GB928647A - Improvements in counter current washing processes for granular or similar material - Google Patents

Abstract

928,647. Washing granular materials. KIRKLEES Ltd. April 28, 1961 [Feb. 2, 1960], No. 3581/60. Class 82 (2). Granular materials are washed by a multistage counter-current process according to a method in which, in each washing stage, wash liquid is introduced from below into wash vessels containing the granular material at such a pressure that it not only percolates through the material but also fluidises it and the liquid remains in the vessels in contact with the fluidized material for a predetermined period of time and is then drained away, leaving the granular material within the vessels. The invention has particular application to washing sodium carboxymethyl cellulose with a washing medium of aqueous methanol or aqueous ethanol. Separate stage tanks A are arranged in a ring around a cylindrical tank B, which can be raised and lowered in relation to the tanks A by a cable C. Each tank A is provided with an inner vessel D having a perforated base, into which the granular material is loaded, and the vessels D may also be raised and lowered by a pulley block E which can run on a circular rail E<SP>1</SP>. The tank B is subdivided into segments b, each being associated with a storage tank A, with which it is in communication through a flexible pipe E<SP>2</SP>. Also the stage tanks A are interconnected, each being in communication with the next vessel but one before it through a flexible pipe e<SP>1</SP>. Washing liquor is introduced to a stage vessel through its conical base, underneath the perforations, at a pressure of 1-5 1b. per square inch, or more, fluidises the material, settles, and is allowed to drain into the associated space b; and the cycle may be repeated. The above cycling is performed by raising and lowering the tank B, air displacement being provided for by flexible pipes e<SP>3</SP> connecting the tops of the tanks A to a space above the liquid level in the segments b. At the end of the cycling a valve is operated to disconnect the tank A from its segment b and to connect it to the stage tank A next but one previous, the whole of the liquor being transferredthe reto. The inner vessels A are raised out of their stage tanks at the end of all the stages of the washing operation. The various stops may be controlled by a process timer of known design.