Calcium Carbide from Limestone (Electrothermic Process)

The process under analysis comprises four major sections: (1) feed preparation; (2) lime kiln; (3) electric furnace; and (4) finishing.

* Feed preparation. Initially, coke is fed to a dryer (cabinet with trays), where hot air enters for reducing the moisture. After drying, coke is transferred to the electric furnace. Limestone is crushed in a jaw crusher into a uniform particle size range. Some gross impurities originating from the limestone are separated in a screener.

* Lime kiln. The crushed limestone is calcined in a vertical shaft lime kiln. The calcium carbonate present in the limestone is decomposed into calcium oxide (lime) and carbon dioxide, used to preheat the limestone feed. The resulting calcium oxide is passed through a screener for removal of gross impurities and then conveyed, along with dry coke, to an electric furnace comprised of electrodes through which high current passes providing heat.

* Electric furnace. The lime-coke mixture flows down the furnace until reaching the high-temperature reaction zone, where molten calcium oxide reacts with coke and originates calcium carbide in molten state. The reaction zone is a packed bed of coke where empty space is filled with molten calcium carbide and gaseous by-product carbon monoxide. The CO gas is treated before it is used as fuel throughout the process. The molten product is removed from the furnace by means of continuous tapping and falls into a water-cooled cylinder where it solidifies.

* Finishing. The solid calcium carbide is transferred to the carbide crusher, where it is sieved and crushed until it reaches the desired particle size for final product. The crushed product is screened for impurities removal and stored.