百万千瓦超超临界锅炉水冷壁缺陷分析及检修质量控制

百万千瓦超超临界燃煤锅炉炉膛大,水冷壁防磨防爆治理工作任务较重。文章通过介绍超超临界直流锅炉水冷壁结构特点,结合锅炉水冷壁运行及检修实际情况,分析典型缺陷原因,从检修过程管理、检修工艺实施、运行控制调整等方面提出专项方案,旨在提升水冷壁检修质量,保证锅炉安全稳定运行。     

电厂锅炉结焦原因及解决对策

随着电力科技的不断发展,在火电机组中大容量的锅炉越来越受到青睐,目前运行的超临界,超超临界机组也逐渐增多,相应而来的锅炉结焦项目也成为困扰锅炉安全运行的重要问题。尤其是锅炉下降管、过热器部位的结焦会直接影响到蒸汽温度、炉膛出口烟气温度、以及锅炉的排烟温度,甚至会导致管壁超温,直接威胁受热面的安全。更严重的是可影响炉内空气动力工况,关系到锅炉正常气流的喷射,导致锅炉灭火,严重影响到机组的安全稳定运行,可见分析锅炉结焦原因,并提出对策已成为迫在眉睫的问题。     

水冷壁更换有效方案研究

天津华能大港发电有限公司#4锅炉大修,更换15．3米至28．3g水冷壁及同层燃烧器,相应变更连接风箱、管道等设备。施工采用临时支撑加固水冷壁下环形集箱,炉内设置施工平台作为作业平台,间隔切除水冷壁管排,交替安装新水冷壁,炉外搭设运输平台,采用炉内检修平台实行炉膛高空作业的方案。     

1000 MW超超临界双切圆燃烧锅炉结焦与高温腐蚀防控研究

针对一台1 000 MW超超临界双切圆锅炉结焦及水冷壁高温腐蚀问题,采用X射线衍射(X-ray diffraction,XRD)和X射线荧光光谱(X-ray fluorescence,XRF)表征分析了锅炉结焦及高温腐蚀机理,结果表明：煤中钠、钙的赋存降低了煤的灰熔点,造成锅炉结焦;硫化物型高温腐蚀是该锅炉高温腐蚀的主要类型。通过配煤掺烧及配风调整对入炉煤质、燃烧器配风方式的优化发现,选用低硫低结焦性煤进行混配,能够有效缓解炉内结焦问题。同时,锅炉总风量的提高与燃烧器二次配风的合理调整能有效降低炉内还原性气氛浓度,缓解炉内高温腐蚀问题。通过数值模拟方法对锅炉腐蚀倾向的预测结果表明,炉内热角区域需要通过加设贴壁风或水冷壁喷涂等方式进一步预防高温腐蚀。     

超临界W火焰锅炉性能研究与实践总结

本文对已投产的5台超临界W火焰锅炉的运行情况进行分析,并对水冷壁易出现的超温拉裂受损的现象进行了研究,针对水冷壁存在的问题,提出切实有效的解决措施,对超临界W火焰锅炉的安全经济运行具有重要意义.     

浅谈循环流化床锅炉生产运行技巧

大庆石化热电厂现有两台循环流化床锅炉,在燃用设计煤种时锅炉负荷为220t／h,短时最大工况可达240t／h,锅炉保证脱硫效率大于80%。锅炉在燃用设计煤种时,不投油长期安全稳定运行的最低负荷为锅炉的50％负荷,锅炉在大于等于60％负荷情况下保证设计蒸汽参数,锅炉各种运行情况下床温均匀,床表面温差最大不超过50℃,锅炉两侧烟温度不大于50℃。给煤机将煤送人落煤管,然后由风吹入炉膛,与流化状态下的的循环物料掺混燃烧,循环物料经炉膛进入分离室,锅炉燃烧所需空气分别由一、二次风机提供。     

炉内CO测量在防高温腐蚀中的应用

一直以来,高温腐蚀是很多火力发电电站锅炉的痼疾,在锅炉运行过程中,无法监测和判断正在运行的锅炉水冷壁是否正在发生高温腐蚀,因此运行人员也就无从调整。等到停炉甚至因腐蚀爆管后,才能在炉膛内观察到高温腐蚀已发生,这种被动和无法预知给锅炉安全运行带来很大的安全隐患。该文针对高温腐蚀发生的原因,采用炉内水冷壁区域烟气中CO的在线测量技术,通过被测量区域CO的浓度值与高温腐蚀的对应关系,确认炉内燃烧是否出现还原性气氛过浓或火焰刷墙,并进行相应的运行调整,以防止或减轻锅炉水冷壁发生高温腐蚀的现象。     

循环流化床锅炉安装

循环流化床锅炉，简称CFB锅炉。是我国近年来新开发的一种技术先进、工艺可靠、运行稳定、热效率高、能燃烧低发热值煤（煤渣、煤歼石）的节能型锅炉。这种锅炉煤耗量大，风耗量大，运行过程中产生的烟量大、灰量大，渣量也大，故高浓度的烟尘随着高速的烟风对炉内设备（水冷壁管、分离器、过热器、省煤器等）及炉墙磨损也比较大。此外，炉内正压运转，炉顶及烟道为负压运转，故对炉膛，一、二级分离器，烟道等系统的密封性能和耐磨性能的要求特别的高。系统的密封、耐磨程度好坏是保证锅炉安全满负荷运行的关键，因此，筑炉材料的选用，…     

锅炉炉膛热负荷分布拟合算法研究

锅炉炉膛辐射热负荷测量及分布规律的研究可为蒸发受热面及节流孔设计提供必需的数据。提出了炉 膛热负荷测量数据的处理方法,将测得的热负荷数据转换成相对于蒸发受热面平均热负荷的分配不均系数,该系数是炉膛相对高度的函数,它的多项式回归模型不仅要使误差平方和达到最小,而且根据平均热负荷的定义,多项 式系数还要满足给定的等式约束。对于采用普通燃烧技术和空气分级燃烧技术的两类燃煤锅炉,利用该回归模型拟合炉膛辐射热负荷数据,得到不同的分布规律,并与某300 MW锅炉炉膛热负荷测量数据进行了对比;这种以最 小二乘法为基础的改进回归模型既满足了回归变量的内在联系,又对测量数据进行了最佳逼近。     

350MW对冲燃烧锅炉侧墙高温腐蚀研究与优化措施分析

以350 MW对冲燃煤锅炉为研究对象,针对侧墙高温腐蚀进行数值模拟分析研究,研究发现对冲燃烧锅炉炉膛内煤粉气流存在向两侧墙扩散流动的漩涡气流现象,该漩涡气流流动会冲刷侧墙水冷壁壁面,并在侧墙区域形成高还原性气氛和高煤粉浓度的炉膛侧墙环境,导致高温腐蚀和结焦发生,根据该现象,该文提出了一种改进的前后墙贴壁风结合侧墙贴壁风综合技术,数值模拟分析表明,在侧墙布置有贴壁风喷口周围O_2浓度大于3%、煤粉颗粒浓度接近0,可以有效地控制高温腐蚀的发生。     

Effects of nanoparticle migration on force convection of alumina/water nanofluid in a cooled parallel-plate channel

Force convective heat transfer of alumina/water nanofluid inside a cooled parallel-plate channel in the creeping flow regime and the presence of heat generation is investigated theoretically. A modified two-component four-equation non-homogeneous equilibrium model is employed for the alumina/water nanofluid that fully accounts for the effects of nanoparticles volume fraction distribution. To impose the temperature gradients across the channel, the upper wall is subjected to a prescribed wall heat flux while the bottom wall is kept adiabatic. Moreover, due to the nanoparticle migration in the fluid, the no-slip condition of the fluid–solid interface at the walls is abandoned in favor of a slip condition that appropriately represents the non-equilibrium region near the interface. The results indicated that nanoparticles move from the adiabatic wall (nanoparticles depletion) toward the cold wall (nanoparticles accumulation) and construct a non-uniform nanoparticle distribution. Moreover, the anomalous heat transfer rate occurs when the Brownian motion takes control of the nanoparticle migration (smaller nanoparticles).     

The Conditions for the Existence of the Optimal Thickness of a Cooled Anisotropic Wall Subjected to Local Heat Exposure

The problem of the determination of sufficient conditions for the existence of the optimal thickness of an anisotropic wall, one of whose surfaces of is exposed to axisymmetric stationary heat flux with the intensity of the Gaussian type, while the other is cooled by the external medium with a constant temperature, was formulated and solved using the two-dimensional exponential integral Fourier transform. The requirement for minimization of the temperature of the most heated point of object of study was used as an optimality criterion. The sufficient condition that was obtained is an inequality that establishes the link between the thermophysical characteristics of the anisotropic material of a wall, the intensity of heat transfer on its cooled surface, and the factor of the concentration of the outer heat flux. These results confirm the well-known effect of the “drift” of the temperature field in an anisotropic material with the common type of anisotropy of its properties.     

Failure analysis of 101-C ammonia plant heat exchanger

Long-term overheating is a major cause of failures in boiler tubes of different designs and operation conditions. These failures are usually related to the formation and growth of internal oxide scales or deposits at areas of high heat flux. Deposits might have different sources; poor water treatment and general corrosion in the system are two common types of these sources. Thickening of the deposit layer hinders heat transfer and local spots of high metal temperature are created in the tube wall. With increasing metal temperature, creep becomes much faster leading to tube failure under internal pressure. In this paper, a case history involving this type of failure is presented. Using finite element modeling the failure are analyzed and some methods to prevent this type of failure are recommended.     

LNG储罐主容器泄漏时外罐壁的传热特性

以一种LNG储罐为研究对象,利用有限单元法(FEM)分析了在主容器泄漏时的混凝土外罐壁的传热特性,研究了泄漏发生时外罐壁温度随着时间的变化过程,泄漏发展后的外罐壁的温度分布和热流密度,以及热保护边角(TCP)对于外罐壁传热的影响,指出了外罐壁热传导达到稳定后的传热特性.     

Coupled simulation and deep-learning prediction of combustion and heat transfer processes in supercritical CO2 CFB boiler

The supercritical CO₂ (S-CO₂) power cycle has a wide application prospect in coal-fired power generation field because it’s highly effective, compactly structured, and flexible of operation. To observe more accurate heat transfer and coal combustion characteristics in the circulating fluidized bed (CFB) with the distinctive S-CO₂ boundary, a 3D computational fluid dynamics (CFD) simulation of the furnace-side combustion process treated by the multiphase particle-in-cell (MP-PIC) method was conducted in a 600 MW S-CO₂ CFB boiler coupled with the heat transfer process on working fluid side based on the polynomial fitting calculation model. Furthermore, a novel method to predict simulation results via Radial Base Function (RBF) neural network was proposed to simplify the computational process, enhance the sample data fusion, and improve the prediction accuracy. Results show that staggered high-temperature fluid and high heat flux was a major concern in S-CO₂ heating surface arrangement. The temperature rise of wall heaters was less than the conventional steam CFB, and the heat flux of spiral and vertical heat transfer tubes decreased along the tube. The predicted temperature distribution of tubes and cold walls was in a good agreement with the coupling simulation results, whose accuracy can meet the engineering requirements.     

Heat‐flux‐specified boundary treatment for gas flow and heat transfer in microchannel using direct simulation Monte Carlo method

Direct simulation Monte Carlo (DSMC) method has been widely used to study gaseous flow and heat transfer in micro‐fluidic devices. For flows associated with microelectromechanical systems (MEMS), the heat‐flux‐specified (HFS) boundary condition broadly exists. However, problems with HFS boundary have not been realized in the simulation of microchannel flows with DSMC method. To overcome this problem, a new technique named as inverse temperature sampling (ITS) is developed. This technique provides an approach to calculate the molecular reflective characteristic temperature from the specified heat flux at the wall boundary. Coupling with DSMC method, the ITS technique can treat the HFS boundary condition in DSMC method for both simple gas and gas mixtures. For validation, heat flux obtained from two‐dimensional Poiseuille flows with wall‐temperature‐specified (WTS) boundary condition is employed as the initial thermal boundary condition of our new method. Sampled wall temperature by the ITS method agrees well with the expected value. Pressure, velocity and temperature distributions under these two thermal boundary conditions (WTS and HFS) are compared. Effects of molecule collision model and gas–surface interaction model are also investigated. Results show that the proposed ITS method could accurately simulate gaseous flow and heat transfer in MEMS. Copyright © 2007 John Wiley & Sons, Ltd.     

Effects of tube flattening on the fluid dynamic and heat transfer performance of nanofluids

In the present article, numerical simulation of Al₂O₃–water nanofluid flow in different flat tubes are performed to investigate the effects of tube flattening on the fluid dynamic and heat transfer performance of nanofluids. The numerical simulations of nanofluids are performed using two phase mixture model by FORTRAN programming language. The flow regime and the wall boundary conditions are assumed to be laminar and constant heat flux respectively. The simulated results are compared with previously published data and good agreement is observed. The effects of tube flattening on different parameters such as heat transfer coefficient, wall shear stress, nanoparticles distribution, temperature distribution, secondary flow and velocity profiles are presented and discussed. The results show that with increasing the flattening, the heat transfer coefficient and wall shear stress increase. The rate of increasing is soft for all flat tubes except for the tube with the most flattening which has a severe increasing in heat transfer and wall shear stress values.     

塔式太阳能热发电吸热器模拟计算

本文建立了塔式太阳能热发电高温吸热器传热性能数值计算模型,采用有限元分析方法进行模拟计算,编制了预测塔式太阳能热发电吸热器热工模拟程序。本文在综合考虑多场耦合特性的情况下,研究了吸热器单模块周向非均匀热流边界条件下吸热介质对流换热系数、吸热管外壁温度、光热转化效率的数值及分布。数值模拟为工程设计提供可靠的科学依据,为塔式太阳能热发电整体控制策略的制定提供参考。     

In-tube cooling heat transfer of supercritical carbon dioxide. Part 2. Comparison of numerical calculation with different turbulence models

Heat transfer of supercritical carbon dioxide cooled in circular tubes was investigated experimentally. The effect of mass flux, pressure, and heat flux on the heat transfer coefficient and pressure drop was measured for four horizontal cooling tubes with different inner diameters ranging from 1 to 6 mm. The radial distribution of the thermophysical properties (i.e. specific heat, density, thermal conductivity and viscosity) in the tube cross-section was critical for interpreting the experimental results. A modified Gnielinski equation by selecting the reference temperature properly was then developed to predict the heat transfer coefficient of supercritical carbon dioxide under cooling conditions. This proposed correlation was accurate to within 20% of the experimental data.     

Thermal boundary layers over a shrinking sheet: an analytical solution

In this paper, the heat transfer over a shrinking sheet with mass transfer is studied. The flow is induced by a sheet shrinking with a linear velocity distribution from the slot. The fluid flow solution given by previous researchers is an exact solution of the whole Navier–Stokes equations. By ignoring the viscous dissipation terms, exact analytical solutions of the boundary layer energy equation were obtained for two cases including a prescribed power-law wall temperature case and a prescribed power-law wall heat flux case. The solutions were expressed by Kummer’s function. Closed-form solutions were found and presented for some special parameters. The effects of the Prandtl number, the wall mass transfer parameter, the power index on the wall heat flux, the wall temperature, and the temperature distribution in the fluids were investigated. The heat transfer problem for the algebraically decaying flow over a shrinking sheet was also studied and compared with the exponentially decaying flow profiles. It was found that the heat transfer over a shrinking sheet was significantly different from that of a stretching surface. Interesting and complicated heat transfer characteristics were observed for a positive power index value for both power-law wall temperature and power-law wall heat flux cases. Some solutions involving negative temperature values were observed and these solutions may not physically exist in a real word.