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Limestone & Calcium Carbide & Acetylene

 

 

 

 

 

Limestone

Limestone often contains variable amounts of silica in the form of chert or flint, as well as varying amounts of clay, silt and sand as disseminations, nodules, or layers within the rock. The primary source of the calcite in limestone is most commonly marine organisms. These organisms secrete shells that settle out of the water column and are deposited on ocean floors as pelagic ooze or alternatively is conglomerated in a coral reef (see lysocline for information on calcite dissolution). Secondary calcite may also be deposited by supersaturated meteoric waters (groundwater that precipitates the material in caves). This produces speleothems such as stalagmites and stalactites. Another form taken by calcite is that of oolites (oolitic limestone) which can be recognized by its granular appearance.

Uses include:

  • The manufacture of quicklime (calcium oxide) and slaked lime (calcium hydroxide);
  • Cement and mortar;
  • Pulverized limestone is used as a soil conditioner to neutralize acidic soil conditions;
  • Crushed for use as aggregate - the solid base for many roads;
  • Geological formations of limestone are among the best petroleum reservoirs;
  • As a reagent in desulfurizations;
  • Glass making, in some circumstances;
  • Toothpaste;
  • Suppression of methane explosions in underground coal mines
  • Added to bread as a source of calcium

 

Lime stone is used for manufacturing cement, as a building stone, as a flux in the metallurgy industry, for manufacturing Calcium Carbide and Calcium Cyanide etc.

There so much limestone resource in Turkiye.  The datas are in adition county by county. 

 

Calcium carbide

Calcium carbide is a chemical compound with the chemical formula of CaC2. The material is colorless, but most samples appear black through to grayish white lumps, depending on the grade. Its main use industrially is in the production of acetylene.

 

Calcium Carbide Manufacturing

Calcium carbide (CaC2) is manufactured by heating a lime and carbon mixture to 2000 to

2100°C (3632 to 3812°F) in an electric arc furnace. At those temperatures, the lime is reduced bycarbon to calcium carbide and carbon monoxide (CO), according to the following reaction:

CaO + 3C → CaC2 + CO

Lime for the reaction is usually made by calcining limestone in a kiln at the plant site. The sources of carbon for the reaction are petroleum coke, metallurgical coke, and anthracite coal. Because impurities in the furnace charge remain in the calcium carbide product, the lime should contain no more than 0.5 percent each of magnesium oxide, aluminum oxide, and iron oxide, and 0.004 percent phosphorus.

Also, the coke charge should be low in ash and sulfur. Analyses indicate that 0.2 to 1.0 percent ashand 5 to 6 percent sulfur are typical in petroleum coke. About 991 kilograms (kg) (2,185 pounds [lb])of lime, 683 kg (1,506 lb) of coke, and 17 to 20 kg (37 to 44 lb) of electrode paste are required toproduce 1 megagram (Mg) (2,205 lb) of calcium carbide.

The process for manufacturing calcium carbide is illustrated in Figure 1. Moisture is removed from coke in a coke dryer, while limestone is converted to lime in a lime kiln. Fines from coke drying and lime operations are removed and may be recycled. The two charge materials are then conveyed to an electric arc furnace, the primary piece of equipment used to produce calcium carbide.

There are three basic types of electric arc furnaces: the open furnace, in which the CO burns to carbon dioxide (CO2) when it contacts the air above the charge; the closed furnace, in which the gas is collected from the furnace and is either used as fuel for other processes or flared; and the semi-covered furnace, in which mix is fed around the electrode openings in the primary furnace cover resulting in mix seals. Electrode paste composed of coal tar pitch binder and anthracite coal is fed into a steel casing where it is baked by heat from the electric arc furnace before being introduced into the furnace. The baked electrode exits the steel casing just inside the furnace cover and is consumed in the calcium carbide production process. Molten calcium carbide is tapped continuously from the furnace into chills and is allowed to cool and solidify. Then, the solidified calcium carbide goes through primary crushing by jaw crushers, followed by secondary crushing and screening for size. To prevent explosion hazards from acetylene generated by the reaction of calcium carbide with ambient moisture, crushing and screening operations may be performed in either an air-swept environment before the calcium carbide has completely cooled, or in an inert atmosphere. The calcium carbide product is used primarily in generating acetylene and in desulfurizing iron.(Table 2)

 

Emissions And Controls

Emissions from calcium carbide manufacturing include particulate matter (PM), sulfur oxides

(SOx), CO, CO2, and hydrocarbons. Particulate matter is emitted from a variety of equipment and operations in the production of calcium carbide including the coke dryer, lime kiln, electric furnace, tap fume vents, furnace room vents, primary and secondary crushers, and conveying equipment.

Particulate matter emitted from a process source such as an electric furnace is ducted to a PM control device, usually a fabric filter or wet scrubber. Fugitive PM from sources such as tapping operations, the furnace room, and conveyors is captured and sent to a PM control device. The Otto cycle engine exhaust emission standard in Table 3.

 

Emission Factors

Equipment or operation, but the primary components are calcium and carbon compounds, with significantly smaller amounts of magnesium compounds.

Sulfur oxides may be emitted both by the electric furnace from volatilization and oxidation of sulfur in the coke feed, and by the coke dryer and lime kiln from fuel combustion. These process sources are not controlled specifically for SOx emissions. Carbon monoxide is a byproduct of calcium carbide production in the electric furnace. Carbon monoxide emissions to the atmosphere are usually negligible. In open furnaces, CO is oxidized to CO2, thus eliminating CO emissions. In closed furnaces, a portion of the generated CO is burned in the flames surrounding the furnace charge holes, and the remaining CO is either used as fuel for other processes or is flared. In semi-covered furnaces, the CO that is generated is either used as fuel for the lime kiln or other processes, or is flared.

The only potential source of hydrocarbon emissions from the manufacture of calcium carbide is the coal tar pitch binder in the furnace electrode paste. Since the maximum volatiles content in the electrode paste is about 18 percent, the electrode paste represents only a small potential source of hydrocarbon emissions. In closed furnaces, actual hydrocarbon emissions from the consumption of electrode paste typically are negligible because of high furnace operating temperature and flames surrounding the furnace charge holes. In open furnaces, hydrocarbon emissions are expected to be negligible because of high furnace operating temperatures and the presence of excess oxygen above the furnace. Hydrocarbon emissions from semi-covered furnaces are also expected to be negligible because of high furnace operating temperatures.

Table 1 gives controlled and uncontrolled emission factors in metric and English units, respectively, for various processes in the manufacture of calcium carbide. Controlled factors are based on test data and permitted emissions for operations with the fabric filters and wet scrubbers that are typically used to control PM emissions in calcium carbide manufacturing.

 

Acetylene

Acetylene (IUPAC name: ethyne) , C2H2, is a hydrocarbon belonging to the group of alkynes. It is considered to be the simplest of all alkynes as it consists of two hydrogen atoms and two carbon atoms. Acetylene is an unsaturated organic compound because its two carbon atoms are triply bonded.

The carbon-carbon triple bond leaves the carbon atoms with two sp hybrid orbitals for sigma bonding, placing all four atoms in the same straight line, with CCH bond angles of 180°.

Acetylene was discovered in 1836 by Edmund Davy who identified it as a "new carburet of hydrogen." It was rediscovered in 1860 by French chemist Marcellin Berthelot, who coined the name "acetylene." The Nobel Laureate Gustaf Dalén was blinded by an acetylene explosion.

Calcium carbide (or calcium acetylide) and water are then reacted by any of several methods to produce acetylene and calcium hydroxide. This reaction was discovered by Friedrich Wohler in 1862.

CaC2 + 2H2O → Ca(OH)2 + C2H2

 

Compression

Due to the carbon-to-carbon triple bond, acetylene gas is fundamentally unstable, and will decompose in an exothermic reaction if compressed to any great extent. Acetylene can explode with extreme violence if the pressure of the gas exceeds about 100 kPa (≈14.5 psi) as a gas or when in liquid or solid form, so it is shipped and stored dissolved in acetone or dimethylformamide (DMF), contained in a metal cylinder with porous filling (Agamassan), which renders it safe to transport and use.

Fire hazard

Mixtures with air containing between 3% and 82% acetylene are explosive on ignition. The minimum ignition temperature is 335 °C. The majority of acetylene's chemical energy is what is not contained in the carbon-carbon triple bond; that is, it is greater than that of three carbon-carbon bonds spread out, but is disallowed therefrom because of the spaces between its mate carbon and all other carbons likewise shielded in charge.

C2H2 +2 (O2+3.76N2) → 2CO2 + H2O+(3.76*2)N2

Gasoline &acetylene comparision

(United States Patent 4054423)

 

The advantages of the apparatus of the present invention for on-board generation of acetylene gas as fuel for internal combustion engines are illustrated further by the following calculations. The heating value of one gallon of gasoline is equal to 115,000 BTU per gallon, and since gasoline weighs 7 pounds per gallon, in each pound of gasoline the heating value is 16,428.571 BTU. The heating value of one gram of acetylene is 47.6110 BTU, and since there are about 453.6 grams in one pound, one pound of acetylene by weight has a heating capacity of 21,596.311 BTU.

When acetylene is compared to one gallon of gasoline of gasoline by weight, i.e. 7 pounds of gasoline and 7 pounds of acetylene, the heating value of acetylene is then 151,174.17 BTU compared to the one gallon of gasoline that has a heating value 115,000 BTU. Thus acetylene has a heating value factor of 1.3145 greater than that of gasoline by unit weight.

The molar weight of calcium carbide is 3.56 times greater than the molar weight of water. If one pound of water is used then 3.56 pounds of calcium carbide must be used to balance the chemical reaction. The end result of the reaction is 3.1 pounds of calcium oxide and 1.46 pounds of acetylene, according to the relationship.

CaC2 + H2O CaO + C2H2

the formula for determining the weight of acetylene derived from a certain weight of calcium carbide mixed with the proper amount of water is W acetylene = W calcium carbide (0.410) where W is the weight in pounds. For example, if one hundred pounds of calcium carbide is used in the car, then twenty eight pounds of water would be required. Actually, a slight excess of water should be used to allow for water loss through vaporization. One hundred pounds of calcium carbide occupies space that is equal to ten gallons, and twenty eight pounds of water is equal to 3.1 gallons since water weighs 9 pounds per gallon. Thus, the total space occupied by the two reactants is 13.1 gallons, and forty one pounds of acetylene will be generated.

Assuming that a given vehicle operates at 20 miles per gallon of gasoline, when the two fuels are compared in terms of BTU, the vehicle can travel 153.98 miles on the 41 pounds of acetylene generated while the same vehicle can travel only 117.14 miles on forty one pounds of gasoline. The foregoing calculations were based only on BTU of the two fuels. Actually, it is expected that the vehicle can travel more than 153.98 miles on 41 pounds of acetylene due to the fact that acetylene is already in gasoline form so there is no need to vaporize it, and being in gaseous form it mixes better with air than a liquid fuel.

 

 

Limestone Reservoir of Türkiye

Tables

Figures

Calcium Carbide Manufacture Cost (example)

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