Centrifuges for
Paper Mill Waste Sludge Dewatering
W. C. MATTHEWS, Senior Staff Consultant
GEORGE H. ANDREWS, Technical Director
Central Research Laboratory
The Mead Corporation
Chillicothe, Ohio
JOHN K. SULLINS, Technical Director
Kingsport Division
The Mead Corporation
Kingsport, Tennessee
INTRODUCTION
The use of centrifuges in the paper industry has had a long history of successful operation in the concentration of solids materials in the papermaking operations. Mead and others have used centrifuges for the recovery of lime from the
water softening process. In the Chillicothe Division of Mead, this has resulted in
the recovery and reuse of 20 to 25. tons of material each day that previously was
discharged to the stream.
In a cooperative study (1) carried out in 1958 and 1959 by the Ohio Mills Research Group and the National Council For Stream Improvement on the sludge de-
watering of paper mill wastes, it was indicated that the use of centrifuges for the
concentration of sludges from the clarification of paper mill effluent nad much
promise. At approximately this same time, technological improvements were
being made in the design of centrifuges with the higher "G" forces and greater
load capacities that made the use of this equipment more feasible than had previously been the case.
As an outgrowth of these studies, centrifuges were installed in three mills in
the Miami Valley in Ohio, and the results from these operations have been described in a paper presented by Bamford (2).
Since that time, the number of centrifuges in the industry has increased
many times so that there are now some 27 installations using a total of 34 centrifuges for the concentration of sludges resulting from the clarification of paper mill
effluents. There are now more than 30 plants using centrifuges for the concentration of lime mud, and four installations using such units for the recovery of lime
from water softening sludges.
The two main types of centrifuges of interest are the solid bowl conveyor type
and the disk centrifuge with nozzle discharge. It is the solid bowl type that has
found extensive use in the paper industry, since up to the present time our main
concern has been with primary treatment. As we become involved with secondary treatment, where a higher centrifugal force is needed, the disk type may
be of increasing importance.
The solid-bowl horizontal-conveyor type centrifuge is available in different
gravitational forces.    A sketch of one such unit, capable of operating up to 3200
'G" force is shown in Figure 1.   This unit has a solid cylindrical bowl supported
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