Method for producing a carbonaceous solid reductant for direct reduction of iron ore

In a method for producing a reactivity promoted carbonaceous solid reductant used for direct reduction of iron ore by means of an additional alkaline earth metal compound, and improved method wherein the improvement comprises grinding and mixing the carbonaceous solid reductant with the alkaline earth metal compound and agglomerating the resulting mixture to produce the reactivity promoted carbonaceous solid reductant of a definite grain size.

The present invention relates to an improved method for producing a 
reactivity promoted carbonaceous solid reductant used for direct reduction 
of iron ore which comprises grinding and mixing the carbonaceous solid 
reductant with an alkaline earth metal compound and agglomerating the 
resulting mixture to produce the reactivity promoted carbonaceous solid 
reductant of a definite grain size. 
Petroleum coke is used as a carbonaceous solid reductant in the direct 
reduction of iron ore for the reason that carbon monoxide gas produced by 
the so-called Boudouard reaction (C+CO.sub.2 .fwdarw.2CO) is used as a 
reductant. The reaction rate of the Boudouard reaction varies with the 
kind of carbon sources used, and the result of the reactivity test 
according to JIS K-2151 shows that petroleum coke is not superior to coal. 
However, petroleum coke does have an advantage over coal in that it 
contains little ash. It is therefore certain that petroleum coke can be a 
far more favorable reductant than coal if only the above reactivity is 
improved. 
For this purpose, various studies have been made, and for example, with 
consideration given to alkaline earth metal compounds, a method to improve 
the reactivity of petroleum coke by incorporating said compounds or 
impregnating with said compounds was proposed (Japanese Patent Application 
Kokai (Laid-Open) No. 101190/1983 and Japanese Patent Application No. 
113860/1982). 
The present invention also makes use of alkaline earth metal compounds, and 
it provides a method to produce the reductant by grinding petroleum coke 
and an alkaline earth metal compound, mixing the both at a required mixing 
ratio and agglomerating the resulting mixture to grain size. According to 
the present invention, not only improvement in the reactivity but also 
selection of the making ratio of the alkaline earth metal compound 
sufficient to reduce the generation of gaseous sulfur compounds can be 
accomplished with ease.

Explanation will be given hereinbelow with reference to one example 
embodying the present invention. 
In FIG. 1, petroleum coke A and an alkaline earth metal compound B are sent 
to a grinding/mixing apparatus 1 wherein the both are ground to a grain 
size suitable for agglomerating and at the same time mixed at a required 
mixing ratio, and the resulting mixture is then sent to an agglomerating 
apparatus 2. In the apparatus 2, said mixture is agglomerated to grain 
size of 1 mm or more and sent to a screen 3 from which agglomerates having 
a grain size of 1 mm or more are charged to a reduction furnace as a 
product and those having grain size of less than 1 mm are returned to the 
agglomerating apparatus 2. As the agglomerating apparatus 2, any of 
pelletizers, extruders and briquetting machines may be used, and water W 
and a binder Bi may be added as the case may be. In addition, the 
agglomerating apparatus 2 is sometimes heated for facilitating 
agglomeration. 
The following is a reactivity test of agglomerates according to the present 
invention. 
Test example (1) 
(1) Agglomerating condition 
(a) Material 
Petroleum coke (grain size, 1 mm minus) 
______________________________________ 
Total Fixed Volatile 
carbon Sulfur carbon matter Ash 
______________________________________ 
Wt (%) 90.0 4.64 85.9 14.0 0.1 
______________________________________ 
Limestone (grain size, 0.25 mm minus) 
______________________________________ 
Al.sub.2 O.sub.3 + 
Loss on 
CaO MgO SiO.sub.2 
ignition 
______________________________________ 
Wt (%) 55.31 0.97 0.2 43.53 
______________________________________ 
Quick lime (grain size, 0.25 mm minus) 
______________________________________ 
Al.sub.2 O.sub.3 + 
Loss on 
CaO MgO SiO.sub.2 
ignition 
______________________________________ 
Wt (%) 97.5 -- 0.3 1.0 
______________________________________ 
(b) Agglomerating condition 
(i) Agglomerating apparatus extruder 
(ii) Agglomerating condition 
Added water 10 wt(%) (based on dry coke) 
Mixing condition (weight ratio) 
dry coke/limestone=100/13.32 
dry coke/quick lime=100/7.56 
No binder 
(2) Product 
(a) Calcium content (dry basis) 
______________________________________ 
Ca wt (%) 
______________________________________ 
Petroleum coke + limestone 
4.25 
Petroleum coke + quick lime 
3.52 
______________________________________ 
(b) Grain size 3 mm or more 
Test example (2) 
(1) Agglomerating condition 
(a) Material 
Petroleum coke (grain size, 0.5 mm minus) 
______________________________________ 
Total Fixed Volatile 
carbon Sulfur carbon matter Ash 
______________________________________ 
Wt (%) 91.9 3.95 83.48 15.78 0.74 
______________________________________ 
Barium Hydroxide, Ba(OH).sub.2.8H.sub.2 O--Reagent 
______________________________________ 
Barium Carbonate 
hydroide (as BaCO.sub.3) 
Iron 
______________________________________ 
Wt (%) &gt;97 3&gt; 0.001&gt; 
______________________________________ 
Dolomite (grain size, 0.25 mm minus) 
______________________________________ 
Al.sub.2 O.sub.3 + 
Loss on 
CaO MgO SiO.sub.2 
ignition 
______________________________________ 
Wt (%) 36.51 14.97 0.47 46.42 
______________________________________ 
(b) Agglomerating condition 
(i) Agglomerating apparatus extruder 
(ii) Agglomerating condition 
Added water 15 wt(%) (based on dry coke) 
Mixing condition 
Dry coke/Barium hydroxide=100/5.0 
Dry coke/Dolomite=100/11.4 
No binder 
(2) Product 
(a) Chemical analysis (dry basis) 
______________________________________ 
Petroleum coke + Barium hydroxide 
2.60 wt. % Ba 
Petroleum coke + Dolomite 
2.69 wt. % Ca 
1.17 wt. % Mg 
______________________________________ 
(b) Grain size 3 mm or more 
The results of reactivity tests for a reductant produced under the 
foregoing conditions are shown in FIG. 2 and FIG. 3. FIG. 2 and FIG. 3 are 
a graphs illustrating the results of the reactivity tests, and the 
reactivity of reductant referred to herein means reactivity with carbon 
dioxide in the Boudouard reaction. The reactivity tests were carried out 
according to JIS K-2151, and the reactivity index is expressed by the 
following equation: 
##EQU1## 
As apparent from these graphs, the reactivity of petroleum coke is 
remarkably improved by adding limestone, quick lime, dolomite or barium 
hydroxide to the coke. As illustrated in FIGS. 2 and 3, a reactivity index 
of above 80% may be achieved according to the present invention after a 
few minutes of reaction time. 
Further, in the present invention, the generation of gaseous sulfur 
compounds can be inhibited by adding a Ca compound to the coke. The test 
result thereof is shown in FIG. 4. In this test, sulfur compounds (H.sub.2 
S+COS) in the exhaust gas from the foregoing reactivity test were 
detected. As apparent from this figure, it is seen that the formation of 
gaseous sulfur compounds is remarkably reduced. 
By increase in the reactivity of the reductant, operation of the reduction 
furnace at low temperatures becomes possible, and besides, by reduction of 
gaseous sulfur compounds, exhaust gas treatment of the process becomes 
easy. 
As described above, the present invention has advantages that a reductant 
having high reactivity and generating few gaseous sulfur compounds can be 
obtained, and besides that the amount of alkaline earth metal compound in 
the agglomerates can be easily changed. This makes it possible to regulate 
the reactivity and besides to determine the optimum amount of alkaline 
earth metal compound according to the sulfur content of solid reductant, 
especially petroleum coke.