Assessment of Power Generation from Biogas on Greenhouse Gas Emissions and Environment Impact
Date Issued
2016
Date
2016
Author(s)
Hsu, Wei-Li
Abstract
Biogas is one of gaseous fuel biomass energies in renewable resourcse. It can be used for heating and power generation. Improvement of the use of surplus biogas can effectively decrease the impact of greenhouse gas emissions of CH4 and CO2 in biogas on global warming, and reduce wasting energy resource. In this study, the life cycle assessment was performed to investigate the feasibility of adopting Bali sewage treatment plant, which is the largest of anaerobic sludge treatment plant in Taiwan, for the anaerobic treatment of sludge and foodwaste to produce biogas and generate the electricity. The study consists of two parts. The first part employed gas turbine and reciprocal engine to generate electricity from biogas. The composition of exhausts and performance characteristics of power generators were exmined to provide information of parameters needs for the second part. The second part conducted life cycle assessment to investigate the process of anaerobic digestion of sludge to produce biogas and generate electricity at Bali sewage treatment plant. The scenario of process of anaerobic digestion of foodwaste was also assessed. Finally, according to the emissions of exhausts of the generator, comparation of CO2 emissions of power generation from biogas with fossil fuel was made. The results from part I show, as the output power exceeds 20 kW, emission concentration of NOx using conventional reciprocal engine is about 20 times than that using gas turbine. The higher the output power, the greater the difference in NOx concentration. For 1 kWh output electricity, the emitted amount from reciprocal engine were 4.8×10-2 kg CO and 1.92 ×10-2 kg NOx with combustion efficiency (CE) of 0.97. Those from gas turbine were 4.1×10-3 kg CO and 1.63×10-3 kg NOx with CE of 0.99. The amount of exhausts of CO and NOx from gas turbine are about one-tenth of those from reciprocal engine. The results from part II indicate that the anaerobic digestion unit process exhibits the highest environmental impact in the whole processes from the input of raw matterials to the output of power generated from biogas. The impact extents of anaerobic digestion of sludge and power generation via gas turbine using biogas are 10-3 pt and 9.81×10-5 pt, respectively. The benefits of anaerobic digestion of foodwaste as a raw material are better than those of sludge. Because of the high content of organic matter of raw material of foodwaste and its large biogas output, the environmental impact using foodwaste is in half comparing with sludge. The impact extents for power generation via gas turbine using biogas with raw inputs of foodwaste and sludge are 5.6×10-4 pt and 1.11×10-3 pt, respectively. Without counting the CO2 emission from the production of biogas by anaerobic digestion, for generating 1 kWh, the gas turbine using biogas emitted CO2 of 266 g with 734 g, 203 g and 574 g less than those of power generators using coal, nature gas and oil, respectively. The use of available biogas for gas turbine in replacing the composed energy sources and sole fossil fuels for electricity generation of Taiwan can reduce at least 51.25% and 67% of CO2 emission, respectively. Therefore, the application of power generation from biogas can effectively not only solve the problem of the surplus biogas, but also offer an alternative energy to fossil fuels, effectively reducing the impact of greenhouse gas emissions.
Subjects
gas turbine
reciprcal engine
power generation from biogas
anaerobic digestion
life cycle assessment
greenhouse gas emissions
Type
thesis
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