GB987638A - Apparatus for effecting intimate contact between particulate material and liquid - Google Patents

Abstract

A starter of calcium carbonate pellets is placed at the bottom of the main chamber 10 in the annular column 24. The raw-water and lime slurry are pumped through the tangential inlet pipes 26 and injectors 28 respectively and are forced round and up the column. Due to the tapering core which extends from 1/3 to 1/2 the height of the chamber the rotational speed of flow of the water and slurry mixture decreases as it rises in the column so that considerable turbulenece of the mixture is achieved. The water is softened by the chemical reaction of the calcium hydroxide with the calcium bicarbonate and the solution becomes, after a short period of operations, super-saturated with calcium carbonate. The latter crystallizes out of solution and forms on the already present calcium carbonate pellets. The crystallization is greatly assisted by the turbulence brought about by the increasing cross-sectional area of the annular column. The pellets are carried up the column and then fall to the bottom again as they reduce speed. The pellets fall down to <PICT:0987638/C1/1> the region of at least cross-sectional area where they are swept up again by the inflowing slurry and water. The pellets gradually increase in size and other pellets form. From time to time pellets are removed by means of the draw-off pipe 29. For this purpose it is desirable to turn off the flow from the injector and inlet adjacent the draw-off pipe. The softened water rises in the funnel-shaped chamber 12 and flows over the inner wall 14 which forms a weir. The flow proceeds from the trough 17 through the outlet 18. Instead of the construction of a core made up to two tapering portions a simple cone may be provided. Alternatively the core may have a curved profile but the curve must be convex to ensure maximum velocities at the base of the chamber.