Cupola working process

The working process of cupola: firstly, a certain amount of coal is put into the furnace as bottom coke, and its height is generally more than one meter. After ignition, the bottom coke is added to the specified height, and the height from the tuyere to the top surface of the bottom coke is the bottom coke height. Then, according to the melting speed of the furnace, the prepared limestone, metal charge and layer coke are added from the charging port in turn and in batches. During the whole furnace opening process, the top surface of the furnace charge is kept at the lower edge of the charging port. The air blown into the furnace through the tuyere has a combustion reaction with the bottom coke, and the generated high-temperature furnace gas flows upward to heat the furnace material and melt the first batch of metal charge on the top surface of the bottom coke. Iron water droplets are further heated by high temperature furnace gas and hot coke in the process of falling into the furnace, which is called overheating. With the burning loss of bottom coke and the melting of metal charge, the material layer gradually drops. After each batch of burden is melted, additional layer coke is used to supplement fuel, so that the height of bottom coke remains basically unchanged, and the whole melting process continues. Application: Cupola is mainly used in steel, metallurgy, mining and other industries.

Limestone in the furnace charge is decomposed into lime and carbon dioxide under the action of high temperature furnace gas. Lime is an alkaline oxide, which can combine with acid substances such as ash in coke, impurities in furnace charge and metal oxides to form low melting point slag. Slag also falls into the furnace and floats on the molten iron.

In cupola, there are three important processes: bottom coke combustion, heat transfer and metallurgical reaction. According to the different physical and chemical reactions, the cupola is divided into five zones from top to bottom: preheating zone, melting zone, reduction zone, oxidation zone and furnace. Due to the action of furnace gas, coke and slag, the composition of molten metal also changes to some extent. Among the five elements of cast iron, carbon and sulfur generally increased, silicon and manganese generally burned out, and phosphorus changed little. The final chemical composition of molten iron is the comprehensive result of the original composition of metal burden and the change of composition during melting.