Powdered coal circulating fluidized bed combustion technology

Under the background of dual-carbon target,the circulating fluidized bed combustion technology,as an important part of coal-fired power generation,realizes an efficient and clean utilization of inferior fuel and is also a main force to participate in deep peak regulation of power grid in the future. However,CFB boilers still have a lot of room for improvement in load regulation rate,NOx emission control at deep low and low loads,and heating surface wear. Therefore,the powdered coal circulating fluidized bed (PC-CFB) combustion technology is proposed. By reducing the fuel particle size from the wide sieve distribution of 0 - 10 mm to a narrow sieve distribution of 0 - 1 mm, a sufficiently high circulating flow rate can be achieved at a low bed stock. Regulating chemical reactions through flow regimes,the reducing atmosphere needed for low-NOx combustion is strengthened,and the residence time of fine limestone in the furnace is extended,the combustion performance of the boiler can also be improved. More importantly,the rate of change in chemical reaction,i.e. heat release,increases due to the decrease of fuel particle size. Supplemented by cyclic interventions that can increase the rate of change in heat transfer rate,the combination of which can improve the rate of load regulation. The change of fuel particle size inevitably leads to the reduction of bed particle size, and significantly improves the deep low load capability and the in-furnace control of NOx emissions at low loads. This idea is confirmed by the modelling prediction, which shows that when the range of fuel particle size is reduced from the conventional size distribution to 0-1 mm,the average bed particle size decreases greatly and the material concentration in the dilute phase zone increases,and the circulating flow rate increases by about 27%. The reducing atmosphere in the furnace is enhanced,and the original emission concentration of NOx is reduced by about 35%. The improved performance of the circulation system can prolong the residence time of fine limestone in the furnace, improve the efficiency of desulfurization reaction,and reduce the original SO2 emission concentration under the same conditions of calcium-sulfur ratio and NOx emission. Meanwhile, the combustion efficiency is significantly improved,the carbon content of bottom slag is reduced by 89%,and the heat loss of incomplete solid combustion is reduced by 52%,indicating that PC-CFB combustion technology has more advantages in enhancing the operational flexibility of CFB boilers,strengthening the low-NOx combustion,and improving the combustion performance. © 2023 China Coal Society. All rights reserved.