Physical Zones | Blast Furnace | Tech It Eze

Physical Zones | Blast Furnace | Tech It Eze
Hi friends
Today we will discuss about Blast furnace different zones
Like Physical zones
and thermal zones
Lets start
What is Blast Furnace Process?
The blast furnace is a counter-current heat exchanger used to extract iron from iron or . The process involves several zones, where raw materials undergo various physical and chemical transformations before molten iron and slag are obtained.
Physical Zones Inside the Blast Furnace
As the materials move downward and gases move upward, different zones form inside the furnace.
Throat (Topmost Zone)
• Raw materials enter the furnace at ambient temperature.
• No chemical reactions occur here.
Granular Zone (Solid State)
• The burden materials (Sinter, Pellet, iron or, coke, and additives) begin heating as they descend.
• Endothermic drying occurs (that is removal of moisture).
Cohesive Zone (Softening and Melting Zone)
• Temperature: thousand to thousand fifty degree Celsius
• Iron bearing raw materials starts to soften and forms a pasty mass.
• Major reduction reactions occur:
• Reduction of iron oxides by carbon monoxide :
• three F E two O three plus C O is equal to two F E three O four plus C O two
• F E three O four plus C O is equal to three F E O plus C O two
• F E O plus C O is equal to F E plus C O two
• At this stage, iron bearing raw material is completely reduced to metallic iron.
Active Coke Zone
• Temperature: thousand fifty to thousand seventy degree celcius
• Coke reacts with Carbon dioxide to form carbon monoxide, which acts as a reducing agent:
C plus C O two is equals to 2 C O
• The reduced iron starts melting and trickles downward.
Combustion Zone
• Temperature: two thousand one hundred to two thousand three hundred degree Celsius (hottest part)
• Oxygen from hot blast reacts with carbon (coke) to form C O:
o C plus O two is equals to C O two
o C O two plus C is equals to 2 C O
• The intense heat melts iron and slag, allowing them to separate.
Reactions near the Tuyeres
The tuyere zone is the region where hot air (blast) is injected into the blast furnace through the tuyeres (nozzles). This is a critical area where combustion reactions occur, generating the necessary heat and gases for iron reduction.
1. Combustion of Coke (Primary Reaction)
• The hot blast (oxygen-enriched air) reacts with coke (carbon) in front of the tuyeres to produce C O and heat:
• C plus O two is equals to C O two (Highly exothermic) This reaction releases a large amount of heat, raising the temperature to thousand eight hundred to two thousand two hundred degree Celsius in this zone.
Raceway Zone in the Blast Furnace
• The raceway zone is a cavity or void space formed in front of the tuyeres when the hot blast enters the blast furnace at high velocity. This zone is critical for combustion and gas generation, significantly impacting the efficiency and stability of furnace operation.
• When the hot blast (air plus oxygen) is injected through the tuyeres, it penetrates into the coke bed, displacing solid particles and creating a hollow cavity.
Boudouard Reaction (Solution Loss Reaction)
• The C O two produced in the first reaction reacts with excess carbon (coke) to form C O gas: C O two plus C is equals to C O (Endothermic)
• This reaction consumes heat, cooling the gas slightly and increasing the C O by C O two ratio, which is important for the reduction of iron oxides in the upper furnace.
Partial Combustion of Pulverized Coal
(if injected)
• Pulverized coal (or oil, natural gas) injected into the tuyeres undergoes partial combustion, generating C O and H two:
• C plus half O two is equals to two C O
Hydrogen contributes to indirect reduction of iron oxides and improves energy efficiency.

Heat Transfer and Gas Flow
• The hot gases, Carbon Monoxide, Nitrogen, Hydrogen and some Carbon dioxide, rise through the furnace, providing the necessary heat and reducing agents for iron oxide reduction.
• Proper control of blast flow rate and oxygen enrichment ensures efficient combustion and heat distribution.
Hearth Zone (Bottom of the Furnace)
• The hearth is the lowest zone of the blast furnace, where molten iron and slag are collected before being tapped. The key reactions occurring in this region include:
Carbon Saturation of Molten Iron
• Molten iron in the hearth absorbs carbon from the coke. This reaction lowers the melting point of iron, making it easier to separate from slag: F e plus C equals to Fe − C (carbon-saturated molten iron).
• The carbon content in molten iron typically ranges from 3.5 to 4.5%, forming hot metal (pig iron).