Defoamer is used in a pulp mill and a paper mill to reduce foam problems. It tackles both problems with surface foam and entrained or entrapped air. Defoamer also hinders the formation of foam. Defoamers are surface active agents such as esters or amides of fatty acids and polyethylene glycols. It is also called antifoaming agent.
Properties of defoamer
Defoamer (antifoaming agent) has surfactant properties. Defoamer is highly insoluble in the foaming water medium. The viscosity of defoamer (antifoaming agent) is very low therefore it is spread very rapidly on foamy surfaces as tiny droplets. Defoamer has affinity to spread air-liquid interface and this is the causes for collapse of surface foam. Some other important parameter of defoamer (antifoaming agent) are pH value, solid content, active material content, specific gravity, emulsifier type (ionic/non-ionic), diluent and shelf life.
Why foam is generated
There are many causes to create foam in a paper mill and pulp mill. Many mechanical factors are involved to create foam. Every paper mill must have several pumps. If the pump is leaky seals it may be caused to create foam. A high pressure pump can also be created foam. Moreover agitation also builds up foam. Especially air bubble or foam raise during coating color circulation.
There are many chemical used in paper mill for paper making process. Some of them build up foam. Foam creation also depends on sizing agent. When acid sizing agent or rosin sizing agent is used then foam produce more than the use of alkaline or neutral sizing agent.
Various trouble that caused by foam in paper mill
Various kinds of troubles occur due to build up foam, dissolved and entrained air in a paper mill. Such as-
1. Formation problem in a paper mill.
2. Lessening of pump effectiveness
3. Development of bacteria.
4. Formation of deposit
5. Drainage problems
6. Coating color may be contain by air bubbles until drying
7. Downtime to cleaning system, ultimate increasing cost due to chemical drainage.
Benefits of defoamer or antifoaming agent
Defoamer (antifoaming agent) improves drainage in the paper mill. It is also improves drainage in the Kraft pulp stock, sulfite stock, bleaching plant screen room area in the pulp mill. A defoamer (antifoaming agent) reduces paper breaking and hence improves paper machine runnability. Therefore increases paper mill production. Defoamer (antifoaming agent) also lessen steam consumption in the dryers and resultant energy savings as well as cost savings. Defoamer avoids paper formation of holes by removing fine bubbles in fibers.
Dosage of defoamer or antifoaming agent
For batter effectiveness of defoamer (antifoaming agent) should be used proper dosages. If insufficient defoamer is used, the paper mill does not attain its goal. On the other hand, if too much defoamer is used, it negatively affects the performance of sizing agents and dry strength additives, moreover deposit dilemma. Hence to use of proper dosage of defoamer, it should be test the air content of headbox furnish.
Types of defoamer or deaerator
A wide variety of defoamer are available for paper mill such water based defoamers, oil based defoamers, powder defoamers, silicone based defoamers, polymer defoamers (EO/PO based defoamers) and alkyl polyacrylates defoamers.