The propane pre-cooling cycle has been widely used in most LNG plants as the first cooling cycle in the natural gas liquefaction process. As LNG plants consume high amounts of energy, enhancements in the process design and plant operation will minimize the overall energy consumption of the plant. The aim of this study is to enhance the process efficiency of.J! three stage propane pre-cooling cycle of the Cascade LNG process for the large-scale LNG train by determining the optimal operating conditions of 2 the propane evaporator that will minimize the overall energy consumption. Energy and exergy analysis methods are adopted to evaluate the process efficiency of the propane pre-cooling cycle. Six case studies were presented to determine the optimal operating conditions of the propane evaporator that gives maximum energy reduction. The propane pre-cooling cycle is modelled and simulated using Aspen 7 HYSYS with detailed thermodynamic information obtained to calculate the exergy loss. The results of the energy and exergy analysis indicate that Case 6 gives the highest coefficient of performance (COP) 9 and the maximum exergy efficiency compared to the baseline case, which are 15.51% and 18.76% respectively. The results indicate that by reducing the cooling duty at the intermediate stage §. of propane evaporator about 13.5% energy saving can be achieved compared to the baseline case.
The natural gas liquefaction process consists of a sequence of refrigeration cycles that consumes a considerable amount of energy. The separation of natural gas (NG) from the natural gas liquids (NGL) is considered to be one of the significant parts in the liquefaction of natural gas, as this will influence the LNG product quality. The integration of NGL section with the liquefaction process is one of the fundamental ways to improve the efficiency of the process and provide economic benefit from operating and capital cost perspectives.
In this extended abstract, two different configurations of NGL section integrated with the ethylene refrigeration cycle for the Cascade LNG plant—processing 5 million tonnes per annum (MTPA)—are proposed. The objectives of the proposed concepts are to meet the LNG higher heating value (HHV) specification and to achieve minimum power consumption for the refrigeration cycle. Exergy analysis is used as a thermodynamic tool to evaluate the efficiency of the process.
The process was simulated using Aspen HYSYS and the results of the proposed configurations are presented and analysed. The proposed configurations can be used to produce LNG and NGL with minimum energy consumption.
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