Numerical and experimental investigation of the effects of impinging streams to enhance Ca-based sorbent capture of SO2

A reactor design combining impinging streams and a circulating fluidized bed reactor (IS-CFB) was developed to improve the gas–solid mixing in fluidized beds. The Eulerian two-fluid model and a sulfation model for a CaO/fly ash sorbent were used for numerical simulations of a pilot-scale IS-CFB reactor, and the simulation results indicate that the introduction of impinging streams to a CFB reactor significantly improves the desulfurization efficiency from 89.5% to 95.1%, due to the more homogeneous radial particle volume fraction distributions and the much larger effective SO2 capture zone. The lateral gas flow in the impingement zone intensifies the gas–solid mass transfer. Effects of the bed bulk density and the impinging particle material on the desulfurization efficiency were also investigated. Experiments were conducted using two Ca-based sorbents in a small-scale IS reactor at 750 °C. The experimental results show that the Ca/bio-based sorbent gives higher desulfurization efficiencies than the CaO/fly ash sorbent, for the latter which is large and dense cannot be effectively entrained by the impinging streams. A method for combining experiments and calculations is developed to estimate the gas–solid residence time in the impingement zone. It is found that the residence time is significantly influenced not only by the gas velocity but also by the solid to gas mass ratio.

► Impinging streams significantly improve the desulfurization efficiency in a CFB reactor.
► The lateral gas flow in the impingement zone intensifies the gas–solid mass transfer.
► A method is developed to estimate the gas–solid residence time in the impingement zone.
► The residence time is significantly influenced by the gas velocity and the solid to gas mass ratio.