Dry сoolers and air-condensing units (Review)

The analysis of factors affecting the growth of shortage of freshwater is performed. The state and dynamics of the global market of dry coolers used at electric power plants are investigated. Substantial increase in number and maximum capacity of air-cooled condensers, which have been put into operation in the world in recent years, are noted. The key reasons facilitating the choice of developers of the dry coolers, in particular the independence of the location of thermal power plant from water sources, are enumerated. The main steam turbine heat removal schemes using air cooling are considered, their comparison of thermal efficiency is assessed, and the change of three important parameters, such as surface area of heat transfer, condensate pump flow, and pressure losses in the steam exhaust system, are estimated. It is shown that the most effective is the scheme of direct steam condensation in the heat-exchange tubes, but other schemes also have certain advantages. The air-cooling efficiency may be enhanced much more by using an air-cooling hybrid system: a combination of dry and wet cooling. The basic applied constructive solutions are shown: the arrangement of heat-exchange modules and the types of fans. The optimal mounting design of a fully shopassembled cooling system for heat-exchange modules is represented. Different types of heat-exchange tubes ribbing that take into account the operational features of cooling systems are shown. Heat transfer coefficients of the plants from different manufacturers are compared, and the main reasons for its decline are named. When using evaporative air cooling, it is possible to improve the efficiency of air-cooling units. The factors affecting the faultless performance of dry coolers (DC) and air-condensing units (ACU) and the ways of their elimination are described. A high velocity wind forcing reduces the efficiency of cooling systems and creates preconditions for the development of wind-driven devices. It is noted that global trends have a significant influence on the application of dry coolers in Russia, in view of the fact that some TPP have a surface condensers arrangement. The reasons that these systems are currently less efficient than the direct steam condensation in an air-cooled condenser are explained. It is shown that, in some cases, it is more reasonable to use mixing-type condensers in combination with a dry cooler. Measures for a full import substitution of steam exhaust heat removal systems are mentioned.     

火电站直接空冷凝汽器设计及校核计算和性能分析

掌握火电站直接空冷凝汽器的设计和校核计算方法并进行性能分析,对于提高我国直接空冷机组的设计和运行水平具有重要意义。以600MW机组直接空冷凝汽器为例,在传热理论模型分析的基础上,分别对其设计和校核计算过程进行了讨论,对直接空冷凝汽器性能影响因素进行了分析,对性能变化规律进行了研究。结果表明直接空冷凝汽器的设计过程要综合考虑气象条件尤其是环境大风的影响、换热要求和空冷电站的平面布局,而校核计算则需充分考虑凝汽器积灰的影响,并建立汽轮机背压和凝汽器积灰厚度之间的关系,为凝汽器清洗提供理论依据。冷却空气流量、凝汽器凝结蒸汽量、空冷凝汽器积灰会显著影响空冷凝汽器的性能,进而影响汽轮机背压,影响机组运行的经济性。     

直接空冷机组冬季启停冻结问题及防范措施

大型直接空冷燃煤发电机组在冬季启停过程中,空冷凝汽器常常会发生大面积冻结、损坏等事故。针对空冷凝汽器冻结的主要原因,提出了控制运行参数,在停机过程中合理调整冷却风机组的运行方式,退出部分空冷凝汽器,投入旁路系统以增加空冷岛的进汽量等措施,以防止空冷凝汽器冻结。     

组态王在凝汽器胶球清洗系统中的应用

汽轮机凝汽器采用循环水冷却时,冷却水中所夹带的杂质和污物会附着在凝汽器铜管的冷却水侧,甚至堵塞冷却管,使凝汽器的冷却效果降低,影响凝汽器管的真空度和汽轮机的效率。为了提高汽轮机的效率,现在一般都采用胶球清洗的方式来达到保持凝汽器铜管内表面的清洁。文章介绍了利用组态王kingview6．01组成汽轮机凝汽器胶球清洗控制系统的步骤、调试方法等。     

冷却空气迎面风速和温度对直接空冷系统动态特性的影响

直接空冷机组和常规湿冷机组由于在冷端系统上差别较大,使得空冷机组的控制必须考虑外部环境变化对于汽轮机冷端的影响。该文在空冷凝汽器静态变工况计算的基础上,考虑空冷系统凝汽器的蓄热效应,建立了直接空冷凝汽器动态数学模型,该模型能够分析冷却空气迎面风速和环境温度对直接空冷系统凝汽器动态特性的影响。得到了冷却空气迎面风速和环境温度对直接空冷机组背压的影响曲线,仿真结果表明随着环境温度的升高和冷却空气迎面风速的降低,系统的稳定时间变长,证明直接空冷系统凝汽器的时间常数随着空冷凝汽器的散热能力的强弱而有相应变化,并为进一步研究适用于直接空冷机组的背压保护控制策略提供了参考。     

核电站汽轮机旁路排放系统全排凝汽器设计优化

CPR1000核电机组常规岛采用半转速汽轮发电机组,凝汽器换热面积和循环冷却水量较全转速汽轮机都有大幅增加,凝汽器具备接收常规岛旁路排放系统(GCT-c)全部蒸汽排放量的能力.通过对防城港核电厂一期工程GCT-c系统进行设计优化,降低了除氧器设备工程造价,提高了GCT-c系统的可用性.     

三排管直接空冷凝汽器冻结原因

针对山西漳山发电有限责任公司300MW机组发生三排管直接空冷凝汽器冻结问题,分析了三排管直接空冷凝汽器管束冻结的原因,内因是在迎风侧第1排翅片管内蒸汽倒流并有空气聚积,外因是环境温度低。文章阐述了三排管直接空冷凝汽器在设计中所存在的不足及其改进建议,供已投运的三排管直接空冷凝汽器改造和拟建机组设计参考。     

High-efficiency condenser of steam from a steam–gas mixture

The design of a module for a high-efficiency condenser of steam with a high content (up to 15%) of noncondensable gases (NCGs) with a nearly constant steam–gas mixture (SGM) velocity during the condensation of steam has been developed. This module provides the possibility to estimate the operational efficiency of six condenser zones during the motion of steam from the inlet to the SGM suction point. Some results of the experimental tests of the pilot high-efficiency condenser module are presented. The dependence of the average heat transfer coefficient k? on the volumetric NCG concentration v? has been derived. It is shown that the high-efficiency condenser module can provide a moderate decrease in k? from 4400–4600 to 2600–2800 W/(m² K) at v? ≈ 0.5–9.0%. The heat transfer coefficient distribution over different module zones at a heat duty close to its nominal value has been obtained. From this distribution, it can be seen that the average heat transfer coefficient decreases to 2600 W/(m² K) at an NCG concentration v? = 7.5%, but the first condenser sections (1–3) retain high values of k? at a level of no lower than 3200 W/(m² K), and the last sections operate less well, having k? at a level of 1700 W/(m² K). The dependence of the average heat transfer coefficient on the water velocity in condenser tubes has been obtained at a nearly nominal duty such that the extrapolation of this dependence to the water velocity of 2 m/s may be expected to give k? = 5000 W/(m² K) for relatively pure steam, but an increase in k? at v? = 8% will be smaller. The effect of the gas removal device characteristic on the operation of the high-efficiency condenser module is described. The design developed for the steam condenser of a gas-turbine plant with a power of 25 MW, a steam flow rate of 40.2 t/h, and a CO₂ concentration of up to 12% with consideration for the results of performed studies is presented.     

Simulating film condensation of steam from steam-gas mixtures with different compositions on the outer surface of vertical tubes used in a heat exchanger

A mathematical model of heat-and mass transfer processes in surface-type heat exchangers that use mixtures of steam with various noncondensable gases as heat carriers is presented. The results of numerical calculations are compared with experimental data reported in the literature. It is shown that the thermal-physical properties of the noncondensable component in a steam-gas mixture have an essential effect on the distribution of concentrations and temperatures over the heat exchanger length and on the heat flux transferred in it.     

火电站直接空冷凝汽器性能考核评价方法

火电站直接空冷凝汽器性能决定了直接空冷机组能否安全高效运行。研究直接空冷凝汽器性能的影响因素，从而制定空冷凝汽器性能考核评价方法具有重要意义。通过分析直接空冷凝汽器的传热过程，建立凝汽器压力与凝结蒸汽流量、冷却空气流量、凝汽器传热系数、凝汽器总传热面积以及环境温度之间的关系，分析各因素对凝汽器性能的影响规律。对以凝结蒸汽量和以凝汽器压力作为性能考核标准进行了对比研究，指出了2种性能考核评价方法存在的缺点，即仅仅考核凝汽器传热能力会导致传热面积过大，系统投资增加。在考核空冷凝汽器传热能力的基础上，还需测定凝汽器传热系数，以传热系数保证值作为直接空冷凝汽器性能考核的补充指标。     

Open‐cycle OTEC systems with freshwater product: Effects of noncondensable gases on performance of condenser

An open‐cycle ocean thermal energy conversion (OC‐OTEC) system is one of the energy conversion methods used to generate electricity from ocean thermal energy. For the OC‐OTEC system, steam evaporated from the surface seawater due to flash evaporation drives the turbine. At that time, dissolved gas such as air is introduced into the low‐pressure system (OC‐OTEC system) as the noncondensable gas, which degrades the performance of condensation heat transfer. In this paper, a small‐scale OC‐OTEC experimental unit experimentally investigates the effect of noncondensable gas on the heat transfer performance in a condenser. The experimental results are discussed in comparison with theoretical estimation by the Sparrow–in method. It is shown that the condensation is occupied by heat and mass transfer near a condensation surface and that the condensation efficiency is affected by exhaust quantity of noncondensable gas at a relatively high concentration ratio of condensable gas. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 154(1): 29–35, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20179     

考虑污垢因素的凝汽器经济性分析

凝汽器冷凝压力的变化引起汽轮机组微功率的变化,而凝汽器冷却水管内流速通过影响冷却水侧换热系数和污垢热阻来直接影响冷凝压力的变化。在考虑凝汽器冷却水侧污垢热阻随冷却水流速改变而改变的情况下,在对电站凝汽器污垢热阻进行模拟实验的基础之上建立数学模型,以最大经济效益为目标函数来求解最优冷却水流速和最优冷却水输水管直径,并分析了影响最优流速和最优直径的影响因素。     

用标准传热系数评价凝汽器水侧、汽侧清洁程度

对凝汽器清洁系数和汽侧空气修正系数的概念与物理意义进行了论述,提出了以良好状态实测标准传热系数作为凝汽器传热系数的比较标准,分析了标准传热系统的计算方法,提出了在HEI公式中对水温、水量等试验条件的修正算法,以及在线计算凝汽器清洁系数,汽测空气量修正系数的方法。     

空冷凝汽器验收考核实验中的几个原则

对空冷凝汽器进行性能测试,以考核是否达到验收标准,对于我国火电站空冷岛的设计、生产和运行都具有重要意义。从空冷凝汽器传热模型出发,分析了VGB-R131Me验收考核实验导则中存在的缺陷。针对我国直接空冷机组运行中存在的诸如夏季满负荷高背压运行,冬季防冻等问题,指出了单纯增加空冷凝汽器传热面积以满足设计要求的不足,建议制定不同工况不同容量机组的考核传热系数值。空冷凝汽器验收考核应在设备供应商提供凝汽器传热性能,即传热关联式的基础上,由用户计算不同轴流风机转速,不同凝汽器饱和蒸汽凝结量和不同进口空气温度条件下的凝汽器传热系数并进行实验测试,只有当该传热系数大于考核传热系数之后,才能绘制凝汽器性能曲线以检验是否达到设计要求。     

联合循环机组启动中凝汽器真空度下降的原因

介绍了M701F4型燃气-蒸汽联合循环机组冷态启动时,由于余热锅炉中积聚的大量不凝结气体不能及时排出而涌入凝汽器,造成凝汽器真空度下降的情况;建议在机组启动前对高、中、低压主汽管道及再热器系统有效抽排不凝结气体,启动过程中手动控制余热锅炉高、中、低压过热器出口和再热器出口对空排气阀的开启时间,以尽量排出各系统内的不凝结气体,避免机组启动过程中凝汽器真空度的过度下降。     

Modernizing the K-1000-60/1500 turbine unit’s condensers by replacing the material of cooling tubes

The results obtained from modernization of the K-1000-60/1500 turbine’s lateral condensers are described. This modernization, in which tubes with thinner walls were used, resulted in a larger heat-transfer surface area and in better average vacuum. A 3.2-MW gain in the power unit capacity was obtained, and better reliability of the condenser itself was achieved.     

Studying the operation of a VVER steam generator in the condensing mode at different parameters of emergency processes

The article presents the results of the experimental study of heat and mass transfer processes in an NPP steam generator during the operation of passive safety systems of new-generation VVER reactor installations. At the GE2M-PG test rig in the Leypunsky Institute for Physics and Power Engineering, two series of experiments corresponding to different stages of the accident were completed. In these experiments, the performance of VVER steam generator in the condensing mode with and without the removal of gas-vapor mixture from the “cold” header has been studied. As a result of the first series of experiments, it was found that, for any of the parameters of the emergency process, the steam generator’s power does not drop below 80% of the original value. Furthermore, we revealed that the composition and physical properties of gases in the investigated concentration range did not notably affect the processes in the steam generator. In the second series of experiments without removal of noncondensable gases, the influence of parameters of the emergency process on the efficiency of heat transfer in the steam generator operating in the condensing mode was investigated. In order to study the heat transfer processes, we studied the change of the temperature difference between the media of the first and second circuits in our experiments. We found that the value of the temperature difference depends on both the mass of noncondensable gases accumulated in the tube bundle and their accumulation rate. The accumulation rate is determined by the power of the steam generator and the concentration of gases entering the steam generator. As a result of the analysis of experimental data, we obtained the analytical dependence reflecting change in the power of the steam generator operating in the emergency condensing mode.     

边界条件变化对凝汽器热力设计的影响

就热力边界条件变化对凝汽器设计的影响进行讨论,结论是电厂应结合机组运行经济性、厂用电耗功以及凝汽器、循环泵、冷却塔等一次性投资成本等因素综合优化凝汽器背压、面积、循环倍率等外部条件,以获得一次投资成本和机组运行经济性最佳的结合点.     

双背压凝汽器的水环真空泵汽蚀特性及防汽蚀措施研究

通过对双背压凝汽器配套水环真空泵汽蚀特性的分析,证明低压凝汽器对应水环真空泵易发生汽蚀、容量不足问题,使低压凝汽器压力升高。通过实例验证了双背压凝汽器真空泵易发生汽蚀且严重损害了机组的经济性。针对如何预防真空泵汽蚀问题,有效提高真空泵汽蚀余量,阐述了以降低真空泵工作液温度和提高真空泵入口压力为目标的多种优化措施,对双背压凝汽器的真空泵工作液冷却及抽气系统的设计及改造工作具有指导意义。     

滨海核电厂配置单、双背压凝汽器技经分析

针对目前国内滨海核电厂凝汽器的配置情况,论述单、双背压凝汽器的热力特性,并对它们进行技经分析。对比结果表明,双背压凝汽器热力特性优良,但缺少应用经验;在冷却水温较低的滨海核电厂,宜采用单背压凝汽器;当冷却水温大于21℃后,可通过单、双背压凝汽器的技经比较来决定取舍;在进行技经比较时,需考虑采用双背压凝汽器的风险。