Multi-scale characteristics and gas-solid interaction among multiple beds in a dual circulating fluidized bed reactor system

•Gas-solid mixing and interaction among reactors were systematically explored.•Acoustic wave and pressure pulsation are simultaneously employed for signal measurement.•Multi-scale characteristics of the gas-solid flow were studied with the analyses of Hurst and fractal dimension.•Differences of particle clusters and bubble behavior between the upper and lower parts of the riser were obtained. To investigate the gas-solid mixing and interaction among reactors of Dual Circulating Fluidized Bed Reactor (DCFBR), the detecting methods of acoustic emission and pressure fluctuation are employed to study the effects of operating parameters including riser gas velocity, bubbling bed gas velocity and pot-seal gas velocity on the gas-solid behavior and multi-scale characteristics of the DCFBR system. The experimental results demonstrate that gas disturbance makes bed particles fully mixed and the intensity of inter-particle mixing increases as gas disturbance intensifies. Meanwhile, inter-particle mixing can also cause changes in voidage. Therefore, gas and solid phases in the reactor have a mutual effect on each other. In addition, the particle circulation rate varies as the operating gas velocity changes, which in turn causes variations in both particle and bubble behaviors in the riser and the bubbling bed with particles and bubbles interacting with each other. By combining the methods of Hurst and fractal dimension analysis, the multi-scale variation of acoustic signals in the upper and lower parts of the riser under fast fluidization is obtained. As the results reveal, there are certain differences in particle clusters and bubble phase behaviors between the upper and lower parts of the riser. The larger the particle cluster size, the more uneven the flow inside the bed, indicating an intensified effect of the inter-granular particle cluster. Moreover, the size of particle cluster, which is related to particle concentration, increases as the concentration intensifies.