The control strategy utilized in a proposed project will be dependent upon the wastes to be processed, the thermal processing and energy recovery system, and its projected emissions and requirements imposed by regulators.
Control of Stack Emissions
The pollutants contained in the stack emissions from gasification and pyrolysis systems are the same as those in combustion systems. The measured levels of emissions are influenced by the thermal conversion technology employed and the nature of the waste being processed. A 2009 report by the University of California at Riverside compiled emissions data from fifteen (15) gasification and pyrolysis facilities [15].
The data was obtained from independent source test reports, compliance reports from regulatory agencies, and peer- reviewed publications. It includes air emissions data for several pollutants from facilities employing a variety of gasification and pyrolysis technologies, and various synfuel utilization approaches.
Twelve (12) of the facilities process municipal waste, two (2) process medical waste, one (1) processes circuit boards, and one (1) processes a combination of industrial and municipal waste. Eleven (11) of the sixteen (16) facilities are not in North America. The technologies include fluidized bed, fixed bed, plasma arc, high temperature gasification, and pyrolysis plus gasification. The synfuel utilization approaches include close-coupled combustion, IC engines, and gas turbines. The emissions ranges reported are summarized in Exhibit 2. Also included for comparison are emissions reported from mass burn and controlled air waste-to-energy facilities, all processing municipal waste [16, 17, 18, 19 and 20]. Given the variation in fuel-feedstocks being processed, conclusions regarding comparative emissions would be premature.
However, it appears that the emissions from the gasification/pyrolysis, mass burn, and controlled air systems lie within the same ranges, with the exception of low end nitrogen oxides, mercury, and dioxin/furans from gasification/pyrolysis, which are one (1) or more orders of magnitude less than mass burn and controlled air. A closer look at the gasification/pyrolysis emissions seems to indicate that the fluidized bed and plasma arc gasification and pyrolysis systems achieve the very low dioxin/furan emissions, whereas the close-coupled gasification systems emissions lie within the same range as mass burn and controlled air combustion. The lowest dioxin/furan emissions reported are associated with a plasma gasification facility that processed circuit boards.
Due to the variety of gasification technologies, the varying waste types processed, and the relative newness of the technology, there is no industry-standard air pollution control strategy or technology. The air pollution control devices employed by gasification and pyrolysis vendors in existing facilities vary and include electrostatic precipitators and scrubbers alone and in combination, including selective non-catalytic nitrogen oxide control, scrubbers, and baghouses.
The control strategy utilized in a proposed project will be dependent upon the wastes to be processed, the thermal processing and energy recovery system, and its projected emissions and requirements imposed by regulators.
Proceedings of the 18th Annual North American Waste-to-Energy Conference NAWTEC18 May 11-13, 2010, Orlando, Florida, USA
NAWTEC18-3521
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STATUS OF EXISTING BIOMASS GASIFICATION AND PYROLYSIS FACILITIES IN NORTH AMERICA
Theodore S. Pytlar, Jr.
Vice President-Solid Waste Group
Dvirka and Bartilucci Consulting Engineers
South Plainfield, New Jersey, USA
ABSTRACT
A search of websites for firms in the United States and Canada identifying themselves as gasification or pyrolysis system suppliers indicates that there are a number of existing facilities where their technologies are installed. According to the websites, the companies’ existing installations focus on processing biomass and industrial residuals, rather than mixed refuse. The biomass processed, according to the websites includes yard waste, wood, and wastewater treatment sludge. The existence of these facilities provides a potential opportunity for communities in areas with a high density of development, who experience difficulties in siting “traditional” facilities for processing these biomass wastes. Such traditional facilities include yard waste and sludge composting, wood mulching, sludge drying, chemical treatment or pelletization, and combustion-based waste-to-energy. As a result of these facility siting difficulties, these communities often resort to long-haul trucking of the biomass wastes to processing facilities or landfills. Certain potential advantages associated with gasification and pyrolysis technologies could ease the siting difficulties associated with the traditional technologies, due to smaller facility footprints, reduced odors, and the potential for energy production through combustion of syngas/synfuel to power internal combustion engines or produce steam using boilers. Lower stack emissions may result as compared to direct combustion of biomass wastes.
Locally sited biomass gasification facilities could reduce the environmental impacts associated with long-haul trucking and generate an energy product to meet nearby demand.
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