Integrated Performance Evaluation Of Jet Fuel Production From Biomass Based On Exergy Theory

It is significant to easing the energy crisis and ecological protection that the use of clean and renewable biomass instead of traditional fossil fuels for gasification Fischer-Tropsch?FT?synthesis hydrocracking conversion to Jet fuel?Bio-Jet fuel?.In this paper,the integrated evaluation of three Bio-Jet fuel systems,that is,by-product steam is for heat supply?Case 1?and power generation?Case 2?,and by-product waxis recycling?Case 3?,on thermodynamic performance,environmental impact and economic performance were carried out based on the thoery of exergy.First,based on Aspen Plus simulation,exergy analysis of Bio-Jet fuel was carried out,and the effects of operation parameters on thermodynamic performance were studied,the results show that:?1?the exergy loss of gasification subsystem is much more than that of the FT synthesis subsystem,and that the exergy loss of the whole process is mostly from the irreversibility due to the change of biomass macromolecular structure,which accounts for 88.3%of the total exergy loss.?2?The effect of mass ratio of steam to biomass?S/B?is the most important and the available molar ratio of H₂ to CO is at 1.95-2.0.It is beneficial to enhancing the yield of aviation fuel and the whole system exergy efficiency by increasing FT synthesis temperature and pressure.?3?The parameters for producing aviation fuel from corn stover are suggested that the gasification temperature,pressure and S/B are at 750 ?,0.1-0.2 MPa,0.4-0.5,respectively,and FT synthesis temperature and pressure are 240? and 1.5-2.0MPa,respectively.The attained maximum yield of aviation fuel can reach 85.3 kg/t and exergy efficiency of the system is 54.3%.?4?For Case2,the system exergy efficiency will reduce to 45.3%;For Case 3,the yield of aviation fuel can be increased by 3.9%and the favorable S/B is decreased to 0.3-0.4.By means of exergetic life cycle assessment?ELCA?,the integrated performance evaluations of three different cases on environmental impacts and resource consumptions for Bio-Jet fuel were carried out.The results show that:?1?the resource conversion efficiency in heat supply system is higherer than that in power generation system,which values are 17.21%,12.71%and 15.97%respectively.The power generation system belongs to renewable system with the renewability performance indictor of 1.53,however the heat supply system is non-renewable system with the renewability performance indictor of 0.72?Case 1?and 0.67?Case 3?.Three Case 3,environmental performance indicators of which are 1.75,4.48 and 1.63,respectively,are able to achieve positive benefit from the environment,and the power generation system get the most positive earnings.The resource conversion efficiency of the power genenration system is inferior to the heat supply system,but the environment performance is superior to the heat supply system.?2?Thermal power generation is the main cause of non-renewable resources consumption,accounting for 8.06%.Without the external power supply in Bio-Jet fuel,the accumulation exergy of chemical fertilizers and crude oil are the main causes of non-renewable resources,the abtatment exergy of Bio-Jet fuel are mainly from the use of CO₂ emissions of fossil fuels,and the second is from a large number of agricultural sewage discharge in corn stalk growth.?4?The comprehensive sensitivity analysis of Casel and Case 2 shows that the reduction of raw material consumption is the main way to improve the system resource performance,the ues of fossil energy indirectly from raw materials and pollutant disposal is a major factor in the improvement of environmental performance of the system.Finally,life cycle assessment?LCA?is combined with the economic cost balance equation,and three indictors of the exergy economic cost are suggested,unit exergy economic benefit and cost profit rate to evalutae two Bio-Jet fuel systems,The results show that:?1?The environmental costs of Case 1 and Case 2 are 708.90???/t and 356.63???/,respectively,and the proportion of environmental cost to total production cost is 6.2%and 3.9%,respectively.?2?Considering the environmental cost,the exergy economic costs of two cases are 0.105???/MJ and 0.106???/MJ,respectively.The exergy economic profits are 0.050???/MJ and 0.056???/MJ,respectively,and the cost profit rate is 48.5%and 53.2%respectively.?3?Based on the sensitivity analysis,the economic cost of the product is mostly affected by the fixed investment in the production stage and biomass cost.The price of Jet fuel mainly affects the economic profit of product.