To reduce the security risk of a steam turbine high-pressure main stop valve during full stroke test, and ensure the safe and stable operation of the unit, an analysis was conducted to the test process and common risks, so as to find out specific ideas and methods to further improve the test logic and strengthen the equipment maintenance. Practice shows that attention should be paid to the changes of monitor light plate, DCS display and other light signals, and the test should be ended immediately in case of any abnormal signals observed, when corresponding countermeasures should be taken to reduce the security risk occurring in full stroke test of the high-pressure main stop valve.

The tensile properties of P92 steel, a domestic main steam pipe material, were investigated by means of small punch test technology based on micro loss sampling. The results show that the test machine and method have good repeatability. The results of loading rates of 0.2 mm/min and 0.5 mm/min are close, while the results of 2 mm/min are quite different. The yield strength at 25-650℃ can be well estimated by using the yield strength correlation formula at room temperature. When the sample thickness is determined, the estimation error can be effectively reduced by the appropriate fitting formula.

Compared with single-reheat steam turbine, the start-up process of 1 000 MW ultra-supercritical double-reheat steam turbine is faced with such difficulties as more complex system and higher start-up parameters, etc. Combining the typical start-up process of steam turbine in a 1 000 MW double-reheat unit during production and commissioning period, an introduction is presented to the optimization and adjustment on start-up mode and parameter control of similar steam turbines.

The highly humid gas from wet flue gas desulfurization (WFGD) system was cooled to build the supersaturated vapor environment in condensation chamber. An experimental setup was designed for indirect measurement of the supersaturation and a model was established for calculation of heat and mass transfer in the condensation chamber, so as to theoretically and experimentally analyze the effects of cooling water temperature on the supersaturation. Both results show that cooling the highly humid gas of WFGD system can effectively build the supersaturated environment, and with the decrease of tube wall temperature, the supersaturation in condensation chamber increases obviously. Calculation results indicate that the highest supersaturation appears in the area near chamber wall under the condition of same wall temperature. The supersaturation first increases and then decreases along axial direction of the chamber.

Process analysis was conducted to the first overhaul of a M701F gas turbine, including the main procedure and construction items. Corresponding countermeasures were proposed for problems found in the overhaul, such as radial clearance out of tolerance, damage of compressor stator blade and cracking of exhaust diffuser, etc. Results show that the overhaul process analysis is reasonable and the treatment measures are effective, which may serve as a reference for overhaul of similar projects.

Difficulties encountered in feed water control of a 660 MW unit with small bypass system under FCB conditions were analyzed, while the feasibility of using coal mill RB test to verify the feed water control strategy under FCB conditions was studied. Deep coal mill RB tests were conducted at high loads, and the test procedure was analyzed in detail, based on which relevant feed water control loops were optimized, and subsequently a control strategy was proposed by the automatic way of single steam pump water supply under FCB conditions. The deep coal mill RB test results conducted at medium and high loads prove the optimized control strategy to be effective, which may serve as a reference for FCB feed water control retrofit of similar units.

The effects of following factors on the heat collection efficiency of parabolic trough collector and on the maximal surface temperature rise of both the heat-absorbing tube and the glass sleeve were analyzed, such as the direct solar radiation intensity, the inlet fluid temperature and the inlet fluid velocity, etc. Results show that the heat collection efficiency of solar collector increases with rising direct solar radiation intensity, rising inlet fluid velocity and reducing inlet fluid temperature; the maximal surface temperature difference of heat-absorbing tube increases with rising direct solar radiation intensity and reducing inlet fluid velocity, which first increases and then reduces with the rise of inlet fluid temperature; the maximal surface temperature difference of glass sleeve increases with rising direct solar radiation intensity, rising inlet fluid temperature and reducing inlet fluid velocity.

To clear the faults occurring within 1 000 times of starts in the generator rotor of a 9E gas turbine generator set, the formation causes and common problems are analyzed, and subsequently corresponding countermeasures as well as technological and material requirements are proposed for troubleshooting of the generator rotor, which may serve as a reference for troubleshooting of similar problems.

Based on detailed analysis of the operating principle of V/Hz limiter for GE EX2100 excitation regulator, the reason of frequently misstated excitation restriction occurring in the generator excitation system of a domestic power plant was found to be caused by design deficiency in the GE EX2100 excitation regulator, for which corresponding improvement measures were suggested.

To solve the problem of instable flame and flame loss occurring in the dry-type low-nitrogen (DLN1.0) combustion system of a 9E gas turbine, an analysis was conducted on factors that may influence the flame from the aspect of design, installation, combustion adjustment and hardware fault, etc., based on key operation parameters on site, after which corresponding preventative and treatment measures were proposed. Operation results show that the failure of flame loss in 9E gas turbines can be effectively avoided by taking above countermeasures and the unit safety is thus guaranteed.

To solve the problem of unstable vibration existing in a 135 MW steam turbine, an analysis was conducted, after which the error was found to be caused by mass unbalance of the rotor and collision between the rotary and static parts. Stable vibration satisfying safety operation requirements of the steam turbine is now obtained, after taking following countermeasures, such as high-speed dynamic balancing of rotor, elimination of pipeline defects in the thermal system of steam turbine, etc.

To ensure the manufacturing quality of the third generation nuclear steam generator, many new technologies of welding and postweld heat treatment are developed by analyzing the structural features of the steam generator, including determination of welding filler materials and welding processes for the manufacturing process. Results show that the successful application of above new technologies in the manufacture of the third nuclear steam generator has laid a solid foundation for the subsequent AP1000 third generation and CAP1400 projects.

Based on the principle of cascaded utilization of energy, an organic Rankine cycle (ORC) system was developed using high-temperature flue gas discharged from a micro gas turbine, of which the system performance was studied by setting up a mathematic model for the ORC system, taking R134a as the working fluid, and choosing screw expander as the engine. Results show that the power output and cycle efficiency of the ORC system are respectively 20.40 kW and 12.65%. The power system can not only recover low grade heat source, but also achieve zero emission of pollutants, having a wide application prospect.

To reduce the pollutants emission from a boiler, the original electrostatic precipitator was changed into bag-type dust collector, which was staggeringly arranged with auxiliary flow-equalizing device equipped to ensure the uniformity of flue gas flow. After retrofit, the emission concentration of dust has been reduced from 99.47 mg/m³ to 5.93 mg/m³, with the dust collecting rate up to 99.94%, achieving the intended purpose.

After normal shutdown of a 9FA gas-steam combined cycle unit for several hours, the temperature difference between upper and lower casing of its high-pressure cylinder in the 158 type turbine changes violently, resulting in startup termination of the unit in purging stage due to shaft vibration. The causes are finally found through analysis and calculation on the temperature distribution at different areas of the high-pressure main steam pipe.

An introduction is presented to the equipment selection, configuration optimization and application effect of the condenser vacuum pump in a 1 089 MW nuclear power station, including an analysis on the necessity of adding air ejector to the water-ring vacuum pump and on the factors influencing the configuration optimization of the condenser vacuum pump. Meanwhile, design requirements and configuration schemes of 3×100%, 3×50% and 3×75% capacity were proposed for the condenser vacuum pump. Analysis and application results show that the scheme of 3×75% capacity is relatively reasonable and economical.

To improve the boiler thermal efficiency and reduce the pollutant emission, a model of boiler combustion system was established using Bayesian neural network, to which multi-objective optimization was carried out by genetic algorithm. Simulation results with field test data of a boiler show that the method could well predict both the thermal efficiency of boiler and the mass concentration of nitrogen oxides, achieving multi-objective optimization purposes, which therefore may serve as a reference for boiler operation in an economic and environmental-friendly way.

To overcome the frequent failures occurring in the valve of steam turbines, an automatic diagnostic system has been developed based on DEH internal hardware monitoring and communication technology, which is able to integrate following processes into the human-machine interaction interface, such as the status diagnosis, alarming, testing and maintenance of valve, by directly collecting the data of DEH and servo mechanism, programming, analyzing real-time and historical data, and so on. Application results show that the diagnosis of the proposed system is timely, accurate and reliable, convenient and intuitive, producing obvious economic effects.

Focusing on the deficiency of built-in alarm function module in DCS control system of power plant that the function module cannot filter out important alarms from large amount of messages, it is proposed to separate the alarm function module from the control system, for which a set of integrated sound alarm system is developed, so as to overcome the deficiency of original warning systems.

For a certain overseas power plant to be expanded to the capacity of 100 MW class and operated under long-term low-frequency conditions due to the weak local power grid, an analysis was carried to the steam turbine for stable operation under above conditions. The 135 MW reaction steam turbine with untuned blade was then proposed for the retrofit of unit considering the technical and structural features of domestic steam turbines. Results show that for steam turbines to be operated under long-term low-frequency conditions, the scheme proposed has certain advantages in the aspect of unit thermal efficiency, floor area and construction cost, etc., which may serve as a reference for similar projects.

To solve the problem that the denitrification system of domestic power units above 300 MW can not be put into operation at low load after denitrification retrofit, a flue gas temperature coordinated scheme was proposed and implemented for wide load operation of the denitrification system. Structural features and control strategy of the scheme were introduced, while the effectiveness of the scheme in engineering applications was analyzed, which may serve as a reference for similar engineering projects.

The mode and operating difficulty of an MPS medium-speed mill for grinding lignite have been studied, while conditions under which normal operation of the mill can be kept are analyzed based on project examples, and subsequently suggestions on selection of some important operating parameters are proposed, including the moisture of pulverized coal, primary air ratio, primary air temperature, outlet temperature of mill and pulverized coal fineness, etc. Practices indicate a medium-speed coal mill can be adopted directly for raw coal with moisture content of less than 35%, which can be conditionally adopted through parameter adjustments for raw coal with moisture content of 35% to 40%, while a drying system needs to be added extraordinarily when the moisture content is greater than 40%.

Through analysis on the gas turbine ignition process, safety measures were summarized to prevent M701F unit from deflagration during ignition period, based on which reasonable purging time was determined according to existing gas turbine standards on the premise of considering the unit safety and economy, while an optimization scheme was proposed for the ignition process.

A general mathematical model was set up to study the dynamic characteristics of a wet desulfurization tower respectively by wet ammonia method and wet limestone-gypsum method, based on analysis of the technological design and reaction process of the tower in different flue gas desulfurization systems, using lumped parameter modeling method and modular modeling method, with which the dynamic process of desulfurization tower in the whole operation process can be simulated, while the real-time dynamic operation data within control objects can be calculated, such as the temperature, pressure, pH value, SO₂ mass concentration and the desulfurization efficiency, etc. Taking the desulfurization tower in a thermal power plant as an object of study, dynamic simulations were repeatedly conducted on the tower, and the simulation results conformed to the design requirements on dynamic characteristics of the tower, proving the model to be correct and universal.

To guarantee the safety operation of gas turbine in an overhaul life, a comprehensive inspection and analysis were implemented on the rotor status according to gas turbine working conditions and technical data provided by GE (OEM) in combination with onsite overhaul experiences. Results show that it is possible to effectively monitor and improve the operation conditions of gas turbine rotors and prevent them from serious accidents through implementing comprehensive inspection and analysis on gas turbine rotors as well as by taking proper treatment measures.

An introduction is presented to the beam fracture failure of constant hangers for high-temperature reheater outlet piping in a 600 MW supercritical boiler, together with an analysis performed on both the fracture and the beam, such as macrostructure, microstructure, chemical composition and mechanical properties, etc., and subsequently corresponding countermeasures are proposed, which may serve as a reference for treatment on beam fracture of constant hangers in similar boilers.

For the workshop assembly module of condenser tube bundles in large nuclear power stations, focus points of the module were discussed from the technical point of view, while corresponding advantages and disadvantages were economically analyzed, based on which a suggestion was proposed to perform ID eddy current testing for all the titanium tubes.

In the light ofactual situation that supercritical power units have to take part in peak regulation, influence factors on the coal-fired boiler are analyzed from the aspects of security, economy and environmental protection during deep participating in peak regulation of the unit, to which countermeasures are put forward for possible problems. Practices indicate that the peak regulation requirements can be satisfied only after following problems are comprehensively considered, such as the boiler's low-load combustion stability, hydrodynamic stability, prevention of tube wall overheating and corrosion of tail heating surfaces, etc.

An introduction is being presented to the reactor-turbine control logic of a CPR1000 nuclear power station, together with an analysis on possible operation risks caused by parameter mismatching between the reactor and the steam turbine. By collecting actual operation parameters of a running nuclear power station, building up mathematical model, and performing necessary calculation and fitting, a reasonable load limit is determined for turbo-generator sets, which is already applied in a nuclear power station.

Experimental studies were conducted to optimize the sliding pressure operation of a domestic 300 MW subcritical unit. Through comparative tests on performance of the unit between constant and sliding pressure operation respectively, an optimal sliding pressure operation curve was obtained. The new sliding pressure operation mode has helped to effectively reduce the heat rate of steam turbine, thus improving the operation economy of the unit under variable load conditions.

To guarantee that the flow rate of relevant circulating water pumps is higher than the minimum requirement and the top of the main pipeline can be filled with seawater after frequency conversion retrofit, operation limits are set through analysis and commissioning tests to secure the safety of related equipment and systems. Meanwhile, optimal operation conditions are found by tests and calculations after frequency conversion retrofit, so that the circulating water system can be operated under the best vacuum condition and become more flexible to the DSS operation mode, thus bringing remarkable economic benefit to the power plant.

An assessment was made to major risks possibly existing in the desulfurization system of a power unit after its desulfurization bypass flue duct was blocked, with focus on problems concerning the 2 induced draft fans and 1 booster fan, to which RB control design was proposed for the booster fan by fully opening the moving blades as the flue gas passage after tripping of the booster fan. Results show that the method has helped to improve the reliability of relevant equipment, which may serve as a reference for similar necessary blocking of desulfurization bypass flue duct in thermal power plants.

An introduction was proposed to the control principles for steam distribution in mixing valve and sequence valve control mode of steam turbines. To solve the problem of large throttling loss under mixing valve control mode, flow characteristic tests were performed, based on which the steam distribution control mode was optimized. Meanwhile, reasonable operation order was proposed for the sequence valve control, with corresponding flow characteristic curves presented simultaneously. In addition, the process of valve switching was described to achieve undisturbed switching between mixing valve and sequence valve control. After application of the sequence valve control mode, the unit now runs safely and stably, resulting in reduced throttling loss and improved unit economy.

According to structural features of the AP1000 steam generator, reactor pressure vessel and pressurizer, relevant purchasing requirements of welding consumables as well as the welding processes were determined, and during the manufacture of above equipment, a number of new processes and technologies were adopted. Results show that not only the welding quality and production efficiency are improved, but also the production cost is reduced, after the adoption of the welding consumables and the application of new welding technologies.

Analysis was performed to the leakage at weld joint of T23 steels in service as low-temperature reheater tubes, and the reheating cracks formed at heat-affected zone of the weld were believed to be the main cause. There are two reasons leading to formation of reheating cracks: one is the stress concentration, resulted from compulsive alignment of the tubes during welding; the other is that the microstructure in heat-affected zone is coarse martensite with obvious pores, making the strength and toughness of the weld reduced, and therefore promoting the formation of reheating cracks.

Based on analysis of the sliding pressure operation theory of steam turbines, an initial valve position of sliding pressure operation was found by throttling tests on the regulating valve, and then variable load operation tests were conducted at different valve positions near the initial point to verify its correctness. This method is applicable to actual engineering projects, which could help to reduce the number of test points and improve the efficiency of sliding pressure tests.

Taking a domestic 600 MW supercritical air-cooling steam turbine as an object of study, vibration behavior of the steam turbine was analyzed in variable modes of operation, such as in run-up period, variable load operation and shutdown of sliding parameters, for which essential concerns were mentioned for control of the turbine vibration.

As for following three typical details easily neglected in the design of constant supports and hangers, such as choosing supports and hangers without considering their weight, designing supports and hangers without adequately considering their actual sizes, and choosing the snubber without fully considering the travel margin, etc., an analysis was conducted, which may serve as a reference for the design and retrofit of piping supports and hangers.

To solve the problems existing in RELAP5 steam turbine model, a method is presented to modify the RELAP5 model based on stage group formula, and to correct the calculating formulas in the turbine subprogram module, thus achieving updating of the turbine model. Taking the stage group of a nuclear power unit as a prototype, a single-stage group modeling of steam turbine was completed using the updated RELAP5 model, and subsequently the transient and steady state calculation results were compared with the design parameters. Results show that the modified turbine model with higher accuracy can meet the requirements of the unit on dynamic response.

Problems concerning incineration technology of solid wastes in circulating fluidized bed (CFB) boilers were discussed, while technical experiences about incineration of pure solid wastes without addition of coal were summarized to prevent ash bridge. Meanwhile, an analysis on design principles of the boiler furnace was carried out and factors to be considered during the design process were listed, based on an actual design example of boiler furnace, which may serve as a reference for persons of the same occupation.