Pemaco was formerly a chemical facility located in a light industrial and residential area of Maywood, CA, adjacent to the Los Angeles River. No one knows how long hazardous substances had been leaking into the ground but the operations date back to the 1940's. Up until closure of the facility in 1991, chlorinated solvents, aromatic solvents, and flammable liquids had all been used in the chemical mixing, blending, storage and distribution processes at this location.
After a fire at the abandoned Pemaco location, the Environmental Protection Agency (EPA) was called in to stabilize the site and conduct an emergency assessment to determine the extent of contamination into the soil and groundwater.
The EPA worked with several environmental consultants to define a detailed remediation plan for the superfund site. It was determined that solvents and other compounds from tanks and drums caused soil contamination deeper than 90 feet. A 14-acre groundwater plume that migrated into a complex aquifer system under residential properties threatened local water supply wells with Perchloroethylene (PCE), Trichloroethylene (TCE), Trichloroethane (TCA), Dichloroethane (DCA) and Vinyl Chloride (VC).
The remediation technologies used would include Electrical Resistance Heating (ERH), Soil Vapor Extraction (SVE), thermal oxidation, acid gas scrubbing and carbon absorption. The goal was to completely remediate the 1.4-acre site of these Volatile Organic Compounds (VOCs) and redevelop it as a public park. The vapor treatment portion of the project combined ceramic core flameless thermal oxidation (FTO) with acid gas scrubbing, vapor conditioning, and a carbon adsorption polishing step to control potential dioxin emissions.
Working with several environmental engineering firms and the US Army Corp of Engineers, Global Technologies (The Remediation Division of Anguil Environmental) supplied a 1,000 SCFM Flameless Direct Fired Thermal Oxidizer (DFTO) with a caustic scrubber for emission treatment from the SVE units. The vapor treatment system was designed to handle typical averages of 315 parts per million (ppm) but capable of maximum spikes up to 25,000 ppm.
The oxidizer was designed to achieve over 99.9% destruction of hydrocarbons with a unique gas-fired burner that generates virtually no nitrogen compounds (NOX) during combustion. The patented surface combustion technology ensures that all emissions are exposed to the high temperature zone only along the innermost surface. Another important advantage of this arrangement is that hot combustion gases are completely contained within the burner and the oxidizer outer shell remains cool. Therefore the flameless oxidizer can be processing toxins in a matter of seconds after ignition.
A gas flow control valve was integrated to reduce operating costs. By reducing gas flow as the energy content of the VOCs increases the oxidizer uses less supplemental fuel for combustion. It operates in response to control signals from a thermocouple located immediately downstream of the oxidizer burner.
Downstream of the burner, exhaust gases flow into the integral scrubber quench chamber via Fiberglass Reinforced Polymer (FRP) ducting. Adjacent to the oxidizer, the skid mounted scrubber uses polypropylene packing to treat the acid gases. It was optimized to reduce the water usage without sacrificing spray coverage and the design allowed for a max HCl loading of 472 lbs/hr.
The flameless DFTO and scrubber were arranged in an induced draft configuration, pulling exhaust through the system and keeping it under negative pressure to prevent the escape of any corrosive gases.
The United States EPA filmed a documentary about the Pemaco remedial action for internal training purposes. The documentary highlights several "firsts" for the EPA including the use of a flameless thermal oxidizer for vapor treatment. More information can be found on the EPA website.