What Is Calcium Carbide?

Calcium carbide, with the chemical formula CaC2, is a grey-black crystalline industrial chemical produced by carbothermal reduction of lime and coke in an electric arc furnace at temperatures above 2,000 degrees Celsius. It is best known for its reaction with water, which produces acetylene gas, and it is also used in steelmaking and in the production of chemical intermediates. This article explains what calcium carbide is, how it is made, and how it is used and handled safely.

How Calcium Carbide Is Produced

Calcium carbide is made by heating a mixture of quicklime and a carbon source, usually coke or anthracite, in an electric arc furnace. The carbon reduces the calcium oxide to calcium carbide, releasing carbon monoxide as a by-product. The molten carbide is tapped from the furnace, cooled, crushed and screened into the particle sizes required by different applications. The process is energy intensive, and the electricity consumption is a major part of the production cost.

Grades and Particle Sizes

Commercial calcium carbide is graded by its gas yield, expressed as liters of acetylene per kilogram of carbide. Common grades range from around 250 to 300 liters per kilogram, and the gas yield reflects the purity of the carbide: impurities such as unreacted lime and oxides reduce the yield. The material is supplied in particle size ranges from fine granules to large lumps, and the correct size is chosen according to the generator type and the required reaction rate.

Main Uses of Calcium Carbide

The most important use of calcium carbide is the generation of acetylene, which is used in oxy-acetylene welding and cutting and as a chemical feedstock. In steelmaking, calcium carbide is used as a desulfurizer, because calcium combines with sulfur in the melt and removes it into the slag. It is also used in the production of calcium cyanamide fertilizer and as a source of carbide-derived chemicals.

Safety and Handling

Calcium carbide reacts vigorously with water to release acetylene, which is flammable, so the material must be kept dry and stored away from moisture, in sealed containers or in well-ventilated storage with controlled humidity. Containers that have been opened must be protected from rain and humidity. When carbide is handled, the dust should not be inhaled, and contact with eyes and skin should be avoided. Acetylene generated from carbide should be used only with equipment designed for acetylene service.

Frequently Asked Questions

Q: What is calcium carbide?
Calcium carbide (CaC2) is a grey-black crystalline industrial chemical produced by carbothermal reduction of lime and coke in an electric arc furnace at high temperature.

Q: How is calcium carbide made?
Quicklime and coke are heated together in an electric arc furnace above 2,000 degrees Celsius, and the molten carbide is tapped, cooled, crushed and screened into the required particle size ranges.

Q: What is the gas yield of calcium carbide?
Gas yield is the litres of acetylene released per kilogram of carbide, commonly around 250 to 300 litres per kilogram. It depends on grade and purity, since impurities such as unreacted lime and oxides reduce the yield.

Q: What is calcium carbide used for?
Mainly to generate acetylene for oxy-acetylene welding and cutting and as a chemical feedstock, and also as a desulfurizer in steelmaking where calcium combines with sulfur in the melt and removes it into the slag, plus in calcium cyanamide fertilizer and other carbide-derived chemicals.

Q: Why must calcium carbide be kept dry and how is it stored?
It reacts with water to release flammable acetylene, so it must be kept dry in sealed containers or well-ventilated storage with controlled humidity, protected from rain, and handled without inhaling dust or contacting eyes and skin.

Q: Is calcium carbide dangerous to handle?
The main hazards are the flammable acetylene released on moisture contact and the caustic residue left after reaction, so dry storage, good ventilation, appropriate protective equipment and acetylene-rated equipment are required.