The supercritical carbon dioxide (S-CO₂) cycle power generation technology has become an epoch-making and revolutionary frontier technology in the field of thermal power generation because of its own technical advantages. Due to the very harsh working environment, S-CO₂ is easy to cause corrosion problems of equipment materials. In order to ensure the safe and effective operation of S-CO₂ system, the range of working medium parameters and candidate materials of the system’s key equipment are introduced. The current research status of corrosion behavior of metal materials in S-CO₂ environment are then reviewed. The corrosion mechanism in S-CO₂ carbon environment is elaborated in detail. The influences of temperature, pressure, impurities, flow rate and material composition on S-CO₂ corrosion process are summarized. Meanwhile, the research progress of S-CO₂ corrosion prevention and control technology is introduced. Finally, the shortcomings of existing research and the main direction of future research wereare summarized, so as to provide scientific basis for the safe operation of S-CO₂ recycling system in China.

The blockage and burst failure of steam tubes caused by exfoliated oxide scales is the major risk faced by supercritical boiler in thermal power generations. With the development of advanced ultra-supercritical thermal power technology, especially, more severe oxidation scale problems will carry over into the higher steam parameters thermal power plants. High temperature coating technology shows a new research methods and approaches in solving exfoliated oxide scale problems. It can not only satisfy the performance requirements of heat resistant steel to high temperature steam oxidation resistant in harsh service environment, but also release the temperature limit of currently used heat-resistant steels due to its inadequate oxidation resistance, which has great application potential in the energy sector. The R&D plans of steam oxidation resistant coatings for steam flow parts of ultra-supercritical thermal power units in the EU, the United States and China are briefly described. The current research progress in preparation and service performance of these coatings is emphatically introduced. The basic research and engineering application issues restricting the large-scale application of aluminide coatings in thermal power units are proposed. And the application prospect of high temperature aluminide coating technology for complex heat-resistant steel tubes of ultra-supercritical power plant boiler is prospected.

A concentrated downcomer stub of a boiler drum with 13MnNiMoR steel in a power plant, which was replaced due to cracks and non-metallic inclusions after 14 years in service, was dissected, and the behavior characteristics and influence of the non-metallic inclusion were analyzed through chemical composition analysis, mechanical property testing, microstructure and defect morphology observation. The results show that under service load, non-metallic inclusions become crack sources and microcracks by means of self cracking, interface separation from matrix or hole formation at the end, and microcracks converge to form macro cracks. When tensile and impact tests on the serviced materials, the area without inclusions was cracked and expanded in plastic mode. While innon-metallic inclusions area, the cracks nucleated with non-metallic inclusions and expanded in a brittle mode, resulting in a significant reduction in the strength and plastic toughness of the materials compared with that before service.

The synergy of fireside corrosion and stress is one of the challenges for austenitic steels used in modern fossil-fuel power plants during their service process. The creep rupture tests of Super 304H steel are carried out under static air and fireside corrosion environment at 650 ℃. The stress range is set at 200 to 300 MPa. The creep rupture life and microstructure evolution of different samples were studied. The results show that creep rupture life of Super 304H steel in corrosion condition decreases significantly, compared with that in static air. The rupture life decreases more seriously as the stress decreases, up to 83% at 200 MPa. The complete and continuous corrosion products scale is damaged by fireside corrosion, including the occurrence of cracks and spallation of these surface products. The formation of internal sulfide in the matrix caused by fireside corrosion leads to the deterioration of grain boundaries. Then it tends to crack along grain boundaries during creep rupture tests to accelerate the accumulation of creep damage. The surface of matrix undergoes recrystallization upon to the combination of high temperature and stress due to the loss of alloy elements caused by corrosion/oxidation. The formation of these fine recrystallized grains is unfavorable to creep properties of metals. The ferrite transformation also occurs in the same area during the cooling process after creep tests. Fireside corrosion increases the width of recrystallized grains area, thus expands its influence on the creep rupture life of the alloy. The fireside corrosion accelerates the creep rupture of Super 304H steel by promoting its corrosion process and the microstructure evolution.

The static corrosion behavior of 316L stainless steel and 347 stainless steel at 500 ℃ in Solar Salt (60%NaNO₃ + 40%KNO₃) was investigated via static corrosion test. Corrosion kinetic curves of 316L stainless steel and 347 stainless steel in molten salts at 500 ℃ were obtained through measuring the weight changes of the specimens at each time intervals. XRD and ICP-MS were employed to characterize the phase and component of molten nitrate salts; XRD, SEM/EDS were used to characterize the morphology, composition and microstructure of the corrosion products on the surface and the cross section of corroded specimens. Finally, combining the changes of molten salt and stainless steels, the corrosion mechanism of 316L stainless steel and 347 stainless steel in Solar Salt was discussed respectively. Results showed that the corrosion behavior of 347 SS in Solar Salt at 500 ℃ was characterized by mass gain. As time goes on, the trend of 316L stainless steel increased first and then decreased, while the trend of 347 stainless steel was on the increase. SEM/EDS showed that 347 stainless steel was more likely to be oxidized, while the chromium element in 347 was prone to dissolve, comparing to 316L stainless steel is better stability in Solar Salt, that is, 316L stainless steel is more corrosion resistant.

In recent years, thermal power units have frequently participated in peak shaving to build a new type of power system with new energy as the theme. Accidents of pipeline weld cracking and failure often occur. The welds on both sides of the intersection between the pipeline behind the intermediate pressure bypass valve and the condenser casing frequently crack. The opening area of the muffler pipeline also frequently crack. The heat transfer process from the pipeline behind the medium pressure bypass valve to the condenser muffler is studied by using the finite element method，The distribution of thermal stress under normal and peak shaving conditions was compared. To investigate the causes of the problem, a comprehensive calculation model for the medium pressure bypass pipeline is first established to obtain the distribution of primary and secondary stresses in the pipeline under normal working conditions, as well as the displacement and bearing values of each node. The finite element method is used to study the heat conduction process from the local medium pressure bypass valve to the condenser silencer pipeline. The thermal stress distribution under normal and peak shaving conditions is studied. The results indicate that under peak shaving conditions, the poor atomization effect of the nozzle results in severe water entrainment in the steam, The temperature difference between the pipeline behind the bypass valve and the pipeline of the condenser muffler is larger and repeated operation and shutdown of the desuper heating water cause thermal fatigue fracture of the weld seam and the opening area.

The growing complexity observed in the structures of cast aluminum fittings has posed significant challenges to conventional non-destructive testing techniques, rendering them inadequate in fulfilling the requirements for swift on-site inspection of irregularly shaped cast aluminum fittings. Consequently, an ultrasonic testing method based on flexible phased array probes was proposed. Firstly, a dynamic focusing algorithm for flexible phased array ultrasonic probes was introduced, and the basic simulation theory of CIVA multi-technique software platform was analyzed. Then, the dynamic focusing algorithm used to achieve deflection and focusing of ultrasonic beam was verified by simulation with CIVA, and the parameters of the flexible phased array ultrasonic probes were optimized through simulation. Finally, the effectiveness and feasibility of the testing method were verified through the inspection of typical cast aluminum fittings. The results show that phased array ultrasonic testing technology based on flexible array probes can meet the requirements of outgoing quality control and on-site rapid inspection of cast aluminum fittings with irregular shape.

The recompression carbon dioxide Brayton cycle has the advantages of simple structure and high cycle efficiency. However, the recompression cycle faces the problems of large boiler pressure drop, high cooling wall temperature and difficult waste heat utilization when applied to coal-fired power plants. The partial cooling carbon dioxide cycle can effectively alleviate the above problems when integrated with coal-fired boilers by virtue of its own circulation characteristics. A thermal calculation program for a 600 MW coal-fired power generation system with partial cooling carbon dioxide cycle is written using MATLAB. Firstly, the effect of single parameter variation on the thermodynamic performance of the system is investigated. The results show that the system efficiency is highest when the main compressor inlet pressure and temperature are near the critical point; the system efficiency drops suddenly when the pre-compressor works near the critical point; the system efficiency is highest when the split ratio and reheat pressure are 0.35 and 17 MPa, respectively. The particle swarm optimization is applied to the partial cooling cycle, and the results show that the partial cooling cycle can achieve the efficiency close to that of the recompression cycle under the suitable design parameters. Compared with the recompression cycle, the mass flow rate of the partial cooling cycle decreased by 17.46% and the boiler inlet temperature decreased from 462.45 ℃ to 429.39 ℃.

The Shockley-Queisser (SQ) limit sets an upper limit on the efficiency of conventional semiconductor photovoltaic devices. A thermophotovoltaic system (consisting of a heat source, a spectrally selective emitter and low bandgap photovoltaic cell) can work as an alternative to break this theoretical efficiency limit. To further improve the power generation efficiency of thermophotovoltaic (TPV) systems, an emitter with a multilayer cross structure based on metamaterials was designed in this work. Through optimization of its geometric size, the emitter demonstrates an excellent narrow-band emission spectrum. This effectively reduces the loss of low-energy photons below the bandgap of PV cells and avoids the absorption of high-energy photons that exacerbate lattice vibrations to cause thermal losses. Its application to TPV systems enables a perfect match with In_0.69Ga_0.31As cells with a bandgap of 0.6 eV. Detailed theoretical calculations of this TPV system show that the power generation efficiency can exceed the Shockley-Queisser (SQ) limit (41%) at 1 117 ℃, and will be further improved as the emitter temperature increases. When the temperature reaches 2 000 K, the efficiency is as high as 46.75%. Additionally, the narrowband emitter shows good angular insensitivity in the range of 0~60 degrees.

In order to reduce the cost of fuel procurement, a power plant plans to burn economical coal with low calorific value, such as carbon 3500 and Shenhun 4500.The quality characteristics of the coal to be blended deviate from the coal currently used, which affects the safety, economy and environmental protection of the boiler operation.Through coal quality analysis, laboratory test, theoretical analysis and calculation, on-site pulverizing system optimization test, economic coal blending test and operation parameter optimization test, the technology of economic coal blending combustion of boiler is studiedsystematically .The research results show that the low grindability and serious wear characteristics of the carbon 3500 lead to its poor adaptability to the pulverizing system and the boiler, and the comprehensive power supply cost of the unit increases after blending combustion.The fuel characteristics of Shenhun 4500 are close to the main coal types of the power plant, the operation performance of large proportion of mixed burning boilers is good, the comprehensive power supply cost of the unit is reduced, and the economic benefits are significant.It is suggested that the power plant can determine Shenhun 4500 as an economic coal for long-term combustion.This study can provide reference for power plants with similar demand for mixed combustion.