Evaluating the Air Quality, Climate and Economic Impacts of Biogas Management Technologies
Williams, R., C. Ely, T. Martynowicz, AND Mike Kosusko. Evaluating the Air Quality, Climate and Economic Impacts of Biogas Management Technologies. U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-16/099, 2016.
Innovative alternatives such as upgrading biogas for injection into natural gas pipelines, fuel cells and the use of biogas as a transportation fuel can achieve cross-media environmental benefits, including: GHG emission mitigation, air and water quality improvements, odors and waste reduction and fossil fuel displacement. However, organic waste managers and regulators alike lack sufficient information about the overall environmental and economic performance of available biogas management technologies. A more complete understanding of the environmental and economic performance of biogas-to-energy technologies will assist state and local governments, regulators, and potential project developers to identify geographically-appropriate and cost-effective biogas management options. This paper presents the economic and environmental performance of seven different biogas management technologies: flaring; combustion in a reciprocating engine; combustion in a gas turbine; combustion in a microturbine; conversion in a fuel cell; processing for natural gas pipeline injection or for CNG vehicle fuel.
Anaerobic digestion is a natural biological process in which microorganisms break down organic materials in the absence of oxygen. When anaerobic microbes metabolize organic waste – i.e., the carbon-based remains of plants, animals and their waste products, e.g. animal manure, sewage sludge and food waste – they produce biogas. Biogas consists mainly of methane and carbon dioxide and can be used as a renewable energy fuel in a variety of applications. The impacts of biogas generation and utilization processes differ, depending on the source material (e.g., sewage, manure, food processing waste, municipal solid waste) and end uses (e.g., on-site electricity generation, conversion to a vehicle fuel, injection into the natural gas pipeline, etc.). Organic waste managers and regulators alike lack sufficient information about the overall environmental and economic performance of available biogas management technologies. A more complete understanding of the environmental and economic performance of biogas-to-energy technologies will assist state and local governments, regulators, and potential project developers in identifying geographically appropriate and cost-effective biogas management options.The backdrop for this research was California. The state has unique air quality challenges due to the combination of meteorology and topography, population growth and the pollution burden associated with mobile sources. However, with the strengthening of National Ambient Air Quality Standards for ground level-ozone, challenges unique to California could become more commonplace.The focus of this research was to evaluate the impacts associated with biogas management technologies; specifically, to evaluate the emissions and costs associated with using biogas in particular applications. Seven different technologies were evaluated in terms of their individual cost, efficiency and emissions — both greenhouse gas and criteria air pollutant emissions. The technologies examined include: combustion in a reciprocating engine; combustion in a gas turbine; combustion in a microturbine; conversion in a fuel cell; processing for pipeline injection; processing to create Compressed Natural Gas; and flaring.The scope of the analysis was at once broad and narrow. It was broad in that it did not consider differences in biogas composition, which vary considerably depending on the source material. The analysis was narrow in that the system boundary begins with already-produced biogas and ends with on-site use or upgrading. It did not include upstream impacts, such as fugitive emissions or material handling and transportation; or downstream impacts, such as the carbon temporarily sequestered by land-applying digestate or the carbon and criteria pollutants emitted by combusting CNG in a vehicle. Comprehensively, the analysis evaluated capital, operations, and maintenance costs, including those for biogas pre-treatment or conditioning (e.g., removing siloxanes and sulfur compounds) and exhaust gas treatment (i.e., for air pollution control equipment). Narrowly, it only evaluated costs pertaining to biogas management. The characteristics evaluated and compared in this research include the following: • Conversion efficiency: percent energy efficiency for electricity production systems, higher heating value basis and percent yield for compressed renewable natural gas (RNG) and pipeline injection processes.• Levelized cost of energy (LCOE): dollar per kilowatt hour ($/kWh), dollar per million British thermal units ($/MMBtu) or $/gasoline gallon equivalent ($/GGE).• On-site criteria pollutant and GHG emissions.Only California-based systems were evaluated. Source information included peer-reviewed and ‘gray’ literature, operating permits, source test reports, and expert and developer interviews.