Process Integration and Assessment of Biogas System

Abstract

Abstract In this work, we established the material and energy flow charts of a base case which contains the following units: biomass collection and transportation, pretreatment, anaerobic digestion, biogas upgrading and waste management. For this biogas system, the input feedstock are fixed to human feces and corn straw, the anaerobic digestion is performed at normal temperature 25 °C, and the biogas coming from anaerobic unit is upgraded via high pressure water scrubbing method to obtain the 98 % purity biomethane. The system material and energy flows are presented to indicate that the anaerobic digestion unit generate 90 wt % of the biogas slurry and residue, and 70 % of the energy was loss with the emission of the biogas slurry and residue. As for the system energy balance, we calculate the low heating value (LHV) based system energy efficiency considering the biomass feedstocks’ LHV. Furthermore, a system energy efficiency comparison between the base case and the modified case with heat exchange between biogas slurry and feedstock is made. The system energy efficiency results indicate that the heat exchange between the biogas slurry and the feedstock can enhance the system efficiency by about 0.3 %.