Numerical simulation of fuel staged swirl combustion in the invert furnace of boiler on advanced ultra-supercritical steam parameters

The paper considers the schemes of Kuznetsky lean coal combustion for the M-shaped boiler. With such a boiler profile, it is possible to significantly reduce the length of main steamlines, which is especially important for the advanced ultra-supercritical parameters of the superheated steam. The furnace in this boiler unit is performed downward (invert). In this work, the aerodynamics of 6 combustion schemes was simulated by means of computational fluid dynamics. All considered schemes were designed on the basis of direct-flow burners and nozzles. For the most aerodynamically reasonable scheme the thermal processes in the boiler furnace firing Kuznetsky lean coal have been simulated by means of computational hydrodynamics. The simulation results showed a high efficiency of fuel burnout: loss due to unburned combustible equaled 0.1%, carbon-in-ash loss equaled 0.8%. Carbon monoxide concentration at the furnace outlet in conversion to excess air equal α = 1.4 amounted 226 mg/m3, the nitrogen oxides concentration in the flue gases (in conversion to normal conditions) equaled 424 mg/m3. It is appropriate to use the results obtained in this research in the development of new solid fuels combustion schemes.

Stable and Effective Online Monitoring and Feedback Control of PCDD/F during Municipal Waste Incineration

For the long-term operation of municipal solid waste incineration (MSWI), online monitoring and feedback control of polychlorinated dibenzo-p-dioxin and dibenzofuran (PCDD/F) can be used to control the emissions to national or regional standards. In this study, 500 PCDD/F samples were determined by thermal desorption gas chromatography coupled to tunable-laser ionization time-of-flight mass spectrometry (TD-GC-TLI-TOFMS) for 168 h. PCDD/F emissions range from 0.01 ng I-TEQ/Nm3 to 2.37 ng I-TEQ/Nm3, with 44% of values below 0.1 ng I-TEQ/Nm3 (the national standard). In addition, the temperature of the furnace outlet, bed pressure, and oxygen content are considered as key operating parameters among the 13 operating parameters comprising four temperature parameters, four pressure parameters, four flow parameters, and oxygen content. More specifically, maintaining the furnace outlet temperature to be higher than 800 °C, or bed pressure higher than 13 kPa, or the oxygen content stably and above 10% are effective methods for reducing PCDD/F emissions. According to the analysis of the Pearson coefficients and maximal information coefficients, there is no significant correlation between operating parameters and PCDD/F I-TEQ. Only when there is a significant change in one of these factors will the PCDD/F emissions also change accordingly. The feedback control of PCDD/F emissions is realized by adjusting the furnace outlet temperature, bed temperature, and bed pressure to control the PCDD/F to be less than 0.1 ng I-TEQ/Nm3.

Research on Dynamic Characteristics of Furnace in 670 t/h Ultra-high Pressure Pulverized Coal Furnace after Burner Transformation

The power field characteristics of a 670t/h boiler in a power plant were studied after the burner transformation. The results show that the size of the aerodynamic fluid in the hearth of the burner is appropriate, the furnace is full, and the center of the strong wind ring is basically in the center of the hearth. The wind speed of the wall around the water-cooled wall is within a reasonable range; there is a certain wind speed deviation on the side, and the angle of the SOFA reverse wind can be adjusted appropriately to eliminate the residual rotation existing at the furnace outlet. The research results can provide a reference for the transformation of burners of the same type.

NOx formation of swirl burner under air-staged combustion with flue gas recycle

Air-staged and flue gas recycle (FGC) combustion are important technologies to reduce NOx emissions. This study explores FGC ratios on the NOx formation in the primary combustion zone under air-staged combustion for a HT-NR3 swirl burner at different air excess coefficients. The coal combustion characteristics including gas velocity, temperature, gas components and NOx emission under different FGC ratios were analyzed. The results show that higher the FGC ratio will larger the gas temperature decrease and lower the NOx emission. Combined FGC technology with lower air excess coefficients technology, the NOx emission at outlet of furnace will be further reduced. When the air consumption excess coefficient is 0.8 with FGC ratio 20%, the NOx concentration at the furnace outlet will decrease from 208ppm to 138ppm, lower 33.6%.

Numerical Investigation on Co-firing Characteristics of Semi-Coke and Lean Coal in a 600 MW Supercritical Wall-Fired Boiler

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 (NOx) 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 NOx generation characteristics of the utility boiler were extensively analyzed. The simulation results indicated that as the blending ratio of semi-coke increased, the NOx emission at furnace outlet decreased. The blending methods (in-furnace versus out-furnace) had certain impacts on the NOx 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 NOx 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, NOx 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 NOx generated from the supercritical wall-fired boiler could be reduced with an increase of the OFA height.

The Application of Adaptive BP Neural Predictive Fuzzy Control in Cement Decomposing Furnace Temperature Control System

Cement decomposing furnace is a typical multi-variable, nonlinear, large delay and strong coupling complex control object, its difficult to establish accurate mathematical model, the conventional control algorithm is difficult to get satisfactory control effect. By applying adaptive BP(back propagation) algorithm in neural network modeling, make the neural network predicts the decomposing furnace outlet temperature, then modify the pulverized coal flow rate value that obtained by the fuzzy controller to control the decomposing furnace outlet temperature. The field application shows that the control software which is designed by the control algorithm in this paper responses quickly, the error between actual temperature and the expected value is small, it has a good reliability, adaptability and robustness.