Shear induced agglomeration experiments on caco3 for geothermal energy production

Geothermal energy is produced by pumping cold water into an underground reservoir. The reservoir exists of narrow channels in which the water is heated before it is pumped up. The heat transfer in the reservoir improves when all the channels are uniform in diameter. The oil company Shell wants to make the channels uniform by using shear induced agglomeration. Agglomeration is a secondary process frequently encountered in reactive crystallization. Particles collide, cement together due to deposition of material on the contact plane and may continue as an agglomerat. The rate at which particles agglomerate is determined by the particle concentration and the agglomeration rate constant. For shear induced agglomeration this constant is a function of the shear rate, the van der Waals forces, the lubrication force, and the supersaturation. It is the aim of this research to determine this function experimentally for CaCOa particles in the region of interest (shear rates between 0 to 25 s""^) for the technique that Shell wants to use. In the experiments, a Couette-flow device is used to create a constant shear field. A CCD camera makes images of a measurement volume in the Couette-flow device that is illuminated by a laser to measure the particle concentration decrease in a non-intrusive way. An image analysis program counts the particles on the images. From the decay of the particle number concentration in time, the agglomeration rate constant is derived. Results show that the van der Waals force causes CaCOs particles to stay together. In a theoretical model of Mumtaz and Hounslow, this was not taken into account. A maximum was found for the agglomeration rate constant as a function of shear around 30 s~^ for the saturated suspension used in that experiment. Uncontrolled particle concentrations and a not completely reliable particle concentration measuring device made it not possible to determine the role of supersaturation in agglomeration in our agglomeration experiments. The agglomeration setup, fit program and image analysis program worked well and the aim of the research could be fulfilled.Kramers Laboratorium voor Fysische TechnologieApplied Science