Experimental Study Of The Flow Characteristics Of Fine Particles Of Gypsum

Chemical looping combustion (CLC) technology is considered as a promising technology of carbon dioxide capture. The key problems of CLC technology are design of combustor and oxygen carrier characteristics. At present, fluidized bed is a promising reactor for CLC technology. Sulphric calcium (CaSO4) with characteristic of cheap and high efficiency has been focused on by more and more researchers. Therefore, it is important to study the fluidization characteristics of CaSO4 for development and application of CLC technology. In this paper, the fluidization characteristics of gypsum (including natural gypsum and dry flue gas desulphurization gypsum) were carried out by experimental and theoretical methods. The detailed research work and conclusions are listed as follows:(1) Fluidization characteristics and improving method of fluidization quality of fine particles was reviewed. A method by adding coarser particles to improve fluidization quality of gypsum fluidization was put forward on basis of analyzing finer particle characteristics.(2) Fluidization experiments of natural gypsum, dry FGD gypsum, quartz sand and river sand were carried out in a self-built fluidization facility. The results indicatied that two kinds of gypsums (average particle diameter is 13μm and 33μm, respectively) are very diffcult to achieve stable fluidization due to channeling and particle agglomeration However, both quartz sand and river sand (particle diameter is 450～600μm,300～450μm, 200～300μm) can achieve stable fluidization, whose minimum fluidization velocity is 0.25m/s,0.14m/s,0.075m/s and 0.17m/s, 0.lOm/s,0.065m/s. Fluidization characteristic of two gypsums was improved when a quality of coarse particles of quartz sand and river sand were blended with the tested gypsum.(3) The fluidization characteristics of natural gypsum by blening with different particle size (particle diameters are 450～600μm,300～450μm,200～300μm, respectively) and different mass ratioof blended quartz sand and river sand (40%,60%,90%) was carried out experimentally. The results indicated that fluidization quality of particle mixture system of nature gypsum and blending constituent was improved with increasing of mass ratio of blending coarse particles of quartz sand and river sand. The optimal mass ratio of quartz sand and river sand is 40%. In the range of experimental blending particle size, the smaller quartz sand and river sand size is, the better the fluidization quality is. The optimal particle size is 200～300μm for three blended particle sizes. The improving effect of fluidization quality of blending river sand with high sphericity is better than that of blending with quartz sand.(4) The fluidization characteristics of dry FGD gypsum blending with the different particle size (particle diameters are 300～450μm and 200～300μm, respectively) and mass ratio of blended quartz sand and river sand (60%,90%) was carried out. The results indicated that the fluidization characteristic of nature gypsum was not improved until the blended mass ratio of quartz sand and river sand is up to 60%. The smaller particle size of quartz sand and river sand is, the better the fluidization quality is. The optimal particle size is 200～300μm for two blended particle sizes. However, the improving effect of fluidization characteristic of blending river sand with better sphericity is worse than that of blending quartz sand at the same blended particle size of 200～300μm.(5) On the basis of experiments, the agglomeration mechanism of gypsum particles was analyzed, and the model of gypsum agglomerations was put forward. Based on the model, the agglomeration sizes of two kinds of gypsum were predicted. The results show that the agglomeration sizes of gypsums blended with amount of quartz sand or river sand are less than that of gypsum without any blending at the same fluidization condition. The agglomeration diameters of nature gypsum and dry FGD gypsum are 10.7 mm and 14.7 mm, respectively, however, agglomeration diameter of the binary mixture are 5.0 mm and 4.4 mm at optimal blended mass ratio and blended particle size. Results based on experiment and prediction also indicate that it is very effective method to improve the fluidization quality by blending coarse particles into fine particles.