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K Ostergaard - One of the best experts on this subject based on the ideXlab platform.
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high temperature reaction between sulphur dioxide and Limestone v the effect of periodically changing oxidizing and reducing conditions
Chemical Engineering Science, 1993Co-Authors: P F B Hansen, Kim Damjohansen, K OstergaardAbstract:Abstract Sulphur capture by Limestone has been studied in a laboratory reactor developed to simulate the periodically changing oxidizing and reducing conditions experienced by Limestone particles in a fluidized-bed combustor. Under oxidizing conditions, sulphur is captures ad CaSO 4 . Under reducing conditions, and in the presence of CO, sulphur is captured as CaS. Transformation of CaSO 4 to CaS and vice versa appears to proceed via CaO. Substituting CO with H 2 reducing agent causes an increase in the rate of reductive decomposition of CaSO 4 , and no formation of CaS is observed. Using CH 4 neither reductive decomposition of CaSO 4 nor formation of CaS is observed. The sulphur capacity of 14 European Limestones was studied under constant oxidizing as well as under alternating oxidizing and reducing conditions. The relative ranking of the Limestones appears to be little influenced by the reaction conditions. Generally, a slight reduction in the sulphur capacity is observed under alternating conditions. The exceptions are Limestones with a high content of Fe 2 O 3 , which lowers the sulphur capacity significantly, presumably due to reduced stability of the sulphated Limestone under reducing conditions. Rates of CaS formation and of reductive decomposition of CaSO 4 differ greatly for different Limestones. Reduction of particle size increases the SO 2 release due to CaS oxidation but decreases the release of SO 2 due to reductive decomposition. Both CaS oxidation and reductive decomposition of CaSO 4 may lead to a diminished degree of desulphurization in real combustors. A temperature optimum observed for desulphurization in fluidized-bed combustors appears to be caused primarily by the competition between sulphur capture and sulphur release, the latter of which becomes increasingly important at high temperatures.
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high temperature reaction between sulphur dioxide and Limestone i comparison of Limestones in two laboratory reactors and a pilot plant
Chemical Engineering Science, 1991Co-Authors: Kim Damjohansen, K OstergaardAbstract:Abstract Twenty-three different Limestones were studied with respect to their capacity for reaction with sulphur dioxide, and were found to differ markedly. Geologically young Limestones have the highest capacity, and geological old Limestones the lowest. The presence of ferric oxide affected the sulphur dioxide capacity of Limestones adversely, but otherwise no general relationship was observed between chemical composition and sulphur dioxide capacity. A negative correlation exists between the time required for calcination and the sulphur dioxide capacity. Experiments were carried out in three different reactor systems: a laboratory recycle reactor, a laboratory fluidized-bed reactor, and a coal-fired fluidized-bed pilot plant. Qualitatively, the rankings of Limestones with respect to sulphur dioxide capacity were identical for the three reactor systems, and laboratory experiments may thus be used for the determination of such a ranking. The pilot plant was less efficient with respect to Limestone utilization than the other reactor systems, elutriation from the bed or locally reducing conditions in the bed being assumed to be the major cause of this difference.
Kim Damjohansen - One of the best experts on this subject based on the ideXlab platform.
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high temperature reaction between sulphur dioxide and Limestone v the effect of periodically changing oxidizing and reducing conditions
Chemical Engineering Science, 1993Co-Authors: P F B Hansen, Kim Damjohansen, K OstergaardAbstract:Abstract Sulphur capture by Limestone has been studied in a laboratory reactor developed to simulate the periodically changing oxidizing and reducing conditions experienced by Limestone particles in a fluidized-bed combustor. Under oxidizing conditions, sulphur is captures ad CaSO 4 . Under reducing conditions, and in the presence of CO, sulphur is captured as CaS. Transformation of CaSO 4 to CaS and vice versa appears to proceed via CaO. Substituting CO with H 2 reducing agent causes an increase in the rate of reductive decomposition of CaSO 4 , and no formation of CaS is observed. Using CH 4 neither reductive decomposition of CaSO 4 nor formation of CaS is observed. The sulphur capacity of 14 European Limestones was studied under constant oxidizing as well as under alternating oxidizing and reducing conditions. The relative ranking of the Limestones appears to be little influenced by the reaction conditions. Generally, a slight reduction in the sulphur capacity is observed under alternating conditions. The exceptions are Limestones with a high content of Fe 2 O 3 , which lowers the sulphur capacity significantly, presumably due to reduced stability of the sulphated Limestone under reducing conditions. Rates of CaS formation and of reductive decomposition of CaSO 4 differ greatly for different Limestones. Reduction of particle size increases the SO 2 release due to CaS oxidation but decreases the release of SO 2 due to reductive decomposition. Both CaS oxidation and reductive decomposition of CaSO 4 may lead to a diminished degree of desulphurization in real combustors. A temperature optimum observed for desulphurization in fluidized-bed combustors appears to be caused primarily by the competition between sulphur capture and sulphur release, the latter of which becomes increasingly important at high temperatures.
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high temperature reaction between sulphur dioxide and Limestone i comparison of Limestones in two laboratory reactors and a pilot plant
Chemical Engineering Science, 1991Co-Authors: Kim Damjohansen, K OstergaardAbstract:Abstract Twenty-three different Limestones were studied with respect to their capacity for reaction with sulphur dioxide, and were found to differ markedly. Geologically young Limestones have the highest capacity, and geological old Limestones the lowest. The presence of ferric oxide affected the sulphur dioxide capacity of Limestones adversely, but otherwise no general relationship was observed between chemical composition and sulphur dioxide capacity. A negative correlation exists between the time required for calcination and the sulphur dioxide capacity. Experiments were carried out in three different reactor systems: a laboratory recycle reactor, a laboratory fluidized-bed reactor, and a coal-fired fluidized-bed pilot plant. Qualitatively, the rankings of Limestones with respect to sulphur dioxide capacity were identical for the three reactor systems, and laboratory experiments may thus be used for the determination of such a ranking. The pilot plant was less efficient with respect to Limestone utilization than the other reactor systems, elutriation from the bed or locally reducing conditions in the bed being assumed to be the major cause of this difference.
Narayana Neithalath - One of the best experts on this subject based on the ideXlab platform.
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ternary blends containing slag and interground blended Limestone hydration strength and pore structure
Construction and Building Materials, 2016Co-Authors: Aashay Arora, Narayana NeithalathAbstract:Abstract The influence of high volume cement replacement using a combination of slag and Limestone, on the hydration, reaction products and pore structure, and strength of cementitious systems is reported in this paper. Total replacement levels vary from 20% to 50% by volume. Slag is blended with: (i) Portland-Limestone cement (PLC) that contains Limestone interground with cement, or (ii) OPC and Limestone of four different sizes in such a way that the resulting particle size distribution of the composite matches that of the corresponding PLC-based mixture. The hydration response of cement and cement–slag mixtures are found to be modified in the presence of Limestone. It is observed from calorimetric and thermogravimetric analysis that a favorable slag–Limestone synergy exists, that enables high volume replacement of cement without concomitant loss in properties. The early-age compressive strengths are beneficially impacted by the presence of Limestone whereas the clinker factor does not play a significant role in later-age strengths in both the blended and interground systems. The study paves the way for development of multiple-material binders containing higher levels of cement replacement that demonstrate early and later age properties that are comparable to or better than that of traditional straight cement systems.
Harald Justnes - One of the best experts on this subject based on the ideXlab platform.
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hydration mechanisms of ternary portland cements containing Limestone powder and fly ash
Cement and Concrete Research, 2011Co-Authors: K De Weerdt, K O Kjellsen, Harald Justnes, Ben M Haha, Le G Saout, Barbara LothenbachAbstract:The effect of minor additions of Limestone powder on the properties of fly ash blended cements was investigated in this study using isothermal calorimetry, thermogravimetry (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM) techniques, and pore solution analysis. The presence of Limestone powder led to the formation of hemi- and monocarbonate and to a stabilisation of ettringite compared to the Limestone-free cements, where a part of the ettringite converted to monosulphate. Thus, the presence of 5% of Limestone led to an increase of the volume of the hydrates, as visible in the increase in chemical shrinkage, and an increase in compressive strength. This effect was amplified for the fly ash/Limestone blended cements due to the additional alumina provided by the fly ash reaction.
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synergy between fly ash and Limestone powder in ternary cements
Cement & Concrete Composites, 2011Co-Authors: K De Weerdt, K O Kjellsen, E J Sellevold, Harald JustnesAbstract:The interaction between Limestone powder and fly ash in ternary composite cement is investigated. Limestone powder interacts with the AFm and AFt hydration phases, leading to the formation of carboaluminates at the expense of monosulphate and thereby stabilizing the ettringite. The effect of Limestone powder on OPC may be restricted due to the limited amount of aluminate hydrates formed by the hydration of OPC. The additional aluminates brought into the system by fly ash during its pozzolanic reaction amplify the mentioned effect of Limestone powder. This synergistic effect between Limestone powder and fly ash in ternary cements is confirmed in this study and it translates to improved mechanical properties that persist over time.
S Tsivilis - One of the best experts on this subject based on the ideXlab platform.
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sulfate resistance of Limestone cement concrete exposed to combined chloride and sulfate environment at low temperature
Cement & Concrete Composites, 2012Co-Authors: K Sotiriadis, E Nikolopoulou, S TsivilisAbstract:Abstract Concrete durability was investigated, taking under consideration the Limestone content of the cement used, as well as the effect of chlorides on concrete’s deterioration due to the thaumasite form of sulfate attack. A normal Portland cement and two Portland Limestone cements (15% and 35% w/w Limestone content) were used for concrete preparation. The specimens were immersed in two corrosive solutions (chloride-sulfate; sulfate) and stored at 5 ± 1 °C. Visual inspection of the specimens, mass measurements and compressive strength tests took place for 24 months. Concretes containing Limestone, as cement constituent and/or as aggregate, suffered from the thaumasite form of sulfate attack, which was accompanied by brucite and secondary gypsum formation. Limestone cement concretes exhibited higher deterioration degree compared to the concrete made without Limestone cement. The disintegration was more severe and rapid, the higher the Limestone content of the cement used. Chlorides inhibit sulfate attack on concrete, thus delaying and mitigating its deterioration.
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thaumasite form of sulfate attack in Limestone cement mortars a study on long term efficiency of mineral admixtures
Construction and Building Materials, 2009Co-Authors: A Skaropoulou, S Tsivilis, G Kakali, J H Sharp, R N SwamyAbstract:Abstract Concrete and mortar made from Limestone cement may exhibit a lack of durability due to the formation of thaumasite. The addition of minerals that improve the concrete durability is expected to slow down the formation of thaumasite. In this work the effect of natural pozzolana, fly ash, ground granulated blastfurnace slag and metakaolin on the thaumasite formation in Limestone cement mortar is examined. A Limestone cement, containing 15% w/w Limestone, was used. Mortar specimens were prepared by replacing a part of Limestone cement with the above minerals. The specimens were immersed in a 1.8% MgSO4 solution and cured at 5 and 25 °C. The status of the samples after a storage period of 5 years was reported based on visual inspection, compressive strength, mass measurements, ultrasonic pulse velocity measurements and analytical techniques. It is concluded that the use of specific minerals, as partial replacement of cement, inhibits thaumasite formation in Limestone cement mortar.
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the permeability of portland Limestone cement concrete
Cement and Concrete Research, 2003Co-Authors: S Tsivilis, E Chaniotakis, G Kakali, J Tsantilas, A SakellariouAbstract:Abstract The effect of Limestone addition on the air permeability, water permeability, sorptivity, and porosity of Limestone cement concrete has been investigated. Six Portland Limestone cements (PLCs) with different Limestone content (10–35% w/w) were produced by intergrinding clinker, gypsum, and Limestone. A water-to-cement ratio (w/c) of 0.70–0.62—depending on the cement strength class—was used to prepare concrete of the compressive strength class C20/25 of EN 206-1. A modified commercial triaxial cell for 100-mm-diameter samples was used for the determination of the gas (N2) and the water permeability of concretes. In addition, the sorptivity and porosity of the samples were measured, while thin sections of the concrete specimens were examined by means of optical microscopy. It is concluded that the PLC concrete indicates competitive properties with the ordinary Portland cement (OPC) concrete. Furthermore, the Limestone addition has a positive effect on the water permeability and the sorptivity of concrete.
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an analysis of the properties of portland Limestone cements and concrete
Cement & Concrete Composites, 2002Co-Authors: S Tsivilis, E Chaniotakis, G Kakali, G AtisAbstract:In this paper the main factors affecting the properties of Portland Limestone cements are discussed while the hydration behavior of Limestone cements is examined. In addition, the intergrinding process, concerning the production of the Limestone cements, is studied. Finally the properties and the behavior of Limestone cement concrete as well as the corrosion behavior of Limestone cement mortar are investigated. It is concluded that the fineness of clinker and Limestone is strongly connected with the Limestone content and the fineness of the cement. The Limestone cements indicate satisfactory strength and generally demand less water than the relative pure cements. The Limestone addition improves the clinker reactivity and the exploitation of its hydraulic potential. The Portland Limestone cements indicate competitive concrete properties and improve the corrosion performance of the concrete.
