Abstract: Bottom ash from municipal solid waste incinerator plants in Catalonia was characterised to investigate some alternatives for its utilisation and their potential environmental impact. After a detailed chemical and mineralogical characterisation, physical and geotechnical properties were investigated. The study focused on the use of bottom ash as an aggregate substitute in pavement applications. The results show that this material may be successfully used as a compacted material in unbound road sub-bases. According to Spanish Specifications for road construction, bottom ash complies with the technical requirements for sub-bases. Data obtained from the leaching test satisfy the limit values established by Catalan Specifications for bottom ash utilisation. The use of bottom ash in the envisaged application should therefore not result in any environmental impact. © 2002 Society of Chemical Industry

Abstract: Coal-burning power plants in Turkey produce large quantities of coal-related wastes, which are collected through the use of various systems. Coal ash is presently accumulating in Turkey at a rate in excess of 10 million tons (t) annually. Roughly 1% of this is being used in a variety of products such as concrete, aggregate in stabilizing roadways, etc. When coal is burned, loss of material results in an increased concentration of most radionuclides found in the waste material. The object of this study is to analyze radiochemical element concentration of coal, bottom ash, and fly ash, and to evaluate the gross radium isotope activities in groundwaters around Yatagan Thermal Power Plant. The results show that the waste disposal site near the thermal power plant contains a major enhancement of radioactivity.

Abstract: Coal bottom ash produced from a thermal power plant was used in a batch experiment to investigate the adsorption characteristic of this bottom ash. The adsorbate solutions were synthetic wastewaters contained copper (Cu2+) or COD and a sanitary landfill leachate. The influences of various factors, such as contact time, pH, initial adsorbate concentration and temperature on the sorption have been studied. Experimental results show that coal bottom ash had a good adsorption capacity for copper and COD and could reduce the concentrations of various pollutants in the leachate. The adsorption capacities of each gram of coal bottom ash were 0.48 mg Cu (at pH 4 and temperature 25°C) and 7.5 mg COD (at pH 5 and temperature 25°C); their adsorption behaviors conformed to Freundlich's adsorption model. In treating leachate, the removal efficiencies of COD, NH3–N, total Kjeldah nitrogen, phosphorus, Fe3+, Mn2+ and Zn2+ were 47, 39.4, 31.1, 92.9, 96.5, 94.3 and 82.2%, respectively. Based on these results we c...

Abstract: A number of the more important environmental impacts of the operation of large coal-fired power plants are associated with the very large quantities of solid materials resulting from these processes. These are, principally: coal ash residues, and solid residues of flue gas desulfurisation processes. By far the greater proportion of these materials, generally around 80% of the total solid discards from the electricity supply industry, comprise fly ash from the particulate collection equipment and bottom ash from the hoppers under the economisers and air preheaters of large pulverised coal boilers. The utilisation and disposal of the fly ash residues has been the subject of a great deal of development activity over many decades. In the main, the emphasis has been on the increased use of fly ash materials in high volumes, as constituents of cements and mortars, or for the manufacture of concrete and aggregate materials. The unsold ashes are used for land reclamation and for beneficial landfill, wherever possible. In recent years, there has been increasing interest in the processing of boiler fly ashes to improve ash quality and consistency, and in the manufacture of high-value secondary products. The utilisation of power station fly ashes depends on their physical and chemical properties, and there have been a number of recent developments in power plant design and operation, which have resulted in significant changes in the characteristics of fly ashes, eg the progressive introduction of NO x emission control technologies and in-furnace NO x reduction technologies. The increasing interest in the co-firing of non-conventional fuels such as petroleum coke and biomass/waste materials has resulted in the production of mixed and more complex materials. The paper will present a review of the major developments, which can affect coal fly ash quality and discuss the impact of these issues on the utilisation of fly ashes as feed materials for the manufacture of high-value secondary products.

Abstract: This report discusses greenhouse gas emissions from the cement industry, and opportunities for CO{sub 2} management. Cement-related greenhouse gas emissions originate from fossil fuel combustion at cement manufacturing operations (about 40% of the industry's emissions), transport activities (about 5%) and the combustion of fossil fuel that is required to make the electricity consumed by the cement manufacturing operations (about 5%). The remaining cement-related emissions (about 50%) originate from the manufacturing process that converts limestone (CaCO{sub 3}) to calcium oxide (CaO), the primary precursor to cement. It is chemically impossible to convert CaCO{sub 3} to CaO, and then cement clinker, without generating CO{sub 2}. The report favourably projects the use of fly ash blended cements as a conventional CO{sub 2} management approach. The report states that the use of pozzolans, such as blast furnace slag, fly ash, and natural pozzolans for clinker substantially reduces process-related CO{sub 2} emissions. It represents one of the best technically proven approaches for reducing process emissions. The report further suggests advanced CO{sub 2} management options such as 'Hybrid Energy-Cement Plants' in which the fly ash and bottom ash may be converted to cement clinker. 29 refs., 19 figs., 13 tabs., 1 app.

Abstract: Coal ashes produced in coal-fired power plant could be converted into zeolites and can be used as low-cost adsorbents for the treatment of effluents contaminated with high levels of toxic metals. The capacity of synthetic zeolites for the removal of cadmium, zinc and copper ions from aqueous solutions has been investigated under different operating conditions. Zeolite from bottom chimney showed higher removal efficiency for metals ions than zeolite from feed hopper and mixing mill. The results indicated that the treated bottom ash could be applied in environmental technology as an immobilizer of pollutants.

Abstract: This paper reports a laboratory study investigating the use of incinerator bottom ash (IBA) as cement bound material (CBM) for use in sub-base and roadbase layers Engineering properties associated with its use are determined and practical limits on IBA content discussed It was found that IBA could be practically used in proportions of 40% or more by mass for all CBM categories defined in the UK Highway specification However, the use of IBA as aggregate in CBM required higher cement contents to achieve the same compressive and tensile strength Tests carried out to confirm that leachable constituents were bound in the mixture and raised no environmental concern were carried out by comparing the results of tank leach tests with a one-dimensional model It was observed that despite the tests and models being designed to maximise release of species, that leachates were well within typical regulatory drinking limits

Abstract: A hydrometallurgical circuit process combining the leaching of metals with the electrolytic regeneration of the mass separating agent is an option to effectively treat heavy metal contaminated solids. This process aims towards a dosed loop utilisation of the extractant by its regeneration and recycling, enabling the use of high cost extractants and the recovery of the heavy metals as well. The circuit process, in which each cycle consists of an extraction step followed by the electrolytic regeneration of the mass separating agent and a second extraction to finally recycle the separating agent and start a new cycle, was applied on a lead contaminated soil from an accumulator manufacturing facility and for the removal of copper from a municipal solid waste incinerator bottom ash. For the first case a 0.13 M citrate solution was used at a pH of 5; for the second 10%; sulphuric acid (pH=0.5). The results showed that above 80% of lead and copper were removed from soil and ash, respectively, when the concentration of mass separating agent was controlled and kept constant. The extraction efficiency of metals from the solid materials was in the same range as the one obtained by two extaction steps using fresh extracting agent. However, due to losses of the mass separating agent the operation in a complete closed loop configuration was not possible. Nevertheless, a substantial reduction in separating agent consumption was achieved. The process proved to be suitable for treating highly contaminated materials, for which the operation parameters of extraction and regeneration are more favourable, also increasing the recovery of metals.

Abstract: Two experiments were performed with an atmospheric circulating fluidized bed gasifier (ACFBG), the first with pelletized straw and the second with loose straw, to investigate the occurrence of polycyclic aromatic hydrocarbons (PAHs), chlorophenols (ClPhs), polychlorinated biphenyls (PCBs), polychlorinated benzenes (ClBzs), polychlorinated dibenzo-p-dioxins (PCDDs), and polychlorinated dibenzofurans (PCDFs) in the bottom ash and fly ash formed during gasification. Only PAHs were present in large amounts, and only in the fly ash, ranging from 300 to 555 mg/kg ash in the tests with pelletized straw and from 73 to 118 mg/kg ash in those with loose straw. These amounts are so high that environmentally safe disposal or reuse of the ash would be difficult, so the development of a technique to handle the problem was included in the project. The method investigated was to burn the fly ash in a circulating fluidized bed (CFB) boiler in order to destroy the PAHs. This worked surprisingly well, eliminating 99% of the...

Abstract: In this paper, we first develop a new numerical scheme for a computational fluid dynamics code and then investigate the impact of the airflow configuration on the performance of a 300 MW tangentially fired furnace by both simulations and experiments. Four different secondary and two tertiary air arrangements are tested. It is shown that the newly developed 27-point discrete scheme enhances the performance of the code, offering a satisfactory prediction of the velocity field for the isothermal furnace flow. Further effort is made to examine the effects of airflow configuration on combustion performance, outlet temperature deviation, and heat loss due to combustibles in the bottom ash. Both simulations and operation trials suggest that, for the furnace investigated, when firing bituminous coal, the double V-shaped secondary air configuration has the best performance.

Abstract: A method of removing carbon from fly ash may include introducing the fly ash into one of a plurality of interconnected vertically stacked hearths of a multiple hearth furnace, heating the fly ash, exposing the fly ash to oxygen, allowing at least a portion of the carbon in the fly ash to undergo combustion, and conveying the fly ash to another of the plurality of interconnected vertically stacked hearths.

Abstract: Previous research has shown that the natural cycle of minerals within the process of energy production from biomass is disturbed by deposition of heavy metals on the forest ecosystem. By separating a side stream rich in heavy metals (filter fly-ash) it should be possible to recycle the major part of the ashes produced (usable ash – a mixture of bottom ash and cyclone fly-ash). The aims of technological development are to reduce heavy-metal concentrations in the usable ash and to upgrade them in the filter fly-ash by implementing primary measures during the combustion process. In the first phase of the present research project large-scale tests were carried out in a state-of-the-art biomass combustion plant. The results have shown that some variables have a significant influence on the Cd and Zn fluxes. These variables include the reducing potential of the gaseous phase around the ash particles, the temperature of ash precipitation in an oxidizing atmosphere and the size of the ash particles at temperatures below 800 °C. Based on these results a new combustion technology with integrated fractionated heavy-metal separation was developed. In order to achieve reducing conditions in the primary combustion zone an "air staging" technology was implemented. Part of the flyash is precipitated at high temperatures in a relaxation zone in the secondary combustion chamber and in a high-temperature cyclone placed before the boiler. The filter fly-ash rich in heavy metals is efficiently precipitated in a flue-gas condensation unit followed by an aerosol electrostatic filter. The new combustion technology was realized in a biomass district heating plant in Austria. The results of test runs carried out at the new plant show a high fractionation potential of Cd and Zn under reducing conditions. On an average the bottom ash produced in the new plant contains 27 times less Cd and 5 times less Zn than the respective ash fraction generated by state-of-the-art plants. In hot-precipitated flyashes the levels of Cd are 5 to 15 times lower than in fly ashes generated in multicyclones, whereas the fractionation potential of Zn is low. Furthermore, the amount of filter fly-ash with high heavy metal content increased due to the lower precipitation efficiency of the hot cyclone as compared to multi-cyclones. Therefore, hot cyclones are considered not efficient enough for fractionated heavy metal separation. Future research and development will especially focus on the high fractionation potential for volatile heavy metals under reducing conditions.

Abstract: A process for the production of a slurry of bottom ashes from incineration of Municipal Solid Wastes (MSW) and the use thereof in the manufacture of cement mixes with improved properties.

Abstract: One of the main problems involved in straw combustion is related to the behaviour and fate of the ash forming inorganic species contained in the fuel. These elements can end up in fly ash‚ bottom ash or may be incorporated in various types of deposits. The inorganic species in straw either occur disseminated or ionically bound in the organic structure‚ are located in inorganic straw constituents or they are constituents of terrigeneuos dirt that is incorporated in the straw during harvesting and handling. Clearly the fate of the inorganic species during combustion depends on their mode of occurence in the straw. Knowledge of straw ash composition and melting behaviour is important to be able to predict‚ at least to some extent‚ the fate of the inorganic elements in terms of practical operation of boilers. The aim is to be able to predict and possibly avoid formation of troublesome deposits and potential corrosion. Additionally‚ knowledge of straw ash compositions and morphology is useful in terms of possible utilization or disposal of the ash. This paper presents part of a project that aims to acquire knowledge about the formation‚ composition and physical-chemical behaviour of ash from combustion of straw and co-combustion of straw and coal. One of the goals is to develop or modify useful analysis techniques for straw ash characterization. The techniques utilized in the project involves Computer Controlled Scanning Electron Microscopy (CCSEM)‚ High Temperature Light Microscopy (HTLM) (Hjuler‚ 1997) and Simultaneous Thermal Analysis (STA) (Hansen‚ 1997). The CCSEM analysis provides information of the composition and morphology of the ash whereas HTLM and STA provides information about melting temperatures and melting behaviour. The combined data on composition and melting