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CHARWATER C R O U P, I N C IAn IC engine burns the hydrocarbon vapors in the air stream as fuel The exhaust from the IC engine passes through a catalytic converter emission control unit and is ' then released to the atmosphere IC engines are well suited to high concentrations (>3,000 ppmv), moderate to high vacuums (up to 120 in w c ), and low to moderate flowrates (<150 cfm) As hydrocarbon concentrations decrease, additional make-up fuel (typically from portable propane tanks) is required for the engine to run properly Anticipated flowrates, vacuums, and hydrocarbon concentrations at the site are well suited for treatment by an IC engine, at least for the initial period of operation lasting several months after system start-up until extracted hydrocarbon concentrations fall below optimal levels These units usually come self-contained, mounted on trailers and do not require utility hook-ups Thermal oxidation involves oxidizing the hydrocarbons to carbon dioxide and water The method typically requires make-up fuel to supplement the hydrocarbons in extracted vapors The unit heats incoming vapors to a temperature of approximately 1,500 °F, which induces the oxidation of hydrocarbons in the vapor These units can handle a wide range of incoming hydrocarbon concentrations, but typically operate best at concentrations ranging from 3,500 to 12,000 ppmv Most thermal units operate best at high flowrates (>150 cfm) and provide moderate vacuums (up to 100 in w c ) Most thermal units run on 240-volt, 3-phase, 200- ampere electricity and require a natural gas supply to provide make-up fuel Thermal oxidation could be used in the early phases of vapor extraction similar to the IC engine The operation of the catalytic oxidizer is similar to that of the thermal oxidizer, however, it operates at a lower temperature (-600°F) and a catalyst is used in combustion of the hydrocarbon vapors Catalytic oxidizers typically operate best at low to moderate flowrates (100 to 250 cfm) and low to moderate vacuums (up to 100 in w c ) Treatable influent hydrocarbon concentrations are usually limited to 3,000 ppmv Initial influent hydrocarbon concentrations are expected to well exceed typical operating limits of a catalytic oxidizer This treatment may be feasible in the latter phases of soil vapor remediation Vapor-phase GAC treats incoming hydrocarbon vapors by adsorbing hydrocarbons to the surface of the carbon Because the hydrocarbons are not destroyed, the GAC must be replaced when the carbon is saturated with hydrocarbons GAC is a very efficient at hydrocarbon removal, but GAC vessels are usually limited influent hydrocarbon concentrations less than 1,000 ppmv by permits GAC vessels can generally accept high flowrates (up to 400 cfm), and low to moderate vacuums (up to 100 in w c ) GAC vessels can typically absorb 15 to 25% of their weight in gasoline hydrocarbons Using the estimate of 5,000 lbs of gasoline hydrocarbons in soil from Section 2 6, it would take 251000 lbs of vapor-phase GAC to remediate the soil Vapor-phase GAC should not be used in early phases of vapor extraction ' D-107,PAR/RAP 18Y Februar 21 1996