A Case Study Assessment of the Suitability of Small-Scale Biogas Plants to the Dispersed Agricultural Structure of China

摘要

This study focuses on small-scale biogas plants with unit volumes of between 30 and 200 m(3). Most small-scale biogas plants in China are in poor condition and have low utilization rates due to inaccurate designs and inappropriate maintenance. The aim of this study was to find efficiency measures to improve plant operation, and assess the suitability of the plants in the rural Chinese agricultural system. A 30 m(3) plant was operated for a 1-year period to test its performance using an assessment system. The results showed that biogas production reached 99.96 and 96.85 % of the maximum theoretical levels at temperatures of 25 +/- A 2 and 20 +/- A 1 A degrees C, respectively. Through correct installation of insulation and proper construction of the feeding process, the daily average biogas production rate was raised to 0.47 m(3)/(m(3) days). This was enough to completely supply 11 households with a sufficient amount of biogas for 9 months out of the year (CH4 > 55 %). The digestate produced from the biogas production process can also be used efficiently as fertilizer on farmland, and does not lead to nitrogen and phosphorus accumulation or excessive heavy metal content (outside of the permitted range). In the study area, rice and wheat yields increased 14.5 and 15.4 % respectively. Furthermore, we found that a trained farmer could complete all of the regular maintenance tasks of the plant, with the maintenance costs allocated from the biogas supply at an input-output ratio of 1.41. Marginal income was achieved by comprehensive biogas-digestate utilization at an input-output ratio of 7.55. We conclude that small-scale biogas plants currently provide a suitable system for comprehensive biogas-digestate utilization within the dispersed Chinese agricultural structure.