A STUDY OF BIOGAS UTILIZATION EFFICIENCY HIGHLIGHTING INTERNAL COMBUSTION ELECTRICAL GENERATOR UNITS
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Date
2009-06
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The Ohio State University
Abstract
The purpose of the study was to determine the efficiency of methane utilization for a currently operating anaerobic digestion system on an agricultural facility. A dairy anaerobic digester was chosen for the study. A cogeneration system was implemented at this location using three biogas gen-set’s, each with a 710 kW capacity. Methane flow and pressure data, and electrical output (kW) data were collected on three units operating at the facility from January 23, 2009 to February 2, 2009. A sample was taken every minute. Hourly averages were then calculated and analyzed. An energy balance was then used to calculate instantaneous efficiency.
Instantaneous gen-set efficiency over this period was found to be 25.51% with a 5.93% standard deviation. This value was higher than that found in previous studies, of 22% electrical power to methane power. Lower methane energy flow rates were found to have a positive effect on gen-set efficiency; however total output was small compared to the generator size. Efficiency stabilized from 1358 kW (29% efficient) to 1958 kW (22% efficent) methane flows. Gen-set efficiency had a similar trend when compared to biogas flow rate, with higher efficiency at lower flow rates and lower efficiency at higher flow rates. Efficiency stablized when biogas flow was 117 cubic feet per minute to 148 cubic feet per minute. Methane content in the biogas was assumed 55.5% by volume from previous tests.
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biogas methane efficiency generator