For a wind power tower barrel manufacturing project, a research was conducted on the flux-cored arc welding with CO₂ gas shielding (FCAW) process of Q420NE thick plate butt joint for door frame of wind power tower barrel, and the Q420NE thick plate welding procedure was evaluated. Additionally, through solid wire control group experiments, the influence of different shielding gases on the solid wire gas shieled welding was analysed. Results show that, the FCAW process meets the welding procedure requirements for Q420NE thick plate and can be used for the tower barrel door frame welding. For solid wire gas shielded welding, the type of shielding gas has a significant impact on the welding of Q420NE steel, and welding Q420NE steel with pure CO₂ gas cannot ensure that the weld meets the technical requirements.

Taking a PG9351FA gas turbine combined cycle unit as the research object, the unit model was established based on Thermoflex software. The performance of unit under full load and constant load conditions was calculated respectively, and the key parameters of the system were analysed. Results show that, compared with the full load condition and the constant load condition, the increase of ambient temperature has the same effect on the efficiencies of steam turbine, waste heat boiler and combined cycle, but the difference on the efficiency of gas turbine is significant. When the combined cycle unit is operating under constant load condition, a suitable low-grade heat source can be used to improve the inlet air temperature of the gas turbine, so as to improve the efficiency of the gas turbine. At the same time, the back pressure of steam turbine can be reduced to improve the performance of steam turbine by cold end optimization and other measures.

Adiabatic compressed air energy storage system has the characteristics of large capacity, long-term performance, safety, stability, and flexibility. In this type of energy storage system, the heat exchangers, as key components, have particularly important impact on system efficiency. Therefore, by establishing an adiabatic compressed air energy storage thermal system model, the impact of heat exchanger final temperature difference and air side pressure drop on system efficiency was analysed, and the cost of heat exchangers was comprehensively evaluated. Results show that, the increase of the upper final temperature difference of heat exchangers can lead to a decrease in system efficiency, and the lower final temperature difference should be matched with the upper final temperature difference in practical engineering design. Compared to high-pressure heat exchangers, the air side pressure drop of low-pressure heat exchangers has a greater impact on system efficiency. The smaller the final temperature difference and pressure drop of the heat exchangers, the higher the system efficiency, but the higher the equipment cost. Therefore, there is an optimal combination of final temperature difference and pressure drop to minimize the cost of the heat exchangers while meeting the system efficiency requirements.

At present, selective catalytic reduction (SCR) is widely used for flue gas denitration in coal-fired power plants. SCR reactor is the main equipment for flue gas denitration treatment, and its design scheme directly affects the flue gas denitration performance. The SCR reactor is subjected to various loads and effects during operation, and the conventional design usually adopts a conservative frame form, which has limitations in material utilization and stress performance. In order to achieve high-performance design of SCR reactor structure, the stress characteristics and structural scheme were studied, and the key technical solutions such as structural spatial layout and section optimization, structural stiffness improvement, thermal stress and expansion deformation control, internal pressure control, and ash deposition prevention measures were formed. A new type of SCR reactor structure was designed. Results show that, the new type of SCR reactor structure is reasonably arranged, the height of the catalyst layer beam can be reduced by about 50%, and the total steel consumption can be saved by about 20%. At the same time, finite element simulation analysis shows that the structure has good stress performance and safety performance. The new type of SCR reactor has been applied in many projects, effectively controlling the nitrogen oxides (NO_x) emission from power plants and generating significant benefits.

A 1 000 MW ultra-supercritical double reheat unit experienced an abnormal drop in control (EH) oil pressure during a valve activity test (ATT), which led to the closure of all turbine control valves, triggering the generator reverse power protection and causing the unit to trip. The causes of the accident were analysed, and the treatment suggestions and subsequent preventive measures were put forward based on the working principle of the oil motor and the control valve anti-jamming logic in the logic of the digital electrohydraulic control system (DEH). Results show that, by strictly controlling the quality of EH oil, optimizing the test process, and enhancing the inspection of logic configurations, the turbine trip caused by ATT can be effectively avoided. The research results have a certain reference significance for the commissioning and operation of similar types of units.

In view of the low power generation efficiency of refuse-fired generators set with mid-temperature and mid-pressure, the quality and efficiency improvement measures such as upgrading main steam parameters, adding reheat cycle and waste heat recovery and utilization device were researched. A 15 MW refuse-fired generators set was selected to analyse, according to mid-temperature and sub-high pressure scheme and mid-temperature, sub-high pressure and reheating scheme respectively, the performance parameters and economic benefit after transformation were analysed. Results show that, after the application of mid-temperature and sub-high pressure technology scheme, the mass of boiler heating surface increases by 9%, the power generation efficiency increases by 1.52 percentage points, the waste power generation increases by 43 kW·h/t, the transformation cost is about 20.05 million yuan, the cost of pipes replacement increases by 6.57 million yuan, the internal rate of return is 17.47%, and the investment payback time is 6.31 years. After the application of mid-temperature, sub-high pressure and reheating technology scheme, the mass of boiler heating surface increases by 24%, the power generation efficiency increases by 2.35 percentage points, the waste power generation increases by 64 kW·h/t, the transformation cost is 24.90 million yuan, the cost of pipes replacement increases by 13.63 million yuan, the internal rate of return is 21.53%, and the investment payback time is 5.15 years. The research results can provide some reference for the application of reconstruction engineering for refuse-fired generators set with mid-temperature and mid-pressure.

The spiral tube of the water wall of a supercritical boiler was leaked in many places. After sampling the leakage tube, the macroscopic examination, chemical composition, metallographic structure and tensile properties were analysed. Results show that, the original leakage point is located in the fusion zone of the water wall tube fin weld, which is caused by a large number of welding defects in the fin weld. The leakage of steam water blows adjacent pipe. The adjacent pipe appears multiple secondary leakage points, and the medium flow rate in adjacent pipe is reduced, resulting in short-term overheating in the downstream area of the secondary leakage points. It is recommended that the welding quality of fin welds should be strictly controlled and checked.

Based on the investigation and analysis of the imported hydraulic actuator of gas fuel control valve in gas turbine, and combined with considerable experience in use and design, a 100% domestically produced hydraulic actuator for gas turbine gas fuel control valve has been newly developed. The principle design of the hydraulic actuator of gas fuel control valve was emphatically introduced, and the frequency response of the hydraulic actuator was simulated and analysed by building a simulation model. After which, the reliability verification and multiple performance tests were carried out for the hydraulic actuator with an established test system. Simulation and test results indicate that, the performance of the domestically produced hydraulic actuator for gas turbine gas fuel control valve is superior to that of the imported actuator in many aspects. The successful development of hydraulic actuator sample for gas turbine gas fuel control valve has broken through the localization problem.

To investigate the influence of random variables, such as structural dimensions, material property parameters, and temperatures, on the equivalent stress of steam turbine rotor during material preparation, processing, installation and operation, taking the high pressure rotor in a 300 MW class steam turbine as the research object, the time and location of the maximum equivalent stress during cold start-up was obtained by calculating with finite element method. Meanwhile, combined with the randomness of variables, the relationship between the rotor maximum equivalent stress and the random variables was fitted with both of polynomial response surface method and support vector regression (SVR) response surface method, and analyses and comparisons were conducted on the fitting effects of above two methods. Additionally, the reliability of rotor equivalent stress and the sensitivity of various random variables during cold start-up process were investigated by Monte Carlo simulation method, while the sensitivity index order of six random variables including rotor radius, was determined. Results reveal that the fitting effect of SVR response surface method is better than that of polynomial response surface method, and the strength reliability indexes of above two response surface methods for the cold start-up curves are 96.99% and 94.16%, respectively. Among the six random variables, the elastic modulus of rotor material is identified as having the most significant impact on the equivalent stress of steam turbine rotor.

To meet the requirements of increasingly stringent standards for nitrogen oxides (NO_x) emission, the lean-premixed combustion mode is widely applied in heavy-duty gas turbines for power generation. With the application of this technology, the flame temperature can be reduced, so as to decrease the NO_x emission. To verify the combustion mode control system in an F-class heavy-duty gas turbine, based on the mechanism model of simplified chemical reaction for natural gas combustion, a network module library for chemical reactor was established, and a simulation research was conducted on the switching process of combustion mode. Based on the modelling technology of Simulink model diagram, a dynamic modelling for the dramatic changing process such as ignition and burn out is realized. Through simulating, it is verified that the established model can accurately reflect the influence of flow distribution ratios of different fuel nozzles on the combustion temperature and emission component, while the real-time simulation with a lower computational expense for combustion mode switching can be realized.

The no load commissioning test should be conducted on an industrial back pressure steam turbine after manufacturing stage according to technology agreement, while there is a distinct difference between the commissioning tests of back pressure and condensing steam turbines from the aspects of process and scheme. Combined with an actual application, researches were carried out for the process and scheme of no load commissioning test of the back pressure steam turbine, and key and difficult points of actual commissioning test were analysed. This may serve as a reference for the no load commissioning test in similar back pressure steam turbines.

To address the issue of large heat absorption deviation between the left and right of the high-temperature superheater in a 660 MW boiler, an initial attempt was made to apply the self-correcting method used in another boiler of the same power plant. This involved studying the relationship between the damper opening deviation of the separated overfire air (SOFA) and steam temperature deviation. When this approach did not achieve the expected results, the failure causes were further analysed. By coupling the SOFA damper horizontal swinging angle and opening deviation, the relationship between these factors and the steam temperature deviation on the left and right of the boiler was established successfully. Results show that, adjusting the SOFA damper horizontal swinging angle can effectively change the thrust distribution on the left and right of the furnace incircle. Adjusting the opening of SOFA dampers on the upper three layers, it is found that when the opening of the left dampers increases and the opening of the right dampers decreases, the heat absorption increases on the left side and decreases on the right side, which makes the steam temperature deviation between the two sides of the superheater decrease firstly and then stabilize gradually with the adjustment of SOFA damper opening deviation. The implementation of the self-correcting optimization control system, which couples the SOFA damper horizontal swinging angle and opening deviation, successfully achieves self-correcting control of the boiler steam temperature.

For a heat and power cogeneration unit, analyses were conducted on energy efficiency characteristics based on adaptive multi-level filtering fuzzy C-means (FCM) algorithm with the optimal clustering number. Through improving the traditional clustering algorithm, an adaptive optimal clustering method was proposed based on multi-level strict screening mechanism, so as to obtain the energy efficiency characteristics of unit under different load conditions. The curves of unit operation characteristics were fitted by least squares method, while comparisons and analyses were carried out based on the surfaces of unit operation energy efficiency characteristics from Newton interpolation algorithm. Results show that, the unit performances have certain differences with different external constraints. From the surfaces of energy efficiency characteristics, the difference between the energy efficiency characteristics of two units under different loads and the load condition with a better operation performance of each unit can be visually displayed. Under the condition of 225 MW electric load and 72.5-88.5 t/h heat load (heat-supply steam mass flow rate), the net coal consumption rate of No.1 unit is higher than that of No.2 unit, and with the increase of heat load, the difference in coal consumption rate firstly increases and then decreases. Therefore, No.2 unit can be prioritized to operate under low load condition.

In a continuous feeding fixed bed furnace, researches were conducted on the influence of simulated rural solids with different component proportions on the producing characteristics of pyrolysis gas and tar. Experimental results show that, compared with single component, the pyrolysis of rural solid waste with mixed components is more conducive to promoting the sufficient cracking of materials, reducing the tar production, and improving the cold gas efficiency (CGE) when the pyrolysis temperature is 800 ℃. The pyrolysis with mixed components can reduce the content of O element and corrosivity of tar, while the presence of chlorine-containing substance (polyvinyl chloride in this paper) could effectively promote the decomposition of functional groups containing N or S element in pyrolysis tar, which ensures that tar has a higher heat value and a better stability. The pyrolysis with mixed components is effective in reducing heterocyclic and alicyclic compounds in tar, but the proportion change of chain compounds and aromatic compounds is related to the component proportions of simulated rural solid waste.

In response to the problems existing in the original deep coupled waste heat utilization system of a 660 MW coal-fired unit, the reasons for the failure to achieve the design goals of the system were analysed. Four optimization and renovation schemes were strategically adopted, including the optimization of bypass flue, the optimization of water intake position for condensate heat exchanger, the optimization of recirculation pipeline and adding a water side bypass for the flue gas cooler. The final optimization and renovation effect was calculated and analysed in detail. Results show that, after the optimization, the proportion of bypass flue gas volume increases to 13.5%, the inlet water temperature of the condensate heat exchanger can be stabilized at 70 ℃ for a long time, and the steam consumption of the auxiliary steam heat exchanger is basically reduced to 0. After optimization, the system is put into operation to reduce the net coal consumption rate of the unit by 2.73 g/(kW·h).

The method of statistical analysis for the reliability of nuclear power units was proposed, and the meaning and computational formula for five reliability characteristic quantities of nuclear power units were introduced. The weighted arithmetic means of reliability characteristic quantities of nuclear power units were presented, while following items of 1 000 MW class nuclear power units in China and America from 2008 to 2022 were given, namely the statistic results of reliability, the calculation results of weighted arithmetic means of reliability characteristic quantities, and the change curves of reliability characteristic quantities. Results show that, for 1 000 MW class nuclear power units in China, the availability, reliability and maintainability in general, all present a trend of increase, while the equivalent availability factor of 1 000 MW class nuclear power units from 2008 to 2022 in China is 1.81 percentage points higher than that in America.

By using optical microscopy (OM), scanning electron microscopy (SEM), X-ray energy dispersive spectroscopy (EDS), and multi-phase separation technology, a research was conducted on the precipitates along grain boundary of HT700T alloy tubes after thermal exposure. Results show that, the precipitates along grain boundary under etching condition appear as flocculent clusters, which are significantly different from precipitates within grain. The precipitates along grain boundary has already appeared after thermal exposure at 500 ℃, while the quantity of precipitates increases with an increase of temperature, reaching a peak value at around 750 ℃, and then gradually decreases until completely dissolving and disappearing at 1 000 ℃. The precipitates along grain boundary are composed of Cr-rich phase, γ' phase, and γ matrix phase, and the volume fraction of γ' phase in grain boundary micro region is higher than that within grain. Through observing different regions in the creep rupture specimen at a high temperature of 700 ℃, no evidence has been found that the precipitates along grain boundary promote the creep cracking of sample, but the stress has a certain effect on promoting the precipitation along grain boundary.

A 1000 MW coal-fired boiler experienced a decrease in efficiency due to the long-term mixed combustion of sludge and lignite. During boiler inspections, slagging was found on the water walls near the burners and the first-stage superheater tube panels. To improve the boiler efficiency and solve the problem of slagging, the combustion characteristic test of common coal and sludge was carried out, and the combustion condition in the furnace was optimized by combining the pulverization system and combustion adjustment test. Results show that, the optimized combustion condition can effectively realize the combustion of "wind-wrapped powder" in the furnace, and successfully eliminate the slagging problem in the water wall area and first-stage superheater tube panels. Furthermore, for the 1 000 MW coal-fired boiler under various load conditions, a sludge mixed combustion strategy based on secondary air distribution and excess air coefficient control was proposed to further improve boiler efficiency.

High-strength structural steel (referred to as high-strength steel) Q460 was selected to optimize the most frequently used H-shaped section bending members and box-shaped section axially loaded members in large boiler steel structure. Results show that, the application of high-strength steel in large power plant boiler steel structure has significant economic benefits. For large plate-bent bending members, the optimal design using high-strength steel Q460 can save 32.5% of the steel quantity. For axially loaded members, the proportion of steel quantity saved decreases with the increase of slenderness ratio and thickness, but the maximum saving ratio can reach 21.7%.

A photovoltaic power generation model was reasonably established through comparing with several monitoring methods, and comparisons were conducted between the photovoltaic power generation per unit area of actual equipment and model, so as to verify whether the established photovoltaic power generation model can realize the status monitoring of photovoltaic power generation equipment with low cost. The abnormal photovoltaic power generation equipment is visually detected from the status monitoring results in the first practical application. Following problems have been solved during analysing and treatment process, such as the string fault caused by hot spots, power limitation caused by unreasonable string connection, and abnormal fluctuation caused by condensation cloud covering. Finally, it is confirmed that this method could indeed be implemented with low cost and demonstrate a certain level of effectiveness.

Using ethanol hydration modified calcium oxide as the adsorbent, the influence of different modification parameters on the dechlorination effect was studied in a fixed bed experimental device, and analyses were conducted on the kinetics of HCl adsorption experimental results. Afrter which, the nonlinear fitting was carried out for the experimental data by five apparent kinetic models. Researches results show that, the order of fitting effect is Bangham model, quasi-second-order model, Elovich model, quasi-first-order model and particle internal diffusion model. The process of mass transfer and diffusion always has a significant influence on HCl adsorption, which is the key control step. In the initial stage of reaction, when the surface-active site is not occupied and the internal pore is not blocked, the external mass transfer process is the dominant control step. In the middle stage of reaction, because the original developed pore structure is blocked by the product layer, the diffusion resistance in the particles become the dominant factor in HCl adsorption process. Meanwhile, the chemical reaction in surface always plays a leading role in HCl adsorption process.

For the combination of boiler steel frame and front coal bunker in a large power plant, the seismic performance under frequent and rare earthquake conditions was researched by using ABAQUS finite element software, and analyses were conducted on the seismic time-history response and the influence of beam-column connection type on the seismic performance of the structure system. Subsequently, the torsional deformation of structure with beam-column pinned connection under rare earthquake condition was quantitatively evaluated based on torsional angle, and corresponding measures were proposed to reduce the torsional deformation. Research results show that, the overall stiffness of structure would be influenced by the beam-column connection types, and the application of a structural system with beam-column pinned connection may result in lower overall stiffness, leading to increased structural deformation. Both articulated structures with additional reasonable braces and rigidly connected structures demonstrate good seismic performance, while articulated structures are more economical.

For the boiler plant in a refuse-fired power generation unit, design methods and cautions were introduced and analysed for the application of tight sealing steel structure, while comparisons were carried out with other types of boiler plants in terms of site area and total height of building. Results show that, the design of boiler plant with tight sealing steel structure can protect the maintenance platform from wind and rain with a heat insulation effect, and there is no need to build a separate building envelope, resulting in a smaller site area, less material consumption, and a lower overall construction cost.

Grid-connected inverter is the core of direct current (DC) and alternating current (AC) conversion, and its performance is directly related to the efficiency of grid-connected photovoltaic and the power quality of the power system. However, during the long-term service of the inverter, the instability factors such as DC voltage fluctuation and power grid disturbance put forward higher requirements for the control strategy of the inverter. The voltage and current closed-loop control mechanism and its equivalent model of three-phase inverter were analysed systematically, and the strong robust closed-loop control strategy was proposed by combining the proportional-integral-derivative (PID) controller and feedforward control idea. At the same time, based on the equivalent model and power consumption, the design of inductance and capacitance in the filter circuit was improved. Finally, a complete simulation circuit model was built by using MATLAB Simulink software, and the performance of closed-loop control circuit and the filtering effect of filter were analysed comprehensively. Results show that, the disturbance removal time of the control strategy does not exceed 0.02 s, and it has good synchronization between output voltage and current. The harmonic distortion rate of the output voltage and current of the inverter is less than 1%, and the power quality of the three-phase voltage and current is good.

The flow rate and system resistance are not matched with the characteristics of the induced draft fans in thermal power units under low load condition for deep peak regulation, leading to the vibration of fans is more sensitive to external disturbance and its own state change. To solve the problem that the vibration exceeded the limit of an axial flow induced draft fan with adjustable rotor blade under low load condition, according to the vibration characteristics and the feedback effect of vibration treatment, it is investigated that following reasons existed, such as a larger vibration in power frequency caused by an unbalance effect on the impeller of the induced draft fan, a larger vibration in frequency doubling and a fluctuation of fan vibration with the change of operation condition caused by the insufficiency and asymmetry of support stiffness. The vibration of induced draft fan with different openings of rotor blade has been finally controlled within a reasonable level through decreasing the amount of unbalance by field dynamic balancing test, adding welding ribs, and increasing the support stiffness with secondary grouting reconstruction.

For a tube burst accident occurred at a high temperature superheater in a power plant boiler, to avoid the similar accidents, the reason of tube burst was investigated from the aspects of macroscopic inspection, alloy composition analysis, hardness test, metallographic inspection, and energy spectrum analysis through using alloy analyzer, Brinell hardness tester, metallographic microscope, and scanning electron microscope (SEM). Results show that, the reason of the tube burst is the thick corrosion products attached to the inner wall of the tube, which leads to the decrease of flow area and the deterioration of heat transfer with the long time over temperature service of boiler tube. In response to this issue, it is necessary to strengthen the management of the construction and installation process of boiler heating surface tubes in power plants. Measures such as sealing the tube leak and strengthening the wall temperature monitoring during operation should be adopted, thereby improving the reliability of boiler operation.

Taking the thermal control reliability check of a thermal power unit as an example, analyses were conducted on the reliability of single point signal in the protection and interlock of main and auxiliary engines in the unit, so as to identify the risk of equipment misoperation and refusal-operation, and corresponding improvement measures were put forward subsequently. Using case analysis method, the function of single point signal in protection, interlock, start-stop permit and so on was analysed by taking master fuel trip (MFT) signal and air preheater full stop MFT protection signal as examples. It is found that the single point signal not only has the problem of refusal-operation or misoperation in main engines protection, but also has similar problems of the protection and interlock of important auxiliary engines, which will lead to a serious impact on the safe operation of the unit. In view of the problems found, some suggestions were proposed to improve the reliability of single point signal logic, such as adding the same type of redundant single point signal to form redundant logic, adding different types of single point signals to form redundant logic, and cancelling or changing the limit of single point signal to start.

Taking two commonly used blades types of adjustment baffles in practical engineering as research examples, analyses with 3D modelling were conducted by applying finite element software. Comparisons were carried out between the resistance characteristics and adjustment performance of two types of adjustment baffles through flow field analysis; meanwhile, comparisons were carried out between the stresses and deformations of two types of adjustment baffles through mechanical property analysis. Results show that, the flat plate blade baffle has better adjustment performance than the streamlined blade baffle, while the streamlined blade baffle has better mechanical property performance than the flat plate blade baffle.

During the routine inspection of major maintenance in a nuclear power plant, it was discovered that the flange bolts of outer heat shield and inner sleeve of the main pump cooling system had fractured during operation. Macroscopic observation, chemical composition analysis, vickers hardness test, metallographic inspection, and energy spectrum analysis were conducted on the fractured flange bolts. The reasons of the fracture were analysed in combination with the operating environment of main pump flange bolts. Results show that, the failure mode of the bolts is low-cycle fatigue fracture. In normal operation, temperature cycle changes and mechanical constraints form the two necessary conditions for fatigue fracture failure of bolts. In order to ensure the reliable operation of the main pump cooling system in the nuclear power plant, it is recommended to shorten the inspection cycle of bolts from 5 years to 2-3 years.

To optimize the operation strategy of combined heat and power unit under different deep peak regulation conditions and electricity price periods, methods such as mathematical modelling, deep coupling, and intelligent optimization were adopted for research. The study found that during single unit operation, when the peak regulation assessment price is higher, the heat-supply amount can be appropriately increased, so as to balance profits and avoid negative profit situations at certain nodes. Profits vary significantly under different peak regulation periods: the profit of low load operation is prior to that of high load operation during heat-supply period, while the priority dispatch of power generation can obtain higher profits during non heat-supply period. Further researches were conducted on load distribution based on single unit research. Results reveal that, the coal consumption rate of double units operation is higher than that of single unit operation under same operation conditions. However, due to the support from peak regulation compensation policies, the profit of double units operation is much higher than that of single unit operation. Researches on the coupling of electricity price policies show that, the profit can be significantly increased with the high load operation of the unit during peak electricity price period, while the unit should be avoided to operate near peak regulation load nodes during valley electricity price period, so as to prevent serious losses. Research findings can provide a scientific basis for optimizing the dispatch of combined heat and power units.

To clarify the actual thermal performance of a 660 MW coal-fired unit under deep peak regulation condition with 30% rated load, thermal performance tests were conducted in accordance with relevant testing standards. The test results show that, the boiler thermal efficiency and steam turbine heat rate of the unit under this condition are 92.81% and 8 529.4 kJ/(kW·h), respectively. The gross coal consumption rate is 317.1 g/(kW·h), which is equivalent to the design value [316.3 g/(kW·h)]. By using a deviation analysis method, it is determined that the main reason for the lower boiler thermal efficiency compared to the design value is the high actual flue gas loss. Although the efficiencies of the high, medium, and low pressure cylinders of the steam turbine have decreased to varying degrees, the overall steam turbine heat rate is still better than the design value due to the actual back pressure of the unit being significantly lower than the design value. Based on the test results, it is inferred that the error of gross coal consumption rate calculated by positive balance method is mainly due to sampling, preparation, and analysis errors of coal and the statistical error of coal consumption measurement device. Compared with the 50% rated load condition, the operation safety of the unit under the deep peak regulation condition is decreased, the auxiliary power rate of the unit is increased by 3.45 percentage points, the boiler thermal efficiency is reduced by 1.72 percentage points, and the steam turbine heat rate is increased by 157.5 kJ/(kW·h). The research results provide a reference for similar units to master the thermal performance under deep peak regulation condition.

For an ultra-supercritical unit with a back pressure steam turbine for heat supply, researches were conducted on the unit with deep peak regulation under different heat supply modes. Through theoretical calculations, the economic benefits of the back pressure turbine under operational and non-operational modes during deep peak regulation conditions were analysed, while comparisons and analyses were conducted on the economic benefits of the steam from the back pressure turbine for the regenerative heating system and directly for external heat supply. Result show that the comprehensive economic benefit of the back pressure turbine under operational mode in low load is increased by 198 400 yuan per year compared with under non-operational mode. The unit heat rate of the back pressure turbine for the regenerative heating system is improved by 171.83 kJ/(kW·h) under 50% load compared with directly for external heat supply.Under deep peak regulation condition, the method of the back pressure turbine directly for external heat supply can be adopted when the flow rate for heat supply is higher than the minimum flow rate at the back pressure turbine inlet, and the method of the back pressure turbine for the regenerative heating system can be adopted when the flow rate for heat supply is lower than the minimum flow rate at the back pressure turbine inlet. Finally, the flexibility of unit operation can be improved with the back pressure turbine put into operation under deep peak regulation condition.

Based on a typical recompression Brayton cycle, a thermodynamic model was established for a supercritical carbon dioxide (sCO₂) power generation cycle, and analyses were conducted on the influence of key parameters on the system performance. Through design optimization by applying genetic algorithm, the maximum efficiency of system and corresponding operation parameters were obtained. Results show that, a higher system cycle efficiency can be obtained when the inlet temperature and pressure of main compressor are close to the critical point and the inlet temperature of turbine is higher. With the increase of the pressure ratio of main compressor, the cycle efficiency increases at first and then decreases, while there is an optimal pressure ratio. Research results can serve as a technical reference for the engineering application of sCO₂ power generation technology.

Aiming at the variable-diameter and variable-pitch spiral shaft structure in the biomass fuel compression and conveying equipment, a parametric calculation model was established through the analysis of its compression and conveying mechanism. A 14 inches spiral shaft was taken as an example to design the structure, and the compression and conveying process of corn stalk was numerically simulated. Finally, the compression and conveying performance of the spiral shaft was further verified by prototype test. In numerical simulation, the compression ratio of corn stalk reaches 2.408. The experimental results of corn stalk compression and conveying show that the compression and conveying effect of the variable-diameter and variable-pitch spiral shaft structure designed by the parametric calculation model is good, which is in line with the expected standard of corn stalk compression and conveying. The design method using parametric calculation model has certain feasibility and can be extended.

By using macroscopic inspection, chemical composition analysis, fracture analysis, metallo-graphic inspection and mechanical property test methods, the fracture position of Inconel 718 alloy valve stem of a supercritical 600 MW unit was analysed. The specific improvement suggestions were given through failure causes analysis. Results show that, the chemical composition, metallographic structure, hardness and impact properties of the valve stem can meet the requirements. The grain structure of the valve stem sample is slightly coarse, with many inclusions and mainly carbides, and the tensile property parameters are lower than the standard value. The reason for the valve stem fracture failure is that the strength of the material is insufficient. Meanwhile, the groove root and screw thread groove on the component are stress concentration points. Under the action of stress, the groove root cracks will be generated and then be expanded, leading to the fracture.

A new type of drainage device selected for the gland steam condenser in a domestic new-built power generation unit was introduced, detail analyses were conducted on its composition, structure, and working principle, while comparisons were carried out between this device and the traditional gland steam condenser (adopting multistage water sealing). It is concluded that this device has the advantages of simpler equipment operation, stronger adaptability to back pressure, higher safety of the equipment itself and the unit, as well as being beneficial for the operation of air-cooled condenser units and peak regulation units. Based on above researches, a further energy-saving retrofit scheme of "zero leakage" of gland steam condenser was proposed. By optimizing the interface position with changing the installation height of internal pipelines, it is estimated to save an annual cost of 3 600 yuan in desalinated water production for the power plant.

To establish a broadly applicable design framework of fuel flow control method for an F-class gas turbine, researches were conducted on the total fuel flow control design, fuel distribution control loops design, Wobbe index adjustment, and pressure regulation valve design, a general control method of gas turbine fuel flow was formed, and the simulation verification of fuel flow control strategy was completed. Results show that, based on the proposed fuel flow control strategy, the fuel flow control effect of this F-class gas turbine can be realized under all conditions from ignition, warm-up, acceleration, grid-connection, load ramp-up to full load. Research results can serve as a reference for the design and improvement of relevant control algorithms for F-class gas turbine fuel flow, further supporting the efficient, stable, and safe operation of the gas turbine.

After switching the heating mode of a steam turbine in a gas-steam combined cycle unit, there was a sudden increase in vibration of the low-pressure rotor of the steam turbine, prompting an emergency switch back to the previous mode. Through the analysis of changes of operation parameters before and after the incident, the preliminary determination of the incident cause was the change in steam admission parameters of the low-pressure cylinder after mode switching. To solve this problem, the set value for the exhaust steam pressure of the intermediate-pressure cylinder was adjusted, and another mode switching test was conducted. During this test, the changes in steam admission parameters of the low-pressure cylinder were reduced, and there was no significant change in vibration after mode switching. This case can serve as a reference for analysing other similar incidents.

Using the finite element method, a model was established for the persistent leakage phenomenon occurring during load variation at the split-plane end of the high-pressure cylinder in a Russian-made nuclear power steam turbine, the influence of factors such as load level, bolt preload, and external shaft gland insulation on the leakage was significantly researched. Firstly, a finite element model of the high-pressure cylinder end was developed to analyse the impact of load level variations on the steam supply parameters of the shaft glands, and subsequently, the variation rule of the contact pressure at the split-plane end of the high-pressure cylinder under different loads was discussed. Secondly, the influence of bolt preload on the distribution of contact pressure was investigated. Finally, based on research findings, a solution involving external pressurized sealing was proposed, and a simulation body and sealing fixture for the end of the high-pressure cylinder were designed. Results show that bolt preload has a significant local impact on the contact pressure but has a relatively minor direct impact on the leakage area, while the external shaft gland insulation can improve the end contact condition to a certain extent. When the gap between the sealing fixture and the cylinder wall is less than 0.2 mm, the internal pressure within the simulation body of cylinder can be effectively maintained. While field implementation effects can further validate this conclusion.