FINAL TECHNICAL REPORT

September 1, 1996, through August 31, 1997

Project Title: ADVANCED PILOT PLANT TESTING OF ILLINOIS COAL FOR BLAST FURNACE INJECTION

ICCI Project Number 96-1/5.2A-1

Principal Investigator: John C. Crelling, Southern Illinois University Carbondale, IL 62901

Project Manager: Ronald Carty, ICCI

ABSTRACT

A potentially new use for Illinois coal is its use as a fuel injected into a blast furnace 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. The overall purpose of this study was 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 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 28% 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). The results of the current research support the following conclusions: 1) 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: 2) 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; 3) 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. 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.

EXECUTIVE SUMMARY

A potentially new use for Illinois coal is its use as a fuel injected into a blast furnace 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. 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. This proposal is a follow-up to one funded for the 1994-95 period. It is intended to advance 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). The reason for doing this work now is that as the industry attempts to go to higher and higher coal injection rates to cut the cost of using expensive coke, the coal char entering the blast furnace is accumulating to the point of interfering with the proper operation of the blast furnace. While the blast furnace operators have steps available to them to alleviate this problem, an additional step is to use coals such as those from the Illinois Basin, which produce a char that burns much faster in the blast furnace than the coals that are presently being used. An additional saving that some steel companies are studying is to eliminate the cost of pulverizing(-200 mesh,0.075mm) the injected coal by injecting granular coal (1-3mm). Illinois Basin coals have not yet been used in this way and, therefore, a test at the CANMET facility is planned to show the suitabity of the coal for this process.

As recently as 1992, the Amanda blast furnace of Armco Steel in Middletown, Ohio was the only one in north America injecting coal. Today there are eleven blast furnaces either injecting coal or about to come on line. There is also a great effort in the ironmaking industry to replace an ever increasing amount of metallurgical coke. This single-minded effort has led to new practices such as enriching the oxygen content of the blast air to enhance the coal combustion and using higher BTU coals and coal blends for a greater energy throughput. The disadvantages of these practices are the cost of the added oxygen and the much lower reactivity of the higher rank coals and their associated chars. An additional development is the introduction of the British granular coal injection system by the Bethlehem Steel Co. In this system granular coal (1-3mm) is used in contrast to the much finer pulverized coal (0.075mm) used elsewhere. In this case the savings in pulverization costs are gained, but at the expense of some combustion efficiency.

Because these developments are of current concern to the industry and, therefore, may have a bearing on the selection of coals for injection in the immediate future, an evaluation of behavior of Illinois coal under these conditions is proposed as the final phase of this project.

The results of previous research on the blast furnace injection properties of Illinois basin coal indicate that when it is injected under the same conditions as the Appalachian coal the Illinois Basin coals will give the more desirable results of putting less char into the raceway and that this char will burnout more quickly.

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

1. The char burnout did not show the expected increase with increasing oxygen enrichment. Indeed, the purpose of enriching the oxygen content of the blast air is to achieve more complete combustion. While some limited experience with very low rank coals shows no enhanced combustion, results from tests using bituminous coal of slightly higher rank than the Herrin No. 6 coal have shown better combustion with the increased oxygen enrichment. Although these results could be interpreted as indicating that the Herrin No. 6 coal may not need oxygen enriched blast air, the results are still surprising and further oxygen enrichment tests are planned.

2. While it is expected that the shock heating that the coal experiences when it is injected will cause it to shatter into finer particles, this apparently did not happen in the current tests. When the particle size of the pulverized and granular chars are compared the major fraction of the char particles was in -60 to -200 mesh size for the granular char. For the pulverized coal the minor fraction of the char particles was in this range. The extremely low burnouts for the granular coal indicate that the Herrin No. 6 is probably not suitable for granular coal injection. Previous tests, however, have shown that the Herrin No. 6 is a very suitable for pulverized coal injection.

3. The calculated burnout of the 50/50 mix 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 seem to be comparable.

This latter result indicates that Herrin No. 6 coal can be blended at least up to equal proportions with higher rank Appalachian coals with no significant change in the more desirable high burnouts and high reactivities of the Illinois coal.

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. In addition, results indicate that the Herrin No. 6 coal can be blended at least up to equal proportions with higher rank Appalachian coals with no significant change in the more desirable high burnouts and high reactivities of the Illinois coal.