Search Results (8)

To accommodate the integration of renewable energy, coal-fired power plants must take on the task of peak regulation, making the low-load operation of boilers increasingly routine. Under low-load conditions, the phase transition point (PTP) of the working fluid fluctuates, leading to potential flow instability, which can compromise boiler safety. In this paper, a one-dimensional coupled dynamic model of the combustion and hydrodynamics of a supercritical boiler is developed on the Modelica/Dymola 2022 platform. The spatial distribution of key thermal parameters in the furnace and the PTP position in the water-cooled wall (WCW) are analyzed in a 660 MW supercritical boiler when parameters on the combustion side change under full-load and low-load conditions. The dynamic response characteristics of the temperature, mass flow rate, and the PTP position are investigated. The results show that the over-fire air (OFA) ratio significantly influences the flue gas temperature distribution. A lower OFA ratio increases the flue gas temperature in the burner zone but reduces it at the furnace exit. The lower OFA ratio leads to a higher fluid temperature and shortens the length of the evaporation section. The temperature difference in the WCW outlet fluid between the 20% and 60% OFA ratios is 11.7 °C under BMCR conditions and 7.4 °C under 50% THA conditions. Under the BMCR and 50% THA conditions, a 5% increase in the coal caloric value raises the flue gas outlet temperature by 32.7 °C and 35.4 °C and the fluid outlet temperature by 6.5 °C and 9.9 °C, respectively. An increase in the coal calorific value reduces the length of the evaporation section. The changes in the length of the evaporation section are −2.95 m, 2.95 m, −2.62 m, and 0.54 m when the coal feeding rate, feedwater flow rate, feedwater temperature, and air supply rate are increased by 5%, respectively. Full article

The temperature of the water wall in the furnace chamber is extremely important for the daily operation of a boiler. Considering the high temperature and dusty environment in the furnace, a temperature measurement device mainly composed of four parts (armored temperature sensor, in-furnace heat-collecting block, out-furnace fixing base, and protective cannula) was designed in this study, which could be used to directly obtain the temperature of the in-furnace water-wall. Numerical simulations of temperature measurement devices with different heat-collecting block structures were carried out using the computer fluid dynamics method. After comparing the measurement accuracy and considering the practical application scenarios, the optimized heat-collecting block structure with a specific expansion gap (0.5 mm wide and 4 mm deep) was selected for practical application. Such a temperature measurement device was then applied to a 1000 MW ultra-supercritical coal-fired boiler in China, and the tested in-furnace water-wall temperature data were in good agreement with relevant research. Compared with the conventional temperature measurement device arranged outside the furnace, the in-furnace water-wall temperature-measurement device adopted in this study has a more sensitive response characteristic and can directly reflect the temperature of the water wall inside the furnace. In addition, it can also reflect the local slag formation state of the water wall and has a long service life. Full article

To meet the Chinese government’s energy-saving and emission-reduction policies, flexible peak regulation is necessary for traditional coal-fired boilers. Flexible peaking leads to large changes in boiler load, which affects the safety of the boiler water wall. In this paper, a 1000 MW ultra-supercritical unit was tracked for three years, and effective data were selected to study the temperature characteristics of the water wall under flexible peak regulation. The results show that the lower the load, the greater the temperature fluctuation of the water wall. The temperature distribution of the spiral water wall is more uniform. The position of the temperature valley value of the rear spiral water wall was found, and the load of more even temperature distribution was also found. The temperature change of the front vertical water wall was the most complex of all the water walls. The 643.9 MW load case showed different behavior to the temperature distribution of the water wall. The side water walls were heated evenly under the different loads. The characteristics of the temperature distribution of the side vertical water wall were found through statistical analysis. The fitting equation for the change rule of the temperature is presented. The higher the load, the better the equations. Finally, this paper gives some advice on how to avoid temperature deviation in the water wall, and the detailed research highlights the safe running of water walls. Full article

The opposed wall-fired boiler is widely used in Chinese power plants due to its adaptability. However, deviations from design conditions can cause the reduction of combustion efficiency and combustion stability, and the overheating of heating surfaces. This study conducted numerical simulations on a 600 MW supercritical opposed wall-fired boiler at 75%, 50%, and 30% Turbine Heat Acceptance (THA) load conditions. The variation of temperature field and heat flux in the furnace under different loads, and parameters such as distributions of heat flux, temperature, and the stress of the high-temperature heating surface are analyzed. Results indicate that reducing the load from 75% to 30% THA lowers the furnace outlet temperature from 1158 to 1009 K and reduces the average gas temperature of the high-temperature heating surface from 1800 to 1570 K. Under a high load, the maximum heat flux concentrates on the side water-cooled wall of the combustion zone. However, when the load decreases, the heat absorption shifts towards the main combustion zone. Furthermore, under a high load, the average wall temperature of the high-temperature heating surface remains at 1600 K with a uniform temperature distribution. In contrast, when the load drops to 30% THA, significant temperature differences appear on the heating surface, with a maximum difference of 400 K. This leads to excessive expansion and slagging on the high-temperature heating surface, particularly in the middle and lower sections, due to the increased stress. These findings offer valuable insights for optimizing the combustion characteristics of opposed wall-fired boilers and preventing overtemperature explosions on the platen heating surface. Full article

Local over-temperature is one of the main reasons for boiler tube failures (BTF). By accurately monitoring and controlling tube wall temperature, local over-temperature can be avoided. Based on the measured flue gas parameters and numerical simulation, a method of thermal deviation calculation is proposed in this study for the on-line calculation of the tube wall temperature of boiler superheaters. The full-size three-dimensional numerical simulation was presented on the combustion in a pulverized coal-fired boiler of 1000 MW ultra-supercritical (USC) unit. A difference in the thermal deviation of the vertical direction was innovatively introduced into a segmented discrete model, and the thermal deviation condition conforming to reality was introduced into the calculation. An on-line calculation system developed based on the current calculation method was applied in a 1000 MW USC unit. The calculated local high-temperature zone was consistent with the actual over-temperature position and conformed to the law of the allowable metal temperature of the final superheater (FSH) serpentines segment. The comparison results showed that the calculated data by this method were more reflective of tube wall temperature change with boiler loads than the measured data. According to the calculated local over-temperature zone, the immediate warning response can effectively reduce the possibility of over-temperature BTF. Full article

In order to meet the flexibility operation needs of coal-fired units under the goal of carbon peak and carbon neutralization, it is imperative for circulating fluidized bed (CFB) units to participate in deep peak regulation. By systematically summarizing deep peak regulation operation practice of existing SC and subcritical-parameter-levels CFB units, the feasibility of deep peak regulation technology of an ultra-supercritical (USC) CFB unit under development and being built is analyzed and demonstrated; meanwhile, the deep peak regulation capacity of the boiler is also predicted. The results show that by analyzing the structural characteristics and design performance of the USC-CFB boiler, for technical problems such as stable combustion under low load, hydrodynamic safety, denitration performance under wide load, and rapid boiler load change rate existing in deep peak regulation, technical measures were implemented by selecting advanced boiler furnace type, adopting good design technology of the secondary rising water wall and uniformity design of bed temperature and bed pressure, strengthening the reducing atmosphere inside the furnace, improving the performance of wear-resistant refractory materials, quickly controlling the furnace bed material stock under variable load, optimizing the control strategy of CFB unit, and so on. The boiler achieved good operation characteristics and good deep peak regulation performance, and the pollutant emissions can steadily achieve ultra-low emission standards. When the USC-CFB unit participates in deep peak regulation, the minimum stable combustion load of the boiler can reach 20~30% BMCR, and a boiler load change rate under 30% BMCR or above could reach 1.5~2% BMCR/min, while that below 30% BMCR could reach 1% BMCR/min. The research results can provide references for the deep peak regulation of in-service supercritical (SC) CFB units and design optimization of similar USC-CFB units. Full article

With the development of power plant units of higher capacity and with improved parameters, the proportion of high-capacity units for generating power has increased; this requires large capacity units to take responsibility for power-grid peak shaving. When the boiler operates at low loads, the working fluid in the boiler water wall tubes is subjected to high heat flux in the furnace, which can cause heat transfer deterioration, tube overheating or even leakage. Therefore, it is particularly important to study the reliability of the boiler hydrodynamic cycle during peak shaving (low load operation). This study takes a 1000 MW ultra-supercritical single-reheat Π type boiler with single furnace and double tangential firing as the research object. A furnace Computational Fluid Dynamics (CFD) and hydrodynamic coupling analysis model is established and verified according to the actual operating conditions on site. The calculation results show that the simulated value is in good agreement with the actual operating value. Therefore, the model established in this study can reflect the real situation of the on-site furnace to a certain extent, and has high reliability. Based on the fitting results, the causes of steam temperature deviation of the boiler water wall are analyzed, and measures to reduce the deviation are proposed to provide a necessary basis for power plant operation and boiler design. Full article

Semi-coke is one of the principal by-products of coal pyrolysis and gasification, which features the disadvantages of ignition difficulty, low burnout rate, and high nitrogen oxides (NO_x) emission during combustion process. Co-firing semi-coke with coal is a potential approach to achieve clean and efficient utilization of such low-volatile fuel. In this paper, the co-firing performance of semi-coke and lean coal in a 600 MW supercritical wall-fired boiler was numerically investigated which has been seldom done previously. The influences of semi-coke blending ratio, injection position of semi-coke, excess air ratio in the main combustion zone, the co-firing method, and over fire air (OFA) arrangement on the combustion efficiency and NO_x generation characteristics of the utility boiler were extensively analyzed. The simulation results indicated that as the blending ratio of semi-coke increased, the NO_x emission at furnace outlet decreased. The blending methods (in-furnace versus out-furnace) had certain impacts on the NO_x emission and carbon content in fly ash, while the in-furnace blending method showed more flexibility in co-firing adjustment. The injection of semi-coke from the upper burners could significantly abate NO_x emission at the furnace outlet, but also brought about the rise of carbon content in fly ash and the increase of outlet temperature. Compared with the condition that semi-coke and lean coal were injected from different burners, the burnout ratio of the blend premixed outside the furnace was higher at the same blending ratio of semi-coke. With the excess air ratio in the main combustion zone increased, NO_x concentration at the furnace outlet was increased. The excess air ratio of 0.75 in the main combustion zone was recommended for co-firing 45% semi-coke with lean coal. The operational performance of the boiler co-firing semi-coke was greatly affected by the arrangement of OFA as well. The amount of NO_x generated from the supercritical wall-fired boiler could be reduced with an increase of the OFA height. Full article