Small-Scale Energy Use of Agricultural Biogas Plant Wastes by Gasification

In Poland, there are 78 biogas plants producing a total electrical power of 85.94 MW. The byproduct of biogas plants is called a digestate. A single biogas plant with a power of 500 kW produces more than 10,000 ton of digestate per year. The goal of this chapter is to present a low-cost method of raw digestate processing with water content of about 94.55%, and also the results of thermal gasification of dried and pelletized digestate. Initial dehydration method is based on mechanical separation of the solid fraction in screw separator with a slot filter. Pre-dewatered digestate had been dried in biodrying process in semi-technical scale bioreactor. Afterward, the digestate was dried in tubular dryer and pelletized. The chapter covers the energy consumption for each stage of preparation of digestate for thermal gasification process. The gasification tests were conducted in fixed bed downdraft reactor. The chapter also features the physicochemical properties of digestate used in gasification process. The result of research on the gasification of drier digestate was gaseous fuel that does not differ from the quality of fuels obtained from the thermal treatment of other types of biomass.