Abstract:
Abstract: Chinese government has been encouraging the use of crop straw as energy sources in the latest decades. Straw biogas project can not only provide clean energy for rural household, but also make full use of crop residue and reduce air pollution caused by straw open burning. Straw biogas industry has developed fast in the latest decades, with a total number of 458 projects by 2015. Crop straw biogas project is environmental-friendly, but pollutants emission will be caused during the biogas project construction, the crop straw transportation and pretreatment, the products utilization processes. The research on the environment performance of straw biogas is a hot topic with the straw biogas industry development of China. Life cycle assessment (LCA) can be used to calculate a product's environment performance by building an integrated framework of processes. LCA is used to analyze overall inputs, outputs and potential synthetical environmental impacts throughout biogas's lifetime. Some researchers have been studying the environmental impact of straw biogas system by the method of LCA. However, the pollutants emission and energy and material input of construction unit of biogas project were seldom considered in the boundary of the system. The straw biogas system was divided into construction unit, operation unit and product utilization unit during the inventory analysis. This paper analyzed the environment impact of each unit and the whole system of straw biogas project for central gas supply by the LCA method, and it started to focus on the environment performance of construction unit, which is different from previous studies. Taking the straw biogas project of Xijie Village in Anyang County, Henan Province as a case for empirical analysis, this paper made inventory analysis and impact assessment for life cycle of the biogas project including construction unit, project operation unit and product utilization unit. All the raw data were obtained by survey. Data of energy coefficient, emission factor, standardization criteria, and weight factor were acquired from publications and literatures of previous study. Five types of impacts including global warming, acidification, photochemical smog, aerosol, human toxicity were assessed. The result showed that the straw biogas project of Xijie Village produced the biogas of 13.6? 104 m3 per year, and the total global environmental impact load was 129.94 equivalent/(person?year). The environmental impact load of construction unit, operation unit and product utilization unit accounted for 65.62%, 32.76% and 1.62%, respectively. The coal is used to warm the biogas digester in winter in order to increase the biogas yield. The biogas produced can replace the standard coal of 9.71?104 t in a year. The total global environmental impact load of coal burning was 262.55 equivalent/(person?year). In the view of energy substitution for coal consumption, the environmental impact load of the biogas project system was reduced by 132.48 equivalent/(person?year), that is to say, the biogas project in this study decreased the environment impact by 50.50% compared to standard coal burning as household fuel. Straw biogas as a clean renewable energy can reduce utilization of coal and improve the environment quality. Construction unit of the straw biogas project contributes the most and product utilization unit contributes the least to the biogas project environment impact. The coal and electricity consumption are 2 main contributors for the environment impact of the biogas project. It is significant to reduce coal and electricity consumption and find low-carbon and environmental-friendly way of straw biogas digester heating in the future.