Research And Application Of Exergy-based Characterization Model For Water Resource Depletion In Materials Life Cycle Assessment

Materials as a symbol of social civilization and progress, promote the development of human society and economy. At the same time, material industry are big users of resources, energy consumption and pollution emitters, with the increasingly shortage of resources and serious environmental issues, people have paid more and more attention to how to coordinate development of environment and material. In this area, life cycle assessment(LCA) method as the current international mainstream environmental load quantitative tools have been widely recognized, obtained the fast development and application. In the current life cycle assessment method research,the water resources depletion problem is one of the hot research topic, and specific to the current situation of our country, water resources have become important environmental problem to restrict the sustainable development of social economy in our country. In the report on the work of the government 2016, China’s prime minister emphasized the significance of decreasing the water consumption per domestic gross product; water-saving has become the principal task of environment-protection in the thirteenth five years project of China. But due to the corresponding method is not perfect in the life cycle assessment, the evaluation of depletion for water resources use did not get corresponding development and application.In this study, the current international method of water resources use in life cycle impact assessment were analyzed, under the life cycle assessment method technology framework, the thermodynamic functions exergy, which is more suitable for the application in the characterization of the resource depletion problem, was introduced into water resources depletion of the material life cycle evaluation, combined the essence of different physical meaning of water resource depletion with exergy. In order to quantify resource depletion potential in the material life cycle assessment caused by the use of water resources, the exergy characterization model of water resources depletion is established through the material production, which expanded the field of material life cycle assessment method, and formed a single index of exergy for water, mineral, energy and land resource depletion potential.Based on the evaluation model research, the calculation of China’s water resource depletion index of the unit basic energy production was conducted by hybrid inventory model and collecting data, water resource depletion index from coal, oil and natural gas and electricity production were 6.48E-01MJ/kg, 6.24E-01 MJ/kg, 5.81E-01 MJ/m3 and 1.57E+01 MJ/kWh; at the same time, the sea water as a reference material and the quality of the third type surface water as the reference standard, the water resources depletion index of nine categories of unit industry wastewater including steel industry, aluminum industry, iron al oy, coal industry, iron ore mining industry, lead-zinc industry, copper, nickel and cobalt industry, magnesium and titanium industry and rare earth industry were calculated, providing data and support for further analysis water resource depletion potential of material products production due to wastewater discharge.Eventual y, the relevant research results of water resources depletion characterization model and basic inventory were applied to the life cycle assessment of steel products and steel slag asphalt concrete road, and took a quantification of water resource depletion potential for these two kinds of typical materials and the comparative analysis of impact from water resources to products resource consumption.For the steel, the calculated steel water resource depletion potential is 5.89GJ/t based on research and data analysis, the water resource depletion potential of upstream process is 4.56GJ/t, and the water resource depletion potential of production process is 1.33GJ/t, namely direct consumption accounted for about 22.65% of the water resources depletion of steel production. In total resource depletion of steel production, energy, water resources and minerals were 71.42%, 22.49% and 3.18%, so from the point of thermodynamic exergy view, the importance of water resources on the production of steel even super mineral resources. When the inventory distributed by ferrum content as a benchmark, the size of resource depletion potential of steel products are crude steel, steel slag and slag. If the slag and steel slag utilization rate were 82% and 30%,the crude steel resources efficiency ratio increased by 0.67%, when the steel slag utilization rate reached 100%, namely achieved "zero emissions", the resource efficiency of crude steel is increased by 2%, by estimating, the reduction of fresh water consumption is 0.57 billion cubic meters, wastewater discharged is 0.15 billion cubic meters, the iron ore consumption is 3044 mil ion tons and energy consumption is 92.18 billion kilograms of standard coal for whole country every year.For the steel slag asphalt concrete road, through the detailed research and field data collection from steel slag production and process improvement to the construction of the concrete road, the life cycle inventories of steel slag asphalt concrete road construction have been established. The results show that:(1) water resource depletion potential of the steel slag asphalt concrete road is 729.2482 GJ, upstream water and process water were 56.47% and 43.53% respectively;(2) when the steel slag as a resource input, the overall resource depletion potential of road reach to 5.26E+04GJ and 1.74 times larger than the original, in which the water resource depletion potential contribution ratio increased from 2.41% to 8.90%;(3) when the steel slag completely as waste without considering the environment load, the resource depletion potential for three concrete roads built by different raw materials from big to small sequentially is natural stone asphalt concrete road, steel slag asphalt concrete road and cement concrete road, in which the maximum water resource depletion potential is cement concrete road. The resource efficiency of steel slag asphalt concrete road compared to the natural stone asphalt concrete road increased by 5%. At the same time, steel slag asphalt concrete road per functional unit can save 201 GJ land resources due to the steel slag storage.The research results of this study can be used to quantify the depletion potential of water resources in the materials process, which can provide scientific basis for improving the resources comprehensive utilization efficiency of materials.