Biogas Production and Heat Transfer Performance of a Multiphase Flow Digester

Abstract

Traditional static anaerobic digestion technology presents the disadvantages of a low gas production rate and long digestion cycle, which is not conducive to the treatment of livestock manure. A 12 m3 multiphase flow anaerobic digester (MFD) was developed in this study to improve the biogas production rate and maintain constant temperature digestion during winters. Full-scale field experiments were conducted on the biogas production rate at different temperatures, the dynamic digestion effects, and the dynamic heating digestion effects of the system at Sichuan, China. A comparison of the dynamic and static digestion results of 50 days indicated that the biogas production for the dynamic digestion (DD) group was 115.22 m3 or 127.1% higher than that of the static digestion (SD) group with the same digestion temperature. The results of the heat transfer performance experiment revealed that the heat transfer rate of the system increased significantly, and the temperature of the biogas slurry increased rapidly. The optimization analysis of the system was based on the experimental results of the relationship between the slurry temperature and biogas production rate, and the economical digestion temperature of the system was proposed and calculated. Different insulation materials or insulation thicknesses have an influence on the economical digestion temperature. Additionally, the economical digestion temperature of the system in which the polystyrene insulation layer with a thickness of 90 mm was used, was found to be 27.2 °C. When digestion temperature was 22.3 °C, the energy efficiency ratio (EER) of dynamic anaerobic digestion system is 1. The advantages of MFD are low biogas production unit cost and high heat and mass transfer rate. However, the disadvantage of high operation energy consumption needs further improvement. And additional energy was required when system digestion temperature below 22.3 °C. The proposed MFD and dynamic anaerobic digestion system can play a significant role in using biomass resources and promoting the development of biogas projects.

Keywords

• multiphase flow
• anaerobic digestion
• experiment
• biogas production
• optimization analysis