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 °C 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 °C.

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.

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.

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.

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.

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.

Experimental Study on the Effect of Bed Material Amount and Fuel Particle Size on Load Change of Circulating Fluidized Bed

The large-scale integration of new energy generation has put forward higher requirements for the peak-shaving capability of thermal power.The circulating fluidized bed(CFB)depends on the advantages of a wide load adjustment range and low cost of pollutant control to become a good peak shaving power supply.However,the large delay and inertia caused by its unique combustion mode make it very difficult to change the load quickly.To further understand the factors that affect the load change of CFB,and explore the method of increasing CFB load change rate,the load change experiment on the combustion side was carried out in the 0.1 MW CFB experiment platform.The influence law of bed material amount and fuel particle size on load change of CFB combustion side was revealed for the first time.The results indicated that the increase of bed material amount was beneficial to improve the load change rate on the combustion side of CFB and reduce the carbon content of fly ash,but had no obvious effect on NO_(x)emission.When the bed height at rest increased from 200 mm to 400 mm,the load change rate of the CFB combustion side load from 50%to 75%increased from 0.78%/min to 1.14%/min,and the carbon content of fly ash at 75%load decreased from 26.6%to 24.9%.In addition,the reduction of fuel particle size positively improved the load change rate on the combustion side of the CFB and reduced NO_(x)emission but had a negative effect on reducing the carbon content of fly ash.When the fuel particle size decreased from 0-1 mm to 0-0.12 mm,the load change rate of CFB combustion side load from 50%to 75%increased from 0.78%/min to 1.09%/min,and the NO_(x)emission and carbon content of fly ash at 75%load decreased from 349.5 mg/m^(3)to 194.1 mg/m^(3)and increased from 26.6%to 31.8%,respectively.

The Simulation of Influence of Different Coals on the Circulating Fluidized Bed Boiler's Combustion Performance

The combustion performance of the boiler largely depends on the coal type.Lots of experimental research shows that different fuels have different combustion characteristics.It is obvious that fuel will change the whole operating performance of Circulating Fluidized Bed Combustion (CFBC).We know even in a pilot-scale running boiler,the measurement of some parameters is difficult and costly.Therefore,we developed the way of simulation to evaluate the combustion performance of Chinese coals in CFB,The simulation results show that,different coals will result in different coal particle diameter and cominution depending on their mineral component and the change will affect the distribution of ash in CFBC system.In a word.the computational results are in accordance with experimental results qualitatively but there are some differences quantitatively.

Combustion Model For Staged Circulating Fluidized Bed Boiler

A mathematical model for atmospheric staged circulating fluidized bed combustion, which takes fluiddynamics, combustion, heat transfer, pollutants formation and retention, into account was developedin the Institute of Engineering Thermophysics (IET) recently. The model of gas solid flow at the bot-tom of the combustor was treated by the tworphase theory of fluidized bed and in the upper regionas a core-sannulus flow structure. The chemical species CO, CO2, H2, H2O, CH4, O2 and N2 wereconsidered in the reaction process. The mathematical model consisted of sub-models of fluid namics,coal heterogeneous and gas homogeneous chemical reactions, heat transfer, particle fragmentation andattrition, mass and energy balance etc. The developed code was applied to simulate an operating stagedcirculating fluidized bed combustion boiler of early design and the results were in good agreement withthe operating data. The main submodels and simulation results are given in this paper.

Reactive gas-solids flows in large volumes—3D modeling of industrial circulating fluidized bed combustors

A model is presented for the simulation of reactive gas-solids flows in large industrial reactors. Circulating fluidized bed （CFB） combustors with several thousands of cubic meters reaction volume are probably the largest reactors of this type. A semi-empirical modeling approach has been chosen to model the three-dimensional concentration distributions of gas and solids components and temperatures inside the combustion chamber of such boilers. Two industrial CFB boilers are investigated in detail： the 105 MWe Duisburg combustor in Germany and the 235 MWe Turow combustor in Poland. The semi-empirical model approach is described first. Then the model is used to show how the three-dimensional concentration and temperature fields are formed by the interaction of several local phenomena. Good agreement between simulation and measurements has been achieved.

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。

300 MW循环流化床锅炉燃煤耦合生物质燃烧及污染物排放特性试验研究

在碳达峰、碳中和背景下,发展燃煤与生物质耦合发电是加快电力转型升级、实现煤电低碳发展的重要途径之一。在某台300 MW循环流化床(CFB)锅炉上设计建设了一套燃煤直燃耦合生物质的燃烧发电系统,并利用该系统进行了燃煤直燃耦合生物质的燃烧特性试验研究。结果表明:该生物质直燃耦合系统运行稳定可靠;CFB锅炉在掺烧木屑颗粒燃料时,随着掺烧比的增加,混合燃料的飞灰含碳量下降、CO排放量降低,混合燃料的燃尽性得以改善;掺烧后经过锅炉燃烧配风优化,锅炉NOx排放量比纯烧原煤排放量略有降低。试验典型工况污染物测试表明:掺入木屑颗粒燃料后,锅炉烟气二噁英排放量为0.0088 ng TEQ/m^(3)(标准工况,φ(O_(2))=11%,下同),飞灰中二噁英排放量为0.0206 ng TEQ/m^(3);飞灰中重金属及P、As、Se等有害微量元素排放值总量为32.121mg/L;底渣中重金属及P、As、Se等有害微量元素排放值总量为3.918 mg/L,烟气和飞灰中的二噁英和重金属等有害物质排放均满足国家环保标准排放限值。

预热空气当量比对循环流化床掺混煤泥预热燃烧的影响

煤泥灰含量大、颗粒细、热值低,煤泥的高效清洁燃烧是固废资源化利用的重要方式之一。采用煤粉流态化预热耦合循环流化床燃烧技术,在30 kW预热燃烧综合评价试验台上,控制煤泥掺混比、给料量、还原区当量比、二/三次风比例及过剩空气系数等参数不变,并借助煤气分析仪和烟气分析仪等测量仪器,开展了循环流化床烟煤掺混煤泥的预热燃烧试验。结果表明,循环流化床预热燃烧系统运行稳定可靠,预热温度800℃以上,预热燃料可持续稳定输送到循环流化床中;烟煤掺混高灰分的煤泥,循环灰量增加,循环流化床燃烧室温差小,温度均匀;预热空气当量比由0.36增至0.51时,预热器内温度增加,预热煤气中CO_(2)、HCN体积分数增加,CO、H_(2)、CH_(4)及NH_(3)体积分数降低,煤气热值由2.02 MJ/m^(3)降至1.49 MJ/m^(3);且随着预热空气当量比的增加,循环流化床燃烧室沿程NO体积分数增加,CO体积分数底部高、上部低,NO_(x)排放量由172 mg/m^(3)增至242 mg/m^(3)(6%O_(2)),可见,较低预热当量比有利于烟煤掺混煤泥的高效清洁燃烧。研究结果可为煤泥的高效燃烧利用提供新型技术路线和数据支持。

基于数据驱动660 MW循环流化床锅炉多目标燃烧优化

为降低某电厂循环流化床锅炉污染物排放,同时提高锅炉燃烧运行经济性,本文采用数据驱动技术实现循环流化床锅炉多目标燃烧优化。基于改进粒子群优化长短期记忆神经网络建立循环流化床锅炉NO_(x)/SO_(2)排放数学模型和锅炉排烟温度数学模型,以相对误差为预测性评估指标以确定最佳网络参数;其次,基于改进粒子群优化长短期记忆神经网络(IPSO-LSTM)、长短期记忆神经网络(LSTM)、广义回归神经网络(GRNN)和反向传播神经网络(BPNN)分别构建NO_(x)/SO_(2)排放数学模型和锅炉排烟温度数学模型,通过比较预测性评估指标,证明本文构建预测模型有效性;最后,基于非支配排序遗传算法(NSGA-Ⅱ)获取不同运行工况下循环流化床锅炉燃烧优化调整方案,以降低NO_(x)/SO_(2)排放浓度,同时维持排烟温度稳定性。结果表明:相比优化前,优化后NO_(x)排放浓度平均降低了10.58%,SO_(2)排放浓度平均降低了25.81%,最大降低了650 mg/m^(3),且排烟温度平均降低0.14%。

循环流化床NOx和SO_(2)协同脱除技术试验研究

结合循环流化床后燃技术(简称“后燃技术”)和炉内喷钙脱硫技术,在0.1 MW循环流化床试验台上研究了循环流化床NOx和SO_(2)协同脱除潜力,主要研究了后燃室脱硫剂添加量对NOx和SO_(2)排放影响以及炉内添加脱硫剂时燃烧温度对NOx和SO_(2)排放的影响。结果表明:通过后燃室注入脱硫剂可以降低SO_(2)排放,能够达到一定的脱硫效果。当燃烧温度较高时,后燃技术下炉内添加脱硫剂,脱硫效果很差。通过适当降低燃烧温度可以实现NOx和SO_(2)的协同脱除。当温度为845℃时,后燃技术下炉内脱硫时可直接实现超低NOx排放,而SO_(2)排放可以降至92.09 mg/m^(3)。后燃技术下炉内低温脱硫时,如果后燃室添加适量脱硫剂,则SO_(2)排放可进一步降低,有望实现NOx和SO_(2)双超低排放,进一步降低循环流化床污染物脱除成本。

探讨CFB锅炉结焦事故原因和应对措施

循环流化床锅炉在实际生产中,因锅炉煤炭燃烧、物料流化不良、风帽大面积损坏、操作控制不当等各种原因,导致锅炉出现结焦,严重影响设备安稳运行。通过对锅炉结焦原因和案例分析,进行技术改造和参数优化,加强日常管理,避免了锅炉结焦事故,确保了装置长周期运行。

600 MW CFB锅炉汽冷式旋风分离器受热面管失效分析及优化措施

基于超临界循环流化床(CFB)锅炉汽冷式旋风分离器受热面管发生的1次失效,为防止类似失效的再次发生,对失效进行试验分析。超低排放选择性非催化还原(SNCR)脱硝系统对耐火材料和受热面管有腐蚀,在高温下分解的产物与受热面管金属发生反应,引起受热面的有效壁厚减薄,最终受热面管因无法承受内部介质的压力而发生失效。结合运行状况及失效原因分析,对耐火材料进行固定方式优化和材料优化,以及提高防磨防爆检查力度、优化雾化空气压力等优化措施,有效提升了运行的可靠性,在汽冷式旋风分离器检修管理方面有推广意义。

800 t/h循环流化床锅炉关键技术的研究与应用

基于某石化企业800 t/h高温超高压循环流化床锅炉的设计条件,为提高锅炉的可靠性与经济性,深入研究了炉内防磨技术、冷却式分离器出口烟道技术、等压二次风箱技术等关键技术。结果表明,采用炉内防磨技术有效减缓了水冷壁、分离器、尾部受热面的磨损现象,锅炉可靠性显著提高;采用冷却式分离器出口烟道技术,浇注料用量降低,锅炉散热损失减小;采用等压二次风箱技术,布风均匀性得到提高,燃尽性也大大改善。锅炉自运行以来,运行稳定,运行参数优于设计要求,具有良好的可靠性和经济性。

碳中和背景下循环流化床燃烧技术在中国的发展前景

循环流化床(CFB)燃烧技术因其独特的低成本污染控制优势得到了高度重视,近年来我国在此领域的技术发展取得了长足的进步。回顾了我国CFB燃烧技术的发展历程,从最初的跟踪学习到技术创新,走出了一条适应中国国情的独立创新发展道路,先后开发出高性能CFB锅炉、节能型CFB锅炉和超低排放CFB锅炉,同时提高蒸汽参数和大型化,引领了CFB技术的国际发展。目前我国成为世界上CFB锅炉最大的设备供应商和使用者,CFB发电机组作为我国燃煤发电体系中的重要组成部分,为可靠廉价电力供应和劣质燃料消纳做出了重要贡献。碳中和条件下,煤炭作为保底能源在电力系统安全托底中不可或缺。作为低热值煤以及难燃高硫无烟煤的高效清洁发电利用的主要方式,CFB锅炉应在深度调峰和快速变负荷灵活性方面展现更大优势。结合新能源高比例消纳的调峰需求,可以开发粉煤CFB锅炉技术、探索分布式小容量高参数CFB锅炉、挖掘CFB机组0~100%负荷长周期压火与快速热态启动潜力,进一步提高CFB机组运行灵活性;在运行灵活性基础上发挥CFB锅炉燃料灵活性的优势,突破高硫无烟煤超超临界高效发电与超低排放同步实现的难题,消纳煤炭绿色开采洗选副产的劣质燃料,纯烧或者掺烧城市污泥、生活垃圾、生物质等低碳可燃废弃物,开发灵活性下的超低排放控制技术,实现CFB机组智能化,助力我国能源结构转型发展。

粉煤循环流化床燃烧技术

双碳背景下,作为燃煤发电的重要组成部分,循环流化床(CFB)燃烧技术实现了劣质燃料的高效清洁利用,也是未来参与电网深度调峰的主力。然而,CFB锅炉在负荷调节速率、深度低负荷及低负荷下的NOx排放控制、受热面磨损等方面还有较大改善空间。为此,提出了粉煤循环流化床(Powdered Coal-Circulating Fluidized Bed,PC-CFB)燃烧技术,将燃料粒度由传统的0~10 mm宽筛分分布缩减为0~1 mm的窄筛分分布,在低床存量下实现足够高的循环流率,通过流态调控化学反应,强化低氮燃烧需要的还原性气氛,并为延长细颗粒石灰石在炉内的停留时间提供了保证,同时改善锅炉燃烧性能。更为重要的是,由于燃料粒度降低,化学反应速度即热量释放变化速率得以提高;辅助以循环干预措施,可提高传热率的变化速度,二者综合可以改善负荷变化率。燃料粒度的变化必然导致床料粒度降低,显著改善了深度低负荷能力以及低负荷下的NOx排放炉内控制能力。该思想得到模型验证:当燃料粒度由常规缩减到0~1 mm时,床料粒度大幅降低,稀相区物料悬浮浓度提高,循环流率提高了约27%;炉内还原性气氛得到增强,NOx原始排放浓度降低约35%;循环系统性能的改善可延长细颗粒石灰石在炉内的停留时间,提高脱硫反应效率,在钙硫比、NOx排放相同条件下,降低了SO2原始排放浓度;同时,燃烧效率显著改善,底渣含碳量降低89%、固体不完全燃烧热损失降低52%,表明PC-CFB燃烧技术在增强CFB锅炉运行灵活性、强化低氮燃烧、提升燃烧性能等方面更具优势。