Volume 6 chemical pulping part 1, fibre chemistry and technology book editor. The cooking chemicals and lignin, called black liquor, is pumped to evaporators 11, which remove water. A major advantage of mechanical pulping is the high yields of pulp that can be. Petersburg, florida, january 710, 2008 kraft pulping process most important chemical pulping process global kraft pulp production.
Chemical processes have a low yield in the range of 4055% but the pulp produced is of very high quality. It is the kind of pulp that dissolve plant fiber by chemical method. The 4 processes principally used in chemical pulping are kraft, sulfite, neutral sulfite semichemical nssc, and soda. The choice of pulping process is determined by the desired product, by the wood species available, and by economic considerations. Mechanical pulping leaves the lignin and the cellulose intact, whereas the purpose of chemical pulping is to chemically separate the lignin from the cellulose fibers and remove it from the pulp. Then, the mixture is blown out of the pressurized digester into a nonpressurized blow tank 9. The main objective is to facilitate the disintegration of wood into fibrous product. This is achieved by breaking the bonds in the lignin macromolecule. Washers 10 clean the mixture by removing the cooking chemicals and lignin, turning it into pulp. People use chemical agent that can start selective chemical reaction with the lignin in the raw materials.
The kraft chemical recovery process is a mature, effective technology that provides for recycling of the pulping chemicals, efficient generation of steam and electrical power from the fuel value of the black liquor, and effective disposal of dissolved wood substances. The four principal processes used in chemical pulping are kraft, sulfite, neutral sulfite semi chemical nssc, and soda. Dahl in 1879 and the first kraft mill started in sweden in 1890. The raw materials for making chemical paper pulp are plant fiber. The first three have great potential for causing air pollution.
Four nonwoods such as, dhaincha sesbania bispinosa, jute stick corchorus capsularis, wheat straw triticum aestivum and corn stalks zea mays were cooked by potassium hydroxide koh. The kraft pulping and recovery basic process flow pulp mill dale proctor, 2003 white liquor naoh na2s pulp mill cooking washing black liquor turpentine pulp. The following discussion centers on chemical pulping processes, which supply more than two tive thirds of worlds wood pulp. The pulp and paper industry converts fibrous raw materials into pulp, paper, and paperboard. In the papermaking industry the pulping process is an important technology. These fragments dissolved with the solution and wood disintegrates into fiber. The cooked pulp is then washed and screened to achieve a more uniform quality.
The success of kraft pulping is attributed to the recovery of inorganic reactants. Lignin obtained from kraft pulping process has a complex and recalcitrant structure. Today, thermomechanical pulping process is the most dominate mechanical pulping process. Pulping is done mechanically, thermomechanically, chemically, or with combinations of these treatments. The paper manufacturing process has several stages. Pulp bleaching technology the bleaching process bleaching is the treatment of cellulosic fiber with chemicals to increase brightness see box 4a. Olson pulp and paper centre, department of mechanical engineering, university of british columbia mechanical pulping comparison of mechanical and chemical pulps debarking stone groundwood refiner mechanical pulp thermo mechanical pulping tmp. Chips are then screened for size, cleaned, and temporarily stored for further processing. The advantages of kraft pulping include not only increased pulp strength, but also a better heat and chemical recovery system which reduces processing costs, its effectiveness in digesting nearly every known species of tree, and the insertion in the process of bleaching processes which increase pulp brightness. Lignin remains a major constituent of pulp even after digestion by chemical pulping. The predominant chemical pulping process used nowadays is the kraft process, which, at high temperatures and under forceful alkaline conditions, is able to remove large amounts of lignin from the. Bleaching of mechanical pulp is much different than that for chemical pulp.
Chemical pulping operations present the opportunity for exposures to digestion chemicals as well as gaseous byproducts of the cooking process, including reduced kraft pulping and oxidized sulphite pulping sulphur compounds and volatile organics. The purpose of pulping is to reduce wood or other fibrous raw material to individual cellulose fibers. Chemical pulping is the most common pulping process krotscheck, 2006. Chemical pulping edited by johan gullichsen and carljohan fogelholm item number.
About million tonsyear of kraft pulp are produced globally, accounting for twothirds of the worlds virgin pulp production and for over 90% of chemical pulp. The kraft chemical recovery process is a mature, effective technology that provides for recycling of the pulping chemicals, efficient generation of steam and electrical power from the fuel value. The most widely used chemical pulping process in papermaking is the kraft, or sulfate, process. Those debarked wood bolts are then chipped in a chipper if the pulping process calls for chemical digestion.
It involves cooking of raw materials using aqueous chemical solutions and elevated temperature and pressure to extract pulp fibers. Most chemical pulp is made by the sulphate or kraft process, in which caustic soda and sodium sulphate cook the woodchips. Kraft pulping process is the most used pulping process in the world. Chemical pulp manufacturing process kraft pulp processing in japan, most chemical pulp is produced using kp kraft pulp processing because this method produces strong pulp, is highly adaptable to any wood species, and pulping chemicals can be recovered and recycled. Sixta and others published chemical pulping processes find, read and cite all the research you need on researchgate. So we share our knowledge with customers, providing them with samples, specifications, ideas, technical information and a complete range of brochures. This technology has the potential for completely eliminating the causticizing plant and the lime kiln, making the kraft process much simpler. Pulp and paper pulp is the fibrous mass that results when a pulping process ruptures the bonds in the wood structure that hold the woody cells together. The chemical contents including cellulose, lignin, ash, and extractives soluble in alcoholacetone measured 55. High intensity process creates more collapsed fibres at. Pulping new technology in pulping and bleaching 91 9 much of the chemical pulping industry is focused on use of the kraft pulping process, and efforts to make the process more efficient continue. About million tons per year of kraft pulp are produced worldwide bruijnincx et al. Other chemical pulping process mainly using acid sul.
Chemical pulping edited by johan gullichsen and carljohan. Semichemical pulping results in stiff fibers, and the process is used to make corrugated paperboard, cardboard roll cores, and containers. The kraft process entails treatment of wood chips with a hot mixture of water, sodium hydroxide naoh, and sodium sulfide na 2 s, known as white liquor, that breaks the bonds that link lignin. Mechanical, semichemical, and sulfite pulp mills differ in detail, particularly in wood preparation, fiber separation, and bleaching, but many of the downstream refining. The kraft process is the dominating pulping process, which accounts for almost 60% of all mechanical and chemical pulp produced worldwide. Overall view of papermaking from chemical pulp by the kraft process. The kraft caustic plant process flow diagram dregs washer or filter slaker causticizers green liquor clarifier white. The kraft process, which uses sodium hydroxide naoh and sodium sulphide na2s to pulp wood, is the dominant pulping process in the pulp and paper industry. A method of converting wood chips into paper pulp for use in papermaking accomplished by chemical cooking of the chips, as opposed to mechanical pulping. Application of nssc pulping to sugarcane bagasse ahmad samariha a, and alireza khakifirooz b the nssc pulping process was investigated to produce pulp from bagasse for corrugating board manufacture. Brightness may be achieved by either lignin removal delignification or lignin decolonization. The main aim in chemical pulping is to separate the wood fibers from each other to render them suitable for further industrial processing. The kraft pulping and recovery process flow diagram caustic plant power plant pulp mill black liquor green.
By 1900 sulfite pulping had become the dominant means of producing wood pulp, surpassing mechanical pulping methods. Chemical pulping is the other common pulping process. This book will tell you, step by step, the research and technology behind the process of obtaining fibres from wood by chemical pulping. Kraft pulping process an overview sciencedirect topics. The black liquor is separated out from the pulp before the bleaching process. The first 3 display the greatest potential for causing air pollution. Mechanical pulping is the process in which wood is separated or defibrated mechanically into pulp for the paper industry the mechanical pulping processes use wood in the form of logs or chips that are mechanically processes, by grinding stones from logs or in refiners from chips, to separate the fibers. A typical layout of a mill using the kraft chemical pulping process is shown in figure 21. Pulp and paper manufacturing process in the paper industry. In this process lignin goes into the reactions with the cooking liquor chemicals and split into fragment. Thermomechanical pulping rapidly displaced traditional mechanical pulping, grinding, because similar paper properties could be achieved using fewer amounts of expensive reinforced kraft pulp. The competing chemical pulping process, the sulfate or kraft process was developed by carl f. Chemically, the sulphite pulping is still, with a few exceptions, the same acid one stage process it was ninety years ago, the ph of the cold cooking liquor being.
Delignification of woody material is carried out by two major types of processes. Comparison of chemical pulping and mechanical pulping. Mixed with water and other chemical or plantbased additives, pulp is the major raw material used in papermaking and. The kraft process also known as kraft pulping or sulfate process is a process for conversion of wood into wood pulp, which consists of almost pure cellulose fibers, the main component of paper. Today, the kraft process is the dominating chemical pulping process worldwide due to the superior pulp strength properties compared with the sulfite process, its application to all wood species, as well as to the efficient chemical recovery systems that have. The processes involved in papermaking include raw materials preparation, pulping chemical, semi chemical, mechanical, or waste paper, bleaching, chemical recovery, pulp drying, and paper forming and drying. The main chemical reactions in the cooking process can be described as. Generally, pulp can be classified into two main types. The kraft process alone accounts for over 80 percent of the chemical pulp produced in the united states. These high quality pulps are mainly used for higher quality paper production, such as office paper. Two chemical pulping methods exist using sodium sulfate kraft and sodium sulfite. Pulp is a lignocellulosic fibrous material prepared by chemically or mechanically separating cellulose fibers from wood, fiber crops, waste paper, or rags. The 4 processes principally used in chemical pulping are kraft.
Pulping and papermaking introduction and overview course. The paper making process, the fifth technical brochure from sappi idea exchange idea exchange sappi is committed to helping printers and graphic designers use paper in the best possible way. Surely, still there are other types of pulp actually. Kraft process is the foremost pulping process in the board and paper industry and the biggest lignin supplier. The chemical recovery process dictates the quality and quantity of the white liquor, which in turn, limits pulp production and the profitability of the kraft pulp mill. Thermomechanical pulping as a pretreatment for agricultural biomass for biochemical conversion ronalds gonzalez, hasan jameel, houmin chang, trevor treasure, adrian pirraglia, and daniel saloni the use of thermomechanical pulping tmp, an existing and well known technology in the pulp and paper industry, is proposed as a. Kraft pulping process is the most dominant lignocellulose pulping process producing about million tons of pulp annually 228.