Research in particle coating and agglomeration at West Virginia University

Over the last three years, work in the Particle Coating Laboratory at West Virginia University has focused on three main areas. The first area concerns the reversible agglomeration of cement to produce a granular product (2-10 mm) that can be transported easily and can be broke n down and hydrated to form a cement slurry with properties identical to vi rgin cement. This agglomeration process uses a binding agent consisting of calcium chloride (CC) and tartaric acid (TA) dissolved in methanol that can be considered an inert solvent. By adjusting the proportions of the cement set accelerating agent (CC) and the retarding agent (TA) a granular cement product can be formed that gives a cement slurry with essentially the same characteristics as that obtained from virgin cement. The resulting concret e also has the same compressive strength, obtained in a standard 3-day test , as virgin cement. The second research area concerns the formation of encapsulated brittle par ticles of ammonium persulfate (AP) that are used as viscosity breaking agen ts for fracturing fluids. In order to obtain a coat that under goes brittle fracture when subjected to a compressive load, a coating of a cross-linked acrylate polymer containing up to 80 wt.% of fine (< 15 (mum) silica was u sed. By varying the coating level of acrylate, the release of the ammonium persulfate using a standard leach test can be reduced to acceptably low lev els (< 3%). By changing the fraction of silica in the coat, the release of the ammonium persulfate when the particles are subjected to a known compres sive stress (13.8 MPa) can be increased to approximately 70%. The particles formed by this process comprise of agglomerates of between 10 and 20 indiv idually coated particles. When subjected to an applied load, these agglomer ates fracture and the coating on the individual particles is sheared away t hus releasing AP. These particles can be used as viscosity breaking agents in drilling well fracturing operations. The third project consists of the video imaging of particle movement in a s emicircular fluidized bed typically used in coating operations. The particl es of interest are 8-mm-diameter tablets. The technique used to capture par ticle velocity data utilizes two CCD cameras that are synchronized to captu re images that are between 1 and 5 ms apart. The mapping of particle veloci ty within the spray region in the draft tube insert under a variety of cond itions is currently underway. Preliminary data is presented and discussed. (C) 2001 Elsevier Science B.V. All rights reserved.