A Case Study on the Electricity Generation Using a Micro Gas Turbine Fuelled by Biogas from a Sewage Treatment Plant

Combined heat and power production from biogas is now playing an important role in energy and resource utilization as well as pollution control in waste water treatment. This research used biogas from the Bali Sewage Treatment Plant in New Taipei City, Taiwan, as a major source of fuel for the electricity generation. A micro gas turbine electricity generator, Capstone CR-30, which possesses a maximum rated power load (P-WL) of 30 kW, was equipped to convert biogas into electricity. The biogas is mainly composed of CH4 (56.1 +/- 8.0 vol.%), CO2 (25.5 +/- 9.8 vol.%), H-2 (0.5 vol.%), and H2S (0.99 +/- 0.07 ppmv). During the test operation period of the generator, it was found that the thermal efficiency increases from 19.8% to 23.4% kWh(e)/kWh(th), while the electricity generation efficiency (eta(EB)) also rises from 0.93 to 1.09 kWh(e)/m(3) biogas as the P-WL increases from 10 kW to 30 kW. The results indicated that the generator has a better performance with higher P-WL. At P-WL = 30 kW, the average adjusted concentrations of CO and NOx (adjusted to 15 vol.% O-2) emitted from the generator are 86 ppmv and 17 ppmv, respectively. Both are much lower than the emission standards of stationary sources in Taiwan of 2000 ppmv and 150 ppmv, respectively. Thus, P-WL of 30 kW was selected in cooperation with biogas inflow = 0.412 m(3)/min and air/fuel ratio (i.e., air/biogas ratio) = 76.0 vol./vol. for the long-term regular operation. At the above setting conditions for long-term operation, the generator continuously consumed the biogas and provided stable electricity generation at a rate of 19.64 kWh(e)/h for a 2-year running period. Moreover, the greenhouse gas can be cut off with a rate of 10.78 kg CO(2)e/h when using biogas as fuel for electricity generation. Overall, this research proves that the application of a micro gas turbine electricity generator not only has promising performance for using biogas but also gives a significant reduction of greenhouse gas emission, which fits the concepts of the circular economy and environmental protection.