Life Cycle Assessment And System Analysis Of Coking Poly-generation System

In recent years,the issues of energy and environment have been considered hot spots in the world.As a traditional coal chemical industry in China,coking production is associated with extensive energy consumption and high emissions.Therefore,developing poly-generation economic system is an inevitable trend.According to the requirements of sustainable development,the research boundary should be extended to the whole life cycle,then systematically seek the opportunities to improve resource utilization efficiency and reduce environmental pollution.Based on two representative coking poly-generation system cases,life cycle assessment(LCA)method were introduced in this study to systematically analyze the energy consumption and environmental impacts of the whole system,coking production and different coke oven gas(COG)utilization approaches.In addition,economic analysis and energy efficiency were combined to identify the optimal COG utilization approach.The results aim to provide useful insights for the further promotion and optimization of coking poly-generation system.First of all,the study built a LCA model of the whole system based on the annual production reports for the year of 2013 in Case 1 system to determine the contribution of different subprocesses to the total environmental impacts.The results indicate that,coal mining,ammonia process and coking process contribute higher environmental impacts,while the proportions of methanol process and brick process are almost zero.The reason can be explained that the main raw materials and energy in these processes are the by-products or wastes from other units.The results demonstrate the advantage of energy conservation and emission reduction by using poly-generation system.Secondly,LCA method was applied to evaluate the environmental impacts of coking production based on subdivision method.The results show that,the chemical recovery process plays a significant influence on the total impacts of coking production.In the chemical recovery process,ammonia recovery unit and blowing cooler system are the main contributors,due to the consumption of sulfuric acid,steam and electricity in each unit,respectively.Washed coal,heating gas and electricity are the key input parameters in the LCA results of coke product.Compared to subdivision method,allocation by physical or economic relationships lead to a certain of deviations.Additionally,using coke dry quenching technology shows better environmental performance that with coke wet quenching technology.Then,the LCA of COG-based methanol production was conducted and compared with the coal route and natural gas routes.Besides,economic analysis of the three methanol routes were carried out.The results show that,more than 80% of the overall environmental impacts occurs at methanol production stage,mainly due to the consumption of electricity and medium-pressure steam.Coking stage contributes less than 10%,for the reason that COG was allocated only 16.06% of the upstream environmental burden.Compared with coal route,COG route shows better benefits in both environmental and economic aspects.The environmental impact of COG route could be reduced by supplying medium-pressure steam from coke dry quenching system for methanol production.In addition,the LCA of COG to liquefied natural gas(LNG)was carried out based on decarbonization process,and compared with other alternative routes.The results indicate that,LNG production stage and vaporization stage are the dominated units in the overall environmental impacts of COG-based LNG process.In LNG production stages,mediumpressure steam,COG and electricity are the key substances.Compared with the domestic natural gas liquefaction route,COG route for LNG shows lower resource and energy consumption.In COG-based LNG route,methanation process show better environmental performance than decarbonization process.Finally,in order to determine the optimal COG utilization approach,seven kinds of routes(methanol,ammonia,compressed natural gas,LNG,hydrogen,co-generation of methanol and ammonia,and co-generation of LNG and methanol)were compared from environmental,energy efficiency and economic perspectives.After comprehensive evaluation,it is recommended that CNG route with methanation process,co-generation of LNG and methanol and LNG route by methanation process should be preferred,while ammonia and hydrogen route are inadvisable.