Geometric optimization of thermo-hydraulic performance of multistream plate fin heat exchangers in two-stage condensation cycle: Thermodynamic and operating cost analyses

Abstract

LNG is an energy carrier with growing importance, but LNG cryogenic cycles are energy-intensive. Because the thermo-hydraulic performance of heat exchangers affects the operation and energy consumption of a compressor. The optimization of heat exchangers is key to improving the energy efficiency of a cryogenic plant. In this work, the screening analysis and optimization procedures are performed for a two-stage condensation plant to enhance the Coefficient of Performance (COP) as the operating performance criterion. Five geometric design categories of applied fins, such as fin type, fin height, fin thickness, fin frequency, and the number of layers of MPFHEs (Multistream Plate Fin Heat Exchanger) are selected as input parameters for the optimization process. Then, a thermodynamic analysis including the second law analysis and capital and operating costs assessment are carried out to show the improvements of applied optimization in the mentioned objectives. The results of the optimization procedure have indicated a considerable improvement in the COP of up to 13.7% and significant mitigation in total power consumption of up to 11.8 MW. Furthermore, the optimal configuration of heat exchangers presents an increase in exergy efficiency of up to 4.1%, a saving in exergy destruction of 10.2 MW and up to 8.6 M USD/year in the operating cost when compared with conventional cases.