Process for producing a constant distribution of a selected property across the width of pulp mat on a pulp washing surface

Claim 1

In a pulp washing process where a cellulosic pulp slurry stream and a dilution liquid are continuously introduced into a headbox from which an admixture of these overflows into a vat to form a level of admixture comprising pulp and liquid in said vat wherein a mat comprising pulp and liquid continuously forms on a washing surface which is moved at a surface speed and wherein wash liquid is directed at said mat on said washing surface and vacuum filtering is carried out to produce a product stream of washed pulp and liquid at a downstream location on said surface and a filtrate which is divided so that part of it is recirculated to provide said dilution liquid and where there is obtained a substantially constant percentage of pulp in said admixture and a substantially constant average weight of liquid in the pulp mat per unit area of the washing surface despite change of production rate, the improvement comprising controlling the weight per unit area of liquid alone or liquid and pulp combined in said mat across its width to obtain a substantially constant distribution of a selected property in the pulp mat across its width by steps comprising: (a) determining said property in a plurality of selected locations across the width of said mat and also the average value of said property across the width of said mat, and (b) controlling a plurality of dilution liquid inputs into said headbox, each of said dilution liquid inputs being positioned to discharge at a location corresponding to a different one of said plurality of selected locations and each of said dilution liquid inputs being controlled in response to said determining to produce a substantially constant distribution of said property across the width of said mat.