Blast Furnace

Modern blast furnace plant consists of the following importance section
1. Blast furnace proper
2. Hot blast supply equipment
3. Gas cleaning system and gas storage
4. Raw material storage and handling
5. Liquid product disposal
6. Process control equipments

Furnace details :

Foundation :  It is massive Steel reinforced concrete mass partially embedded below the ground level. It should be sufficiently strong to stand the loaded furnace weight, which may be as much as 10,000t for a 2000 ton per day furnace. It may be about 15 metre in diameter and 6 to 8 metre thick upon which is placed the furnace bottom consist about 4 to 5m thick of fire bricks.

Hearth : It is a receptacle to collect the liquid slag and metal is also referred to as a crucible. The old practice of using fire bricks for hearth construction is almost universally replaced by carbon blocks. Water cooled copper or steel plates are laid in the sidewall to protect the lining. The carbon wall maybe more than metre of uniform thickness or Stadium type construction.

● In the hearth wall are located a tap hole for iron. 12 to 15cm dis and about 0.3 to 0.6 m above the heart level, and slag notch 1.2 to 1.6 m above the iron tap hole level, but staggered through a right angle in the horizontal plane. These hole are closed with clay when not in used and are open for tapping of metal and slag when necessary.
Blast furnace
Blast furnace

Bosh :  The top of the bosh has the maximum dia of the furnace and it is the zone of intense heat. It is a Stadium type (bricks stacked cut) construction with steel reinforcement. Water cooled copper or steel plates are inserted at regular intervals in the furnace lining in this zone. To effect protection against high temperature.

Mantle and Columns :  The furnace structure above the bosh level is supported on a heavily braced steel ring encircling the furnace at the top of the bosh. This called the mantle which is supported by uniformly spaced upright heavy columns, which is attached with concrete foundation at the bottom.

Stack :  It is a huge cone mounted on the mantle and extended to the top of the furnace. The furnace top or the bell, the charging arrangements, the gas off takes etc are mounted on the top the stack. 

● The stack is welded steel plate construction lined form inside to a thickness of about a meter of hard firebrick. Flat water cooled plates are inserted in the lower stack lining. The top 2 to 3 m height, stock line is protected from abrasion caused by the falling charge by providing armour plates on the inner surface of the lining.
Blast furnace proper

Tuyere and Bustle pipe :  Immediately above the hearth are located the tuyere through which hot air is blown to the furnace as a fuel. The number of tuyeres vary with the size of the furnace. Usually it is any even number and uniformly spaced all over for periphery for better heat distribution in side the furnace.

● Air from the blast stove is supplied to a huge circular pipe encircling the furnace at the bosh level, locate the bustle pipe. The individual tuyere are connected to the bustle pipe which equalise the pressure of the blast, at all tuyere.

Bell and Hooper :  The bell and hopper or the cup and cone arrangements is commonly used on blast furnace for charging. In modern blast furnace designs the two bell arrangements to be used for charging, but now bell less charging system is being preferred. The double bell arrangements ensures that charging continues without the exhaust gas leaking out of the furnace. Furnace provided with high top pressure have introduction of several complex seals in the charging.

Off-takes :  There are four exhaust pipes which are connected to the furnace top evenly at four points. These rise vertically up above the furnace top and then join to a bigger single pipe known as the downcomer which delivered the gas to the cleaning system through dust catcher.

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