Question

It is required to melt 5 tonnes/ hour of iron from iron metal charge at ${15}^{o}C$ to molten metal at ${1650}^{o}C$. The melting point is ${1535}^{o}C$. and latent heat is 270 kJ/ kg. Specific heat in solid state is 0.502 kJ/ kgK and in liquid state is 0.534 kJ/ kgK. If electric furnace has 70% efficiency, what is the required kW rating of furnace?

• A. 2.17MW
• B. 3.2MW
• C. 1.05MW
• D. 2.7MW

Answer 1

The correct option is A 2.17MW

Heat required to melt 1 kg of iron at 15°C to molten metal at 1650°C = Heat required to raise temperature

from 15°C to 1535°C + Latent heat + Heat required to raise the temperature from 1535°C to 1650°C.

$=0.502\times [1535-15]+270+0.534[1650-1535]$

$=1094.5kJ/kg$

Melting rate $=5\times {10}^{3}kg/hr$

Rate of heat supply required $=1094.5\times 5\times {10}^3$ kJ/hr)

kW rating of furnace required $=\frac{HeatRate}{FurnaceEfficiency}=\frac{1094.5\times 5\times {10}^3}{0.7}kJ/hr$

$=\frac{1094.5\times 5\times {10}^3}{0.7\times 3600}kJ/s$

$=2171.6kW=2.17MW$