Influence of the reheat temperature on the efficiency of the wet-steam turbines of thermal power plants that operate under variable conditions

A brief analysis of the existing methods for controlling the operating conditions of the turbine units that operate at variable loads is presented. In practice, the outdated rule of operation is most frequently used that states that the higher the parameters of the live and reheat steam and the lower the condenser pressure are, the higher is the efficiency of the turbine unit. However, in the technical literature, there is sufficiently substantiated evidence that this approach is not always correct, especially under low loads. This applies to both the regulation of the initial and final pressure and reheat temperature t _r. In the article, particular stress is laid on the controllable parameter t _r, the effect of which in the operational practices, according to the results of the analysis, is underestimated. The causes are considered that constrain more effective use of reheat temperature t _r as a process variable. The results of field trials to investigate the influence of t _r on the efficiency of turbine units of various capacities, viz., of 210, 250, 300, and 325 MW, during operation at varying loads are presented. It is shown that a decrease in t _r to an optimal value of 10–30°C, depending on the load and the condenser pressure, increases the thermal efficiency by 1–2%. The following general pattern has been set: the lower the load, the lower the optimal reheat temperature. The main causes and factors that result in more efficient use of the heat phase transition in the steam path of the low-pressure cylinder and increased efficiency of the unit under rational choice of the reheat temperature are studied.     

Cogeneration steam turbines from Siemens: New solutions

The Enhanced Platform system intended for the design and manufacture of Siemens AG turbines is presented. It combines organizational and production measures allowing the production of various types of steam-turbine units with a power of up to 250 MWel from standard components. The Enhanced Platform designs feature higher efficiency, improved reliability, better flexibility, longer overhaul intervals, and lower production costs. The design features of SST-700 and SST-900 steam turbines are outlined. The SST-700 turbine is used in backpressure steam-turbine units (STU) or as a high-pressure cylinder in a two-cylinder condensing turbine with steam reheat. The design of an SST-700 single-cylinder turbine with a casing without horizontal split featuring better flexibility of the turbine unit is presented. An SST-900 turbine can be used as a combined IP and LP cylinder (IPLPC) in steam-turbine or combined-cycle power units with steam reheat. The arrangements of a turbine unit based on a combination of SST-700 and SST-900 turbines or SST-500 and SST-800 turbines are presented. Examples of this combination include, respectively, PGU-410 combinedcycle units (CCU) with a condensing turbine and PGU-420 CCUs with a cogeneration turbine. The main equipment items of a PGU-410 CCU comprise an SGT5-4000F gas-turbine unit (GTU) and STU consisting of SST-700 and SST-900RH steam turbines. The steam-turbine section of a PGU-420 cogeneration power unit has a single-shaft turbine unit with two SST-800 turbines and one SST-500 turbine giving a power output of N _{el. STU} = 150 MW under condensing conditions.     

Substantiation of the cogeneration turbine unit selection for reconstruction of power units with a T-250/300-23.5 turbine

The selection of a cogeneration steam turbine unit (STU) for the reconstruction of power units with a T-250/300-23.5 turbine is substantiated by the example of power unit no. 9 at the cogeneration power station no. 22 (TETs-22) of Mosenergo Company. Series T-250 steam turbines have been developed for combined heat and power generation. A total of 31 turbines were manufactured. By the end of 2015, the total operation time of prototype power units with the T-250/300-23.5 turbine exceeded 290000 hours. Considering the expiry of the service life, the decision was made that the reconstruction of the power unit at st. no. 9 of TETs-22 should be the first priority. The main issues that arose in developing this project—the customer’s requirements and the request for the reconstruction, the view on certain problems of Ural Turbine Works (UTZ) as the manufacturer of the main power unit equipment, and the opinions of other project parties—are examined. The decisions were made with account taken of the experience in operation of all Series T-250 turbines and the results of long-term discussions of pressing problems at scientific and technical councils, meetings, and negotiations. For the new power unit, the following parameters have been set: a live steam pressure of 23.5 MPa and live steam/reheat temperature of 565/565°C. Considering that the boiler equipment will be upgraded, the live steam flow is increased up to 1030 t/h. The reconstruction activities involving the replacement of the existing turbine with a new one will yield a service life of 250000 hours for turbine parts exposed to a temperature of 450°C or higher and 200000 hours for pipeline components. Hence, the decision has been made to reuse the arrangement of the existing turbine: a four-cylinder turbine unit comprising a high-pressure cylinder (HPC), two intermediate pressure cylinders (IPC-1 & 2), and a low-pressure cylinder (LPC). The flow path in the new turbine will have active blading in LPC and IPC-1. The information is also presented on the use of the existing foundations, the fact that the overall dimensions of the turbine unit compartment are not changed, the selection of the new turbine type, and the solutions adopted on the basis of this information as to LPC blading, steam admission type, issues associated with thermal displacements, etc.     

Review of the coal-fired,over-supercritical and ultra-supercritical steam power plants

The article presents a review of developments of modern high-capacity coal-fired over-supercritical (OSC) and ultra-supercritical (USC) steam power plants and their implementation. The basic engineering solutions are reported that ensure the reliability, economic performance, and low atmospheric pollution levels. The net efficiency of the power plants is increased by optimizing the heat balance, improving the primary and auxiliary equipment, and, which is the main thing, by increasing the throttle conditions. As a result of the enhanced efficiency, emissions of hazardous substances into the atmosphere, including carbon dioxide, the “greenhouse” gas, are reduced. To date, the exhaust steam conditions in the world power industry are p ₀ ≈ 30 MPa and t ₀ = 610/620°C. The efficiency of such power plants reaches 47%. The OSC plants are being operated in Germany, Denmark, Japan, China, and Korea; pilot plants are being developed in Russia. Currently, a project of a power plant for the ultra-supercritical steam conditions p ₀ ≈ 35 MPa and t ₀ = 700/720°C with efficiency of approximately 50% is being studied in the EU within the framework of the Thermie AD700 program, project AD 700PF. Investigations in this field have also been launched in the United States, Japan, and China. Engineering solutions are also being sought in Russia by the All-Russia Thermal Engineering Research Institute (VTI) and the Moscow Power Engineering Institute. The stated steam parameter level necessitates application of new materials, namely, nickel-base alloys. Taking into consideration high costs of nickel-base alloys and the absence in Russia of technologies for their production and manufacture of products from these materials for steam-turbine power plants, the development of power plants for steam parameters of 32 MPa and 650/650°C should be considered to be the first stage in creating the USC plants as, to achieve the above parameters, no expensive alloys are require. To develop and construct OSC and USC head power plants, joint efforts of the government, experts in power industry and metallurgy, scientific institutions, and equipment manufacturers are required.     

Experience gained from making the incineration of solid domestic wastes a factory standard at thermal power stations in Russia

Using the results of activities on developing and adjusting the processes pertinent to thermal reprocessing of solid domestic wastes (SDWs), that were carried out by VTI specialists along with GUP Ekotekhprom specialists in 1999–2005, we selected operating conditions under which the power installations run in compliance with the requirements (adopted both in Russia and in the EU countries) imposed on the incineration of SDWs and purification of flue gases. It is indicated that ways are currently being considered of increasing the parameters of steam generated at SDW-fired power stations from the existing p = 1.2?1.4 MPa and t _sup = 300?320°C to p = 4.0 MPa and t _sup = 400°C to make the generation of electricity at them more efficient. Experience gained in this field by the boiler manufacturing plants in Russia is analyzed.     

基于能耗特性分析的双抽燃煤机组供汽优化

以优化运行、降低能耗为研究目标,考虑到大型燃煤机组热电联产变工况供汽运行模式的复杂性,建立了供热机组能耗分析模型.以某1 GW双抽机组为例,对9种供汽方案进行了能耗特性分析.结果表明,电负荷较低时,最优的供汽方式为冷再供中压、冷再供低压运行方式;电负荷较高时,最优的供汽方式为冷再供中压、中排供低压运行方式.在典型工况(...     

Proposal and Evaluation of a New‐Type Cogeneration System for Energy Saving and CO2 Emission Reduction

The paper proposes a cogeneration system which generates four types of energy or material resources: electricity, steam, hot water, and freshwater. The proposed system can capture CO₂, and be constructed on the basis of a combined cycle power generation system which consists of a gas turbine and a back‐pressure extraction turbine. In the proposed system, power is produced by driving the gas turbine system. High‐pressure saturated steam with medium temperature is produced in the heat recovery steam generator by using gas turbine exhaust gas, and then superheated with a regenerative superheater in which the fuel is burned by using oxygen instead of air for driving the steam turbine generator. Water and CO₂ are recovered from the flue gas of the regenerative superheater. It has been estimated that the proposed system has a net power generation efficiency of 41.2%, a heat generation efficiency of 41.5%, and a total efficiency of 82.7%. Freshwater of 1.34 t/h and CO₂ of 1.76 t/h can be recovered. It has also been shown, when a case study was set and evaluated, that the proposed system can save 31.3% of energy compared with the conventional energy supply system, and reduce CO₂ emission by 28.2% compared with the conventional cogeneration system. Copyright © 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

三压再热蒸汽系统的热力参数优化分析

针对燃气-蒸汽联合循环中三压再热汽水系统的热力参数对汽轮机功率及循环效率的影响,建立了汽水系统的计算模型,以汽轮机功率和蒸汽流量为目标函数,采用Matlab计算软件对系统热力参数进行计算。结果表明,再热蒸汽压力和中、低压蒸汽压力直接影响着汽轮机功率的大小。     

Heat flow diagrams with and without a deaerator for steam turbine plants with T-250/300-23.5 turbines

A T-250/300-240 turbine (currently known as T-250/300-23.5), which is operated at 31 steam turbine plants, is the largest in the world extraction turbine (by the heating extraction load) and one of the largest by the nominal capacity. All steam turbine plants equipped with T-250/300-23.5 turbines of different modifications are operated in large cities of Russia and the neighboring countries covering a significant part of the needs of cities for the electric power and almost fully supplying them with heat power. The design life of a significant part of the operated steam turbine plants of this family is either expired or almost expired. It refers to both the turbine unit (including a turbine and a generator) and the turbine plant equipment. For steam turbine plants equipped with T-250/300-23.5 turbines, which were initially designed and mounted for work with deaerators at electric power stations, the heat flow diagrams with and without a deaerator were compared. The main advantages and disadvantages of each scheme were shown. It was concluded that, for the newly constructed power units with supercritical steam parameters, it is preferable to use the heat flow diagram without a deaerator; for the upgraded blocks, if there are no objective reasons for the removal of a deaerator, it is recommended to keep the existing heat flow diagram of a turbine plant.     

300MW机组供热蒸汽余压发电汽轮机选型研究

为解决热电联产机组供热蒸汽压力过高而造成高品质蒸汽能量浪费的问题,提出了增设功–热汽轮机以回收利用供热蒸汽中的高品质能量.针对某300 MW机组供热蒸汽余压发电改造方案,结合采暖期机组热网系统实际运行参数,在分析选取功?热汽轮机的进汽参数、排汽参数及进汽量时需考虑的主要影响因素基础上,通过核算确定了功?热汽轮机的主要技...     

The longitudinal layout alternate version of cogeneration steam turbines with the generator placed on the side of the high-pressure cylinder

The schematic design of a cogeneration steam turbine with the generator placed on the side of the high-pressure cylinder is proposed. It is shown that the use of this solution is most promising for turbines with a longitudinal layout (like a T-175/210-12.8 turbine).     

Effective ways to modernize outdated coal heat power plants

An analysis of the state of equipment of 72 outdated coal HPP (heat power plants) of a total capacity 14.3 GW with steam parameters before the turbines p _before ≤ 9 MPa, t _before = 420–540°С was performed. The equipment is characterized by a considerably low efficiency factor, even if it were converted to burning the natural gas, and by increased release of harmful substances. However, on the most part of the considered HPP, the steam turbines, unlike the boilers, have thus far retained the operation applicability and satisfactory reliability of performance. The analysis has shown that it makes sense to effectively modernize the outdated coal HPP by transformation of their equipment into combined-cycle plant (CCP) with coal gasification, which has high economic and ecological indicators due to thermodynamic advantage of the combined cycle and simpler purification of the generator gas in the process under pressure. As the most rational way of this transformation, the one was recognized wherein—instead of the existing boiler (boilers) or parallel to it—a gasification and gas turbine system is installed with a boiler-utilizer (BU), from which steam is fed to the HPP main steam pipe. In doing this, the basic part of the power station equipment persists. In the world, this kind of reconstruction of steam power equipment is applied widely and successfully, but it is by use of natural gas for the most part. It is reasonable to use the technology developed at Heat Engineering Research Institute (HERI) of hearth-steam gasification of coal and high-temperature purification of the generator gas. The basic scheme and measures on implementation of this method for modernization of outdated coal HPP is creation of CCP with blast-furnace of coal on the basis of accessible and preserved HPP equipment. CCP power is 120 MW, input-output ratio (roughly) 44%, emissions of hazardous substances are 5 mg/МJ dust, 20–60 mg/МJ SO₂, and 50–100 mg/МJ NO _х . A considerable decrease of specific CCP cost is expected: down to approximately half compared to that of CCP with coal gasification created elsewhere abroad. Verification and debugging of accepted solutions can be carried out at a small-scale pilot plant.     

Optimization of cogeneration thermal power units

We present a procedure for comparing the efficiencies of cogeneration thermal power units that takes variable conditions of their operation into account. A combined-cycle plant operating in accordance with the STIG cycle (i.e., with mixing of working fluids), a gas turbine unit equipped with a gas economizer, and a steam turbine unit equipped with a backpressure turbine are compared during their operation as part of a cogeneration station.     

Development of a thermal scheme for a cogeneration combined-cycle unit with an SVBR-100 reactor

At present, the prospects for development of district heating that can increase the effectiveness of nuclear power stations (NPS), cut down their payback period, and improve protection of the environment against harmful emissions are being examined in the nuclear power industry of Russia. It is noted that the efficiency of nuclear cogeneration power stations (NCPS) is drastically affected by the expenses for heat networks and heat losses during transportation of a heat carrier through them, since NPSs are usually located far away from urban area boundaries as required for radiation safety of the population. The prospects for using cogeneration power units with small or medium power reactors at NPSs, including combined-cycle units and their performance indices, are described. The developed thermal scheme of a cogeneration combined-cycle unit (CCU) with an SBVR-100 nuclear reactor (NCCU) is presented. This NCCU should use a GE 6FA gasturbine unit (GTU) and a steam-turbine unit (STU) with a two-stage district heating plant. Saturated steam from the nuclear reactor is superheated in a heat-recovery steam generator (HRSG) to 560–580°C so that a separator–superheater can be excluded from the thermal cycle of the turbine unit. In addition, supplemental fuel firing in HRSG is examined. NCCU effectiveness indices are given as a function of the ambient air temperature. Results of calculations of the thermal cycle performance under condensing operating conditions indicate that the gross electric efficiency η _{el NCCU} ^gr of = 48% and N _{el NCCU} ^gr = 345 MW can be achieved. This efficiency is at maximum for NCCU with an SVBR-100 reactor. The conclusion is made that the cost of NCCU installed kW should be estimated, and the issue associated with NCCUs siting with reference to urban area boundaries must be solved.     

Using computer-aided design systems for developing layouts of steam-turbine units

Results of work on developing a system of computer-aided tools for designing the layouts of steamturbine units are described. An example illustrating how this technology is implemented for a steam-turbine unit equipped with a T-50/60-8.8 cogeneration turbine is given.     

Gland seal heaters and steam jet ejectors with surface coolers used in the steam units produced by the Ural Turbine Works

The designs of coolers for gland seal heaters, as well as the main ejectors and seal ejectors, used as part of cogeneration steam turbine-based steam turbine units developed by specialists of the Ural Turbine Works are described. The design features of the apparatuses connected with the specific features of their operation as part of combined-cycle plants equipped with cogeneration turbines are shown.     

Prospects for the development of coal-steam plants in Russia

Evaluation of the technical state of the modern coal-fired power plants and quality of coal consumed by Russian thermal power plants (TPP) is provided. Measures aimed at improving the economic and environmental performance of operating 150–800 MW coal power units are considered. Ways of efficient use of technical methods of NO _x control and electrostatic precipitators’ upgrade for improving the efficiency of ash trapping are summarized. Examples of turbine and boiler equipment efficiency upgrading through its deep modernization are presented. The necessity of the development and introduction of new technologies in the coal-fired power industry is shown. Basic technical requirements for a 660–800 MW power unit with the steam conditions of 28 MPa, 600/600°C are listed. Design solutions taking into account features of Russian coal combustion are considered. A field of application of circulating fluidized bed (CFB) boilers and their effectiveness are indicated. The results of development of a new generation coal-fired TPP, including a steam turbine with an increased efficiency of the compartments and disengaging clutch, an elevated steam conditions boiler, and a highly efficient NO _x /SO₂ and ash particles emission control system are provided. In this case, the resulting ash and slag are not to be sent to the ash dumps and are to be used to a maximum advantage. Technical solutions to improve the efficiency of coal gasification combined cycle plants (CCP) are considered. A trial plant based on a 16 MW gas turbine plant (GTP) and an air-blown gasifier is designed as a prototype of a high-power CCP. The necessity of a state-supported technical reequipment and development program of operating coal-fired power units, as well as putting into production of new generation coal-fired power plants, is noted.     

1000MW级超超临界火电厂再热蒸汽系统管道规格的优化

从初投资及收益的经济性角度出发,对某2×1000 MW级超超临界空冷火力发电厂的再热蒸汽系统的管道规格尺寸进行了优化计算.根据设计参数选取了一系列不同直径、壁厚的管道规格,利用AFT流体分析软件对其进行了流速、压损模拟计算,通过量化压损对汽轮机功率、汽轮机热耗的影响,进行经济性对比分析,进而确定低温再热蒸汽、高温再热蒸...     

广义预测控制在6 0 0 MW超临界机组协调及汽温控制系统优化中的应用

针对安徽淮南平圩发电有限责任公司3号和4号 600 MW超临界机组存在的变负荷速率仅为1%/min、主蒸汽压力和温度的波动分别达0.7 MPa和15 ℃以上及再热汽温无法投入自动控制的实际情况,采用广义预测控制技术,提出了先进的协调及再热汽温控制策略。实际应用表明：新的协调控制策略使机组的变负荷速率达到1.5%/min以上;在变负荷过程中主蒸汽压力和温度的最大动态偏差控制在0.4 MPa和6 ℃以内,且参数不再振荡,有效提高了机组的运行稳定性;新的再热汽温控制策略实现了烟气挡板对再热汽温的有效控制,再热汽温的最大动态偏差控制在6 ℃以内,且减少了再热喷水量20 t/h以上,提高了机组的运行经济效率。     

二次再热机组的热耗变换系数和汽耗变换系数

热耗变换系数和汽耗变换系数是反映抽汽品质的重要参数，便于分析定功率下机组的特点。文中给出了二次再热机组热力系统的矩阵热平衡方程，对其填写规则进行了阐述。提出了二次再热机组热力系统的热耗变换系数、汽耗变换系数、抽汽效率和等效热降的数学表达式。对二次再热机组抽汽间相互作用的特性进行了分析。以某二次再热机组为例，对以上4个参数进行了计算，计算结果不仅证明了hM=hi/ξi和dM=ki/Hi0，而且也说明主循环效率和汽耗率只和热力系统的节点参数有关。通过对计算结果进行分析，发现热耗变换系数随抽汽级数由高压级到低压级逐渐减小。