FINAL TECHNICAL REPORT

September 1, 1996, through August 31, 1997

Project Title: PROCESS DEMONSTRATION: DIOXIN PREVENTION IN WASTE COMBUSTORS BY COAL COFIRING

ICCI Project Number: 96-1/5.2B-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. Ronald Carty, ICCI

ABSTRACT

In this project, a field demonstration was performed of process technology in which a municipal waste combustor (MWC) is co-fired with high-sulfur Illinois coal to prevent formation of polychlorinated dibenzo-p-dioxin (PCDDs) and polychlorinated dibenzofuran (PCDFs). Previous ICCI-funded pilot-scale research in the PI's laboratory has shown, in a simulated MWC environment, that sulfur dioxide released during coal combustion can inhibit PCDD/PCDF formation. Last year's research provided a proof-of-concept for this technology through scaled-up tests in EPA's Multi-Fuel Combustor (MFC). In this facility, two different types of RDF (refuse-derived fuel) were co-fired with high-sulfur Illinois No. 6 coal, resulting in significant reduction in PCDD/PCDF levels. The current work aims to demonstrate, in a commercial field unit, the benefits of the coal co-firing technology in preventing PCDD/PCDF formation.

Field demonstation tests were run in the Navy Public Works Center Power Plant located at Portsmouth, Virginia, and operated by Southeastern Public Service Authority (SPSA). Tests consisted of baseline and coal co-fired tests. Two types of stoker coals were used: a high-sulfur Illinois coal and a low-sulfur "Navy" coal. Each coal was fed at two different feed rates. Sampling for dioxins/furans was carried out using EPA Method 23, and gas composition data for O2, CO, HCl, SO2, and H2O were obtained through continuous emission monitors (CEMs). The sampling location was the inlet to the spray dryer absorber (SDA), prior to the plant's air pollution control units.

Results show that co-firing RDF with high-sulfur coal reduces PCDD/PCDF formation, even after adjusting for the fact that less RDF was used for some of the co-fired tests. It also appears that high-sulfur coal co-firing leaves a residual effect -- the reduction in PCDD/PCDF yields persists even after coal feed has been stopped. Net reduction in yields from the initial baseline levels were as high as 73% with the Illinois coal at a sulfur to chlorine ratio of about 1.5. At these conditions, the co-fired coal was about 8% of the total fuel on a heating value basis.

EXECUTIVE SUMMARY

The Air Pollution Prevention and Control Division (APPCD) of the US EPA and the Illinois Clean Coal Institute (ICCI) are co-funding this program to demonstrate technology for preventing formation of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) in municipal waste combustors (MWCs) by co-firing with high-sulfur Illinois coal. This demonstration program aims to determine whether high-sulfur Illinois coals can be effective in reducing emissions of dioxins/furans in incinerators burning municipal solid waste (MSW), hazardous waste, or medical waste, or in waste-fired cement kilns. Successful demonstration may create a market for high sulfur coal in waste combustion, providing the industry a low-cost option for controlling emissions of chlorinated organic compounds.

The objective of this project was to demonstrate in a commercial unit that co-firing high-sulfur Illinois coal with solid waste is effective in preventing PCDD/PCDF formation and that this technology may provide a critical component of strategies to meet current and future emission standards for dioxins/furans. Recent ICCI-funded research in the PI's laboratory in a large pilot-scale unit has provided a proof-of-concept for the coal co-firing technology -- for two types of waste-derived fuels it was shown that coal co-firing can reduce PCDD/PCDF formation.

The Navy Public Works Center Power Plant, located in Portsmouth, Virginia, and operated by Southeastern Public Service Authority (SPSA), was chosen as a site for running the demonstration program. Navy and SPSA personnel were cooperative participants in this demonstration. This site was chosen for a number of reasons:

The facility already had the capabilities, hardware, and experience in co-firing coal

Navy and SPSA authorities showed cooperation and interest in accommodating this program

Past data on plant operation and emissions were available for this project as a comparative benchmark

There was convenient sampling access for obtaining measurements for this project

Flue gas cleaning equipment located beyond the sampling location would ensure continued emission compliance throughout the range of test conditions.

The facility was located reasonably close to the EPA laboratories at Research Triangle Park, NC.

Under normal operation at this facility, coal is used as a substitute to the RDF in the event of RDF feed problems or lack of RDF supply. However, for the duration of this project (one week), the power plant personnel and Navy authorized operation under the co-fired mode, which is a deviation from their standard operation. However, SPSA monitored and controlled plant operations to ensure that all the compliance requirements were met during our tests. Note that due to design constraints, it is not possible to co-fire RDF and coal on a continuous basis without causing damage to the boiler of this facility.

An extensive Quality Assurance Test Plan was prepared for the test program, and copies were sent to the Navy, SPSA, the Virginia Department of Environmental Quality (DEQ) and EPA Region III to ensure that the objectives and limitations of the test program were understood. All the samples for our tests were collected at the spray dryer adbsorber (SDA) inlet, which is upstream of the pollution control devices. Therefore, the reader should note that our sampled data do not correspond to stack emissioins and are not relevant to the plant's permit or applicable regulations. In fact, emission testing conducted in April 1996 for the Virginia DEQ Air Division at this facility obtained samples at the SDA inlet as well as the stack; the PCDD/PCDF levels at the stack were within the permit limits while those at the SDA inlet were similar to the values measured under this program.

The RDF used at the facility is derived from municipal solid waste, processed to remove non-combustibles such as metal and glass and sized to be a majority of 4"x 4"x 12". The plant is set up to feed coal to make up the steam load in case of a feed failure or shortage in the RDF system. This "Navy" coal is a low-sulfur stoker coal from West Virginia. About 80 tons of high-sulfur Illinois No. 6 stoker coal were transported to the test site for our tests. Each coal was fed at two different feed rates with targets of between 5 and 10% of the boiler's firing rate coming from the coal.

Sampling for dioxins/furans was carried out using EPA Method 23, and gas composition data for O2, CO, HCl, SO2, and H2O were obtained through continuous emission monitors (CEMs). The sampling location was the inlet to the SDA, prior to the plant's pollution control units. Results show that co-firing RDF with coal reduces PCDD/PCDF formation, even after adjusting for the fact that less RDF was used during some of the co-fired tests. It also appears that coal co-firing leaves a residual effect -- the reduction in PCDD/PCDF yields persists for some period even after coal feed has been stopped. Net reduction in yields from the initial baseline levels were as high as 73% with the Illinois coal at a sulfur to chlorine ratio of about 1.5. At these conditions, the co-fired coal was about 8% of the total fuel on a heating value (Btu) basis.

Although the reduction in PCDD/PCDF yields is significant with high-sulfur Illinois coal co-firing, the reduced levels were not low enough to meet regulatory requirements with coal co-firing alone. However, additional considerations should be taken into account in assessing this technology as a PCDD/PCDF control option:

The effect of co-firing coal is to prevent formation of PCDD/PCDF rather than simply to control it, as in all current, applied technologies. Thus, all efforts to prevent formation of PCDD/PCDF will eliminate considerable public concern about residues of these toxics ending up in bottom ash or fly ash and presenting additional disposal concerns.

The PCDD/PCDF concentrations formed at MWCs are generally higher than most other industrial sources. Therefore, it is likely that for MWCs with lower PCDD/PCDF concentrations prior to the air pollution cleaning devices or for industrial sources that have lower concentrations of PCDD/PCDF, that coal co-firing may be a sufficient, single measure for PCDD/PCDF control.

Illinois coal is a readily available fuel. Part of the coal costs is recovered through the energy generated during its combustion. Thus, this PCDD/PCDF prevention technology is energy positive.