Power To Gas Technology Of Renewable Energy And Its Life Cycle Assessment

Renewable energy such as wind energy,biomass energy and solar energy is rich in reserves and environmentally friendly.Power generation using renewable energy can effectively deal with the severe energy crisis and environmental pollution problems,but its power generation is unstable,fluctuating and unable to supply energy continuously and stably,resulting in the phenomenon of energy abandonment commonly.Power to gas（P2G）is a new type of energy storage technology,which can convert unstable renewable electric energy into stable chemical energy in combustible gas,making the cooperative use of renewable energy power generation and power-to-gas technology well.In order to evaluate the feasibility of renewable energy power-to-gas technology,wind power-to-gas technology and biomass power-to-gas technology are taken as the research objects.Based on technological processes of these two kinds of renewable energy power-to-gas technologies,life cycle assessment（LCA）method is used to evaluate the economic and environmental impacts of each stage in the life cycle of renewable energy power-to-gas technology.Aspen Plus V10.0 software and Sima Pro V9.0 software are used to simulate the process flowchart and evaluate the environmental impact of those two renewable energy power-to-gas technologies in the whole life cycle,respectively.Firstly,the LCA of wind power-to-gas technology is carried out.1kg CH₄ is determined as the functional unit,and system boundary of the wind power-to-gas technology is established.The inventory analysis is carried out,and the amount of electric energy and reactants consumed in the production of 1kg CH₄ in the power-to-gas stage is calculated by using Aspen Plus software,and the resource consumption and pollutant emissions in each stage are summarized.The LCA of wind power-to-gas technology is carried out by using Sima Pro software.The results of LCA show that global warming,human toxicity and marine toxicity are the most prominent environmental impact types.It shows a decreasing trend of the global warming potential（GWP）in stages of the fan and electric transfer equipment manufacturing,fan and electric transfer equipment transportation and construction,and CH₄ and H₂ production.CH₄ transport and utilization stage has the largest contribution to GWP,accounting for 58.6%;equipment production stage has the largest contribution to marine toxicity potential（MTP）,accounting for 69.22%.Human toxicity potential（HTP）is next only to MTP,in which the main influence stages are equipment manufacturing and water electrolysis process.In the whole life cycle,Acidification（AP）,Photochemical Pollution（POF）and Eutrophication（EP）have little environmental impact.The environmental impact potential of methanation reaction is always negative.The environmental impact assessment of ordinary power-to-gas technology（that is,coal-fired power generation as the power supply side of power-to-gas technology）is carried out by using Sima Pro software.It is found that the environmental impacts of global warming,human toxicity,marine aquatic toxicity and freshwater aquatic toxicity are particularly prominent.By comparing the values of those four environmental impact types with the corresponding values of wind power-to-gas,it is found that the GWP of wind power-to-gas is 8.24%of that of ordinary power-to-gas technology,and the MTP and freshwater toxicity potential（FTP）of wind power-to-gas are12.40%and 28.63%of that of ordinary power-to-gas technology,respectively.Only in the index of HTP,the wind power-to-gas technology is higher than the ordinary power-to-gas technology.Secondly,LCA of the biomass power-to-gas technology is carried out.Two different kinds of biomass,rice stalk and cornstalk,were selected for analysis.The process simulation diagrams of biomass pretreatment stage and biomass direct combustion power generation stage are established by using Aspen Plus software,and the pollutant emissions and raw material consumption in the process of direct combustion power generation are calculated respectively,and the resource consumption and pollutant emissions in each stage are summarized.LCA of the two biomass power-to-gas technologies is carried out by Sima Pro.The results show that GWP,MTP and AP are the main environmental impact types.Biomass direct combustion power generation is the most important influence stage of GWP and AP,and biomass acquisition is the most important influence stage of MTP.The environmental impact types of the GWP,HTP and AP are similar,but there are great differences between the two biomass power-to-gas technologies in MTP.The potential value of power-to-gas technology of rice stalk is much higher than that of the corn stalk.Finally,by comparing the main environmental indexes of biomass power-to-gas and wind power-to-gas,it is found that MTP is always the most influential environmental index in the life cycle.Among them,rice stalk power-to-gas technology has the greatest MTP.In terms of GWP,the environmental impact potential of biomass power-to-gas technology is higher than wind power-to-gas technology.In terms of FTP,wind power-to-gas technology is slightly higher than biomass power-to-gas technology.In terms of HTP,wind power-to-gas technology has a greater impact on HTP.The environmental impact of these two kinds of renewable energy power-to-gas technologies is better than that of ordinary power-to-gas technology,and it is pointed out that renewable energy power-to-gas technology is a new energy utilization technology with broad prospects.