Simulation And Experimental Research On Natural Gas Liquefaction Cycle Using Mixed-refrigerant

Liquefied natural gas (LNG) industry plays a more and more important role in the worldenergy consumption due to the energy tension and technology development. It’s widely usedin China and it has been researching for several years. However the liquefaction process ishuge and complicated, it’s difficult to achieve the optimum working condition because of themutual influence among each part of the process. Meanwhile the mixed-refrigerant adopted inthe cycle bring out some problems. The exergy loss in heat exchanger remains high due tounreasonable matching of the hot and cold flow, which will decrease the coefficient ofperformance (COP) of the entire system. Moreover the component of refrigerant and the inletstate of gas will affect the performance of the centrifugal compressor. In addition, in thepractical operation any inappropriate adjusting will cause system halted.In this paper, the related issues of LNG process have been simulated and analyzed. Atypical refrigeration system has been set up to testing the calculation model of the refrigerantcharging mass in the cycle that was based on the heat transfer theory. The experimental resultsdemonstrated that condensors occupied about55%~64%of the total refrigerant, whileevaporators only took up17%~32%. The comparison of the experiment and theoretical datahas proved the rationality of the calculation model.The major energy consumption in the LNG process is occupied by centrifugal compressor,and the adjusting of which will influence the following part of the system. A performanceprediction model has been set up in this paper and analyzed with the variables of differentcomponent and inlet state of refrigerant. Eventually the trend of the centrifugal compressorperformance was obtained.The optimizing of heat exchanging and reducing of the energy consumption becomesmore and more important in industry researching. In this paper, the heat exchangers of twolarge LNG plants have been simulated by using Aspen Plus. After analyzing, it can be knownthat the ideal temperature approach in heat exchanger is5°C~10°C，while which are12°C~18°C for plant A and17.1°C,34°C and27.5°C for plant B. Therefore some improvedmeasures can be proposed since the performances of practical and designing workingcondition were compared.