New Technology Enhances Pulp Washing, 1996 Pulping Conference Proceedings

I. D. Barton, D. R. Ester, J. K. Pease

Betz PaperChem

A challenge facing the pulp and paper industry is to develop technology that minimizes impact on the environment and meets the high product quality standards of the marketplace while minimizing capital and operating costs. Since the replacement of existing equipment to meet these demands may not be a viable alternative for some mills, enhancing the existing system’s perfor-mance by other means becomes increasingly important. Improving brown and bleached stock washing is an area that should be considered. The objective of pulp washing is to remove as much of the soluble impurities as possible with minimum levels of fresh water usage. Poor washing can lead to resin buildup which can manifest itself as pitch deposits, causing downtime and production problems. While large amounts of resin are removed in brown stock washing, substantial amounts can still remain with the pulp. Increasing washing efficiency will reduce resin content as well as total solids in the pulp. Reducing carryover of total dissolved solids to subsequent processes will enhance recovery and bleaching operations. Resin and chemical carryover can negatively affect surface and strength properties of unbleached paper, as well as cause deposit problems on the papermaking equipment in bleached mills. Additionally, high carryover in brown stock and bleach plant areas can limit the functioning of bleach chemicals destroying their bleaching capabilities and increasing chemical demand. The market place prefers new chemical technology to be environmentally- friendly. Examples of this trend are oil-free defoamers and alkyl phenol ethoxylate-free (APE) surfactants. Trials with the new wash-aid in actual mill conditions with a new APE-free surfactant technology have resulted in improved washing, lower organic and inorganic carryover, increased mat consistency, and lower shower flows. These benefits have been demonstrated in brown stock and bleach plant vacuum drum washers and chemi-washers. Other mill objectives such as reduction of mill bottlenecks, decreased deposition, lower bleach chemical cost, increased production, and reduced environmental discharge can be realized using this technology. This paper will discuss the technology, its benefits, and case histories.