In batch digestion, the pulp and black liquor are mechanically conveyed or "blown" into an atmospheric blow tank upon completion of the cooking cycle. The tank is a large cylindrical vessel which functions as intermediate storage of the cooked pulp, and from which the pulp (now called "Brown Stock" due to its color) is discharged in an even flow to a washing process.
Level control of the blow tank helps to maintain balance between the digestion and washing processes. Level controls facilitate ontime blow spacing in the digester while promoting improved product quality by maintaining consistent washer production and efficiency. The presence of a tank agitator will affect level control selection, which is typically a high level switch.