Environmental and exergetic life cycle assessment of lignite pyrolysis-based polygeneration system

Both environmental and exergetic life cycle assessment (LCA) of lignite circulating fluidized bed combus- tion (CFBC) system and lignite pyrolysis-based polygeneration system are compared in this study. The environmental LCA is used to quantify environmental burdens;while the exergetic LCA is applied to measure thermodynamic perform- ance. Results from the environmental LCA reveals that the impact categories of global warming potential,acidification potential,nutrient enrichment potential,and photochemical ozone formation potential caused by the polygeneration sys- tem are 61. 7% ,62. 9% ,38. 5% and 20. 0% lower than that caused by the CFBC system. The reasons are mainly at- tributed to the higher electricity generation efficiency,lower direct emission of the polygeneration system. Besides,the co-production of high added value products like methanol,fuel oil,and sulphur also offsets the potential impacts to pro- duce these materials. Regarding to the exergetic LCA results,the cumulative exergy consumption (CExC) efficiency of the CFBC system and the polygeneration system are 94. 4% and 111. 9% ,respectively. The CExC efficiency is even higher than 100% for the polygeneration system,which means more CExC are generated from the products compared to the total CExC consumed from the input energy and materials. This is mainly attributed to the cogeneration of electricity and high added value products,such as methanol (70. 37 kg / ton lignite),fuel oil (12. 3 kg / ton lignite),and sul- phur (6. 72 kg / ton lignite) from the polygeneration system.