Low NOx,High Efficiency Multistaged Burner: Fuel Oil Results

A multistaged combustion burner designed for in-furnace NO_x control and high combustion efficiency is being evaluated for high nitrogen content fuel and waste incineration application in a 0.6 MW package boiler simulator. A low NO_x precombustion chamber burner has been reduced in size by approximately a factor of two (from 600 to 250 ms first-stage residence time) and coupled with (1) air staging, resulting in a three-stage configuration, and (2) natural gas fuel staging, yielding up to four stolchlometric zones. Natural gas, doped with ammonia to yield a 5.8 percent fuel nitrogen content, and distillate fuel oil, doped with pyridine to yield a 2 percent fuel nitrogen content, were used to simulate high nitrogen content fuel/waste mixtures. The multistaged burner reduced NO emissions by 85 percent from emission levels from a conventional unstaged burner mounted on a commercial package bollerTA minimum NO emission level of 110 ppm was achieved in the fuel oil tests, from a level of 765 ppm for conventional firing. This is compared with a 160 ppm minimum NO level achieved in gaseous fuel tests, from an uncontrolled level of 1000 ppm. Boiler fuel staging, or reburnlng, appears to be superior to air staging for high combustion efficiency due to its minimal fuel-rich core and second flame front in the boiler.     

Analysis of Industrial Boiler Solid Waste Impacts

This paper presents an examination of industrial coal-fired boiler waste products. Presently the atmospheric emissions from all new boilers larger than 250 × 10⁶ Btu/hr are controlled by existing New Source Performance Standards, and boilers smaller than 250 × 10⁶ Btu/hr are controlled to levels required by the regulations of the particular state in which the facility is located. The 1977 Clean Air Act Amendments, however, specify categories of sources for which EPA must develop revised New Source Performance Standards. Industrial coal-fired boilers are included as one of these categories, and a relevant issue concerns the potential amount of solid waste generated as a result of tightened emission standards that require flue gas desulfurization. This paper examines the air quality and solid waste impacts of moderate and stringent emission controls for particulate and SO₂ emissions from industrial coal-fired boilers.

Comparisons are presented of physical and chemical characterizations of the emissions and solid wastes produced when boilers are equipped with particulate and SO₂ control equipment. The SO₂ systems examined are lime spray drying, lime/limestone, double alkali, sodium throwaway, physically cleaned coal, and fluidized-bed combustion. The solid waste disposal alternatives and the disposal costs are discussed. The most common disposal methods used are landfill for dry wastes and impoundment for sludges, with special wastewater treatment requirements for the sodium throwaway aqueous wastes.     

Assessment of contribution of SO2 and NO2 from different sources in Jamshedpur region, India

Contribution of pollution from different types of sources in Jamshedpur, the steel city of India, has been estimated in winter 1993 using two approaches in order to delineate and prioritize air quality management strategies for the development of region in an environmental friendly manner. The first approach mainly aims at preparation of a comprehensive emission inventory and estimation of spatial distribution of pollution loads in terms of SO₂ and NO₂ from different types of industrial, domestic and vehicular sources in the region. The results indicate that industrial sources account for 77% and 68% of the total emissions of SO₂ and NO₂, respectively, in the region, whereas vehicular emissions contributed to about 28% of the total NO₂ emissions. In the second approach, contribution of these sources to ambient air quality levels to which the people are exposed to, was assessed through air pollution dispersion modelling. Ambient concentration levels of SO₂ and NO₂ have been predicted in winter season using the ISCST3 model. The analysis indicates that emissions from industrial sources are responsible for more than 50% of the total SO₂ and NO₂ concentration levels. Vehicular activities contributed to about 40% of NO₂ pollution and domestic fuel combustion contributed to about 38% of SO₂ pollution. Predicted 24-h concentrations were compared with measured concentrations at 11 ambient air monitoring stations and good agreement was noted between the two values. In-depth zone-wise analysis of the above indicates that for effective air quality management, industrial source emissions should be given highest priority, followed by vehicular and domestic sources in Jamshedpur region.     

NOx Reduction in a Gas Fired Utility Boiler by Combustion Modifications

Data on the effect of several combustion modifications on the formation of nitrogen oxides and on boiler efficiency were acquired and analyzed for a 110 MW gas fired utility boiler. The results from the study showed that decreasing the oxygen in the flue gas from 2.2% to 0.6% reduced the NO_x formation by 33% and also gave better boiler efficiencies. Flue gas recirculation through the bottom of the firebox was found to be ineffective. Staged combustion was found to reduce the NO_x emissions by as much as 55 % while decreasing the efficiency by about 5%. Adjustment of the burner air registers reduced the NO_x formation by about 20 ppm. The lowest NO_x emissions of 42 ppm (at about 3% O₂) in the stack was obtained for air only to one top burner and 0.5% oxygen in the flue gas.     

The Regulation of Toxic Air Pollutants A Critical Review

ABSTRACT

Passage of the 1990 Clean Air Act Amendments launched the Acid Rain Program in the United States. This initiative, based on the market mechanism of a sulfur dioxide tradable “allowance” system, was a dramatic departure from traditional command and control strategies designed to reduce air pollution emissions. Power plant managers have flexibility under the program to select and implement a variety of options to reduce emissions below mandated levels. Federal agencies have collected annual performance data for affected facilities covered by the program for a number of years. Coal-burning plants are typically greater generators of sulfur dioxide (SO₂) than oil burners of equivalent size. This study examined the effect of fuel type as a significant factor influencing a plant's achievement in reducing pollution emissions. Achievement was measured by using a derived variable, delta (A), defined as the difference between pounds of SO₂ produced divided by the energy (in million Btu) generated, for the years 1990 and 1995. Rigorous nonparametric statistical analyses were used to compare the two populations of coal-fired and oil-fired plants. Results indicated that coal-burning facilities achieved greater program success, measured by the expected value of delta, than the oil combustors for the five-year period reviewed. Since utility managers must take steps to ensure all applicable requirements of the program are met, findings of the inquiry should prove to be useful in assessing achievable emissions reductions and aid in long-range facility planning.     

Development of Federal Air Standards to Reduce Sulfur Dioxide Emissions from New Industrial Boilers

Federal new source performance standards to control air emissions of sulfur dioxide from new industrial boilers were proposed by EPA on June 19, 1986. These standards would require boiler owners to reduce SO₂ emissions by 90 percent and meet an emission limit of 1.2 lb/MM Btu of heat input for coal-fired boilers and 0.8 lb/MM Btu for oil-fired boilers. In developing these standards, several regulatory options were considered, from standards that could be met by firing low sulfur fuels to standards that would necessitate flue gas treatment. The environmental, economic, and cost impacts of each option were analyzed. National impacts were estimated by a computer model that projects the population of new boilers over the 5-year period following proposal, predicts the compliance strategy that will be used to comply with the particular option (always assuming that the lowest cost method of compliance will be selected), and estimates the resulting emission reductions and costs. Impacts on specific industries and on model boilers were also analyzed. This paper focuses on these analyses and their results. The Agency's conclusions from these analyses, which led to the decision to establish percent reduction standards, are provided, and the proposed SO₂ standards are summarized. The proposed standards also include an emission limit for particulate matter from oil-fired boilers (0.1 lb/MM Btu). However, this article focuses only on the SO₂ standards.     

Part I: lead peroxide candles and dustfall collectors

A diffusion flame burner was operated to determine the effect of several parameters on the quantity of NO_x and unburned hydrocarbons produced. The statistical analysis indicated the unburned hydrocarbon emissions to be dependent upon the rate of heat release in the system, the amount of excess combustion air, the fuel molecular structure, and the interaction between the fuel structure and the amount of excess air. Analysis of the NO_x emissions, after an adjustment to a common temperature to eliminate the temperature effect, showed them to be dependent upon the fuel molecular structure and the amount of excess air. The NO_x emissions reached a maximum at the conditions which yielded minimum unburned hydrocarbon emissions. Multiple regressions were made which yielded predicting equations for both the unburned hydrocarbon and the NO_x for the apparatus used.     

A Life-Cycle Inventory Model of Municipal Solid Waste Combustion

ABSTRACT

Evaluation of alternate strategies for municipal solid waste (MSW) management requires models to calculate environmental emissions as a function of both waste quantity and composition. A methodology to calculate waste component-specific emissions associated with MSW combustion is presented here. The methodology considers emissions at a combustion facility as well as those avoided at an electrical energy facility because of energy recovered from waste combustion. Emission factors, in units of kg pollutant per metric ton MSW entering the combustion facility, are calculated for CO₂-biomass, CO₂-fossil, SO_x , HCl, NO_x , dioxins/furans, PM, CO, and 11 metals. Water emissions associated with electrical energy offsets are also considered. Reductions in environmental emissions for a 500-metric-ton-per-day combustion facility that recovers energy are calculated.     

Metal partitioning in products of incineration of municipal solid waste

Metals contained in the waste transfer to the waste incineration products, including flue gas, fly ash, and bottom ash, as different oxide, nitride, carbides, and other phases. Most of the metal-based phases formed in incineration are toxic and their emissions need to be strictly controlled. Therefore, behavior of metal species during incineration must be well understood. Such understanding is possible based on the experimental identification of the metal phases formed in the waste combustion and determination of their concentration in various incineration products. To avoid well-known experimental difficulties of the industrial waste incinerators associated with the poor fuel/conditions reproducibility and limited instrumentation, a 140,000 Btu/h pilot-scale, laboratory burner was constructed, characterized and operated at NJIT. A synthetic fuel representative of the municipal solid waste in the US was formulated and produced in 600-Lb batches. The solid fuel contained Fe and SiO2 as main constituents, and was doped with trace amounts of Al, Ni, Cr, Hg and PbO. Several experiments have been conducted on combustion of the synthetic fuel in the pilot-scale incinerator with varying fuel-air equivalence ratio. Both gaseous and condensed combustion products were sampled and analyzed. Atomic absorption spectroscopy and X-ray diffraction were used to analyze total metal contents and metal containing phases in the incineration products. Thermodynamic equilibrium computations were performed to obtain the adiabatic flame temperature and identify the phases of the metal-containing products formed at the equilibrium conditions. The results of the equilibrium computations performed at the varied fuel/air ratios were compared with the observed experimental results.     

The impact of CO2 capture in the power and heat sector on the emission of SO2, NOx,particulate matter,volatile organic compounds and NH3 in the European Union

This study quantifies the trade-offs and synergies between climate and air quality policy objectives for the European power and heat (P&H) sector. An overview is presented of the expected performance data of CO₂ capture systems implemented at P&H plants, and the expected emission of key air pollutants, being: SO₂, NO_X, NH₃, volatile organic compounds (VOCs) and particulate matter (PM). The CO₂ capture systems investigated include: post-combustion, oxyfuel combustion and pre-combustion capture.For all capture systems it was found that SO₂, NO_x and PM emissions are expected to be reduced or remain equal per unit of primary energy input compared to power plants without CO₂ capture. Increase in primary energy input as a result of the energy penalty for CO₂ capture may for some technologies and substances result in a net increase of emissions per kWh output. The emission of ammonia may increase by a factor of up to 45 per unit of primary energy input for post-combustion technologies. No data are available about the emission of VOCs from CO₂ capture technologies.A simple model was developed and applied to analyse the impact of CO₂ capture in the European P&H sector on the emission level of key air pollutants in 2030. Four scenarios were developed: one without CO₂ capture and three with one dominantly implemented CO₂ capture system, varying between: post-combustion, oxyfuel combustion and pre-combustion.The results showed a reduction in GHG emissions for the scenarios with CO₂ capture compared to the baseline scenario between 12% and 20% in the EU 27 region in 2030. NO_x emissions were 15% higher in the P&H sector in a scenario with predominantly post-combustion and lower when oxyfuel combustion (?16%) or pre-combustion (?20%) were implemented on a large scale. Large scale implementation of the post-combustion technology in 2030 may also result in significantly higher, i.e. increase by a factor of 28, NH₃ emissions compared to scenarios with other CO₂ capture options or without capture. SO₂ emissions were very low for all scenarios that include large scale implementation of CO₂ capture in 2030, i.e. a reduction varying between 27% and 41%. Particulate Matter emissions were found to be lower in the scenarios with CO₂ capture. The scenario with implementation of the oxyfuel technology showed the lowest PM emissions followed by the scenario with a significant share allocated to pre-combustion, respectively ?59% and ?31%. The scenario with post-combustion capture resulted in PM emissions varying between 35% reduction and 26% increase.     

The change in O3, SO2 and NO2 concentrations in Lithuania

Due to the dynamic nature of the atmosphere, substantial amounts of gaseous and particulate pollutants are transported to the areas distant from their sources. In order to determine the regional concentration levels of atmospheric pollutants in Lithuania, concentrations of gaseous O₃, SO₂, NO₂ and other pollutants have been measured at the Preila background station (55°20′ N and 21°00′ E, 5 m a.s.l.) since 1981. The long-term concentration data set enabled us to get temporal trends, both on a seasonal and longer time scale, to identify source areas of pollutants and to relate them to the emission data. Based on the data obtained, the different tendencies in the pollutant concentration changes were revealed. Positive trends for ozone (of 2.9% per year during 1983–2000) and a distinct negative trend for both sulphur dioxide (of 3.8% per year during 1981–2000) and nitrogen dioxide (of 3.8% per year during 1983–2000) were found. The air mass back-trajectory analysis was used to assess the source region of air pollutants transported to Lithuania. The pollutant concentration levels were compared with their emission changes in Europe and Lithuania. The general trends in SO₂ as well as in NO₂ concentrations observed are consistent with changes in SO₂ and NO₂ emissions in Europe and Lithuania.     

Emissions and risks associated with oxyfuel combustion: State of the science and critical data gaps

Oxyfuel combustion is a promising technology that may greatly facilitate carbon capture and sequestration by increasing the relative CO₂ content of the combustion emission stream. However, the potential effect of enhanced oxygen combustion conditions on emissions of criteria and hazardous air pollutants (e.g., acid gases, particulates, metals and organics) is not well studied. It is possible that combustion under oxyfuel conditions could produce emissions posing different risks than those currently being managed by the power industry (e.g., by changing the valence state of metals). The data available for addressing these concerns are quite limited and are typically derived from laboratory-scale or pilot-scale tests. A review of the available data does suggest that oxyfuel combustion may decrease the air emissions of some pollutants (e.g., SO₂, NOx, particulates) whereas data for other pollutants are too limited to draw any conclusions. The oxy-combustion systems that have been proposed to date do not have a conventional “stack” and combustion flue gas is treated in such a way that solid or liquid waste streams are the major outputs. Use of this technology will therefore shift emissions from air to solid or liquid waste streams, but the risk management implications of this potential change have yet to be assessed. Truly useful studies of the potential effects of oxyfuel combustion on power plant emissions will require construction of integrated systems containing a combustion system coupled to a CO₂ processing unit. Sampling and analysis to assess potential emission effects should be an essential part of integrated system tests.

Implications: Oxyfuel combustion may facilitate carbon capture and sequestration by increasing the relative CO₂ content of the combustion emission stream. However, the potential effect of enhanced oxygen combustion conditions on emissions of criteria and hazardous air pollutants has not been well studied. Combustion under oxyfuel conditions could produce emissions posing different risks than those currently being managed by the power industry. Therefore, before moving further with oxyfuel combustion as a new technology, it is appropriate to summarize the current understanding of potential emissions risk and to identify data gaps as priorities for future research.     

Studies of potential sources that contributed to atmospheric mercury in Toronto,Canada

This study identified sources of mercury (Hg) in downtown Toronto, Canada by analyzing gaseous elemental mercury (GEM), mercury associated with particles with sizes less than 2.5 microns (PHg < 2.5), and gaseous oxidized inorganic mercury (GOIM), commonly referred to as reactive gaseous mercury (RGM), and air pollutants (CO, NO_x, O₃, PM_2.5, SO₂) concentrations between Dec 2003 and Nov 2004. The data were analyzed using Positive Matrix Factorization (PMF) model, Principal Components Analysis (PCA), ratio analysis, back trajectories, and correlation analyses. The analyses suggest industrial sources (chemical production, metal production, sewage treatment), rather than coal combustion, were the major contributors to measured Hg levels. Overlap in source profiles for the Hg sources listed in the Canadian National Pollutant Release Inventory (NPRI) and lack of source profiles for urban sources were the major limitations to positively identifying sources from the PMF and PCA factors. Correlation analyses revealed direct emissions were the sources of GOIM in spring, summer, and fall, and the occurrence of GEM oxidation by ozone in the summer. Elevated Hg events are attributed to emissions from urban sources near the sampling site, regional point sources, and photochemical processes involving ozone.     

Assessing multi-year changes in modeled and observed urban NOX concentrations from a dynamic model evaluation perspective

An investigation of the concentrations of nitrogen oxides (NO_X) from an air quality model and observations at monitoring sites was performed to assess the changes in NO_X levels attributable to changes in mobile emissions. This evaluation effort focused on weekday morning rush hours since urban NO_X concentrations are strongly influenced by the significant loading of emissions associated with heavy commuter traffic. On-road vehicle NO_X emissions generated by the MOBILE6 model revealed a steady decline with an overall decrease of 25% for 2002–2006. In this study, a dynamic model evaluation was undertaken that entails an assessment of the predicted concentration response of the Community Multiscale Air Quality (CMAQ) model due to changes in NO_X emissions as well as to meteorological variability spanning 3-month summer periods over five consecutive years (2002–2006) against observed concentration changes at NO_X monitoring sites located primarily in urban areas of the eastern United States. Both modeled and observed hourly NO_X concentrations exhibited maximum values that coincided with the morning peak NO_X emissions. The notable results, based on 3-h average (6–9 AM local time) NO_X concentrations, derived between the 50th and 95th percentiles of cumulative concentration distributions, revealed that modeled changes at these elevated NO_X levels generally tracked the year-to-year variations in the observed concentration changes. When summer 2002 values were used as a reference, both modeled and observed results also showed definitive decreases in weekday morning urban NO_X concentrations over this multi-year period, which can be primarily attributed to the reductions in mobile source emissions. Whereas observed NO_X concentrations have declined by about 25% over this period consistent with the decline in the modeled mobile emission sector, modeled NO_X concentration changes were close to the decreases exhibited in all (mobile + other sectors) surface NO_X emissions whose overall decline was about 15% over this multi-year period.     

Nonmethane Organic Compound to Nitrogen Oxide Ratios and Organic Composition in Cities and Rural Areas

The observed ranges in nonmethane organic compound (NMOC) concentrations, NMOC composition and nitrogen oxides (NO_X) concentrations have been evaluated for urban and nonurban areas at ground level and aloft of the contiguous United States. The ranges in NMOC to NO_X ratios also are considered. The NMOC composition consistently shifts towards less reactive compounds, especially the alkanes, in air parcels over nonurban areas compared to the NMOC composition near ground level within urban areas. The values for the NMOC to NO_X ratios, 1.2 to 4.2, in air aloft over nonurban areas are lower than in air at ground level urban sites, ≥8, and much lower than in air at ground level nonurban sites, ≥20.

The layers of air aloft over a number of nonurban areas of the United States tend to accumulate NO_X emissions from the tall stacks of large fossil fuel power plants located at nonurban sites. During the night into the morning hours, the air aloft is isolated from any fresh NMOC emissions predominately coming from near surface sources. Conversely, during this extended period of restricted vertical mixing, air near the surface accumulates NMOC emissions while this air is isolated from the major NO_X sources emitting aloft. These differences in the distribution of NMOC and NO_X sources appear to account for the much larger NMOC to NO_X ratios reported near ground level compared to aloft over nonurban areas.

Two types of experimental results are consistent with these conclusions: (1) observed increases in surface rural NO_X concentrations during the morning hours during which the mixing depth increases to reach the altitude at which NO_X from the stacks of fossil fuel power plants is being transported downwind; (2) high correlations of total nitrate at rural locations with Se, which is a tracer for coal-fired power plant NO_X emissions.

The implications of these conclusions from the standpoint of air quality strategies are suggested by use of appropriate scenarios applied to both urban and regional scale photochemical air quality models. The predictions from urban model scenarios with NMOC to NO_X ratios up to 20 are that NO_X control will result in the need for the control of more NMOC emissions than necessary in the absence of NO_X control, in order to meet the O₃ standard. On a regional scale, control of NO_X emissions from fossil fuel power plants has little overall effect regionally but does result on a more local scale in both small decreases and increases in O₃ concentrations compared to the baseline scenario without NO_X control. The regional modeling results obtained to date suggest that NO_X control may be effective in reducing O₃ concentrations only for a very limited set of conditions in rural areas.     

Sulfur Dioxide and Nitrogen Oxides Emissions from U.S. Pulp and Paper Mills, 1980–2005

Abstract

Comprehensive surveys conducted at 5-yr intervals were used to estimate sulfur dioxide (SO₂) and nitrogen oxides (NO_x) emissions from U.S. pulp and paper mills for 1980, 1985, 1990, 1995, 2000, and 2005. Over the 25-yr period, paper production increased by 50%, whereas total SO₂ emissions declined by 60% to 340,000 short tons (t) and total NO_x emissions decreased approximately 15% to 230,000 t. The downward emission trends resulted from a combination of factors, including reductions in oil and coal use, steadily declining fuel sulfur content, lower pulp and paper production in recent years, increased use of flue gas desulfurization systems on boilers, growing use of combustion modifications and add-on control systems to reduce boiler and gas turbine NO_x emissions, and improvements in kraft recovery furnace operations.     

Shock Wave Cleaning of Air Filters

The trends in and relationships between ambient air concentrations of sulfur dioxide and sulfate aerosols at 48 urban sites and 27 nonurban sites throughout the U.S. between 1963 and 1972 have been analyzed. The substantial decreases in ambient SO₂ concentrations measured at urban sites in the eastern and midwestern U.S. are consistent with the corresponding reductions in local SO₂ emissions, but these decreases have been accompanied by only modest decreases in ambient sulfate concentrations. Large differences in the amounts of SO₂ emitted within individual air quality control regions are associated with much smaller differences in the corresponding ambient sulfate concentrations. Substantial changes in the patterns of SO₂ emissions between air quality regions result in essentially no differences between ambient sulfate concentrations in those air quality regions. Comparisons of several air quality regions in the eastern and western U.S. with similar SO₂ emission levels and patterns of emissions clearly demonstrates the higher ambient sulfate concentration levels in eastern air quality control regions. Relationships between SO₂, sulfates, and vanadium concentrations at eastern nonurban U.S. sites cannot be explained by local emission sources. These various observed results can be best explained by long distance sulfur oxide transport with chemical conversion of SO₂ to sulfates occurring over ranges of hundreds of kilometers. This conclusion has been suggested earlier and the present analysis strongly supports previous discussions. An impact of long range transport of sulfates is to emphasize the need for Consistent strategies for reduction of sulfur oxides throughout large geographical regions. Additions of large capacities involving elevated sources in mid-continental or western regions could result in significant increases in sulfate concentrations well downwind of such sources. Some of the types of research activities required to quantitate crucial experimental parameters are discussed.     

Authors’ Reply

Emissions from oil-fired residential heating equipment can be reduced by improved steady running and cyclic efficiencies. Techniques which reduce the heating demand (thermostat cut-back) or reduce envelope losses (chimney damper) lead to reductions in SO₂ and NO emissions proportional to the fuel saving. Higher savings in CO and particulates result from cyclic modification. Reductions in nozzle size lead to an increase in unit cycle duration, reducing the off-cycle losses, with emissions reduced similarly. Changing the thermostat anticipator yields little reduction in fuel, SO₂ or NO, but significantly reduces CO and particulate emissions, by decreasing the number of cycles. Improved burner performance, with combustion at low excess air, offers the largest fuel savings, with commensurate reductions in SO₂ and NO, and greater reductions in CO and particulates.     

Problems of Meeting Multiple Air Quality Objectives for Coal-Fired Utility Boilers

Gaseous wastes and particulate emissions are produced in the process of burning coal to produce electrical energy. In attempting to control these gaseous wastes, changes in the operation efficiency of boilers and secondary equipment are likely to result, and in addition liquid and solid waste streams are produced. The interrelationships among the various forms of wastes and the effects of air quality control on process efficiency are often overlooked in studies of environmental quality management.

The study was undertaken to evaluate the technical alternatives for handling gaseous and particulate emissions from coal-fired boilers and to determine the feasibility of meeting several standards simultaneously. The gaseous emissions of major importance in the combustion of coal are parti culates, oxides of sulfur, and oxides of nitrogen. Particulates can be controlled by a tradeoff among further preparation at the mine (for additional ash removal), type of boiler, use of dust control equipment and high stacks for dispersion of residual emissions, if ambient air standards are considered. Oxides of sulfur reduction depends currently on fuel substitution, limestone additives in the boiler and some form of contact process such as wet scrubbing, or the use of high stacks. Oxides of nitrogen control in coal fired boilers is restricted to small reductions by either changes in boiler operation, such as lower excess air levels, adsorption during wet scrubbing or by dispersion from high stacks.     

Atmospheric mercury emissions from waste combustions measured by continuous monitoring devices

Atmospheric mercury emissions have attracted great attention owing to adverse impact of mercury on human health and the ecosystem. Although waste combustion is one of major anthropogenic sources, estimated emission might have large uncertainty due to great heterogeneity of wastes. This study investigated atmospheric emissions of speciated mercury from the combustions of municipal solid wastes (MSW), sewage treatment sludge (STS), STS with waste plastics, industrial waste mixtures (IWM), waste plastics from construction demolition, and woody wastes using continuous monitoring devices. Reactive gaseous mercury was the major form at the inlet side of air pollution control devices in all combustion cases. Its concentration was 2.0–70.6 times larger than elemental mercury concentration. In particular, MSW, STS, and IWM combustions emitted higher concentration of reactive gaseous mercury. Concentrations of both gaseous mercury species varied greatly for all waste combustions excluding woody waste. Variation coefficients of measured data were nearly equal to or more than 1.0. Emission factors of gaseous elemental mercury, reactive gaseous mercury, and total mercury were calculated using continuous monitoring data. Total mercury emission factors are 0.30 g-Hg/Mg for MSW combustion, 0.21 g-Hg/Mg for STS combustion, 0.077 g-Hg/Mg for STS with waste plastics, 0.724 g-Hg/Mg for industrial waste mixtures, 0.028 g-Hg/Mg for waste plastic combustion, and 0.0026 g-Hg/Mg for woody waste combustion. All emission factors evaluated in this study were comparable or lower than other reported data. Emission inventory using old emission factors likely causes an overestimation.

Implications Although waste combustion is one of major anthropogenic sources of atmospheric mercury emission, estimated emission might have large uncertainty due to great heterogeneity of wastes. This study investigated speciated mercury emissions from the combustions of municipal solid wastes, sewage treatment sludge with/without waste plastics, industrial waste mixtures, waste plastics from construction demolition, and woody wastes using continuous monitoring devices. Reactive gaseous mercury was the major form in all combustion cases and its concentration in the gas had large fluctuation. All emission factors evaluated in this study were comparable or lower than other reported data. Emission inventory using old emission factors likely causes an overestimation.