Experimental Analysis of the Solids Acceleration Region in a Circulating Fluidised Bed Riser

Systematic experimental work was conducted to study the solids acceleration length in a 15-m high riser. A more feasible method is proposed in this study to determine the solids acceleration length from the standard deviations of the measured pressure fluctuations. With this method and the experimental results, the clear relationship of the solids acceleration length versus solid circulating rate is obtained. Generally, the solids acceleration length (expressed in Lacc) increases with the Gs rising and decreases with the Gs reducing gradually. Reasonable explanations are also provided for the observed variation trends of the solids acceleration length. In addition, it is found that the pressure fluctuations in the riser have two sources. One is the feeding flow oscillation at the inlet of the riser and the other is the fluctuations by solids back-mixing, solids dispersion and solids reunion in the process of the solids movement in the riser. The method can be used to distinguish the boundary of solids movement between the solids acceleration region and the fully developed region. It is very important to take the solids acceleration into account both for the modelling of gas-solid flow in the riser and for the design and operation of circulating fluidised bed (CFB) reactors.