Desulfurization characteristics of slaked lime and regulation optimization of circulating fluidized bed flue gas desulfurization process--A combined experimental and numerical simulation study

Circulating fluidized bed flue gas desulfurization(CFB-FGD) process has been widely applied in recent years. However, high cost caused by the use of high-quality slaked lime and difficult operation due to the complex flow field are two issues which have received great attention. Accordingly, a laboratory-scale fluidized bed reactor was constructed to investigate the effects of physical properties and external conditions on desulfurization performance of slaked lime, and the conclusions were tried out in an industrial-scale CFB-FGD tower. After that, a numerical model of the tower was established based on computational particle fluid dynamics(CPFD) and two-film theory. After comparison and validation with actual operation data, the effects of operating parameters on gas-solid distribution and desulfurization characteristics were investigated. The results of experiments and industrial trials showed that the use of slaked lime with a calcium hydroxide content of approximately 80% and particle size greater than 40 μm could significantly reduce the cost of desulfurizer. Simulation results showed that the flow field in the desulfurization tower was skewed under the influence of circulating ash. We obtained optimal operating conditions of 7.5 kg·s^(-1)for the atomized water flow, 70 kg·s^(-1)for circulating ash flow, and 0.56 kg·s^(-1)for slaked lime flow, with desulfurization efficiency reaching 98.19% and the exit flue gas meeting the ultraclean emission and safety requirements. All parameters selected in the simulation were based on engineering examples and had certain application reference significance.

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.

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.

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.

Optimization of the Internal Circulating Fluidized Bed Using Computational Fluid Dynamics Technology

The computational fluid dynamics(CFD)technology is analyzed and calculated utilizing the turbulence model and multiphase flow model to explore the performance of internal circulating fluidized beds(ICFB)based on CFD.The three-dimensional simulation method can study the hydrodynamic properties of the ICFB,and the performance of the fluidized bed is optimized.The fluidization performance of the ICFB is improved through the experimental study of the cross-shaped baffle.Then,through the cross-shaped baffle and funnel-shaped baffle placement,the fluidized bed reaches a coupled optimization.The results show that CFD simulation technology can effectively improve the mass transfer efficiency and performance of sewage treatment.The base gap crossshaped baffle can improve the hydraulic conditions of the fluidized bed and reduce the system energy consumption.The cross-shaped baffle and funnel-shaped baffle can perfect the performance of the reactor and effectively strengthen the treatment in the intense aerobic process of industrial sewage.

Numerical simulations and comparative analysis of two- and three-dimensional circulating fluidized bed reactors for CO2 capture

Carbon dioxide(CO2),the main gas emitted from fossil burning,is the primary contributor to global warming.Circulating fluidized bed reactor(CFBR)is proved as an energy-efficient method for post-combustion CO2 capture.The numerical simulation by computational fluid dynamics(CFD)is believed as a promising tool to study CO2 adsorption process in CFBR.Although three-dimensional(3D)simulations were proved to have better predicting performance with the experimental results,two-dimensional(2D)simulations have been widely reported for qualitative and quantitative studies on gas-solid behavior in CFBR for its higher computational efficiency recently.However,the discrepancies between 2D and 3D simulations have rarely been evaluated by detailed study.Considering that the differences between the 2D and 3D simulations will vary substantially with the changes of independent operating conditions,it is beneficial to lower computational costs to clarify the effects of dimensionality on the numerical CO2 adsorption runs under various operating conditions.In this work,the comparative analysis for CO2 adsorption in 2D and 3D simulations was conducted to enlighten the effects of dimensionality on the hydrodynamics and reaction behaviors,in which the separation rate,species distribution and hydrodynamic characteristics were comparatively studied for both model frames.With both accuracy and computational costs considered,the viable suggestions were provided in selecting appropriate model frame for the studies on optimization of operating conditions,which directly affect the capture and energy efficiencies of cyclic CO2 capture process in CFBR.

Model prediction of the operating behavior of a circulating fluidized bed boiler

An improved mathematical model for a circulating fluidized bed (CFB) boiler based on the model developed earlier by the authors was applied to simulate the operation of a 12 MW CFB boiler. The influences of the excess air ratio, primary air ratio, coal particle size distribution, coal properties (ash content and volatile content) and Ca/S ratio on the boiler operation were analyzed. The results showed that the model simulation may be applied to the optimum design and economic operation of the CFB boiler.

基于TF-NGO算法的CFB锅炉床温系统建模研究

床温是循环流化床(CFB)锅炉重要的运行参数之一。针对床温耦合性强、干扰因素多、控制复杂的问题,亟需建立床温的数学模型,以实现床温控制,从而保证CFB锅炉安全、平稳地运行。为此,首先引入了混沌映射、切线飞行(TF)和柯西变异策略改进北方苍鹰优化(NGO)算法,并用实际工况的系统模型测试TF-NGO算法。测试结果表明,TF-NGO算法拥有更快的收敛速度和更高的寻优精度。其次,采集并预处理山西某电厂350 MW超临界CFB锅炉的现场运行数据。最后,采用TF-NGO算法对所建模型的参数进行辨识,并用实际工况数据进行模型验证。辨识和验证结果表明,由TF-NGO算法辨识的床温模型与实际输出拟合度高,能有效反映床温的动态特性,证明所建模型的有效性。该研究为后续对350 MW超临界CFB锅炉床温的优化控制研究奠定了基础。

Modeling of gas-solid flow in a CFB riser based on computational particle fluid dynamics

A three-dimensional model for gas-solid flow in a circulating fluidized bed（CFB） riser was developed based on computational particle fluid dynamics（CPFD）.The model was used to simulate the gas-solid flow behavior inside a circulating fluidized bed riser operating at various superficial gas velocities and solids mass fluxes in two fluidization regimes,a dilute phase transport（DPT） regime and a fast fluidization（FF） regime.The simulation results were evaluated based on comparison with experimental data of solids velocity and holdup,obtained from non-invasive automated radioactive particle tracking and gamma-ray tomography techniques,respectively.The agreement of the predicted solids velocity and holdup with experimental data validated the CPFD model for the CFB riser.The model predicted the main features of the gas-solid flows in the two regimes;the uniform dilute phase in the DPT regime,and the coexistence of the dilute phase in the upper region and the dense phase in the lower region in the FF regime.The clustering and solids back mixing in the FF regime were stronger than those in the DPT regime.

低负荷下CFB锅炉二次风优化对NO_(x)排放影响的数值模拟

为控制循环流化床(circulating fluidized bed,CFB)锅炉低负荷下NO_(x)的原始排放,以某350 MW超临界CFB锅炉为研究对象,基于计算颗粒流体力学(computational particle fluid dynamics,CPFD)方法对40%负荷下燃烧过程进行数值模拟。分析了不同二次风角度、新增二次风量对NO_(x)排放的影响。结果表明:随着射流角度的减小,炉膛出口NO浓度逐渐降低,CO浓度无明显增加。部分二次风上移后炉膛密相区氧浓度降低,不完全燃烧增加,还原性氛围增强,抑制了NO的生成。当新增风量从10%增加到30%时,NO排放浓度降低了17.2%。但随着比例的进一步提高,炉膛密相区的缺氧环境造成燃烧效率下降,温度大幅降低。因此,在不影响燃烧的前提下可以通过提高新增二次风比例来降低NO的原始排放浓度。

Combustion characteristics of low-quality lignite for different bed material sphericities in a circulating fluidized bed boiler:A numerical study

This study delves into the combustion behavior of various lignite types within a circulating fluidized bed boiler(CFBB),with a primary focus on the impact of different bed material sphericity ratios(0.5,0.7,and 0.9).Utilizing bed material with a sphericity ratio of 0.9 sourced from theÇan power plant and verified through experimentation,the research reveals several key findings.Notably,furnace temperatures tended to rise with higher sphericity ratios,albeit with variations between lignite types,particularly highlighting the complexity of this relationship in the case of GLI-Tunçbilek lignite.Pressure levels in the combustion chamber remained consistent across different sphericity ratios,indicating minimal influence on pressure dynamics.Improved combustion efficiency,especially at the bottom of the boiler,was observed at lower sphericity levels(0.5 and 0.7)forÇan lignite,as reflected in CO_(2) mole fractions.While NO_(x) emissions generally decreased with lower sphericity,the sensitivity to sphericity varied by lignite type,with Ilgın lignite showcasing low NO_(x) but high SO_(2) emissions,underscoring the intricate interplay between lignite properties,sphericity,and emissions.Overall,this study advances our understanding of CFBB combustion dynamics,offering insights valuable for optimizing performance and emissions control,particularly in lignite-based power.

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。

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。

大型CFB锅炉床压横向波动的机制研究

大型循环流化床(CFB)锅炉在低负荷运行时,较多存在沿宽度方向两侧床压交替大幅度波动的床压横向波动现象,严重影响锅炉的正常、安全运行。为了深入分析床压横向波动问题,在2台300MW亚临界单炉膛、三分离器循环流化床锅炉上进行测试。在50%负荷的工况下,炉膛发生了床压横向波动,波动周期分别为83和116s,波动幅度分别达到5和11kPa。运行数据分析表明:产生床压横向波动的原因并非外循环回路不均匀导致。提出了大尺度气固两相流动系统固有波动频率的概念,认为炉膛横向压力波动是由风–床系统的压力波动的共振引起的,并建立压力波动简化模型,模型计算能够较好的符合实验结果。建议通过流态重构和调整一次风管网结构来避免床压横向波动的发生。

600MW超临界CFB锅炉炉内稀相区燃烧均匀性的实炉试验研究

在一台600MW超临界循环流化床锅炉上进行了炉内稀相区燃烧均匀性的实炉试验研究,测量了不同负荷下一、二次风优化后距布风板25和38m沿炉膛四周的烟气成分分布及炉膛出口的氧量分布。研究表明：给煤分布决定了烟气的主要分布趋势,二次风标高处的炉内烟气成分分布对炉膛出口烟气成分分布有重要影响。当距布风板25m处的炉膛前后墙烟气氧量标准差达到2.8%时,烟气向上流动到距布风板38m处后仍存在1.8%烟气氧量的标准差。在60%至75%的中低负荷时,距布风板25~38m区域内炉膛单位高度（1m）的耗氧量约为0.13%。通过补充试验与回归分析,得到了炉膛稀相区氧量扩散速率的计算关联式。

二次风分布对CFB锅炉炉内气固混合及燃烧的影响

对于循环流化床锅炉,通常是将总风量分为一次风和二次风来控制燃烧过程的进行,而大型循环流化床锅炉又进一步将二次风沿炉膛高度方向分为若干层并分布在燃烧室四面墙上来加强对燃烧过程的控制。首先介绍了横向二次风射流对促进循环流化床锅炉气固混合及煤燃烧的作用。在一台燃烧低挥发分煤的循环流化床锅炉上进行的实验,分析炉内流场对该锅炉不同供风模式下二次风在炉内分布情况的影响。在此基础上考察二次风在炉内不同的分配方式对煤的燃尽和炉内温度场的影响。实验结果表明,通过二次风优化可以加强炉内气固混合,促进气体和燃料的扩散,提高燃烧低挥发份煤的CFB锅炉燃烧效率。

基于CFB-FGD技术的烟气超低排放工程性能测试评估

以基于烟气循环流化床脱硫除尘技术的中国中部地区某新建350 MW循环流化床机组超低排放工程为研究对象,对100%和75%负荷工况下SO_2、颗粒物等常规污染物和PM_(2.5)、SO_3、汞等非常规污染物的浓度进行现场检测,评估CFB锅炉炉内脱硫+炉外CFB-FGD脱硫除尘技术实现SO_2和颗粒物超低排放的达标能力。现场监测及评估结果表明,该技术组合能实现SO_2小于35 mg/m^3和颗粒物小于10 mg/m^3的超低排放要求,对SO_3、汞等非常规污染物具有一定的协同脱除作用。

大型CFB锅炉并联布置分离器烟气流动特性的数值模拟

针对大型CFB锅炉并联布置分离器的气固流动均匀性问题,采用1:1的实炉结构尺寸建立计算模型,完成了5种分离器出口烟道布置条件下的并联分离器烟气流动均匀性数值模拟计算。计算结果表明,分离器出口烟道的布置形式,对并联三分离器的烟气流动均匀性有重大影响。进一步的分析表明,采用单独的分离器出口烟道布置方式,可以显著改善各分离器的烟气流动均匀性。

CFB锅炉内石灰石同时煅烧/硫化反应动力学及孔结构演变模拟

综合考虑石灰石的分解、CaO烧结和硫化,建立石灰石同时煅烧/硫化反应的随机孔模型。模型计算结果与实验测试结果吻合良好,并采用该模型研究温度、粒径和SO2浓度等因素对同时煅烧/硫化反应动力学特性的影响。循环流化床内石灰石煅烧反应同时发生硫化反应,所生成的CaSO4阻碍了煅烧反应,主要通过两种机制:孔壁面CaSO4产物层阻碍CO2从煅烧部位向颗粒孔道扩散,以及CaSO4阻碍颗粒孔道内CO2向颗粒外扩散。硫化反应中,由于CaSO4的生成而导致的颗粒表层孔隙的快速堵塞是颗粒整体硫化速度下降、硫化程度低于理论值的主要原因。850~910℃范围内反应温度升高明显加速石灰石分解的速度;温度升高增加快速硫化反应阶段的反应速度,但由于颗粒表层以更快的速度发生堵塞而更早地进入慢速硫化反应阶段,导致反应进行到90min时的硫化转化率变化不大。颗粒粒径下降加速硫化反应速度;对于0.4%SO2气氛中850℃下的反应,粒径对煅烧速度在100s前后的影响不同。在100s之前,硫化反应进行程度较低,煅烧反应速度受CaSO4的阻碍作用弱,煅烧速度随粒径减小而增加;100s之后CaSO4对煅烧速度的阻碍作用显现,粒径越小,CaSO4积累量越大,对煅烧速度的阻碍越明显,致使100s后煅烧速度随粒径减小而下降。