Carbon footprint evaluation of coal-to-methanol chain with the hierarchical attribution management and life cycle assessment

Abstract

Coal is considered as an abundant energy source in China and coal-to-methanol chain is an essential routing on account of methanol’s irreplaceable status in chemical industries. However, coal-based methanol production aroused controversy due to its intensive energy consumption and high greenhouse gas emission, compared with other processes by oil or natural gas. Carbon footprint is an improved indicator that evaluates both direct and indirect greenhouse gas emissions in the life cycle perspective and guides policymakers for better industry-chain planning. In this study we proposed the idea of hierarchical attribution management (HAM) to provide a classified method for evaluating carbon footprint of coal-to-methanol chain, combined with life cycle assessment (LCA) and the tool of ASPEN Plus. The results show that the life cycle carbon footprint was 2.971t CO2,e/t methanol. By the HAM, it’s concluded that methanol production process was the largest emission contributor in the defined life cycle system with a share of 92.86%, followed by coal mining process with 4.34%. Gasification unit and water-gas shift unit were two major greenhouse gas generators, accounting for 21.26% and 52.80% of life cycle emission, respectively, while methanol synthesis unit showed the potential for CO2 utilization and emission reduction. Additionally, the results of sensitivity analysis showed that electricity emission factor with a sensitivity factor of 189.11 was the most extensive influence factor on life cycle emission due to its widest application. The discuss on effects of CCS on life cycle emission showed that carbon footprint approximately decreased by 64.9% when the methanol plant was retrofitted with CO2 capture and compression, indicating that CCS is an effective way to alleviate global warming.