Cupola Furnace zone :
A number of chemical reaction take place in these zones which are explained below :
1. Well :
It is the space between the bottom of the tuyeres and the sand bed. The metal, after melting, trickles down and collects in this space before it is tapped out.
2. Combustion zone :
It is also known as oxidizing zone. It is located between the top of the tuyeres and a theoretical level above it. The total height of this zone is normally from 15 cm. To 30 cm. The actual combustion takes place in this zone, consuming all free oxygen from the air blast and producing a lot of heat, which is sufficient enough to meet the requirements of other zones of cupola. More heat is evolved due to oxidation of silicon and manganese. A temperature of about 15400C to 18700C is produced in this zone. The exothermic reactions taking place in this zone can be represented thus.
3. Reducing zone :
It is also known as the protective zone. It is located between the top of the combustion zone and the top level of the coke bed. CO2 is reduced to CO in this zone through an endothermic reaction, as a result of which the temperature falls from combustion zone temperature to about 12000C at the top of this zone. The reaction is as follows : Nitrogen, the other main constituent of the upward moving hot gases does not participate in the reaction. This zone, on account of the reducing atmosphere in it, protects the charge against oxidation.
4. Melting zone :
The first layer of metal charge above the coke bed constitutes this zone. The solid metal charge changes to molten state in this zone and trickles down through the coke to the well. The molten metal picks up sufficient carbon content in this zone as represented by the following reaction :
5. Preheating zone :
It extends from above the melting zone to the bottom level of the charging door and contains a number of alternate layers of coke and metal charges. The function of this zone is to preheat the charges from atmospheric temperature to about 10930C before they settle downwards to enter the melting zone. This preheating takes place due to the upward advancing hot gases, from which the solid metal also picks up some sulfur content.
6. Stack zone :
The empty portion of cupola above the preheating zone, which provides the passage to hot gases to go to atmosphere, is known as stack zone.