Limestone operability

Ammonia from coal gasification has been used for fertilizer production at Sasol since the beginning of operations in 1955. In 1964 a dedicated coal-based ammonia synthesis plant was brought on stream. This plant has now been deactivated, and is being replaced with a new faciUty with three times the production capacity. Nitric acid is produced by oxidation and is converted with additional ammonia into ammonium nitrate fertilizers. The products are marketed either as a Hquid or in a soHd form known as Limestone Ammonium Nitrate. Also, two types of explosives are produced from ammonium nitrate. The first is a mixture of fuel oil and porous ammonium nitrate granules. The second type is produced by emulsifying small droplets of ammonium nitrate solution in oil. 

Purification of Carbide Acetylene. The purity of carbide acetylene depends largely on the quaUty of carbide employed and, to a much lesser degree, on the type of generator and its operation. Carbide quahty in turn is affected by the impurities in the raw materials used in carbide production, specifically, the purity of the metallurgical coke and the limestone from which the lime is produced. The nature and amounts of impurities in carbide acetylene are shown in Table 4. 

Limestone Production. Because more than 99% of U.S. limestone is sold or used as cmshed and broken stone, rather than dimension-stone, most of the description of limestone s extraction and processing herein focuses on the former (Fig. 4). Most stone is obtained by open-pit quarrying methods. Underground mining is pursued by some important operations, but the toimage quarried exceeds that mined by nearly 20-fold. There is, however, a slight trend toward increased mining which should continue. 

Miscellaneous Kilns. A U.S. kiln, the Fluo-Sohds, appears to be another vertical kiln type, but this is its only similarity. It operates on a different principle. It utilizes as kiln feed only a discrete granulation of 0.225—2.4 mm (65—8 mesh) sizes. DeHcately controlled by air and exhaust gas pressure, the kiln feed of granules is fluidized as a dense suspension. Because it is instmmented, this kiln can produce a very reactive lime at better than average thermal efficiency. The kiln, however, has limited utifity because the cost of obtaining the kiln feed with many hard, compact limestones is prohibitive. 

Portland Cement Manufacture. The second greatest use of limestone is as raw material in the manufacture of Pordand cement (10). The average limestone factor per ton of Pordand cement is 1.0—1.1 t of pulverized limestone. The limestone, calcined to lime in the cement rotary kiln, combines with siUca and alumina to form tricalcium siUcate and tricalcium aluminate and other lesser cementing compounds (see Cement). Most cement companies operate captive limestone quarries. 

Drying a.nd Calcination. The simplest pyrometaHurgical operation is the evaporation of free water and the decomposition of hydrates and carbonates. A typical reaction is the decomposition of pure limestone [1317-65-3] CaCO, to calcium oxide [1305-78-8] and carbon dioxide ... 

Pig iron consists of iron combined with numerous other elements. Depending on the composition of the raw materials used in the blast furnace, principally iron ore (beneficiated or otherwise), coke, and limestone, and the manner in which the furnace is operated, pig iron may contain 3.0—4.5% carbon, 0.15—2.5% or more manganese, as much as 0.2% sulfur, and 0.025—2.5% phosphoms siUcon can be as low as 0.15% with modern techniques and is almost always less than 0.8%. Sulfur, phosphoms, and siUcon can be reduced significantly by treating the hot metal between the blast furnace and the steelmaking vessel. During the steelmaking process, many but not all solutes are reduced, often drastically. 

Coal pipelines have been built in countries such as France (8.8 km), and Russia (61 km), and pipelines are also used for transporting limestone, copper concentrates, magnetite, and gHsonite in other parts of the world. The first coal pipeline, built in Ohio, led to freight rate reductions. The pipeline stopped operation after introduction of the unit train, used exclusively to transport coal from the mine to an electric power generation station. 

Whereas an explosion from methane tends to be localized, it may start coal dust explosions resulting in more widespread injury and loss of life. AH coal breaking operations result in formation of fine coal particles some are controlled with water during the mining operation. Breakage associated with hauling disperses dust, and dust accumulations can be made safe by rockdusting. Powdered limestone is spread over the mine surfaces to cover the dust. 

In ECS s 1986 repowefing project Babcock and Wilcox (B W) constmcted a bubbling-bed section to ECS s existing 125 MWe pulverized-coal furnace to produce 31.3 t/h of lime, usiag cmshed coal as the source of heat to calciae limestone ia the fluidized bed. A portion of the lime is drawn from the bed as bottom ash and a portion is collected as fly ash. Both portions are transferred to a cement (qv) plant adjacent to the boiler. The hot flue gas from the EBC flows iato the existing main pulverized-coal furnace, ia which a B W LIMB system was also iastaHed to absorb sulfur dioxide dufing those times when the EBC is not operating. 

PressurizedFIuidized-Bed Combustors. By 1983 the pressurized fluidized-bed combustor (PFBC) had been demonstrated to have capacities up to 80 MWt (49). PFBCs operate at pressures of up to 1500 kPa (220 psi) and fluidization velocities of 1—2 m/s. Compared to an AFBC of the same capacity, a PFBC is smaller, exhibits higher combustion efficiencies with less elutfiation of fine particles, and utilizes dolomite, CaCO MgCO, rather than limestone to capture SO2. 

Wet-Throwaway Processes. By 1978, three wet-throwaway systems were in commercial operation lime scmbbing, limestone slurry scmbbing, and dual alkah (1). Time/limestone wet scmbbing (Fig. 11) remains the most common post-combustion control technique appHed to utiHty boilers (67). The waste product from the scmbbers can either be sent to a landfill or be upgraded by oxidation to become saleable gypsum. 

Fluidized combustion of coal entails the burning of coal particles in a hot fluidized bed of noncombustible particles, usually a mixture of ash and limestone. Once the coal is fed into the bed it is rapidly dispersed throughout the bed as it bums. The bed temperature is controUed by means of heat exchanger tubes. Elutriation is responsible for the removal of the smallest soHd particles and the larger soHd particles are removed through bed drain pipes. To increase combustion efficiency the particles elutriated from the bed are coUected in a cyclone and are either re-injected into the main bed or burned in a separate bed operated at lower fluidizing velocity and higher temperature. 

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