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.