| Coal dominates China's fuel consumption and contributing to chemical manufacturing as an important feedstock.The large-scale coal mining and the water consumption by coal chemical industry have attracted much attention from the academic community.This is because coal is geographically unevenly distributed in water-scarce areas of northern China.However,data shortage have hindered the researchers'investigation on the water consumption of coal mining activities.Meanwhile,China's methanol production highly depends on coal exploration,with downstream products widely used.However,water footprint of coal mining and related chemical manufacturing,such as methanol production based on coal,is rarely reported.Thus,this study is aim to quantify the water footprint of coal mining and washing,and calculate the virtual water of interprovincial coal trade,and explore the water-saving potential of the coal industry through scenario analysis based on enterprise data.Then,I further selected two typical coal-to-methanol routines,i.e.,coal gasification and coal coking,to calculate the water footprint of the chemical manufacturing.Monte Carlo simulation was used to quantify the uncertainties.The main findings of the paper are as follows:?1?The water footprint of coal mining and washing in China?mean[standard deviation;5%and 95%percentiles]?is 0.96[0.57;?0.85,1.07?]m3t-1.Among them,the average direct blue water(0.41 m3t-1)is slightly lower than the direct gray water(0.49 m3t-1),and significantly lower than previous studies?p<0.01?.Underground recovery-method generates higher water footprint(0.98 m3t-1)compared with open-pit mining(0.60 m3t-1).Water footprint of medium?small?scale mining,i.e.,1.21?1.16?m3t-1,is higher than that of large scale(0.67 m3t-1).Water consumption varies across coal types.The water footprint of anthracite,coking coal,bituminous coal,and ordinary bituminous is 1.25 m3t-1,1.20 m3t-1,0.80 m3t-1,and 0.64 m3t-1,respectively.The three northern provinces?i.e.,Inner Mongolia,Shanxi and Shaanxi?takes up72%of China's total coal production.Scenario analysis shows that the China's maximum potential of water-saving for coal-mining industry is 28%,and increasing the production percentage of large-scale coal mining as the most effective measure.Besides the mass function unit?1 kg coal?,we generated a parallel estimate by using energy as function unit?i.e.,1 GJ?to provide basic parameters for evaluating water consumption of downstream industries of coal-mining sector.?2?Based on two typical enterprise as cases study,I quantified the water footprint of coal gasification to methanol?CGT?and coal coking to methanol?CCT?.The results show that the water footprint of CGT(7.61[1.81;?4.50,11.32?]m3t-1)is significantly higher than that of CCT(3.06[0.60;?1.98,4.27?]m3t-1,p<0.01).The indirect water footprint of coal production exceeds 62%of the total metrics.If coal-related water lowered by 5%-20%,the water footprint of coal-to-methanol would be reduced by 43%.Under the same production capacity,the increasing the share of CCT by 10%can lower the total water footprint of the coal-to-methanol industry by 45%.The Eco-indicator 99 model was used to evaluate the environmental impact of two coal-to-methanol processes.The results show that the CCT routine performs better than CGT does in environmental performance.Ecological damage mainly sources from acidification and eutrophication,human health damage from climate change,natural resource damage from fossil fuel consumption.The manufacturing processes of air separation,shift and low-temperature methanol washing contribute to the largest environmental impacts.The findings of this paper provide data reference for further accounting water consumption of olefins,dimethyl ether,formaldehyde,etc.manufactures,in the downstream of the coal chemical industry chain. |
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