R&D and Demonstration of Large Domestic CFB Boilers

In order to develop large CFB boilers with independent intellectual property, Xi'an Thermal Power Research Institute (TPRI) established a laboratory with complete functions for the technical development of CFB boilers. This laboratory consists of a 1-MW and a 4-MW CFB combustion test facilities and a laboratory for limestone desulphurization performance evaluation. It carried out tests on CFB combustion and desulphurization for Chinese typical coals and limestone and research on heat-transfer characteristics and key parts, and developed the first home-made 100-MW CFB boiler. Based on the experience of R&D, the laboratory further researched key techniques for enlarging capacity systematically, and cooperating with Harbin Boiler Co. (HBC), developed the first domestic 210-MW CFB boiler with independent intellectual property and put it into engineering demonstration, laying a solid foundation for the development of CFB boilers of even larger capacity.

Fault Analysis and Innovation in Slag Discharge System of 440-t/h CFB Boiler

CFB boilers have been widely used in China in recent years with their perfect performances in coal adaptability, load variation capability and lower pollutant emission. The No.3 135-MW CFB unit in Lianzhou Power Plant is the f irst 440-t/h series CFB unit in Guangdong Province. It f inished 72-hour trial operation in Feb. 2004 and was transferred to trial operation. During the trial operation and the next commercial operation, there were some problems happened in the boiler slag discharging system, seriously affecting the safe and reliable operation and the loading capability. After innovation, these problems have been completely solved. Hopefully the solutions may be used for reference to the units with similar problems.

Flexible Co-Combustion of High Ratios of Sustainable Biomass with Coal in Oxy-CFB Boiler for CO₂Capture

Coal-fired plants are under pressure to reduce their carbon-intensity. Available options include co-firing CO2-neutral biomass, oxy-fuel-combustion as part of a carbon capture process or a combination of both to give a “CO2-negative” power plant. BioCCS, the combination of CO2 Capture and Storage (CCS) with sustainable biomass conversion, is the only large-scale technology that can achieve net negative emissions. Combining, developing and demonstrating the oxy-combustion of high ratios of sustainable biomass with coal in flexible circulating fluidized bed (CFB) boiler will bring significant advances in the reduction of greenhouse gases (GHG) emissions. Areas addressed include possibilities for: biomass characterization;handling and feeding;co-firing ratios definition;CFB oxy-co-combustion studies;combustion performance;boiler flexibility in fuel and load;main emissions analysis;slaging, fouling and agglomeration;corrosion and erosion;and implications on plant operation and associated costs. The article will detail a comprehensive understanding on sustainable biomass supply, co-firing ratios and how direct biomass co-combustion under oxy-fuel conditions can be implemented. It seeks to push biomass co-combustion in future large-scale oxy-fuel CFB power stations to high thermal shares while enhancing the power plants’ operational flexibility, economic competitiveness and give operational procedures. There will be a need to consider the public acceptance of power production from coal and coal sustainability, by its combination with renewable sources of energy (biomass).

Influence of Limestone Addition on Combustion and Emission Characteristics of Coal Slime in the 75 t/h CFB Boiler with Post-Combustion Chamber

Coal slime can be disposed in quantity and fully utilized in a well-designed circulating fluidized bed(CFB)boiler,but the nitrogen oxides(NO_(x))and sulphur dioxide(SO_(2))emissions generated in the combustion of coal slime have contributed to serious atmospheric pollution.High Temperature&Post-combustion Technology,a novel and high-efficient way to reduce the NO_(x)emission in the process of combustion,is applied to a 75 t/h CFB boiler burning exclusively coal slime,which will succeed to meet the ultra-low NO_(x)emission standard.To further explore an appropriate method to reduce the SO_(2)emission under the condition of new technology,the experiments were conducted on a 75 t/h CFB boiler with post-combustion chamber to study the influence of limestone addition on the combustion and emission characteristics of coal slime.The experimental results showed that High Temperature&Post-combustion Technology combined with the sorbent injection in the furnace is a very promising technology to control the NO_(x)and SO_(2)emissions simultaneously.Limestone addition can cause the slight decrease in combustion temperature.Limestone addition will lead to the increase in NO_(x)emission in the combustion of coal slime.In 75 t/h coal slime CFB boiler,the desulfurization efficiency of limestone injection in furnace is close to 98%,achieving the ultra-low SO_(2)emission.To meet the standard of ultra-low NO_(x)and SO_(2)emission,the two technologies for simultaneous removal of NO_(x)and SO_(2)emissions are economical and feasible currently:Removal of SO_(2)under ultra-low NO_(x)emission and Removal of NO_(x)under ultra-low SO_(2)emission.

CPFD modeling of hydrodynamics,combustion and NOx emissions in an industrial CFB boiler

The ultra-low NOx emission requirement(50 mg/m^(3))brings great challenge to CFB boilers in China.To further tap the NOx abatement potential,full understanding the fundamentals behind CFB boilers is needed.To achieve this,a comprehensive CPFD model is established and verified;gas-solid flow,combustion,and NOx emission behavior in an industrial CFB boiler are elaborated;influences of primary air volume and coal particle size on furnace performance are evaluated.Simulation results indicate that there exists a typical core-annular flow structure in the boiler furnace.Furnace temperature is highest in the bottom dense-phase zone(about 950℃)and decreases gradually along the furnace height.Oxygen-deficient combustion results in high CO concentration and strong reducing atmosphere in the lower furnace.NOx concentration gradually increases in the bottom furnace,reaches maximum at the elevation of secondary air inlet,and then decreases slightly in the upper furnace.Appropriate decreasing the primary air volume and coal particle size would increase the CO concentration and intensify the in-furnace reducing atmosphere,which favors for NOx reduction and low NOx emission from CFB boilers.

Numerical Investigation on the Heat Transfer Characteristics of Supercritical Water in a Non-Uniformly Heated Tube for a Supercritical CFB Boiler

In this paper,a numerical model was built by ANSYS FLUENT to investigate the heat transfer performances of supercritical water in a circumferential non-uniformly heated vertical tube.The Shear Stress Transport(SST)k-ωmodel was adopted for describing turbulence.The operating parameters are chosen according to a 660 MW ultra-supercritical CFB boiler.The heat transfer performances under different operating parameters,such as boiler load,flow direction and heat flux distribution are analyzed.The temperature and heat flux on inner wall varies along the circumference and show symmetric distributions.The overall heat transfer performances at each cross section are better than the local heat transfer performance of midpoint of heating side.Flow direction has a great influence on heat transfer performance;it changes the radial distribution of axial velocity and then affects the turbulence distribution.Therefore,upward flow condition shows a better heat transfer performance.Smaller heat flux improves both the overall and local heat transfer performances.Reducing the heat flux area is not conducive to the overall heat transfer,but does not affect the local heat transfer at the midpoint of heating side.Finally,a new correlation is fitted based on the simulated results of supercritical water heat transfer with circumferential non-uniform heat flux distributions.

300 MW CFB锅炉旋风分离器改造数值模拟研究

旋风分离器分离性能会显著影响循环流化床锅炉的运行。为解决某300 MW循环流化床锅炉旋风分离器分离器性能差的问题,基于欧拉-拉格朗日框架,使用UGNX12.0软件对该300 MW循环流化床锅炉的炉膛、旋风分离器、返料阀按照实际尺寸1∶1建立全回路几何模型,根据实际参数设置边界条件,并通过Barracuda软件进行数值模拟,分析旋风分离器烟道入口各参数(入口烟道高度、入口烟道宽度、入口下倾角大小及中心筒插入深度)对旋风分离器效率及压降的影响;综合考虑分离器的分离效率、压降以及磨损量,提出了2个改造方案。仿真结果表明:炉膛内压力模拟值与实际值的偏差均在5%以内,模拟结果较为精确;2个方案在各负荷下均能提升旋风分离器分离性能,方案1满负荷下效率相较于较改造前提升了0.260%,压降降低了13.1 Pa,方案2满负荷下效率相较于改造前提升了0.240%,压降降低了53.7 Pa;随着负荷降低,旋风分离器效率提升逐渐不明显,在300、260和160 MW负荷下,方案1分别提升0.263%、0.178%和0.023%,方案2分别提升0.243%、0.174%和0.020%。

CFB锅炉掺烧气化细渣技术研究进展

煤气化渣产量大、存量多,常规的填埋和堆积处理不但占用大量土地资源,而且还存在严重的污染风险和安全隐患。本文介绍了气化细渣的组成、结构和燃烧特性,综述了残碳富集、脱水干化等气化细渣预处理方法的研究进展,从气化细渣的含水率、灰分、掺烧比例及污染物排放情况等方面分析了气化细渣掺烧对循环流化床(CFB)锅炉燃烧的影响,指出CFB锅炉掺烧气化细渣具备显著的环保和经济效益,是气化细渣实现减量化、无害化和资源化利用的主要途径之一。

CFB锅炉输煤系统增设筛分破碎设施方案研究

苏晋朔州电厂循环流化床锅炉所需合格的燃煤(0~8 mm)原设计由附近选煤厂筛分破碎后直接提供,自公司2×660 MW机组投产后,因配套选煤厂供电厂煤量不足且其燃煤粒径超标,同时电厂从周边露天矿协调调入汽运煤,汽运煤颗粒度更是超标严重,造成锅炉频繁结焦、下渣口堵塞等问题,严重时造成停机事故。为严格控制入炉煤粒径,提高设备运行稳定性和经济性,针对燃煤粒径超标问题,电厂提出在厂内增加筛分破碎设施,由于电厂设计阶段未做预留,没有合适的场地可供筛分破碎系统建设。专家组经过对生产厂区进行踏勘,提出2种较为可行的方案,经分析论证,最终选择在1号转运站处向地下深挖并采用大倾角皮带等方式建造紧凑型筛分破碎楼的创新方案,有效解决了建造空间不足的问题,改善了入炉煤的颗粒度,为同类型电厂新增破碎设施改造工作提供参考和依据。

循环流化床锅炉(CFB)系统流程模拟

以某石化项目450 t/h超高压循环流化床锅炉系统为对象,采用Thermoflex软件建模并对其进行变工况分析,通过与锅炉厂提供的实际数据进行对比,验证了该流程模拟的准确性。利用该模型进行了不同煤种工况对系统的影响因素分析,研究结果可为该锅炉系统设计和设备选型提供理论依据,对该项目动力站实际生产运行提供指导。

COAL COMBUSTION EFFICIENCY IN CFB BOILER

The carbon content in the fly ash from most Chinese circulating fluidized bed (CFB) boilers is much higher than expected, thus directly influencing the combustion efficiency. In the present paper, carbon burnout was investigated both in field tests and laboratory experiments. The effect of coal property, operation condition, gas-solid mixing, char deactivation, residence time and cyclone performance are analyzed seriatim based on large amount of experimental results. A coal index is proposed to describe the coal rank, defined by the ratio of the volatile content to the coal heat value, is a useful parameter to analyze the char burnout. The carbon content in the fly ash depends on the coal rank strongly. CFB boilers burning anthracite, which has low coal index, usually have high carbon content in the fly ash. On the contrary, the CFB boilers burning brown coal, which has high coal index, normally have low carbon content. Poor gas-solid mixing in the furnace is another important reason of the higher carbon content in the fly ash. Increasing the velocity and rigidity of the secondary air could extend the penetration depth and induce more oxygen into the furnace center. Better gas solid mixing will decrease the lean oxygen core area and increase char combustion efficiency. The fine char particles could be divided into two groups according to their reactivity. One group is 'fresh' char particles with high reactivity and certain amount of volatile content. The other group of char particles has experienced sufficient combustion time both in the furnace and in the cyclone, with nearly no volatile. These 'old' chars in the fly ash will be deactivated during combustion of large coal particles and have very low carbon reactivity. The generated fine inert char particles by attrition of large coal particles could not easily burn out even with the fly ash recirculation. The fraction of large coal particles in coal feed should be reduced during fuel preparation process. The cyclone efficiency controls the particle residence time in CFB loop, especially for that of the fine particles. So the cyclone efficiency, especially the cut size, will greatly influence the carbon content in the fly ash.

Restart-up Performance of a CFB Boiler after a Sudden Power Failure Accident

Due to the massive bed materials in its typical main loop,a circulating fluidized bed(CFB)boiler may face greater trouble in operation and restart-up if an unplanned sudden power failure happens in the power plant.This study aims to explore the restart-up performance of a 170 t/h natural circulation CFB boiler after a sudden power failure and evaluate whether the hot restart-up can be realized.The heat transfer process after the restoration of the primary air is modeled.Validating the isothermal property of the bed after the restoration of the power and air supply,the correlation among the accident duration time,bed temperature after the power restores,inlet air temperature,air supply time,and air velocity is proposed.The predicted results indicate that the major influencing factor of the bed temperature during this process is primary air velocity.To provide guidelines for judgment on whether the hot restart-up can be realized,the maximum values of the air supply time and accident duration time for hot restart-up for different types of coals are given.The results show both of them have a rapid decrease as the coal ignition temperature in a CFB boiler increases from 450°C to 650°C,which also means that the coal ignition temperature plays a very important role in the restart-up process.Based on the simulation results of bed temperature during the accident,it is also estimated that the drum level drops by 77.7 mm after 8 hours but still stays in the permissible range.

基于ISO-PSO的350 MW超临界CFB锅炉主汽温建模研究

针对火电厂目前主蒸汽温度数学模型不准确、不能有效地反应实际生产过程、辨识结果偏差较大等问题,使用学习因子动态调整及随机惯性权重策略改进的二阶振荡粒子群优化(ISO-PSO)算法进行建模。首先,采用学习因子动态调整、随机惯性权重策略对二阶振荡粒子群算法进行改善。测试结果表明,改进算法拥有更好的收敛速度及寻优精度。其次,处理山西某电厂350 MW超临界循环流化床(CFB)锅炉在300 MW工况下采集到的主蒸汽温度数据。最后,对比ISO-PSO算法和粒子群优化(PSO)算法。辨识结果及验证结果表明,ISO-PSO算法辨识的主蒸汽温度模型与实际输出的拟合度更高,能够更加准确、快速地反映主蒸汽温度的变化。所建立的主蒸汽温度模型可以及时跟踪实际曲线。该研究为后续350 MW超临界CFB锅炉主蒸汽温度优化控制研究奠定了良好的基础。

基于COLGWO算法的CFB锅炉燃烧系统模型辨识

建立循环流化床(circulating fluidized bed,CFB)锅炉燃烧系统的准确模型对提升锅炉燃烧系统控制性能尤为重要。针对现有建模方法存在的待调节参数过多、精度不足等问题,提出一种基于莱维飞行策略的混沌对立学习灰狼优化(chaotic opposite-learning grey wolf optimization,COLGWO)算法进行建模。首先,利用混沌序列和对立学习策略改善初始种群,并引入莱维飞行策略、可调节学习衰减率和扰动因子,增加寻优速度的同时避免陷入局部最优。然后,利用350 MW CFB锅炉燃烧系统的数据进行建模,利用COLGWO算法辨识得到模型的最优参数值。最后,使用现场实际运行数据对所建模型的有效性进行验证。实验结果表明,相较于对比算法,所提算法能建立较为准确的燃烧系统模型,具有更优良的收敛性能,为系统模型的快速辨识提供了新途径。

基于CPFD方法的660MW超临界CFB锅炉循环回路均匀性研究

采用计算颗粒流体力学(CPFD)方法对某660 MW超临界循环流化床锅炉的炉膛、分离器和下部料腿进行了模拟,分析了锅炉负荷、分离器出口压力、一二次风配风和非均匀二次风对各回路固体流率的影响。结果表明:在稳定性分析中,压力模拟值与锅炉运行数据的平均偏差为9.6%,循环回路固体流率平均值与设计物料流量的平均相对偏差为9.49%;中间循环回路固体流率较高,回料口与中间分离器的非对应布置对左、右半炉的总固体流率影响不大;较高的分离器出口压力对不同回路固体流率的分布影响较大,当出口压力较低时,其影响减少;均匀性最好的配风比为50∶50,在此条件下,分离器固体流率的相对极差为5.97%;当炉膛中部的二次风量减少至24%时,相对极差减小到8.45%。

基于改进差分进化算法的CFB锅炉主蒸汽压力建模

建立准确的主蒸汽压力数学模型对提升循环流化床(CFB)锅炉主蒸汽压力控制系统性能有着实际意义。受现场条件制约,近年来基于数据驱动的闭环建模已趋于实用化。针对模型参数辨识过程寻优速度和精度指标,提出一种引入两个权重系数的改进差分进化(IDE)算法。与传统差分进化算法相比,改进后的算法在模型参数辨识过程中的寻优速度和精度均有提升,辨识所得模型更加准确。该结果证明了改进后算法的稳定性。通过采集山西某电厂350 MW超临界CFB锅炉现场的实际运行数据并进行预处理,将燃料量和汽机阀门开度同时作为输入、主蒸汽压力作为输出,并利用IDE算法寻优得到主蒸汽压力的最佳模型参数。对比结果表明,模型有着更高的拟合度。该研究对350 MW超临界CFB锅炉主蒸汽压力优化控制有一定的指导意义。

The Heat Transfer Coefficients of the Heating Surface of 300 MWe CFB Boiler

A study of the heat transfer about the heating surface of three commercial 300 MWe CFB boilers was conducted in this work. The heat transfer coefficients of the platen heating surface, the external heat exchanger (EHE) and cyclone separator were calculated according to the relative operation data at different boiler loads. Moreover, the heat transfer coefficient of the waterwall was calculated by heat balance of the hot circuit of the CFB boiler. With the boiler capacity increasing, the heat transfer coefficients of these heating surface increases, and the heat transfer coefficient of the water wall is higher than that of the platen heating surface. The heat transfer coefficient of the EHE is the highest in high boiler load, the heat transfer coefficient of the cyclone separator is the lowest. Because the fired coal is different from the design coal in No.1 boiler, the ash content of the fired coal is much lower than that of the design coal. The heat transfer coefficients which calculated with the operation data are lower than the previous design value and that is the reason why the bed temperature is rather high during the boiler operation in No.1 boiler.

大型CFB锅炉低负荷再热汽温稳定特性

作为灵活发电的关键环节之一,长期稳定低负荷运行技术在可再生能源并网规模不断扩大的过程中发挥着重要作用。循环流化床(CFB)锅炉负荷调节过程中,为降低污染物排放或调平床温,常采用不均匀给煤的运行方式,这对CFB锅炉的设计和运行提出了更高要求。同时,低负荷时CFB锅炉炉膛出口烟气温度较低,如何保证再热蒸汽参数达到额定值是实现CFB锅炉灵活性运行亟待解决的问题之一。针对2台350 MW超临界CFB锅炉断煤低负荷运行工况参数进行深入计算分析,研究了低负荷时稳定再热汽温措施。研究发现,锅炉在部分给煤点中断的断煤工况下运行时,床温、炉膛出口烟温、炉膛出口氧量、高温再热器管屏出口蒸汽温度的变化趋势与各给煤口的给煤量基本呈正相关。但由于超临界CFB锅炉水冷壁具有正流动响应特性,给煤偏差及床温偏差对水冷壁的出口汽温偏差影响不大。基于上述研究,提出了一种针对长期调峰与低负荷运行超临界CFB锅炉稳定炉内高温再热器出口汽温的锅炉改造与运行优化技术方案。在低负荷下可保证高温再热器出口汽温基本稳定。