A pulp mill is a manufacturing facility that converts wood chips or other plant fiber source into a thick fiber board which can be shipped to a paper mill for further processing. Fiber crops are field crops grown for their Fibers which are used to make Paper, Cloth, or Rope. A paper mill is a Factory devoted to making Paper from wood pulp and other ingredients using a Fourdrinier Machine or similar apparatus Pulp can be manufactured using mechanical, semi-chemical or fully chemical methods (kraft and sulfite processes). Wood pulp is a dry fibrous material prepared by chemically or mechanically separating the fibers which make up Wood. The Kraft process (also known as Kraft pulping or sulfate process) describes a technology for conversion of wood into Wood pulp consisting of almost pure The sulfite process produces Wood pulp which is almost pure Cellulose fibers by using various Salts of Sulfurous acid to extract the Lignin The finished product may be either bleached or non-bleached, depending on the customer requirements. Bleaching of wood pulp is the Chemical processing carried out on various types of Wood pulp to decrease the color of the pulp so that it becomes whiter
Wood and other plant materials used to make pulp contain three main components (apart from water): cellulose fibres (desired for papermaking), lignin (a three-dimensional polymer that binds the cellulose fibres together) and hemicelluloses, (shorter branched carbohydrate polymers). Wood is hard fibrous lignified structural tissue produced as secondary Xylem in the stems of Woody plants notably trees but also shrubs Cellulose is an Organic compound with the formula, a Polysaccharide consisting of a linear chain of several hundred to over ten thousand β(1→4 Fiber or fibre is a class of Materials that are continuous filaments or are in discrete elongated pieces similar to lengths of thread. Paper is thin material mainly used for writing upon printing upon or packaging Lignin or lignen is a complex Chemical compound most commonly derived from Wood and an integral part of the secondary Cell walls of Plants Cellulose is an Organic compound with the formula, a Polysaccharide consisting of a linear chain of several hundred to over ten thousand β(1→4 A hemicellulose can be any of several Heteropolymers (matrix polysaccharides present in almost all plant cell walls along with Cellulose. Carbohydrates (from ' Hydrates of Carbon ' or saccharides ( Greek σάκχαρον meaning " Sugar " are the most The aim of pulping is to break down the bulk structure of the fiber source, be it chips, stems or other plant parts, into the constituent fibers.
Chemical pulping achieves this by degrading the lignin and hemicellulose into small, water-soluble molecules which can be washed away from the cellulose fibers without depolymerizing the cellulose fibres (chemically depolymerizing the cellulose weakens the fibers). The various mechanical pulping methods, such as groundwood (GW) and refiner mechanical (RMP) pulping, physically tear the cellulose fibres one from another. Much of the lignin remains adhering to the fibres. Strength is impaired because the fibres may be cut. There are a number of related hybrid pulping methods that use a combination of chemical and thermal treatment to begin an abbreviated chemical pulping process, followed immediately by a mechanical treatment to separate the fibers. These hybrid methods include thermomechanical pulping (TMP) and chemithermomechanical pulping (CTMP). The chemical and thermal treatments reduce the amount of energy subsequently required by the mechanical treatment, and also reduce the amount of strength loss suffered by the fibers.
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The mill
The first step in mills using trees as the fiber source is to remove the bark. Bark, also known as periderm is the outermost layer of stems and Roots of Woody plants such as Trees It overlays the Wood and consists Bark contains relatively few useable fibers and is burned, along with other unusable plant material, to generate steam to run the mill.
Much of the information about the technology in following subsections is from the book by C. J. Biermann. [1]. The chemistry of the various pulping processes can be found in Sjöström's book. [2]
Chemical pulp mills
Chemical pulping processes such as the kraft (or sulfate) process and the sulfite process remove much of the hemicelluloses and lignin. The Kraft process (also known as Kraft pulping or sulfate process) describes a technology for conversion of wood into Wood pulp consisting of almost pure The sulfite process produces Wood pulp which is almost pure Cellulose fibers by using various Salts of Sulfurous acid to extract the Lignin The Kraft process (also known as Kraft pulping or sulfate process) describes a technology for conversion of wood into Wood pulp consisting of almost pure The sulfite process produces Wood pulp which is almost pure Cellulose fibers by using various Salts of Sulfurous acid to extract the Lignin The kraft process does less damage to the cellulose fibers than the sulphite process, thereby producing stronger fibers, but the sulfite process makes pulp that is easier to bleach. The chemical pulping processes use a combination of high temperature and alkaline (kraft) or acidic (sulphite) chemicals to break the chemical bonds of the lignin.
The material fed into the digester must be small enough to allow the pulping liquor to penetrate the pieces completely. In the case of wood, the logs are chipped and the chips screened so that what is fed to the digester is a uniform size. The oversize chips are rechipped or used as fuel, sawdust is burned. The screened chips or cut plant material (bamboo, kenaf, etc) goes to the digester where it is mixed an aqueous solution of the pulping chemicals, then heated with steam. Bamboo is a group of Woody perennial Evergreen Plants in the True grass family Poaceae, subfamily Kenaf Persian Hibiscus cannabinus, is a plant in the Malvaceae family A digester is a device used in Papermaking which takes small Wood chips and cooks them for a number of hours to remove Lignin. In the kraft process the pulping chemicals are sodium hydroxide and sodium sulfide and the solution is known as white liquor. Sodium hydroxide ( Na[[hydroxide OH]]) also known as Lye, caustic soda and (incorrectly according to IUPAC nomenclature Sodium sulfide is the name used to refer to the Chemical compound Na2S but more commonly its hydrate In the sulfite process the pulping chemical is a mixture of metal (sodium, magnesium, potassium or calcium) or ammonium sulfite or bisulfite.
After several hours in the digester, the chips or cut plant material breaks down into a thick porridge-like consistency and is "blown" or squeezed from the outlet of the digester through an airlock. The sudden change in pressure results in a rapid expansion of the fibers, separating the fibres even more. The resulting fiber suspension in water solution is called "brown stock".
Brown stock washers, using countercurrent flow, remove the spent cooking chemicals and degraded lignin and hemicellulose. Countercurrent exchange is a mechanism used to transfer some property of a Fluid from one flowing current of fluid to another across a Semipermeable membrane or thermally-conductive The extracted liquid, known as black liquor in the kraft process, and red or brown liquor in the sulfite porcesses, is concentrated, burned and the sodium and sulfur compounds recycled in the recovery process. Black liquor is a Byproduct of the Kraft process, (also known as Kraft pulping or sulfate process) during the production of paper pulp Lignosulfonates are a useful byproduct recovered from the spent liquor in the sulfite process. Lignosulfonates, or sulfonated lignin, ( CAS number 8062-15-5 are water-soluble anionic Polyelectrolyte Polymers they are byproducts from the [3] The clean pulp (stock) can be bleached in the bleach plant or left unbleached, depending on the end use. Bleaching of wood pulp is the Chemical processing carried out on various types of Wood pulp to decrease the color of the pulp so that it becomes whiter The stock is sprayed onto the pulp machine wire, water drains off, more water is removed by pressing the sheet of fibers, and the sheet is then dried. At this point the sheets of pulp are several millimeters thick and have a coarse surface: it is not yet paper. The dried pulp is cut, stacked, bailed and shipped to another facility for whatever further process is needed.
Bleached kraft pulp and bleached sulfite pulp are used to make high quality, white printing paper. One of the most visible uses for unbleached kraft pulp is to make brown paper shopping bags and wrapping paper where strength is particularly important. A special grade of bleached sulfite pulp, known as dissolving pulp, is used to make cellulose derivatives such as methylcellulose which are used in a wide range of everyday products from laxatives to baked goods to wallpaper paste. Methylcellulose (or methyl cellulose) is a Chemical compound derived from Cellulose. Laxatives (or purgatives) are foods compounds or drugs taken to induce bowel movements or to loosen the stool most often taken to treat Constipation. Baking is the technique of prolonged Cooking of Food by dry heat acting by conduction, and not by radiation, normally in an Oven, This page refers to the material used for Interior decoration.
Mechanical pulp mills
The earliest mills used sandstone grinding rollers to break up small wood logs called "bolts", but the use of natural stone ended in the 1940s with the introduction of manufactured stones with embedded silicon carbide or aluminum oxide. Silicon carbide ( is a compound of Silicon and Carbon bonded together to form Ceramics but it also occurs in nature as the extremely rare mineral The pulp made by this process is known as "stone groundwood" pulp (SGW). If the wood is ground in a pressurized,sealed grinder the pulp is classified as "pressure groundwood" (PGW) pulp. Most modern mills use chips rather than logs and ridged metal discs called refiner plates instead of grindstones. If the chips are just ground up with the plates, the pulp is called "refiner mechanical" pulp (RMP), if the chips are steamed while being refined the pulp is called "thermomechanical" pulp (TMP). Steam treatment significantly reduces the total energy needed to make the pulp and decreases the damage (cutting) to fibers. Mechanical pulp mills use large amounts of energy, mostly electricity to power motors which turn the grinders. A rough estimate of the electrical energy needed is 10,000 megajoules (MJ) per tonne of pulp (2,500 kW·h per short ton)
Chemi-mechanical pulp mills
Some mills pretreat wood chips or other plant material like straw with sodium carbonate, sodium hydroxide, sodium sulfite and other chemical prior to refinng with equipment similar to a mechanical mill. The joule (written in lower case ˈdʒuːl or /ˈdʒaʊl/ (symbol J) is the SI unit of Energy measuring heat, Electricity This article is about the tonne or metric ton For other tons see Ton. The short ton ( S/T) is a unit of mass equal to 2000 lb (around 907 The conditions of the chemical treatment are much less vigorous (lower temperature, shorter time, less extreme pH) than in a chemical pulping process since the goal is to make the fibers easier to refine, not to remove lignin as in a fully chemical process. Pulps made using these hybrid processes are known as chemi-thermomechanical pulps (CTMP). Sometimes a CTMP mill is located on the same site as a kraft mill so that the effluent from the CTMP mill can be treated in the kraft recovery process to regenerate the inorganic pulping chemicals.
Environmental issues
The United Nations Environmental Program (UNEP) has approved only two processes for making the chemical bleach chlorine dioxide, which produce 99. The UN Environment Programme (or UNEP) coordinates United Nations environmental activities assisting developing countries in implementing environmentally sound policies Chlorine dioxide is a Chemical compound with the formula ClO2 8% chlorine dioxide and contain only 0. Chlorine dioxide is a Chemical compound with the formula ClO2 2% elemental chlorine. Contamination of the chlorine dioxide with elemental chlorine is considered undesirable, and may lead to environmental pollution. While properly treated effluent may be safe to discharge into water catchment areas, mills which discharge untreated effluent pollute water ways with persistent organic pollutants (organochlorides and dioxins), and may breach the Stockholm Convention. Persistent organic pollutants ( POP s are organic compounds that are resistant to environmental degradation through chemical, biological, and photolytic Applications The simplest form of organochlorides are chlorinated Hydrocarbons These consist of simple Hydrocarbons in which one or more hydrogen atoms have Not to be confused with Dioxane or Digoxin. Dioxin is a heterocyclic, organic, antiaromatic compound Stockholm Convention is an international legally binding agreement on persistent organic pollutants (POPs
References
- ^ Biermann, Christopher J. (1993). Essentials of Pulping and Papermaking. San Diego: Academic Press, Inc. . ISBN 0-12-097360-X.
- ^ Eero Sjöström (1993). Wood Chemistry: Fundamentals and Applications. San Diego: Academic Press. Academic Press ( London, New York and San Diego) was an Academic Book Publisher that is now part of Elsevier. ISBN 0-12-647481-8.
- ^ Uses of lignosulfonates. Retrieved on 2007-10-07. Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. Events 3761 BC - The epoch (origin of the modern Hebrew calendar ( Proleptic Julian calendar)
See also
External links
A paper mill is a Factory devoted to making Paper from wood pulp and other ingredients using a Fourdrinier Machine or similar apparatus Wood pulp is a dry fibrous material prepared by chemically or mechanically separating the fibers which make up Wood. The Kraft process (also known as Kraft pulping or sulfate process) describes a technology for conversion of wood into Wood pulp consisting of almost pure The sulfite process produces Wood pulp which is almost pure Cellulose fibers by using various Salts of Sulfurous acid to extract the Lignin Bleaching of wood pulp is the Chemical processing carried out on various types of Wood pulp to decrease the color of the pulp so that it becomes whiterDapyx Software network: MP3 Explorer | Ebook Manager | Zenithic