Characterization of Coal for Blast Furnace Injection

Characterization of Coal for Blast Furnace Injection - a program of evaluating the potential of Illinois coal as a feedstock for use in blast furnace injection.

Abstract of Recent Work: Advanced Pilot Plant Testing of Illinois Coal for Blast Furnace Injection

Background: A potentially new use for Illinois coal is its use as a fuel injected into a blast furnace (see Figure 1) to produce molten iron as the first step in steel production. Because of its increasing cost and decreasing availability metallurgical coke is now being replaced by coal injected at the tuyere area of the furnace where the blast air enters (see Figure 2).

Fig. 2

Previous work done at SIUC has examined the petrography and combustion reactivity of the chars derived from injected coal as well as the pilot plant testing of three coals. The results of that work are:

Petrography - petrographic analysis of material collected from an active blast furnace showed that coal derived char is entering into the raceway of the blast furnace (see figure 3).

Fig. 3

Reactivity - the reactivity of the Illinois Basin yield chars with significantly higher reactivities in both air and CO2 than chars from higher rank Appalachian coals and blast furnace coke (see Figure 4). These results indicate that the chars from the lower rank coals should have a superior burnout rate in the tuyere and should survive in the raceway environment for a shorter time.

Fig.4

Pilot Plant Testing
A) Illinois Basin coals showed higher combustion rates resulting in higher coal burnout than the Appalachian coal tested under the same conditions.

B) Illinois Basin coals showed higher char combustion reactivities than the Appalachian coal tested under the same conditions.

C) These results indicate that when injected under the same conditions as the Appalachian coal the Illinois Basin coals will put less char into the raceway and that this char will burnout more quickly.

Objectives: The overall purpose of this study is to evaluate the combustion of Illinois coal, during the blast furnace injection process, and to determine the suitability of Illinois coal to become a feed coal in this process. This investigation is significant to the use of Illinois coal in that the research to date suggests that coals of low fluidity and moderate to high sulfur and chlorine contents are suitable feedstocks for blast furnace injection.

Procedures: This work advanced earlier pilot plant testing with the Canadian Centre for Mineral and Energy Technology (CANMET) Energy Research Laboratories in Ottawa, Canada by running injection tests on the Herrin No. 6 coal under conditions that match the experimental conditions that are now being studied in the ironmaking industry. These conditions include oxygen enrichment of the blast air (up to 25% O2), increased coal particle size (granular coal 1-3mm), and coal blends (in this case Herrin No. 6 coal and a higher BTU Appalachian coal).

Results: The results of the current research support the following conclusions:

The char burnout did not show the expected increase with increasing oxygen enrichment and suggests that oxygen enrichment may not be needed with Illinois coal:
Although it is expected that the shock heating that granular coal experiences when it is injected will cause it to shatter into finer particles, this apparently did not happen in the current tests. The resulting extremely low burnouts for the granular coal indicate that the Herrin No. 6 is probably not suitable for granular coal injection. Previous test, however, have shown that the Herrin No. 6 is a very suitable for pulverized coal injection;
The calculated burnout of the 50/50 mix with Appalachian coal is as good as or even slightly better than the Herrin No. 6 sample alone. These results indicate that the Herrin No. 6 is quite acceptable as a blend component with higher rank coals for use in blast furnace injection. Also the reactivities of the Herrin No. 6 and the Herrin No. 6/Pittsburgh blend are similar.

Conclusions: These results and the results of previous studies show that coal from the Illinois Basin have excellent combustion properties for use in blast furnace injection. The Illinois Basin coals burnout more completely and give a higher reactivity char than higher rank coals. These properties make them more desirable as a fuel for high injection rates. Results further indicate that the Herrin No. 6 coal can be blended at least up to equal proportions with higher rank coals with no significant change in the most desirable high burnouts and high char reactivities of the Illinois coal.

References:

Crelling, John C., 1996, Pilot plant testing of Illinois coal for blast furnace injection: Ironmaking Conference Proceedings-Iron and Steel Society of A.I.M.E, v. 55, p. 51-55.

Crelling, John C., 1995, Coal combustion under conditions of blast furnace injection: Ironmaking Conference Proceedings-Iron and Steel Society of A.I.M.E, v. 54, p.73-79.

Crelling, John C., Thomas, K. Mark, and Marsh Harry, 1992, Aspects of the combustion reactivity of coal macerals: Ironmaking Proceedings-Iron and Steel Society of A.I.M.E, v. 51, p.407-413.

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Background: A potentially new use for Illinois coal is its use as a fuel injected into a blast furnace (see Figure 1) to produce molten iron as the first step in steel production. Because of its increasing cost and decreasing availability metallurgical coke is now being replaced by coal injected at the tuyere area of the furnace where the blast air enters (see Figure 2).
	Fig. 2