Life Cycle Assessment Of Bio-jet Fuel Production From Lignocellulosic Biomass Via Aqueous Conversion Based On Exergy Theory

Air transportation is one of the fastest-growing traffic modes,so that energy and environmental problems caused by fossil jet fuel are becoming increasingly serious.The production of jet fuel from biomass can significantly reduce the consumption of fossil energy and alleviate the greenhouse effect.Therefore,it is highly significant to analyze and evaluate the bio-jet fuel production system.According to the different utilization of hydrolyzed residue lignin,this paper studied two systems of bio-jet fuel production from lignocellulosic biomass via aqueous phase conversion,namely,lignin combustion for heat and steam（Case 1）,and lignin gasification for hydrogen production（Case 2）.The conversion processes of corn stalk as the feedstock are simulated based on Aspen Plus.Moreover,the energy and exergy analyses of systems are carried out based on the first and second laws of thermodynamics.According to the results of study,the corresponding improved systems（Case 1-R and Case 2-R）and the bio-jet fuel and electricity co-production systems（Case 1-PG and Case 2-PG）are established.To compare and improve the resource and environment performances of the systems,a resource-environment model is established based on the exergy theory and life cycle assessment.The main results are shown as follows.Firstly,energy and exergy analyses of the bio-jet fuel production systems indicate that:（1）For the basic schemes of Case 1 and Case 2,the largest exergy loss of the system occurs in the combustion&heat exchange unit;the largest energy loss occurs in the furfural production unit,followed by the levulinic acid production unit.（2）the₀9),)of the improved system Case 1-R and Case 2-R achieve 41.35%and 39.85%,respectively,and the₀,)achieve 24.25%and23.12%,respectively.The values of₀9),)increase by 139.1%and 137.0%,respectively,and₀,)increase by 57.2%and 55.7%,respectively,compared with those under the basic schemes of Case 1 and Case 2.This indicates that the utilization of waste heat and wastewater mainly brings out the low-quality energy.（3）The lignin combustion system（Case 1 and Case 1-R）has higher jet fuel efficiency and system efficiency,but the lignin hydrogen production system（Case 2 and Case 2-R）has a higher energy upgrading rateβ₀).（4）The main output product of the bio-jet fuel and electricity co-production systems（Case 1-PG and Case 2-PG）is power,and the₀,)of the two systems achieve 26.63%and 26.19%,respectively.The values of₀,)increase by 9.8%and 13.3%,respectively,compared with those under the Case 1-R and Case2-R.（5）Relative to the hydrolyzed biomass of 2t/h,When the hydrolyzed biomass consumed is 2t/h and the evaporation rate of boiler is 40 t/h,the optimal power generation efficiency and system efficiency can be obtained.At this point,steam extraction rateθis 0.31,the values ofω₀9))andω₀)are 4.05 and 3.79,respectively,and the values of^′₀,0))and₀,s) are 29.0%and 27.4%,respectively.Secondly,based on the exergtic life cycle assessment,the results are shown as follows:（1）For the jet fuel production of Case 1-R and Case 2-R,Case 1-R has higher cumulative exergy efficiency,but Case 2-R has better renewability.The values of_,0)achieve 15.43%and14.84%,respectively,and the values of_,achieve 19.23%and 18.50%,respectively.And the I_r of the two cases are 0.57 and 0.70,respectively.The_,of Case 1-PG and Case2-PG can reach 23.95%and 23.68%,respectively,and the I_r reach 1.97 and 2.35,respectively,indicating that the cumulative exergy efficiency and renewability of the co-production system are better.（2）For Case 1-R and Case 2-R,the sensitivities of₀,0))and_,0)present similar trends to the different influence factors.The sensitivities of both₀,0))and_,0)to S4（the conversion efficiency of the oxygenates to bio-jet fuel）and S3（the conversion efficiency of levulinic acid to the oxygenated precursor）are the greatest for two cases,respectively.The recovery rate of methanol has a significant impact on the cumulative exergy efficiency and renewability.（3）In the lignin hydrogen production schemes（Case 2-R and Case2-PG）,the environmental impact indexes of global warming,human toxicity,thermal pollution are lower than those in the lignin combustion schemes（Case 1-R and Case 1-PG）,respectively.The environmental performance indexes(₀))are all greater than 1,which indicates that the system has good environmental performance,and the integrated environmental performance of the bio-jet fuel and electricity co-production system is better.（4）All kinds of environmental impact loads mainly come from the production stage of bio-jet fuel.For Case1-R and Case 2-R,the main cause of thermal pollution in the production stage is direct emission.Global warming is mainly caused by the indirect emissions resulted from the resource input in the production stage.