Rotary fine lime

As with most powders, fine quicklime may compact, leading to arching . Bunkers should, therefore, be fitted with aeration pads, vibrators or mechanical devices to break any hold-ups. Conversely, aerated fine lime flows readily and equipment to prevent flooding , such as rotary valves, should be fitted to silo discharges. 

Raw Materials. The basic raw materials limestone and coke or coal (qv) should be high quaHty. Limestone should contain a minimum of 95—97% CaCO and a maximum of 1.5% MgCO, 1—1.5% Si02, 1% Fe202 plus AI2O2, and 0.006% phosphoms (see Lime and limestone). The limestone is first converted to lime in a rotary or vertical shaft kiln. The lime is screened to eliminate fines that interfere with the evolution of carbon monoxide in the smelting process. 

Pregnancy, exposure to organic solvents during, 23 119 Preheater rotary kiln, 25 53 Preheat trains, 23 221-223 Preinstalled piping system, in fine chemical production, 2 2 428-429 Prekallikrein, 4 86-87 Prekallikrein activator (PKA), 22 145, 146 Pre-liming, in beet juice purification, 23 459... 

Rotary wheel atomizers require 0.8 to 1.0 kWh/1000 L. The lateral throw of a spray wheel requires a large diameter to prevent accumulation on the wall the ratio of length to diameter of 0.5 to 1.0 is in use in such cases. The downward throw of spray nozzles permits smaller diameters but greater depths LID ratios of 4 to 5 or more are used. Spray vessel diameters of 15 m (50 ft) or more are known. Liquid/gas ratios are 0.2 to 0.3 gal/MSCF. Flue gas enters at 149°C (300°F) at a velocity of 2.44 m/s (8 ft/s). Utilization of 80 percent of the solid reagent may be approached. Residence times are 10 to 12 s. At the outlet the particles are made just dry enough to keep from sticking to the wall, and the gas is within 11 to 28°C (20 to 50°F) of saturation. The fine powder is recovered with fabric filters. In one test facility, a gas with 4000 ppm S02 had 95 percent removal with lime and 75 percent removal with limestone. 

Manufacture Finely powdered chromate, FeO.Cr Oj, is mixed with sodium carbonate and slake lime. It is heated and melted in a rotary kiln to 10001300 0, Water is poured into the product and sodium chromate is extracted as a solution. Sulphuric acid is added to the solution until the pH value becomes about 3i thus producing sodium bichromate, Ua r Orj 0 Insoluble matter is removed and the solution is concentrated by vacuum evaporation. A theoretical amount of potassium chloride is added to the solution and it is cooled to obtain raw crystals of potassium bichromate, Kj>Cra07, which are purified further by recrystallization. 

Probably the rotary horizontal kiln is the most versatile, since it allows a feed of lumps or fines of limestone or marble, or wet or dry calcium carbonate sludges (Fig. 7.1). The main component of this calcination system is a 2.5- to 3.5-m diameter by 45- to 130-m long firebrick-lined inclined steel tube. Heat is applied to the lower end of this via oil, gas, or coal burners [7]. The feed to be calcined is fed in at the top end. Slow rotation of the tube on its axis gradually moves the feed down the tube, as it tumbles countercurrent to the hot combustion gases. In this way, wet feed is dried in the first few meters of travel. Further down the tube, carbon dioxide loss begins as the temperature of the feed rises. By the time the solid charge reaches the lower, fired end of the kiln it reaches temperatures of 900-1,000°C and carbon dioxide evolution is virtually complete. Normally the temperature of the lower end of the kiln is not allowed to go much above this as it reduces the life of the kiln lining. It also adversely affects the crystal structure of the lime product since it produces a dead-burned or overburned lime. Overburned lime is difficult to slake to convert it to calcium hydroxide and raises... 

A feature of rotary kilns is the formation of rings . These consist of an accumulation of material on the refractory in a part of the kiln which has the appropriate temperature for a semi-liquid phase to form. Such rings can form from ash in coal-fired kilns and from calcium sulfate deposits. Alkalis (sodium and potassium oxides), clay and lime can contribute to the build-ups, which can be troublesome. In the case of coal-firing, fine grinding of the fuel can significantly reduce the rate of build-up. 

The fines fraction in ROK lime from rotary kilns also contains enhanced levels of impurities. It does not, however, contain a significant amount of over-burned lime, as the fines tend to concentrate at the centre of the rotating bed and are insulated by the larger particles. This enables the % CaCOs in the coarser fractions to be reduced to low levels without over-burning. 

One non-standard desulfurisation technique, used on a rotary kiln by a producer of calcined dolomite, is to include finely divided dolomite in the feedstone. The fines calcine, become airborne as a result of the action of the kiln internal fittings (i.e., trefoils and lifters), and remove a significant amount of the sulfur dioxide. It is not known whether this technique would be as successful with high calcium limestone, which calcines at higher temperatures than dolomite. Other techniques will no doubt be evaluated, such as the injection of hydrated lime into the back-end of the kiln. The cost-effectiveness of such techniques in relation to alternatives, and their effects on kiln operation, would need to be assessed. 

Kiln dusts (KD) are fine by-products of Portland cement and lime high-tem-perature rotary kiln production operations [88-98] that are captured in the air pollution control dust collection systems (cyclones, electrostatic precipitators, and baghouses). Different types of KD are discussed in Table 4. 

Cements Portland cement is produced by heating a mixture of clay and lime-bearing minerals in a rotary Idln. The resulting clinker is ground into very fine particles to which a small amount of gypsum is added. 

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