Investigations On The Turbulent Gas-solid Two-phase Interactions In Fluidized Desulfurization Process

For the optimization and prediction of the moderate temperature flue gas desulfurization (FGD) process in the fluidized bed reactor, an investigation was conducted on the turbulent gas-solid two-phase interactions from the fluctuation level and mean flow level.To study the two-phase interaction occurs at fluctuation level, which is the so called"turbulence modulation", PDA was used to measure the turbulent gas-solid two-phase flow field. A criterion that is to eliminate the elongation effects and inlet effects was first proposed to unify the basis for comparison of flow field variables. It is approved that fine particles attenuate turbulence. And in the under developing flows, the turbulence modulation will be accumulated. The intense shear can strengthen the turbulence modulation. The linear relationship between the gas fluctuation velocity and velocity gradient can be used as an important criterion to distinguish whether there is intense shear in the flow and further, whether the turbulence modulation occurs.The drag force in the heterogeneous dense fluidized flows, as a key problem of interactions in the mean flow level, was studied with theoretical analysis. The Energy Minimization Multi-scale (EMMS) theory was combined with Computational Fluid Dynamics (CFD) to develop an auto-adaptive drag force model, which is called QL-EMMS model. Comparison between the simulation and the experiment data approves the advances of the model. The model again was combined with the reasonable kernel of the O-S model to develop the QL-EMMSn model which was proved to be more close to physical reality. However, the new model is still need to be verified by numerical method.In the numerical study of dry FGD process at moderate temperature in CFB, an improved sulfur capture model for T-T sorbent is first obtained based on the finding that the reaction rate is proportional to the square of calcium conversion rate in different ranges.The FGD process in CFB was simulated by using the O-S model and QL-EMMS model respectively. The results show that the heterogeneity of the particle volume fraction reaches a maximum at the transition region with a small peak near the outlet beneath the hat chamber structure. The sulfating reaction rate as well as the desulfurization efficiency increase as the heterogeneity of the particle volume fraction distribution decreases. Higher inlet gas velocity will intensify the uniform distribution of particles; however, it will also reduce the effective reaction time.A new reactor structure was proposed based on the impinging stream theory. It was found that, the new reactor can intensify two-phase mass transfer thus to improve the desulfuration efficiency. The present investigation provides an important potential for further study.