Consider a furnace originally operating with natural gas. We want to substitute it by blast furnace gas. The following procedure may be adopted:
- First calculate the flame temperature of the natural gas. At this flame temperature the furnace was operating.
- Make a mixture 90%natural gas and 10% blast furnace gas and calculate the composition of the mixture and its calorific value.
- Recalculate the flame temperature and analyze. If the flame temperature of the mixture is lower than that of natural gas, preheating of the fuel is required to attain the same flame temperature as that with natural gas. The following table illustrates the effect of preheating efficiency of substitution of blast furnace gas in a natural gas fired furnace
BF gas (%) |
(AFT)BF + NG/AFTNG |
Preheating efficiency (%) |
0 |
1 |
0 |
0.2 |
0.990 |
4 |
0.4 |
0.975 |
9 |
0.6 |
0.950 |
17 |
0.8 |
0.895 |
34 |
1.0 |
0.706 |
84 |
|
In the table BF= blast furnace gas, NG = natural gas. (AFT)BF + NG/AFTNG = 1 means %BF is zero
The table indicates that a mixture of 40%BF+60%NG would have adiabatic flame temperature lower than natural gas. A preheater efficiency of 9% would make the adiabatic flame temperature of the mixture to that of natural gas.
References:
H A fine and G.H. Geiger: Hand book on material and energy balance in Metallurgical Processes |
