Research on Non-Uniform Phenomena Due to Spatial Scale Effect in the Scaling up Process of CFB Boilers

Circulating fluidized bed (CFB) boilers have the advantages of wide fuel adaptability, low-cost emission control, and width of load regulation range. So CFB boilers have been widely used as a clean coal combustion technology. To improve the efficiency of power generation, the scaling up process is the necessary development direction of CFB boilers. However, many non-uniform phenomena have occurred during the scaling up process caused by the effect of spatial scale, including the fluidization transformation of the gas-solid flow in the super high furnace, the gas-solid flow deviation under the condition of the multi-cyclone parallel arrangement, the vibration of external loops, the large margin and long-term pressure fluctuation of the large cross-section air distribution furnace, etc. These non-uniform phenomena seriously affect the stability and safety of the boiler operation. In recent years, combined with the actual running data of CFB boilers, targeted experiments have been designed and carried out. And corresponding physical models and mathematical models have been built and gradually improved. In this paper, these phenomena are introduced in detail based on the data from actual boilers and experiments. The important physical mechanism of the gas-solid flow behavior of CFB boilers is analyzed, including the multi-value of gas-solid flow under the multi-cyclone arrangement, the pulsation mechanism of the loop seal, the resonance mechanism of lateral fluctuations in the dense phase area of the furnace, etc. Eventually in this paper, effective engineering solutions are given to promote the scaling up process of CFB boilers and help the utilization of world energy and the development of the economy and society.