Standpipe models for diagnostics and control of a circulating fluidized bed

Abstract

Two models for a Circulating Fluidized Bed (CFB) standpipe were formulated, implemented and validated to estimate critical CFB operational parameters. The first model continuously estimates standpipe bed height using incremental pressure measurements within the standpipe. The second model estimates variations in the void fraction along the standpipe using the Ergun equation in conjunction with the overall pressure drop across the bed, solids circulation rate and the standpipe aeration flows introduced at different locations of the pipe. The importance of different standpipe parameters obtained from these models is discussed in terms of successful operation of the overall CFB system. Finally, the applications of these models are shown in improving the solids circulation rate measurement and in calculating riser inventory. The dense bed height and voidage in the moving bed of a circulating fluid bed’s standpipe were determined from measured incremental pressures as well as aeration and solids flow rates using mass balance and Ergun relationships. The significance of these parameters on CFB stability and accuracy of solids circulation rate measurements are considered.