| Fuels derived from biomass resources represent a promising option for alleviating the energy crisis and mitigating anthropogenic carbon emissions.However,there are concern about the environmental sustainability and economic cost of biofuels,for the production of fuels derived from biomass is a complexed chemical process.Accordingly,it is essential to establish a composite model of biofuels with the consideration of environment,energy and resource.In this study,biomass fast pyrolysis and upgrading in supercritical ethanol(PY-USE)system,catalytic hydrotreating system(PY-CH)and biomass gasification and Fischer-Tropsch synthesis to bio-aviation fuel system(FT-BAF)were considered,the energy efficiency and environmental potential impacts of these systems were calculated,respectively.The evaluation work can offer a theory guidance for the biofuels production processes optimization.Firstly,process simulation models of PY-USE,PY-CH and FT-BAF based on Aspen Plus software were developed.The thermodynamic parameters from simulation(mass flow rate,heat flow rate,power consumption,enthalpy,entropy,and so on)are the bases for the following research work.Secondly,the exergy analysis was conducted to PY-USE,PY-CH and FT-BAF.The results of this work reveal that the exergy loss during biomass drying processes contribute to 33.17%,25.69%and 26.46%to the total exergy loss of PY-USE,PY-CH and FT-BAF,respectively.The exergy losses of PY-USE and PY-USE systems are mainly caused by the pyrolysis reactor,the coke and incondensable gas combustion reactor,bio-oil upgrading reactor and off-gas combustion process,besides the pre-treatment subsystem.The exergy efficiency of PY-CH bio-oil upgrading reactor is lower than that of PY-USE reactor,but extra ethanol was consumed by PY-CH bio-oil upgrading reactor.The exergy loss of FT-BAF system is mainly caused by biomass gasification reactor and off-gas combustion process,accounting for 42.32%and 14.60%of the total system loss,respectively.In the whole,the exergy efficiencies of PY-USE,PY-CH and FT-BAF system are 52.47%,31.79%and 19.12%,respectively.Thirdly,the environmental potential impacts of PY-USE,PY-CH and FT-BAF were calculated and compared based on LCA models.The results of this work reveal that FDP,GWP,ODP,POCP and AP of the PY-CH are lower than those of the PY-USE,while the HTP and EP is higher than that of PY-USE system.The fossil ethanol,which is consumed during fast pyrolysis and upgrading process and agriculture subsystem,is both the main source of the PY-USE and PY-CH potential environmental impacts.Moreover,it is founded that the impact of the pyrolysis fuels is lower than that of the fossil fuels for FDP,GWP and ODP,but higher for HTP,POCP,AP and EP.LCA results showed that greenhouse gas(GHG)saving of 38.83%and 45.93%for the produced fuel of PY-USE system compared to conventional gasoline and diesel,while the GHG saving of 73.50%and 76.58%for the PY-CH production.For the bio-aviation fuel,FDP,GWP,HTP,ODP and POCP of the FT-BAF are both lower than those of the fossil jet fuel,but higher for AP and EP.The GWP of RH/FT-BAF,RS/FT-BAF,CS/FT-BAF and WS/FT-BAF are 19.86%,30.52%,15.00%,and 22.58%of fossil jet fuel,respectively.The environmental impacts potential of CS/FT-BAF is lowest within the four FT-BAFs.Finally,combining the results of exergy analysis and LCA,exergoenvironmental model of PY-USE,PY-CH and FT-BAF was established.The exergy environmental cost was calculated to confirm the sources of environmental impacts during the bio-oil production progress.The results show that the exergy environmental cost of bio-fuels are 2.32×10-14Pt/kJ,9.31×10-15Pt/kJ and 6.54×10-14Pt/kJ,respectively.Exergoenvironmental analysis results reveal that P-H,P-DRYER,PY-COMB,PY-H3,U-COMB and U-H4 reactors offer relatively higher improvement potential in reducing environmental impacts of the PY-USE system,for PY-CH and FT-BAF,PY-COMB,P-H,U-COMB,P-DRYER,PY-H3 reactors and P-H,G-COMB,G-GF,P-DRYER reactors offer higher potential,respectively. |
PDF Full Text Request