Papermaking Kraft Pulping Process

While the Kraft process initially had two distinct disadvantages, it produced a dark pulp and required chemical recovery, the pulp is stronger and has better dimensional stability than in the old soda process. Chemical recovery systems rapidly became quite advanced and most advanced mills are now aiming for 98-99% chemical recovery. 

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The Kraft pulping is the predominant process used in papermaking. This process involves the high temperature cooking of wood fibers in alkali, followed by the extraction of the colored lignin, using oxidative chemicals [136]. The treatment of wood pulp with hemicellulases has been shown to be a feasible way to enhance the extraction of lignin, in the... 

The basic experiment that demonstrated the effects of molecular ordering is a rather simple one. Southern pine chips were delignified using the acid chlorite process at 60°C, then extracted with caustic solutions to remove the hemicelluloses. The pulp was then divided into two batches. One was used as a control the other was immersed in distilled water inside stainless steel vessels and heated through the temperature cycle of a typical kraft cook. During this cycle, the pulp was held at 170°C for approximately 2 h. The two batches of pulp were then used to make handsheets, and their papermaking properties were compared. 

Barium sulphate is also becoming a rather common scale, particularly in closed pulp mills. When it occurs, the problem of its formation is exbemely troublesome as it is a salt with very low solubility. Because barium sulphate is a salt of such low solubility, barium sulphate scale may form even if barium concenbation, relative to other cations, is low, particularly when concentration in the system of sulphate ions is high. Barium is dissolved from the wood in the digester. The sulphate ion comes into the system through additives such as alum, and high sulphate ion concenbation may develop as a result of accumulation of the sulphate ion from papermaker s alum (used in the rosin sizing process) or from sulphuric acid used for pH conbol. A particular problem is Barium sulphate deposition in the headbox of Kraft liner machines. 

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