Life cycle assessment of ammonia synthesis in China

Purpose Synthetic ammonia is not only the basis of the fertilizer industry in China but also has the highest energy consumption and pollution emissions in the chemical industry. The objective of this study was to conduct a cradle-to-gate life cycle assessment (LCA) of ammonia production based on different raw materials to identify the crucial processes and parameters and to provide suggestions for clean and sustainable development of the ammonia industry in China. Methods Based on actual industrial data, this study comprehensively evaluated the resource consumption and pollution emissions caused by different raw material routes and coal-to-ammonia technologies from a life cycle perspective according to the LCA standards ISO 14040 series and using the CML 2001 method and identified the key environmental impact categories and stage contributions. In addition, the effects of various input parameters on the environmental burden were specified through sensitivity analysis. Accordingly, suggestions for improving the environmental performance of ammonia production are proposed. Results The environmental burdens of the coal-based and coke oven gas-based routes were 1.43 and 1.7 times higher than that of the natural gas-based route, respectively. The significant differences were mainly reflected in the greenhouse effect, acidification, and fossil energy depletion. Advanced coal-to-ammonia technology, represented by coal water slurry gasification, showed a lower environmental burden than the traditional intermittent gasification technology, especially in terms of greenhouse gas (GHG) emissions and energy consumption. The GHG emissions involved in producing ammonia decreased from 3.88 to 2.18 kg per 1 kg of ammonia, and energy consumption decreased by approximately 17%, from 5.69 to 4.71 MJ. Conclusions Coal is the main raw material used for ammonia production in China, and the results showed that the application of advanced coal gasification with energy-saving technologies can effectively improve the environmental performance of synthetic ammonia production in China.