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

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

3. 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

4. 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

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

6. Crude Pre-heat network

7. 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

8. 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

9. 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

10. 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

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

12. 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.

13. 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

14. ACHEs
Banks of Air Cooled Heat Exchangers are used as condensers in baseload LNG liquefaction plants
heatexchangers.com/products/finned- tube-heat-exchangers/air-fin-coolers-for- oil-and-gas/

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

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

17. 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

18. HX TEMA classification
TEMA standard for S&T exchangers

19. Design Codes

20. 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

21. 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

22. 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

23. 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!

24. 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

25. 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

26. 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

27. 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

28. Some links Movie on heat exchanger incident at the Tesoro refinery
Prices