Investigation of gas–solid flow characteristics in the cyclone dipleg of a pressurised circulating fluidised bed by ECT measurement and CPFD simulation

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Abstract
To optimize the design and operation of a pressurised circulating fluidised bed (PCFB) system, it is necessary to understand the gas–solid flow characteristics and properly measure the solid circulation flux in the cyclone dipleg and loop-seal of the PCFB. In this research, electrical capacitance tomography (ECT) measurement and computational particle fluid dynamic (CPFD) simulation are combined to investigate the multiphase flow behaviour of a ‘cold’ PCFB, in particular the cyclone dipleg. A dual-plane ECT sensor is used for visualisation and online monitoring of the particle distribution. The particle velocity is measured by cross-correlation of two signals from capacitance electrodes, and the circulation flux is analysed. In addition, 3D full-loop CPFD simulation incorporating an energy-minimization multi-scale (EMMS) drag model is performed on a Barracuda platform, to understand the gas–solid hydrodynamic behaviour, validate and supplement the experimental measurements. The results show that the CPFD prediction agrees well with the ECT measurement in terms of the particle volume fraction distribution, velocity and circulation flux. The time-averaged gas–solid flow behaviour, instantaneous hydrodynamic features and the effects of operating pressure on particle distribution and the flow regime in the PCFB dipleg are unravelled. This is the first investigation of a solid circulation flux measurement in the cyclone dipleg and loop-seal of a PCFB system using a combination of ECT measurements, cross-correlation and CPFD simulation with high-pressure operational conditions.

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