To utilize CFBC Al-rich fly ash, a mild hydrochemical extraction process was investigated for recovery of alumina. An alumina extraction efficiency of 92.31%was attained using a 45%NaOH solution, an original caustic r...To utilize CFBC Al-rich fly ash, a mild hydrochemical extraction process was investigated for recovery of alumina. An alumina extraction efficiency of 92.31%was attained using a 45%NaOH solution, an original caustic ratio （molar ratio of Na2O to Al2O3 in the sodium aluminate solution） of 25, a molar ratio of CaO to SiO2 in the fly ash of 1.1, a liquid volume to solid mass ratio of 9, a reaction temperature of 280 ℃, and a residence time of 1 h when treating fly ash with an alumina to silica mass ratio （A/S） of 0.78 and an alumina content of 32.43%. Additionally, the alumina leaching mechanism was explored via structural and chemical analysis, which revealed that after alkaline digestion, the main solid phase containing silica was NaCaHSiO4 with a theoretical A/S of zero.展开更多
A comparative study of the influence of elevated temperature on foam geopolymer using circulating fluidized bed combustion fly ash（CFA） was reported. Foam geopoymers were prepared with different amounts of foam agen...A comparative study of the influence of elevated temperature on foam geopolymer using circulating fluidized bed combustion fly ash（CFA） was reported. Foam geopoymers were prepared with different amounts of foam agent and different Si O2/Al2O3 molar ratios of 3.1, 3.4, and 3.8. The mechanical, thermo-physical properties and microstructure of the foam geopolymers before and after exposure to elevated temperature of 800, 1000, and 1200 ℃ were investigated. The specimen with Si O2/Al2O3 molar ratio of 3.8 exhibits the highest compressive strength, better microstructure and dimension stability before and after firing. Carnegeite, nepheline, and zeolite crystalline phases appearing after exposure may contribute to the good post-exposure strength. Low weight foam geopolymer using CFA can increase strength and maintain higher stability as high as 1000 ℃.展开更多
In order to seek the effective method of increasing the coal combustion effi-ciency and to obtain the dcsign data for a certain kind of coal in fluidized bed combustors(FBCs),the experiments of coal combustion charact...In order to seek the effective method of increasing the coal combustion effi-ciency and to obtain the dcsign data for a certain kind of coal in fluidized bed combustors(FBCs),the experiments of coal combustion characteristics were conducted in a FBC facil-ity with the cross-section of 0.3m×0.3m and 6m in height.The variations of carbon con-tent of particles with recycle ratio,particle diameter,sample location and flow direction,the effects of bed temperature and fluidizing velocity on combustion efficiency and the va-riations of the temperature characteristic and combustion fraction in freeboard were inves-tigated.The experimental results indicate that using fly ash recycle not only can increasethe combustion efficiency,but also can improve the operation performances obviously.展开更多
Coal combustion technologies are changing in order to burn coal more cleanly.Many 'clean combustion' and post-combustion technologies are developed to remove SO_2 and NO_xgases, particulate matter during combu...Coal combustion technologies are changing in order to burn coal more cleanly.Many 'clean combustion' and post-combustion technologies are developed to remove SO_2 and NO_xgases, particulate matter during combustion, or from the flue gases leaving the furnace. This paperfocuses on three types of fly ash (flue gas desulfurization (FGD) residuals, atmospheric fluidizedbed combustion (AFBC) residuals and sorbent duct injection (SDI) residuals) which produced by 'theclean combustion' and post-combustion technologies. The residuals formed by FGD are PCFA (pulverizedcoal fly ash) grains entrained with reacted and unre-acted sorbent and have lower bulk densitiesthan PCFA grains because it contains higher concentrations of calcium and sulfur, and lowerconcentrations of silicon, aluminum and iron than PCFAs. AFBC residuals consist of spent bed whichis a heterogeneous mixture of coarse-grained bed material and irregularly shaped, unfused, sphericalPCFAs. The main crystalline phases in AFBC residuals are anhydrite (reacted sorbent), quartz andlime (unreacted sobent), calcite, hematite, periclase, magnetite and feldspars. The residualsproduced by SDI contained 65 percent-70 percent PCFA with the larger sizes material beingirregularly shaped, fused or rough-edged. The reaction products of sorbent (portlandite and lime)included calcium sulfate (anhydrite) and calcium sulfate. The chemical properties of these residualsare similar to those of high calcium PCFAs because of the high alkalinity and high pH of theseresiduals.展开更多
Circulating fluidized bed combustion （CFBC） ash can be used as supplementary cementitious material for concrete production for its high pozzolanic activity. We investigated the effect of curing conditions on the hyd...Circulating fluidized bed combustion （CFBC） ash can be used as supplementary cementitious material for concrete production for its high pozzolanic activity. We investigated the effect of curing conditions on the hydration and performance of CFBC ash-Portland cement system （30： 70, by mass） including hydration products, paste microstructure, linear expansion ratio, chemically combined water content and compressive strength. The results show that tobermorite rather than ettringite is generated under the condition of autoclaved curing. The expansion and mortar strength of the system cured in water is higher than those cured in air at a given age, and the strength and bulk volume may retract under the condition of air curing. In addition, autoclaved curing facilitates the increase of strength gain at early curing ages （the increase rate lowers down in the following ages） and the improvement of system volume stability. It is suggested that sufficient water is necessary for the curing of CFBC ash cementitious system, and autoclaved curing may be considered where volume stability is a primary concern.展开更多
基金Project (2012BAF03B01) supported by the National Science and Technology Support Program of ChinaProject (2011AA060701) supported by the Hi-tech Research and Development Program of China
文摘To utilize CFBC Al-rich fly ash, a mild hydrochemical extraction process was investigated for recovery of alumina. An alumina extraction efficiency of 92.31%was attained using a 45%NaOH solution, an original caustic ratio （molar ratio of Na2O to Al2O3 in the sodium aluminate solution） of 25, a molar ratio of CaO to SiO2 in the fly ash of 1.1, a liquid volume to solid mass ratio of 9, a reaction temperature of 280 ℃, and a residence time of 1 h when treating fly ash with an alumina to silica mass ratio （A/S） of 0.78 and an alumina content of 32.43%. Additionally, the alumina leaching mechanism was explored via structural and chemical analysis, which revealed that after alkaline digestion, the main solid phase containing silica was NaCaHSiO4 with a theoretical A/S of zero.
基金Project(20120023110011) supported by Doctoral Program of Higher Education of ChinaProjects(2009KH09,2009QH02) supported by the Fundamental Research Funds for the Central Universities of China
文摘A comparative study of the influence of elevated temperature on foam geopolymer using circulating fluidized bed combustion fly ash（CFA） was reported. Foam geopoymers were prepared with different amounts of foam agent and different Si O2/Al2O3 molar ratios of 3.1, 3.4, and 3.8. The mechanical, thermo-physical properties and microstructure of the foam geopolymers before and after exposure to elevated temperature of 800, 1000, and 1200 ℃ were investigated. The specimen with Si O2/Al2O3 molar ratio of 3.8 exhibits the highest compressive strength, better microstructure and dimension stability before and after firing. Carnegeite, nepheline, and zeolite crystalline phases appearing after exposure may contribute to the good post-exposure strength. Low weight foam geopolymer using CFA can increase strength and maintain higher stability as high as 1000 ℃.
文摘In order to seek the effective method of increasing the coal combustion effi-ciency and to obtain the dcsign data for a certain kind of coal in fluidized bed combustors(FBCs),the experiments of coal combustion characteristics were conducted in a FBC facil-ity with the cross-section of 0.3m×0.3m and 6m in height.The variations of carbon con-tent of particles with recycle ratio,particle diameter,sample location and flow direction,the effects of bed temperature and fluidizing velocity on combustion efficiency and the va-riations of the temperature characteristic and combustion fraction in freeboard were inves-tigated.The experimental results indicate that using fly ash recycle not only can increasethe combustion efficiency,but also can improve the operation performances obviously.
文摘Coal combustion technologies are changing in order to burn coal more cleanly.Many 'clean combustion' and post-combustion technologies are developed to remove SO_2 and NO_xgases, particulate matter during combustion, or from the flue gases leaving the furnace. This paperfocuses on three types of fly ash (flue gas desulfurization (FGD) residuals, atmospheric fluidizedbed combustion (AFBC) residuals and sorbent duct injection (SDI) residuals) which produced by 'theclean combustion' and post-combustion technologies. The residuals formed by FGD are PCFA (pulverizedcoal fly ash) grains entrained with reacted and unre-acted sorbent and have lower bulk densitiesthan PCFA grains because it contains higher concentrations of calcium and sulfur, and lowerconcentrations of silicon, aluminum and iron than PCFAs. AFBC residuals consist of spent bed whichis a heterogeneous mixture of coarse-grained bed material and irregularly shaped, unfused, sphericalPCFAs. The main crystalline phases in AFBC residuals are anhydrite (reacted sorbent), quartz andlime (unreacted sobent), calcite, hematite, periclase, magnetite and feldspars. The residualsproduced by SDI contained 65 percent-70 percent PCFA with the larger sizes material beingirregularly shaped, fused or rough-edged. The reaction products of sorbent (portlandite and lime)included calcium sulfate (anhydrite) and calcium sulfate. The chemical properties of these residualsare similar to those of high calcium PCFAs because of the high alkalinity and high pH of theseresiduals.
基金Funded by the National Natural Science Foundation of China(Nos.51132010 and 51272222)the Programs for Science and Technology Development of Yantai City,Shandong Province,China(No.2012ZH249)
文摘Circulating fluidized bed combustion （CFBC） ash can be used as supplementary cementitious material for concrete production for its high pozzolanic activity. We investigated the effect of curing conditions on the hydration and performance of CFBC ash-Portland cement system （30： 70, by mass） including hydration products, paste microstructure, linear expansion ratio, chemically combined water content and compressive strength. The results show that tobermorite rather than ettringite is generated under the condition of autoclaved curing. The expansion and mortar strength of the system cured in water is higher than those cured in air at a given age, and the strength and bulk volume may retract under the condition of air curing. In addition, autoclaved curing facilitates the increase of strength gain at early curing ages （the increase rate lowers down in the following ages） and the improvement of system volume stability. It is suggested that sufficient water is necessary for the curing of CFBC ash cementitious system, and autoclaved curing may be considered where volume stability is a primary concern.
