Acid

This post is somewhat grade specific. Acid is used in some mills to control pH. In multiply linerboard it can also be used to improve drainage. However, too much will damage the fiber and lead to reduced strength. The reward of improved drainage may allow for the machine to be sped up, resulting in increased production.

Using acid on the base sheet is generally not an issue since there is plenty of flow to dilute the acid. On a secondary or top sheet controlling the amount of acid can be an issue due to the low acid addition rates. The acid addition should be controlled with a pH setpoint. The control response should be fairly quick. Some bump tests should be performed to determine how the control should be set up. This should be done with the assistance of the controls engineer and E&I personel. To improve the control, the pressure going to the control valve can be reduced to allow the valve to operate at a larger opening range.

Acid is relatively cheap. Increasing acid usage can not only increase production, but also reduce alum usage. This should not be a high priority project but is definitely worth looking at.