Pulping Applications

Removing impurities from the process stream is crucial.

Pulp from cooking always contains some unwanted solid material. Some of the fibrous material may not be completely in the form of individual fibers. The main purpose of the pulp screening process is to separate harmful impurities from pulp with minimal fiber loss, and at an acceptable cost level.

Bark, sand, shives, and rocks are typically found within the cooked chips and must be removed. It is important for these impurities to be removed from the process stream as they can have negative effects on end product quality, may damage downstream process equipment, and may cause operational problems.

Effective operation of the brown stock washing process can be extremely challenging.

This difficulty is caused by the inherent challenge of filtrate level control, the coupling between the filtrate tank levels, the multiple production rates within the process, and process problems such as foaming. Another difficulty is caused by the large time delay between changes in wash flows and the resulting unbleached stock cleanliness.

Further, the process may be subject to changing process limitations such as evaporator capacity. Under-washing the pulp drives up bleaching costs and results in high soda loss, but over-washing overloads the evaporators and creates large steam costs. Ideally, the system should run to an operating point that minimizes this total cost. In practice, while this operating point is often achievable, the control system must also be robust enough to cope with process upsets and limitations, and mismatched production rates.

Magnetic meters operating in high temperature and harsh environments often experience failures within weeks of installation.

This results in unplanned downtime. These failures create challenges in process control, as well as capital and labour costs associated with replacement.