Introduction. The purpose of pulp washing is to obtain pulp that is free of unwanted solubles

The purpose of pulp washing is to obtain pulp that is free of unwanted solubles.

In the most basic case, this can be done by replacement of the contaminated

liquor accompanying the pulp fibers by clean water. In a modern pulp mill, washing

operations include also displacement of one type of liquor by another type of

liquor. Aside from its washing function, washing equipment must at times also

allow the effective separation of chemical regimes or temperature levels between

single fiberline process steps.

Various benefits result from pulp washing, such as minimizing the chemical

loss from the cooking liquor cycle;maximizing recovery of organic substances for

further processing or incineration;reducing the environmental impact of fiberline

operations;limiting the carry-over between process stages; maximizing the re-use

of chemicals and the energy conservation within a single bleaching stage;and last

– but not least – obtaining a clean final pulp product.

Ideally, pulp washing is carried out with the minimum amount of wash water

in order to conserve fresh water resources and to take capacity burden from downstream

areas which process the wash filtrate. Very often, pulp washing is a compromise

between the cleanness of the pulp and the amount of wash water to be

used.

In the mill, pulp washing operations can be found in brownstock washing, in

the bleach plant and, as the case may be, also in digesting and on the dewatering

machine.

Handbook of Pulp. Edited by Herbert Sixta

Copyright © 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

ISBN: 3-527-30999-3

©2006 WILEY-VCHVerlag GmbH&Co.

Handbook of Pulp

Edited by Herbert Sixta

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