Heat flux distribution on circulating fluidized bed boiler water wall

The future of circulating fluidized bed (CFB) combustion technology is in raising the steam parameters to supercritical levels. Understanding the heat flux distribution on the water wall is one of the most important issues in the design and operation of supercritical pressure CFB boilers. In the present paper, the finite element analysis (FEA) method is adopted to predict the heat transfer coefficient as well as the heat flux of the membrane wall and the results are validated by direct measurement of the temperature around the tube. Studies on the horizontal heat flux distribution were conducted in three CFB boilers with different furnace size, tube dimension and water temperature. The results are useful in supercritical pressure CFB boiler design.     

超超临界锅炉水冷壁传热特性和温度偏差

叙述了变压运行超超临界锅炉水冷壁的运行特点,传热恶化、温度偏差与水动力稳定性的国内外研究结果,提出了对垂直内螺纹管水冷壁质量流速的选取和水动力不稳定性校核的看法.     

The study on the heat transfer characteristics of oxygen fuel combustion boiler

According to 350MW and 600MW boilers, under oxygen fuel condition, through the reasonable control of the primary and secondary flow and the correct option and revision of mathematical model, the temperature distribution, heat flux distribution and absorption heat distribution, etc. was obtained which compared with those under air condition. Through calculation, it is obtained that the primary and secondary flow mixed well, good tangentially fired combustion in furnace was formed, the temperature under air condition obviously higher than the temperature under O26 condition. The adiabatic flame temperature of wet cycle was slightly higher than that of dry cycle. The maximum heat load appeared on the waterwall around the burner area. The heat load gradually decreased along the furnace height up and down in burner area. The heat absorption capacity of the furnace under O26 was lower than that under the air condition. The heat absorption capacity of the platen heating surface under O26 was equal to that under air condition. And the heat absorbing capacity of waterwall under O26 was about7%~12% less than that under air condition.     

Heat flux distribution on circulating fluidized bed boiler water wall

The future of circulating fluidized bed (CFB) combustion technology is in raising the steam parameters to supercritical levels. Understanding the heat flux distribution on the water wall is one of the most important issues in the design and operation of supercritical pressure CFB boilers. In the present paper, the finite element analysis (FEA) method is adopted to predict the heat transfer coefficient as well as the heat flux of the membrane wall and the results are validated by direct measurement of the temperature around the tube. Studies on the horizontal heat flux distribution were conducted in three CFB boilers with different furnace size, tube dimension and water temperature. The results are useful in supercritical pressure CFB boiler design. __________ Translated from Journal of Power Engineering, 2007, 27(3): 336–340 [译自: 动力工程]     

1000MW超超临界锅炉水冷壁壁温计算

采用分区计算简化大容量高参数超超临界锅炉炉内辐射、对流传热模型,研究炉膛水冷壁热负荷及壁温的空间分布情况,并与试验数据进行了对比,计算结果与试验值之间的偏差较小,最大为5.72%.该模型与算法可给出不同锅炉负荷条件下,水冷壁壁面热负荷与壁温沿炉膛宽度方向的分布规律.结果表明,水冷壁热负荷与壁温均呈现出中间高两端低的弧形分布.四角切圆燃烧锅炉火焰位置对炉内传热有很大影响.模拟计算可为超超临界锅炉的运行提供参考,预测了在材料允许温度范围内,火焰中心偏斜最大不超过2 m.     

循环流化床锅炉水冷壁的热流密度分布

超临界循环流化床锅炉的一个主要技术关键是炉膛受热面的横向热流分布.在管内工质温度不同、容量不同的3台循环流化床锅炉上,测量了不同高度上膜式水冷壁的金属壁温.将有限元算法用于水冷壁的换热分析,得到了循环流化床锅炉炉膛内烟气向水冷壁的换热系数分布.该结果为超临界CFB锅炉的设计提供了依据.     

1000MW塔式直流锅炉炉膛水冷壁管壁温度和热负荷分布的试验研究

对2台1 000MW超超临界压力塔式直流锅炉炉膛水冷壁管壁温度和热负荷分布进行了测量和计算,并对不同负荷工况、不同磨煤机投运方式下的热负荷和管壁温度分布规律以及炉膛上部垂直水冷壁的热负荷分布进行了分析.结果表明:1 000MW塔式直流锅炉炉膛热负荷的分布规律与其他四角切圆燃烧锅炉炉膛热负荷的分布规律基本一致.由于在最上层的燃烧器上方布置了燃尽风,对炉内烟气的扰动加强,导致沿管长方向的热负荷在54m标高处波动较大;在燃尽风喷嘴中心线以上,因受到燃尽风进入炉膛的影响,水冷壁热负荷大幅度下降.为了避免炉膛大比热区传热恶化,可以将处于拟临界点附近的水冷壁布置在低热负荷区域.     

负荷变化对900 MW超临界锅炉炉内燃烧影响的数值模拟

利用Fluent软件对1台900 MW四角切圆燃烧锅炉在不同负荷下炉内燃烧过程进行了数值模拟,分析了负荷变化对炉内流动和传热的影响规律.结果表明:在高负荷工况下运行时,炉内燃烧充分且稳定,但是炉内火焰更容易冲刷水冷壁,可能发生局部结渣现象;在低负荷工况下运行时,炉内火焰充满度较差,切圆燃烧的稳定性显著下降,炉膛水冷壁灰污表面温度也相应降低,水冷壁表面结渣的倾向弱化,沿高度方向水冷壁吸热不均匀性增大.由于该锅炉的低NOx燃烧器采用了分离燃尽风,使得高温区扩展,火焰中心高度比采用有关标准推荐的方法计算所得结果高4~5 m.     

煤粉锅炉炉膛燃烧_传热一维数学模型的研究

本文建立的大型煤粉锅炉炉膛燃烧、传热一维数学模型可以对各种运行工况条件下的炉膛介质温度、水冷壁吸收热流密度、燃烧释热率等热力参数的一分布值进行分析计算。通过对三个不同型号锅炉的计算分析并与原设计计算结果进行比较,证明此数学模型是合理的。     

Efficiency analysis of radiative slab heating in a walking-beam-type reheating furnace

The thermal efficiency of a reheating furnace was predicted by considering radiative heat transfer to the slabs and the furnace wall. The entire furnace was divided into fourteen sub-zones, and each sub-zone was assumed to be homogeneous in temperature distribution with one medium temperature and wall temperature, which were computed on the basis of the overall heat balance for all of the sub-zones. The thermal energy inflow, thermal energy outflow, heat generation by fuel combustion, heat loss by the skid system, and heat loss by radiation through the boundary of each sub-zone were considered to give the two temperatures of each sub-zone. The radiative heat transfer was solved by the FVM radiation method, and a blocked-off procedure was applied to the treatment of the slabs. The temperature field of a slab was calculated by solving the transient heat conduction equation with the boundary condition of impinging radiation heat flux from the hot combustion gas and furnace wall. Additionally, the slab heating characteristics and thermal behavior of the furnace were analyzed for various fuel feed conditions.     

横火焰玻璃窑炉燃烧空间流动与传热的数值模拟

对横火焰玻璃窑炉燃烧空间内的流动、燃烧及辐射传热等过程进行了数值模拟研究,建立了玻璃窑炉燃烧空间内的综合数学模型,给出了诸控制方程的统一的数值解法,得到了炉内燃烧空间的速度场、温度场、组分浓度分布及燃烧空间向玻璃液面传递的热流分布。     

Solved and Thermal-Hydraulic Problems Systems: Learning from Accidents Unsolved in Boiler

This article begins with a brief review of the similarity law of conventional fossil fuel-fired boilers. The concept is based on the fact that the heat release due to combustion in the furnace is restricted by the furnace volume but the heat absorption is restricted by the heat transfer surface area. This means that a small-capacity boiler has relatively high specific furnace heat release rate, about 10 MW/m 3 , and on the contrary, a large-capacity boiler has a lower value. The surface heat flux limit is dominated mainly by the critical heat flux (CHF) inside the water wall tubes of the boiler furnace. This heat flux limit is almost the same order, independent of the capacity of the boiler. For the safety of water walls, it is essential to retain a good amount of water circulation, i.e., the circulation ratio and velocity of the water must be high enough above the respective critical values. This principle is common knowledge in boiler designer, but the actual situation is not the case. Newly designed boilers often suffer from similar accidents, especially burnout due to water circulation problems. This article demonstrates recent accidents encountered in practical boilers, and raises rather classical but important problems related to two-phase flow and heat transfer.     

燃煤锅炉三维CFD数值模型水冷壁热边界条件设定方法

目前,燃煤锅炉三维CFD数值模拟中对炉膛水冷壁传热分布的预测大都基于给定的壁面温度边界条件。然而,此方法无法体现锅炉运行状态对壁面传热与壁温分布的影响。提出了一种基于锅炉烟气侧放热与汽水侧吸热间热平衡关系的壁面传热计算方法,并重点讨论了壁面传热系数的物理意义及取值方法。研究发现,壁面传热系数基本由壁面结渣状态决定,因此可根据壁面渣层的传热系数确定。本文方法将影响壁面传热的关键因素合理地体现在计算过程中,同时在模型复杂性与工程适用性之间保持了合理的平衡。采用此方法对一台320 MW锅炉的燃烧与传热分布进行了数值模拟,水冷壁吸热量的预测结果与锅炉运行数据吻合良好。     

超超临界锅炉垂直水冷壁热偏差监测系统的应用

针对大容量双切圆锅炉水冷壁热偏差问题,根据水冷壁管结构特征及下水冷壁管出口汽温等运行数据,研究开发B/S架构垂直管圈水冷壁热偏差监测系统。系统实现了水冷壁管工质流量偏差,工质热偏差,沿炉宽、炉深烟气热负荷偏差的在线监测。监测结果为判定水冷壁管内异常阻力特性、分析炉膛热负荷分布规律、优化锅炉燃烧、避免超温引起的降参数运行,提供了有效可靠的数据支持,并为下一步水冷壁监测技术研究工作打下基础。     

A heat transfer model for the analysis of transient heating of the slab in a direct-fired walking beam type reheating furnace

A mathematical heat transfer model for the prediction of heat flux on the slab surface and temperature distribution in the slab has been developed by considering the thermal radiation in the furnace chamber and transient heat conduction governing equations in the slab, respectively. The furnace is modeled as radiating medium with spatially varying temperature and constant absorption coefficient. The steel slabs are moved on the next fixed beam by the walking beam after being heated up through the non-firing, charging, preheating, heating, and soaking zones in the furnace. Radiative heat flux calculated from the radiative heat exchange within the furnace modeled using the FVM by considering the effect of furnace wall, slab, and combustion gases is introduced as the boundary condition of the transient conduction equation of the slab. Heat transfer characteristics and temperature behavior of the slab is investigated by changing such parameters as absorption coefficient and emissivity of the slab. Comparison with the experimental work show that the present heat transfer model works well for the prediction of thermal behavior of the slab in the reheating furnace.     

Performance Evaluation of Two Heat Transfer Models of a Walking Beam Type Reheat Furnace

Two different heat transfer models for predicting the transient heat transfer characteristics of the slabs in a walking beam type reheat furnace are compared in this work. The prediction of heat flux on the slab surface and the temperature distribution inside the slab have been determined by considering thermal radiation in the furnace chamber and transient heat conduction in the slab. Both models have been compared for their accuracy and computational time. The furnace is modeled as an enclosure with a radiatively participating medium. In the first model, the three-dimensional (3D) transient heat conduction equation with a radiative heat flux boundary condition is solved using an in-house code. The radiative heat flux incident on the slab surface required in the boundary condition of the conduction code is calculated using the commercial software FLUENT. The second model uses entirely FLUENT along with a user-defined function, which has been developed to account for the movement of slabs. The results obtained from both models have a maximum temperature difference of 2.25%, whereas the computational time for the first model is 3 h and that for the second model is approximately 100 h.     

环形加热炉热工过程CFD数值模拟及其应用

借助CFD商业软件CFX，考虑流动、辐射、燃烧等，对宝钢环形加热炉的热工过程进行了数值模拟，得到了炉膛内的温度、速度矢量等热工参数的分布图。通过简化处理，对环形加热炉各控制段内的加热过程进行了模拟分析，并根据所得到的管坯表面辐射热流、热电偶温度及管坯表面温度研究了各个段总括热吸收率的分布情况，主要分析了总括热吸收率在管坯圆周方向、长度方向以及各个段之间的变化规律。     

基于燃烧与水动力耦合模型的锅炉蒸汽管超温特性研究

提出一种基于燃烧与水动力耦合模型的锅炉蒸汽管壁温度数值模拟方法,对某660 MW超临界切圆燃烧锅炉壁温进行了计算分析。以均匀外壁温为边界条件,利用Fluent软件模拟了煤粉气固流动、燃烧和辐射等过程,获得了炉内不同位置受热管的传热热流。再以热流分布为边界,采用MATLAB软件建立了工质流动及气-壁-汽换热方程组,Fluent软件重新计算的壁温边界。通过编写模型间的网格映射函数,实现壁温的耦合计算。研究表明:壁温计算值与实测值的最大相对误差在2%以内;炉膛出口残余旋转使水平烟道左侧和右上方热流较大,高温再热器和末级过热器的外壁温沿炉宽方向呈双峰分布;高温再热器整级受热管出口壁温的峰谷差值远高于末级过热器,实际运行中应特别注意高温再热器靠烟道左侧管屏外圈管子向火侧弯头处的超温。     

空气分级燃烧对再热汽温动态特性的影响及控制策略

四角切圆燃烧锅炉低NOx空气分级燃烧改造后的运行实践表明,空气分级燃烧技术对锅炉变负荷运行特性有着明显影响,主要表现为变负荷过程中,汽压反应滞后,再热汽温波动幅度增加,加负荷过程中汽温容易超温,减负荷过程中出现汽温偏低现象。通过分析低NOx空气分级燃烧对锅炉变负荷汽温动态性能影响的机理,提出了二次风挡板变负荷动态附加开度的概念,并进行了工程应用,取得了显著效果。     

超超临界二次再热高压缸流热耦合特性研究

为满足大型核电汽轮机高压缸的开发要求,采用耦合流动计算和共轭传热的数值方法研究了超超临界二次再热高压缸的流热耦合,给出了高压缸排汽腔室和抽汽腔室流体域的流动特性、外缸和内缸固体部件的温度场分布特性。研究结果表明:抽汽腔室进口重量流量不均匀,靠近抽汽管道的进口质量流量整体偏高;双分流波整体内缸的表面强化与排汽腔室的对流换热承受了高压缸几乎全部的温差应力,因此外缸温度场比内缸的温度场相对要更加均匀。研究结果为研发超超临界二次再热高压缸提供理论支持。