Evaluation of life cycle inventory at macro level: a case study of mechanical coke production in China

Purpose: Most existing methods for evaluating the national environmental impact of product manufacturing follow a top–down approach based on national annual statistical data. However, such approach fails to include many important data points and has a low level of quantification, which causes the difficulty in identifying insights on the location, causes, and characteristics of environmental problems. Hybrid life cycle assessment (LCA), which combines input–output data and process-based LCA, has recently been proposed and widely implemented for the collection of regional inventory. However, the limitation of using input–output data, which involves the adoption of averaging data associated with different inputs within various industry subsectors, has been highlighted. In this study, national and provincial statistical data combined with the bottom–up approach is used to solve the aforementioned problems and to assess the environmental effects of mechanical coke production at a national level. Methods: A bottom–up approach combined with national and regional statistical data on product yield is used in this study to estimate the environmental effects and improvement potential of mechanical coke production at the national level. Results and discussion: The total mechanical coke production and environmental burden generated by global warming, respiratory inorganics, and nonrenewable energy in 2010 were approximately 3.31 × 10⁸ t, 1.01 × 10⁸ t-CO₂ eq., 1.98 × 10⁵ t PM_2.5 eq., and 1.05 × 10¹⁰ GJ Primary, respectively. The highest coke production fluxes were found in Shanghai, followed by Tianjin, Hebei, Shanxi, Shandong, and Henan. The lowest coke production was observed in Hainan and Xizang. The difference can be attributed to coal mining and economic levels. From 2008 to 2012, the CO₂, SO₂, and NOx emissions as well as nonrenewable energy consumption for mechanical coke production accounted for 0.5 to 1.4, 1.5 to 2.2, 3.8 to 4.7, and 4.8 to 13.2 % of the total CO₂, SO₂, and NOx emissions and nonrenewable energy consumption in China, respectively. The following processes are highly important in reducing the environmental burden imposed by mechanical coke production in China: optimizing the transport distance and type, using underground coal washing technology, decreasing coke exports, and improving the efficiency of coking coal consumption, the average usage rate of seam gas drainage, the energy recovery rate of coke dry quenching technology, and the amount of imported coking coal. Conclusions: The most significant processes, substances, and potential environmental impact categories that contribute to the overall environmental burden in China can be easily evaluated. The combination of national information, provincial statistical data, and LCA results on mechanical coke production represents a large group of LCA products that can further determine the key improvement factors for reducing the national overall environmental burden imposed by the manufacturing of mechanical coke.