Cold Experimental Study On Circulating Fluidized Beds With Multiple Parallel Cyclones

Maldistribution of gas-solid two-phase flow is a big problem in up-scale circulating fluidized bed (CFB) boilers with multiple cyclones in parallel. And the two-phase flow field in a CFB boiler is affected directly by its operation parameters and structure figures.Cold experiments are conducted in two cold-test models of large scale CFB boilers, including one with four cyclones placed in an array and another with annual furnace and six cyclones, to investigate the different influence factors of gas-solid two-phase flow in the circulating fluidized bed. And some theoretical analysis is done to find out the cause of Maldistribution of gas-solid two-phase flow among different cyclones.In the CFB cold model with four cyclones placed in an array the effects of its operation parameters including the fluidizing velocity and the static bed height is focused on. And the results show that the gas-solid two-phase flow is affected by the operation parameters, and that the effects of fluidizing velocity are greater. And the Maldistribution of gas-solid two-phase flow presents that the circulating rate in the middle is larger than the circulating rate in the side. Theoretical analysis shows that problems of non-uniform distribution of two-phase flow among cyclones in unilateral symmetrical arrangement are caused by two parts:one part is the incomplete symmetry of layouts; the other part is the pulsatility in aggregative fluidization and the multiplicity of solutions even in completely symmetrical arrangement. And the crux of determining the distribution regularity of two-phase flow between separators is to know the function relationship between the separator pressure drop and the mass flux.The effects of furnace structure figures are also studied in the CFB cold model with annual furnace and six cyclones. The results show that there is no evident distribution regularity of solids circulating rates, and that the inserted heat exchanger panels as well as the inlet velocity and angle have little influence on the distribution of solid circulating rates in experimental conditions. The change of inlet angle can significantly change the separating efficiency.Different types of furnace, including six cyclones placed in two arrays and four cyclones placed in an array and annual furnace and six cyclones, have its own strengths and weaknesses in furnace area and penetration of secondary air and distribution uniformity of material in a circulating fluidized bed.