The kraft pulping process allows the conversion of wood, composed of cellulose, hemicellulose, lignin and extractives, into a wood pulp containing mainly pure cellulose. Since then the kraft process has become the leading chemical pulping process. Kraft pulping is an alkaline process wherein lignin is removed by the action of sodium hydroxide and sodium sulfide. Kraft process variability reduction in pulping, washing. Sulfite process, sulfite also spelled sulphite, chemical process for the manufacture of paper pulp that employs an acid bisulfite solution to soften the wood material by removing the lignin from the cellulose. Since the source of sodium hydroxide was from caustic soda, this alkaline pulping process was called the soda process. Wood chips are delignified by harsh chemicals white liquor to produce pulp and spent liquor black liquor. An anthology of papers on the subject of kraft pulp yield is also available 1. The kraft pulping industry was the first known to combine pulp washing with the recovery of materials used and produced in the wood cooking process. In spite of extensive experimental investigations on kraft pulping process, the modeling of pulp characteristics of eucalyptus camaldulensis versus pulping variables is yet missing.
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. The choice of pulping process is determined by the desired product, by the wood species available, and by economic considerations. Jun 30, 2015 kraft pulping process is the most used pulping process in the world. In this study, the effect of various sulfidity and active alkali charges of cooking liquor. The main chemical reactions in the cooking process can be described as. The process was invented by theodor kleinert in 1968 as an environmentally benign alternative to kraft pulping. The chemical emissions of the kraft process are what give pulp mills their. The kraft process differs from the sulfite process in that 1 the. These fragments dissolved with the solution and wood disintegrates into fiber. The air pollution is mainly caused by the release of organic sulphur compounds and dust particles. As the carbon to carbon bond are stable in alkaline conditions, the cleavage of oxygen carbon bonds are the most significant reaction in the cooking process. Kraft pulping process an overview sciencedirect topics.
Semichemical pulping accounts for about 7% of production, and various mechanical pulping processes account for the remainder. The kraft process also known as kraft pulping or sulfate process 1 is a process for conversion of wood into wood pulp, which consists of almost pure cellulose fibers, the main component of paper. The rest ends up as sludge which is burned, spread on land or land field. Our online kraft pulping training courses provide essential training for pulp manufacturers these courses cover the processes and equipment used in kraft pulping. Paper pulp manufacturing papermaking process in the. Balakshin,b houmin chang,a, and hasan jameel a in an attempt to explain variations in delignification behaviors among different hardwood species, the kraft pulping delignification rates of. The kraft pulping process was the most commonly used chemical pulping process, accounting for 98 percent of chemical pulp production in the united states and 92 percent of chemical pulp production in the world. Pulping wood by a sulfite process rather than the kraft process has advantages in producing a pulp that can be used in some lightcolored products without bleaching and can be readily bleached for others. Within a few years the process was in commercial operation both in europe and in north america. Paper pulping equipment for chemical pulping cnbm paper. Dahl, a german chemist, later developed the sulfate or kraft process in 1879 when he replaced the sodium. The weak black liquor is separated from the pulp by washing.
In a global context, a shift in the capacity for bleached hardwood and. In the kraft process, about half of the wood is dissolved, and together with the spent pulping chemicals, forms a liquid stream called weak black liquor figure 1. An important part of the program is the comparison. For example, the condensates from an evaporation system that processes both weak black liquor from a kraft pulping process and spent liquor from a semi. This is achieved by breaking the bonds in the lignin macromolecule. Wood chip preparation and handling at the pulp mill. Pulp bleaching technology the bleaching process bleaching is the treatment of cellulosic fiber with chemicals to increase brightness see box 4a. A typical layout of a mill using the kraft chemical pulping process is shown in figure 21. Pse 4766 kraft pulping chemicals free download as powerpoint presentation.
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. Kraft pulping process 155oc 900 kpa a td kraft pulp mill 0 500 1500 2000 2500 3000 chemicals wood dissolved organics fibre chemicals td black liquor pulp 8000 10,000 td weak black liquor produces 1500 td bl d. Kraft pulping process is the dominating pulp manufacturing process in the world. If pine heartwood is used, however, conventional sulfite pulping liquors of calcium bisulfite plus a. 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 kraft pulping process is the main chemical pulping m ethod for producing highquality woodbased fibers. In particular, the ability to obtain relatively high quality lignin adds value to a process stream otherwise considered as waste. Pulp statistics are usually reported in units of weight. Our production facilities are designed to recover and reuse much of the water. Impact of sulfidity on the kraft pulping of eucalyptus. The motivation behind materials recovery is economic and more recently, environmentally. The sulphite pulping process is an alternative method best suited for speciality pulp which can be easily bleached, generally with hydrogen peroxide. The purpose of the process is to remove the lignin from the cellulose in the wood fibers that are placed in side larger pressure vessels that are called digesters.
It depends on the pulping process and the origin of the raw material. 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. Kraft pulping has replaced the older soda process, in which sodium hydroxide was the primary pulping chemical. The kraft process also known as kraft pulping or sulfate process is an industrial process for conversion of wood into wood pulp consisting of almost pure cellulose fibers treatment of wood chips with a mixture of sodium hydroxide and sodium sulfide, known as liquor, that breaks the bonds that link lignin to the cellulose. Brightness may be achieved by either lignin removal delignification or lignin decolonization. Since the amount of bleach needed is related to the lignin content of the pulp, the kappa number can be used to monitor the effectiveness of the ligninextraction phase of the pulping process. The kraft process, also referred to as the sulfate process or as kraft pulping, is a process used to produce paper pulp. Pdf handbook of pulping and papermaking semantic scholar.
A process of producing cooking liquor for addition to a digester for enhancement of the yield derived from kraft pulping of wood chips in which a portion of the black liquor is treated with lime under certain conditions and then reused as cooking liquor. T1 preextraction of hemicelluloses and subsequent kraft pulping part i. This process evolved from the soda pulping process which was patented in 1884 by the german chemist c. Sulfate cooking a commercially dominating and continuously. The kraft process is a process for conversion of wood into wood pulp, which consists of almost. N2 a mild alkaline treatment was applied to aspen chips prior to kraft pulping in order to extract hemicelluloses for use as biofuels. The spent liquor is later regenerated to white liquor in the causticizer. Magnesium bisulfite pulping and papermaking with southern. Sulfite cooking liquor used in the process consists of free sulfur dioxide obtained by the burning of sulfur or by the roasting of iron pyrites, dissolved in water at a concentration of. Two chemical pulping methods exist using sodium sulfate kraft and sodium sulfite.
These are air and water pollution and the high investment costs. These pulps fulfil the demand for chlorinefree products in the hygiene paper sector and also in printing and writing papers. Lignin remains a major constituent of pulp even after digestion by chemical pulping. Kraft process is the foremost pulping process in the board and paper industry and the biggest lignin supplier. The kraft process entails treatment of wood chips with a hot mixture of water.
The kraft pulping process is much more tolerant of bark because most bark particles are soluble in the alkaline liquor. Today this process is most widely used with a production of 7080% of the total pulp. About million tons per year of kraft pulp are produced worldwide bruijnincx et al. The kraft pulping process is the dominant manufacturing process by which wood chips are transformed into pulp, the intermediate material from which a very broad spectrum of finished or semifinished paper products are made. Although soft wood are mostly used but any type of soft or hard pulp wood can be used for kraft pulp manufacturing. This process is also the most intensive steam user among pulping. Economical of pulping chemicals in the kraft process was a necessity in order for it to compete with the sulfite process, which. The main source of water pollution in the kraft process are the effluent. The high strength of kraft pulp, the ability of the process to handle. However, the kraft pulping process shows some disadvantages, among which include low yield wood conversion into pulp, high investment for the implementation of pulp production mills, high production cost, and the generation of odorific gases gomide et al. It may be received as bolts short logs of roundwood with the bark still attached, as chips about the size of a halfdollar that may have been produced from sawmill from debarked round wood elsewhere. The kraft pulping process we make kraft pulp by mixing wood fibres with a solution of caustic soda and sodium sulphide, and cooking them inside a digester. Alkaline kraft pulping is the dominant chemical pulping process today, but it has some serious shortcomings.
First commercially viable kraft mill, sweden, 1885. 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 kraft paper process is particularly efficient because it involves continuous recycling of raw materials. Economical of pulping chemicals in the kraft process was a necessity in order for it to compete with the sulfite process, which from the very beginning, in 1874, re. Influence of sulfidity and active alkali charge on the. The kraft process alone accounts for over 80 percent of the chemical pulp produced in the united states. Environmental protection agency office of science and technology engineering and analysis division 401 m street, s. Kraft process last updated february 20, 2020 international paper. For every ton of pulp produced, the kraft pulping process. This process is also the most intensive steam user among pulping processes. 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. This separates the fibres from the lignin, which is a natural gluelike substance that binds them together. The white liquor chemically dissolves the lignin that binds the cellulose fibers together. The most common are short ton 2,000 lb 907 kg metric tonne 1,000 kg 2,204 lb.
Dec 31, 2014 it is manufactured by alkaline method. The pulping digester operates at about 175 c for 25 h. Pollution prevention technologies for the bleached kraft segment of the u. Mechanical, semichemical, and sulfite pulp mills differ in detail, particularly in wood preparation, fiber separation, and bleaching, but many of the downstream refining. During the 1870s the sulfite process for pulping wood was the subject of experimental work in sweden, england, germany, and austria. 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. Kraft process variability reduction in pulping, washing and bleaching. Catalysisa potential alternative to kraft pulping alan w. The chemical reactions in kraft pulping process pulp paper mill. Technical support document for best management practices. 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. The chemical reactions in kraft pulping process pulp.
The kraft process differs from the sulfite process in that 1 the cooking liquor is alkaline and therefore is less corrosive to iron and steel, so that the. A thorough analysis of the kraft pulping process makes it obvious why it has dominated for over a century as an industrial process with no replacement in sight. Process integration studies on kraft pulpmill based. Kraft and modified kraft pulping of bamboo phyllostachys bambusoides 81 chips were screened scancm 40. Preparation of wood pulp by sulfate kraft process nptel. For many decades the sulfite process was the leading process for. Organosolv has several advantages when compared to other popular methods such as kraft or sulfite pulping. Kraft process, from german kraft, strong, chemical method for the production of wood pulp that employs a solution of caustic soda and sodium sulfide as the liquor in which the pulpwood is cooked in order to loosen the fibres. Kraft pulping is a full chemical pulping method using sodium hydroxide and sodium. Chemical pulping is a means of removing lignin from. Preextraction of hemicelluloses and subsequent kraft.
In this process lignin goes into the reactions with the cooking liquor chemicals and split into fragment. Pdf kraft pulping of reduced metal content eucalyptus wood. Possibilities for improving the pulping process peter axegard stfi, swedish pulp and paper research institute peter. Chemical pulping is the most common pulping process. Technical support document for best management practices for spent pulping liquor management, spill prevention, and control u.