Experimental study of a Volatiles Distributor for Improving the Cross-sectional Gas Distribution in Fluidized Beds

Licentiate thesis, 2022

Chemical looping combustion (CLC) is a promising carbon capture technology due to its inherent CO2 separation. Significant progress has been made in CLC of solid fuels in recent years. However, one key technical challenge for using solid fuels in CLC is to minimize the presence of unreacted gases coming from the fuel reactor together with CO2, in particular for CLC of biomass, i.e. high-volatile fuel. Poor contact between volatiles and oxygen carriers is one reason for the lower gas conversion in the fuel reactor. Hence, the concept of a volatiles distributor (VD) is proposed for achieving a uniform cross-sectional distribution of volatiles, providing better gas-solid contacting and improving the gas conversion in the fuel reactor.

In this thesis, the VD was designed with different configurations and investigated in a cold-flow model under different fluidization velocities, volatiles flows and fluidization regimes. It was found that the VD gives a more uniform lateral distribution under higher fluidization velocity. Also, higher volatiles flow gives a more even distribution along the VD. It also shows that less open distribution area of the VD increases the pressure drop over the distribution holes, thus improving the lateral gas distribution. Moving holes from the vicinity of the volatiles injection towards the far end also improves the lateral distribution of volatiles even though it doesn’t change the pressure drop over the distribution holes significantly.

The single bubble regime, i.e. large single bubbles formed at the bottom, and multiple bubble regime, i.e. multiple bubbles with different sizes formed at the bottom, were investigated with the VD. It was found that the VD gives a more uniform lateral distribution in single bubble regime compared to the multiple bubble regime. The installation of internal baffles at the bottom of the VD was found to reduce the bottom air flowing into the VD, thus improving the uniformity of the horizontal distribution of the volatiles and further reducing the risk of volatiles slip below the lower edge of the VD.