This study shows an efficient configuration method of a multiple units of cogeneration system (CGS) fueled by biogas in a sewage treatment facility. The efficient configuration was clarified by classifying a relation between exhaust heat recovery efficiency (
ηehr) of the CGS, and the ratio of yearly average heat demand to yearly average biogas production of the facility (
Qh.d/Qb.p). The CGS was assumed to be used under
Qh.d/Qb.p <
ηehr,
Qh.d/Qb.p ≈
ηehr,
Qh.d/Qb.p >
ηehr conditions. Results shown that, although the CGS was sufficiently capable to cover the total heat demand of the facility by only using biogas produced, on the point of view of energy utilization efficiency, reduction of unutilized biogas efficiency and reduction of electrical demand efficiencies, the most efficient CGS was obtained under
Qh.d/Qb.p ≈
ηehr condition. It was found that under
Qh.d/Qb.p ≈
ηehr condition, energy utilization, reduction of unutilized biogas and reduction of electrical demand efficiencies were 0.64, 0.99, and 0.32, respectively. Whereas, under
Qh.d/Qb.p <
ηehr and
Qh.d/Qb.p >
ηehr conditions, energy utilization, reduction of unutilized biogas and reduction of electrical demand efficiencies were in a ranges of 0.56-0.64, 0.43-0.99, and 0.16-0.20, respectively. If a CGS with a lower
ηehr such as fuel cell is used under
Qh.d/Qb.p <
ηehr condition, or a CGS with a higher
ηehr such as steam turbine is used under
Qh.d/Qb.p >
ηehr condition, more efficient system can be obtained.
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