Exercise-I

An oil fired reheating furnace consumes 100 Kg/ hr oil to heat 1 ton billet to 1400 K. Oil analyses  and and is burnt with excess air. Gross calorific value of oil is 45000 kJ/kg. The POC exits the furnace at 1500 K. What are the heat losses & thermal efficiency?

Solution:

Heat balance:
Heat input = Heat carried by POC + Heat carried by steel +Heat losses.

We can calculate amount of POC / 100 kg fuel and heat to POC. All the sensible heat values are taken from the reference given at the end of this lecture. Heat to POC

Heat to steel

Heat input 

Heat losses

Thermal efficiency which means that  of the calorific value of fuel is used in heating billet.

For this furnace let us install a preheater which can recover of heat to preheat air. Heat losses and heat to steel are unchanged. Calculate the carbon offset due to preheater.

Preheater installation results in fuel saving. Let is now fuel required. Heat balance

Saving in fuel

For and 25 days in month

Fuel saving