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Refractories for Electric Furnace Production of Calcium carbide

March 08, 2021

Calcium carbide is an industrial name, its chemical name is calcium carbide, its molecular formula is CaC. What we usually call calcium carbide is actually impure calcium carbide. It is composed of calcium carbide and lime and a small amount of other impurities.

The industrial calcium carbide is produced by the reaction of quicklime and carbon raw materials (coke, anthracite, petroleum coke) in an electric furnace under high temperature conditions of 1800~2200℃ by arc heat or resistance heat according to the following chemical equations: CaO 3C---CaC₂CO-111.3kcal

Calcium carbide furnace is the main equipment for the production of calcium carbide. In calcium carbide furnace, calcium carbide is formed by melting reaction of charge due to high temperature caused by arc. Because the reaction temperature is more than 2000℃, such a high temperature, the general refractory is difficult to bear, so the volume of the furnace body must be larger than the reaction space. That is to say, a layer of charge is reserved in the reaction area to protect the lining, which is also called "false lining ".

According to the structural characteristics of calcium carbide furnace, it can be divided into open calcium carbide furnace, semi-closed calcium carbide furnace and closed calcium carbide furnace.

The open calcium carbide furnace has simple structure, relatively easy manufacture and low cost. But because the flame on the furnace surface is large, when its capacity reaches 25000 kV·A, it can not be expanded any more. Moreover, the furnace gas can not be recovered, the environmental pollution is serious, the operating conditions are bad, and its use is restricted.

A gas collecting cover is placed between the electrodes of the open calcium carbide furnace to extract part of the carbon monoxide gas generated in the furnace, and the remaining part is still burned on the furnace surface. Such an calcium carbide furnace is called a semi-closed calcium carbide furnace. The capacity of the calcium carbide furnace is expanded to 35000~40000 kV·A. because it can extract part of the furnace gas and reduce the heat of burning flame on the furnace surface

 Closed calcium carbide furnace is to cover the open furnace with a furnace cover, the furnace produced carbon monoxide gas with extraction equipment. Since the furnace cover is covered and the air is isolated, there is no combustion phenomenon on the material surface, and the electric furnace power has been developed, and a large capacity closed calcium carbide furnace of 75000~10000 kV·A has appeared. Moreover, the closed calcium carbide furnace has the advantages of convenient operation, high mechanization degree, good working conditions and reduced environmental pollution.

Calcium carbide furnace mainly includes furnace shell, furnace body (including furnace cover), electric furnace transformer and short net, electrode (including oil pressure pressure discharge system), discharge system equipment, furnace gas purification system equipment (including sewage treatment).

Shell structure. In addition to bearing the weight of lining, charging, semi-finished calcium carbide, the shell is also subjected to high temperature and lining thermal expansion and contraction. Therefore, it is necessary to design the shell :(1) the strength of the shell should satisfy the thermal expansion of the lining without serious deformation;

(2) In order to meet the strength requirements, efforts should be made to save steel and reduce weight;

(3) Easy to process, easy to disassemble, assemble and transport, and quick to install. The shell of calcium carbide furnace is generally made of ordinary carbon steel plate or boiler steel plate. At present, most calcium carbide furnaces adopt cylindrical shell, which is characterized by small heat dissipation area, compact structure, large strength and easy processing. Before the domestic design of large capacity calcium carbide furnace, it is generally necessary to add vertical reinforcement and horizontal reinforcement outside the shell shell, the purpose is to increase the strength of the shell and prevent deformation.

The working conditions of different parts of calcium carbide furnace body are different, and the performance requirements of refractories are different. The furnace lining of calcium carbide furnace is the working interval of chemical reaction of charge, which not only bears strong high temperature action, but also bears the friction of charge, the physical and chemical erosion and scour of high temperature furnace gas and molten calcium carbide. In order to ensure that calcium carbide production can proceed smoothly under high temperature conditions, the requirements for furnace lining are as follows:

 (1) Can withstand high temperature and protect the shell from serious thermal stress deformation;

(2) Heat insulation and insulation performance to minimize heat loss in the furnace;

(3) Solid structure, long service life, safety and reliability.

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