Exergetic Life Cycle Assessment Of Oil Shale Retorting Processes With Gas Heat Carrier

In this paper,the chemical process simulator Aspen Plus was used to model and simulate Fushun-type oil shale retorting process and SJ-type oil shale retorting process.Besides,the simulated results were compared with the actual commercial data.The results indicate that the simulated results are reasonably consistent with the results of actual production process.The simulated results are able to represent the running status of actual production process.For the results of Fushun-type oil shale retorting process,there is a certain deviation between the simulated and actual commercial results with respect to the volume fractions of O₂ and CO in the outlet retorting gas and the mass flow of recycle retorting gas.For the results of SJ-type oil shale retorting process,there is a certain deviation between the simulated and actual commercial results with respect to the mass flow of water in the outlet gas and the system loss.The concept of exergy was explained in detail and the exergy values of unconventional materials were calculated.The results indicate that the standard chemical exergy values of Fushun oil shale and shale oil are 7292.40 k J/kg and43212.02 k J/kg,respectively.And the standard chemical exergy values of Yaojie oil shale and shale oil are 13697.61 k J/kg and 48028.84 k J/kg,respectively.Based on the results and thermodynamic parameters of streams obtained in the simulation,the conventional exergy analysis of oil shale retorting processes was conducted.From the results,it is clearly found that Fushun-type oil shale retorting process has a lower overall exergy efficiency,only 39.40%.In the process,the largest subunit in exergy loss is the power generation subunit and its exergy loss is 179.76 MJ,which accounts for31.13%within the exergy loss of the whole system.The overall exergy efficiency of SJ-type oil shale retorting process is 45.16%.In SJ-type oil shale retorting process,the largest subunit in exergy loss is also the power generation subunit and its exergy loss is522.72 MJ,which accounts for 54.63%within the exergy loss of the whole system.On the basis of the conventional exergy analysis and life cycle assessment method,the novel exergetic life cycle assessment method was constructed.From the view points of the resource utilization efficiency and environmental sustainability,besides,the resource utilization efficiency indicator and the environmental sustainability factor were defined to evaluate the environmental impact performance of an energy conversion system.The method was used to evaluate the resource utilization efficiency and environmental impacts of pollutants discharge for two oil shale retorting processes.The results indicate that the resource utilization efficiency indicator??_k?of the power generation subunit is the lowest?22.48%?in the all subunits of Fushun-type oil shale retorting process.And the environmental sustainability factor??_k?of the semi-coke gasification subunit is the highest?44.79%?in all subunits of the process.The total resource utilization efficiency indicator(?_tot)and the total environmental sustainability factor(?_tot)of the process are 36.51%and 49.21%,respectively.In SJ-type oil shale retorting process,the?_k value of the power generation subunit is also lower?23.36%?and the?_tot value of the whole system is 42.12%.In SJ-type oil shale retorting process,the?_k values of power generation subunit and recycle retorting gas burning subunit are higher?43.49%and 29.10%,respectively?and the?_tot value of the whole system is48.05%.Finally,improved suggestions were proposed to improve the resource utilization efficiency and environmental sustainability of oil shale industry.