A pulp cooking system, a new plant for generating polysulfide and a minor upgrade of existing bleach plant, all supplied by Valmet, are part of plant improvement at Clearwater Paper's mill in Lewiston, Idaho. Construction is expected to begin in October and is slated to be completed in September 2017.

The delivery is part of Clearwater Paper's $160 million project to install a continuous pulp digester that will replace 12 batch digesters. Benefits include a reduction in air emissions, improved pulp quality, increased production and a more efficient utilization of wood chips.

"The efficient utilization of raw material is a vital part from a sustainability perspective. We decided to base our new cooking process on polysulfide to optimize yield. The concept and process included in the CompactCooking system from Valmet was a perfect match to our targets," says John Deuser, project manager in Lewiston.

Valmet’s CompactCooking G2 cooking plant is the first stage in a chemical pulping line. Lignin is chemically separated from the fiber. The two-vessel continuous cooking system consists of an impregnation system and a digester for cooking of chips. Using a two-vessel design ensures well defined impregnation as well as cooking zones. According to the company, Valmet’s ImpBin impregnation technology enables higher kappa level operation with low reject content.