FINAL TECHNICAL REPORT
September 1, 1995, through August 31, 1996
Project Title: REDUCTION OF CHLORINATED ORGANICS BY COAL CO-FIRING
ICCI Project Number: 95-1/5.2B-2
Principal Investigator: Dr. Brian K. Gullett, U.S. EPA
Other Investigators: Dr. K. Raghunathan and K.R. Bruce, Acurex Environmental Corporation
Project Manager: Dr. Ken Ho, ICCI
ABSTRACT
Research has been conducted toward developing technology for co-firing of
coal with municipal solid waste (MSW) in order to reduce emissions of chlorinated
organic compounds, particularly polychlorinated dibenzo-p-dioxins and furans
(PCDDs and PCDFs). Previous bench- and pilot-scale research has shown that
sulfur present in coal can inhibit the PCDD and PCDF formation; scaled-up
tests in EPA's 2-MM Btu/hr combustor, showed that co-firing high-sulfur Illinois
coal with refuse derived fuel (RDF) reduces the PCDD and PCDF yields
substantially.
The objective of this research is to identify the effect of process and co-firing
options in reducing the PCDD and PCDF yield. Densified refuse derived fuel
(dRDF) and high-sulfur Illinois coal were the fuels used for testing. The
research program involved two phases: under Phase I, experiments 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. The MFC was fired, at varying rates, with dRDF and coal,
and sampled for PCDD and PCDF. Tests were conducted over a range of process
variables such as lime injection, HCl concentration, flue gas temperature,
quench, and residence time so that the results are applicable to a wide variety
of waste combustors. Phase II involved developing a comprehensive statistical
model for PCDD and PCDF formation and control from the Phase I data: the
model considered variables such as coal/RDF feed; temperature and residence
time; combustion quality indicators; SO2 and HCl concentrations;
and emissions of volatile organics.
A 21-run statistical test matrix was derived for Phase I and all the tests were completed. PCDD and PCDF yields from dRDF combustion were significant, and majority of the formation took place in the temperature range 600 to 300C, within about 0.5 sec. Coal co-firing reduced PCDD and PCDF formation substantially. Model results also show that coal addition is effective at both high and low HCl levels in the combustor. Therefore, it appears that co-firing coal with waste-derived fuel is a promising technology for PCDD and PCDF prevention.
EXECUTIVE SUMMARY
The United States Environmental Protection Agency (EPA) conducted 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 demonstrate that co-firing high-sulfur
coal with solid waste can be effective in meeting with emission standards
and is applicable over a range of waste characteristics. Under this program,
tests will be performed in a MSW combustion environment to characterize the
effects of coal sulfur in reducing the emissions of chlorinated organic compounds
under a range of waste combustor process conditions. The proposed research
team is well qualified and includes several recognized authorities on the
mechanisms and kinetics of PCDD and PCDF formation. Furthermore, the team
has conducted significant previous research on the effects of sulfur on PCDD
and 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 objective is to identify the effect of process and co-firing
options in reducing the PCDD and PCDF yield. Densified refuse derived fuel
(dRDF) and high-sulfur Illinois coal were the fuels used for testing. The
research program involved two phases: under Phase I, experiments 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. The MFC was fired, at varying rates, with dRDF and coal,
and sampled for PCDD and PCDF. Tests were conducted over a range of process
variables such as lime injection, HCl concentration, flue gas temperature,
quench, and residence time so that the results are applicable to a wide variety
of waste combustors. Phase II involved developing a comprehensive statistical
model for PCDD and PCDF formation and control from the Phase I data: the
model considered variables such as coal/RDF feed; temperature and residence
time; combustion quality indicators; SO2 and HCl concentrations;
and emissions of volatile organics.
A 21-run statistical test matrix was derived for Phase I and all the tests
were completed. PCDD and PCDF yields from dRDF combustion were significant,
and majority of the formation took place in the temperature range 600 to
300C, within about 0.5 sec. Coal co-firing reduced PCDD and PCDF formation
substantially. Model results also show that coal addition is effective at
both high and low HCl levels in the combustor. Therefore, it appears that
co-firing coal with waste-derived fuel is a promising technology for PCDD
and PCDF prevention.