Predictions of NOx/N2O emissions from an ultra-supercritical CFB boiler using a 2-D comprehensive CFD combustion model

NOx and N2O emissions from an ultra-supercritical circulating fluidized bed(CFB)boiler were predicted using a two dimensional(2-D)comprehensive computational fluid dynamics(CFD)combustion model.This model was developed from a three dimensional model for a supercritical CFB boiler previously constructed by our group.Based on an analysis of the NOx and N2O conversion processes in a CFB boiler,the primary formation and destruction reactions were introduced into the 2-D model and coupled.The resulting model was validated using data from the Baima 600 MW supercritical CFB boiler,and then applied to a 660 MW ultra-supercritical CFB boiler.The effects of excess air,the secondary air(SA)to(primary air(PA)plus SA)ratio and the SA injection height on NOx and N2O emissions were investigated.The results show that a higher excess air volume increases both NOx and N2O emissions,while increasing the SA/(PA+SA)ratio somewhat reduces both the NOx and N2O concentrations.On the basis of the results of this work,optimal locations for SA injection ports so as to lower NOx and N2O emissions are recommended.

Fuzzy disturbance rejection predictive control of ultra-supercritical once-through boiler-turbine unit

In order to overcome the wide-range load tracking and unknown disturbance issues of an ultra-supercritical boiler- turbine unit, a fuzzy disturbance rejection predictive control approach is proposed using the techniques of fuzzy scheduling, model predictive control and extended state observer. Local state-space models are established on the basis of nonlinearity analysis and subspace identification. To eiJiance thedisturbance rejection capability of the controller, a extended state observer is employed to estimate unnown disturbances and model mismatches. The disturbance estimation ennaced local predictive controllers ae subsequently devised based on the local models, the performance of which is further strengthened by incorporating the fuzzy scheduling technique. The simulation results verify the merits of the proposed strategy in achieving satisfactory wide-range load tracking ad disturbance rejection performance.

Ultra-Supercritical——A Preferential Choice for China to Develop Clean Coal Technology

The ultra-supercritical pressure coal-fired power-generation technology (USCT) isa mature, advanced and efficient power generation technology in the world. Comparisonsamong several principal clean coal power-generation technologies show that USCT withpollutant-emission control equipment is superior to others in efficiency, capacity, reliability,investment and environment protection etc. Analyzing the main problems existing in thermalpower industry, it is concluded that the USCT is the preferential choice for China to developclean coal power-generation technology at present. Considering the foundation of thepower industry, the manufacturing industry for power generating equipment and otherrelated industries, it is concluded that China has satisfied the qualifications to develop USCT.

季冻影响下路用CFB灰混凝土孔隙特征及动态力学性能研究

通过室内冻融循环试验和SHPB动力学试验,探究冻融循环对CFB灰混凝土孔隙率的影响特征,分析高应变率作用下冻融循环次数和CFB灰掺量对混凝土动态力学性能的影响。根据公路建设季冻灾害与动载扰动的影响规律,分析CFB灰混凝土的路用可行性。研究表明:在冻融循环作用下,CFB灰混凝土的孔隙率与混凝土可承受的冻融循环次数呈对数关系,CFB灰掺量的增加使混凝土密实度提高,孔隙率减小;随着冻融循环次数的增加,混凝土的动态弹性模量、动态抗压强度呈对数减小,动态峰值应变呈对数增加,掺量为20%的CFB灰混凝土具有较强的动态抗压性能;在公路建设中,掺量不大于20%的CFB灰能有效降低混凝土孔隙率、提高动荷载承载力、改善混凝土的抗冻性。研究成果对于探究CFB灰混凝土力学性能、促进CFB灰混凝土在公路建设中的应用具有重要意义。

CFB飞灰压浆料的制备及高强微膨胀机理研究

利用循环流化床燃煤固硫灰(CFB飞灰)的活性与膨胀性制备压浆料,研究了CFB飞灰掺量和水胶比对压浆料工作性能、强度和膨胀率的影响;CFB飞灰与矿粉以不同比例复配,对比研究了CFB飞灰压浆料的高强微膨胀特性,并采用XRD与SEM分析验证。结果表明,随CFB飞灰替代水泥掺量的增加,压浆料的需水性增强,抗压强度降低,20%(质量分数)CFB飞灰的试样28 d抗压强度与基样接近,可达85.8 MPa,而抗折强度先升高后降低,膨胀率一直升高。随用水量的增加,压浆料的膨胀率降低但均为正值。随CFB飞灰取代矿粉率的提高,压浆料的工作性能降低,28 d抗压强度先升高后降低,其中20%(质量分数)CFB飞灰、10%(质量分数)矿粉复合的试样28 d抗压强度最高,为99.8 MPa,膨胀率一直升高。通过CFB飞灰与矿粉复合配制了各项性能均满足铁标要求的压浆料。CFB飞灰不仅自身水化产生膨胀,还能激活矿粉活性,产生复合增强作用。

Multi-model Predictive Control of Ultra-supercritical Coal-fired Power Unit

The control of ultra-supercritical(USC) power unit is a difficult issue for its characteristic of the nonlinearity, large dead time and coupling of the unit. In this paper, model predictive control(MPC) based on multi-model and double layered optimization is introduced for coordinated control of USC unit. The linear programming(LP) combined with quadratic programming(QP) is used in steady optimization for computation of the ideal value of dynamic optimization. Three inputs(i.e. valve opening, coal flow and feedwater flow) are employed to control three outputs(i.e. load, main steam temperature and main steam pressure). The step response models for the dynamic matrix control(DMC) are constructed using the three inputs and the three outputs. Piecewise models are built at selected operation points. Double-layered multi-model predictive controller is implemented in simulation with satisfactory performance.

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。

Exergy Analysis and Thermal Optimization of a Double-Turbine Regeneration System in a Ultra-Supercritical Double-Reheat Unit

Improving the primary steam parameters is one of the most direct ways to improve the cycle efficiency of a powergeneration system. In the present study, the typical problem connected to the excessively high superheat degree ofextraction steam in an ultra-supercritical (USC) double-reheat unit is considered. Using a 1000 MW power plantas an example, two systems (case 1 and case 2) are proposed, both working in combination with a regenerativesteam turbine. The thermal performances of these two systems are compared with that of the original systemthrough a heat balance method and an exergy balance strategy. The results reveal that the two coupled systemscan significantly reduce the superheat degree of extraction steam, turbine heat rate, and coal consumption of theunit and improve the energy utilization efficiency. These results will provide useful theoretical guidance to futureinvestigators wishing to address the general problem relating to energy conservation and modelling of the coupledextraction steam regenerative system of USC double-reheat units.

生物质CFB氮氧化物排放建模与优化控制

由于生物质循环流化床(CFB)燃烧不稳定,为实现负荷波动过程中机组NO_(x)的动态预测,从锅炉燃烧机理切入,建立了氧量模型与即燃碳模型;对炉内NO_(x)自生成与自还原机理进行分析,并结合数学建模的方法,建立了NO_(x)动态排放模型。进行给料量、二次风量开环阶跃试验;分析NO_(x)排放与氧量耦合情况,采用简化对角解耦与前馈补偿解耦法解除耦合。结合某130 t/h生物质CFB实际运行数据进行仿真试验。结果表明:模型拥有较好的预测效果,能反映氧量及NO_(x)排放过程的动态特性,可实现给料量控制NO_(x)排放质量浓度、二次风控制氧体积分数的单回路控制,所设计的NO_(x)排放质量浓度模型及解耦控制方法可以为今后生物质CFB机组适应动态运行以及智能控制策略设计提供参考。

Development Features of Supercritical (Ultra-Supercritical) Technology in the World and Experiences We Can Learn

The development and technical characteristics in different stages of supercritical (ultra-Supercritical) technology abroad are introduced in this paper. At the same time, according to the development trend of supercritical (ultra-supercritical) technology, the corresponding revelations are given in this paper. That is: It is an inevitable choice to develop supercritical (ultra-supercritical) technology if we want to improve the thermal efficiency and heat efficiency.

Min-max fuzzy model predictive tracking control of boiler-turbine system for ultra-supercritical units

To improve the control performance of nonlinear ultra-supercritical(USC)thermal power units,an improved min-max fuzzy model predictive tracking control(FMPTC)strategy is proposed.First,a T-S fuzzy model is established to approximate the dynamics of the nonlinear boiler-turbine system.Then,based on an extended fuzzy model containing state variables and output variables,a min-max FMPTC is derived for output regulation while ensuring the closed-loop system stability and the inputs in their given constraints.For greater controller design freedom,the developed controller adopts a new state-and output-based objective function.In addition,the observer estimation error is regarded as a bounded disturbance,ensuring the stability of the entire closed-loop control system.Simulation results on a 1000 MW USC boiler-turbine model illustrate the effectiveness of the proposed approach.

CFB灰渣混凝土的组成设计与应用研究

随着循环流化床(CFB)锅炉清洁燃烧技术的大规模应用,所排放的CFB灰渣的处理成为亟待解决的问题。本文以碎石作粗集料、CFB炉渣作细集料以及CFB飞灰作矿物掺合料来制备CFB灰渣混凝土,探讨了CFB炉渣砂率、CFB飞灰掺量对CFB灰渣混凝土的工作性能与力学性能的影响,优化设计了CFB灰渣混凝土配合比,对比研究了CFB灰渣混凝土与机制砂混凝土抗Cl-渗透性能、抗冻性和干燥收缩等耐久性能,并进行了CFB灰渣混凝土小型预制构件的工程应用。结果表明:随着CFB炉渣砂率的增加,CFB灰渣混凝土的抗压强度先增大后降低,随着CFB飞灰掺量的增加,CFB灰渣混凝土的坍落度逐渐降低,抗压强度先增大后降低,优化的最佳配合比为水泥280 kg/m^(3)、CFB飞灰120 kg/m^(3)、矿粉40 kg/m^(3)、CFB炉渣620 kg/m^(3)、碎石1 013 kg/m^(3)、水223 kg/m^(3)、减水剂8.8 kg/m^(3);相比于机制砂混凝土,CFB灰渣混凝土具有良好的抗Cl-渗透性能、抗冻性和较小的干燥收缩,且采用CFB灰渣混凝土制备的小型预制构件在实际工程中具有更好的应用效果。

CFB炉渣细骨料纤维砂浆干燥收缩特性研究

为了实现CFB炉渣的高效利用,提高预拌砂浆的抗裂性,以粉煤灰取代量(体积分数)、CFB炉渣细骨料取代量(体积分数)和PVA纤维掺量(体积分数)为因素,设计正交试验方案L_(16)(4~5),试验研究CFB炉渣细骨料纤维砂浆的干燥收缩特性,分析作用规律,建立回归模型。结果表明:增加粉煤灰取代量可以提高CFB炉渣砂浆稠度,增加CFB炉渣取代量和PVA纤维掺量不利于砂浆稠度的提升;粉煤灰取代量、CFB炉渣取代量为CFB炉渣纤维砂浆的干燥收缩特别显著性影响因素,PVA纤维掺量为显著性影响因素;粉煤灰取代量、PVA纤维掺量对CFB炉渣纤维砂浆的干燥收缩起明显的抑制作用,CFB炉渣使砂浆的干燥收缩呈先降低后增大的变化趋势;砂浆干燥收缩的模型预测相对残差在±5%以内,模型预测结果准确可信。

CFB灰渣对水泥稳定红砂岩集料的增强改性作用

针对红砂岩均质性差,红砂岩集料性能和水泥稳定红砂岩集料路用性能不明确的问题,以水泥稳定石灰岩集料为对照,分别研究了红砂岩粗、细集料取代率。研究了循环流化床(CFB)炉渣、CFB飞灰掺量对水泥稳定红砂岩集料7 d无侧限抗压强度、长期强度、抗干缩性能和抗冻性能的影响规律。采用SEM揭示了CFB灰渣对水泥稳定红砂岩集料的改性作用机理。结果表明:红砂岩集料的组成成分和物理性能与粒径大小存在明显相关性,集料粒径越小,集料中的黏土矿物含量越高,压碎值越低,塑性指数越高,表明可以通过破碎筛分将不同类型红砂岩分离,提高红砂岩集料均质性。水泥稳定红砂岩集料的强度、抗裂性能、抗冻性受红砂岩粗集料替代率影响小,受红砂岩细集料替代率影响大。采用CFB炉渣和CFB飞灰作复合细集料可显著提高水泥稳定红砂岩集料的路用性能。与同水泥掺量水泥稳定石灰石集料相比,经改性后的水泥稳定红砂岩集料7 d无侧限抗压强度高0.8 MPa,干缩应变低49.5%,抗冻性持平。从SEM的试验结果中可以观察到针棒状钙矾石和絮状C—S—H凝胶,这表明CFB灰渣的水化产物起到了胶结增强作用,针棒状钙矾石形成产生的膨胀与CFB炉渣的多孔“内养生”作用可协同降低干缩、防止冻融破坏。

超临界CFB锅炉水冷壁管分区段热应力分析

为确保循环流化床锅炉水冷壁的正常运行,以避免发生蠕变变形、高温腐蚀等生产事故。以600 MW超临界循环流化床(circulating fluidized bed,CFB)锅炉为研究对象,建立了水冷壁温度应力场数值模型。并利用分区段炉膛热力计算理论和新IAPWS-IF97公式,对运行状态中水冷壁分区段进行壁温和热应力分析。结果表明:各区段管壁温度与应力场分布变化一致,但由于工质焓值和高温烟气的交叉作用,区段5存在最高壁温与最大热应力。进一步对区段5进行传热恶化分析可得,管壁最高温度部位发生转移,且壁温与热应力最大值皆超过设计值,可能导致水冷管爆管或断裂。随后针对安全隐患,通过数值模拟方法从降低局部热负荷和控制质量流速的角度来防止锅炉传热恶化,为锅炉安全监测提供了有效建议与防治手段。

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%。

Study on Calculation Method for Partition of Heat Transfer in an Ultra-supercritical Boiler

Use a 1000MW ultra-supercritical tower boiler as the research object. On the basis of one dimensional model, simplify the tube heat transfer model and the radiation heat transfer model;establish the two-dimensional area calculation model with the regional method;?summarize the heat load distribution of flue gas temperature and water wall surface;and compare with the measured data. The error range of the result is acceptable on the project. The distribution of water wall surface heat load along the furnace width and the area where heat transfer deterioration?cause easily along the furnace height direction are studied with the model and algorithm on different boiler load conditions. All these provide the reference for the design and operation of the ultra supercritical boiler.

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。

CFB锅炉宽筛分颗粒临界流化风速研究

基于计算颗粒流体力学(CPFD),通过表征常规CFB锅炉床料(Set 1)、增加炉内细颗粒含量(Set 2)和减小初始床支撑料粒度(Set 3) 3种筛分分布的SiO_(2)颗粒,研究颗粒筛分变化对临界流化风速的影响。研究结果表明:在相同床层高度下,Set 1、Set 2和Set 3床料的临界流化风速分别为0.51、0.30和0.20 m/s。表明增加炉内细颗粒含量和减小初始床支撑料粒度均可明显降低临界流化风速。将宽筛分颗粒临界流化风速的数值模拟结果与相关关联式预测结果进行对比,表明ERGUN关联式的预测结果偏差较小,WEN-YU关联式的预测结果明显偏低。

大掺量CFB灰基泡沫轻质土疲劳特性研究

采用循环流化床灰(CFB灰)对泡沫轻质土进行大掺量改良,可以实现改善泡沫轻质土性能和降低工程造价的双重统一。研究以山西吕梁国峰电厂生产的CFB灰为研究对象,在前期研究基础上,通过四点弯曲小梁疲劳试验对大掺量CFB灰基泡沫轻质土的疲劳特性进行研究。研究结果表明:影响大掺量CFB灰基泡沫轻质土疲劳寿命的一个显著因素是应力比,二者呈负相关关系;疲劳寿命结果服从威布尔分布,离散性较大,且随着应力比的增大,离散性表现得越明显;相比较于传统水泥基泡沫轻质土,CFB灰的掺入,可以增加泡沫轻质土的疲劳寿命,提高其抗疲劳性能。