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Solid circulation in chemical looping combustion (CLC) is very important and affects the mass and heat balance and autothermal operation of a CLC system. A key task in developing CLC technology is to control the solid circulation. In this work, the solid circulation characteristic of a 1.5 MWthCLC cold flow model is reported. The solid circulation between the fuel reactor and the simplified air reactor riser is controlled by the overflow method. Three kinds of quartz sands are selected as fluidized particles, and their median particle diameters are 392, 249, and 122 μm, respectively. A reasonable pressure profile is obtained in the 1.5 MWthCLC cold flow model. The effects of operational parameters, including the fuel reactor gas velocity, loop seal gas velocity, simplified riser gas velocity, particle size, and static bed height, on the solid circulation and hydrodynamic characteristics are measured and analyzed. The maximum solid circulation rate can approach 130 kg/(m2·s), and this value satisfies the requirements of mass and heat balance in the CLC system. The static bed height in the fuel reactor should be higher than the overflow port to prevent it from becoming a constraint factor on the solid circulation rate. An overflow model is developed to predict the solid circulation rate, and the relative errors between the predicted result and the experimental data are within 25%.

A circulating turbulent fluidized bed connected with a riser and an annular carbon stripper (CS) is proposed to be used as a fuel reactor (FR) in chemical looping combustion. The bottom section of the FR is operated under a turbulent fluidization regime, which can achieve enough solid residence time and enhance the mixing of the oxygen carrier with solid fuel. A 1.5 MWthcold model of the FR was designed, constructed, and tested to investigate the hydrodynamics of solid particles with different sizes. Three kinds of quartz sands with different particle sizes (d50= 122, 249, and 392 μm) were used as bed materials to simulate the oxygen carrier. Continuous operation with a reasonable pressure balance was achieved in the cold model. The effects of important variables, including gas velocity, static bed height, and particle size, on the gas–solid hydrodynamics of the FR were measured and discussed. It was found that the transition velocities from bubbling to turbulent fluidization for different particles of d50= 122, 249, and 392 μm were measured to be 0.78, 0.95, and 1.06 m/s, respectively, indicating that the transition velocity increased with increasing the particle size. The solid fraction profile along the reactor height and solid circulation rate were affected by gas velocity and static bed height. A modified correlation was proposed to predict the solid fraction of the annular CS dilute phase, and the predicted results agree well with the experimental data under a wide range of operational conditions.

Autothermal operation is a big challenge for a chemical looping combustion (CLC) demonstration plant. One of the key points of CLC autothermal operation is to achieve a high solid circulation rate and enough solid residence time. To address this challenge, a dedicated lifter is proposed to control the solid circulation rate and residence time in the dual fluidized bed reactor system. This dedicated lifter is integrated into a 1.5 MWthCLC cold flow model to evaluate the control of the solid circulation rate and residence time of this new CLC scheme. Continuous and stable circulation of solid particle operation is achieved in the cold flow model, and it has been demonstrated that the dedicated lifter can effectively control the solid circulation rate. The effect of gas velocity, bed inventory, and particle size on the fluidization in the whole loops is studied. The dedicated lifter can control the solid circulation rate in the range of 20–68 kg m–2s–1, and residence time in the fuel reactor is maintained in the range of 180–610 s. The solid circulation rate and residence time obtained in this work satisfy the theoretical requirements of CLC autothermal and char gasification, respectively, which indicates that the autothermal operation of the CLC unit as well as high carbon capture efficiency can be realized in this new CLC scheme.