The influence of defoaming agent on my country’s papermaking engineering
Foam in pulp is a headache. It hinders the implementation of process conditions and the normal operation of equipment, and may become a serious problem in pulping, papermaking and waste liquid treatment. So what is the help of defoaming agents in the papermaking industry? Let’s take a look together.
With the development of my country’s papermaking industry, degassing and defoaming have become an important research topic in production. For pulp engineering, the generation and existence of foam will seriously affect the normal operation of pulp washing, screening, bleaching and beating, and hinder the normal performance of these process equipment.
Foam has a greater impact on papermaking engineering. The presence of foam in paper stock will cause the concentration of the headbox to fluctuate and the flow state of paper stock to be unstable; it can close the micropores on the surface of the wet paper web, making it difficult to dehydrate the net, causing fibers and undispersed fillers to condense on the net, affecting the uniformity of the paper web. Foam will also form floating pulp, causing lumps to appear on the paper web, and in severe cases, cause breakage. When making paperboard, foam exists between the paperboard layers, reducing the interlayer bonding strength. Foam can also cause paper or paperboard to have foam holes, foam spots, resin spots and other paper defects. In the process of coated paper processing, if there is a large amount of foam in the storage tank and the coating roller, the foam will overflow, which will not only affect the normal operation of coating, cause the loss of coating, but also pollute the environment. When the coated paper with foam is dried, the foam will burst due to the heat expansion of the air inside, forming a depression on the paper surface, thereby destroying the smoothness and smoothness of the paper surface and affecting the exquisiteness and integrity of the printed pattern on the paper. When the foam is serious, it will increase the viscosity of the coating, make the coating flow performance worse, and bring difficulties to production.
In the process of waste liquid treatment, foam reduces the efficiency of waste liquid treatment, and causes wastewater to flow and splash, polluting the environment. For example, when sewage treatment adopts the surface accelerated aeration process of activated sludge, a large amount of foam will be generated during the surface aeration and oxygenation process to cover the surface, which not only makes oxygenation difficult, affects the growth of microorganisms, and reduces the efficiency of biochemical treatment, but also the foam overflows, making surface aeration impossible. The impact of foam on the papermaking industry has been gradually recognized by people and has been increasingly valued. In the world, in some countries with developed papermaking industries, the proportion of expenses for degassing and defoaming is very large.
Foam often accompanies people’s lives and production. Sometimes bubbles and foam are needed, such as flotation, fire extinguishing, dust removal, washing, making foam ceramics and plastics, etc.; but some occasions need to eliminate bubbles and foam, such as fermentation, coatings, papermaking, printing and dyeing, eliminating flatulence in organs, boiler water, wastewater treatment and prism (or glass) manufacturing, etc. When drinking beer, the carbon dioxide in the beer is transformed into gaseous state due to vibration, resulting in a large amount of foam in the beer. This is because adding a drop of oil to the beer bottle can eliminate the foam, which is actually the principle of the defoamer.
Generally speaking, pure water and pure surfactants do not foam because their surfaces and interiors are uniform and it is difficult to form an elastic film. Even if it is formed, it is unstable and will disappear instantly. But when there is the presence of surfactant in the solution, after the bubble is formed, due to the effect of intermolecular force, the hydrophilic group and the hydrophobic group in its molecule are adsorbed by the bubble wall, forming a regular arrangement, with its hydrophilic group facing the water phase and the hydrophobic group facing the bubble, thereby forming an elastic film on the bubble interface, which has strong stability and is not easy to break under normal conditions. The stability of the foam is related to factors such as surface viscosity and elasticity, electrical repulsion, movement of the surface film, temperature, and evaporation. Moreover, the surface tension of the bubble and the liquid is reversely related, and the smaller its tension is, the easier it is to foam. In life and production, the appearance of foam often brings many inconveniences to people, so defoaming is necessary.
