Authors: M. Franceschini & J. Woloshyn
SAIMM Southern Africa Hydrometallurgy Conference, February 24, 2009
Abstract
The ability to control the velocity distribution of a fluid flow is a fundamental problem in many industrial applications of fluid engineering. This problem is compounded in hydrometallurgy because the process fluid is typically two phase, as well as corrosive and abrasive in nature. This paper investigates the use of a perforated plate to achieve a stable and uniform flow field downstream of a shock wave in a blast shroud entering a quench vessel from pressure oxidation autoclave. Fluid mechanics analysis has been used to provide insight into the proper diffuser geometry in order to produce an adequate flow field both downstream and upstream of the plate. The addition of a perforated plate is found to reduce the maximum velocity entering the quench vessel to one fifth of the original velocity, mitigating the risk of wear on the vessel bottom and excessive splashing of the water pool. The analysis also indicates that both the open area and the number of holes in the plate are important parameters in stabilizing upstream gas flow and minimizing flow separation downstream of the shock.
The mechanical design of the shroud and perforated plate addresses concerns around thermal expansion, natural vibration frequency, strength limitations of nitride-bonded silicon carbide, and the erosive environment created by supersonic flow with entrained particulate. Prudent mechanical design is required to ensure a durable long lasting perforated plate, which will reduce wear on pressure letdown equipment. Placing the perforated plate in a metal spacer ring allows it to float between top and bottom supporting flanges. Strict control of fabrication tolerance is required to maintain clearance between the plate, spacer ring, and other ceramic components, limiting stresses induced by thermal expansion to 0.5 MPa. Soft packing and gasket materials, which are susceptible to erosion, are isolated from the flow by a tongue-and-groove joint between the ceramic shroud liner and perforated plate.
