Using Direct Fired Thermal Oxidizer Systems to Control Hazardous Emissions During Site Remediation

Pemaco was a former chemical mixing facility based in Maywood, California, next to the Los Angeles River. Many people were unaware of the fact that hazardous substances were leaking into the ground since the 1940s. Before the closure of the facility in 1991, flammable liquids, aromatic solvents, and chlorinated solvents had been utilized in the chemical blending, mixing, storage and distribution processes at this site.

Soil Contamination

When a fire erupted at the abandoned Pemaco location, the Environmental Protection Agency (EPA) was called-in to control the site and perform an emergency evaluation to ascertain the extent of contamination in the groundwater and soil. In collaboration with several environmental consultants, the EPA defined a comprehensive remediation plan for the superfund site. It was concluded that solvents and other compounds from drums and tanks had caused soil contamination deeper than 90 feet. A groundwater plume, which moved into a complicated aquifer system under residential areas, posed a major threat to the local water supply wells with Vinyl Chloride (VC), Perchloroethylene (PCE), Dichloroethane (DCA), Trichloroethane (TCA), and Trichloroethylene (TCE) compounds.

Remediation Technologies

The remediation technologies included Soil Vapor Extraction, Electrical Resistance Heating, Thermal Oxidation, Carbon Absorption, and Acid Gas Scrubbing. The aim was to entirely rectify the 1.4-acre site and rebuild it as a public park. The vapor treatment part of the project integrated ceramic core flameless thermal oxidation with vapor conditioning, acid gas scrubbing, and a carbon adsorption polishing step to manage potential dioxin emissions.

Flameless Direct Fired Thermal Oxidizer

Flameless Direct Fired Thermal Oxidizer

Figure 1. Flameless Direct Fired Thermal Oxidizer

In collaboration with the US Army Corp of Engineers and several environmental engineering firms, Global Technologies division of Anguil Environmental Systems, provided a 1,000 SCFM Flameless Direct Fired Thermal Oxidizer (DFTO) with a caustic scrubber (Figure 1) for emission treatment from the Soil Vapor Extraction units. The vapor treatment system was specifically developed to handle normal averages of 315 parts per million (ppm), but also capable of maximum spikes of up to 25,000 ppm.

The oxidizer was developed to attain 99.9% destruction of hydrocarbons with a special gas-fired burner that creates almost no nitrogen compounds during combustion. The surface combustion technology guarantees that all emissions are subjected to the extreme temperature zone only along the innermost surface. Another major benefit of this arrangement is that hot combustion gases are totally contained within the burner, while the outer shell of the oxidizer remains cool. Thus, the flameless oxidizer can process hazardous substances within a matter of seconds following ignition.

A gas flow control valve was incorporated to cut down operating expenses. When gas flow is reduced as the energy content of the VOCs increases, the oxidizer utilizes less supplemental fuel for combustion. It works in response to control signals from a thermocouple placed downstream of the oxidizer burner.

Downstream of the oxidizer, exhaust gases enter into the integral scrubber quench chamber through Fiberglass Reinforced Polymer ducting. Next to the oxidizer, the skid-mounted scrubber employs polypropylene packing so as to treat the acid gases. The scrubber was designed to reduce water consumption without affecting spray coverage, and the design enabled a maximum HCl loading of 472lbs/hr. The scrubber and the flameless DFTO were arranged in an induced draft configuration, pulling exhaust via the system and maintaining it under negative pressure to prevent any corrosive gas from escaping.

Conclusion

A documentary about the Pemaco remedial action was filmed by the United States EPA for internal training purposes. The documentary highlights a number of "firsts" for the EPA, including the application of a flameless thermal oxidizer for vapor treatment.

This information has been sourced, reviewed and adapted from materials provided by Anguil Environmental Systems.

For more information on this source, please visit Anguil Environmental Systems.

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