(399d) Mass Transfer Resistance in Downer Reactors

Experimental observations on gas-solid catalytic reactions in downer reactors reported in the literature indicate conversions to be lower than the expected from a pseudo homogeneous plug flow model at higher solid loadings. This was attributed to particles moving as clusters. Axial gas mixing and gas to particle mass transfer may be affecting the conversions at lower gas velocities and higher solid flow rates.

In the present paper, a two phase tanks in series model is developed for the downer reactor considering gas to particle mass transfer. The model is compared with recent experimental observations on a downer reactor, reported in the literature, to estimate mass transfer coefficients. Estimated Sherwood Numbers are observed to increase as a function of the ratio of gas to particle velocities. This result is in line with the recently reported direct measurements on gas to particle mass transfer in downers.