Abstract: Municipal (bottom ash and glass cullet coming from the municipal solid waste incineration and a community glass recycling program, respectively) and industrial (steel fly ash) wastes are particularly suitable to be subjected to a vitrification/devitrification process, leading to the production of alkaline and alkaline-earth silicate differently colored glasses with good chemical properties, capable to be transformed into surface nucleated basaltic glass-ceramics. These materials were investigated by means of differential thermal analysis, durability and release tests, X-ray diffraction and scanning electron microscopy.

Abstract: Laboratory experiments with synthetic samples are conducted to obtain information on the evaporation behavior of metals in incinerators. In combining the results obtained through field measurements presented in a companion paper in this issue, hypotheses are postulated on the influence of physical and chemical conditions as well as of kinetics on the evaporation behavior of the chosen elements in the furnace bed. These are validated by thermal treatment of bottom ash samples in the laboratory. A temperature increase of from 500 °C to 900 °C causes higher transfers of most metals into the gaseous phase. Mo and Sb are the exceptions. Chlorine availability generally favors evaporation. Increasing oxidative conditions cause lower Sn transfers. Transfer of the elements Cd, Mo, Sb, Sn, and Zn is negatively affected by their reaction with reaction partners other than oxygen and chlorine occurring in municipal solid waste. Oxidation of organic carbon to CO and CO2 as well as HCl formation determine the distributi...

Abstract: Fluidized-bed combustion has been increasingly applied for combustion of low-grade fuels, such as solid biomass and waste, Sometimes the use of certain fuels may be limited due to unanticipated deposition and corrosion in the boiler. Consequently, mechanistic understanding of the behavior of ash-forming compounds in Hindized-bed combustion is crucial for further increase in the use of fluidized-bed combustion for biomass and waste fuels. The mechanisms of ash formation during circulating fluidized-bed combustion of two wood-based biomass fuels, forest residue and willow were determined experimentally at a 35 MW cogeneration plant. In-duct fly ash samples were collected in two locations in the boiler. The fly ash particle mass size distributions were determined with a low-pressure impactor. In addition, samples of fly ash from electrostatic precipitator (ESP) hoppers. bottom ash, sand, and fuels were collected periodically for analysis. Flue gas composition and process parameters were monitored throughout the experiments. Approximately 25% of the ash was removed from the furnace as bottom ash The bottom ash was found to be formed by deposition of the ash particles on the surface of the quartz sand and by diffusion of the ash compounds into the sand. Fly ash consisted of two distinctly different modes. Fine fly ash particle mode was formed hynucleation of volatilized species and contained mainly KCL and K2SO4 during combustion of forest residue and willow, respectively, Coarse fly ash mode contained particles which were irregular agglomerales and they were formed from the non-volatile ash species by coalescence and agglomeration inside the char particles and on their surfaces. The agglomerate structure of the coarse ash was effective in capturing volatile species in coarse particles, and it may have a significant effect on the deposition tendency of the particles.

Abstract: A system for combustion and removal of residual carbon within fly ash particles in which the fly ash particles are fed into an array of process units for combustion. The fly ash particles are subjected to heat and motive air such that as the fly ash particles pass through the particulate bed, they are heated to a sufficient temperature to cause the combustion of the residual carbon within the particles. The fly ash particles thereafter are conveyed in a dilute phase for further combustion through the reactor chamber away from the particulate bed and exhausted to an ash capture. The fly ash is then separated from the exhaust air that conveys the ash in its dilute phase with the air being further exhausted and the captured fly ash particles being fed to a feed accumulator for re-injection to the reactor chamber or discharge for further processing.

Abstract: Electricity generation from biomass is an attractive option from an environmental perspective. Pilot studies have indicated that alfalfa (Medicago sativa L.) stems are suitable feedstock for energy generation via gasification. Detailed information on chemical characteristics of the ash generated from gasification of alfalfa stem is required to develop environmentally and economically sound ash management strategies. Alfalfa fly and bottom ashes were characterized with respect to chemical properties that are important in developing ash management practices with emphasis on beneficial utilization as a soil amendment. Mean concentrations of total C, K, Ca, and Cl were 424, 120, 85, and 26 g kg{sup {minus}1}, respectively, in fly ash. In bottom ash, the mean concentrations of C, K, and Ca, were 63, 61, and 193 g kg{sup {minus}1}. Concentrations of total Pb, As, Cd, Co, and Se were below detection limits in both ash types. Naphthalene ranged from 6.2 to 74 mg kg{sup {minus}1}, but concentrations of many other polyaromatic hydrocarbons were low or below mg kg{sup {minus}1} detection limits. Available K and P in fly ash were 90 to 120 and 8 to 10 g kg{sup {minus}1}, respectively. Mean CaCO{sub 3} equivalent value of fly ash was 400 g kg{sup {minus}1}, itsmore » electrical conductivity (EC) and pH were 127 dS m{sup {minus}1} and 11.5, respectively. These results suggest that when managed properly, gasified alfalfa ash could potentially be utilized as a beneficial soil amendment with few potential environmental concerns.« less

Abstract: The general objective of this study is the innovative use of MSWI bottom ash as aggregates for hydraulic concretes, especially in ready to use concretes and in prefabrication. As first, a complete physical, chemical and mineralogical characterization of a MSWI bottom ash provided by the company YPREMA, was undertaken, in relation to requirements of the experimental standard XP P18-540 («Aggregates for hydraulic concretes) and environment aspects (composition and concentration of the potential pollutant by fractions). Following this characterization, the aptitude of the MSWI bottom ash to be used with the hydraulic cements (CEM I and CEM III) was evaluated in mortars. The experience with different additions allowed a meaningful treatment protocol to be defined, especially by addition of silica fume which shows a relatively fast set of the mixture and good mechanical resistance. Concretes were first formulated using a CEM I with silica fume. Concretes with a silico-alumineous fly ash, a pouzzolan cement CEM IV/B and a diatomaceous powder were then studied. Results show the possibility of obtaining plastic B20 and B25 concretes with a partial or total replacement of natural aggregates by MSWI bottom ash.

Abstract: A method and apparatus for the application of heat to remove ammonia compounds from fly ash, thereby making the fly ash a marketable product is disclosed. The method includes the steps of providing an amount of fly ash wherein at least a portion of the amount of fly ash comprises particulates having ammonia compounds affixed to the particulates, and exposing the fly ash to flowing air having a temperature of at least 1,500 °F (815 °C) such that the fly ash is maintained in the flowing air until the fly ash reaches a temperature of at least 900 °F (482 °C). The apparatus (8, 9) includes a source of fly ash (10) comprising particulates having ammonia compounds affixed to at least some of the fly ash particulates, a heating chamber (17) including a treatment bed comprising a floor (20) having openings, a fly ash supply conduit (16) in communication with the heating chamber (17) and the source of fly ash (10) for transferring fly ash from the source of fly ash to the treatment bed of the heating chamber, a source of heated air (45), an air supply conduit (55) in communication with the source of heated of heated air (45) and the heating chamber (17) for providing a flow of heated air to the treatment bed of the heating chamber for contacting the fly ash on the treatment bed with the flow of heated air, a heated air conduit (27) in communication with the heating chamber (17) for transferring the flow of heated air form the heating chamber, and an ash removal conduit (31) in communication with the heating chamber (17) for transferring heated fly ash from the heating chamber.

Abstract: Municipal solid waste incineration bottom ash is a highly reactive material, especially toward atmospheric CO 2 , which is why we decided to carry out rapid and simple tests combining accelerated ageing and batch leaching to forecast the long-term behaviour of bottom-ash samples of various origins. By speeding up one of the major reactions, i.e. the carbonation that occurs during the natural maturation of bottom ash, it was possible to determine the maximum pollutant release of the elements (metals, sulphates) most detrimental to upgrading. The final products present higher calcite contents and are characterized by a reduction in leachate metals and an increase in leachate sulphates. The laboratory results are in agreement with a full-scale field study carried out elsewhere. Thermodynamic calculations were also undertaken to determine the cause of the high exothermicity evidenced during the tests because, even though the oxidation of metals (Fe, Al) is mainly invoked to explain the general increase of bottom-ash temperature during maturation, the contribution of the carbonation reactions (with portlandite, wairakite, larnite anorthite) cannot be ignored.

Abstract: This paper discusses the observations made during erosive wear testing of a high-carbon steel (0.65% C) in coal and bottom-ash slurries. The slurry was made by separately dispersing 30% coal and bottom ash (collected from a thermal power plant) in tap water. The tests were performed using a sample rotation method in the slurry at a fixed linear velocity of 5 m/s for different traversal distances at room temperature. To see the influence of microstructural features on slurry wear response, the steel was subjected to hardening and annealing heat treatments. Test results indicate that material loss of the specimens increased with traversal distance in all cases. Further, the hardened steel showed a lower rate of material loss when compared with steel in an annealed condition in either of the test environments. Moreover, irrespective of heat-treatment conditions, the samples revealed significantly higher material loss when tested in the bottom-ash slurry than in the coal slurry. The higher rate of material removal in the case of the former was attributed to the more efficient transfer of the kinetic energy of the moving (hard) bottom-ash particles to the specimen surface than in the case of the softer coal particles. Fracture of coal particles as a result of impact during the course of slurry erosion further supported the view. Results have been explained on the basis of the characteristics of the affected surfaces and changes in the morphology of the erodent particles after the test.

Abstract: The amount of bottom ash resulting from solid waste incineration typically ranges from 30 to 35% of burnt waste. Although such a residue stream is not classified as a hazardous waste according to the European waste catalogue, disposal of bottom ash may heavily weigh on the overall incineration costs. Furthermore, the present tendency for solid waste management in industrialised countries is towards reduction of the amount of wastes to be landfilled. With a view to that, technical approaches aimed at reusing residual streams in industrial applications as secondary materials must be strongly encouraged. As far as bottom ash is concerned, a promising option is represented by blended cement formulation. Bottom ash is indeed characterised by the presence of oxides and aluminosilicates, which might be responsible for strength development during cement hydration. In some cases, depending both on the composition of the original waste and on the combustion technology adopted, bottom ash may also exhibit pozzolanic activity. It is well known that the properties of hardened cement mixtures made with impuritiesbearing materials are strongly affected by the physical-chemical characteristics of the components, as well as the waste/cement dosage. This paper presents the results of an experimental investigation on the behaviour of mixtures made with Portland cement and bottom ash coming from an Italian medical waste incinerator. In particular, the influence of waste/binder replacement levels and water/solids ratios on strength development and acid neutralisation capacity was investigated. Different samples were prepared at low and high waste/binder ratios at various amounts of added water in each mixture. Physical properties consisting of setting time, unconfined compressive strength and evaporable water content were measured at different ages. Also, the acid neutralisation capacity of the hardened material was evaluated in order to investigate the leaching behaviour under different pH conditions. In order to quantify to what extent do the above parameters affect the properties of the solidified products, a factorial design was arranged and the analysis of variance carried out.

Abstract: The composition of water leachable organics in municipal solid waste incineration (MSWI) residues is not well known. Therefore the utilisation of ashes is restricted due to the concern about their long-term environmental impact. Previous studies have focused on some highly toxic organic compounds present only in trace amounts. It is also important to know the composition of the bulk organic matter since dissolved organic carbon can alter the leachability of metals. In order to characterise water leachable organic matter in incineration residues a fractionation procedure using polymeric adsorbents was successfully developed and applied. The technique uses XAD-8 and XAD-4 resins in tandem and has been implemented on bottom ash samples from two incineration plants in Sweden in order to characterise the bulk organic matter.

Abstract: The use of bottom ash in road construction as an aggregate for both roadway surfaces and base courses has been limited because of its absorbency and friability. The former tends to increase asphalt binder demand, and the latter adversely affects its ability to withstand the crushing effects of traffic loads. Nevertheless, bottom ash is lighter in weight and generally much cheaper than conventional quality aggregates such as crushed limestone, sand, and gravel. Research was undertaken to upgrade the load-bearing characteristics of bottom ash and maximize its use in asphaltic concrete mixtures through sulfur modification. The process essentially coats the ash with liquid sulfur, which, upon cooling, fills the voids on the surface of the particles while increasing their crushing resistance. The results of laboratory investigations indicate that asphaltic concrete mixture designs in which bottom ash represents 50 to 100 percent of the aggregate fraction can be achieved. Sulfur-modified bottom ash (SMBA) mixtu...

Abstract: Oxychloride systems are very important in the disposal of ashes generated from municipal wastes. The alkali metal-oxychloride system is a basic system of secondary fly ash generated in the process to reduce the volume of bottom ash and fly ash from incineration processes. Toxic materials such as compounds of heavy metals and dioxin may be absorbed by or contained in the secondary fly ash. In this study, the phase stability of three binary systems was examined using a chemical equilibrium technique and a new hot filament technique, and a phase diagram for the NaCl-Na2CO3 system and liquidus for the NaCl-Na2SiO3 and LiCl-Li2SiO3 systems were obtained.

Abstract: A rough estimate of the bulk organic matter composition in bottom ash was made in this study. This estimate is based on the earlier results of characterisation of aqueous and non-aqueous bottom ash leachates by different analytical techniques, such as TOC measurements, gas chromatography-mass spectrometry, size exclusion chromatography, UV-VIS spectrophotometry, fractionation on XAD resins, and also on other data presented in the literature. These results suggest that cellulose and lignin are the major organic constituents of the bottom ash. Also fractions of water-soluble high-and low-molecular-weight substances as well as a fraction of organics, extractable with non-polar organic solvents were defined. In these extractable aqueous and non-aqueous fractions a number of individual organic substances have been identified.

Abstract: The use of bottom ash in road construction as an aggregate for both roadway surfaces and base courses has been limited because of its absorbency and friability. The former tends to increase asphalt binder demand, and the latter adversely affects its ability to withstand the crushing effects of traffic loads. Nevertheless, bottom ash is lighter in weight and generally much cheaper than conventional quality aggregates such as crushed limestone, sand, and gravel. Research was undertaken to upgrade the load-bearing characteristics of bottom ash and maximize its use in asphaltic concrete mixtures through sulfur modification. The process essentially coats the ash with liquid sulfur, which, upon cooling, fills the voids on the surface of the particles while increasing their crushing resistance. The results of laboratory investigations indicate that asphaltic concrete mixture designs in which bottom ash represents 50 to 100 percent of the aggregate fraction can be achieved. Sulfur-modified bottom ash (SMBA) mixtures compare favorably with typical Texas Department of Transportation surface course mixtures in terms of strength, durability, and asphalt demand. Results of a field demonstration project in which SMBA was incorporated into hot-mix asphalt concrete are presented. An asphalt batch plant was successfully used to incorporate the sulfur into the bottom ash and produce the hot-mix asphalt concrete. The mixture was successfully placed as a 50-mm (2-in.) overlay on an existing asphalt surface at the entry to the asphalt plant facility, and adequate density was achieved with standard compaction equipment. The SMBA hot-mix overlay is currently under traffic by heavy haul trucks entering the plant facility, and early indications of performance are good.

Abstract: The invention pertains to a process for immobilising toxic metals in industrial residues, such as fly ash, bottom ash and filter cake, wherein the residues are contacted with a phosphate and a cement. The cement is added to the solid residues in such an amount that a granular product is obtained. It is preferred that the industrial residues are simultaneously contacted with a phosphate, which has a solubility in water in the range from 0.01 to 5.0 g/100ml. The treated material can be used as an aggregate or can be compressed into a compacted building material.

Abstract: The measurement of the flow rates of flyash and bottom ash from a Circulating Fluidized Bed (CFB) boiler has a number of uses. Among these are the requirements of boiler performance testing, the development of particle population models for assessing key chemical interactions taking place in the combustion chamber, and the partitioning of key species between flyash and bottom ash. Identification of partitioning of key species between flyash and bottom ash (combustibles, calcium, sulfur) can lead to improvements in key parameters of boiler operation. Current methods for the computing of the flow rates of these ash streams include the measurement of the flow rates of feed solids, one ash stream flow rate, and inference of the other from a material balance. This is effort intensive and as such, not routinely feasible. Offered here is a method for computing the flow rates of ash streams through measurement of the solids feed rates to the system, and solving material balances around inorganic solids (total ash), calcium, and/ or sulfur, using these material balances as a simple set of simultaneous equations. This method permits the calculation of the ash stream flow rates without the direct measurement of either, and can be practiced on a routine basis.