Eventos Anais de eventos
ENCIT 2016
16th Brazilian Congress of Thermal Sciences and Engineering
Exergy analysis of a natural gas liquefaction cascade cycle
Submission Author:
Hugo Valença de Araújo , AL
Presenter: Hugo Valença de Araújo
doi://10.26678/ABCM.ENCIT2016.CIT2016-0646
Abstract
Nowadays, natural gas is an important energy source and its consumption tends to grow. Pipelines are the most common mean of transport for natural gas. When large distances separate the producer and the end consumer, risks associated to pipelines become more significant and a liquefaction process can be used to reduce natural gas volume up to 600 times, hence producing liquefied natural gas (LNG), which enables other modes of transport. This work presents an exergy analysis of a simple cascade cycle for LNG production, aiming to contribute to further elucidate its thermodynamic performance. Main locations and causes of irreversibilities occuring in the process and ways to reduce them from a base case to an optimized one were discussed. Additionally, a parameter called exergy transfer effectiveness (ETE) was applied to quantify the exergetic efficiency in all equipment of the cascade cycle. Manipulating pressures of the streams leaving compressors and valvesat each subcycle of the cascade cycle, total exergy destruction rate was decreased from 18626.01 kJ/h in the base case to 9649.47 kJ/h in the optimized case. Free expansion in valves represented the most important cause of irreversibilities, accounting for about 50% of total exergy destruction rate in both base case and optimized case. Irreversibilities generation verified in heat exchangers and compressors correspond to approximately to 30% and 20% of the total, respectively, also in both base case and optimized case. Despite exergy destruction rates decrease significantly in all equipment from the base case to the optimized one, ETE increases more expressively only in heat exchangers and some valves, and very little pronounced reductions of ETE occurred only in some compressors.
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