Pulp & Paper - Paper Mill
Paper Machine Wet End
From stock blending the pulp, now known as “stock”, flows to a machine chest that feeds a specific paper machine. The stock flows through a stuff box or de-aerator to get the air out, then flows to the fan pump where it mixes with “white water”, or water that has been removed from the paper machine. The flow meter just before the fan pump is called the basis weight mag meter, and is critical to the final weight of the sheet. Stock flow at 3.0-3.5% consistency is diluted to ½% consistency for the head box and improper control has a big impact on cost/ton. Customers run the weight target a little high, especially if they have too much variation, to be sure the minimum weight target is reached, which leads to high cost/ton. High variation can cause the sheet to break, which not only loses production but also increases cost/ton. Machine downtime is very expensive, because it takes a while to get running again, on-spec.