Probable causes of damage of heat-exchange tubes of low-pressure-exchanges of PND-3 type and repair methods

The structures of low-pressure heaters (LPH), which are installed at nuclear power plants with the K-1000-60/1500 type turbine plants are considered. It was revealed that only the PND-3 type low-pressure heaters have the damages of the heat exchange tubes. For a short operation life, the number of the damaged heat-exchange tubes of PND-3 is approximately 50 pcs for Kalinin NPP and 100–150 pcs for Balakovo NPP. The low-pressure heaters were manufactured at AO Ural Plant of Chemical Machine-Building “Uralkhimmash,” OAO Taganrog Boiler-Making Works “Krasny Kotelshchik,” and Vitkovice Machinery Group, but the damage nature of the heat-exchange tubes is identical for all PND-3. The damages occur in the place of passage of the heat exchange tubes through the first, the second, and the third partitions over the lower tube plate (the first path of the turbine condensate). Hydraulic shocks can be one of the possible causes of the damage of the heat-exchange tubes of PND-3. The analysis of the average thermal and dynamic loads of the tube systems of PND-1–PND-4 revealed that PND-3 by the thermal power are loaded 1.4–1.6 times and by the dynamic effects are loaded 1.8–2.0 times more than the remaining LPHs. Another possible cause of damage can be the cascaded drain of the separate into PND-4 and then through the drainage heat exchange into PND-3. An additional factor can be the structure of the condensate drainage unit. The advanced system of the heating steam flow and pumping scheme of the separate drain using the existing drainage pumps of PND-3 for K-1000-60/1500 turbine plants for Balakovo and Kalinin NPPs were proposed. The considered decisions make it possible to reduce the flow rate of the heating steam condensate from PND-3 into PND-4 and the speed of the heating steam in the tube space of PND-3 and eliminate the occurrence of hydraulic shocks and damages of the heat exchanger tubes.     

基于无量纲的电站加热器变工况建模和研究

回热系统是发电机组热力系统重要组成部分,加热器是其主要的辅助设备。传统回热系统加热器变工况运行的数学模型非常复杂,建模过程中涉及流体相变问题。本文基于电站加热器在实际运行中的数据,采用无量纲方法建立加热器运行模型,无需考虑加热器内部复杂的传热过程。将模型用于某660 MW超超临界汽轮机组的低压加热器上,结果表明:利用该模型计算的加热器出口水温和实际测量数据偏差很小;在满足精度要求的情况下,该模型简单方便,工程上可用于回热系统加热器的经济运行指导和故障诊断。     

Investigation of Technical and Economic Viability of the 450-MW CCGT Unit’s Operation in the GTU Based CHP Mode

Technical viability and economic feasibility of improving the technology of a 450-MW CCGT unit’s participation in power load leveling of the power system operating in a GTU based CHP mode by transferring a 450-MW CCGT T-125/150 steam turbine to the driving mode instead of its shutdown are considered. It is shown that the shutdown of the steam turbine is associated with increased fuel consumption under start-up conditions, delayed steam turbine loading and the CCGT unit as a whole, and a loss of steam turbine life characteristics. The technology of transferring the 450-MW CCGT unit to the GTU based CHP mode, possible schemes of high- and low-pressure steam distributions between line water heaters, and methods and results of calculation of power parameters of the 450-MW CCGT unit with the turbine shutdown and transferring it to the driving mode in the absence and presence of peak-load heaters in the heat balance are presented. It is shown that switching the 450-MW CCGT unit from the base 290 MW electric load and 1006 GJ/h heat production to the GTU based CHP mode leads to a decrease in electric capacity of the CCGT unit by 90 MW and an increase in heat production by 335–348 GJ/h. Comparative graphs of the steam turbine start-up and the CCGT unit rated loading in the comparable variants after its operation in the GTU based CHP mode for 8–10 h are given. Evaluation techniques and results of the economic efficiency of the generator driving mode are compared with the shutdown of the steam turbine. Based on the performed calculations, it is shown that, for various combinations of fuel equivalent and electricity costs and heating tariffs, the expedient time for switching the steam turbine to the driving mode is 10–18 h. Additional advantages of the driving mode are noted, such as improvement of the steam turbine reliability due to the elimination of cyclic temperature variations of its steam-inlet elements and vibrational oscillations in the final stages of the low-pressure cylinder and the possibility of the steam turbine generator to operate as a synchronous condenser.     

Development of High-Powered Steam Turbines by OAO NPO Central Research and Design Institute for Boilers and Turbines

The article provides an overview of the developments by OAO NPO TsKTI aimed at improvement of components and assemblies of new-generation turbine plants for ultra-supercritical steam parameters to be installed at the power-generating facilities in service. The list of the assemblies under development includes cylinder shells, the cylinder’s flow paths and rotors, seals, bearings, and rotor cooling systems. The authors consider variants of the shafting–cylinder configurations for which advanced high-pressure and intermediate-pressure cylinders with reactive blading and low-pressure cylinders of conventional design and with counter-current steam flows are proposed and high-pressure rotors, which can increase the economic efficiency and reduce the overall turbine plant dimensions. Materials intended for the equipment components that operate at high temperatures and a steam cooling technique that allows the use of cheaper steel grades owing to the reduction in the metal’s working temperature are proposed. A new promising material for the bearing surfaces is described that enables the operation at higher unit pressures. The material was tested on a full-scale test bench at OAO NPO TsKTI and a turbine in operation. Ways of controlling the erosion of the blades in the moisture–steam turbine compartments by the steam heating of the hollow guide blades are considered. To ensure the dynamic stability of the shafting, shroud and diaphragm seals that prevent the development of the destabilizing circulatory forces of the steam flow were devised and trialed. Advanced instrumentation and software are proposed to monitor the condition of the blading and thermal stresses under transient conditions, to diagnose the vibration processes, and to archive the obtained data. Attention is paid to the normalization of the electromagnetic state of the plant in order to prevent the electrolytic erosion of the plant components. The instrumentation intended for monitoring the relevant electric parameters is described.     

Start-up circuit upgrading to reduce the erosion of the rotor blades of the last stages of steam turbines and prevent the mass strips of stellite plates

At turbine starts with low steam flow rates in idle mode, the low-pressure rotor blades consume energy, causing the ventilation heating of the stages and creating higher depression in them than in the condenser. This leads to the return steam flows in the exhaust of the low-pressure cylinder (LPC), reducing the heat due to the moisture of starting steam damps and cooling injections. It is shown that, as a result of upgrading with the transition to fully milled shroud platforms of rotor blades, the depression in the stages decreases and their cooling efficiency is reduced due to the removal of an elastic turn of the rotor blades under the action of centrifugal forces and seal of them by periphery. Heating the rotor blades of the last stages exceeds the temperature threshold of soldering resistance of stellite plates (150°C), and their mass strips begin. The start-up circuit providing both the temperature retention of the last stages lower the soldering resistance threshold due to overwetting the steam damps up to saturation condition and the high degree of removal from the dump steam of excessive erosive-dangerous condensed moisture was proposed, applied, and tested at the operating power unit. The investment in the development and application of the new start-up circuit are compensated in the course of a year owing to guaranteed prevention of the strips of stellite plates that lengthens the service life of the rotor blades of the last stages as well as increase of the rotor blade efficiency due to the sharp decrease of erosive wear of the profiles and reduction of their surface roughness. This reduces the annual consumption of equivalent fuel by approximately 1000 t for every 100 MW of installed capacity.     

300MW机组启停过程中全程使用汽动给水泵的设计与优化

为降低厂用用电率,四川广安电厂在机组启停过程中以汽动给水泵代替电动给水泵,但在实际运行中遇到了辅助蒸汽疏水不畅和压力不够大、给水泵汽轮机受到热冲击等问题。为此,从实际出发提出了一系列解决问题的措施：增加低压辅助蒸汽管道以加强疏水,通过提高邻机负荷或邻机高压辅助蒸汽带低压辅助蒸汽联箱来提高低压辅助蒸汽压力,切断高压进汽管道,直接由低压汽源供汽来减小给水泵汽轮机的热冲击。措施实施后,广安电厂4台300MW机组2008年启停28次,节约厂用电约60MWh。     

Achieving More Efficient and Reliable Operation of Geothermal Turbines by Using a Secondary Flash Steam Superheating System

Problems encountered in operation of saturated steam geothermal turbine units that stem from the specific features of a geothermal heat carrier are considered. A two-phase state, increased content of salts, and corrosiveness of geothermal working medium have a negative influence on the efficiency and reliability of the turbine’s first and last stages. Owing to high concentrations of impurities in the liquid phase, the first stages suffer from intense generation of deposits. The resulting decrease in the power output is due to both fouling of the flow path and significantly growing roughness of the turbine cascade blades. The flow of wet steam in the geothermal turbine flow path is accompanied by droplet impingement erosion of the last-stage blades and corrosion fatigue of the metal of rotor elements. In addition, the losses due to steam wetness in the flow path cause an essential decrease of the geothermal turbine efficiency. The article gives examples of erosioninduced damage inflicted to the last-stage rotor blades, corrosion fatigue of the metal of integrally-machined shroud elements, and deposits in the nozzle vane cascades of geothermal turbine stages. The article also presents the results from numerical investigations of the effect that the initial steam wetness has on the silicic acid concentration in the wet steam flow liquid phase in a 4.0 MW geothermal turbine’s stages. A method for achieving more efficient and reliable operation of the geothermal turbine low-pressure section by applying a secondary flash steam superheating system with the use of a hydrogen steam generator is proposed. The article presents a process arrangement for preparing secondary flash steam supplied to the geothermal turbine low-pressure section in which the flash steam is evaporated and superheated through the use of a hydrogen steam generator. The technical characteristics of the system for preparing secondary flash steam to be used in the intermediate inlet to the turbine were preliminarily assessed (taking the upgrading of the Mutnovsk geothermal power plant as an example), and it has been shown from this assessment that the wetness degree in the low-pressure section can be decreased down to its final value equal to 2.0%.     

热电厂切除高压加热器运行的热经济性研究

以cc250-16．67／1．609／0.785型机组为例，运用热量法和焓降法，对抽汽凝汽式机组在尖峰电负荷下切除高压加热器运行的绝对内效率和热经济性进行了理论研究。研究结果表明在一定条件下，切除高压加热器后机组绝对内效率可以提高。对于回水人冷凝器的抽汽凝汽式机组，保持新蒸汽耗量不变，在尖峰电负荷下切除高压加热器运行，其绝对内效率与对外供汽量有关。当机组对外供汽量超过某一值时，切除高压加热器获得额外电功率的同时还可提高机组绝对内效率。通过计算其煤耗量，表明切除高压加热器后热经济性始终是降低的，与对外供汽量无关。     

1000 MW机组汽轮机低压转子现场车削技术

针对某电厂1 000 MW汽轮机低压转子经检修发现存在的动静碰摩现象,研制了低压转子现场车削装置,比较了低压转子返厂车削和现场车削两种方案,成功实施了转子现场车削,消除了设备隐患.     

1000 MW二次再热超超临界汽轮机组摩擦故障分析与处理

国电泰州电厂3号机组为1000 MW二次再热超超临界机组,机组调试期间超高压转子、高压转子和低压转子发生不稳定振动,振动不断爬升,严重影响机组的安全稳定运行。通过对振动数据的分析,指出摩擦故障是导致超高压转子、高压转子和低压转子不稳定振动的根本原因,现场分析故障原因,改变机组启动方式,并采取现场动平衡处理,处理后摩擦故障消除,机组稳定运行。     

600MW超临界机组汽轮机低压转子末级叶片损坏原因分析

介绍某发电厂发生的一起超临界机组低压转子末级叶片损坏事故,宏观检查发现是因为反向第6级蜂窝汽封跌落引起的。进一步开展材质分析、力学性能试验、金相试验,并对蜂窝汽封的加工工艺综合分析,得出如下结论:钎焊工艺影响了汽封体的原始热处理状态,使汽封体的综合机械性能下降,而且汽封体结构不合理,加上运行蒸汽的冲击,导致汽封体跌落断裂,造成末级叶片损坏。分析结论对汽轮机的检修、改造具有指导意义。     

300MW汽轮机凝汽器喉部出口流场的三维数值模拟

为了减少占地面积,国产优化引进型300MW汽轮机将压力最低的2个低压加热器放置于凝汽器喉部,从而导致汽轮机喉部流场出现不均匀,最终导致凝汽器热负荷的不均匀。文中采用κ-ε模型并结合壁面函数法,利用SIMPLEC 算法编程,对300 MW汽轮机喉部流场进行了三维数值模拟,分析了凝汽器喉部出口流场的不均匀性和造成流场不均匀的原因。结果表明,由于内置式低压加热器的影响和凝汽器喉部棱台扩散的作用,使凝汽器喉部出口流场的速度分布产生很大的不均匀性。汽流在低压加热器两侧形成局部的高速区,并延续到喉部出口截面。同时,在低压加热器的正下方形成低速涡流区,在喉部斜壁下方也产生一定的回流,并且在靠近凝汽器入口截面的4个角处形成低速区。对该凝汽器喉部流场的三维数值模拟结果,有助于了解具有内置式低压加热器凝汽器喉部汽流的流动机理,为凝汽器喉部的设计和改造以及汽轮机的经济运行奠定一定的基础。     

Application of variable-frequency electric drives for controlling the drain pumps of low-pressure heaters used in turbine units at cogeneration stations

Results obtained from equipping the drain pumps of low-pressure heaters used in a T-250/300-23.8 turbine unit with a standard adjustable drive are presented. It is shown that the use of this drive allows the level in the high-pressure heater to be efficiently controlled in different modes of operation with smaller consumption of energy for station auxiliaries.     

A numerical analysis of the serial design of the T-250/300-23.5 cogeneration turbine low-pressure cylinder’s exhaust hood

A mathematical model of the low-pressure cylinder’s exhaust compartment used in the serial design version of the T-250/300-23.5 turbine is constructed. The exhaust compartment consists of the turbine flow path last stage, a moisture removal chamber, and an exhaust hood (the EH stage). The effect of individual elements of the low-pressure cylinder exhaust compartment’s flow path on its gas dynamic characteristics in condensing modes of operation is numerically modeled for a wide range of steam flow rates. For the compartment with the exhaust hood completely filled with its inner elements, the flow patterns are calculated in partial modes of operation with presenting data on losses and flow-averaged integral characteristics at the diffuser inlet. The calculation results have been verified against the data of full-scale and model tests.     

130MW机组低加抽空气系统节能改造

萧山发电厂1和2号两台130 MW汽轮发电机组自投产以来,6和7号低加凝结水进出口温升率明显偏小,与额定工况设计温升相比,分别偏低约2.39/7.69℃和10.66/8.58℃。通过对低加运行方式、运行参数的研究分析,提出低加抽空气系统的不合理连接方式是低加系统温升明显不足的主要原因,对此进行了低加抽空气系统改造,6,7号低加的凝结水温升率已基本接近设计值,取得了良好的节能效果。     

加装低压省煤器对汽轮机排汽量的影响研究

为研究低压省煤器吸收的排烟余热的有效利用水平,基于等效焓降法的基本原理,建立了汽轮机低压加热系统中凝结水抽出与引入对其排汽量影响的通用计算模型,进而推导出低压省煤器在各种连接方式下投入运行后对汽轮机排汽量影响的通用计算模型。以某国产330 MW机组为例,利用所提出的计算模型得出两种不同工况下汽轮机排汽量和排汽损失的增加值,结果表明,低压省煤器吸收的排烟余热能用于汽轮机做功的仅为10%左右,其余热量最终都进入冷源损失。     

大型空冷汽轮机的设计特点

空冷汽轮机运行工况具有平均背压高、背压变化幅度大和背压变化频繁的特点,给汽轮机结构设计带来变化,特别是在低压模块的设计方面与湿冷机组相比具有明显的区别。结合直接空冷600MW两排汽汽轮机的设计,对其结构、功率及辅助系统的选择等问题进行论述,为大型空冷汽轮机的设计提供参考。     

Numerical investigation of three-dimensional flows of steam-water mixture in the housing of the PGV-1000 steam generator

Results are given of numerical simulation of three-dimensional pattern of flow of a two-phase steam-water mixture in the house of a PGV-1000 horizontal steam generator obtained using the BAGIRA best-estimate thermohydrodynamic computer codes. The space distributions of velocities and local void fractions in the steam generator housing for different modes of operation of power-generating unit are calculated and compared with available experimental data.     

提高超临界和超超临界机组发电效率的关键技术

根据国内外超临界和超超临界机组的研究结果和运行数据,比较全面地阐述了提高超临界和超超临界机组热效率的关键技术。主要包括:提高机组蒸汽参数;采用优化的变反动度的新型汽轮机叶片;采用可调间隙的汽封结构;降低凝汽器背压;增加回热加热级数,提高给水温度;采用内螺纹管水冷壁降低水冷壁质量流速,减小水冷壁流动阻力;控制过热器和再热器减温水量;开发高效燃烧低污染排放和低负荷无油稳燃的燃烧技术;采用带有循环泵的启动系统,加快机组启动速度;优化运行方式;优化辅机配置。新技术的综合采用可提高新一代超临界机组的发电效率,降低发电煤耗。最后提出了国内电站实际需要研究的课题。     

给水泵汽轮机推力瓦磨损的原因及对策

针对某330MW供热机组跳闸后给水泵汽轮机推力瓦损坏故障,从推力瓦工作失常、汽轮机叶片结垢、给水泵异常运行、进汽量增大、汽轮机水冲击和热工保护系统等方面对其进行了分析。结果表明:给水泵汽轮机运行中进汽量骤增、汽轮机转子局部发生水冲击导致的转子轴向推力增大,热工保护逻辑不完善造成磨损进一步加剧。从系统设计和运行方面提出了处理措施和防治对策。