Study On Influences Of Heavy Hydrocarbons In Mixed Refrigerant To Natural Gas Liquefaction Processes And Adsorption

The oil-injected screw compressor has several advantages such as smaller size,higher efficiency and fewer moving part,which is pretty applicable to small scale liquefaction plants.But when compressing,the lubricant is fully contacted with the working medium and they are miscible.This project is to recognize the restrictions of oil-injected screw compressor applied in mixed refrigerant liquefaction process.The following three aspects are discussed.First:effect of butane and pentane content in mixed refrigerant(MR)on performance of liquefaction processHeavy hydrocarbons in MR,usually butane and pentane,are more likely to dissolve in the lubricant.HYSYS software is adopted to simulate and optimize the effect of butane and pentane content on performance of liquefaction process.The results are as follows.(1)With butane and pentane content increasing,MR flow and the specific power consumption in the process decrease first and then increase,and the optimal specific power consumption is respectively 0.28kWh/Nm~3and 0.25kWh/Nm~3.Specific power consumption increases 14.3%and 25.0%without butane or pentane in the mixed refrigerant.(2)When butane and pentane content deviates from the optimal value,the efficiency of LNG heat exchanger declines and the maximum temperature difference raises.There is much exergy loss in heat exchanger.Exergy efficiency of the system decreases.(3)Compared with butane,pentane component makes more contribution on improving the performance of the process.(4)Adding a precooling cycle can reduce the specific power consumption of the process.With R507 precooling,specific power consumption has 24%reduction.Second:analysis of three-component MR liquefaction processMiscibility makes it difficult for MR to match and monitor.To solve the problem,the three-component MR liquefaction process is studied in this work.The results are as follows.(1)Among several three-component MR liquefaction processes,nitrogen-methane-propane MR process consumes the least power with value0.359kWh/Nm~3.Compared with nitrogen expander(NE)process,specific power consumption reduces 41.91%and exergy efficiency raises 42.07%.(2)Comparing to MR Process,the NE process has less UA but more rotary machinces.Taking power consumption into consideration,the nitrogen-methane-propane MR process has more advantages.Third:dynamic adsorption characteristics of activated carbon(AC)to methane-propane mixturesAC adsorption technology is usually adopted to removing the lubricant in MR when using oil-injected screw compressor.The MR component may be adsorbed by activated carbon simultaneously.In this paper,an AC dynamic adsorption system is built,and the adsorption breakthrough curve of methane-propane mixture is studied.The results are as follows.(1)With adsorption pressure increasing and temperature decreasing,adsorption capacity of AC to methane and propane enhances.High propane content and large flow rate cut down the breakthrough time.(2)The breakthrough time of methane and propane is in ten minutes for all conditions.The time is far less than the starting time of the process.MR component can be adjusted when starting the process,so the adsorption effect can be eliminated before the process operates normally.