In iron and steel making, the basic equipment used is a blast furnace, which generally contains the composite materials for producing a specific type of metal. Today, you’ll get to know the definition, components, diagram, and maintenance of a blast furnace. You’ll also get to know the term blast stove.
What is a Blast furnace?
A blast furnace is a type of metallurgical furnace used for smelting to produce industrial metals, generally pig iron, but also others such as lead or copper. Blast refers to the combustion air being “forced” or supplied above atmospheric pressure.
The components of a blast furnace include the Charge, exhaust gas outlet, charging bells, gas outlet, tuyeres, taphole, bustle pipe, slag hole, refractory lining, and conveyor system.
Working of a Blast Furnace
A blast furnace is typically about 30m high and 10m in diameter at the widest part, though some modern blast furnaces are even larger than this. The furnace casting is of heavy steel plates with a very thick lining of refractory brickwork which is water-cooled around the melting zone (or bosh) to avoid damage from the extremely high temperature inside. A slight increase in diameter towards the base allows for some expansion of the stock as it descends, and at the bosh there is a reduction in the diameter where melting begins and stock volume decreases.
Read more: Process of Heat treatment of ferrous metals
Encircling the bosh is the bustle pipe which distributes the hot air blast to ten or more nozzle or tuyeres (pronounced ‘tweers’) spaced evenly around the furnace. The tuyeres, water-jacketed for cooling are each about 125 – 175 mm in diameter and they deliver the powerful and very hot air blast right to the middle of the furnace, causing the coke to burn fiercely. This force draught carries the hot furnace gas up the stack, through the offtake, and into the downcomer. It passes through the gas cleansing plant and onto the gas holders and is ready for use in the hot blast stove to heat air for the furnaces.
Watch the video below to learn more about the working of a blast furnace:
Read more: Properties and Composition of Pig Iron
The stock level must be maintained in the furnace and at regular intervals, weighed charges ore; coke and limestone (and sometimes some scrap metal) are added. The raw materials are carried up in skips which discharge into a rotating hopper, this spread the charge evenly around and it then enters the furnace through a double bell mechanism. This is necessary to provide a gas seal since the blast furnace cannot be shut off at any time during the lengthy period of operation.
Hot Blast Stove
Each blast furnaces are usually equipped with three stoves that burn furnace gas to heat the air blast. Each is almost as high as the blast furnace, up to 7 and 8m in diameter. Inside it, there is a honeycomb of fire brickwork and a combustion chamber in which gas is ignited, the frame sweeping through the honeycomb and heating it on the way to the chimney damper is closed and the blast stove is put on air; i.e. the air blast is driven by powerful turbo blowers, passes through and absorbs the stored heat. The air temperature reaches from 650 to 800°C.
Read more: Raw materials used in making iron and steel
Usually, two blast stoves are ‘on gas’ (heating up) whilst the third is on air. When this one cools down, it is put back on gas, and another blast stove is put on the air, all the three being used in rotation.
Maintenance of Blast Furnace
Blast furnaces normally work day and night for several years. There is a possibility that the bricks lining begins to crumble, the furnace is then shut down for maintenance. The blast furnace operation is monitored continually in such that, temperatures and times are checked and recorded.
The chemical content of the iron ores received from various mines are cracked, and the ores are blended with other iron ore to achieve the desired charge. Samples are expected to be taken from each pour and check for their chemical content and mechanical properties which include strength and hardness. Considering these done will serve as the quality control of a blast furnace.
That is all for this article, where the definition, working, components, diagram, and maintenance of blast furnace is being explained. I hope you get a lot from the reading, if so, kindly share with other students. Thanks for reading, see you next time!