To solve the problems of slow milling response and poor control precision occurred in direct-blow pulverizing systems, a novel pulverizing system adding small pulverized coal silos is designed, and the corresponding air-powder control strategy is proposed. Moreover, based on the dynamic simulation model of an ultra-supercritical unit, the operation and control strategy of the novel pulverizing system is simulated and validated. The results demonstrate that, the proposed control strategy enables precise and rapid response of air-powder parameters. In the load response simulation tests conducted within the load variation range of 75%~85% of rated load, after the small pulverized coal silos were put into operation, the load response rate of the unit’s model can reach 5%/min and recover stability faster. Therefore, the novel pulverizing system and its operational control strategy significantly enhance the unit flexibility. The research provides a viable technical approach and guidance for improving the flexibility of coal-fired boilers.

In order to study the unstable characteristics of vapor-liquid two-phase flow in water-cooled wall pipe of an opposed combustion natural circulation boiler during deep peak shaving, a frequency domain mathematical model suitable for different working conditions is established. By performing small perturbation linearization on the mass, energy, and momentum equations, eliminating high-order infinitesimal perturbations and steady-state quantities, and conducting Laplace transformation, the transfer function used to describe stability of the vapor-liquid fluid flow in the pipeline is obtained through the Nyquist diagram. The graphical method is used to judge the stability of the working fluid flow in the pipe. The calculation results show that, the critical heat flux densities of typical circuits operating at 25% BMCR and 50% BMCR are 182.20 kW/m² and 240.13 kW/m². Moreover, this model is used to calculate the unstable boundary of the water wall pipe section of a 350 MW natural circulation boiler and study the influence of parameters such as inlet subcooling, mass flow rate, pipe length, inclination angle and inlet throttling coefficient on the flow instability characteristics. The calculation results show that, the influence of inlet subcooling on critical heat flux density is non-unique, and the unstable boundary diagram shows a “double-C” shape. Increasing the mass flow rate reduces the density difference between the inlet and outlet of the fluid, which is beneficial to the flow stability. Increasing the heat flow density increases the density difference between the inlet and outlet of the fluid, which is not conducive to the stability of the flow. Enhancing the inlet throttling coefficient can suppress the pulsation of the flow at the inlet, which is conducive to the stability of the flow. Increasing the inclination angle of the pipe will increase the weight pressure drop and increase the disturbance caused by it, which is not conducive to the stability of the flow.

The effect of chloride ion mass concentration (0, 1, 20 mg/L) on stress corrosion cracking of Inconel 740H, a candidate nickel based alloy for high parameter ultra-supercritical units at 630~700 ℃, were investigated by slow strain rate tensile testing and stress corrosion crack propagation testing. Moreover, the relevant mechanism of high mass concentration chloride ions promoting the initiation and propagation of stress corrosion cracks was explored. The results showed that, high mass concentration of chloride ions promoted the stress corrosion cracking of 740H alloy, and the stress corrosion sensitivity index I_scc(δ) of the alloy increased with the chloride ion mass concentration. When the mass concentration of chloride ions increased to 20 mg/L, both the middle and edge of the fracture exhibited intergranular brittle fracture characteristics, with a large number of secondary intergranular cracks near the fracture. At this point, the alloy experienced stress corrosion cracking. The average crack propagation rate in a 20 mg/L chloride ion water environment reached 1.15×10^–6 mm/s, which is 111.7 times the average crack propagation rate in high-purity water.

To investigate the microstructural and mechanical properties of 1 000 MPa grade ultra-high strength steel submerged arc welding welded joints for hydroelectric engineering, the microstructure of different regions of the welded joint was characterized using scanning electron microscopy (SEM). Mechanical properties of the welded joint were determined through tensile testing, impact testing, and bending testing. The results reveals that, the weld metal of the root pass and fill passes is composed of columnar, dendritic, and equiaxed grains, with a microstructure dominated by acicular ferrite and a small amount of granular bainite. The heat-affected zone (HAZ) exhibits multiple typical regions, including a critical coarse grain zone and a coarse grain zone near the fusion line along the thickness direction. Away from the weld, fine grain zones and critical zones are observed, with a microstructure primarily consisting of granular bainite, M-A constituents, and lath martensite. The weld metal of the cap pass exhibits typical columnar grains with a microstructure primarily composed of acicular ferrite. The HAZ of the cap pass includes coarse grain, fine grain, critical, and subcritical zones. Due to the absence of subsequent welding passes, no critical coarse grain zone is formed, and the microstructure is primarily composed of lath martensite, granular bainite, and M-A constituents. The average tensile strength of the welded joint reaches 980 MPa grade, the low-temperature impact absorption energy of the weld zone and the HAZ at –40 ℃ is 118.7 J and 149.3 J (at T/4), 67.0 J and 154.0 J (at T/2), respectively. No cracks appear in the lateral bending.

The requirements of over limit evaluation and measuring points layout of vibration/swing in hydropower units in industry standards and national standards are compared. The layout of vibration/swing measurement points on the project site is also described. It is found that the standards related to evaluation and the ones related to measuring points arrangement are inconsistent or unclear with the engineering site, such as vibration evaluation boundary conditions, evaluation criteria, evaluation working conditions and measuring points arrangement. Analysis shows that all the differences between the standards appear in vibration evaluation and measuring points arrangement for fixed parts, and the provisions on radial vibration (swing) of the unit shafting are relatively unified. Inconsistencies in all standards are not conducive to broad-spectrum application, and are prone to ambiguity and disagreement. The phenomenon that the evaluation standard is inconsistent with the measuring points standard, is not conducive to on-site comprehensive vibration evaluation of large or giant units. All the standard evaluation criteria lack the consideration of weight coefficient of amplitude exceeding the limit and cumulative duration, which is not conducive to the development of vibration fault and condition based maintenance, and data accumulation in the new role of hydropower units. The conclusion is expected to provide analytical help and reference for the practitioners of vibration standard compilation, installation and acceptance, operation management and scientific research and test of hydropower units.

Based on a typical 600 MW coal-fired cogeneration unit, novel systems with integrated steam jet and external steam cooler are proposed. In novel system I, the waste heat from exhaust steam is recovered through a steam jet, in which reheat steam is chosen as the working fluid. In novel system II, an external steam cooler is used to reduce the superheat of the mixed steam and the heat load of the boiler. Based on EBSILON professional modeling, the system is analyzed considering the peak shaving performance and thermodynamic performance under the maximum heating condition (extracted steam for heating: 800 t/h) and variable conditions. Moreover, the effects of mixed steam pressure and heat exchanger end difference on the system performance are also investigated. The results show that, under the maximum heating condition, compared with those of the reference system, the heating capacities of the novel system I and II increase by 21.59 and 14.47 percentage points, and the power generation efficiencies are increase by 2.48 and 2.78 percentage points, respectively. With the heating load of 300 MW, the power load regulation ratios of the novel system I and II improve by 6.00 and 3.91 percentage points compared with the reference system, and the lower limits of generation reduce by 84.75 MW and 74.32 MW. The gross efficiency of the novel system I and II improve by 3.02 and 2.65 percentage points, respectively, when the mixing steam pressure is increased from 50 kPa to 85 kPa. With the upper temperature difference increasing from 1 ℃ to 9 ℃, the gross efficiencies of the novel system I and II decrease by 1.67 and 1.51 percentage points, respectively. The result can provide technical references for expanding heating capacity and deep peaking of coal-fired cogeneration systems.

Under the premise that deep peaking of thermal power units has become normal operation, it poses a higher challenge to transformation of industrial steam supply of thermal power units. Three steam supply schemes using reheater recirculation cooling as the core technology are proposed to meet the requirements of high-pressure steam supply transformation of 660 MW supercritical units. Moreover, the feasibility and economy of these schemes are analyzed by thermodynamic calculation under varying working conditions. The calculation results show that, all the three schemes can ensure the safe operation of the reheater under non-overtemperature conditions, and greatly improve the wide load high pressure steam supply capacity of the unit at 30% rated power load or above and under conditions that meet the demand of single unit with 200 t/h, 6.0 MPa and 480 ℃ steam supply. In order to avoid overspeed of the flow rate at the reheater outlet, it is necessary to coordinate the operation of the immediate pressure (IP) control valve to reduce the flow rate of the reheated steam by increasing the pressure of the reheated steam. With the decrease of the load, the reheater recirculation flow rate under the rated steam supply flow rate will increase. The recirculation flow rate under the whole working conditions of scheme 1 and scheme 3 is not much different, and the ratio of the recirculation flow rate under the high and low load of scheme 2 can reach more than 5 times. Among the three steam supply transformation schemes, scheme 2 is the most energy efficient, scheme 3 is second, and the three schemes can produce economic benefits of 39.51, 44.45 and 41.78 million yuan each year, but in the implementation process, the selection of schemes should consider factors such as investment cost, operation and maintenance amount and energy saving income.

The beam-down concentrating solar power plant has the advantages of high concentrating ratio, low installation and maintenance requirements, and low pump consumption. Relying on the 50 MW beam-down tower concentrating solar power station in Yumen Xinneng First Power Co., Ltd., the mathematical models of the heliostat field, hyperboloid mirror, receiver, molten salt tank, and power generation cycle are established and verified. The run-test results reveal that, the maximum outlet temperature of the molten salt can be maintained at 559 ℃ for 50 minutes at an average direct normal irradiation of 739.70 W/m². The cosine efficiency, shading and blocking efficiency, shading efficiency of the hyperboloid mirror, and attenuation efficiency of the heliostat field at 12:00 are 0.856 8, 0.999 7, 0.994 1, and 0.974 6, respectively. The average hyperboloid mirror flux density and receiver flux density are 11.3 kW/m² and 400.5 kW/m², respectively. Meanwhile, the power station is maintained for 16 h at the rated generation power of 50 MW. The research has certain reference significance for the operation of a beam-down concentrating solar power plant.

Compressed air energy storage is a new form of large-scale and long-term physical energy storage. Gas storage is a crucial component of compressed air energy storage system. The characteristics of common gas storage devices are summarized, and the underground artificial chamber is discussed in detail. The advantages of underground artificial chamber of compressed air energy storage system compared with other types of gas storage are summarized. The design factors such as bearing structure, sealing system and heat transfer management system of underground artificial chamber are analyzed. The key technologies affecting operation of the underground artificial chamber such as site selection, buried depth and pressure design criteria are analyzed and discussed. The evaluation method and evaluation indexes of the factors affecting stable operation of the artificial chamber are put forward. On this basis, the future development direction of compressed air energy storage underground artificial chamber is prospected, which provides a reference for rational design and stable operation of the underground artificial chamber.

To improve steam parameters for better power generation efficiency and economy and meet the development needs of nuclear power plants, a duct-type steam generator is proposed, which is suitable for high-temperature gas-cooled reactors with ultra-supercritical parameters. The main features of the duct-type steam generator’s structure are introduced, and the advantages of this structure in terms of heat transfer performance, operation safety, and production cost are analyzed. Through the establishment of a theoretical calculation model, thermal engineering analysis and heat transfer performance study of axial, radial, and quasi-three-dimensional temperature distributions and other parameters of the steam generator with direct countercurrent heat transfer mode are carried out. The calculation results show that, the duct-type steam generator is mainly based on convection heat transfer mode, with obvious temperature distribution segments and excellent heat transfer performance, which meets the relevant heat transfer requirements. This study can provide a reference for design and development of steam generators in nuclear power plants.