In a heat treatment shop, steel components are heat-treated in batches of 80 Tons. The 

heat treatment cycle is as follows;

 Increase temperature from 30 OC to 850 OC in 3 hours.

 Maintain 850 OC for 1 hour (soaking time).

 Cool the material to 60 OC in 4 hours.

a) Calculate the efficiency of the furnace, if the specific heat of steel is 0.12 kcal/kgOC 

 and fuel oil consumption per batch is 1400 litres. 

 GCV of fuel oil - 10200 kcal/kg,

 Cost of fuel oil - Rs. 46,000/kL, 

 Sp. gr. of fuel oil - 0.92.

b) Due to high cost of oil, the plant management decides to convert to a lower operating 

cost LPG fired furnace lined on the inside with ceramic fibre insulation and with an 

operating efficiency of 80%, for same requirement. The investment towards installation of 

the new furnace is Rs. 50

1 Answer

Answer :

Quantity of steel treated per batch - 80 Tons

a. Efficiency of Furnace:

Useful heat supplied to steel - 80000 x 0.12 x (850 – 30) 

 = 7872000 kcal/batch

…………………….1 mark

Total heat supplied by fuel - 1400 x 0.92 x 10200

= 13137600 kcal/batch

Efficiency of Furnace - 7872000/12067824 = 59.9%

…………………….1 mark

b. Return on Investment (RoI):

Cost of operating fuel oil furnace - 1400 x 46 = Rs. 64400/batch

Efficiency of new LPG furnace - 80%

Heat supplied in new LPG furnace - 7872000/0.8

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