COP optimization of propane pre-cooling cycle by optimal Fin design of heat exchangers: Efficiency and sustainability improvement

Abstract

The demand for LNG (liquefied natural gas) increases each year, and relevant studies have been developed in order to reduce both power consumption and greenhouse gas emissions of LNG plants. Multistream plate-fin heat exchangers (MPFHE) are widely used in these plants due to their large heat transfer surface area per unit volume for multi-phase flows. The thermal-hydraulic performance of heat exchangers also impacts on compressor shaft work of liquefaction plants. In this study, an automated optimization procedure is performed for commonly used MPFHE in a three-stage propane pre-cooling cycle to maximize the coefficient of performance (COP) of liquefaction plants. Four geometric input parameters (fin type, fin height, fin thickness, and fin frequency) have been selected for the optimization. The optimal heat exchangers and operating conditions of the entire refrigeration cycle and their feasibility are taken into account. The optimal fin designs of the heat exchangers affect the cycle operating conditions, which results in COP improvements of 18.9%, 2.5%, and 9.4%, and ranging from 7% to 32% of mitigation in CO2 emission when compared to the literature cases. Compared with the baseline case, the COP is improved by 9.4%, compressor shaft power is reduced by 7.1% (about 11.2 MW), heat transfer is augmented by 1.5% (3.8 MW), and CO2 emission is reduced by 6.3 t/h, which result in more efficient and sustainable LNG production.