Combustion operating conditions for municipal Waste-to-Energy facilities in the U.S

This paper reports the first known comprehensive survey of combustion operating conditions across the wide range of municipal waste-to-energy facilities in the U.S. The survey was conducted in a step-wise fashion. Once the population of 188 units operating at over 70 facilities was defined, this population was stratified by distinguishing characteristics of combustion technology. Stratum-level estimates for operating conditions were determined from data collected in the survey. These stratum-level values were weighted by corresponding design capacity share and combined to infer national-level operating parameter estimates representative of the overall population. Survey results show that typical municipal waste-to-energy combustion operating conditions in the U.S. are (1) furnace temperature above 1160 °C, (2) gas residence time above 2.4 s, (3) exit gas concentrations of nearly 10% for oxygen (dry basis), and (4) over 16% for moisture. These operating parameter values can serve as benchmarks for laboratory-scale studies representative of municipal waste-to-energy combustion as typically practiced in the U.S.

Highly efficient combustion with low excess air in a modern energy-from-waste (EfW) plant

The effect of low excess air and high adiabatic combustion temperatures on CO and NOx formation has been investigated on a commercially operated energy-from-waste plant. With optimal combination of low O₂ levels and stable combustion control, uncontrolled NOx levels could be lowered to 100-150mg/Nm³ (dry, at 11% O₂) while keeping CO emissions at low levels. Even at adiabatic temperatures above 1400°C thermal NOx hardly contributed to the total NOx emissions in a grate-fired EfW plant. An advanced combustion control system allowed continuous operation with very little excess air (λ<1.2) while keeping CO and NOx at levels well below the legal emission limits.

Attitudes toward waste to energy facilities and impacts on diversion in Ontario, Canada

Despite progress in residential waste diversion, residual waste - that fraction which cannot be recycled or composted - must continue to be managed by municipalities. Zero waste and environmental groups worry that waste-to-energy (WtE) incinerators discourage diversion, while both incineration and landfill have been stigmatized in the popular consciousness such that WtE incinerators in particular are being cancelled more often than they are approved. We conducted a mail-back survey of 217 residents in Toronto, Durham and Peel, Ontario, to understand attitudes toward diversion, levels of support for WtE incineration and WtE landfill (landfill gas recovery) facilities, and predictors of facility support. Contrary to experiences elsewhere, diversion seems threatened by WtE when measured as attitudes with 18%, and 14% agreeing that they would be less inclined to divert recyclable/compostable materials if they knew materials went to a WtE landfill or incinerator. When forced to choose between four options landfill or incineration with and without energy recovery, WtE incineration is most preferred (65%) and landfill without WtE is the least preferred option (61%). However, measurement has a large influence on public opinion results in the sense that support for WtE incineration drops to 43% when asked as a "vote in favor" question and to only 36% when measured as a 4-item index of support. When the indexes of support for landfill and WtE incineration are modeled, the prominence of odor in the landfill model distinguishes it from the WtE incinerator model which is dominated more by community and concern about health effects. Implications for policy are discussed, particularly mandatory diversion targets to accompany WtE.

Site specific risk assessment of an energy-from-waste/thermal treatment facility in Durham Region, Ontario, Canada. Part B: Ecological risk assessment

The regions of Durham and York in Ontario, Canada have partnered to construct an energy-from-waste (EFW) thermal treatment facility as part of a long term strategy for the management of their municipal solid waste. In this paper we present the results of a comprehensive ecological risk assessment (ERA) for this planned facility, based on baseline sampling and site specific modeling to predict facility-related emissions, which was subsequently accepted by regulatory authorities. Emissions were estimated for both the approved initial operating design capacity of the facility (140,000 tonnes per year) and the maximum design capacity (400,000 tonnes per year). In general, calculated ecological hazard quotients (EHQs) and screening ratios (SRs) for receptors did not exceed the benchmark value (1.0). The only exceedances noted were generally due to existing baseline media concentrations, which did not differ from those expected for similar unimpacted sites in Ontario. This suggests that these exceedances reflect conservative assumptions applied in the risk assessment rather than actual potential risk. However, under predicted upset conditions at 400,000 tonnes per year (i.e., facility start-up, shutdown, and loss of air pollution control), a potential unacceptable risk was estimated for freshwater receptors with respect to benzo(g,h,i)perylene (SR=1.1), which could not be attributed to baseline conditions. Although this slight exceedance reflects a conservative worst-case scenario (upset conditions coinciding with worst-case meteorological conditions), further investigation of potential ecological risk should be performed if this facility is expanded to the maximum operating capacity in the future.

Site specific risk assessment of an energy-from-waste thermal treatment facility in Durham Region, Ontario, Canada. Part A: Human health risk assessment

The regions of Durham and York in Ontario, Canada have partnered to construct an energy-from-waste thermal treatment facility as part of a long term strategy for the management of their municipal solid waste. This paper presents the results of a comprehensive human health risk assessment for this facility. This assessment was based on extensive sampling of baseline environmental conditions (e.g., collection and analysis of air, soil, water, and biota samples) as well as detailed site specific modeling to predict facility-related emissions of 87 identified contaminants of potential concern. Emissions were estimated for both the approved initial operating design capacity of the facility (140,000 tonnes per year) and for the maximum design capacity (400,000 tonnes per year). For the 140,000 tonnes per year scenario, this assessment indicated that facility-related emissions are unlikely to cause adverse health risks to local residents, farmers, or other receptors (e.g., recreational users). For the 400,000 tonnes per year scenarios, slightly elevated risks were noted with respect to inhalation (hydrogen chloride) and infant consumption of breast milk (dioxins and furans), but only during predicted 'upset conditions' (i.e. facility start-up, shutdown, and loss of air pollution control) that represent unusual and/or transient occurrences. However, current provincial regulations require that additional environmental screening would be mandatory prior to expansion of the facility beyond the initial approved capacity (140,000 tonnes per year). Therefore, the potential risks due to upset conditions for the 400,000 tonnes per year scenario should be more closely investigated if future expansion is pursued.