Apparatus and method for separating heavy impurities from feed stock

Abstract

An apparatus and method are described for separating heavy impurities from feed stock. Feed stock is introduced into a first classifying zone defined by a chamber, usually circular in cross-section. The feed stock is normally liquid being made up of stock suspensions of up to 10% A.D. (air dried) consistency. This feed stock contains heavy impurities in the form of trash such as rocks, sand and the like. The feed stock enters the first zone tangentially where an outer vortex flow is generated. Where the apparatus is intended to pass (and not reject) knots in the feed stock, dilution water may be introduced tangentially in the same direction as the feed stock to control knot rejection. The impurities are subjected to a primary classifying action here, and clarified stock is extracted as central, upwardly rising vortex flow. The impurities form an outer layer which passes from the bottom of the first zone into a second zone. The second zone is defined by a chamber, again usually circular in cross-section, and having a shape which diverges from the exit from the first zone and then converges to a bottom outlet. An inlet introduces a fluid diluent in the second chamber with flow countercurrent to the flow of residual stock and impurities. The diluent, aided by the configuration of the second chamber inhibits vortex flow therein and thus promotes settling out, or separation, of the impurities by gravity. A reject chamber is also provided, preferably having an inlet for further diluent, which back flushes the stock impurities contained therein.