Stock preparation, in general, consists of raw material handling, pulping, cleaning, screening, flotation, washing and refining. The short circulation is a wet end process located between the paper machine and stock preparation in which water from the wires of a paper machine is circulated to dilute thick stock to headbox consistency.
In modern stock preparation and wet end operations, the focus is on controlling the flows. The basis weight of the paper needs to be strictly controlled to meet high-quality requirements.
Many unit operations with different media add pressure to a cost-efficient valve selection. Also pulp consistency control can cause problems. Some additives used in papermaking cause erosion in the valve structure. Additives, too, can cause environmental problems if they leak into the environment
The precision of V-port segment valves is recommended when flows need good controllability.
To control the basis weight, nelesACE™ valves can be used. These are specially designed for even better flow control.
Valmet's triple eccentric disc valves are a good and cost-efficient way to handle flows with large pipe sizes and low pulp consistencies of below 2.5% in control and 4% in on-off applications. Segment and ball valves can be used for higher consistency flows. Erosion problems can be prevented by using ceramic materials in the valves.
Low cost of ownership
- Good controllability results in lower losses and higher product quality
- Total valve costs can be significantly reduced and fouling prevented with the right valve selection
- Erosion lowers the valve lifespan; preventing erosion reduces maintenance demand
- A plant's environmental impact can be reduced and safety improved with a tight shaft sealing