Life-Cycle Implications of Using Crop Residues for Various Energy Demands in China

Crop residues are a critical component of the sustainable energy and natural resource strategy within a country. In this study, we use hybrid life-cycle environmental and economic analyses to evaluate and compare the atmospheric chemical, climatic, ecological, and economic issues associated with a set of energy conversion technologies that use crop residues for various energy demands in China. Our analysis combines conventional process-based life cycle assessment with economic input-output life cycle assessment. The results show that the return of crop residues to the fields, silo/amination and anaerobic digestion (household scale) offer the greatest ecological benefits, with net greenhouse gas reduction costs of US$3.1/tC, US$11.5/tC, and US$14.9/tC, respectively. However, if a positive net income for market-oriented operations is the overriding criterion for technology selection, the cofiring of crop residues with coal and crop residue gasification for power generation offer greater economic scope and technical feasibility, with net incomes of US$4.4/Mg and US$4.9/Mg, respectively. We identify that poor economies of scale and the absence of key technologies mean that enterprises that use pure combustion for power generation (US$212/tC), gasification for heat generation (US$366/tC) and large-scale anaerobic digestion for power generation (US$169/tC) or heat generation (US$206/tC) are all prone to operational deficits. In the near term, the Chinese government should also be cautious about any large-scale investment in bioethanol derived from crop residues because, with a carbon price of as high as US$748/tC, bioethanol is the most expensive of all energy conversion technologies in China.