Performance Evaluation of Micro Gas Turbine Cogeneration System at Sewage Treatment Facility (2nd Report, Optimized Configuration Method of Cogeneration System)

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 (η_<ehr>) of the CGS, and the ratio of yearly average heat demand to yearly average biogas production of the facility (Q_<h.d>/Q_<b.p>). The CGS was assumed to be used under Q_<h.d>/Q_<b.p> < η_<ehr>, Q_<h.d>/Q_<b.p> ≈ η_<ehr>, Q_<h.d>/Q_<b.p> > η_<ehr> 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 Q_<h.d>/Q_<b.p> ≈ η_<ehr> condition. It was found that under Q_<h.d>/Q_<b.p> ≈ η_<ehr> condition, energy utilization, reduction of unutilized biogas and reduction of electrical demand efficiencies were 0.64, 0.99, and 0.32, respectively. Whereas, under Q_<h.d>/Q_<b.p> < η_<ehr> and Q_<h.d>/Q_<b.p> > η_<ehr> 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 η_<ehr> such as fuel cell is used under Q_<h.d>/Q_<b.p> < η_<ehr> condition, or a CGS with a higher η_<ehr> such as steam turbine is used under Q_<h.d>/Q_<b.p> > η_<ehr> condition, more efficient system can be obtained