In order to understand the key parameters and operating experience on fully burning and high proportion blend burning high-alkali coal in boiler with slag-tap furnace, long-term engineering tests were conducted based on a 300 MW boiler with slag-tap furnace in a power plant. An analysis was conducted on the possible combustion organization, nitrogen oxide control, slag flow, and ash deposition issues. Modifications were made to the combustion system, thermal modification system, and slag flow system. So long-term operational data and key parameter records were conducted, after fully burning and high proportion blending burning of 300 000 tons of high-alkali coal, all operating parameters of the boiler were normal. Based on recent operations and comprehensive tests, the optimized boiler with slag-tap furnace in a specific power plant demonstrates strong adaptability to high-alkali coal. Within the control range of coal ash components with w(Al₂O₃)<25%, w(Fe₂O₃)<15%, 12%<w(CaO)<30%, silica-alumina ratio>1.7, acid/alkali ratio>0.5, the normal operation of the boiler can be ensured without obvious ash deposition. Burning high-alkali coal can effectively reduce the inlet flue gas temperature of the first-level heating surface to below the design value, effectively avoiding the occurrence of slagging on the first-level heating surface of the boiler, and the generation of nitrogen oxides is also reduced by more than 30% compared with using the original design coal.

Xinjiang high-alkali coal is a cost-effective power coal，but when it is used in large proportions, boiler equipment is prone to severe slagging problems. The design principles of the combustion system for boilers using Zhundong coal are inconsistent with conventional technical measures to improve low-load stable combustion performance. To solve this problem, based on the mechanism of stable combustion of pulverized coal, measures such as optimized layout of tiny oil ignition burners, interlaced arrangement of middle layer burners, online adjustable coal powder concentration and burner design optimization have been studied. The technology was applied in a 350 MW unit's deep peak regulation retrofit project using Zhundong high-alkali coal as fuel, and achieved a stable combustion load of less than 18% rated condition without oil injection.

In order to study release characteristics of sodium during thermal conversion of high-alkali coals, the release characteristics of sodium in high-sodium coal and low-sodium coal were compared and analyzed through combustion experiments and pyrolysis experiments of raw coal and water-washed coal, so as to explore the release law changes of different forms of sodium in coal samples during combustion and the influence of atmosphere changes on sodium release. The results show that, during the combustion experiment, the release of sodium from high-alkali coal increases slowly at 300~500 ℃ and rapidly at 500~1 100 ℃, and the release of sodium from low-alkali coal increases rapidly at 300~500 ℃ and slowly at 500~1 100 ℃. It can be seen that, coal quality is one of the main reasons affecting sodium release, and sodium release will be greatly affected by the difference in coal composition. The release law of sodium during combustion and pyrolysis is basically the same, the sodium release rate changes slowly during the pyrolysis process, and is about 7.0% lower than that of the combustion process. The release characteristics of organic sodium and water-soluble sodium are different due to different release routes.

In order to reduce fuel procurement costs and ensure fuel supply, a certain power plant in Gansu burns a large proportion of Xinjiang high-alkali Guanghui coal and Xinjiang Energy coal. After burning the high-alkali coal, the boiler experiences severe high-temperature corrosion and coking on the heating surface, and the maximum load can only be carried to 85% ECR. In order to reduce high-temperature corrosion, research has been conducted on coal quality characteristics, combustion optimization adjustment, and equipment improvement technology for boilers. The research results show that, the boiler still experiences severe high-temperature corrosion even when burning low sulfur coal, which is mainly related to the high content of alkali metals such as sodium and calcium, as well as chlorine in Xinjiang coal. By increasing oxygen content, reducing primary air volume, weakening the swirling strength of outer secondary air of the burner, and increasing wall-attached air, operation adjustment measures can improve the high-temperature corrosion characteristics of the water wall to some extent. But to completely solve this problem, it is necessary to start with the use of additives, high-temperature corrosion prevention spraying, adding soot blowers, improving wall-attached air and burner design, and other corresponding technologies. The results of this study can provide useful reference and guidance for power plants that encounter similar problems during the process of high-alkali coal burning.

With the continuous increase of installed capacity of new energy generation in power grid, thermal power units have to undertake more peak shaving. However, the flexibility and peak shaving capacity of current thermal power units are generally insufficient. A subcritical 300 MW coal-fired unit is retrofitted for molten salt energy storage. Six heat storage strategies and two heat release strategies are proposed and investigated. The influence of heat storage and release process on the peak shaving capacity and thermal performance of the unit under three working conditions is analyzed, the technical and economic analysis is performed in terms of the net present value. The results show the feasibility of extracting reheated steam for heat storage is higher, with a peak shaving depth of 58.9%. However, the coal consumption would increase at the same time. During the releasing heat stage, the maximum increment of power generation up to 11.3% of the rated power generation is achieved by heating the water supply to generate steam, while the higher temperature of the molten salt is required. Using high-temperature molten salt instead of low-pressure heater to preheat water supply is proved to have more advantages, while the power generation increment is relatively small. During the whole process of heat storage and release, the maximum circulating electricity efficiency can reach 0.987. The economic analysis of heat storage transformation is conducted. The dynamic investment payback period is 11.65 years, and the net present value is 49.118 million yuan. Therefore, the renovation scheme is feasible.

As a large number of new energy is connected to the grid, the participation of supercritical thermal power units in peak regulation tends to cause the superheat of intermediate points to fluctuate greatly, resulting in superheated steam over temperature and other problems. In order to better control the intermediate point superheat to achieve stability, a prediction method of intermediate point superheat based on double-depth input convex neural network multi-model (muti-DDICNN model) was proposed. Sub-models with different prediction step sizes were trained respectively, and the intermediate point superheat state prediction network (SPNN) and error prediction network (EPNN) were constructed. Based on the convex property of prediction network, a multi-model predictive controller (DDICNN-MPC) based on convex neural network with double-depth input is designed. The control problem is transformed into a convex optimization problem, the Jacobian matrix of control matrix to objective function is obtained, and the optimal solution of control matrix is calculated by gradient descent method. The simulation results show that, the DDICNN-MPC can track the intermediate point superheat setting quickly and stably, and the steady-state error is small, so it has good adjustment ability.

As a fundamental component of the organic Rankine cycle (ORC), the scroll expander's operating characteristics critically influence the ORC's overall performance. Initially, we establish a three-dimensional transient simulation model of the scroll expander. This allows us to systematically analyze the effects of various operating conditions on aspects such as suction pressure, exhaust pressure, rotational speed, and the output power and isentropic efficiency of the scroll expander, using numerical simulation. Following this, we study the effect of different operating conditions on the transient performance and mechanical properties of the scroll expander, and achieve a more comprehensive understanding of the mechanisms involved. Ultimately, we verify the accuracy of our numerical model using a laboratory-built test bench of the ORC low-temperature waste heat oil-free power generation system. The close correlation between the experimental results and numerical simulation outcomes authenticates the reliability and applicability of our numerical simulation method. In conclusion, this research's findings offer significant referential value for the design and optimization of the scroll expander.

To improve the flexibility of coal-fired units, boilers need to have good controllability and the ability to adapt to rapid load changes. The flexibility of the boiler is closely related to the performance of the control system, which is designed according to the dynamic characteristics of boilers. To study the dynamic characteristics of boilers, a dynamic model of a supercritical 660 MW coal-fired boiler is built in the Dymola platform. The results show that the response time of steam temperature is longer than that of steam flow. When the feedwater temperature, feedwater flow, and fuel quantity are stepped increase by 5%, the main steam temperature changes by 10.2 ℃, –28.5 ℃, and 35.7 ℃, respectively. In the process of adjusting the water-fuel ratio of the boiler, different times of change in feedwater and fuel flow can have different effects on the main steam temperature. The maximum deviation of the main steam temperature during the transient process reduces by 27.4 ℃ when the feedwater flow is delayed by approximately 100 s compared with the fuel flow. When the load change amplitude is the same, the larger the load change rate, the more severe the fluctuation of the main steam parameters, and the longer it takes to stabilize.

In order to further investigate the loss mechanism in supercritical carbon dioxide turbines, the flow characteristics in a turbine stage were studied by numerical method. The losses in the passage of stator and rotor blades were decomposed, and the various loss values and their proportions were quantitatively calculated. The loss sequence of the supercritical carbon dioxide turbine stage was clarified. The results show that, the high density of supercritical carbon dioxide and low blade height result in a very large leakage loss in turbine stage. When the stage load coefficient is 0.93, the relative height of the stator clearance is 0.012 and the relative height of the rotor clearance is 0.010, the leakage loss accounts for 38.23% of the total loss, including 21.94% of the diaphragm seal leakage loss and 16.29% of the tip seal leakage loss. Except for leakage loss, when the average maximum thickness divided by chord length is 0.33 and the aspect ratio is 2.07 in stator passage, the profile loss is much higher than the endwall loss and trailing edge loss, accounting for 9.68% of the total loss. In rotor passage, when the average maximum thickness divided by chord length is 0.28 and the aspect ratio is 1.73, the difference among endwall loss, profile loss, and trailing edge loss is not significant, and the profile loss has the highest proportion, accounting for 15.39% of the total loss. The influence range of secondary flow in rotor is even wider, and its endwall loss is much higher than that of the stator. The main sources of endwall loss are viscous dissipation of fluid near the end wall and secondary loss caused by horseshoe vortices, passage vortices, etc. The research results will provide direction guidance and data support for the design and optimization of supercritical carbon dioxide turbines.

To enhance the whole process safety of fan operations and ensure accurate fault diagnosis and long-term production income of thermal power plants, predicting these risk issues is crucial to enhance the safety of the unit. In this paper, we proposed a fan fault diagnosis model of big data platform that integrates multilayer perceptron and polynomial fitting. The fan early warning model was established by multilayer perceptron and polynomial fitting modeling technology, and integrated into the big data platform to find abnormalities which were difficult to find manually during the operation of the fan. By combining data mining with mechanism analysis and feature value knowledge base, the parameters boundary information of fan stall could be excavated, the stall boundary conditions of the fan were accurately configured under various working conditions, and a stall boundary condition diagram was created. By combining those informations with normal operating conditions, the early stall zone can be obtained. Finally, a fault diagnosis model that covers the entire working condition of the fan can be established. Utilizing the comprehensive big data platform that covers, circulates, and maintains fan operation data, a system of intelligent fan patrol model was constructed. The intelligent patrol disk model which replaces the operator was then used to monitor and diagnose the fan running state regularly, which can achieve accurate and safe diagnosis of fan faults, minimize the fault incidence and maximize the personnel reuse rate.