Three-dimensional computational fluid dynamics simulations are performed for a 650 ℃ grade 1 000 MW ultra-supercritical swirl-opposed firing boiler with low NO_x combustion in the furnace. The flow and combustion characteristics in the furnace and the NO_x concentration in the flue gas are investigated under various conditions of overfire air. It is shown that setting a staggered overfire air and injecting the lower OFA with the angle 15°downward into the furnace is helpful to reduce NO_x concentration and improve the burnout rate. A lower overfire air ratio results in a higher temperature in the region of the combustor and a shorter distance between the high-temperature region and the heating surface. As the overfire air ratio increases, the NO_x concentration of the flue gas at the exit of the furnace first decreases and then increases, and the optimal overfire air ratio is around 33.9%.

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.

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.

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 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 the domestic large circulating fluidized bed boilers designed with side wall and back wall coal feeding system, there are generally prominent problems of coal feeding delay and uneven coal feeding in the actual operation process. By analyzing the coal feeding delay problem of large CFB boiler units and the operation characteristics of the existing coal feeding system, the quantitative calculation method of coal feeding delay problem of large CFB boiler coal feeding line is put forward. Based on the case of a supercritical 600 MW CFB boiler coal feed line, the coal feed delay characteristics of the coal feed line under the condition of wide load and rapid peak regulation are obtained. The calculation results show that the coal feed delay problem is common in the variable load operation process of large CFB boiler units, which will lead to a certain degree of uneven coal feed. The variable load range, variable load rate and the number of coal feed ports on the single feed line are positively correlated with the severity of the delay problem. The calculation method and analysis results can provide design basis and technical reference for large CFB boiler coal feed line to adapt to wide load and fast peaking operation.

The pH values of boiler feed water, steam, boiler water and other measuring points in a chemical power plant were abnormally low, and the problem could not be effectively solved by adjusting the boiler water dosing process. In order to solve this problem and ensure the safe operation of the unit, this paper discusses and analyzes the influence of water sample temperature on pH electrode, Nernst temperature coefficient slope and solution temperature coefficient (ionic activity), and verifies through experiments that the abnormally low pH measurement value is caused by the large deviation of water sample temperature from 25 ℃, and the pH measurement method cannot provide correct temperature compensation. Strict control of water sample temperature, adoption of computational pH meter or selection of high-precision pH meter with precise non-linear temperature compensation function can effectively solve the problem of abnormally low pH measurement in the water and steam system.

To provide guidance for the flexible operation of 350 MW supercritical CFB boiler, experimental investigations were conducted on the flow and heat transfer characteristics of water with low mass flux in vertical upward smooth tube under subcritical pressure. Flow and heat transfer experiments were performed under the conditions of 12~15 MPa pressure, 350~440 kg/(m²·s) mass flux, 135~220 kW/m² inner wall heat flux. Furthermore, the dynamic characteristics of the tube were experimentally studied by decreasing pressure and increasing inner wall heat flux, based on the 26 MPa heat transfer experiments. The results of the heat transfer experiments indicate that changing pressure affects the heat transfer performance and enthalpy range of the saturated boiling region. The influence of mass flux on heat transfer performance is only reflected in the sub cooled zone, and the heat transfer performance is enhanced with the increase of mass flux. Increasing heat flux decreases the heat transfer performance in the saturated boiling region. Meanwhile, the correlations of the heat transfer coefficient and friction resistance of water in the tube were fitted based on the experimental data. The dynamic experimental results show that the greater the pressure step, the greater the mass flux increment, and the greater the change in the outlet enthalpy and outlet wall temperature. The step of heat flux only affects the outlet enthalpy and outlet wall temperature. The greater the step of heat flux, the greater the change in the outlet enthalpy and outlet wall temperature. This work can provide guidance for supercritical CFB boiler in low load and flexible variable load operation.

In order to provide methodological guidance for the load optimal distribution of thermal power units under the condition of deep peak regulation, the objective functions of optimal load distribution under medium-high load and low load are established respectively, and the load optimal distribution under different conditions is studied. The k-means clustering algorithm is used to process the data and the coal consumption characteristic curves of two units under medium-high load and low load are fitted. The objective function of load distribution is established to compare the coal consumption before and after optimization under static load distribution, incremental load distribution and continuous variable load conditions. After setting the total load instructions of the two units under the condition of deep peak shaving, the coal consumption of the two schemes of load average distribution and optimal distribution is compared. The results show that the clustering-based objective function models of optimal distribution under medium-high load and low load established by the coal consumption characteristic curve are reliable, whose optimization effect is remarkable under the condition of deep peak regulation. The k-means clustering algorithm can be used to optimize the load distribution of thermal power units and provide reference for the study of load optimal distribution under the condition of deep peak regulation of thermal power units.