Flue gas recirculation (FGR) is an important technical mean to improve the safety of circulating fluidized bed (CFB) boiler and reduce the generation of NO_x under low-load operation. In the present work, the relationships between temperature distribution of the boiler, NO_x, CO mass concentration and O₂ volume fraction of the flue gas at furnace outlet, the combustible matter content of fly ash and bottom slag and the flow rate of FGR under the load of 20%, 30% and 40% BMCR (boiler maximum continuous rating) were studied using one-dimensional chamber CFB combustion quasi-static model at a supercritical 350 MW CFB boiler. The results show that both the bed temperature and furnace exit flue gas temperature decrease with the increase of FGR flow rate, which the former decreases less than the latter. The temperature difference between the upper and lower furnace gradually decreases with the increase of FGR flow rate, which is more significantly affected by FGR flow rate at lower loads. The NO_x mass concentration of flue gas at the furnace exit shows a trend of decreasing first and then increasing with the increase of FGR flow rate, and the existence of the optimal FGR flow rate can make the unit operation economically and environmentally friendly. In addition, with the increase of the FGR flow rate, the CO mass concentration at the furnace outlet, combustible matter content of fly ash and bottom slag shows an increasing trend. The FGR significantly reduces the primary air oxygen volume fraction while ensuring that the fluidized air flow rate in the dense phase area is always higher than the protection value, which ensures the operation safety of the boiler under low load furtherly.

This paper explains the overall impact of the dual carbon strategy on coal power and the development problems it faces. The status quo and key technologies of clean emissions, energy conservation and carbon reduction, heat supply and efficiency improvement, and flexible operation of coal-fired power units are sorted out and analyzed, and the development prospects of coal power are prospected, and the conclusion is drawn that the development of coal power is positively viewed based on China's resource endowment and energy strategic security, and attention should be paid to the research and development and application of clean, efficient and flexible coal power technology, and the advantages of various new energy sources are complemented and dynamically coordinated to promote the steady development of new power systems.

Aiming at the problem of low probability of occurrence events such as coal mill failures that are difficult to extract and used for machine learning classification, resulting in low fault diagnosis accuracy, a PCA-FINCH high-precision fault diagnosis method for small samples is proposed. Firstly, based on principal component analysis PCA, fault detection is carried out on the historical data that characterizes the operating state of the equipment, and the occurrence of faults is detected and the fault samples are identified through the T² control limit and the Q control limit, and the fault samples are extracted to form a small sample fault set; Secondly, based on the FINCH classifier, the obtained small sample fault set is accurately classified to realize the fault diagnosis of the equipment. Finally, the method is verified using a historical data set containing coal mill faults. The results show that the PCA-FINCH fault diagnosis method proposed can achieve high-precision classification of small-sample faults, and its accuracy is 2.61 percentage points, 1.74 percentage points and 1.85 percentage points higher than that of decision tree CART, random forest RF and support vector machine SVM, respectively, and its convergence speed is excellent.

The natural draft tower of air cooled condenser system require neither mechanical ventilation fan, nor circulating water pump of the indirect dry cooling system, which significantly reduces the noise, house service consumption and net coal consumption of power plant, according with the requirements of the "low-carbon" development era. However, this system has never been applied to large-fossil fired power units, it is necessary to understand the influence of environmental wind direction on heat dissipation of the natural draft tower of air cooled condenser. Using the FLUENT software, numerical simulations of the natural draft tower of air cooled condenser under different wind directions for 2×660 MW unit were conducted to obtain the distribution characteristics of ventilation and heat dissipation of each cooling triangle under different wind directions, the overall heat dissipation performance of the cooling tower and the impact of environmental wind direction on the general layout of the cooling tower and main plant. The results indicate that the central line of the natural draft tower of air cooled condenser of the 2 units should be parallel to the dominant wind direction preferentially.

In view of the heat compensation equipment widely used in combined heat and power (CHP)plant, the feasible operation region model and coal-saving rate model of the CHP plant equipped with a solid heat storage electric boiler are constructed. The effects of the solid heat storage electric boiler, the electrode electric boiler and the water storage heat accumulator on the heat-supply capacity, regulation ability and operation cost of the CHP plant are compared and analyzed. Based on the current status of a CHP plant, a general model for combined dispatching of the CHP plant with flexibility to configure heat compensation equipment is established. Combining with the actual operation data of the CHP plant, the above models are verified and the differences in operation flexibility, scene adaptability, coal-saving effect and operation cost among different heat compensation equipment are quantitatively analyzed. The results show that under the same heating capacity, the solid heat storage electric boiler has the strongest flexibility and the lowest coal saving rate. The heat accumulator has the best coal-saving effect, but the scene adaptability is lower than other heat compensation schemes. The model and research results can provide theoretical tools and reference for the optimal operation of CHP plants.

In order to explore the low-carbon and environmentally friendly thermal power generation technology and improve the utilization efficiency of clean energy, a power generation system consisting of Allam cycle and clean heat sources is proposed. The thermodynamic models of the main equipment in the system are established, the advantages and principles of the coupled system are explained by comparing with the reference system, and the influence of the design parameters on the system performance is studied through parametric analysis. The calculation results show that the low-grade clean heat source can effectively solve the heat imbalance problem of the Allam regenerator, thereby heating the recycling stream to a higher temperature. Under typical design parameters, the exergy efficiency of the coupled system can reach 54.07%, which is 4.01% higher than that of the reference system. The output power and exergy efficiency of the coupling system first increase and then decrease with the increment of the turbine inlet temperature. With the increase of the temperature and the mass flow rate of the clean heat source, the output power of the coupled system increases, while the exergy efficiency first increases and then decreases. The research results of this paper can provide data support and theoretical support for low-carbon power generation technology.

Taking a 660 MW wall-tangentially fired boiler as the research object, the effects of air distribution ratio on the characteristics of in-furnace coal combustion and heat transfer processes and NO_x transformation were numerically investigated. Results show that under the fixed SOFA ratio, the increase of primary air ratio makes the overall boiler performance changes in V type that deteriorates evidently at first and then gets improved somewhat. The increased in primary air ratio leads to the generation of more fuel-NO_x at the initial combustion stage, which thus increases the final NO_x emission at the furnace exit. SOFA ratio does not change the variation trend of combustion performance along with the primary air ratio, but its increase leads to the decrease of the critical primary air ratio at which coal combustion performance deteriorates significantly. The variation of primary and secondary airflow momentums caused by the air distribution ratio is the main factor affecting the overall boiler performance, and coal combustion performance deteriorates significantly when their momentums are too close. Based on this, the large increase in the primary air ratio should be avoided during the practical boiler operation process. If it is inevitable, the SOFA ratio should be decreased to alleviate the deterioration of boiler performance caused by the increased primary air ratio.

During the operation of a trough solar power station, the stability of the outlet temperature of the thermal conductor is an important control objective for the safe and reliable operation of the power station. Due to the structural characteristics of the collector tube, the outlet temperature characteristics of the trough collector have large inertia and large delay, so the outlet temperature control problem is complicated. In order to solve this problem effectively, a dynamic mathematical model of MW trough solar power collector circuit is constructed in this paper, and a temperature control system is constructed at the collector outlet. A step prediction controller for the outlet temperature of trough solar power collector circuit is proposed. Simulation experiments were carried out based on MATLAB/Simulink platform. The simulation results show that, for the groove heat collecting loop, under the disturbance of irradiation, heat conduction oil inlet temperature and ambient temperature, the stepped predictive control system has shorter adjustment time, smaller overshoot, better robustness, and significantly improved control effect compared with the traditional PID control system. The proposed predictive controller can well cope with the situation of heat conduction oil overtemperature and heat conduction oil flow fluctuation at the outlet of heat collecting field, which is conducive to the safe and stable operation of the trough heat collecting field.

With the increasing penetration of new energy in new power system, the influence of the uncertainty of wind power output and the correlation with load on the system operation is increasingly prominent. Thus, the conventional transformer risk assessment can no longer meet the demand. Based on Copula model and Susa model, a joint probability assessment method of transformer operation risk considering wind power and load correlation is proposed. Monte Carlo method is used to calculate each risk index value and evaluate transformer operation risk. The research results show that, the conventional transformer evaluation system that does not consider the wind-load correlation will lead to a low overall risk assessment result, with the maximum error of the index up to 55.02%. Also, with the increase of wind-load correlation, the risk of thermal defects of the transformer is increasing. The research conclusions can assist to improve the accuracy of the operation risk level assessment of new power system transformers, and provide a reference for the later transformer condition assessment and maintenance plan formulation.

In order to improve the flexibility of coal-fired units, a flexible peaking operation method is proposed by combining the heat storage by extracting the reheated steam and secondary air heating by extracting the main steam. Taking the ultra-supercritical 660 MW indirect air-cooled unit as the object of study, the performance of the unit under different peaking schemes at 30% BMCR operating conditions, the energy reuse rates under different heat release conditions and the performance of the combined load reducing operation mode are analyzed. The results show that the energy reuse rates of extracting main steam heat storage, extracting main steam heating secondary air and extracting hot reheat steam heat storage are 55.13%, 84.74% and 46.24%, respectively, at a peak-load shaving capacity of 20 MW with 75% THA heat release condition. Under the premise of ensuring the safety of boiler combustion and heating surface, the combined load reducing operation mode can achieve a peak peak-load shaving capacity of 46 MW, and the energy reuse rate can reach 74% when the heat release condition is 75% THA. This study can provide a reference for flexible peak-load regulation of coal-fired units.