Consideration on Oil Replacement Coefficient in Blast Furnace Operation

Studies for the improvement in the blast furnace practice-II

Abstract

There are many reports on heavy oil replacement coefficient in the blast furnace operation. But in most cases the replacement coefficients have been calculated by the following equation:
Replacement coefficient R= (Standard coke rate)-(coke rate with oil injection)/Oil rate
However the use of this equation for the theoretical study involves many problems because of the various factors in the blast furnace operation.
In this report, we outlined our theoretical study on the oil replacement coefficient and proposed a new method of calculation based on carbon balance in the previous report.
(1) We discussed the heavy oil replacement coefficient R, when top gas ratio γ= (CO/CO₂) and utilization coefficient of hydrogen γ₁, did not change before and after the commencement of oil injection.
The following equation was deduced:
R= 6Bη(1+γ) x+A
Where A: carbon fraction in heavy oil, B: hydrogen fraction in heavy oil, x=O_a/O_b, O_a: proportion of oxygen removed by CO before oil injection in the oxygen reduced by hydrogen from oil during oil injection. O_b: amount of oxygen removed by hydrogen from oil.(x is always between 0 and 1)
(i) When the heat absorption by oil injection is completely compensated by elevating the blast temperature etc.(when there is no change in the total direct reduction rate caused by oil injection).
x=1, ∴R= 6Bη(1+γ) +A
In this case R takes the maximum value.
(ii) When the heat absorption by oil injection is not completely compensated (when direct reduction rate decreases during oil injection),
x<1 ∴R= 6Bη(1+γ) x+A
In the special case when hydrogen produced from heavy oil reacts only with the oxygen that has been removed by direct reduction before oil injection.
x=0 ∴ R= A
In this case R takes the minimum value.
(2) Relations between oil rate Y and R are as follows. Let Y_L be the maximum quantity of oil that can be injected without any change in direct reduction rate.
(i) Y≤Y_L, R= 6Bη(1+γ) +A
(ii) Y>Y_L
R= 6Bη(1+γ)α+A+6Bη(1+γ)(1-α) Y_L/Y
where α: factor depending on thermal balance.
These relations show that the heat compensation is very important to gain high oil replacement coefficient.
(3) Examples of applying the new method of calculation.
(i) When the blast temperature is increased from 900°C to 1000°C for heat compensation. The following are gained:
When Y≤12⋅8 (kg/t) R= 1⋅535
whenY>12⋅8 R= 1⋅035+6⋅170/Y
(ii) The oil replacement coefficients for Kokura No.1 and No.2 blast furnace were calculated as follows:
R: 1⋅32-1⋅59 (No.1 B.F.) R: 1⋅35-1⋅63 (No.2 B.F.)