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 ℃.

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.

Simulation of gas-solid flow characteristics of the circulating fluidized bed boiler under pure-oxygen combustion conditions

Under the pressure of carbon neutrality,many carbon capture,utilization and storage technologies have witnessed rapid development in the recent years,including oxy-fuel combustion(OFC)technology.However,the conventional OFC technology usually depends on the flue gas recirculation system,which faces significant investment,high energy consumption,and potential low-temperature corrosion problem.Considering these deficiencies,the direct utilization of pure oxygen to achieve particle fluidization and fuel combustion may reduce the overall energy consumption and CO_(2)-capture costs.In this paper,the fundamental structure of a self-designed 130 t·h^(-1) pure-oxygen combustion circulating fluidized bed(CFB)boiler was provided,and the computational particle fluid dynamics method was used to analyze the gas-solid flow characteristics of this new-concept boiler under different working conditions.The results indicate that through the careful selection of design or operational parameters,such as average bed-material size and fluidization velocity,the pure-oxygen combustion CFB system can maintain the ideal fluidization state,namely significant internal and external particle circulation.Besides,the contraction section of the boiler leads to the particle backflow in the lower furnace,resulting in the particle suspension concentration near the wall region being higher than that in the center region.Conversely,the upper furnace still retains the classic core-annulus flow structure.In addition to increasing solid circulation rate by reducing the average bed-material size,altering primary gas ratio and bed inventory can also exert varying degrees of influence on the gas-solid flow characteristics of the pure-oxygen combustion CFB boiler.

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.

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.

Properties of Concrete Incorporating Bed Ash from Circulating Fluidized Bed Combustion and Ground Granulates Blast-furnace Slag

The properties of concrete incorporating circulating fluidized bed combustion （CFBC） bed ash and ground granulates blast-furnace slag （GGBS） were studied.Compressive strength,drying shrinkage,mercury intrusion porosimetry （MIP）,scanning electronic microscopy （SEM）,and X-ray diffraction （XRD） of concrete samples containing CFBC bed ash and GGBS were used.This work used initial surface absorption test （ISAT） and rapid chloride penetration test （RCPT） on concrete to measure the absorption and the ability of concrete to resist chloride ion characteristics for different concrete samples containing CFBC bed ash and GGBS.Open circuit potential （OCP）,direct current polarization resistance were obtained to evaluate rebar corrosion.The CFBC bed ash was X-ray amorphous and consist of SiO2,Al2O3 and CaO compounds.As the replacement of CFBC for sand increases,the rate of initial surface absorption （ISA） increases but compressive strength decreases.When the content of CFBC bed ash replacement for sand maintains constant,the replacement of GGBS for cement increases,compressive strength increases but the rate of ISA decreases.Chloride and corrosion resistance of rebar significantly improve by utilizing a proper amount of CFBC bed ash and GGBS in concrete.

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.

I MWth Test Facilities for Circulating Fluidized Bed Combustion

This paper presents the technical parameters and features of 1 MWth test facilities for circulating fluidized bed combustion (CFBC) at Thermal Power Research Institute (TPRI) of State Power Corporation (SP), introduces the test items that can be proceeded and trial combustion projects completed. The development status of CFBC technologies abroad and the level of China in this field are also introduced in the paper.

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.

Synergetic NO reduction by biomass pyrolysis products simulating their reburning in circulating fluidized bed decoupling combustion

The present work investigated the synergetic effect of pyrolysis-derived char,tar and gas(py-gas)on NO reduction,which may occur in circulating fluidized-bed decoupling combustion(CFBDC)system treating N-rich fuel.Experiments were carried out in a lab-scale drop-tube reactor for NO reduction by some binary mixtures of reagents including char/py-gas,tar/py-gas and tar/char.At a specified total mass rate of0.15 g·min^-1 for NO-reduction reagent,the char/py-gas(binary reagent)enabled the best synergetic NO reduction in comparison with the others.There existed effective interactions between char and some species in py-gas(i.e.,H2,CxHy)during NO reduction by pyrolysis products,meanwhile the tar/py-gas or tar/char mixture only caused a positive effect when tar proportion was necessarily lowered to about 26%.On the other hand,the synergetic effects were not improved for all tested binary reagents by increasing the reaction temperature and residence time.

Nano⁃Silica Production by Rice Husk Combustion in a 0.7 MW Double⁃Circulating Fluidized Bed after Acid Pretreatment

Rice husk is an organic silicon source for amorphous nano⁃silica particles.This paper reports the experimental study on the industrial production of nano⁃silica by rice husk combustion in a specially⁃designed 0.7 MW double⁃circulating fluidized bed(DCFB)based on acid pretreatment process.The physicochemical properties of RHA were characterized by various testing instruments.Results showed that acid pretreatment removed a large amount of metal impurities in the rice husk and thus inhibited the formation of crystalline silica or the agglomeration during the fluidized bed combustion process.The combustion efficiencies were as high as 99.5%.The obtained RHA comprised white fine particles and exhibited an amorphous structure,but factors such as collection point and acid type had certain influences on the quality of RHA.The highest SiO2 purity was greater than 98.6 wt.%,the lowest content of unburned carbon was 0.2 wt.%,the specific surface area reached 178 m2/g,and the pore size reached 5 nm.The circulating fluidized bed combustion of rice husk based on acid pretreatment can prepare nano⁃silica while providing heat for industrial processes,which is a highly energy⁃rich process.

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.

Emissions of SO_2, NO and N_2O in a circulating fluidized bed combustor during co-firing coal and biomass

This paper presents the experimental investigations of the emissions of SO2, NO and N20 in a bench scale circulating fluidized bed combustor for coal combustion and co-firing coal and biomass. The thermal capacity of the combustor is 30 kW. The setup is electrically heated during startup. The infuence of the excess air, the degree of the air staging, the biomass share and the feeding position of the fuels on the emissions of SO2, NO and N2O were studied. The results showed that an increase in the biomass shares resulted in an increase of the CO concentration in the flue gas, probably due to the high volatile content of the biomass. In co-firing, the emission of SO2 increased with increasing biomass share slightly, however, non-linear increase relationship between SO2 emission and fuel sulfur content was observed. Air staging significantly decreased the NO emission without raising the SO2 level. Although the change of the fuel feeding position from riser to downer resulted in a decrease in the NO emission level, no obvious change was observed for the SO2 level. Taking the coal feeding position R as a reference, the relative NO emission could significantly decrease during co-firing coal and biomass when feeding fuel at position D and keeping the first stage stoichiometry greater than 0.95. The possible mechanisms of the sulfur and nitrogen chemistry at these conditions were discussed and the ways of simultaneous reduction of SO2, NO and N2O were proposed.

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.

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.

Energy Efficiency Analysis of Oxy-Fuel Circulating Fluidized Bed Combustion System with High Oxygen Concentration

The low net efficiency of oxy-fuel circulating fluidized bed(CFB)combustion is mainly due to the addition of air separation unit(ASU)and carbon dioxide compression and purification unit(CPU).High oxygen concentration is one of the effective methods to improve the net efficiency of oxy-fuel combustion technology in CFB.In this research,a series of calculation and simulation were carried out based on Aspen Plus platform to provide valuable information for further investigation on the CFB oxy-fuel combustion system with high oxygen concentration(40%,50%).A CFB oxy-fuel combustion system model with high oxygen concentration was established including ASU,CPU and CFB oxy-fuel combustion and heat exchange unit.Based on the simulation data,energy and exergy efficiency were analyzed to obtain the following results.The cross-sectional area of furnace and tail flue of 50%CFB oxy-fuel combustion boiler are 43%and 56%of the original size respectively,reducing the construction and investment cost effectively.With the increase of oxygen concentration,the net efficiency of power generation increased significantly,reaching 24.85%and increasing by 6.09%under the condition of 50%oxy-fuel combustion.The total exergy loss increases with the increase of oxygen concentration.In addition,the exergy loss of radiation heat transfer is far higher than convection heat transfer.

燃煤锅炉改燃兰炭燃烧工艺及效益分析

兰炭因热值高、硫含量低的特点被广泛应用于散煤替代,燃煤锅炉改燃兰炭是实现资源合理利用、降低污染物排放和改善企业经济效益的有效途径。以河北某循环流化床锅炉改燃兰炭工程为例,燃烧系统采用掺烧灰渣的方法,解决改燃后机械未完全燃烧导致损失大和物料循环不稳定问题,确定了兰炭和灰渣的最佳掺混比为9∶1;配风系统采用控制总量并降低一次风率的方法,解决兰炭着火困难的问题,确定了最佳一次风比例为55%;换热系统采用增加锅炉尾部受热面的方法,解决因燃料热值提升较大产生的蒸汽超温和锅炉效率下降问题。改燃扩容后锅炉烟尘、SO2和NOx排放分别比原锅炉降低了73%、94%和55%,以原锅炉35 t/h的额定功率运行,每小时节约燃料成本5.51%,产吨蒸汽所需燃料成本降低6.47元。

Geldart C类脱硫灰颗粒在环流耦合提升管内稳定流动特性

我国CO_(2)的排放中70%来自工业领域,故工业过程的碳捕集对实现“双碳目标”十分关键。工业烟气中往往含有的硫氧化物会腐蚀设备并使后续脱碳等过程使用的催化剂中毒。因此,工业烟气的深度脱硫技术对后续的CO_(2)捕集或提纯过程至关重要。循环流化床半干法烟气脱硫因具有脱硫效率高、无污染、停留时间可控等优点受到广泛关注。循环流化床脱硫工艺中作为脱硫剂的脱硫灰颗粒为典型Geldart C类颗粒。由于C类颗粒的强黏附性,其在循环流化床操作中容易结块,从而影响装置稳定运行。为了强化脱硫灰颗粒在循环流化床内的流动稳定性,提出了环流强化的耦合提升管反应器的概念,并自行设计搭建了一套导流筒内径100 mm、高度300 mm,外筒内径160 mm、高度760 mm,输送段内径75 mm、总高度12.6 m的环流耦合提升管。在U_(g)=4 m/s、G_(s)=45 kg/(m^(2)·s),U_(g)=7 m/s、G_(s)=25 kg/(m^(2)·s)的操作条件下,考察了环流段的压力分布、标准差以及功率谱密度。当环隙区气速为0.4 m/s时,环流流动能够实现稳定、连续的密相环流流动。在C类颗粒形成稳定流动基础上,讨论了环流耦合提升管内的流动特性分布规律,包括固含率和颗粒速度。实验发现,环流流动的设计可以强化C类颗粒的流动特性,大幅提高耦合反应器内C类颗粒脱硫灰固含率,并实现了C类颗粒循环流态化装置的稳定运行。同时,这些研究结果可以为C类颗粒新型循环流态化反应器设计提供参考。

硫酸铝对高掺量流化床粉煤灰基泡沫混凝土性能的影响

随着新型循环流化床燃煤技术的发展,循环流化床粉煤灰(CFBFA)的排放量日益增加。结合我国北方地区冬季严寒时保温隔热材料需求量大的现状,采用高掺量CFBFA制备具有保温隔热性能的泡沫混凝土。针对泡沫混凝土存在的凝结时间长以及早期强度低等问题,本工作掺入硫酸铝进行改性,研究并分析了硫酸铝掺量对泡沫混凝土密度、强度和导热系数的影响。利用X射线衍射(XRD)、热重分析(TG)以及扫描电子显微镜(SEM)等研究了硫酸铝作用下CFBFA基泡沫混凝土的水化产物和微观形貌。此外,还利用3D轮廓仪分析了泡沫混凝土的孔隙结构。结果表明,硫酸铝促进了本体系早期AFt的生成,与基准组(硫酸铝掺量为0%(质量分数,下同))相比,15%硫酸铝掺量的CFBFA基泡沫混凝土的初凝时间缩短了470 min,10%硫酸铝掺量的泡沫混凝土3 d强度可达到10.43 MPa,导热系数为0.31 W·m^(-1)·K^(-1)。这种泡沫混凝土具有较快批量化生产的潜力。

有机醇胺TEA-M-无机盐体系对固硫灰渣活性激发的影响

固硫灰渣的处理以及环保型激发剂材料的开发是防止环境二次污染的有效途径。本文开发了一种有机醇胺TEA-无机激发剂M-无机盐复合激发剂,通过SEM、FTIR、XRD等测试方法对所制备的复合激发剂进行表征,先后探索了M、TEA-M、TEA-M-无机盐三个系列的激发剂对水泥胶砂流动度比和抗压活性指数的影响。结果表明,TEA的助磨作用改善了颗粒的粒径,无机激发剂M能影响参与水化反应的Ca(OH)_(2)含量,无机盐CaSiO_(3)后期会产生C-S-H并提供碱性条件。复合激发剂中的不同材料间的协同作用使水泥胶砂7和28 d的抗压活性指数分别提高了29个和18个百分点(与空白样相比),并且胶砂净浆的流动度比仍然保持在较高水平。本文为固硫灰渣提供了一种环保型的复合激发剂材料,促进了固硫灰渣的绿色化应用。