600MW自然循环锅炉屏式过热器爆管分析

针对600MW锅炉分隔屏过热器上升管频繁超温爆管的问题,分析了发生爆管的主要原因,提出了切实可行的改造方案及对策。     

四角切圆燃烧锅炉过热器两侧汽温偏差与管道布置的研究

针对大容量四角切圆燃煤锅炉普遍存在的烟气侧速度与温度偏差以及过热器的汽温偏差,对北疆电厂1000MW锅炉实测运行数据进行了分析,并对炉膛流场进行了模拟．结果表明：由于四角切圆锅炉炉膛上部残余旋转导致气流在屏区左右两侧形成流动差异,在折焰角前后两侧汽温偏差的分布规律截然不同．通过对电厂锅炉后屏过热器与末级过热器之间管道布置形式的调整（由交叉改为平行）,使两级受热面的吸热偏差相互抵消,从而提高减温器的调节性能．     

炉膛高度的选取对高温过热器工况影响的研究

文中从辐射换热的基本原理和简化了的辐射换热模型出发，定量分析了炉膛高度的变化对炉膛出口高温过热器辐射热强度的影响，其结果对在电站锅炉的设计和运行中研究及解决过热器起温问题有一定的参考价值。     

Mathematical Modeling of Cross-Flow Tube Heat Exchangers With a Complex Flow Arrangement

The general principles of mathematical modeling of heat transfer in cross-flow tube heat exchangers with complex flow arrangements that allow the simulation of multipass heat exchangers with many tube rows are presented. The finite-volume method is used to solve the system of differential equations for temperature of the both fluids and the tube wall with appropriate boundary conditions. A numerical model of a multipass steam superheater with 12 passes is presented. The convection and radiation heat transfer on the flue gas side are accounted for. In addition, the deposit layer is assumed to cover the outer surface of the tubes. Comparing the computed and measured steam temperature increase over the entire superheater allows for determining the thermal resistance of the deposits layer on the outer surface of the superheater. The developed modeling technique can especially be used for modeling tube heat exchangers when detailed information on the tube wall temperature distribution is needed.     

亚临界电站锅炉过热器系统阻力特性分析

分析了形成亚临界电站锅炉过热器系统压降设计计算和实际运行值偏差的主要因素,提出了通过优化布置过热器系统来降低其流动阻力的具体方案。     

Long term creep properties and microstructure of SUPER304H,TP347HFG and HR3C for A-USC boilers

Abstract

SUPER304H (18Cr–9Ni–3Cu–Nb–N; ASME CC2328) and TP347HFG (18Cr–12Ni–Nb; ASME SA213) have been developed for high strength oxidation resistant steel tubes to operate at high steam temperatures and pressures. The longest creep rupture tests performed to date (600°C for 85 426 h for SUPER304H; 700°C for 55 858 h for TP347HFG) showed that the stable strength and microstructure were retained, with very little formation of σ-phase compared with conventional austenitic stainless steels and no other brittle phases. The alloy HR3C (25Cr–20Ni–Nb–N; ASME CC2115) has been developed for the high strength and high corrosion resistant steel tubes used in recent ultrasupercritical (USC) boilers with steam temperatures of ～600°C. The longest creep test conducted to date (700°C, 69 MPa for 88 362 h) confirmed a stable creep strength and microstructure at 600–800°C. Superheater and reheater tubes of these alloys installed in the Eddystone No.1 USC power plant since 1991 have been removed and investigated. Updated long term creep rupture properties of the steels and microstructural changes during service are reported. Three steel tubes have been successfully applied as standard materials for superheater and reheater tubes in newly built USC boilers.     

Sensitivity Analysis on Neural Network Algorithm for Primary Superheater Spray Modeling

ABSTRACT

Nonlinear, large inertia with long dead time is always associated with the main steam temperature parameter in coal fired power plant. Successful control of the main steam temperature within ±2°C of its setpoint is the ultimate target for coal-fired power plant operators. Two of the most common main steam temperature circuit are primary superheater spray and secondary superheater spray. Various methods were used to model the primary superheater spray control valve opening, and the neural network remains one of the most popular choices among researchers. It remains inconclusive which neural network algorithm types, setup, number of layers, and training algorithm will give the best result. As such, the paper shows the best setup for the neural network algorithm based on sensitivity analysis methodology for one hidden layer. The inputs selected for the neural network are generator output, main steam flow, total spray flow, and secondary superheater outlet steam temperature, while the output selected is primary spray flow control valve opening.     

Heat Transfer during Annular Tube Contact in a Helically Coiled Tube-in-Tube Heat Exchanger

Abstract

Helically wound tube-in-tube heat exchangers are manufactured by coiling two tubes, one placed inside the other. This method often results in the tubes not sharing the same center line, and therefore annular contact occurs in some cases. An experimental comparison was made of such tubes in a heat exchanger with annular contact, as opposed to an aligned (concentric) device without annular contact, in order to quantify the effect of annular contact in terms of heat transfer coefficients and pressure drop. By comparing the heat transfer characteristics, it was concluded that the heat transfer coefficient in the annulus was found to increase substantially. The result was an improved performance by the heat exchanger where annular contact occurs, compared to the heat exchanger with the inner tube in a concentric position.     

Analysis of Fouling in Six-Start Spirally Corrugated Tubes

Abstract

Fouling on heat exchanger surfaces can weaken the heat-transfer capability, increase the energy consumption, and even cause the failure of the whole system. In coaxial heat exchangers, spirally corrugated tubes perform better than smooth ones concerning heat transfer and antifouling. In this article, a parametric study on the antifouling performance of a six-start spirally corrugated tube is carried out with a solid–liquid two-phase model. First, comparisons between a smooth tube and a specific sample six-start spirally corrugated tube on the solid particle volume fraction distributions are carried out. Then, the effects of solid particle diameter, the main geometric parameters, including pitch and the corrugation depth, are investigated. Analyzing the solid particle volume fraction with different geometries, solid particle diameters and Reynolds number, the roles played by the centrifugal force, drag force, and gravity of solid particles on fouling performance in six-start spirally corrugated tubes are obtained. In addition, the corrugation depth affects the volume fraction range more while the pitch affects more on the steady range of particle volume fraction. This work is of significance for further design of spirally corrugated tubes and analysis of fouling problems in heat exchangers.     

Shell-and-Tube Heat Exchanger Geometry Modification: An Efficient Way to Mitigate Fouling

Abstract

Crude oil fouling of a shell-and-tube heat exchanger sized according to TEMA standard is compared to a No-Foul design under industrial operating conditions. For similar operating conditions, TEMA and No-Foul heat exchangers have the same behavior regarding fouling. Since the No-Foul one has less tubes by design for the same heat duty, shear stress is increased. Consequently, the No-Foul heat exchanger is less prone to fouling at the same throughput. Impact of tube bundle geometry is then investigated. Helically finned tubes are compared to plain tubes in the No-Foul heat exchanger. Under similar operating conditions, fouling rates measured are up to an order of magnitude lower than plain tubes (respectively 10^?11 and 10^?10 m² K/J). However, pressure drop across the tube-side in both No-Foul plain and finned setup are increased in comparison to the TEMA heat-exchanger.     

超临界锅炉前屏过热器传热特性分析

过热器超温爆管是造成火电机组非计划停机的重要原因之一。通过对600MW超临界机组的前屏过热器进行分析，计算25MPa、22MPa、19MPa的壁温、吸热量以及传热系数，优化过热器管的设计与选材。计算结果表明，对于以带基本负荷为设计原则的锅炉，长期在低负荷下运行，发生过热器超温爆管的可能性会增大。     

美国双S余热锅炉高压过热器管变形原因分析

本文介绍从美国引进的燃气轮机余热锅炉高压过热器运行４个月发生严重变形的经过,分析其变形原因,提出改进方向。     

U-Tube Assembly Heat Exchanger Performance Analysis Using Cyclic Iteration

This article outlines a technique to predict the performance of the convection passes of pulverized coal boilers, where the heat exchangers are typically comprised of assemblies of U-tube elements. Therein a heat exchanger comprised of n U-tubes per assembly is modeled as 2n rows in the product gas flow direction, and the portions of the straight tubes making up each assembly are considered to be distinct passes in crossflow. It is assumed that in each pass the tube-side fluid is unmixed and the gas-side fluid is mixed, and likewise the gas-side fluid is mixed between passes. The model employs a straightforward approach to predict the performance of a single pass as a building block to predict the performance of the overall assembly.     

Thermo-Hydraulic Performance Enhancement of Finned Elliptical Tube Heat Exchangers by Utilizing Innovative Dimple Turbulators

Abstract

As a new type of fin structure in finned tube heat exchangers, dimple turbulators exhibit excellent potential for thermo-hydraulic performance enhancement. A three-dimensional numerical simulation study was conducted to investigate the influences of five kinds of innovative concave dimple turbulators (CDTs), namely – elliptical dimple, conical frustum dimple, trapezoidal prism dimple, leeward triangular dimple and upward triangular dimple (UwTD) on the thermo-hydraulic performance enhancement in a plate fin-and-elliptical tube (PFET) heat exchanger, where CDTs are textured on the fin surface transversely between the elliptical tubes. The computational results are analyzed by considering the performance evaluation criterion for the PFET heat exchangers with different types of CDT shapes. The present investigation demonstrates that the heat transfer enhancement is intimately pertained to ejection with longitudinal counter-rotating flow, strengthened secondary flow and vortex structures at the downstream rim of CDT. A parametric study on the CDTs indicated that the UwTD vortex turbulators give better thermo-hydraulic performance under the present conditions. The numerical simulation results illustrated different secondary flow structures and heat transfer characteristics of the CDTs with various shapes, which disclosed the influential mechanisms of differently shaped dimple turbulators on the heat transfer augmentation in PFET heat exchangers.     

过热器再热器爆漏事故的原因分析及对策

过热器、再热器爆漏事故严重影响了锅炉机组的安全性和经济性,而造成过热器、再热器爆漏事故的主要因素有超温爆管、磨损、高温腐蚀、热疲劳、质量失控等。通过对这些因素的主要原因和爆口特征的分析,提出了一些过热器、再热器爆漏事故的防治措施。     

电站锅炉过热器设计的几点浅谈

热器的几种分类结构,并对过热器设计中的传热计算和壁温计算的要点做以阐述。     

Performance investigation of plain and finned tube evaporatively cooled heat exchangers

The performance of two evaporatively cooled heat exchangers is investigated under similar operating conditions of air flow rates and inlet hot water temperatures. The heat exchangers are plain and plate-finned circular tube types which occupy the same volume. Spray water, which is circulated in a closed circuit, is injected onto the exposed surfaces of the tubes and fins. The contact between air and spray water results in evaporative heat transfer. The tubes are copper, 10 mm o.d. The finned configuration is constructed by introducing 0.5 mm thick copper plates between the tubes, with a total area ratio of four. A substantial increase in heat transfer takes place for the plate-finned tubes. The increase is 92–140% for air velocities from 1.66 to 3.57 m s⁻¹. A model is used to calculate the thermal performance of the plain and finned tubes assuming a constant spray water temperature in the heat exchanger. The wet-finned surfaces show low fin efficiency compared with dry surfaces. An energy index defined as the ratio of volumetric thermal conductance to air pressure drop per unit length is found to be close for the two heat exchangers. This reveals higher thermal utilisation of the occupied volume by the finned tubes with the same energy index.     

过热器管束断裂分析

用有限元法对余热锅炉过热器管束与外管网系统进行了热应力计算分析,指出启动时为过热器管束受力最恶劣状态,外管网的布置刚度影响着过热器管束的寿命及安全运行。     

Performance analysis of heat exchangers of an existing naphtha hydrotreating plant: A case study

This paper presents the performance evaluation of heat exchangers of an existing naphtha hydrotreating (NHT) plant. Originally, the NHT plant consisted of six plain tube heat exchangers connected in series. During plant revamps operation, three plain tubes were replaced with the three twisted tube heat exchangers. In this study, the heat exchangers data were collected from the plant before and after installation of the three twisted tube heat exchangers. The data were then analyzed to see the effects of the twisted tube configuration on fouling of heat exchangers and heat transfer. The analysis of the data showed that the twisted tube heat exchangers caused reduction in fouling resistance of tubes and increased the heat transfer. Also, the replacement of the three shells and tube type heat exchangers by the twisted tubes resulted in an increase of feed flow rate by about 7.85%. An economic analysis showed that the simple payback period for the twisted tube heat exchangers is 2.12 years. It can be concluded that considerable benefits in terms of energy and cost savings can be realized through the application of this innovative twisted tube heat exchanger technology in existing or new chemical plants.     

过热器弯管段有限元分析剩余寿命

利用有限元法对过热器弯管段进行了详细的应力分析 ,运用序贯热—应力耦合得出总应力场分布 ,显示热应力和总应力的最大值区域并不完全相同 ,证实了实际电站锅炉管道失效区域为总应力较大的区域 ,并应用Larson Miller参数法计算了弯管段的剩余寿命 ,表明实际电站在设计寿命时全部更换管道系统是非常浪费的。为电站寿命监测系统确定应力集中、预测危险区域提供依据 ,从而准确评估管件寿命