A Comparative Study of Swedish and Chinese Biogas Production with a Brief Economical Feasibility Analysis

Abstract: This Master of Science and Engineering thesis in Chemical Engineering treats biogas production in China. The thesis is divided into two parts. The first part contains an energy potential and situation analysis of biogas in China and a comparison with the situation in Sweden. The biogas potential in China is 950-2180 TWh depending on source. Specially, the potential from fish waste is 11 TWh. Part 1 also includes batch experiments where co-digestion of corn straw and swine manure is performed using substrate from Dajugezhuang in Tianjin. The experiments were executed at Tianjin Academy of Environmental Science. The experiments do not show a significant reduction in COD when co-digesting manure with straw and are connected with uncertainty. The experiments should be executed again with the recommendations given in this report. It is discovered that the inoculum affects the C:Nratio a lot. When co-digesting experiments are being performed, an inoculum that have a C:N-ratio close to the desired must be used. This is due to that the organic loading rate must be kept low. Part 2 of this thesis is an economical feasibility analysis and market investigation of biogas in China. A model is created using excel, where economic data from biogas plants in China are used to estimate the profit of producing biogas in China. The model indicates that the most feasible choice is to upgrade the biogas and inject it to the gas grid. This is due to the lower investment cost for an upgrading unit compared to an electricity-generating unit. The model uses electricity and gas prices from different provinces in China. Guangdong is the province with the highest electricity price and Ningxia the province with the lowest electricity price. The gas price in Guangdong is also high, but highest in Guangxi and Yunnan. The lowest gas price is found in Ningxia. Part 2 also discuss problems with the current situation for biogas producers in China. Investment subsidies from the government instead of product subsidies has led to a situation where China has over 30 million biogas reactors, but very low yield. The current situation means low incentives for selling the products from anaerobic digestion, biofertilizers, bio-methane, electricity and heat. The grid connection limit on electricity generators of >500 kW limits the number of grid-connected plants to less than 10. vi