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Sealing applications in Pulp &Paper can be very complicated and difficult to deal with. From liquors (Black, White & Green) to chlorine and caustics, Durlon® 9200 is a go-to product that helps mills consolidate multiple gasket materials into one product which in turn, helps reduce the danger or risk of improper material selection. Durlon®9200’s high performance saves untimely downtime, saves money and improves overall plant safety.
The focus for this issue is the Pulp & Paper Industry, with a detailed reference to our Durlon®9200 Barium Sulfate/PTFE filled gasket material designed for use in aggressive chemicals. Read about up-coming industry news and events, and to celebrate our annual sales meetings, we’re featuring a video on the making of TFC’s Randy McKay Sales Award of Merit. And don’t forget to try and solve our brain teaser and catch up with our gasket guru comic strip.
Chett Norton, C.E.T., Engineering & QA Manager
Pulp And Paper Manufacturing Process In The Paper Industry
Paper plays a key role in our daily life and papers have been used for many years from now. Papers are made with the pulp of the woods, which is an Eco-friendly product.
Paper is made through the following processes:
1) Pulping procedure will be done to separate and clean the fibres
2) Refining procedure will be followed after pulping processes
3) Dilution process to form a thin fibre mixture
4) Formation of fibres on a thin screened
5) Pressurization to enhance the materials density
6) Drying to eliminate the density of materials
7) Finishing procedure to provide a suitable surface for usage
Pulp and paper are made from cellulosic fibres and other plant materials. Some synthetic materials may be used to impart special qualities to the finished product. Paper is made from wood fibres, but rags, flax, cotton linters, and bagasse (sugar cane residues) are also used in some papers. Used paper is also recycled, and after purifying and sometimes de-inking, it is often blended with virgin fibres and reformed again into paper. Products such as cellulose acetate, rayon, cellulose esters that are made from cellulose will be used for packaging films, explosives.
The pulping process is aimed at removing lignin without loosing fibre strength, thereby freeing the fibres and removing impurities that cause dis-coloration and possible future disintegration of the paper.
Hemicellulose plays an important role in fibre-to-fibre bonding in paper making. It is similar to cellulose in composition and function. Several extractives such as waxes, oleoresins are contained in wood but they do not contribute to its strength properties; these too are removed during the pulping process.
The fibre extracted from any plant can be used for paper. However, the strength and quality of fibre, and other factors complicate the pulping process. In general, the softwoods (e.g., pines, firs, and spruces) yield long and strong fibres that contribute strength to paper and they are used for boxes and packaging.
Hardwoods produce a weaker paper as they contain shorter fibres. Softwoods are smoother, transparent, and better suited for printing. Softwoods and hardwoods are used for paper-making and are sometimes mixed to provide both strength and print ability to the finished product.
Steps involved in the Pulp and Paper making Procedure:
Preparation of raw Material
Wood that has been received at a pulp mill can be in different forms. It depends on the pulping process and the origin of the raw material. It may be received as bolts (short logs) of round-wood with the bark still attached, as chips about the size of a half-dollar that may have been produced from sawmill from debarked round wood elsewhere.
If round wood is used, it is first debarked, usually by tumbling in large steel drums where wash water may be applied. Those debarked wood bolts are then chipped in a chipper if the pulping process calls for chemical digestion. Chips are then screened for size, cleaned, and temporarily stored for further processing.
Separation of Fibre
In the fibre separation stage, several pulping technologies will be diverged. The chips are kept into a large pressure cooker (digester), into which is added the appropriate chemicals in kraft chemical pulping.
The chips are then digested with steam at specific temperatures to separate the fibers and partially dissolve the lignin and other extractives. Some digesters operate continuously with a constant feed of chips (furnish) and liquor are charged intermittently and treat a batch at a time.
After the digestion process, the cooked pulp is discharged into a pressure vessel. Here the steam and volatile materials are tubed off. After that, this cooked pulp is returned to the chemical recovery cycle. Fiber separation in mechanical pulping is less dramatic.
Debarked logs are forced against rotating stone grinding wheels in the stone ground-wood procedure. Refiner pulp and thermo-mechanical pulp are produced by chips. These chips are ground by passing them through rapidly rotating in both processes.
In the second stage after refining, the pulp is screened, cleaned, and most of the process water is removed in preparation for paper making.
Raw pulp contains an appreciable amount of lignin and other dis-coloration, it must be bleached to produce light coloured or white papers preferred for many products. The fibres are further de-lignified by solubilizing additional lignin from the cellulose through chlorination and oxidation. These include chlorine dioxide, chlorine gas, sodium hypochlorite, hydrogen perioxide, and oxygen.
Sodium Hydroxide, a strong alkali is used to extract the dissolved lignin from fibres surface. The bleaching agents and the sequence in which they are used depend on a number of factors, such as the relative cost of the bleaching chemicals, type and condition of the pulp.
Mechanical pulp bleaching varies from chemical pulp bleaching. Bleaching of mechanical pulp is designed to minimize the removal of the lignin that would reduce fibre yields.
Chemicals used for bleaching mechanical pulps selectively destroy colouring impurities but leave the lignin and cellulosic materials intact, These include sodium bisulfites, sodium or zinc hydrosulfide (no longer used in the United States), calcium or sodium hypochlorite, hydrogen or sodium peroxide, and the Sulphur Dioxide-Boron Process (a variation of the sodium hydrosulfide method).
Paper making Procedure
Bleached or unbleached pulp may be further refined to cut the fibres and roughen the surface of the fibres to enhance formation and bonding of the fibres as they enter the paper machine.
Water is added to the pulp slurry to make a thin mixture normally containing less than 1 percent fibre. The dilute slurry is then cleaned in cyclone cleaners and screened in centrifugal screens before being fed into the ‘wet end’ of the paper-forming machine. The dilute stock passes through a head-box that distributes the fibre slurry uniformly over the width of the paper sheet to be formed.
Sited from: Pulpandpaper-technology.com™
Durlon® 9200 is a filled PTFE gasket material designed for use in aggressive chemicals. Including caustics, hydrogen peroxide, sodium hypochlorite, nitric acid, liquors and digester in pulp and paper service. Applications In the chemical, pharmaceutical and plastics industries include butadiene, hydrofluoric acid, vinyl chloride, methyl methacrylates, and styrene. It is also used extensively in railroad tankcar applications and can be used where resistance to highly aggressive chemicals is required. Style 9200 (granite white, branded) conforms to FDA requirements.
Oxygen: Durlon® 9200 has been independently tested and certified by the Federal Institute for Materials Research and Testing, Berlin (BAM) for gaseous oxygen at pressures up to 40 bar (585 psi) and temperatures up to 200°C (392°F), and for service in liquid oxygen. Gaskets for oxygen service can be supplied from distributor stocks, providing proper cleaning procedures for oxygen service are followed before installation.
Note: That as a class, PTFE gasket materials are not recommended in liquid oxygen services where there is thermal cycling due to thermal shock and the difference of the coefficient of expansion between PTFE and steel.
Barium sulfate fillers are homogeneously blended with pure PTFE resins to give Durlon® 9200 its physical and mechanical properties. Independent testing has shown the fillers in Durlon® 9200 to be more evenly dispersed than filled PTFE with layered construction. The result is more consistent physical and mechanical properties without the voids, separation and chemical compatibility problems found in layered filled PTFE. It is suitable for use in steel flanges, will not exhibit the cold flow problems associated with virgin or generic skived PTFE or the hardness problems of some other filled PTFE products. It has excellent sealability, cuts easily and separates cleanly from flanges after use.
News from The FSA
Have you seen FSA’s KnowledgeBase? The content is developed as a service to manufacturers and users of fluid sealing and containment devices. KnowledgeBase offers files of content and videos, each covering and explaining specific topics related to fluid sealing and containment devices. It can be accessed at fsaknowledgebase.org or through the FSA’s website at fluidsealing.com, Take a look today!
Turbomachinery and Pump Symposium
47TH TURBOMACHINERY & 34TH INTERNATIONAL PUMP USERS SYMPOSIA (TPS 2018)
Symposia & Exhibition: Sept. 18 –20, 2018 | Short Courses: Monday, Sept. 17, 2018 – George R. Brown Convention Center, Houston, TX
TPS is a vital industry event, offering a forum for the exchange of ideas between rotating equipment engineers and technicians worldwide. Now surpassing 46 years, TPS is known for its impact on turbomachinery, pump, oil & gas, petrochemical, power, aerospace, chemical and water industries through two pathways: the technical program and exhibition.
Next issue highlights: Industry focus – Food & Beverage and Pharmaceutical. Product focus – Durlon® 9400. We’ll share a new video, news and upcoming trade shows that you many want to look into. And of course, we will put those genius brains to the test again and tickle your funny bone with another adventure from our gasket guru. See you in November!