Simulation Study On Integrated System Of Wastewater Treatment With The Utilization Of LNG Cold Energy

With the intensification of global greenhouse effect,the use of clean energy has been vigorously promoted,and natural gas as a clean energy source has become more and more popular.Liquefied natural gas(LNG)is a common way of natural gas storage and transportation,and it preserves a large amount of high grade cold energy during gasification.In recent years,as the economic development of China,the amount of sewage is increasing,sewage treatment technology is constantly updated.Ice crystallization method and supercritical carbon dioxide wastewater treatment are new sewage treatment methods,which can effectively deal with a large number of industrial wastewater difficult to separate.However,the two methods consume a lot of cold energy during the process of wastewater treatment.Considerable treatment costs can be saved when the cold energy of LNG is utilized in the two wastewater treatment methods.Meanwhile,the cold pollution can be avoided in the LNG gasification process.The integration wastewater treatment systems with the direct and indirect utilization of LNG cold energy were established in this work.The ice crystallization wastewater treatment and ice storage air conditioning system were integrated to directly utilize the cold energy of LNG.The system under different pressures were studied in this paper.It was observed that the system exergy efficiency increased with the increment of LNG gasification pressure,and when the LNG gasification pressure was 4 MPa,the exergy efficiency was 27.1%.When the phase change medium was employed in the system,the flow rate of refrigerant can be decreased with the exergy efficiency slightly reduced.Thus,the size of the corresponding equipment can be reduced.When the cascading utilization of LNG coldness exergy was employed in the system,the exergy efficiency of system could reach up to 35%.The indirect utilization of LNG cold energy system proposed in this paper was integrated with oxy-fuel combustion power plant and supercritical fluid wastewater treatment.The carbon dioxide in the flue gas of the power plant was collected and captured in the system,and was eventually made into supercritical carbon dioxide,and the wastewater treatment can be realized with the excellent extraction effect of supercritical carbon dioxide.Natural gas combined cycle(NGCC)power plants integrated with oxy-fuel combustion were adopted in the system,and the near-zero carbon emissions was achieved in the system.Through the optimization of the system,the total power generation efficiency can reach 69.4%,and the net efficiency was 47.1%.