Black liquor concentration

Black-liquor concentration Effluent disposal and water reuse... 

Rosenblad, A. E., "Evaporator Systems For Black Liquor Concentration", Chemical... 

Black Liquor Soap Recovery. Black Hquor soap consists of the sodium salts of the resin and fatty acids with small amounts of unsaponifiables. The soap is most easily separated from the black Hquor by skimming at an intermediate stage, when the black Hquor is evaporated to 25% soHds (7). At this soHds level, the soap rises in the skimmer at a rate of 0.76 m/h. At higher soHds concentrations, the tall oil soap is less soluble, but higher viscosity lowers the soap rise rate and increases the necessary residence times in the soap skimmer beyond 3—4 hours. The time required for soap recovery can be reduced by installing baffles, by the use of chemical flocculants (8,9), and by air injection into the suction side of the soap skimmer feed pump. Soap density is controUed by the rate of air injection. Optimum results (70% skimmer efficiency) are obtained at a soap density of 0.84 kg/L (7 lb/gal). This soap has a minimum residual black Hquor content of 15% (10—12). 

Black Liquor Soap Acidulation. Only two-thirds of a typical black Hquor soap consists of the sodium salts of fatty acids and resin acids (rosin). These acids are layered in a Hquid crystal fashion. In between these layers is black Hquor at the concentration of the soap skimmer, with various impurities, such as sodium carbonate, sodium sulfide, sodium sulfate, sodium hydroxide, sodium Hgnate, and calcium salts. This makes up the remaining one-third of the soap. Cmde tall oil is generated by acidifying the black Hquor soap with 30% sulfuric acid to a pH of 3. This is usually done in a vessel at 95°C with 20—30 minutes of vigorous agitation. Caution should be taken to scmb the hydrogen sulfide from the exhaust gas. 

Disk or cascade evaporators are used in the pulp and paper industry to recover heat and entrained chemicals from boiler stack gases and to effect a final concentration of the black liquor before it is... 

Recovery of inorganic chemicals is crucial to the cost effectiveness of the Kraft process. The black liquor which is obtained from delignification is rich in solubilised lignin and carbohydrate degradation products and, after concentration, is combusted in a recovery furnace. The Carbon dioxide which is produced during combustion converts unused sodium hydroxide into sodium carbonate. In addition, the sodium sulfate is converted, under the reducing atmosphere of the furnace, to sodium sulfide. 

The pH of the obtained black liquor was 12. 45 and its density 1.02 g/iuL. The soda lignin was then precipitated from the concentrated black hquor by acidifying it to pH 2 using 20% concentrated sulfuric acid (H SO ). The precipitated hgnin was then filtered and washed with water adjusted to pH 2 using H SO. Then, the soda lignin was dried in a vacuum oven at 55°C for 24 hours prior to further analysis [12]. 

Figure 9. Influence of sodium hydroxide concentrations in the eluent on fractionation of lignins in draft black liquor. Column Sephadex G-50. (Reprinted with permission from ref. 3. Copyright 1976 Wiley.)...

Lignin Concentration. Lignin concentrations have been examined in the range of 10 to 100 g/L. These concentrations represent concentrations normally present in black liquors and therefore are of industrial relevance. Typical lignin concentrations in black liquor range from 50 g/L for 15% solids to over 300 g/L at firing. 

Acetates. Anhydrous iron(II) acetate [3094-87-9], Fe(C2H302)2, can be prepared by dissolving iron scraps or turnings in anhydrous acetic acid ( 2% acetic anhydride) under an inert atmosphere. It is a colorless compound that can be recrystallized from water to afford hydrated species. Iron(II) acetate is used in the preparation of dark shades of inks (qv) and dyes and is used as a mordant in dyeing (see Dyes AND DYE intermediates). An iron acetate salt [2140-52-5] that is a mixture of indefinite proportions of iron(II) and iron(III) can be obtained by concentration of the black liquors obtained by dissolution of scrap iron in acetic acid. It is used as a catalyst of acetylation and carbonylation reactions. 

Starting Material. A drum of concentrated, mixed, southern pine kraft black liquor was kindly supplied by the Canton, N. C. mill of the Champion Paper and Fibre Co. Analytical data for the liquor indicated 49.7% total solids and a methoxyl content of the oven-dried solids of 5.54%. The pH of the liquor as received was 12.3. (All melting points are uncorrected. Infrared absorption spectra were determined by Mr. Lowell Sell of The Institute of Paper Chemistry Analytical Group.)... 

Tall oil is the generic name for the oil obtained upon acidification of the black liquor residue from kraft pulp digesters. Kraft processing dissolves the fats, fatty acids, rosin, and rosin acids contained in pinewoods in the form of sodium salts and when the black liquor is concentrated to make it possible to recover some of its chemical and heating value, the soaps become insoluble and can be skimmed off. The brown, frothy curd thus obtained is then made acidic with sulfuric acid, converting the constituents to a dark-brown fluid (tall oil). 

Yields of 50% and reduced energy consumption have been achieved by a history of innovation. Such innovation has included the Tomlinson black liquor recovery boiler, the Kamyr continuous digester and associated diffusion washer, multiple-effect evaporators, and low-odor concentrators. Economic advantages also have been gained by the development of systems for recovering extractives such as tall oil, fatty acids, and resin from the pulping liquor for sale as naval stores. Future innovations may focus on the lime kiln and other related systems. 

Numerous attempts have been made to produce other low molecular weight products from lignin by subjecting concentrated kraft black liquors directly to various treatments, including hydrogenation, oxidation, or only heating in the presence of excess alkali. 

The separated liquor, which is very dark, is known as black liquor. It is concentrated in multi-effect evaporators to 60-65 percent... 

The spent black liquor from the kraft pulping of pines contains the less volatile products of the wood resin in the form of sodium salts or soaps. The liquor first is concentrated in multiple-effect evaporators, and then the concentrate is sent to settling tanks. The soaps rise to the surface, are skimmed off, and then are acidified with sulfurous or sulfuric acid. The crude tall oil rises to the top and is mechanically separated. Crude tall oil from southern pines contains 40-60 percent resin acids and 40-55 percent fatty acids with 5-10 percent neutral substances. These components are separated by fractional distillation under vacuum. 

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