Recovery of alumina from circulating fluidized bed combustion Al-rich fly ash using mild hydrochemical process

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.

Compatibility of Fly Ash and Slag from Circulating Fluidized Bed Boiler for Concrete Beam

The applications of fly ash and slag from circulating fluidized bed boiler were studied as mineral admixture and aggregate for steel reinforced concrete beam.The results show that the concrete beam with fly ash and slag from circulating fluidized bed boilers has a similar ultimate cracking load coefficient as the ordinary cement concrete and a higher bending moment limit.Under the same load,it has a smaller deformation than the ordinary concrete.

Strength and thermal behavior of low weight foam geopolymer using circulating fluidized bed combustion fly ash

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 ℃.

Mechanical,expansion and rheological properties of circulating fluidized bed fly ash based ecological cement:A critical review

Circulating fluidized bed fly ash(CFBFA)is a solid waste product from circulating fluidized bed(CFB)boilers in power plants,and the storage of CFBFA is increasingly become an environmental problem.Previous scholars have made contributions to improve the resource utilization of CFBFA.Especially,ecological cement is prepared by CFBFA,which is more conducive to its large-scale utilization.In recent years,a lot of effort has been paid to improve the properties of ecological cement containing CFBFA.In this work,the physicochemical properties of CFBFA are introduced,and recent research progress on the mechanical,expansion,and rheological properties of CFBFA based ecological cement(CEC)is extensively reviewed.The problem of over-expansion of f-CaO is summarized,which limits the scale application of CFBFA in ecological cement.Hence,the challenge for f-CaO in CFBFA to compensate for cement volume shrinkage is proposed,which is beneficial to the utilization of CFBFA in ecological cement,and the reduction of CO_(2) emissions from the cement industry.In addition,the environmental performance,durability,and economy of CEC should be valued in future research,especially the environmental performance,because the CFBFA contains heavy metals,such as Cr,As,which may pollute groundwater.

Hydrothermal synthesis of zeolitic material from circulating fluidized bed combustion fly ash for the highly efficient removal of lead from aqueous solution

The utilization of coal fly ash derived from circulating fluidized bed combustion(CFBFA)still faces great challenges because of its unique characteristics.In this study,a zeolitic material with Na-P1 zeolite as the main phase was successfully synthesized via a hydrothermal method by using CFBFA as the raw material.The effects of hydrothermal temperature,time,and added CTAB amount on the characterizations of synthesized materials were investigated by XRD,SEM,and XPS.The properties of the optimal zeolitic material and its adsorption performance for Pb^(2+)in aqueous solution were evaluated.The influences of pH,initial concentration,dosage,and temperature on Pb^(2+)adsorption were also examined.Results revealed the following optimal parameters for the synthesis of zeolitic material:NaOH concentration of 2 mol·L^(-1),solid-to-liquid ratio of 1:10 g·ml^(-1),hydrothermal temperature of 110℃,hydrothermal time of 9 h,and CTAB amount of 1 g(per 100 ml solution).The adsorption capacities of the zeolitic material reached 329.67,424.69,and 542.22 mg·g^(-1) when the pH values of aqueous solution were 5,6,and 7,respectively.The Pb^(2+)removal efficiency can reach more than 99%in aqueous solution with the initial concentrations of 100-300 mg·L^(-1) under pH 6 and suitable adsorbent dosage.The adsorption and kinetics of Pb^(2+)on the zeolitic material can be described by Langmuir isotherm and pseudo-second-order kinetic models,respectively.The ion exchange between Pb^(2+)and Na^(+)and chemisorption are the main adsorption mechanism.All these findings imply that the synthesis of low-cost adsorbent for Pb^(2+)removal from weak acid and neutral aqueous solution provides a highly effective method to utilize CFBFA.

Hardening Properties of Foamed Concrete with Circulating Fluidized Bed Boiler Ash, Blast Furnace Slag, and Desulfurization Gypsum as the Binder

Recently, a large amount of circulating fluidized bed boiler ash (CFBA) and desulfurization gypsum (DSG) has been produced, and it is essential to develop technology to utilize them. These materials have CaO and SO3, which are considered to be a stimulant for blast furnace slag (BFS). This study presents an experimental investigation of the compressive strength and heavy metal ions immobilization properties of cement-free materials comprising CFBA, BFS, and DSG. The feasibility of manufacturing foamed concrete using these materials was examined, and field test of foamed concrete was conducted. Experimentally, the flow, compressive strength, and heavy metal ions concentration were evaluated via inductively coupled plasma atomic emission spectroscopy (ICP-AES) of the paste and foamed concrete. The experimental investigation revealed the self-healing hardening ability of fluidized bed boiler ash. In addition, the compressive strength was increased with the increasing replacement rates of BFS and DSG in the CFBA paste, and the compressive strength of 14.6 - 17.2 MPa was recorded over 28 days of curing. From the result obtained, the feasibility of manufacturing foamed concrete with a foam volume of 120 L, incorporating the aforementioned materials, is confirmed. It was also found that after 28 days of age, a 7.9-MPa compressive strength of the foamed concrete was attained, and heavy metal ions elution in this foamed concrete was also significantly reduced. Therefore, CFBA, BFS, and DSG could be used as a binder for the foamed concrete.

Experimental study on the activation of coal gasification fly ash from industrial CFB gasifiers

Coal gasification fly ash(CGFA)is an industrial solid waste from the coal circulating fluidized bed(CFB)gasification process,and it needs to be effectively disposed to achieve sustainable development of the environment.To realize the application of CGFA as a precursor of porous carbon materials,the physicochemical properties of three kinds of CGFA from industrial CFB gasifiers are analyzed.Then,the activation potential of CGFA is acquired via steam activation experiments in a tube furnace reactor.Finally,the fluidization activation technology of CGFA is practiced in a bench-scale CFB test rig,and its advantages are highlighted.The results show that CGFA is characterized by a high carbon content in the range of 54.06%–74.09%,an ultrafine particle size(d50:16.3–26.1 μm),and a relatively developed pore structure(specific surface area SSA:139.29–551.97 m^(2)·g^(-1)).The proportion of micropores in CGFA increases gradually with the coal rank.Steam activation experiments show that the pore development of CGFA mainly includes three stages:initial pore development,dynamic equilibrium between micropores and mesopores and pore collapse.The SSA of lignite fly ash(LFA),subbituminous fly ash(SBFA)and anthracite fly ash(AFA)is maximally increased by 105%,13%and 72%after steam activation;the order of the largest carbon reaction rate and decomposition ratio of steam among the three kinds of CGFA is SBFA>LFA>AFA.As the ratio of oxygen to carbon during the fluidization activation of LFA is from 0.09 to 0.19,the carbon conversion ratio increases from 14.4%to 26.8%and the cold gas efficiency increases from 6.8%to 10.2%.The SSA of LFA increases by up to 53.9%during the fluidization activation process,which is mainly due to the mesoporous development.Relative to steam activation in a tube furnace reactor,fluidization activation takes an extremely short time(seconds)to achieve the same activation effect.It is expected to further improve the activation effect of LFA by regulating the carbon conversion ratio range of 27%–35%to create pores in the initial development stage.

Physicochemical Properties of Coal Gasification Fly Ash from Circulating Fluidized Bed Gasifier

The coal gasification fly ash(CGFA) is an industrial solid waste from coal gasification process and needs to be effectively disposed for environmental protection and resource utilization.To further clarify the feasibility of CGFA to prepare porous carbon materials,the physicochemical properties of ten kinds of CGFA from circulating fluidized bed(CFB) gasifiers were analyzed in detail.The results of proximate and ultimate analysis show that the CGFA is characterized with the features of near zero moisture content,low volatile content as low as 0.90%-9.76%,high carbon content in the range of 37.89%-81.62%,and ultrafine particle size(d50=15.8-46.2 μm).The automatic specific surface area(SSA) and pore size analyzer were used to detect the pore structure,it is found that the pore structure of CGFA is relatively developed,and part of the CGFA has the basic conditions to be used directly as porous carbon materials.From SEM images,the microscopic morphology of the CGFA is significantly different,and they basically have the characteristics of loose and porous structure.XRD and Roman spectroscopy were used to characterize the carbon structure.The result shows that the CGFA contains abundant amorphous carbon structure,and thus the CGFA has a good reactivity and a potential to improve pore structure through further activation.Through thermal gravimetric analysis,it can be concluded that the order of reactivity of the CGFA under CO_(2) atmosphere has a good correlation with the degree of metamorphism of the raw coal.The gasification reactivity of the CGFA is generally consistent with the change trend of micropores combined with the pore structure.According to the physicochemical properties,the CGFA has a good application prospect in the preparation of porous carbon materials.

THE EXPERIMENTAL INVESTIGATION OF COAL COMBUSTION CHARACTERISTICS IN A FBC WITH FLY ASH RECYCLE

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.

Experimental Study on an On-Line Measurement of High Temperature Circulating Ash Flux in a Circulating Fluidized Bed Boiler

A new Kind of measuring method that may be used to measure high temperature circulating solid particles flux in a circulating fluidized bed boiler is studied in this paper. The measuring method is founded on the principle of thermal equilibrium. A series of cold tests and hot tests were carried to optimize the structure and collocation of water-cooling tubes and showed that the method had the advantage of simple, accurate, reliable and good applicability for on-line "usage in a circulating fluidized bed boiler.

利用石灰石系统改善锅炉外循环品质研究

循环流化床锅炉因其燃料适应性强和负荷调节灵活等特点,在火电领域得到广泛应用。与煤粉炉相比,循环流化床锅炉运行期间炉内存有大量物料,通过对流和辐射2种换热方式,实现高效稳定热能传递。辽宁调兵山煤矸石发电有限责任公司2台1065 t/h循环流化床锅炉,由于运行时间延长和分离器效率逐渐降低等原因,导致炉内循环物料不足,引发对流换热量大幅下降,根据能量守恒定律,为维持相同蒸发量,必须增加辐射换热量。这种调整造成床温、回料器及分离器出口温度升高,对机组安全运行构成威胁。此外,还会导致氮氧化物原始生成量增加,进一步影响机组经济运行。为了提高炉内对流换热量,降低物料温度,提高机组安全性及经济性,利用原有的石灰石输送系统,将电除尘及省煤器仓泵中的灰重新送回炉膛参与燃烧换热,通过对比飞灰燃烧试验前后机组运行状态和数据,深入分析飞灰再循环对机组运行状态的影响,最终实现机组安全、经济运行。

循环流化床锅炉掺烧清洁煤制气飞灰替代燃料研究

我国是煤炭资源生产大国,利用清洁煤技术,改变传统煤炭消费方式,是我国工业领域目前迫切需要解决的工作之一。清洁煤制气是煤炭高效清洁利用的重要技术之一。某生产企业一期工程采用2×260 t/h高温高压循环流化床锅炉、1×60000 Nm^(3)/h褐煤制清洁煤气的循环流化床煤气化炉,作为生产工艺用能来源。单台煤气炉年煤耗量22万吨,产生的固体颗粒废弃物飞灰年总量达3万吨。实现煤气炉飞灰替代燃料,可以节省大量燃料成本,并对高效利用煤制气飞灰变废为宝、节能减排提供高效高经济性的优化选项。

CFB锅炉粉煤灰摩擦荷电特性及分选脱炭研究

脱炭是粉煤灰综合利用的前提,摩擦电选是粉煤灰脱炭的有效方式。为了探索粉煤灰摩擦荷电特性和分选脱炭的最佳操作条件,以CFB锅炉粉煤灰为研究对象,基于其物理化学、工艺矿物学特性分析,采用不锈钢、铜、铝和PVC四种材质,通过摩擦荷电试验,对焦炭和粉煤灰主要成分(SiO_(2),CaO,CaSO_(4))进行了摩擦荷电特性研究;通过摩擦电选试验,探究了给料速度、风量、分选电压对粉煤灰摩擦电选脱炭效果的影响;并采用Box-Behnken响应曲面法,对粉煤灰摩擦电选的操作参数进行了优化。试验结果表明:PVC的摩擦荷电效果较好,能使焦炭与粉煤灰主要成分的摩擦荷电量差异较大,可作为摩擦荷电器的摩擦材料;粉煤灰烧失量随给料速度的增加呈先降低后增加的趋势,随着风量的升高呈现逐渐降低的趋势,分选电压提高有利于降低粉煤灰烧失量,三个因素之中以风量对粉煤灰烧失量的影响最为显著;优化得出粉煤灰摩擦电选的最佳操作条件,即风量为70 m^(3)/h、分选电压为20 kV、给料速度为10.8 kg/h,在此条件下,粉煤灰烧失量最低,为8.45%。研究可为粉煤灰摩擦电选脱炭工业生产条件的优化提供有益参考。

基于气固废物再利用的节能环保一体化循环流化床锅炉技术

为了实现锅炉飞灰固废和合成氨系统尾气(低温甲醇洗废气、液氮洗废气)的综合治理及再利用,解决锅炉效率低、锅炉排放烟气中氮氧化物控制困难等问题,河南晋开化工投资控股集团有限责任公司二分公司根据循环流化床锅炉的流化原理、SNCR脱硝理论及燃烧理论,实施了飞灰循环燃烧、废气综合利用、新型旋风分离器构建等技术改造,实现了生产系统的安全、高效、环保运行的目的。

基于风量准确测量的循环流化床锅炉运行优化

为了响应国家节能减排政策,降低企业经营成本,某电厂在准确测量风量的基础上,对其300 MW等级循环流化床锅炉机组进行了优化运行调整。结果表明,优化后飞灰含碳量平均降低了1.44%,底渣含碳量平均降低了0.36%,尿素日均耗量平均降低了1.54 t,月均厂用电率降低了0.16%,预计全年可以实现经济效益近750万元。

循环灰对NH_3氧化反应影响的实验研究

循环灰对NH3氧化的催化作用对循环流化床锅炉的喷氨脱硝效果有重要影响。文中利用固定床反应器研究了石英砂、循环灰和循环灰主要成分对NH3氧化反应的影响。在实验中利用傅里叶红外光谱仪测量了NH3和O2通过反应器后产物气体中的NH3、NO和N2O的体积分数。与NH3气相反应氧化的结果对比,循环灰能够促进NH3的氧化,NH3的转化率显著提高,主要生成NO、N2O和N2。循环灰的主要成分中,铁氧化物Fe2O3和Fe3O4及CaO对NH3的氧化有较强的催化活性,并促进N2O的生成;而SiO2和Al2O3对NH3的氧化性能影响不大。NH3氧化生成产物的选择性与反应温度、循环灰的成分等因素有关。

自主研发600MW超临界CFB锅炉的设计研究

为进一步发展和提高大容量超临界循环流化床锅炉技术,在研制首台国产210MW和330MW循环流化床(CFB)锅炉的基础上,系统研究了CFB锅炉大型化的关键技术,开展了国产600MW超临界CFB锅炉的方案设计,对锅炉的炉型结构、关键部件、汽水系统及辅助系统进行了分析和设计研究。介绍了国产600MW超临界CFB锅炉结构:采用"H"型整体布置,6台高温旋风分离器布置在炉膛两侧,配有相应的紧凑式分流回灰换热器(CHE),炉膛水冷壁为垂直管圈结构,双回路给煤系统可保证均匀可靠地向炉内送入燃料。该锅炉技术方案可为工程应用奠定技术基础。

降低循环流化床锅炉飞灰含碳量的理论及其应用

首先从燃烧角度分析了影响循环流化床锅炉飞灰含碳量的主要因素,然后针对HG-465/13.7-L.PM7型循环流化床锅炉实际运行中存在的飞灰含碳量高的问题,根据理论分析并结合现场试验,分析得到了煤质及运行参数对飞灰含碳量的影响。利用试验结果指导运行,使该炉的飞灰含碳量由原来的18%降低到12%。

影响循环流化床锅炉燃烧效率的因素分析及改善措施

循环流化床锅炉具有高效、低污染、煤种适应性广等优点 ,在我国得到大力发展。但目前存在一个较为普遍的问题 :飞灰含碳量高 ,锅炉燃烧效率达不到设计值。在对实例进行分析的基础上 ,探讨了煤的热值及煤的粒径、燃烧室特点、循环系统运行状况对锅炉燃烧效率的影响。提出了维持锅炉稳定燃烧 ,降低飞灰含碳量 ,提高燃烧效率的一些措施 ,在实践中证明是行之有效的。图 3表 2参

循环流化床锅炉飞灰残碳的生成及其处理

循环流化床燃烧技术因其众多的优点得到广泛应用,但是在运行中普遍存在着飞灰含碳量远远高于预期的问题。影响飞灰含碳量的主要因素包括:煤指标、煤的结构和焦炭反应活性、给煤粒径以及循环流化床的结构和其它运行参数等。目前,降低飞灰含碳量的方法有:飞灰再循环、加强二次风刚性和调整床压降等。实验表明,在低风速条件下,可以将飞灰中的残碳充分燃尽。另外,高压静电分离和飞灰水活化团聚也都为飞灰残碳的利用提供了新思路。