Compressor shaft work targeting using new numerical exergy problem table algorithm (Ex-PTA) in sub-ambient processes

Abstract

One of the major challenges faced by energy intensive industries is an excessive greenhouse gas emission to the atmosphere due to high consumption of fossil fuels throughout the production processes. Due to high electricity usage in intensive industries, it is strongly advisable to all the engineers and other stakeholders to reduce the amount of energy needed for production, thus reducing carbon footprints. This is because the power generation industry emits approximately 37 % of total carbon dioxide emission to the atmosphere. Process improvement via Process Integration enhances the process energy efficiency, which contributes to the minimisation of fossil fuels and electricity consumption. Sub-ambient processes with refrigeration system are one of the highly energy intensive processes, which consumes a vast amount of electrical energy to run the compressors for fulfilling the process cooling demand. It is crucial to optimise the process-utility heat transfer in the system including the placement of compressors and expanders to minimise the exergy losses and shaft work consumption. This paper presents a combined energy analysis technique of Pinch Analysis and Exergy Analysis to determine exergy losses and compressor shaft work targeting in sub-ambient processes via a novel numerical approach known as the Exergy Problem Table Algorithm (Ex-PTA). The validity of the novel approach is demonstrated by using an illustrated case study. Based on the new numerical method, the total exergy loss in the process is 4.42 kW which is equivalent to 7.4 kW potential savings of compressor shaft work. In the economic analysis, the wasted potential shaft work costs a loss of approximately 19,926 MYR/y which should be avoided to minimise process operating cost.