To solve the problems existing in the air heater of a 1 000 MW boiler unit, such as serious ash deposition on the heat sink, high power consumption of the forced draft fan, and frequent occurrence of tube bank leakage, etc., a retrofit was conducted during overhaul period using the air heater of rotary energy-saving type instead of the old one, so as to ensure stable operation of relevant boiler equipment. By comparing the operation parameters before and after retrofit, it can be seen that the inlet temperature of the air heater is significantly improved, with obvious energy saving effect obtained, thus achieving stable operation of the denitrification system.

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.

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.

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.

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 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.

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.

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.

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.

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.

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.

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.

To improve the operation stability of double reheat steam turbine units, an analysis was conducted on the factors affecting the temperature of (super) high-pressure cylinder exhaust steam in double reheat steam turbine units, while a discussion was carried out on the control method applied in the DEH system when abnormal temperature appears. Considering the bypass system capacity and DEH control method, the cutting off strategy was optimized for the steam turbine. Results show that through cooperative operation with the bypass control system, the unit trip probability due to abnormal temperature of (super) high-pressure cylinder exhaust steam could be reduced, while stable operation of the unit could be ensured.

Hot-state and cold-state inspection and adjustment are carried out on the supports and hangers for the main steam pipeline, high-temperature reheat steam pipeline, low-temperature reheat steam pipeline and high-pressure water supply pipeline of a thermal power plant. The stress and displacement of the four pipelines are checked with professional piping stress analysis software CAESAR Ⅱ, based on which safety operation of above thermal pipelines is guaranteed, while service life of the unit is extended.

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.

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.

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.

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 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.

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.

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.

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.

To solve the problem that large power units have poor primary frequency regulation performance due to limited energy storage in the concurrent boiler, an optimization method was proposed for primary frequency regulation by adjusting the amount of extracted steam to high-pressure heaters when severe grid frequency deviation happens. Mutual effects of both the turbine and the regenerative system were achieved by modifying common simulation models of large power units, based on which the optimization method was verified. Results show that the proposed method can remarkably widen the range and improve the performance of frequency regulation.

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.

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.

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.

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 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.

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.

An introduction is presented to the technical specifications, structural features and ventilation cooling effect of a 320 MW fully air-cooled generator in a gas-steam combined cycle unit, including the main structural parameters, material characteristics and related tests. Study results show that compared with hydrogen-cooled generator, the fully air-cooled generator has a simplified auxiliary system and facile operation, resulting in improved unit safety and efficiency.

The 1 000 MW ultra-supercritical double-reheat unit adopts the triple-stage bypass system, and its control logic is newly developed based on traditional control strategies. The control modes and strategies respectively for the high-, medium- and low-pressure bypass system are described under startup, shutdown, normal operation and abnormal operation conditions, combined with analysis on corresponding application situation, existing problems and optimization schemes of relevant bypass systems in a certain unit during commissioning period.

Through deep analysis on the function and principle of the main hoist for refueling machines of AP1000 nuclear power stations, an innovative design was carried out to the main hoist for refueling machines of a CAP1000 project, with improvements on the maintainability and economy, so as to achieve localization of the refueling machines.

Aiming at the problem that the temperature of thrust pad in feed pump turbine of a nuclear power station is too high, the reason has been analyzed according to the disassembly and inspection results during the overhaul of thrust pad, as well as to the parameters recorded in daily tracking. The temperature of thrust pad has finally reduced to a reasonable range through calculation, adjustment, detection with clearance gauge and other maintenance processes and methods.

An introduction is being presented to 5 control modes during start up of the steam turbine in a gas-steam combined cycle unit, such as the TAB control, speed control, load control, pressure control and steam compensation control, and to 4 operation conditions, like the pure condensing condition, extraction condensing condition, back pressure condition and full switching condition, as well as to the 2 control loops for switching operation. Practice indicates that these operation modes and switching/control processes are all reasonable, which have guaranteed the safe operation for both the steam turbine and the whole combined cycle unit.

Energy-saving effects and remaining problems of the large condensate water pump in a thermal power plant were introduced after frequency conversion retrofit. For optimization purposes, the water pump was operated at reduced pressures, while the boundary condition of pressure limits was obtained through experimental tests, following which corresponding countermeasures were taken to achieve maximum effects of energy saving. Results show that the pressure in main condensate pipe can be lowered in the mode of reduced pressure operation, when energy-saving effects at low load approach to that at high load, achieving energy-saving purposes under all conditions. Both the condensate water pump and the motor can operate normally at reduced pressures, indicating high operation stability of the condensate water pump.

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.

Based on the SCR flue gas denitrification technology and its reaction principle, problems existing in traditional method of SCR ammonia injection control were analyzed, to which improvement measures were proposed and taken. Engineering practices have proved that the improved cascade-feedforward control method has a good control performance. On the premise of environmental protection, the denitrification cost of the power plant is reduced, while the automatic input rate of the control system is improved.

Based on Non-uniform rational B-spline (NURBS) theory and characteristic line modeling technology, the airfoil geometry generation of supersonic turbine cascade was researched, while the blade design software was developed by using C++ language and MFC technique. A supersonic turbine cascade profile was designed with the software developed, and its design and off-design performance were analyzed combined with the computational fluid dynamics (CFD) method. Results show that the software previously developed is proved to be effective in the airfoil design of supersonic turbine cascade, which may therefore serve as a reference for airfoil design and development of low-pressure last-stage turbine blade in actual engineering applications.

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%.