Blast Furnace Operations

Fig 1.

Operations

Operating a blast furnace refers to making decisions Operating a blast furnace refers to making decisions regarding the process of iron making.regarding the process of iron making.

These decisions alter the inputs to the furnace in order These decisions alter the inputs to the furnace in order to obtain the desired operating conditions and material to obtain the desired operating conditions and material outputs.outputs.

Many different process factors play into ideal Many different process factors play into ideal operations and equipment limitations can also play a operations and equipment limitations can also play a large role.large role.

Fig 2.

Cost vs. Production

The main goals in iron making can be simplified to The main goals in iron making can be simplified to either cost or production quantity.either cost or production quantity.

Since a blast furnace is usually part of an integreated Since a blast furnace is usually part of an integreated steel making process, the demands place on steel making process, the demands place on operations can change quickly. operations can change quickly.

These demands can shift from making the least costly These demands can shift from making the least costly iron to producing as much iron as possible. iron to producing as much iron as possible.

While these goals often go against one another, they While these goals often go against one another, they share the same process and equipment limitations.share the same process and equipment limitations.

Fig 3.

Cost Limitations

When cost is the primary concern, efficiency and low When cost is the primary concern, efficiency and low cost of operation are sought.cost of operation are sought.

Efficiency is achieved by running the furnace at steady Efficiency is achieved by running the furnace at steady reasonable rates and not pushing it to it limits.reasonable rates and not pushing it to it limits.

Low cost operations are achieved by inputting the Low cost operations are achieved by inputting the lowest cost burden materials. lowest cost burden materials.

Increasing the amount of hot blast injected into the Increasing the amount of hot blast injected into the furnace increases efficiency and lowest the cost of furnace increases efficiency and lowest the cost of production. production.

Fig 4.

Problems with Low Cost Materials

There are operational issues associated with using There are operational issues associated with using low cost materials.low cost materials.

These lower cost materials have more fine materials in These lower cost materials have more fine materials in them. These fines plug up the furnace, impede gas them. These fines plug up the furnace, impede gas flow, and cause erratic burden descent.flow, and cause erratic burden descent.

Low cost materials can also contain unwanted Low cost materials can also contain unwanted materials that will be present chemically in the iron materials that will be present chemically in the iron that is produced. These unwanted chemicals require that is produced. These unwanted chemicals require further processing to be removed from the iron.further processing to be removed from the iron.

Fig 5.

Problems with Efficient Operation

Efficient operation requires smooth and stable process Efficient operation requires smooth and stable process conditions within the furnace.conditions within the furnace.

While efficiency means a high utiliztion of the While efficiency means a high utiliztion of the resources put into the furnce, it cannot always be resources put into the furnce, it cannot always be complished with lower quality materials and it will not complished with lower quality materials and it will not give the highest amount of production.give the highest amount of production.

Typically the lowest cost of operation is achieved by Typically the lowest cost of operation is achieved by blalacing the input of low cost materials and blalacing the input of low cost materials and maintaining efficient operationmaintaining efficient operation

Fig 6.

Production Limitations Any furnace will have a physical limit of how much iron Any furnace will have a physical limit of how much iron

it can produce in a given time frame. it can produce in a given time frame. Certain metallic materials can be used in the burden to Certain metallic materials can be used in the burden to

increase production. These metallics are iron bearing increase production. These metallics are iron bearing materials that have less oxygen in them. They typiclly materials that have less oxygen in them. They typiclly are forms of processed scrap materials. They are very are forms of processed scrap materials. They are very expensive compared to iron ore.expensive compared to iron ore.

Production can be increased by driving the furnace Production can be increased by driving the furnace harder. This is accomplished by pushing more hot harder. This is accomplished by pushing more hot blast in and increasing the amount of material charged blast in and increasing the amount of material charged in the top of the furnace. This strains the furnace in the top of the furnace. This strains the furnace reactions and generally causes instability and reactions and generally causes instability and operational issues.operational issues.

Fig 7.

Environmental Concerns

Since a blast furnace is a closed and pressurized Since a blast furnace is a closed and pressurized system, it has pressure relief valves in order to system, it has pressure relief valves in order to prevent any sort or explosion should the pressure prevent any sort or explosion should the pressure inside get too high. inside get too high.

These valves, known as bleeders, let the gas flow These valves, known as bleeders, let the gas flow coming out of the burden to vent directly to coming out of the burden to vent directly to atmosphere n the event the internal pressure exceeds atmosphere n the event the internal pressure exceeds a set point.a set point.

Fig 8.

Environmental Concerns

Since these bleeder events release chemicals into the Since these bleeder events release chemicals into the environment they are avoided as much as possible.environment they are avoided as much as possible.

Pushing too much hot blast through the furnace can Pushing too much hot blast through the furnace can leads to pressure issues. Having a burden that is not leads to pressure issues. Having a burden that is not permeable also causes pressure issues. Any internal permeable also causes pressure issues. Any internal furnace instability can cause the burden to slip down furnace instability can cause the burden to slip down and cause a spike in pressure. These issues all factor and cause a spike in pressure. These issues all factor into operational decisions such as burden selection into operational decisions such as burden selection and hot blast injection rate.and hot blast injection rate.

Fig 9.

Summary

Many factors such as cost, production rate, and Many factors such as cost, production rate, and environmental concerns determine the operational environmental concerns determine the operational parameters of the blast furnace.parameters of the blast furnace.

These goals often push the furnace to the boundaries These goals often push the furnace to the boundaries of when it can accomplish given the limitations of when it can accomplish given the limitations inherent to the equipment and materials input.inherent to the equipment and materials input.

The manipulation of the operating parameters to The manipulation of the operating parameters to achieve the given production goals is at the heart of achieve the given production goals is at the heart of blast furnace operation.blast furnace operation.

Fig 10.