Heater effects on cyclone performance for the separation of solids from high temperature and pressure effluents

A 25.4-mm diameter hydrocyclone with an underflow receiver was evaluated fo r its ability to achieve separation of fine particles from water at elevate d temperatures and pressures relevant to supercritical oxidation. Temperatu re was varied from 25 degrees C to 340 degrees C, while pressure was mainta ined at 27.6 MPa. The particles studied were alpha-alumina. Particle-remova l efficiency was affected by the separation capabilities of the hydrocyclon e, deposition on the heater surface, and flocculation of the particles. Par ticle-size distributions and suspended solids analyses confirmed that cyclo ne, separation efficiency was controlled by the (density(particle) - densit y(water))/viscosity(water) ratio. Because this ratio is sensitive to temper ature, especially in the neighborhood of the supercritical point, separatio n efficiencies sharply increased with temperature. Contrary to traditional air cyclone theory, removal efficiency was inversely correlated to flow rat e. This result was caused by particle deposition and particle flocculation in the heater. Low now rates increased heater detention times and, thus, op portunities for flocculation and particle deposition. Therefore, the perfor mance of a hydrocyclone used in conjunction with supercritical oxidation de pends on phenomena occurring in the heater and the hydrocyclone.