Research And Application And Energy Optimization Of 20×10~4t/a Natural Gas Liquefaction Unit

In the process of natural gas liquefaction,if the refrigerant mixture ratio of the liquefaction system is unreasonable,it will lead to the temperature rise of the mixed refrigerant at each equipments,further,it will cause too much refrigerant consumption and high energy consumption.In the end,the cost of LNG production will increased.A natural gas liquefaction plant of northern shannxi exists many problems in practical production.For instance,energy consumption of the device is in a high level,it is hardly to achieve the reasonable ratio of mixed refrigerant,the request of system operation is high.In order to deal with these problems in the process of industrial production,a systematic study is conducted on this respect in this paper,and concrete results are as follows.(1)The PR equation was used to calculate the phase balance,the mixture enthalpy and entropy.Meanwhile,thermodynamic analysis of the the liquefaction equipment model was carried out dased on PR equation.The whole process simulation of mixed refrigerant process was established by Aspen HYSYS software.The result showed that the simulated values were highly coincident with the actual values,which proved that this software could successfully simulate and optimize natural gas liquefaction system.(2)The effects of natural gas parameters and mixed refrigerant parameters were analyzed systematically when both refrigerant circulation and unit energy consumption were taken as optimal objective.The optimized conditions of this liquefaction plant were obtained by taking the production cost of Unit liquefied natural gas as an optimization goal.The optimal ratio of mixed refrigerant by HYSYS’s optimizer were as follows: nitrogen of 4.2%,methane of25.9%,ethylene of 37.3%,propane of 16.8% and isopentane of 15.8%.Under the optimized conditions,the mixed refrigerant flow rate and unit energy consumption were decreased by5.52%,5.84% respectively.The optimal ratio of mixed refrigerant by GA genetic algorithm were as follows: nitrogen of 4.9%,methane of 24.8%,ethylene of 38.0%,propane of 18.4%and isopentane of 13.9%.Under the optimized conditions,the mixed refrigerant flow rate and unit energy consumption were decreased by 6.82 %,11.34% respectively.According to the two optimization results,GA genetic algorithm was much better.The mixed refrigerant flow rate and unit energy consumption were decreased by 6.16 %,1.04% respectively compared with HYSYS’s optimizer.(3)The operation of associated equipment such as K-02,P-06,AC-05,AC-06,E-13 and E-14 under optimize process were checked by Aspen HYSYS,HTRI Xchanger Suite andother specialized chemical software.The results showed that the refrigerant compression and refrigerant booster pump satisfied manufacturing needs under optimize process.The heat exchanger of AC-06 could not meet the heat transfer requirements under the optimized conditions,which must be replaced with a wet air cooler.Through transformation,the natural gas liquefaction and LNG production of this natural gas liquefaction unit were increased by3.30%,3.27% respectively,the mixed refrigerant flow rate and unit energy consumption were decreased by 9.08%,5.93% respectively.