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Edward J Anthony - One of the best experts on this subject based on the ideXlab platform.
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characterization of ashes from a 100 kwth pilot scale circulating fluidized bed with oxy fuel combustion
Applied Energy, 2011Co-Authors: Chunbo Wang, Lufei Jia, Yewen Tan, Edward J AnthonyAbstract:Abstract Oxy-fuel combustion experiments have been carried out on an oxygen-fired 100 kW th mini-circulating fluidized bed combustion (CFBC) facility. Coal and petroleum coke were used as fuel together with different Limestones (and fixed Ca:S molar ratios) premixed with the fuel, for in situ SO 2 capture. The bed ash (BA) and fly ash (FA) samples produced from this unit were collected and characterized to obtain physical and chemical properties of the ash samples. The characterization methods used included X-ray fluorescence (XRF), X-ray diffraction (XRD), char carbon and Free Lime analysis, thermogravimetric analysis (TGA), and surface analysis. The main purpose of this work is to characterize the CFBC ashes from oxy-fuel firing to obtain a better understanding of the combustion process, and to identify any significant differences from the ash generated by a conventional air-fired CFBC. The primary difference in the sulfur capture mechanism between atmospheric air-fired and oxy-fuel FBC, at typical FBC temperatures (∼850 °C), is that, in the air-fired case the Limestone sorbents calcine, whereas the partial pressure of CO 2 in oxy-fuel FBC is high enough to prevent calcination, and hence the sulfation process should mimic that seen in pressurized FBC (PFBC). Here, the char carbon content in the fly ash was much higher than that in the bed ash, and was also high by comparison with ash obtained from conventional commercial air-firing CFBC units. In addition, measurements of the Free Lime content in the bed and fly ash showed that the unreacted Ca sorbent was present primarily as CaCO 3 , indicating that sulfur capture in the oxy-fuel combustor occurred via direct sulfation. Limestone utilization for oxy-fuel combustion in this unit was generally lower than that in industrial-scale air-firing CFBCs, with better Limestone performance found during combustion of petcoke running at relatively higher temperatures. The Brunauer–Emmett–Teller (BET) surface area and also the pore volume in the fly ash were much higher than in the bed ash and smaller size pores predominated in the fly ash samples.
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characterization of ashes from a 100kwth pilot scale circulating fluidized bed with oxy fuel combustion
Applied Energy, 2011Co-Authors: Chunbo Wang, Lufei Jia, Edward J AnthonyAbstract:Oxy-fuel combustion experiments have been carried out on an oxygen-fired 100kWth mini-circulating fluidized bed combustion (CFBC) facility. Coal and petroleum coke were used as fuel together with different Limestones (and fixed Ca:S molar ratios) premixed with the fuel, for in situ SO2 capture. The bed ash (BA) and fly ash (FA) samples produced from this unit were collected and characterized to obtain physical and chemical properties of the ash samples. The characterization methods used included X-ray fluorescence (XRF), X-ray diffraction (XRD), char carbon and Free Lime analysis, thermogravimetric analysis (TGA), and surface analysis. The main purpose of this work is to characterize the CFBC ashes from oxy-fuel firing to obtain a better understanding of the combustion process, and to identify any significant differences from the ash generated by a conventional air-fired CFBC. The primary difference in the sulfur capture mechanism between atmospheric air-fired and oxy-fuel FBC, at typical FBC temperatures (∼850°C), is that, in the air-fired case the Limestone sorbents calcine, whereas the partial pressure of CO2 in oxy-fuel FBC is high enough to prevent calcination, and hence the sulfation process should mimic that seen in pressurized FBC (PFBC). Here, the char carbon content in the fly ash was much higher than that in the bed ash, and was also high by comparison with ash obtained from conventional commercial air-firing CFBC units. In addition, measurements of the Free Lime content in the bed and fly ash showed that the unreacted Ca sorbent was present primarily as CaCO3, indicating that sulfur capture in the oxy-fuel combustor occurred via direct sulfation. Limestone utilization for oxy-fuel combustion in this unit was generally lower than that in industrial-scale air-firing CFBCs, with better Limestone performance found during combustion of petcoke running at relatively higher temperatures. The Brunauer–Emmett–Teller (BET) surface area and also the pore volume in the fly ash were much higher than in the bed ash and smaller size pores predominated in the fly ash samples.
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the behavior of Free Lime in cfbc ashes
17th International Conference on Fluidized Bed Combustion, 2003Co-Authors: E M Bulewicz, Edward J AnthonyAbstract:Ash disposal and ash use are critical to FBC technology and in turn the reactions of FBC ash with water are key to both of these two issues. An effective ash reactivation technology would improve the economics for FBC firing of high-sulphur fuels. Similarly, controlled ash hydration before disposal is the standard method for conditioning FBC ashes when firing high-sulphur fuels with Limestone addition. Ashes can be hydrated with liquid water or by steam under pressure and our earlier work suggested that when FBC ashes were hydrated by either method, the components derived from the coal and those from the sorbent can interact chemically. As a result, the amount of “Free CaO” (defined as the proportion of CaO and Ca(OH)2 , expressed as CaO) may change. Usually, “Free CaO” increases after hydration, particularly under pressure. However, there is also evidence that some of the CaO, derived from excess Limestone sorbent, enters into reaction with the ash components, possibly silica or silicates. Such processes must modify the exothermicity of the ashes with water and affect their subsequent behaviour. This implies that it is incorrect to assume, as has often been done, that the heat of the hydration process is directly proportional to the CaO content of the ash. Furthermore, the results presented here also strongly support the view that one must include these interactions when looking at FBC hydration.Copyright © 2003 by ASME
Ian T Burke - One of the best experts on this subject based on the ideXlab platform.
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leaching behaviour of co disposed steel making wastes effects of aeration on leachate chemistry and vanadium mobilisation
Waste Management, 2018Co-Authors: Andrew J Hobson, Douglas I Stewart, William M Mayes, Mike Rogerson, Robert J G Mortimer, Ian T BurkeAbstract:Steelmaking wastes stored in landfill, such as slag and spent refractory liners, are often enriched in toxic trace metals (including V). These may become mobile in highly alkaline leachate generated during weathering. Fresh steelmaking waste was characterised using XRD, XRF, and SEM-EDX. Batch leaching tests were performed under aerated, air-excluded and acidified conditions to determine the impact of atmospheric CO2 and acid addition on leachate chemistry. Phases commonly associated with slag including dicalcium silicate, dicalcium aluminoferrite, a wustite-like solid solution and Free Lime were identified, as well as a second group of phases including periclase, corundum and graphite which are representative of refractory liners. During air-excluded leaching, dissolution of Free Lime and dicalcium silicate results in a high pH, high Ca leachate in which the V concentration is low due to the constraint imposed by Ca3(VO4)2 solubility limits. Under aerated conditions, carbonation lowers the leachate pH and provides a sink for aqueous Ca, allowing higher concentrations of V to accumulate. Below pH 10, leachate is dominated by periclase dissolution and secondary phases including monohydrocalcite and dolomite are precipitated. Storage of waste under saturated conditions that exclude atmospheric CO2 would therefore provide the optimal environment to minimise V leaching during weathering.
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hydration of dicalcium silicate and diffusion through neo formed calcium silicate hydrates at weathered surfaces control the long term leaching behaviour of basic oxygen furnace bof steelmaking slag
Environmental Science and Pollution Research, 2018Co-Authors: Douglas I Stewart, Andrew W Bray, Gideon Udoma, Andrew J Hobson, William M Mayes, Mike Rogerson, Ian T BurkeAbstract:Alkalinity generation and toxic trace metal (such as vanadium) leaching from basic oxygen furnace (BOF) steel slag particles must be properly understood and managed by pre-conditioning if beneficial reuse of slag is to be maximised. Water leaching under aerated conditions was investigated using fresh BOF slag at three different particle sizes (0.5–1.0, 2–5 and 10 × 10 × 20 mm blocks) and a 6-month pre-weathered block. There were several distinct leaching stages observed over time associated with different phases controlling the solution chemistry: (1) Free-Lime (CaO) dissolution (days 0–2); (2) dicalcium silicate (Ca2SiO4) dissolution (days 2–14) and (3) Ca–Si–H and CaCO3 formation and subsequent dissolution (days 14–73). Experiments with the smallest size fraction resulted in the highest Ca, Si and V concentrations, highlighting the role of surface area in controlling initial leaching. After ~2 weeks, the solution Ca/Si ratio (0.7–0.9) evolved to equal those found within a Ca–Si–H phase that replaced dicalcium silicate and Free-Lime phases in a 30- to 150-μm altered surface region. V release was a two-stage process; initially, V was released by dicalcium silicate dissolution, but V also isomorphically substituted for Si into the neo-formed Ca–Si–H in the alteration zone. Therefore, on longer timescales, the release of V to solution was primarily controlled by considerably slower Ca–Si–H dissolution rates, which decreased the rate of V release by an order of magnitude. Overall, the results indicate that the BOF slag leaching mechanism evolves from a situation initially dominated by rapid hydration and dissolution of primary dicalcium silicate/Free-Lime phases, to a slow diffusion limited process controlled by the solubility of secondary Ca–Si–H and CaCO3 phases that replace and cover more reactive primary slag phases at particle surfaces.
Chunbo Wang - One of the best experts on this subject based on the ideXlab platform.
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characterization of ashes from a 100kwth pilot scale circulating fluidized bed with oxy fuel combustion
Applied Energy, 2011Co-Authors: Chunbo Wang, Lufei Jia, Edward J AnthonyAbstract:Oxy-fuel combustion experiments have been carried out on an oxygen-fired 100kWth mini-circulating fluidized bed combustion (CFBC) facility. Coal and petroleum coke were used as fuel together with different Limestones (and fixed Ca:S molar ratios) premixed with the fuel, for in situ SO2 capture. The bed ash (BA) and fly ash (FA) samples produced from this unit were collected and characterized to obtain physical and chemical properties of the ash samples. The characterization methods used included X-ray fluorescence (XRF), X-ray diffraction (XRD), char carbon and Free Lime analysis, thermogravimetric analysis (TGA), and surface analysis. The main purpose of this work is to characterize the CFBC ashes from oxy-fuel firing to obtain a better understanding of the combustion process, and to identify any significant differences from the ash generated by a conventional air-fired CFBC. The primary difference in the sulfur capture mechanism between atmospheric air-fired and oxy-fuel FBC, at typical FBC temperatures (∼850°C), is that, in the air-fired case the Limestone sorbents calcine, whereas the partial pressure of CO2 in oxy-fuel FBC is high enough to prevent calcination, and hence the sulfation process should mimic that seen in pressurized FBC (PFBC). Here, the char carbon content in the fly ash was much higher than that in the bed ash, and was also high by comparison with ash obtained from conventional commercial air-firing CFBC units. In addition, measurements of the Free Lime content in the bed and fly ash showed that the unreacted Ca sorbent was present primarily as CaCO3, indicating that sulfur capture in the oxy-fuel combustor occurred via direct sulfation. Limestone utilization for oxy-fuel combustion in this unit was generally lower than that in industrial-scale air-firing CFBCs, with better Limestone performance found during combustion of petcoke running at relatively higher temperatures. The Brunauer–Emmett–Teller (BET) surface area and also the pore volume in the fly ash were much higher than in the bed ash and smaller size pores predominated in the fly ash samples.
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characterization of ashes from a 100 kwth pilot scale circulating fluidized bed with oxy fuel combustion
Applied Energy, 2011Co-Authors: Chunbo Wang, Lufei Jia, Yewen Tan, Edward J AnthonyAbstract:Abstract Oxy-fuel combustion experiments have been carried out on an oxygen-fired 100 kW th mini-circulating fluidized bed combustion (CFBC) facility. Coal and petroleum coke were used as fuel together with different Limestones (and fixed Ca:S molar ratios) premixed with the fuel, for in situ SO 2 capture. The bed ash (BA) and fly ash (FA) samples produced from this unit were collected and characterized to obtain physical and chemical properties of the ash samples. The characterization methods used included X-ray fluorescence (XRF), X-ray diffraction (XRD), char carbon and Free Lime analysis, thermogravimetric analysis (TGA), and surface analysis. The main purpose of this work is to characterize the CFBC ashes from oxy-fuel firing to obtain a better understanding of the combustion process, and to identify any significant differences from the ash generated by a conventional air-fired CFBC. The primary difference in the sulfur capture mechanism between atmospheric air-fired and oxy-fuel FBC, at typical FBC temperatures (∼850 °C), is that, in the air-fired case the Limestone sorbents calcine, whereas the partial pressure of CO 2 in oxy-fuel FBC is high enough to prevent calcination, and hence the sulfation process should mimic that seen in pressurized FBC (PFBC). Here, the char carbon content in the fly ash was much higher than that in the bed ash, and was also high by comparison with ash obtained from conventional commercial air-firing CFBC units. In addition, measurements of the Free Lime content in the bed and fly ash showed that the unreacted Ca sorbent was present primarily as CaCO 3 , indicating that sulfur capture in the oxy-fuel combustor occurred via direct sulfation. Limestone utilization for oxy-fuel combustion in this unit was generally lower than that in industrial-scale air-firing CFBCs, with better Limestone performance found during combustion of petcoke running at relatively higher temperatures. The Brunauer–Emmett–Teller (BET) surface area and also the pore volume in the fly ash were much higher than in the bed ash and smaller size pores predominated in the fly ash samples.
Luis Felipe Verdeja - One of the best experts on this subject based on the ideXlab platform.
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the treatment of basic oxygen furnace bof slag with concentrated solar energy
Solar Energy, 2019Co-Authors: D Fernandezgonzalez, J Prazuch, I Ruizbustinza, C Gonzalezgasca, J Pinuelanoval, Luis Felipe VerdejaAbstract:Abstract Basic Oxygen Furnace (BOF) slag is one of the sub-products generated in the steelmaking process. This waste is characterized by its Free Lime and Free magnesia contents that limit its application in construction. Moreover, the iron content in BOF slag of 14–30 wt% is a quantity which is problematic in the manufacture of cements. On the other hand, BOF slag is a source of available iron in the steelmaking industry. Concentrated solar energy offers a great potential in high temperature applications, so we used it to treat BOF slag. In this way, the slag was treated to stabilize it combining the Free Lime and Free magnesia to give other phases (silicates, aluminates, and complex oxides), but also to transform iron into a magnetic phase that could be recovered through magnetic methods. The results demonstrate that the Free Lime and Free magnesia reacted with silicates, aluminates, and ferrites to form stable phases which are not hydrated in the presence of water. Due to this, the treated BOF slag might find application in the construction industry. Furthermore, the iron was transformed into magnetite/maghemite, i.e. phases with magnetic properties.
Rob N J Comans - One of the best experts on this subject based on the ideXlab platform.
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changes in mineralogical and leaching properties of converter steel slag resulting from accelerated carbonation at low co2 pressure
Waste Management, 2011Co-Authors: Andre Van Zomeren, Sieger Van Der Laan, Hans Kobesen, W J J Huijgen, Rob N J ComansAbstract:Steel slag can be applied as substitute for natural aggregates in construction applications. The material imposes a high pH (typically 12.5) and low redox potential (Eh), which may lead to environmental prob- lems in specific application scenarios. The aim of this study is to investigate the potential of accelerated steel slag carbonation, at relatively low pCO2 pressure (0.2 bar), to improve the environmental pH and the leaching properties of steel slag, with specific focus on the leaching of vanadium. Carbonation experi- ments are performed in laboratory columns with steel slag under water-saturated and -unsaturated con- ditions and temperatures between 5 and 90 C. Two types of steel slag are tested; Free Lime containing (K3) slag and K1 slag with a very low Free Lime content. The fresh and carbonated slag samples are inves- tigated using a combination of leaching experiments, geochemical modelling of leaching mechanisms and microscopic/mineralogical analysis, in order to identify the major processes that control the slag pH and resulting V leaching. The major changes in the amount of sequestered CO2 and the resulting pH reduction occurred within 24 h, the Free Lime containing slag (K3-slag) being more prone to carbon- ation than the slag with lower Free Lime content (K1-slag). While carbonation at these conditions was found to occur predominantly at the surface of the slag grains, the formation of cracks was observed in carbonated K3 slag, suggesting that Free Lime in the interior of slag grains had also reacted. The pH of the K3 slag (originally pH ± 12.5) was reduced by about 1.5 units, while the K1 slag showed a smaller decrease in pH from about 11.7 to 11.1. However, the pH reduction after carbonation of the K3 slag was observed to lead to an increased V-leaching. Vanadium leaching from the K1 slag resulted in levels above the limit values of the Dutch Soil Quality Decree, for both the untreated and carbonated slag. V-leaching from the carbonated K3 slag remained below these limit values at the relatively high pH that remained after carbonation. The V-bearing di-Ca silicate (C2S) phase has been identified as the major source of the V-leaching. It is shown that the dissolution of this mineral is limited in fresh steel slag, but strongly enhanced by carbonation, which causes the observed enhanced release of V from the K3 slag. The obtained insights in the mineral transformation reactions and their effect on pH and V-leaching provide guidance for further improvement of an accelerated carbonation technology.
