Key Questions
The following key questions are answered in this module:
Are there multiple forms of entrained air?
There are three forms of entrained air that can exist in stock suspensions and white water - free, bound, and dissolved.
What are the differences between free air, bound air, and dissolved air?
Free air consists of larger bubbles that can be removed with time, bound air consists of smaller bubbles that can attach to fibers and be difficult to remove, and dissolved air only presents a problem if it converts into free or bound air.
Is deaeration necessary on every machine?
The amount of entrained air that is tolerable in a paper or board making process depends on many things. So, though all paper and board machines would benefit at least a little from deaeration, not all of them use it.
How do deaerators remove entrained air from the stock suspension?
They use three means: they use vacuum to ""boil"" the stock to remove air, they spray the stock to expose more surface area to the vacuum, and they impinge the stock on hard surfaces to separate the bound air from the fibers.
Can a deaerator cause pulsations in the stock flow to a headbox?
Pulsations in the stock flow to the headbox can be caused by excessive air in the stock going to the deaerator, an undersized or underperforming vacuum system, or low stock flows to the deaerator, which can cause the level inside the vessel to rise and fall, leading to fluctuations in the stock flow to the fan pump.