Simulation Of Plate-fin Heat Exchangers In Complex Liquid-nitrogen Wash Unit

Plate-fin heat exchanger is a kind of compact heat exchanger, which has high heat transfer surface area, high heat transfer efficiency, and compact lightweight structure. It is of good adaptability as well as economic performance, so in recent years it has been developed rapidly in various areas of industries and civil uses. Plate-fin heat exchanger can not only transfer multistream heat in one unit at the same time but also be suitable for single or multiphase heat transfer. when low temperature applications are involved, it is favorable for heat transfer of clean gas and liquid.Liquid-nitrogen wash unit is used to refine scrubbed gas before sending it to ammonia synthesis step in ammonia synthesis industries. This equipment can remove CO and other oxygenated chemicals that will cause toxic action of the catalyst. Match usage of it and rectisol process, the process used for removing the hydrogen sulfide and carbon dioxide, will effectively reduce energy consumption at low temperature. This technology has great advantages and now has been applied in many ammonia plants. Besides the parts that typical liquid-nitrogen wash equipments have, a complex liquid-nitrogen wash also includes the tail gas and purge gas recovery system which is characterized by advanced technology and integrated energy system. As the primary heat transfer equipment in liquid-nitrogen wash unit, plate-fin heat exchanger plays a very important role. In low temperature and high pressure system of liquid-nitrogen wash, the heat transfer of plate-fin heat exchanger deals with multicomponent and multistram, while some of the streams with phase transformation. So the calculation of plate-fin heat exchanger in liquid-nitrogen wash process becomes very difficult, and also has higher accuracy requirements for property methods adopted.In this paper eight high pressure brazed aluminium plate-fin heat exchangers in liquid-nitrogen wash unit were calculated and checked. Fluid physical properties, like the outlet temperature, heat transfer areas, pressure drops, and other parameters of the heat exchanger, are calculated with SRK, PSRK, RK-ASPEN, RP-BM and BWRS property methods. Then the calculation results of various physical methods are discussed by comparing the calculated values with the original design ones. At last, BWRS property method is selected to describe the fluid physical properties in liquid-nitrogen wash process. The simulation results and original design values match well. These data provide theoretical basis and have important guiding significance for designing and checking calculation of plate-fin heat exchangers of the liquid-nitrogen wash unit, which also broaden the scope of application of the BWRS equation of state.