The blast furnace is a tall, vertical shaft that is consists of steel shell with a refractory lining of firebrick and graphite. At the bottom is parallel-sided hearth where liquid metal and slag

The Blast Furnace

The blast furnace is a tall, vertical shaft that is consists of steel shell with a refractory lining of firebrick and graphite. At the bottom is parallel-sided hearth where liquid metal and slag collect, and this is surmounted by an inverted truncated cone known as the bosh. Air is blown into the furnace through tuyeres, water-cooled nozzles made of copper and mounted at the top of the hearth close to its junction with the bosh. A short vertical section called the bosh parallel, or the barrel, connects the bosh to the truncated upright cone that is the stack. Finally, the topmost section, through which the charge enters the furnace, is the throat. The lining in the bosh and hearth, where the highest temperature occurs, is usually made of carbon bricks, which are manufactured by pressing and baking a mixture of coke, anthracite, and pitch. Carbon is more resistant to corrosive action of molten iron and slag than are the aluminosilicate firebricks used for the remainder of the lining. Firebrick quality is measured by alumina (Al₂O₂) content, so that bricks containing 63 percent alumina are used in the bosh parallel, while 45 percent alumina is adequate for stack.

Until recently, all blast furnaces used the double-bell system to introduce the charge into the stack. This equipment consists of two cones, called bells, to prevent gas escaping into atmosphere. Because it is difficult to distribute the burden evenly over the furnace cross section with this system, and because the abrasive action of charge cause the bell to wear so that gas leakage eventually occurs; more and more furnaces are equipped with a belles top, in which the rate of materials flow from each hopper is controlled by an adjustable gate and delivery to stack is through a rotating chute whose angle of inclination can be altered. This arrangement gives good control of burden distribution.

At the beginning of the process the furnace is charged with coke (C), iron ore (Fe₂O₃), and limestone (CaCO₃) which are placed in alternate layers. Then a blast of hot air at high pressure enters through the tuyere. At this stage the coke burns to form carbon dioxide (CO₂).

As the hot carbon dioxide rises in the furnace, it meets more coke and is reduced to carbon monoxide (CO). The carbon monoxide then reacts with hot iron ore, forming iron and carbon dioxide. At the same time, the limestone absorbs earthy impurities from the ore forming a liquid known as slag.

The molten iron and liquid slag drain to bottom of the furnace, where they form two layers –the slag floats on the top of the denser molten iron. The iron and slag pass furnace at different levels. When the iron leaves the furnace, it still contains some impurities. Some of the molten iron is run off into large mold, where it is cooled ready for further refining and processing into cast iron at a later stage. The remainder is taken away in its molten state for further processing into wrought iron or steel.

http://en.wikipedia.org/wiki/File:Blast_furnace_NT.PNG

1: Iron ore + Calcareous sinter

2: coke

3: conveyor belt

4: feeding opening, with a valve that prevents direct contact with the internal parts of the furnace

5: Layer of coke

6: Layers of sinter, iron oxide pellets, ore,

7: Hot air (around 1200°C)

8: Slag

9: Liquid pig iron

10: Mixers

11: Tap for pig iron

12: Dust cyclon for removing dust from exhaust gasses before burning them in 13

13: air heater

14: Smoke outlet (can be redirected to carbon capture & storage (CCS) tank)

15: feed air for Cowper air heaters

16: Powdered coal

17: cokes oven

18: cokes bin

19: pipes for blast furnace gas

Дата добавления: 2015-11-05