Cellulose containing mixtures are well known in different fields of application. In the wood processing and paper making industries there is a need to convey fiber suspensions of pulp having a relatively high consistency (i.e. percentage by weight of dry cellulose material in solution). In other industries, such as the textile industry, there is the need to convey cellulose containing solution to a shaping station where the solution is adapted to be shaped and subsequently regenerated into a cellulosic product, such as a fiber or filament or cellulosic rod, tubing, plate or film.
In the pulp and paper industry, it is often necessary to convey a fiber suspension between different places . When the consistency of the suspension is low, i.e. up to about 5%, there are few problems with the fiber suspension being able to flow freely. Problems occur, however, when the consistency of the fiber suspension is greater than about 5%. When the consistency is higher than about 5%, there is only a small amount of free liquid between the fibers and the fibers form a strong fiber network the strength of which depends mainly on the consistency of the suspension. The characteristics of medium or high consistency fiber suspensions are quite different from those of a true liquid and their handling becomes more difficult the higher the consistency.
Conventionally in the pulp and paper industry, the conveyance of fiber suspensions has been performed with the use of rotary positive-displacement pumps. However, since conventional screw or gear pumps are heavy, large, expensive and break down relatively frequently, there has been a tendency in recent times to replace such rotary positive-displacements with centrifugal pumps, especially where the need is to convey liquid-fiber suspensions having a consistency in excess of 8%. US patents Nos. 4884943, 4981413, 5000658 and 5058615 disclose the use of centrifugal pumps for pumping relatively high consistency fiber suspensions. In pumping liquid-fiber suspensions having a consistency of greater than 8%, it has been proposed to feed the suspension to the suction opening of the centrifugal pump by means of a special screw feeder. However, with such pumps it has not been commercially possible to pump fiber suspensions having a consistency which approaches 15%. An alternative solution to pumping relatively high consistency fiber suspensions has involved diluting the pulp prior to the centrifugal pump and re-thickening the pulp after pumping. However this known technique adds to the complexity and cost of the pumping apparatus