problem
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).
Action
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.
solution
Working with several environmental
engineering firms and the US Army Corp of Engineers, Global
Technologies 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 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 oxidizer, 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.