Experimental Studies On Optimization Of Gas-Solid Flow Field And Application Of ECT On Suspension Bed

Aiming at development of the processes of semi-dry and/or dry flue gasdesulfurization with circulating fluidized beds at low and/or medium temperatures(CFB-FGD), this thesis conducts an experimental study on optimization of gas-solidflow regimes, which mainly depend on geometry configuration and operationparameters of a CFB. Replacement of traditional gas distributor by large gas jetsuniformly arranged reduces pressure drop at entrance of a bed, meanwhile leading tosuspension state of particles in the bed. Low bed density and annular-core flowstructure in a circulating suspension bed (CSB) would result in bad effect onutilization rate of sorbent and desulfurization efficiency. Therefore, it is significant toraise particle concentration and improve uniformity of gas-solid distribution in a CSBreactor.A cold-model experimental facility with a CSB bed, whose cross-section is400mm×400mm and the height is 3940mm, is set up. The particle concentration andparticle velocity profiles in four cross-sections along the height of the CSB riser aremeasured by a fiber optical probe under different conditions corresponding tocombinations of gas jet structure, outlet structure, internals structure, superficial gasvelocity ( U_g0) and particle circulating rate ( G_s). After analyses of the experimentalresults, especially of the effects of the conditions on agglomeration anddisagglomeration of particle clusters at walls and corners of the bed, the bed structureand operation parameters best favorable to contacts between gas-solid two phases aredetermined. The bed should consist of a distributor with uniformly arranged largeholes of gas jets, a cap space at the top of the bed, a triangle-shaped internal justbelow the outlet of the bed, and a combination of triangle-shaped internals whichhave different sizes and are staggered on a couple of opposite walls. The aboveconfiguration is simple and can be made easily. In this study, the best operationparameters are G_s= 8⁹kg/(m²Â·s) and U_g0= 2.8m/s.In this study, the electrical capacitance tomography (ECT) technology is firstapplied for measurement of dilute particle concentration distribution in the CSB riserwith so large cross-section. The author has introduced three iterative algorithms, i.e.semi-Landweber algorithm, general vector sample pattern matching (GVSPM)algorithm and statistical induced global optimization algorithm (SIA) for imagereconstruction in solution of ECT inverse problem. The experimental results showthat all the three algorithms have got better spatial resolution of imaging for thecentral region of the riser with global convergence, and finally, the semi-Landweberalgorithm is recognized as the best one for image reconstruction in this ECTmeasurement. Based on a number of tests, a transducer system with eight electrodesof 200mm long is designed to match the CSB riser and the ECT hardware made byUMIST of UK. The on-line reconstructed images qualitatively provide theinformation about flow regimes in the full measured cross-sections. The particleconcentration distributions (PCD) on the typical symmetric lines of the measuredcross-sections and the probability density distributions (PDD) of mean particleconcentration in the measured cross-sections are obtained by extracting data from thereconstructed images. The PCD and PDD reveal macroscopic characters and flowbehaviors in the CSB riser, verify and supplement the optimization results oftwo-phase flow fields measured by the fiber optical probe.