Optimizing Wet End Chemistry, 1992 TAPPI Conference Proceedings

Pulp and paper producers and their technical support often fail to work together effectively. The result is lower quality and lower profits. By coordinating their activities, it is possible to experience a combined positive effect on both rejects and productivity.

This paper will explore some practical process chemistry situations in two important segments of the paper Industry - Kraft linerboard and newsprint.

In linerboard operations the pulpmaker may be strapped for washing, evaporation, and recovery capacity and send too much soda and dissolved organics in the pulp, as black liquor, to the paper machine. This pulping byproduct is worth much more as fuel and chemical than as furnish.

The papermaker then proceeds to make tall oil and sizing with the addition of copious amounts of sulfuric acid and alum. The acidified stock is “slow” and does not refine or drain well. Consistency is lowered so the stock will screen, and refining then tends to cut the fibers as opposed to hydrating them. The paper mill system therefore has a high level of fines and excessive dissolved solids.

The situation is then aggravated by running a headbox pH of less than 5 so these dissolved solids precipitate in the entire system, further slowing the stock drainage. Reacting to slow drainage, headbox consistency is raised to have less water to drain. As a result of higher consistency, formation, strength properties, and overall product quality decline.

In newsprint operations where pine is a major component of the mechanical pulp, pitch problems are seasonal in nature. This is true in not only the Southern United States but in the Northwest and other regions of the country. Heavy rains can disrupt flow of wood to the mill, which is many times attempting to store minimal quantities of wood for inventory cost reasons. As a result, the TMP or groundwood operations cycle from very green wood to somewhat seasoned wood. This places a demand for pitch control chemistry to cycle with the intensity of the problem, in order to be cost effective.