Comparison of Deinking Processes for High Quality Newsprint Production, 1995 Recycling Symposium Proceedings

S. Dessureault

M.C. Barbe

S. Tremblay

A. Thorn

Kvaerner Hymac Inc.

Three typical deinking process alternatives similar to the ones that are currently used for the production of newsprint from ONP/OMG waste are compared in terms of ink, ash content and dissolved solids in the end-product, yield loss, fresh water consumption and effluent volume generated. The first two alternatives studied and referred to as “single loop” involves a single white water recirculation loop in which a single stage flotation, a double stage dewatering/washing stage and a single stage hydrosulfite bleaching are present in addition to the usual repulping, cleaning and screening stages. In one of these alternatives, the dewatering/washing stage is composed of a disc filter and a twin-wire press (Case A) while in the-other a decker and a screw press are used (Case B). The third alternative studied and referred to as “double loop” involves two white water recirculation loops in which a double stage peroxide- hydrosulfite bleaching, a post flotation stage and a post double stage dewatering/washing step using a decker and a twin wire press are added to the “single loop” process (Case A).

The analysis which makes use of mill and pilot plant data as well as literature data is performed by computer simulation. The work demonstrates the benefits of the double loop process alternative over the single loop. The ink content of the pulp at the outlet of the double loop process is appreciably inferior. The ash content, the dissolved solids content and the process yield are also lower compared to a single loop process (Case A). Furthermore, while in the single loop deinking process of Case A the ash content and dissolved solids level in the end-product can be lowered with increased fresh water consumption, it is considerably less in the deinked pulp from a double loop deink plant at the same water consumption level.

These findings are particularly important in view of the potential benefits of increasing recycled pulp content in the furnish and of the shift in the marketplace towards the production of high quality newsprint and specialty grades. Furthermore, the higher quality achieved at lower fresh water consumption levels is of importance in view of the capital expenditures which are made on effluent treatment plants required to meet the more stringent environmental regulations.