Description:

Catalytic oxidation is a relatively recently applied alternative for the treatment of VOCs in air streams resulting from remedial operations. The addition of a catalyst accelerates the rate of oxidation by adsorbing the oxygen and the contaminant on the catalyst surface where they react to form carbon dioxide, water, and hydrochloric gas. The catalyst enables the oxidation reaction to occur at much lower temperatures than required by a conventional thermal oxidation. VOCs are thermally destroyed at temperatures typically ranging from 320° to 540° C (600° to 1,000° F) by using a solid catalyst. First, the contaminated air is directly preheated (electrically or, more frequently, using natural gas or propane) to reach a temperature necessary to initiate the catalytic oxidation [310 °C to 370 °C (600 °C to 700 °F)] of the VOCs. Then the preheated VOC-laden air is passed through a bed of solid catalysts where the VOCs are rapidly oxidized. Thermal oxidizers can often be converted to catalytic units after initially high influent contaminant concentrations decrease to less than 1,000 to 5,000 ppmv.

Catalytic Oxidation

Catalyst systems used to oxidize VOCs typically use metal oxides such as nickel oxide, copper oxide, manganese dioxide, or chromium oxide. Noble metals such as platinum and palladium may also be used. Most commercially available catalysts are proprietary.

Internal Combustion Engine Oxidation

Organic contaminants in air can be used as fuel and burned in an internal combustion engine. When the concentration of organics is too low, auxiliary fuel is added to enhance the oxidation.

Thermal Oxidation

In most cases, the thermal or catalytic oxidation process can be enhanced to reduce auxiliary fuel costs by using an air-to-air heat exchanger to transfer heat from the exhaust gases to the incoming contaminated air. Typically, about 50% of the heat of the exhaust gases is recovered.

UV Oxidation

Oxidation of organic contaminants in air can also be achieved by UV oxidation. As described in UV Oxidation of Wastewater (Technology Profile Section 4.44), UV oxidation is the process by which chemical bonds of the contaminants are broken under the influence of UV light. Products of photo-degradation vary according to the matrix in which the process occurs, but the complete conversion of an organic contaminant to CO₂, H₂O, etc. is not probable.

Synonyms:

DSERTS Code: F21 (UV Oxidation)

Applicability:

Limitations:

• If sulfur or halogenated compounds or high particulate loadings are in the emissions stream, the catalyst can be poisoned/deactivated and require replacement.
• Destruction of halogenated compounds requires special catalysts, special materials or construction, and the addition of a flue gas scrubber to reduce acid gas emissions.
• Influent gas concentrations must be < 25% of the lower explosive limit for catalytic and thermal oxidation.
• The presence of chlorinated hydrocarbons (see comment above) and some heavy metals (e.g., lead) may poison a particular catalyst.

Data Needs:

Performance Data:

More than 20 firms manufacture catalytic oxidation systems specifically for remedial activities. These firms will generally supply the equipment to remedial action contractors for integration with specific remedial technologies, such as in situ vapor extraction of organics from soil or air stripping of organics from ground water.

Despite its relatively newer application in remedial activities, catalytic oxidation is a mature technology, and its status as an implementable technology is well established. Nevertheless, the technology continues to evolve with respect to heat recovery techniques, catalysts to increase destruction efficiency and/or to extend the operating life of the catalyst bed, and performance data on a wider range of VOCs.

Cost:

The primary factors that will impact the overall cost include quantity, concentration, and type of contaminant; required destruction efficiencies; management of residuals; and utility and fuel costs.  The key cost driver information and cost analysis was developed using the 2006 version of the Remedial Action Cost Engineering and Requirements (RACER) software.

Key Cost Drivers 

·        Approach

o       Catalytic oxidation is more expensive than thermal oxidation at low flow rates, vice versa for high flow rates.  Additionally, thermal oxidation is more economical at very high VOC concentrations and catalytic oxidation is more economical at moderate VOC concentrations.   Commonly at the start of a project VOC concentrations are high for a limited time and the leasing option for a thermal unit should be evaluated for this limited duration.  No other sensitivity analysis is feasible.

Cost Analysis

The following table represents estimated costs (by common unit of measure) to apply oxidation technology at sites of varying size and complexity.   A more detailed cost estimate table which includes specific site characteristics and significant cost elements that contributed to the final costs can be viewed by clicking on the link below.

SCFM = Standard Cubic Feet per Minute

Detailed Cost Estimate

References:

Elliott, Captain Michael G., and Captain Edward G. Marchand, 1989. "U.S. Air Force Air Stripping and Emissions Control Research," in Proceedings of the 14th Annual Army Environmental R&D Symposium, Williamsburg, VA, USATHAMA Report No. CETHA-TE-TR-90055.

EPA, 1987. "Destruction of Organic Contaminants by Catalytic Oxidation", EPA/600/D-87/224.

EPA, 1997. On-Site Incineration: Overview of Superfund Operating Experience.

Federal Remediation Technologies Roundtable, 1995. Remediation Case Studies: Soil Vapor Extraction, EPA/542/R-95/004.

• Soil Vapor Extraction at the North Fire Training Area (NFTA), Luke AFB, Arizona
• In Situ Soil Vapor Extraction at McClellan Air Force Base, California
• Soil Vapor Extraction at the SMS Instruments Superfund Site, Deer Park, New York

Federal Remediation Technologies Roundtable, 1997. Remediation Case Studies: Soil Vapor Extraction and Other In Situ Technologies, EPA/542/R-97/009.

• Flameless Thermal Oxidation at the U.S. Department of Energy's Savannah River Site, M Area, Aiken, South Carolina (In Cooperation With the U.S. Department of Energy, Oak Ridge Operations)

Federal Remediation Technologies Roundtable, 1998. Remediation Case Studies: In Situ Soil Treatment Technologies (Soil Vapor Extraction, Thermal Processes), EPA/542/R-98/012

• Soil Vapor Extraction at Site ST-35, Davis-Monthan AFB, Arizona
• Photolytic Destruction Technology Demonstration at NAS North Island, Site 9, San Diego, California

• Dover AFB
• Wurtsmith AFB
• Former gasoline service station, Santa Monica, CA
• NEL Demo: NAS North Island Installation Restoration (IR) Site 11
• Site ST-35, Davis-Monthan AFB, AZ
• North Fire Training Area (NFTA), Luke AFB, AZ
• McClellan AFB, Operable Unit D, Site S, CA
• NAS North Island, Site 9, San Diego, CA
• SMS Instruments Superfund Site, Deer Park, NY
• U.S. Department of Energy (DOE), Savannah River Site, M Area Process Sewer/Integrated Demonstration Site, Aiken, SC