Skip to main content

Blast Furnace - Production Of Pig Iron

 The Blast furnace is the vertical furnace designed for continuous operation. The smelting room of the blast furnace comprises a throat, stack, body, bosh and hearth.

The Raw materials (alternate layers of ore, coke , flux) , known as the charge, are taken to the top of the furnace by a specially designed bucket called "skip" running along an incline. The charge is then introduced into the throat of the furnace by means of a double bell and hopper arrangement to prevent the escape of blast furnace gas which is used as a fuel. The proportions of the raw materials are approximately one-half iron ore, one-third fuel, and one sixth flux. It may be pointed out , for instance to make 100 tons of pig iron it requires about 180 tons of iron ore, nearly 95 tons of coke, 50 tons of flux, and about 350 tons of preheated air blast. In addition to pig iron, about 60 tons of slag and 50 tons of gas are produced.



 

A hot blast is forced into the furnace through a number of nozzles called Tuyeres. The Tuyeres are cooled by water circulating between the pipe walls. The air blast is heated to minimize fuel consumption by passing the cold air blast through the heated checker-work of hot blast stoves.

The temperatures of the furnace just above the level of the Tuyeres (melting zone) being 1000*C to 1700*C all substances inside the furnace start melting in the heat. The limestone that serves as a flux is combined with the ore to form a molten slag which floats on the top of the molten iron. The slag is tapped off from the furnace through the slag hole. The molten iron is tapped at intervals from six to twelve hours through a tapping hole, the blast being turned of mean while. The furnace is kept in operation until it gets worn out. 

According to the type of the plant the molten iron may be used in one or more of the following ways.

1. Cast in Pig Bed.

2. Cast in Pig-Casting Machine.

3. Transferred in hot metal ladles direct to an adjacent steel - making process.

Pig beds are sand molds in the form a grid prepared in the ground along side the furnace . The bars (pigs) cast in this  way are about 1m long with a D- shaped cross section measuring about 100mm each way. The modern method of casting pig iron which has largely superseded the older pig-bed method is to employ a pig casting machine. This consists of a series of hematite iron or steel molds, each about 600 mm * 200 mm * 90mm, fixed to an endless chain conveyor , the assembly being mounted on a suitable construction arranged on a slight slope. 

While the Iron is in the furnace it picks up 3 to 4 percent of carbon and a small amount of Sulphur from the coke. The silicon, manganese and phosphorus as well as most of the Sulphur in the pig iron are derived from the ore. The high amount of the carbon makes the pig iron very hard and brittle and unsuitable for making any useful article. Pig iron, is therefore refined and re-melted to produce other varieties of iron and steel. 

Labels:

Comments

Post a Comment

Popular posts from this blog

ELECTRICAL COMPARATORS AND ITS WORKING

Electrical Comparators are used as a means of  detecting and amplifying small movements of a work contacting elements. An electrical comparator consists essentially of  a pick-up head or transducer for converting a displacement into a corresponding change in current and a meter or recorder connected in the circuit to indicate the electrical change, calibrated to show in terms of displacement. Generally, an amplifier is needed to provide the requisite sensitivity and to match the characteristics of different parts of  the circuit. Electrical comparators can be classified according to the electrical principle used in the pick-up head. Most of the comparators use either a differential transformer, an inductance bridge, a strain gauge or a capacitor as a means of detecting movement of the gauging element. There are different types of  electrical comparators. One kind called an electrolimit gauge is used to check or measure the outside diameter of a  roll. The object to be checked is place
Post a Comment
Read more

THROTTLE GOVERNING OF STEAM TURBINES

Steam Pressure at inlet to a steam turbine is reduced by throttling process to maintain the speed of the  turbine constant at part load and hence this method of governing is called "Throttle Governing".  Construction : Throttle governing system consists of  a centrifugal governor, a lever , an oil pump , a pilot piston , control valve , a relay piston and a throttle valve. The throttle valve is moved by a relay piston. The relay piston is actuated by pilot piston control valve. There are two piston valves covering ports in the pilot piston control valve without any overlap. These piston valves are operated by lubricating oil supplied by a gear pump at 2 to 4 bar. The oil returns to the drain from this chamber.  Working : When the turbine works on full rated load, the throttle valve will remain open. When the load is decreased, the energy output of the turbine becomes in excess and the turbine shaft speed increases. Hence, governor sleeve will lift. The upward movement of the
Post a Comment
Read more

Advantages And Disadvantages Of Air Refrigeration System :

 Advantages Of  Air Refrigeration : 1. The refrigerant used namely air is cheap and easily available. 2. There is no danger of fire or toxic effects due to leakages. 3. The weight to ton of refrigeration ratio is less as compared to other systems. Disadvantages Of Air Refrigeration : 1. The quantity of  Refrigerant used per ton of refrigeration is high as compared to other systems. 2. The COP of the system is very low. Therefore running cost is high. 3. The danger of frosting at the expander valves is more as the air contains moisture content. 
Post a Comment
Read more