Black liquor, composition

Cortinas et al. [89] eliminated colloidal suspended material (pitch) from kraft black liquors and partly recycled the liquor to the digester to reduce the consumption of chemicals. The colloidal pitch is formed by wood extractives. In particular, compounds such as waxes, sterols, and sterol esters that do not form soluble salts or dissolve during cooking form colloidal particles. The concentrated liquors (14%-15% solids) were filtered at high temperature using a 0.2 xm alumina membrane (USF Shumacher, Crailsheim, Germany). The pitch was almost completely retained (>99.9%), but the flux was sensitive to the black liquor composition and sometimes decreased to less than 100 L/(m h). 

Table 6.6 Average chemical composition of gaseous produets from the precipitate from black liquor at different temperatures...

COMPOSITION OF SPENT PULPING LIQUORS 10.4.1 Kraft Pulping Liquors (Black Liquors)... 

Table 4 shows the typical ranges of black liquor constituents and characteristics of Kraft evaporator condensates. The composition of liquors may vary significantly, depending upon the type of raw material used. Inorganic constiments in black liquor are sodium hydroxide, sodium sulfate, sodium thiosulfate, sodium sulfide, sodium carbonate, and sodium chloride [11]. 

Variations found in CTO composition result primarily from the species of wood pulped and the location and climate where the trees are grown. Pulping process variations further affect CTO composition. The best CTO is produced from pine wood. However, many U.S. mills mix hardwood with pine to reduce fiber costs, or mix hardwood black liquor with pine blackliquor. This lowers the rosin content. The composition of CTO produced in the southeastern United States and of typical Canadian and Scandinavian CTOs are shown in Table 2. 

Derivation The spent black liquor from the pulping process is concentrated until the sodium salts (soaps) of the various acids separate out and are skimmed off. These are acidified by sulfuric acid. Composition and properties vary widely, but average 35—40% rosin acids, 50-60% fatty acids. 

In the earlier operations, the spent wash from both ethanol and butanol fermentations was evaporated to between 40 and 45% solids and then incinerated in a purpose-developed, spray dryer-cum-incinerator in which the organic matter supported its own combustion, on much the same principle as a black liquor furnace, yielding an ash with about 35% K2O content, which was sold to the fertilizer compounders. Then it was found that a better return could be obtained by separating the two different types of spent wash from the ethanol and the butanol fermentations. The butanol fermentation residues contained vitamins of the B group, so this material, after concentration in a multiple effect evaporator, was dried on double-drum dryers to yield a dry powder with the following interesting composition ... 

Table 3A.3 Typical composition of kraft black liquors (% of total dry matter) Component Pine Birch...

Whitty K, Backman R, Hupa M. An empirical rate model for black liquor char gasification as a function of gas composition and pressure. ProcAdv For Prod AIChE Symp Ser 1994 90(302) 73-84. Frederick WJ, NoopilaT, Hupa M. Combustion behavior of black liquor at high sohds firing. Tappi J 1991 74(12) 163-70. 

Typical compositions for softwood and hardwood kraft black liquors are shown in Table 9. Most commercial kraft lignins are sulfonated kraft lignins or lignin amines. A few nonsulfonated products are, however, available. 

With a few exceptions, coatings and linings are not used on the water and steam sides. In an EPRI project, about 50 turbine blade coatings have been evaluated, but none of these are being routinely applied. To reduce steam side oxidation in reheaters and superheaters, chromizing and chromating have been developed but these treatments are also not routinely applied. There is little use of composite materials with the exception of condenser tube sheets, which could be made of explosively clad stainless steel or titanium on carbon steel, and of the surfaces in the primary cycles of nuclear units where carbon or low alloy steels are protected by weld-deposited stainless steels. In pulp mill black liquor recovery boilers, stainless steel clad boiler tubes are often used. 

A methodology based on the minimisation of Gibbs free energy has been successfully adopted to describe the chemical composition of an industrial black liquor recovery boiler smelt. Moreover, the chemical composition reported in the literature from other industrial sources could also be satisfactorily reproduced using this technique. 

Sterols are synthesized in both plants and animals. Sterols and their derivatives, such as hormones and vitamin D2, perform various important functions in living organisms depending on their structure. Consequently, sterol products can be derived from several sources. Plant sterols, or phytosterols, are obtained from the unsaponifiable fraction of vegetable oils and fats. The amount of sterol, as well as its composition including fraction of unsaponifiable portion of the respective oil and fats, depends on the raw materials and is characteristic of the particular base material (Table 1). Soya oil represents a widely available source for commercial production of phytosterols. The unsaponifiable portion is separated into a sterol fraction and a tocopherol fraction. A small amount of tocopherol is usually left in the sterol fraction (approximately 4%), which acts as a natural antioxidant in the final product [2]. Plant sterols are also obtained from the black-liquor soap skimming in commercial pulping of wood. The neutral fraction of this so-called tall oil is relatively rich in sterols (approximately 32% of the neutral fraction [3]), and the sterol... 

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