Simulation Study On The Process Of Gasification Of Municipal Solid Waste Into Synthetic Natural Gas

In China,municipal solid waste(MSW)generation has been increasing dramatically with rapid economic growth and massive urbanization.The traditional MSW treatment methods,including landfill,compost and incineration,give rise to high pollutant emissions and low conversion efficiencies.Thus,discovering environmentally benign and economically feasible methods for the disposal of MSW has become an urgent issue.As a novel waste-to-energy technology,gasification is given more and more attention from domestic and foreign scholars.On the other hand,natural gas plays an important role in energy consumption structure due to its high quality,high efficiency and cleanness.But the natural gas source in China is limited,which leads to a gas supply shortage.Thus,in order to achieve the innocuity treatment and resource utilization of MSW,to relieve the supply shortage of natural gas,and to ensure the energy security simultaneously,the process of synthetic natural gas(SNG)production from MSW gasification is proposed.In this paper,MSW-SNG single-product process,MSW-SNG poly-generation process and SNG production process based on MSW gasification coupled with calcium-looping system,were developed and subsequently simulated by Aspen Plus.In the basis of simulation results,the influences of air equivalence ratio(ER),steam-to-MSW mass ratio(S/M),methanation temperature and methanation pressure on system performance of MSW-SNG single-product process were analyzed.Moreover,the effects of extent of water-gas-shift reaction(a)and recycle ratio of the unconverted gas(Ru)on system performance of MSW-SNG poly-generation system were performed.Meanwhile,for MSW-SNG process coupled with calcium-looping system,the influences of CaO-to-MSW mass ratio(Ca/M),steam-to-MSW mass ratio(S/M)and gasification temperature(tg)on system performance were investigated.And SNG yield,methanation efficiency,net power efficiency,overall efficiency,exergy efficiency,carbon capture efficiency and specific CO2 emission were adopted as the evaluation indicators of system performance.The results of thermodynamic analyzes showed that,for MSW-SNG single-product system,the SNG yield was 0.177 Nm/kg MSW,the methanation efficiency was 35.31%,the overall efficiency was 30.07%,the exergy efficiency was 27.89%,the carbon capture efficiency was 88.15%and the specific CO2 emission was 0.329 kg/kWh when ER was 0.15,S/M was 0.5,methanation temperature was 300 ? and methanation pressure was 0.5 MPa.And for MSW-SNG poly-generation system,when a was 0.6449 and Ru was 0.43,the SNG yield was 0.167 Nm~3/kg MSW,the methanation efficiency was 31.89%,the net power efficiency was 2.91%,the overall efficiency was 34.80%,the exergy efficiency was 32.00%,the carbon capture efficiency was 88.46%and the specific CO2 emission was 0.306 kg/kWh.Besides,for MSW-SNG poly-generation process coupled with calcium-looping system,when Ca/M was 0.6,S/M was 0.5 and gasification temperature was 650 ?,the SNG yield was 0.148Nm~3/kg MSW,the methanation efficiency was 29.57%,the net power efficiency was 2.77%,the overall efficiency was 32.34%,the exergy efficiency was 29.03%,the carbon capture efficiency was 99.81%and the specific CO2 emission was 0.285 kg/kWh.The comparison of the developed processes was achieved,and the results showed that the methanation efficiency of MS W-SNG single-product process was the highest.In terms of overall efficiency and exergy efficiency,the MSW-SNG poly-generation process had outstanding performances.As for MSW-SNG process coupled with calcium-looping system,it had a significant advantage in CO2 capture over MSW-SNG single-product system and MSW-SNG poly-generation system.