Online determination of polycyclic aromatic hydrocarbon formation from a flame soot generator.

In this study, we produced a class of diffusion flame soot particles with varying chemical and physical properties by using the mini-Combustion Aerosol STandard (CAST) and applying varying oxidant gas flow rates under constant propane, quenching, and dilution gas supply. We varied the soot properties by using the following fuel-to-air equivalence ratios (Φ): 1.13, 1.09, 1.04, 1.00, 0.96, and 0.89. Within this Φ range, we observed drastic changes in the physical and chemical properties of the soot. Oxidant-rich flames (Φ < 1) were characterized by larger particle size, lower particle number concentration, higher black carbon (BC) concentration, lower brown carbon BrC.[BC](-1) than fuel-rich flames (Φ > 1). To investigate the polycyclic aromatic hydrocarbons (PAH) formation online, we developed a new method for quantification by using the one (13)C-containing doubly charged PAH ion in a high-resolution time-of-flight aerosol mass spectrometry (HR-ToF-AMS). The time-resolved concentration showed that the larger PAHs prevailed in the fuel-rich flames and diminished in the oxidant-rich flames. By comparison with the offline in situ derivatization-thermal-desorption gas-chromatography time-of-flight mass spectrometry (IDTD-GC-ToF-MS), we found that the concentration by using the HR-ToF-AMS was underestimated, especially for lower mass PAHs (C14-C18) in the fuel-rich flames possibly due to size limitation and degradation of semi-volatile species under high vacuum and desorption temperature in the latter. For oxidant-rich flames, the large PAHs (C20 and C22) were detected in the HR-ToF-AMS while it was not possible in IDTD-GC-ToF-MS due to matrix effect. The PAH formation was discussed based on the combination of our results and with respect to Φ settings.

Waste-to-energy incineration plants as greenhouse gas reducers: a case study of seven Japanese metropolises.

Municipal solid waste (MSW) incineration is a greenhouse gas (GHG) emitter; however, if GHG reductions, achieved by accounting for waste-to-energy, exceed GHG emissions, incineration can be considered as a net GHG reducer. In Japan, only 24.5% of MSW incineration plants perform energy recovery despite 80% of MSW being incinerated; therefore, there is great potential to extract more energy from MSW. In this study, the factors that should be considered to achieve net GHG reductions from incineration were analysed from a life cycle perspective. These considerations were then applied to the energy supply requirements in seven Japanese metropolises. Firstly, the carbon footprints of approximately 1500 incineration plants in Japan were calculated. Then, the incineration plants with negative carbon footprint values were classified as net GHG reducers. Next, the processes that contribute to the carbon footprint were evaluated, and two processes-plastic burning and electricity savings-were found to have the greatest influence. Based on the results, the energy supply requirements were analysed and discussed for seven metropolises (Sapporo, Tokyo, Nagoya, Osaka, Kobe, Takamatsu and Fukuoka) taking into account the energy demands of households. In Kobe, 16.2% of the electricity demand and 25.0% of the hot water demand could be satisfied by incineration to realise a net GHG reducer, although urban design for energy utilisation would be required.

Influence of SO2 in incineration flue gas on the sequestration of CO2 by municipal solid waste incinerator fly ash.

The influence of CO2 content and presence of SO2 on the sequestration of CO2 by municipal solid waste incinerator (MSWI) fly ash was studied by investigating the carbonation reaction of MSWI fly ash with different combinations of simulated flue gas. The reaction between fly ash and 100% CO2 was relatively fast; the uptake of CO2 reached 87 g CO2/kg ash, and the sequestered CO2 could be entirely released at high temperatures. When CO2 content was reduced to 12%, the reaction rate decreased; the uptake fell to 41 g CO2/kg ash, and 70.7% of the sequestered CO2 could be released. With 12% CO2 in the presence of SO2, the reaction rate significantly decreased; the uptake was just 17 g CO2/kg ash, and only 52.9% of the sequestered CO2 could be released. SO2 in the simulated gas restricted the ability of fly ash to sequester CO2 because it blocked the pores of the ash.

Greenhouse gas accounting of the proposed landfill extension and advanced incineration facility for municipal solid waste management in Hong Kong.

The burgeoning of municipal solid waste (MSW) disposal issue and climate change have drawn massive attention from people. On the one hand, Hong Kong is facing a controversial debate over the implementation of proposed landfill extension (LFE) and advanced incineration facility (AIF) to curb the MSW disposal issue. On the other hand, the Hong Kong Special Administrative Region Government is taking concerted efforts to reduce the carbon intensity in this region. This paper discusses the greenhouse gas (GHG) emissions from four proposed waste disposal scenarios, covering the proposed LFE and AIF within a defined system boundary. On the basis of the data collected, assumptions made, and system boundary defined in this study, the results indicate that AIF releases less GHG emissions than LFE. The GHG emissions from LFE are highly contributed by the landfill methane (CH4) emissions but offset by biogenic carbon storage, while the GHG emissions from AIF are mostly due to the stack discharge system but offset by the energy recovery system. Furthermore, parametric sensitivity analyses show that GHG emissions are strongly dependent on the landfill CH4 recovery rate, types of electricity displaced by energy recovery systems, and the heating value of MSW, altering the order of preferred waste disposal scenarios. This evaluation provides valuable insights into the applicability of a policy framework for MSW management practices in reducing GHG emissions.

The impact of incinerators on human health and environment.

Of the total wastes generated by health-care organizations, 10%-25% are biomedical wastes, which are hazardous to humans and the environment and requires specific treatment and management. For decades, incineration was the method of choice for the treatment of such infectious wastes. Incinerator releases a wide variety of pollutants depending on the composition of the waste, which leads to health deterioration and environmental degradation. The significant pollutants emitted are particulate matter, metals, acid gases, oxides of nitrogen, and sulfur, aside from the release of innumerable substances of unknown toxicity. This process of waste incineration poses a significant threat to public health and the environment. The major impact on health is the higher incidence of cancer and respiratory symptoms; other potential effects are congenital abnormalities, hormonal defects, and increase in sex ratio. The effect on the environmental is in the form of global warming, acidification, photochemical ozone or smog formation, eutrophication, and human and animal toxicity. Thus, there is a need to skip to newer, widely accepted, economical, and environment-friendly technologies. The use of hydroclaves and plasma pyrolysis for the incineration of biomedical wastes leads to lesser environmental degradation, negligible health impacts, safe handling of treated wastes, lesser running and maintenance costs, more effective reduction of microorganisms, and safer disposal.

Removal of PCDD/Fs and PCBs from flue gas using a pilot gas cleaning system.

A 100 Nm3/hr capacity pilot scale dual bag filter (DBF) system was tested on the flue gas from an actual hazardous waste incinerator (HWI), the removal efficiency of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) and polychlorinated biphenyls (PCBs) was also studied. The first filter collected most of the fly ash and associated chlorinated organic; then activated carbon (AC) was injected and used to collect phase chlorinated organic from the gas. Concentrations of PCDD/Fs and PCBs after the DBF system were 0.07 and 0.01 ng TEQ/Nm3, respectively, which were both far below the national emission standard. Comparing with the original single bag filter system, the PCDD/Fs concentration dropped a lot from 0.36 to 0.07 ng TEQ/Nm3. Increasing AC feeding rate enhanced their collection efficiency, yet reduced the AC utilization efficiency, and it still needs further study to select an appropriate feeding rate in the system. These results will be useful for industrial application and assist in controlling emissions of PCDD/Fs and other persistent organic pollutions from stationary sources in China.

Hydrodynamics of a fluidized bed co-combustor for tobacco waste and coal.

The fluidization characteristics of binary mixtures containing tobacco stem (TS) and cation exchange resin (a substitute for coal) were studied in a rectangular bed with the cross-section area of 0.3 × 0.025 m(2). The presence of herbaceous biomass particles and their unique properties such as low density and high aspect ratio resulted in different fluidization behaviors. Three fluidization velocities, i.e. initial, minimum and full fluidization velocities, were observed as the TS mass fraction increased from 7% to 20%, and four hydrodynamic stages were experienced, including the static, segregation, transition and mixing stages, with increasing operational gas velocities. The results suggest that the operational gas velocity should be in the range of 2.0-5.0 times of the minimum fluidization velocity of the binary mixtures, and less than 7% TS mass fraction should be used in an existing bubbling fluidized bed. Higher TS fraction inclusion requires the introduction of central jet gas to improve the mixing effect.

Energy and greenhouse gas balances for a solid waste incineration plant: a case study.

Energy and greenhouse gas balances for a waste incineration plant (Reno-Nord I/S, Aalborg, Denmark) as a function of time over a 45-year period beginning 1960 are presented. The quantity of energy recovered from the waste increased over time due to increasing waste production, increasing lower heating value of the waste and implementation of improved energy recovery technology at the incineration plant. Greenhouse gas (GHG) balances indicated progressively increasing GHG savings during the time period investigated as a result of the increasing energy production. The GHG balances show that the Reno-Nord incineration plant has changed from a net annual GHG emission of 30 kg CO(2)-eq person(-1) year(-1) to a net annual GHG saving of 770 kg CO(2)-eq person(-1) year(-1) which is equivalent to approximately 8% of the annual emission of GHG from an average Danish person (including emissions from industry and transport). The CO(2) emissions associated with combustion of the fossil carbon contained in the waste accounted for about two-thirds of the GHG turnover when no energy recovery is applied but its contribution reduces to between 10 and 15% when energy recovery is implemented. The reason being that energy recovery is associated with a large CO(2) saving (negative emission).

Study of composition change and agglomeration of flue gas cleaning residue from a fluidized bed waste incinerator.

Blocking of the collection hoppers of the baghouse filters in a fluidized bed incinerator for co-incineration of high calorific industrial solid waste and sludge was observed. The composition of the flue gas cleaning residue (FGCR), both from a blocked hopper and from a normal hopper, was investigated by (differential) thermogravimetric analysis, quantitative X-ray powder diffraction and wet chemical analysis. The lower elemental carbon concentration and the higher calcium carbonate concentration of the agglomerated sample was the result of oxidation of carbon and subsequent reaction of CO2 with CaO. The evolved heat causes a temperature increase, with the decomposition of CaOHCl as a consequence. The formation of calcite and calcium chloride and the evolution of heat caused agglomeration of the FGCR. Activated lignite coke was replaced by another adsorption agent with less carbon, so the auto-ignition temperature increased; since then no further block formation has occurred.

Mass balance for POPs in hazardous and municipal solid waste incinerators.

The amount of different persistent organic pollutants (POPs) in the input of waste incinerators was compared to that in the output. Three cases were considered: a rotary kiln incinerating hazardous waste, a grate furnace incinerating municipal solid waste (MSW) and the same grate furnace co-incinerating plastics of waste of electrical and electronic equipment (WEEE) and automotive shredder residue (ASR) with MSW. The mass balance for PCBs in the rotary kiln indicates that these POPs are destroyed effectively during incineration. The grate furnace can be a sink or source of PCDD/Fs and PCBs depending on the concentrations in the incinerated waste. In order to compare the total amount of POPs in input and output, a methodology was developed whereby the amount of POPs was weighed according to minimal risk doses (MRDs) or cancer potency factors. For both incinerators the PCDD/Fs, PCBs and polyaromatic hydrocarbons (PAHs) are the main contributors to total weighed POP output. In MSW, the PCDD/Fs, PBDD/Fs and polybrominated diphenylethers (PBDEs) are the main contributors to the weighed POP input. The ratios of the weighed POP-input over -output clearly indicate that the rotary kiln incinerating hazardous waste is a weighed POP sink. The grate furnace incinerating MSW is a weighed POP sink or source depending on the POP-concentrations in the waste, but the difference between output and input is rather limited. When e.g. ASR and plastics of WEEE, containing high concentrations of PBDEs and PCBs, are co-incinerated in the grate furnace, it is clearly a weighed POP sink.

Performance of a flameless combustion furnace using biogas and natural gas.

Flameless combustion technology has proved to be flexible regarding the utilization of conventional fuels. This flexibility is associated with the main characteristic of the combustion regime, which is the mixing of the reactants above the autoignition temperature of the fuel. Flameless combustion advantages when using conventional fuels are a proven fact. However, it is necessary to assess thermal equipments performance when utilizing bio-fuels, which usually are obtained from biomass gasification and the excreta of animals in bio-digesters. The effect of using biogas on the performance of an experimental furnace equipped with a self-regenerative Flameless burner is reported in this paper. All the results were compared to the performance of the system fueled with natural gas. Results showed that temperature field and uniformity are similar for both fuels; although biogas temperatures were slightly lower due to the larger amount of inert gases (CO(2)) in its composition that cool down the reactions. Species patterns and pollutant emissions showed similar trends and values for both fuels, and the energy balance for biogas showed a minor reduction of the efficiency of the furnace; this confirms that Flameless combustion is highly flexible to burn conventional and diluted fuels. Important modifications on the burner were not necessary to run the system using biogas. Additionally, in order to highlight the advantages of the Flameless combustion regime, some comparisons of the burner performance working in Flameless mode and working in conventional mode are presented.

Numerical modelling of the memory effect in wet scrubbers.

Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) can be absorbed in and desorbed from polypropylene (PP) tower packings in wet scrubbers utilized in waste incineration lines. This behaviour, also known as the memory effect, has been modelled using a gas phase-PP surface equilibrium and a numerical solid phase diffusion model describing the transport of PCDD/Fs inside the PP. The diffusivities and gas-PP partition coefficients of TCDD/F to HxCDD/Fs in PP have been estimated using the numerical model. Two incineration lines were modelled. In the first line, the absorption and desorption in PP test rods was followed before and after installation of a fabric filter that was placed before a wet scrubber. In the second incineration line, the accumulation of PCDD/Fs in a wet scrubber during start up periods and the subsequent decline during the following three months was modelled and compared to continuous two-week gas measurements after the scrubber. The obtained diffusivities in PP range from 10(-13) m(2)/s for TCDD to 10(-16) m(2)/s for HxCDD. Lower chlorinated homologues with a distinctive change in concentrations during the desorption period (e.g. TCDF) are easier to model, and show the best agreement between the two incineration lines.

Investigations of ash fouling with cattle wastes as reburn fuel in a small-scale boiler burner under transient conditions.

Fouling behavior under reburn conditions was investigated with cattle wastes (termed as feedlot biomass [FB]) and coal as reburn fuels under a transient condition and short-time operation. A small-scale (30 kW or 100,000 Btu/hr) boiler burner research facility was used for the reburn experiments. The fuels considered for these experiments were natural gas (NG) for the ashless case, pure coal, pure FB, and blends of coal and FB. Two parameters that were used to characterize the ash "fouling" were (1) the overall heat-transfer coefficient (OHTC) when burning NG and solid fuels as reburn fuels, and (2) the combustible loss through ash deposited on the surfaces of heat exchanger tubes and the bottom ash in the ash port. A new methodology is presented for determining ash-fouling behavior under transient conditions. Results on the OHTCs for solid reburn fuels are compared with the OHTCs for NG. It was found that the growth of the layer of ash depositions over longer periods typically lowers OHTC, and the increased concentration of ash in gas phase promotes radiation in high-temperature zones during initial periods while decreasing the heat transfer in low-temperature zones. The ash analyses indicated that the bottom ash in the ash port contained a smaller percentage of combustibles with a higher FB percentage in the fuels, indicating better performance compared with coal because small particles in FB burn faster and the FB has higher volatile matter on a dry ash-free basis promoting more burn out.

Combustion characteristics of simulated gas fuel in a 30 kg/h scale pyrolysis-melting incinerator.

Combustion characteristics of gas fuel in a pyrolysis-melting incinerator having a 30 kg/h capacity were investigated. Pyrolyzed gas from waste was simulated by propane that was injected in the combustion chamber, and burnt through multi-staged combustion by distributing the combustion air to primary, secondary, and tertiary air nozzles. Temperatures and the concentrations of gas components in the combustion chamber were measured. Combustion performance was evaluated with respect to the temperature distribution and combustion gas concentrations of O2, CO and NOx. Using secondary air and/or tertiary air, the combustion performance was improved, and, in particular, NOx concentration decreased significantly following the tertiary air injection.

Performance of CaO and MgO for the hot gas clean up in gasification of a chlorine-containing (RDF) feedstock.

Calcined limestone (CaO) and calcined dolomite (CaO.MgO) were tested at bench scale to study their usefulness in cleaning hot raw gas from a fluidized bed gasifier of a synthetic or simulated refuse-derived fuel (RDF) with a high (3 wt%) content in chlorine. In the gas cleaning reactor two main reactions occurred simultaneously: the elimination of HCl and the elimination of tar by steam reforming. The elimination of HCl formed CaCl2 and MgCl2 with melting points below the high (above 800 degrees C) temperatures required for the simultaneous tar elimination reaction. So, the CaO-based particles progressively melted and the catalytic gas cleaning reactor became a compact, agglomerated or glued, cake. Therefore, the life and usefulness of the CaO-based solids used was very low. Nevertheless, and to further avoid these problems, some positive guidelines for future research are proposed here.

Experimental study on flue gas purifying of MSW incineration using in-pipe jet adsorption techniques.

This paper presents the experimental research process and results about flue gas purifying of municipal solid wastes (MSW) incineration using in-pipe jet adsorption techniques. MSW incineration was carried out in a fluidized bed test rig, and the flue gas purifying was carried out in an in-pipe jet adsorption test rig. The experimental results are as follows: when the feedstock of activated carbon is 1.6g/Nm(3), the desulfurization efficiency is 83%, the denitrification efficiency is 41%, and the dechlorination efficiency is 27%. The order of purifying effect of the three kinds of adsorbents on acidic gases from MSW incineration is activated carbon>activated bauxite>kaolin. Comparison of adsorption capabilities of the three kinds of adsorbents to heavy metals shows that activated carbon is the best additive to remove Cd, Pb and Cu, kaolin is inferior, and activated bauxite is the worst one. However, activated bauxite is the best additive to remove Hg, and it can remove Cd effectively. PAHs in fly ash are dominated by three-, four-, and five-ringed PAHs, and PAHs in the flue gas mainly include three- and four-ringed PAHs. When the injected quantity of additive is constant, the order of cleaning effect on PAHs is kaolin>activated carbon>activated bauxite. These three kinds of adsorbents have different purifying effects on acidic gases, heavy metals and PAHs in the flue gas from MSW incineration. In general, activated carbon has a better adsorption capability.

Health risk assessment of air emissions from a municipal solid waste incineration plant--a case study.

A health risk assessment of long-term emissions of carcinogenic and non-carcinogenic air pollutants has been carried out for the municipal solid waste incinerator (MSWI) of the city of Taranto, Italy. Ground level air concentrations and soil deposition of carcinogenic (Polychlorinated Dibenzo-p-Dioxins/Furans and Cd) and non-carcinogenic (Pb and Hg) pollutants have been estimated using a well documented atmospheric dispersion model. Health risk values for air inhalation, dermal contact, soil and food ingestion have been calculated based on a combination of these concentrations and a matrix of environmental exposure factors. Exposure of the surrounding population has been addressed for different release scenarios based on four pollutants, four exposure pathways and two receptor groups (children and adults). Spatial risk distribution and cancer excess cases projected from plant emissions have been compared with background mortality records. Estimated results based on the MSWI emissions show: (1) individual risks well below maximum acceptable levels, (2) very small incremental cancer risk compared with background level.

Cytotoxicity of the exhaust gas from a thermal reactor of MSWI baghouse ash.

Baghouse ash from municipal solid waste incineration (MSWI) plant was heated from 25 degrees C to 800 degrees C under nitrogen in a fixed-bed reactor. The exhaust gas was passed sequentially through water, acetone and cyclohexane. The cytotoxicity testing of the three adsorbates was done with the MRC-5 cell line and the percentage cell survival was determined by 3-(4,5-dimethylthiazol-2-yl)-5(3-carboxymethoxyphenol)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) analysis. The highest level of toxicity of the exhaust gas was observed at 500 degrees C. The total cytotoxicity of the three adsorbates at any treatment temperature was found to be a function of the sum of organic carbon (TOC), inorganic carbon (IC) and molecular chlorine (Cl(2)), of which, molecular chlorine was quantitatively the greatest.

The benefits of flue gas recirculation in waste incineration.

Flue gas recirculation in the incinerator combustion chamber is an operative technique that offers substantial benefits in managing waste incineration. The advantages that can be obtained are both economic and environmental and are determined by the low flow rate of fumes actually emitted if compared to the flue gas released when recirculation is not conducted. Simulations of two incineration processes, with and without flue gas recirculation, have been carried out by using a commercial flowsheeting simulator. The results of the simulations demonstrate that, from an economic point of view, the proposed technique permits a greater level of energy recovery (up to +3%) and, at the same time, lower investment costs as far as the equipment and machinery constituting the air pollution control section of the plant are concerned. At equal treatment system efficiencies, the environmental benefits stem from the decrease in the emission of atmospheric pollutants. Throughout the paper reference is made to the EC legislation in the field of environmental protection, thus ensuring the general validity in the EU of the foundations laid and conclusions drawn henceforth. A numerical example concerning mercury emission quantifies the reported considerations and illustrates that flue gas recirculation reduces emission of this pollutant by 50%.