FINAL TECHNICAL REPORT

October 1, 1994 through February 29, 1996

Project Title: REDUCTION OF CHLORINATED ORGANICS BY COAL CO-FIRING

ICCI Project Number: 94-1/5.2B-1

Principal Investigator: Dr. Brian K. Gullett, U. S. EPA

Other Investigators: Dr. K. Raghunathan and K. R. Bruce, Acurex Environmental Corporation

Project Manager: Dr. Franklin I. Honea, Illinois Clean Coal Institute

ABSTRACT

Research has been conducted to study the co-firing of coal with municipal solid waste (MSW) in decreasing the formation of chlorinated organic compounds, particularly polychlorinated dibenzo-p-dioxins and furans (PCDDs and PCDFs). Previous research has shown that sulfur present in coal can inhibit the PCDD/PCDF formation. The research is a scale-up of our past pilot-scale work to a demonstration stage and offers a proof-of-concept for co-firing high-sulfur coals. Tests were conducted in US EPA's recently constructed Multi-Fuel Combustor (MFC), a state-of-the-art facility with fuel handling and combustion release rates representative of large field units. Design modifications were performed to teh system to produce refuse-derived fuel (RDF) from MSW and to allow coal-RDF co-firing.

Commercial RDF, further processed at our facility to remove larger fractions, were used in our tests. The coal used was an Illinois #6 coal, pulverized and fed separately into the combustor. The flue gas was sampled for PCDD and PCDF at two locations where the approximate flue gas temperatures were 280 and 140^oC, respectively. Individual baseline tests with RDF and coal were performed, followed by the coal-RDF co-fired test. Results showed that significant levels of PCDD and PCDF were formed during the RDF burn. Most of the formation took place in-flight, i.e., within a few seconds downstream from the burner. However, when only the coal was burned, there was no detectable PCDD or PCDF. Importantly, when RDF was co-fired with coal, the yields decreased sharply from the RDF baseline levels. The sulfur-to-chlorine ratio (S/Cl) in the co-fired test was about 1.5. This finding is consistent with our past ICCI-funded research where, under simulated process conditions, the sulfur inhibition was observed at S/Cl above 1.2. It is also true in our tests, however, that coal addition improved the burn quality, as evidenced by higher flue gas temperatures and lower CO levels. Better burn is also a possible reason for reducing PCDD/PCDF emissions.

Thus, under representative process conditions in the MFC facility, co-firing RDF with coal has been shown to reduce PCDD and PCDF yields substantially. Future testing is planned to examine a gamut of operating and co-firing options so that optimum coal-RDF co-firing conditions can be determined.

EXECUTIVE SUMMARY

The Air Pollution Prevention and Control Division (APPCD) of the United States Environmental Protection Agency (EPA) proposes a co-funded research program in conjunction with the Illinois Clean Coal Institute (ICCI) to evaluate the potential reduction of pollutant emissions by mixing coal with waste-derived fuels. The results of the proposed research will have a positive impact on the use of Illinois coals. Co-firing of coal in incinerators burning municipal solid waste (MSW), hazardous waste, or medical waste, or in cement kilns firing hazardous waste, would provide an economically viable and commercially feasible market for Illinois coal, while providing the waste incineration industry a low-cost option for controlling emissions of chlorinated organic compounds.

The objectives of the research are to perform tests (in a demonstration-scale unit) in a MSW combustion environment to characterize the effects of coal sulfur in inhibiting the formation of chlorinated organic compounds, particularly polychlorinated dibenzo-p-dioxins and furans (PCDDs and PCDFs). The research is aimed at demonstrating the effects of coal sulfur in reducing the emission of chlorinated organic compounds when coal is co-fired with MSW. The proposed research team is well qualified and includes several recognized authorities on the mechanisms and kinetics of PCDD/PCDF formation. Furthermore, the team has conducted significant previous research on the effects of sulfur on PCDD/PCDF formation. The proposed facilities will provide complete in-house capabilities for all facets of the research, including one of the few laboratories solely dedicated to analyzing PCDDs and PCDFs.

The research was performed in EPA's demonstration-scale Multi-Fuel Combustor (MFC) fired by municipal waste-based Refuse-Derived Fuel (RDF) and coal. The MFC facility is newly constructed, and a number of modifications and shake down tests were necessary to accommodate current research. The Commercial RDF and Illinois #6 coal were the fuels used. The results, though from a limited number of tests, support our previous findings from ICCI-funded research that reduced emissions of chlorinated organics are achieved by co-firing MSW combustors with Illinois coal.

Commercial RDF, further processed at our facility to remove larger fractions, were used in our tests. The coal used was an Illinois #6 coal, pulverized and fed separately into the combustor. The flue gas was sampled for PCDD and PCDF at two locations where the approximate flue gas temperatures were 280 and 140^oC, respectively. Individual baseline tests with RDF and coal were performed, followed by the coal-RDF co-fired test. Results showed that significant levels of PCDD and PCDF were formed during the RDF burn. Most of the formation took place in-flight, i.e., within a few seconds downstream from the burner. However, when only the coal was burned, there was no detectable PCDD or PCDF. Importantly, when RDF was co-fired with coal, the yields decreased sharply from the RDF baseline levels. The sulfur-to-chlorine ratio in the co-fired test was about 1.5. This finding is consistent with our past ICCI-funded research where, under simulated process conditions, the sulfur inhibition was prevalent at S/Cl above 1.2. It is also true in our tests, whoever, that coal addition improved the burn quality, as evidenced by higher flue gas temperatures and lower Co levels. Better burn is also a possible reason for reducing PCDD/PCDF emissions.