MODELLING OF THE FLUID DISTRIBUTION IN A PARALLEL PFHE ARRANGEMENT FOR THE LIQUEFIN LNG PROCESS

Liquefin is an innovative LNG process. One of the main novelties of the process is that all the exchange services of the unit take place in Plate Fin Heat Exchangers (PFHE). The use of PFHE technology brings not only an improved efficiency, but also decreases the cost of the unit, partly thanks to the compactness of the arrangement. Large capacity natural gas liquefaction plants require several PFHE in parallel. Such an architecture is already used in air separation, Nitrogen Gas Liquefaction or Ethylene plants, with similar size, number of exchangers or arrangement. However, due to the high amount of investment at stake in a LNG unit, specific studies on this arrangement have been carried out, considering distribution issues as wall as mechanical stress. This paper summarizes the methodology used to study the fluid distribution on a typical industrial case.
The objective of this study is to check that the parallel arrangement of exchangers does not induce unacceptable flow-rate difference between the exchangers, especially on the refrigerant fluid, nor flow instability which could have dramatic consequences for the exchangers efficiency or even reliability. For a real project case under normal operation, it is shown that, with a proper design, fluid distribution remains quite uniform and that under normal conditions as well as turn-down (50% capacity) and overload (133% capacity) conditions, instability cannot occur in the Liquefin process.