Printed Circuit Heat Exchangers (PCHE) are diffusion-bonded type heat exchangers. These are highly compact, highly robust exchangers compare to the other popular heat exchangers such as shell and tube. They are now well established in the upstream, high pressure hydrocarbon processing, petrochemical and refining industries.
Major oil companies such as Cheveron, BP, Shell, ExxonMobil, etc., and operators such as SBM, MODEC, etc., are using PCHEs to projects all over the world.
Some of the advantages of PCHEs are as follows:
- Four to six times smaller than conventional shell and tube heat exchangers for the same duty.
- Extreme pressure capability in excess of 600 bar (9000 psi)
- Extreme temperature capability ranging from cryogenic to 900°C.
- High thermal effectiveness of over 98% in a single unit.
- Has space and weight advantages, as several process streams can be into a single unit.
- Suitable for a range of corrosive and high purity streams.
Due to the fine flow channel sizes in PCHE, a very clean service, like condensate is the best application for PCHE. Any solids, such as corrosion products, pipe scale, ice will cause deteriorated performance for the PCHE.
It is possible to use PCHE for multifluid heat exchanger. As an example, three conventional heat exchanger "gas/gas, gas/condensate and gas/refrigerant" units can be replaced by a PCHE unit as shown below.
However, PCHE are not recommended when sea water is used as cooling medium due to fouling, scaling, etc. issues.
Considerations when selecting the Printed Circuit Heat Exchangers. The use of PCHE should be limited to clean fluid service only. Furthermore, PCHE should not be used to cool gas directly from a separator. The use of a PCHE downstream of an oil lubricated compressor is not recommended.
Special attention should be given to:
- Particles: A permanent strainer (Hellan type or similar) of 250 micron should be fitted on the inlet of both sides of a PCHE in liquid service and for the liquid side only for gas coolers/heaters.
- To mitigate fatigue the temperature control should be designed to limit thermal cycling. A travel stop for 20% minimum flow through the control valve is required to reduce the extent of thermal cycling.
- A temporary strainer contained in a removable spool should be provided on the gas side of gas coolers or heaters.
- Pressure drop of the permanent strainer and the heat exchanger core should be monitored on both sides of the exchanger.
- 3” nozzles shall be provided on each inlet manifold to facilitate off-line Ultra High Pressure (UHP) cleaning.
There is no blockage within PCHE considering dry and clean gas. Filters also typically will be provided for inlet of process as well as cooling medium inlet lines. Therefore, there should not be planning to install for dry gas service. However, if there is a need to specify this requirement, spare PCHE in storage can be provided (one common per duty/rating for export gas compression trains).
PCHE pressure drop assumption for simulation modeling will depend on the type of process:
- Generally in systems where fouling is predicted the pressure drop for the clean printed circuit heat exchanger should be restricted to 90 % of the allowable value.
- In addition pressure drop losses should also include all those occurring in nozzles, header tanks, bends, fittings, manifolds, distribution, thermal sections, etc.
- The pressure drop for the strainer should be additional to the stated printed circuit heat exchanger pressure drop.