryogenic Applications eg. LNG 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

Typical LNG Receiving Terminal Flow Scheme Flare / Vent BOG Compressor Second Metering Station etc. Recondenser LNG Tanks Vaporisers LNG Carrier Metering Station In-tank Pumps HP Pumps BTU adjustment / odorisation Utilities

Open Rack Vaporizer ORV conceptional flow Seawater is the heat source vaporising the LNG (-160C). Seawater is pumped up to the trough by seawater pumps and distributed across the tube panels external heating up the LNG

Open Rack Vaporizer Pix showing 2 banks of ORVs, insert is showing the tubes with seawater flowing on the tube external.

Submerged Combustion Vaporizer – Ext View SCV is more expensive to operate than ORV and is often a back up to the ORV in case there is an outage of seawater flow. Picture is showing 3 SCVs installed.

Submerged Combustion Vaporizer – Int View                                            Small cartoon on the flow of hot flue gas heating up the cold LNG into warm natural gas by bubbling of the flue gas into a water bath

ACHEs 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/

Spool Wound HX Aluminium HX for enhanced heat transfer Very specialised equipment for Air/NG liquefaction

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

Overall Heat Transfer Coefficients In general, gas-gas HX is the worst ending up with very big HX Liquid-liquid is better, the best is with phase change – smallest HX Note the lower OHTC for gas-gas HX

HX TEMA classification TEMA standard for S&T exchangers

Design Codes

Common S&T Fixed Tubesheet (TEMA type BEM) U tube (TEMA type BEU) 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) Kettle Reboiler 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

Plate type HE A B A) PCHE B) Plate Fin type Often applied for narrow temperature differences and clean services like air, N2, natural gas etc

Operations : Process Monitoring (I) 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!

Example : Preheat Train Key process parameters to monitor are Furnace Inlet Temperature Individual exchanger heat transfer coefficient trends Individual exchanger delta P Pix showing tube internal cleaning of the tube bundle

Operations : Process Monitoring (II) 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

Vendors 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

Practical Aspects 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

Some links Movie on heat exchanger incident at the Tesoro refinery https://www.htri.net/ http://www.tema.org/ Prices