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Thermal Drying of Digestate with Acid Scrubbing of Exhaust Air – A Full Scale Study
Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.orgCitation: 2022 ASABE Annual International Meeting 2200188.(doi:10.13031/aim.202200188)
Authors: Alessandro Chiumenti, Francesco da Borso
Keywords: ammonia, ammonium sulfate, biogas, biomethane, circular economy, cogeneration, digestate, dryer, drying, nitrogen, nutrients, phosphorus, scrubber.
The present research was conducted on the first full-scale digestate drying plant realized in Italy, in order to assess the efficiency of the process and its environmental sustainability. The system processes part of the digestate from a 1 MWe biogas plant, fed with bovine manure and other biomasses. The thermal energy for the evaporation is derived from the combined heat and power unit (CHP). Air temperature, pH and nitrogen concentration in digestate are favorable to the stripping of ammonia: the exhaust airflow from the evaporator is treated in an acid scrubber resulting in the recovery of ammonium sulfate.
The inputs and outputs of the process, mass flows and energy consumption, and exhaust emissions were monitored.
The throughput of the system resulted variable: an average of 46.7%, of digestate (mass basis) was treated, with a diversion of 46.7% of nitrogen and phosphorus in dry digestate (4.3%N, 46.3%P) and in ammonium sulfate (4.9-19.7%N, negligible P). These fractions present interesting agronomical characteristics, and could find a market for their content of nutrients, organic nitrogen and phosphorus for the dry fraction (31 gN/kg, 23.5 gP/kg) and ammonium sulfate (31% solution, 31-124gN/kg).(Download PDF) (Export to EndNotes)