| China is a country which is rich in coal and lack of gas and oil.With the increasing consumption of natural gas,the technology of coal to natural gas was undergoing continuous development,among which the key unit,methanation process,was becoming a hot research field.Aspen plus was applied to simulation of TREMPTM adiabatic methanation reaction in this paper.It is found that calculated value coincided well with reference value.Effects of H2/(CO+CO2)ratio,CO2/CO ratio,recycle ratio,pressure and N2 mole fraction on the CH4 concentration were investigated.After the investigation,some parameters were modified and CH4 concentration could reach 95.00%.The standard mole exergy was calculated on the basis of Szargut environmental reference,and exergy balance was achieved by extracting streams parameters from Aspen plus simulation process with auxiliary software Excel-VBA.The results showed that total exergy loss was 216.92 kW,among which exergy loss from cooling unit and mixing unit accounted for the highest proportion.Three intermediate cooling units accounted for 42.26%,9.01%and 23.60%respectively,and mixing unit accounted for 11.85%.Effect of recycle ratio,pressure and feed temperature on exergy loss were investigated.Thus an optimized proposal was put forward which resulted in a 9.31 kW decrease for mixing unit,a 10.51 kW increase for cooling unit in exergy,and the toatal exergy loss kept constant.After adopting the optimized proposal,part of non-recyclable exergy could be recyclable and the quality and flow rate for high pressure steam were enhanced.Composite curves and exergy composite curves of cold and hot streams were obtained by combined pinch-exergy method,which explained the transfer of exergy in heat transfer process.Meanwhile,the effects of inlet temperature and pressure of cold stream on the exergy loss were studied.The results showed that the increasing of inlet temperature and pressure of cold stream could result in a decrease of exergy loss. |
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