Initial Development of a Continuous Emission Monitor for Dioxins (2002)

Under contract DE-AC26-98FT-40370, SRI International has completed the third phase of a planned three-phase effort to develop a laboratory prototype continuous emission monitor (CEM) for dioxins and furans generated during the incineration of waste materials at DOE remediation sites. The project was initiated on July 29, 1998 with the technical effort completed in October 2001. During this research effort, SRI has made numerous improvements in our jet-REMPI instrument. These improvements have involved characterization and optimization of the molecular cooling in the gas jet, implementation of a custom-fabricated, four pulsed valve assembly, new data acquisition and display software, and preliminary development of a wavelength and mass calibration approach. We have also measured the REMPI excitation spectra of numerous organic compounds that are likely to be present in the exhaust stream of a waste incinerator. These spectra must be well characterized in the laboratory to understand any potential interferences that might arise when monitoring for dioxin and furan congeners. Our results to date continue to validate the original concept of using jet-REMPI as the detection method in a dioxin CEM. Using only commercial components with minor modifications, we have already demonstrated a detection sensitivity in the low ppt range with sufficient chemical specificity to separately detect two closely related congeners of dichlorodibenzodioxin present in a mixture. To demonstrate the utility of this methodology outside of the controlled conditions of the laboratory, we performed a series of pseudo-field experiments at the US Environmental Protection Agency's National Risk Management Research Laboratory, Research Triangle Park, NC. The instrument used for those studies was built by SRI under contract with US EPA, and was an exact duplicate of the SRI system. This duplication allowed the experiments to be conducted without transporting the SRI system to the EPA site. Using the jet-REMPI system in conjunction with a combustion flow reactor, the joint SRI-EPA team discovered several new, and unexpected, chemical species in the exhaust stream of a pure methane flame. Based on our work in this project, we have developed a number of concepts for instrumental improvements that will substantially increase our sensitivity while maintaining the exceptional selectivity required of a dioxin CEM. In addition, we have developed several system configurations with varying degrees of functionality that can be further developed and deployed for process monitoring, surrogate measurements, and potentially, as a dioxin control CEM. Due to the extremely demanding regulatory compliance monitoring requirements involving both congener specificity and sub-part-per-trillion sensitivity with near real-time speed, we believe it is not as yet possible to specify a system configuration for a true dioxin compliance monitor. While a true TEQ compliance monitor is not yet possible using the jet-REMPI approach, the technique may prove useful as a surrogate, or indicator monitor. This application would involve continuous measurement of surrogate compounds, such as lowly chlorinated dioxins and furans, whose concentrations have been previously correlated with the TEQ. Such an instrument would not require the extreme sensitivity of a compliance monitor although the high degree of chemical selectivity would remain important.