Computational particle fluid dynamics(CPFD) approach was employed to investigate the gas-solid flow behavior in the recirculation system of the dense transport bed. The influences of the drag model and the particle close packing limit on the simulation results were analyzed

and the appropriate model parameters were determined. Through the comparison of the simulation results under three operation conditions

the variation trends of the pressure distribution and solids circulating rate with the aeration flowrate were obtained

which was in agreement with experimental observation. The pressure gradient distribution

the gas flow direction and the solids concentration distribution were analyzed. The absolute value of the pressure gradient at the aeration inlet was the local maximum. When the aeration flowrate was zero

the pressure gradient was close to zero in a big area above the inlet. When the aeration flowrate was big enough

there was bubble around the inlet. A high pressure gradient would be formed in the lower area of the standpipe due to the lack of aeration at higher elevation

which would slow down the solids moving. The role of aeration gas on loosening particles just existed in a limited region near the inlet and its role on uniform pressure gradient distribution was more important to enable uniform gas-solid flow in the standpipe. In the design of aeration conditions

the standpipe pressure drop was determined by the solids circulating flowrate

and it needed appropriate aeration to keep constant gas velocity

leading to more uniform pressure gradient in the standpipe.