Lime-kiln

Lime kilns are sometimes built in a shaft-furnace configuration. Fuel and air are fed into the descending column of pebble-size limestone from burner beams across the 

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If a plant cmshes to obtain stone of 0.6 and 7.6 cm for lime-kiln feed, coarse aggregate, or fluxstone, much undersized material is also produced. Oversized material can be reduced by recycling through the cmsher system, but the subsized stone, called spall, is wasted in a spall pile. Such spalls have potential value as by-products for use as, eg, asphalt (qv) filler. 

Much of the equipment used in the recovery system is identical with or closely related to equipment used in other chemical industries. This includes multiple-effect evaporators, and forced-circulation concentrators, causticizing equipment, and lime kiln. The function and nature of equipment essentially unique to the kraft recovery system are discussed herein. 

The white Hquor is separated from the calcium carbonate by decantation in a clarifier and is then available for a new cooking cycle. The underflow from the clarifier, which contains the calcium carbonate and is referred to as lime mud, is diluted with water and passed to a second clarifier known as the lime mud washer. The clarified weak white Hquor (weak wash) goes to storage and then enters the dissolving tank. The lime mud residue from the lime mud washer is passed to a rotary filter and subsequently to the lime kiln where calcium carbonate is converted back to calcium oxide, thus completing the lime cycle. 

Lime-Kiln Operation. Gases containing up to 40% carbon dioxide from the lime kiln pass through a cyclone separator, which removes the bulk of entrained dust. The gas is then blown through the two scmbbers, which remove the finer dust, cooled, and passes iato an absorption tower. Here carbon dioxide may be recovered by the sodium carbonate or Girbotol process. 

The sodium carboaate process is used ia a number of dry-ice plants ia the United States, although its operating efficiency is generaHy not as high as that of processes using other solutions. These plants obtain the carbon dioxide from flue gases as weH as lime-kiln gases. 

The carbonization by-products are usually refined, within the coke plant, into commodity chemicals such as elemental sulfur (qv), ammonium sulfate, benzene, toluene, xylene, and naphthalene (qv) (see also Ammonium compounds BTX processing). Subsequent processing of these chemicals produces a host of other chemicals and materials. The COG is a valuable heating fuel used mainly within steel (qv) plants for such purposes as firing blast furnace stoves, soaking furnaces for semifinished steel, annealing furnaces, and lime kilns as well as heating the coke ovens themselves. 

Some commercial performance data for cement and lime kilns are shown in Table 12-20. 

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

Lime kiln Particulates (dust), H2S Venturi scrubbers... 

Electric submerged-arc furnaces Dust-handling equipment Smelt tanks and lime kilns Recovery furnaces Digester, washer, etc. ... 

Lime kilns dust emissions are controlled by baghouse systems. Kiln fuels can be selected to reduce SO, emissions however, this is not normally a problem, since most of the sulfur dioxide that is formed is absorbed in the kiln. 

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

Figure 1. Material balance diagram for fuel savings in a 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. 

Kalk-hiitte,/. lime kiln, -hydrat, n. hydrate of lime (calcium hydroxide). 

Tampella recovery system, falling film black liquid evaporation, lime kiln modifications... 

Calcining. In the calcining process, the lime mud removed from the white liquor is burned to regenerate lime for use in the lime mixing step. The vast majority of mills use lime kilns for this process, although a few mills now use newer fluidized bed systems in which the reactants are suspended by upward-blowing air. 

Calcining (lime kiln) Lime mud Lime Fine and coarse particulates Air... 

In general, PM emissions limits are established on a per ton of pulp produced basis or for specific processes (e.g., lime kilns, smelt tanks, and recovery furnaces). Certain states have also established opacity limits and performance standards for specific processes. Investigations related to the integrated rulemaking identified 17 states with regulations specific to the pulp and paper industry. 

Jarvensivu, M., Saari, K., and Jamsa-Jounela, S.L., Intelligent control of an industrial lime kiln process, Contr. Eng. Pmc., 9, 589, 2001. 

The types of reactions involving fluids and solids include combustion of solid fuel, coal gasification and liquefaction, calcination in a lime kiln, ore processing, iron production in a blast furnace, and regeneration of spent catalysts. Some examples are given in Sections 8.6.5 and 9.1.1. 

Alternate Gas Wood chips LHV Lime kiln, boiler 200 14.7 649-815 Hot Air 745-801... 

Lurgi Energy Bark LHV Lime kiln firing 120 14.7... 

Foster Wheeler Wood LHV Lime kiln firing, 16 14.7 905 Air 700... 

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