Processing of residues from biogas plants for energy purposes

Maize silage (Atletico, FAO 280) is being anaerobically fermented with cow manure (45 °C, pH 7.1, hydraulic retention time 67 days) in a commercial scale (8,210 MWh electric power and 8,700 MWh heat power per year). The fermentation residues are being mechanically separated into the liquid fraction and the solid pulp (0.9 % hemicelluloses, 8.4 % cellulose, 5.7 % lignin). The solid pulp is being predryed and subsequently pyrolyzed. The pyrolysis takes place in the newly developed horizontal continuous pyrolysis reactor. The technology is run by the hot flue gases (410 ± 11 °C) from the biogas combustion engine (383 m³ of biogas per hour). The carbon powder obtained is being technologically and economically analyzed as a solid biofuel instead of biochar. The results obtained by standardized methods show that the new variety of products obtained outperforms many of the conventional solid biofuels not only in technological and environmental indicators, but also from the economical point of view.