Simulation And Optimization Of The Power System Utilizing The Cold Energy Of Liquefied Natural Gas(LNG)

This paper studies the power cycle how to recover cold energy of LNG efficiently,and constructs the cycle which can recover medium-high temperature waste heat.The Kalina cycle is used to recover the medium-high temperature waste heat,meanwhile the LNG is used in cycle to recover the cold energy,two cycles is built to recover the cold energy of LNG.The range of LNG temperature is too large(from-162 ?-20 ?),the vaporization characteristics of LNG are analyzed,and the vaporization process of LNG is divided into three stages: liquid phase,latent heat and gas phase.The cold energy of this three stages is analyzed,then the recovery of cold energy of the LNG is determined to use two-stage cycle.The first cycle is the Rankine cycle to recover the liquid phase and the latent heat.The Kalina cycle is used to recover the cold energy of the gas phase.The working fluids of R20,R125,R134 a,R170 and R1150 in the Rankine cycle were analyzed.Their saturation temperature,latent heat of vaporization and dry-wet characteristics were analyzed.Finally,R170 was chosen as the working fluids of Rankine cycle according to the specific working conditions.On the basis of the traditional Kalina cycle,according to the ultimate goal of recover LNG cold energy in this paper,the traditional Kalina cycle has been changed so that a better heat transfer in the heat exchanger.In the changed Kalina cycle,the concentration of the working solution is lower than that of the base solution.In the Aspen Plus software,the built cycles were simulated by selecting the appropriate physical equation of PR equation and NRTL equation,and the thermophysical data of each node in the cycle were obtained.The thermodynamic analysis and parameter analysis were carried out for each cycle,then the optimal parameters were obtained,When the parameters are optimized,the highest exergy efficiency of the Rankine cycle is 34.9%,the highest thermal efficiency and exergy efficiency of the Kalina cycle is 52.13% and 40.2%,respectively.The economical analysis of this system is studied,it indicates the cost of per power is 4.86$/W less than 5.1$/W,so the system is efficient.Finally,compared with the reference literature,it shows that the thermal efficiency of cycle is higher than the literature cycle,the power output improved due to the recovery of cold energy of LNG.