It is an obvious misinterpretation that GRÜNER'S theory-the unconditionally dominant position of indirect reduction-has been believed to be correct.
In this report, the authors criticized the previous theories and established a new one on Coke (or Carbon) Ratio in the blast furnace operation.
Three following conditions should at least be satisfied in order that the blast furnace operation can be performed, that is to say, the conditions of mass balance, gas-solid equilibrium and thermal balance.
We can express the reducing reaction of iron are in the blast furnace by the equation, FeOn+X
1C+X
2CO=Fe+CO+xCO+yCO
2 (1)
Giving top gas ratio (γ=x/y=CO/CO
2), X
2=an and the rate in fraction of direct reduction (D. R), then the required carbon (X
1+X
2) is shown as follows:
X
1×X
2=n (1+γ)(1-D.R) kg atom C/kg atom Fe (2)
where, n is the rate of kg atom Oxygen per kg atom Iron in the burden.
Supposing iron are only consists of pure hematite, accordingly n=1.50, then the required carbon can be calculated by substituting the values of γ and D.R. into the equation (2).
Carbon ratio expressed by the equation (2) from point of view of carbon balance must be limited in consideration of gas-solid equilibrium and thermal balance. We investigated in detail these conditions, considered “Carbon Ratio Curved Surface” in the blast furnace operation and then decided its limitation.
And we showed clearly that the attainable limitation when the furnace operation was performed ideally was about D.R 39% and γ 0.95, then carbon ratio gained was about 410kg per ton pig at blast temperature 1000°C.
Therefore, the furnace operation should be performed at as near the value mentioned above as possible.
After all, the equation (2) shows decreasing coke ratio of blast furnace operation with increasing D.R at constant γ and decreasing γ at constant D.R.
We showed also the Equal Carbon Ratio Curve quantitatively.
It can be concluded that we should abandon the idea of giving the unconditionally dominant position to indirect reduction and pay attention to direct reduction which plays an important part in the blast furnace.
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