Remediation Technologies Screening Matrix, Version 4.0 4.57 Oxidation
(Off-Gas Treatment Technology)
  Description Synonyms Applicability Limitations Site Information Points of Contact
Data Needs Performance Cost References Vendor Info. Health & Safety
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>>3.14 Air Emissions/Off-Gas Treatment

      >>4.57 Oxidation
Introduction>> Organic contaminants are destroyed in a high temperature 1,000C (1,832 F) combustor. Trace organics in contaminated air streams are destroyed at lower temperatures, 450 C (842 F), than conventional combustion by passing the mixture through a catalyst.

Description:

Figure 4-57:
Typical Oxidation Diagram
 

Oxidation equipment (thermal or catalytic) is used for destroying contaminants in the exhaust gas from air strippers and SVE systems. Thermal oxidation units are typically single chamber, refractory-lined oxidizers equipped with a propane or natural gas burner and a stack. Lightweight ceramic blanket refractory is used because many of these units are mounted on skids or trailers. If gasoline is the contaminant, heat exchanger efficiencies are limited to 25 to 35%, and preheat temperatures are maintained below 180 C (530 F) to minimize the possibility of ignition occurring in the heat exchanger. Flame arrestors are always installed between the vapor source and the thermal oxidizer. Burner capacities in the combustion chamber range from 0.5 to 2 million Btus per hour. Operating temperatures range from 760 to 870 C (1,400 C to 1,600 F), and gas residence times are typically 1 second or less.

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.

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Synonyms:

DSERTS Code: F21 (UV Oxidation)

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Applicability:

The target contaminant groups for oxidation are nonhalogenated VOCs and SVOCs, and fuel hydrocarbons. Both precious metal and base metal catalysts have been developed that are reportedly capable of effectively destroying halogenated (including chlorinated) hydrocarbons. Specific chlorinated hydrocarbons that have been treated include TCE, TCA, methylene chloride, and 1,1-DCA.

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Limitations:

The following factors may limit applicability and effectiveness:
  • 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.

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Data Needs:

A detailed discussion of these data elements is provided in Subsection 2.2.3. (Data Requirements for Air Emissions/Off-Gases). Because of the limitations discussed in the previous section, it is important that the contaminated air stream be well characterized.

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Performance Data:

Thermal oxidation is effective for site remediation. Its use is increasing among remediation equipment vendors, and several variations in design are being marketed. Growing applications include treatment of air stripper and vacuum extraction gas-phase emissions.

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.

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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.

EMISSION TECHNOLOGY:

Oxidation

 

RACER PARAMETERS

Scenario A

Scenario B

Scenario C

Scenario D

Small Site

Large Site

Easy

Difficult

Easy

Difficult

 

 

 

 

 

THOUSAND SCFM TREATED PER YEAR

105,120 

105,120

1,051,200

1,051,200

COST PER THOUSAND SCFM

$0.72

$0.83

$0.17

$0.24

SCFM = Standard Cubic Feet per Minute

Detailed Cost Estimate

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References:

California Base Closure Environmental Committee (CBCEC), 1994. Treatment Technologies Applications Matrix for Base Closure Activities, Revision 1, Technology Matching Process Action Team, November, 1994.

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.

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

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

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Site Information:

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Points of Contact:

General FRTR Agency Contacts

Technology Specific Web Sites:

Government Web Sites

Non Government Web Sites

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Vendor Information:

A list of vendors offering Air Emission/Off-Gas Treatment is available from  EPA REACH IT which combines information from three established EPA databases, the Vendor Information System for Innovative Treatment Technologies (VISITT), the Vendor Field Analytical and Characterization Technologies System (Vendor FACTS), and the Innovative Treatment Technologies (ITT), to give users access to comprehensive information about treatment and characterization technologies and their applications.

Government Disclaimer

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Health and Safety:

Hazard Analysis

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