Lime pulp

This book will become a benchmark for the study of rotary kiln phenomena, for the design of new rotary kiln processes, and for the modeling and analysis of existing processes. It will be an indispensable addition to the bookshelves of engineers in the cement, lime, pulp and paper, and mineral industries. It will prove invaluable to researchers and academics studying the complexities of solid-gas flows, mixing, and transport processes. 

Unha.iring, Unhairing can be done either by a hair save or a hair pulp system. The hair pulp system is preferred by most tanners for its speed and labor efficiency. In the hair pulp system the hides are treated with sodium sulfide (sulfhydrate) and lime (calcium hydroxide). The hair is quickly destroyed by the strong alkaline reducing conditions. 

Rotary kilns and, to a lesser extent, Fluo-SoHds kilns are used to calcine a wet precipitated calcium carbonate filter cake in the kraft or sulfate paper-pulp process (15). Lime is regenerated for use as a causticization reagent in recovering caustic soda for pulp digestion. Losses in lime recovery are replaced by purchased lime (see Paper Pulp). 

Industrial Wastewater Treatment. Industrial wastewaters require different treatments depending on their sources. Plating waste contains toxic metals that are precipitated and insolubiHzed with lime (see Electroplating). Iron and other heavy metals are also precipitated from waste-pidde Hquor, which requires acid neutralization. Akin to pickle Hquor is the concentrated sulfuric acid waste, high in iron, that accumulates in smokeless powder ordinance and chemical plants. Lime is also useful in clarifying wastes from textile dyeworks and paper pulp mills and a wide variety of other wastes. Effluents from active and abandoned coal mines also have a high sulfuric acid and iron oxide content because of the presence of pyrite in coal. 

Modijications to the Recope Cycle. The recovery system is a principal capital cost in a kraft mill. Consequently, any recovery process that is less expensive to build can improve pulping economics. There have been numerous attempts to improve the kraft recovery process. Two examples are the direct alkaline recovery scheme (DARS) and the autocausticizing scheme using sodium borates (37). Both schemes eliminate the lime loop of the conventional kraft mill. As of 1996, neither is commercially used. 

Bleach Liquor. Bleach Hquor or lime bleach Hquor is an aqueous solution of calcium hypochlorite and calcium chloride. It typically contains 30—35 g/L of available chlorine, though it may be as high as 85 g/L. It has been used in pulp bleaching, when it can be made more cheaply than sodium hypochlorite. It is prepared on site by chlorinating lime solutions. 

Calcium sulfite [10257-55-3] and acid sulfite may be prepared by reaction of SO2 and hydrated lime or limestone. Calcium acid sulfite [13780-03-5] Ca(HS02)2, has been used to remove lignin (qv) from wood pulp in paper manufacture (6) (see Paper Pulp). 

The pH of the pulp to the flotation cells is carefliUy controlled by the addition of lime, which optimizes the action of all reagents and is used to depress pyrite. A frother, such as pine oil or a long-chain alcohol, is added to produce the froth, an important part of the flotation process. The ore minerals, coated with an oily collected layer, are hydrophobic and collect on the air bubbles the desired minerals float while the gangue sinks. Typical collectors are xanthates, dithiophosphates, or xanthate derivatives, whereas typical depressants are calcium or sodium cyanide [143-33-9] NaCN, andlime. 

Typical applications in the chemical field (Beaver, op. cit.) include detarring of manufactured gas, removal of acid mist and impurities in contact sulfuric acid plants, recovery of phosphoric acid mists, removal of dusts in gases from roasters, sintering machines, calciners, cement and lime Idlns, blast furnaces, carbon-black furnaces, regenerators on fluid-catalyst units, chemical-recoveiy furnaces in soda and sulfate pulp mills, and gypsum kettles. Figure 17-74 shows a vertical-flow steel-plate-type precipitator similar to a type used for catalyst-dust collection in certain fluid-catalyst plants. 

Kraft pulp mills Digesters hatch and continuous Mercaptans, methanol (odors) Condensers and use of lime kiln. 

Fig. 6-11. Schematic diagram of the kraft pulping process (6). 1, digester 2, blow tank 3, blow heat recovery 4, washers 5, screens 6, dryers 7, oxidation tower 8, foam tank 9, multiple effect evaporator 10, direct evaporator 11, recovery furnace 12, electrostatic precipitator 13, dissolver, 14, causticizer 15, mud filter 16, lime khn 17, slaker 18, sewer.

Pulp and paper Kraft recovery boiler Soda recovery boiler Lime kiln... 

In the pulp and paper industry, the main gas emissions are from the pulp production. The main sources of emission are in the soda recovery boiler, lime kiln, evaporation plant, and bark combustion boiler. 

The paper and pulp industries consume taif/e quantities of Ca(OH)2 and precipitated (as distinct from naturally occurring) CaCOs. The largest application of lime in pulp manufacture is as a causlicizing agent in sulfate (kraft) plants (p. 89). Here the waste NajC solution is reacted with lime to regenerate the caustic soda used in the process ... 

About 93% of the CaCOs mud is dried and lecalcined in rotary kilns to recover the CaO. Calcium hypochlorite bleaching liquor (p. 860) for paper pulp is obtained by reacting lime and CI2. 

Holz-kalk, m. pyrolignite of lime (crude calcium acetate), -kaiton, m. wood-pulp board, -kassle, /. cassia lignea, coarse cassia bark, -kasten, m. wooden box, case or vat. -kirsche. /. wild cherry. -kistchen, n. wooden box. -kitt, m. wood cement, joiner s putty, -klotz, m. wooden block, wood block, -kocher, m. (Paper) digester (for wood), -kokle,/. charcoal (from wood). 

Properties Commercial grades Uses Manufacture White to grayish-white solid. Reacts with water to form calcium hydroxide. Commercial lime is available in lump, pebble, ground, and pulverized forms. One of the oldest commercial chemicals. Used in hundreds of applications. The most important uses are for making steel and chemicals, water treatment, pollution control, pulp and paper, and construction. Limestone (calcium carbonate, CaCOj) from mines or quarries is heated in a kiln (calcined). 

The pulp is ground, neutralized with lime, and pressed. The press liquor is concentrated to make molasses for animal feed. The pressed pulp is dried and used as an animal feed. 

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