System Simulation Exergy Analysis And Life Cycle Assessment Of Biological Fuel Preparation Process

Production of biomass fuel is an important way to ease energy crisis and promote sustainable development.Biological fuel has friendly environment,but it has the disadvantages of low yield and high cost.Two kinds of biomass fuel production processes were studied in this paper,energy,environment and comprehensive performance were considered to evaluate system performance.Suggestions for optimization and improvement were pointed out.Firstly,based on Aspen Plus software,two models of biomass fuel production processes which use rice husk as raw material were built:Biomass Gasification and Fischer-Tropsch to Jet Fuel System?GFT?and Bio-Oil Cracking Gas Fischer-Tropsch Synthesis and Olefin Polymerization to Jet Fuel System?FT-OP?.Both of the processes could realize self-powered power and respectively output power of 322.60kW and 465.48kW.Energy losses mainly came from the pretreatment stages.Secondly,based on the simulation results of Aspen Plus,values of exergy were caculated for FT-OP system and GFT system.All exergy flows were studied,pay and gain of the exergy flows were distinguished.Exergy losses and exergy efficiencies were analyzed.When jet fuels and electricities were considered as profitable exergys,efficiencies of FT-OP system and GFT system were 26.17%and 23.04%.When gasoline components were taken as by-products,exergy efficiencies of the two systems were 44.54%and 33.47%.The largest exergy losses of the two processes were both attributed to the pretreatment subsystems,which accounted for30.56%and 34.23%of the total exergy losses.Internal irreversible losses and heat losses were main reasons of exergy losses.Appropriate reaction conditions and reactors would play important role in improving exergy efficiencies of the two systems.Thirdly,based on life cycle assessment method,environmental impacts and resource consumptions of biomass conversion to jet fuel technologies were analyzed,seven different environmental impact potentials were caculated,environmental impacts of different production stages were studied.Results showed that:environmental impacts and resource consumptions were concentrated in production processes.CO₂ emissions in agriculture,production and use stage respectively accounted for 9.45%,86.97%,and 3.5%.Primary energy consumptions were concentrated in the use of jet fuel.Integrating all environmental impact types,FT-OP process was superior to GFT process.Compared with fossil fuel,biological fuel had obvious advantages in reducing greenhouse gas emission.Global warming potential in fossil fuel production process were 2.79 and 1.92 times that of FT-OP system and GFT system.Production processes were the main sources of carbon emissions,accounting for 86%to 89%of the GWP?Global Warming Potential?.Finally,comprehensive performances of the two processes were compared,comprehensive performance indicators of environment,resource,and economy under different weight factors were analyzed,resource utilization index,environmental benefit index,and renewable index of each process were calculated.Results showed that the environmental performance of FT-OP was better than that of GFT process,economic efficiency was slightly lower than that of GFT process.Resource consumption performances of the two systems were about the same.In environmental impact assessment which was based on thorium analysis,FT-OP process was superior to GFT process.