White liquor, pulp

White Liquor pulp mill 9 " white water, paper 9 " " mill... 

White Liquor pulp mill 9 Acceptable no effect Noryl GE Plastics... 

Kraft pulping is a common process in the paper industry. Figure 8.4 shows a simplifled flowsheet of the process. In this process, wood chips are reacted (cooked) with white liquor in a digester. White liquor (which contains primarily NaOH, NaiS, Na2C03 and water) is employed to dissolve lignin from the wood chips. The cooked pulp and liquor are passed to a blow tank where the pulp is separated from the spent liquor weak black liquor which is fed to a recovery system for... 

Consid - the Kraft pulping process shown in Fig. 8.8 (Dunn and El-Halwa, 1993). The first step in the process is digestion in which wood chips, containing primarily lignin, cellulose, and hemicellulose, are cooked" in white liquor (NaOH, Na2S, Na2C03 and... 

Wood chips are processed in mild chemical liquor and subjected to mechanical refining using disc refiners. Semichemical pulping liquors have variable composition ranging from sodium hydroxide alone, alkaline sulfite (sodium sulfite - - sodium carbonate), mixtures of sodium hydroxide and sodium carbonate, to Kraft green or white liquors [3]. Sodium sulfite/ sodium carbonate liquor is most commonly used and the pulp product obtained thereafter is referred to as neutral sulfite semichemical (NSSC) pulp. 

One of the critical units in the production of paper is a reactor called a digester. In the kraft process this reactor is a two-phase tubular reactor in which the lignin that binds the wood chips together is broken down through a combination of chemical and thermal effects. The white liquor (aqueous solution of sodium hydroxide and hydrosulfide) and solid wood chips flow countercurrently in some zones and co-currently in others. The residence time of the pulp is about 10 h. 

Sulfate or kraft pulping is performed with a solution composed of sodium hydroxide and sodium sulfide, named "white liquor." According to the... 

Of the stabilization methods, the polysulfide pulping process is of practical importance. The influence of polysulfides is based on a specific oxidation of the end groups to carboxyl groups via glucosone intermediates (cf. Section 8.1.3). Polysulfides can be prepared by catalytic oxidation of sulfide in the white liquor or by adding elemental sulfur into the kraft cooking liquor ... 

The Na2S does not react with the lime, so the resultant mixture of NaOH and Na2S (called white liquor ) can be reused to pulp more wood. The CaC03 sludge is filtered off, burned in a lime kiln, and reused. Thus, the chemical... 

In the Kraft recovery process the green liquor, which is an aqueous solution of sodium carbonate, is heated with lime to produce white liquor or caustic soda, which is then returned to the pulp digestion operations. In the production of alumina, lime and soda are fed to bauxite digesters. The CaCO 3 produced during the course of the reaction is rebumed to lime and is recycled. The main difficulties associated with these processes include the extensive mechanical handling through the use of causticizers, settlers, and repulpers in order to produce caustic that is low in carbonate and the high fuel consumption needed to reconvert CaCO to lime. 

TABLE 15.8 Typical Analysis of White Liquor Used for Kraft Pulping"... 

For pulping purposes, the effective alkali present is higher than the actual sodium hydroxide concentration in the white liquor because of the existence of an hydrolytic equilibrium between sodium sulfide and sodium hydrogen sulfide (Eq. 15.14). 

A typical analysis for kraft white liquor for pulping is given below in terms of the sodium oxide equivalence. This puts all the dissolved components on the same sodium ion content basis. Using this information, calculate the actual molarities present of the three dissolved components in this sample of kraft white liquor. 

Kraft pulping is carried with a solution of sodium hydroxide and sodium sulphide, the solution being known as white liquor. In the terminology used by the pulp and paper industry, the chemicals are calculated as sodium equivalents and expressed as weight of NaOH or Na20. Sodium sulphide is hydrolysed largely to a mixture of sodium hydroxide and sodium hydrosulphide ... 

J Gierer, L-A Smedman. The Reactions of Lignin during Sulfate Pulping. Part XL Reactions of Pinoresinol with Alkali and with White Liquor. Acto Chem Scand 25 1461-1467, 1971. 

Kraft pulping chemical recovery consists of passage of black liquor along with the slurry passes through evaporators, recovery boilers, and causticizers to eventually produce white liquor. Corrosion on the fireside of the recovery boiler is accelerated by the presence of reduced sulfur species. The hydroxide mixtures present in black liquor are extremely corrosive to the recovery boilers made of type 304 stainless steel (37). Several phenomena in the recovery section cause different forms of corrosion such as (i) corrosion under ash build-up (ii) corrosion in the thin condensation layers and (iii) high-temperature metal/gas interactions. 

During the past 35 years, the pulp and paper industry had moved from open-water systems to closed-loop systems, thereby increasing the severity of the environment. These white liquors are acidic and very corrosive, and severe crevice corrosion problems may occur whenever the process flow is halted. 

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