1.2) According to source of heat:
According to the source of heat used for heating the load, furnaces can be widely classified in to
A) Fuel fired furnace and
B) Electric furnace.
A)Fuel fired furnaces:
Fuel fired furnaces can be again sub divided in to
1. Solid fuel (which is no longer in use)
2. Liquid fuel and
3. Gaseous fuel
1) Solid fuel fired furnace:
They are least economical and efficient type of furnace, which can be called as first generation furnaces. The atmospheric pollution incurred is too high. Due to such reasons, they are no more in use.
2) Liquid fuel fired furnace:
Most commonly used liquid fuel is fuel oil. Gasoline and kerosene also can be used successfully, but due to their high cost they are not being used generally. Liquid fuels are easy to store and the furnace can be fired at any time. Operating a simple valve connected to the supply line the temperature of such furnaces can be controlled. A maximum temperature of 1200—C can be achieved in such a furnace. The process is more economical only at higher temperature ranges (around 1000—C). Since the temperature is not uniform through out the furnace, a heat circulating mechanism is essential in liquid fuel fired furnace.
3) Gas fired furnace:
Gas fired furnaces have certain advantages over oil fired furnaces. They are more economical and possess better control over temperature. They have simpler design and can be used to temperatures up to 1500—C. They are inferior only to electrically heated furnaces as far as economy and efficiency are concerned. Natural gas, coke-oven gas, water gas, producer gas and refinery gas can be used to fire up these furnaces.
B) Electric furnaces:
They are the most commonly used furnaces now a days. They have superior advantages like uniformity of temperate in the heating camber, close control of temperature, freedom from pollution, neat and clean working conditions, efficient use of heat, minimum requirement of accessories, ease of staring and closing down etc. They are subdivided according to the method of heating. They are
ü Resistance furnace
ü Arc furnace
ü Induction furnace
ü Plasma arc furnace and
ü Electron beam furnace.
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