Local measurements of concentrations of O 2 , CO, SO 2 , and NO x were carried out inside Baima's 300 MWe circulating fluidized bed (CFB) boiler. Custom-made probes with a length of 4.8 m were used to take samples from the boiler's external circulation loop, especially from the cyclones and fluidized bed heat exchangers (FBHEs). Eighteen points were used to introduce the probes, and the penetration depth inside the boiler was up to 3.7 m. Solid particles at the entrance and exit regions of both the cyclones and FBHEs were also sampled for analyzing the particle size distribution and carbon content. Results implied that there was significant combustion in the boiler's external circulation loop, and most of the combustion was from the cyclones. The flue gas temperature at the cyclone outlet could be 135 °C higher than that at the cyclone inlet. The ratio of the oxygen consumption in the cyclone to that of the entire combustion process of the boiler was nearly 12%. The O 2 consumption rate might mainly come from the burn-out of char particles rather than the combustible gas. With regard to the FBHEs, the inside combustion phenomenon was not as severe as that in the cyclones. Obvious differences of gas concentrations were observed at the outlet between those FBHEs with different functions. The experimental results can provide information for adjusting and designing the heat-surface arrangement and lay a foundation for modeling the flow structure, combustion, and heat transfer in similar large-scale CFB boilers.
It is hard to accurately meter the fuel feed into the furnace for a double-in and double-out pulverizing system, which affects the fuel control quality and also the main steam pressure of a boiler. A correction method for the indirect measurement model of the coal metering feed into the furnace for double-in and double-out pulverizing system is proposed based on the combustion state diagnosis of a burner using fuzzy C-mean clustering method, of which is applied in a 620MW super critical power unit. The engineering application results suggested that the method of this work is effective to improve the fuel control quality during the mill start and stop process. By using the method of this work, the controlling deviation between the target value and the measured value of the main steam pressure is within 0.2 MPa, while it is about 0.6 MPa when the fuel control is without correction.
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