Industrial Mixers For The Pulp And Paper Industry
The worldwide pulp and paper industry produces over 400 million metric tons of paper, cardboard, paperboard, and other paper-based products every year. In the U.S. alone, pulp and paper production is a $100 billion industry, and demand continues to grow.
But what is the process by which raw wood is transformed into paper and paper products? And what role do industrial mixers play in paper production?
From Raw Wood to Finished Paper
Manufacture of paper and pulp is directly dependent on the forestry industry. Conservation methods are used to ensure the preservation of our nation's forests for future generations. And only by replanting and careful forest management can a reliable supply of raw materials for the paper industry be guaranteed.
We will look at the process of kraft pulping below since that is the most common method in use in paper production.
The first step is the transport of whole logs or of wood chips to the paper mill. The wood chips are produced as a byproduct at saw mills. Logs are debarked, either by a rotating drum or by powerful jet streams of water. The logs are then turned into chips with a "chipper." Screening must be done to remove any chips that are too large, for the diameter of the woods chips determines how fast and effectively they will absorb important chemicals.
Once you have correctly sized wood chips, the next step is to "pressure cook" them. Sodium hydroxide and sodium sulphide are mixed in with the chips to help break them down. Temperatures must be kept at between 150 and 160 degrees Celsius to finish the job in a reasonable amount of time. But if temperatures run too high, wood chips may break down into their fibers unevenly. And during the process, pressure must be repeatedly raised and lowered.
After cooking, the wood chips are now pulp. The next step is to recover the cooking chemicals from the pulpy soup. This is done so the expensive chemicals can be reused but also to prevent potential problems later in the paper-making process and to prevent environmental contamination.
A wire mesh drum or other piece of machinery squeezes the pulp to extract the chemicals. The pulp forms a mat on the mesh, and then hot water is sprayed on the mat to wash away any residual chemicals.
At this point, any knots or wood fibers that are not fully cooked must be screened out. Special screening equipment rapidly takes care of this job. Then its on to the bleaching stage, which makes the paper white or prepares it to be colored or printed on. Cardboard and brown paper bags may skip this last step.
The Importance of Mixing and Mixers in Paper-making
In kraft pulping, as outlined above, the natural wood chemical "lignin" must be removed to break down the cellulose fibers and to remove the natural brown coloration. Thoroughly and evenly mixing the chemicals needed to remove this lignin is of inestimable importance to the pulp and paper industry.
The greater portion of lignin is removed during the cooking and subsequent washing stage, but residual lignin is removed during bleaching. Yet, despite the multiple steps that are involved in lignin removal, in large part, the success of the endeavor depends upon effective mixing early in the paper-making process.
In reality, industrial mixers are used at virtually all stages of pulp and paper manufacturing. A powerful, well designed mixer that fits the specific job size and process step is key to keeping paper smooth, even, and pure.
Mixing can be of liquids, solids, or gases, and may be done to evenly blend pulp or to evenly disperse reactive chemicals. Mixing of pulp streams, chemical additive injection just before sheet formation, and ensuring "full contact" with bleaching chemicals are all specific uses of industrial mixers in the paper industry.
Using the correct type of industrial mixers for the pulp and paper industry applications is key to success. Everything from small lab stirrers for testing to portable drum mount mixers to enormous tank mixers with capacities in the thousands of gallons range have their place in the process.
Finding a Reliable Mixer Supplier
Anyone in the paper and pulp industry should have a reliable source of new industrial mixers and replacement parts planned out in advance.