Alternative Treatment Technologies

Flameless Thermal Oxidation—(Thermatrix)

Current Status of Technology

Thermatrix states that they are currently providing high performance, effective solutions for the destruction of a wide range of VOC and hazardous air pollutants based on their flameless thermal oxidation technology.

Description of Technology

Flameless Thermal Oxidizers (FTO) are used to treat VOC and chlorinated VOC off-gases by converting them to carbon dioxide, water and hydrogen chloride.  The technology works by generating a uniform thermal reaction zone that oxidizes off-gases without forming incomplete combustion products.  Flame propagation is prevented by the creation of the uniform thermal reaction zone.  This technology has provided DREs in excess of 99.99% for hydrocarbons and CVOCs, with production of extremely low NOx (typically < 2ppmv) and CO (below the limits of detection) formation.  This technology operates over a wide range of flow rates (i.e., 1 to 6500 scfm), with low pressure drops typically less than 3 inches of water.  The FTO technology is equipped with a ceramic matrix that acts as an inherent flame arrestor and heat sink.

 

The physical system consists of a heated packed-bed reactor typically filled with saddle- and spherical-shaped inert ceramic pieces.  A temperature of 1400 to 1700 oF is maintained in the uniform thermal reaction zone contained in the packed bed of the inert ceramic matrix.  Flame suppression within the reactor is provided by the large thermal mass of ceramic that enables the storage or release of large amounts of heat without rapid changes in temperature in the reactor.  During this demonstration a 5 scfm flow rate was fed to the FTO system from one horizontal SVE system.  The vapors from the SVE system were passed through a knockout pot to remove any entrained moisture before being passed through the FTO system.

 

The FTO technology differs from the traditional thermal oxidation systems in that is prevents the formation of products of incomplete combustion (PICs) and hazardous air pollutants (HAPs).  This system coupled with a baseline or innovative in situ remediation technology would be most effective during the early stages of the remediation when contaminant concentrations tend to be high.

 

Figure 1 below shows a basic schematic of the layout of the system. 


 


Figure 1.  Schematic diagram of pilot-scale FTO unit demonstrated at the Savannah River Site, Aiken, South Carolina, in Cooperation with the U.S. Department of Energy, Oak Ridge Operations.  A sidestream of vapors from the SVE wells was diverted from the existing catalytic oxidation unit. 

 

Figure 2 below shows the simplified schematic of the reactor system, labeled as Thermatrix unit in Figure 1 above.


 

 


Figure 2.  More detailed sketch of the thermal treatment unit illustrating internal passage of airstream to be treated.  The unit above illustrates an electrically heated bed, but natural gas can also be used to heat the incoming VOC-contaminated stream.  (Adapted from Thermatrix literature.)

 

This small-scale system permitted operation of the FTO without a caustic scrubber to remove the HCl produced however larger scale systems would require a scrubber to polish the FTO effluent stream.  During the demonstration the FTO was electrically heated.  Full scale operations of >100 scfm throughput would require methane or propane as a heat source.

Site and Contaminants Description

The demonstration site was located at the Savannah River integrated demonstration site.  Specifically, the site was located within a 1-mile square VOC groundwater plume.  The FTO technology was coupled with SVE to treat the contaminants listed in Table I below.  Table I. lists the initial contaminants of concern for this study and their concentrations in the SVE off-gas.

 

Table I. Contaminants of Concern at the Savannah River Site and their initial concentrations.

Contaminant of Concern

Concentration (ppm)

Trichloroethylene (TCE)

157-291

Tetrachloroethylene (PCE)

243-737

1,1,1-Trichloroethane (TCA)

12-21

Performance of Technology and DRE

Over the course of 22 days of continuous operation, a total of 11.17 Kg of total CVOC was destroyed, resulting a total of 99.99% DRE for PCE.  There were no identifiable products of incomplete oxidation observed.  The operating conditions were 1600 oF and 5 scfm.  The inlet concentrations of TCE and TCA were too low to enable a DRE measurement of >99.99%.  However, in further FTO system tests where the stream was spiked with PCE, TCE and TCA the measured DREs were >99.995%, >99.99% and approaching >99.99%, respectively.

The FTO technology can exceed typical DREs achieved by thermal catalytic techniques and by adsorption/recovery systems. Specific tests were not run to analyze for dioxins and furans.

Field Performance Data

CVOC influent concentrations to the FTO varied during the preliminary and continuous demonstration operation from 400 to 1000 ppmv with equilibrium concentrations of 400 to 600 ppmv.

Treatment Effectiveness

Total PCE and CVOC DRE was at least 99% for operational conditions of 3.5 to 7 scfm and 1500 to 1700 oF.  The only exception was for the test run at 1400 oF and 5 scfm which had a PCE DRE of 52.9% and a CVOC DRE of 61.6%.  However, this test had an on stream time of 19 hours.  The system design conditions of 5 scfm and 1600 oF had a DRE of >99.99% for the targeted chlorinated organic compounds.  During the spike testing stage of the demonstration the FTO destroyed a total of >1.5 Kg of CVOC which corresponds to a >99.995% DRE.  Contaminated vapor concentrations (>500 ppmv) and moderate to high flow rates (>100 scfm) improve the overall efficiency of operation and destruction of CVOCs by the FTO.

System Reliability

The Thermatrix FTO is expected to be slightly more reliable and durable than baseline or competing technologies such as thermal oxidation, catalytic thermal oxidation and adsorption/recovery technologies.

Ease of Operation

During the experiment, the FTO was operated with a minimum of attention and required no maintenance or repairs.

Maintenance Requirements

There were no maintenance requirements of the FTO system during the 22 days of continuous operation of the test.  However, the oil in the rotary pump of the mini-SVE needed to be changed during the experiment.  This downtime was for approximately 1 hour and is required every 10 days.

 

The total demonstration of the FTO system took approximately 6 weeks.  There were no required maintenance or repair activities during the demonstration. 

Energy Consumption

This FTO system is most energy efficient when treating compounds with a high heat of combustion where heat recapture can boost operational efficiency.  This system was electrically heated, although methane or propane would be required to heat a larger scale demonstration with a >100 sdfm throughput.

 

Worker Health and Safety Issues

Thermatrix’s FTO contained safety interlocks to prevent potential worker exposure to contaminant vapors in the event of a power or system failure.  Typical health and safety issues of the FTO system during installation and operation are the same as those for other thermal oxidative or thermal catalytic off-gas treatment technologies.  When the caustic scrubber is added to the system, the caustic scrubber waste would have the same safety issues as those associated with adsorption technologies such as GAC.

 

Wastes Produced

Wastes produced include HCl. There were no identifiable products of incomplete oxidation observed.

Risk and Consequence of Catastrophic Failure

There are not any significant routine releases of contaminants to the environment by the FTO system.  There are not any unusual or significant safety concerns associated with the transport of the equipment, samples or other materials associated with the FTO.  Additionally, the FTO technology does not have any open flame, therefore reducing the potential for a fire.

Noise/Aesthetics, etc.

The FTO has a low profile and requires little space therefore the visual impacts are minor. The FTO system creates very little noise or heat.

Data on Key Parameters

This system was operated in a continuous mode for 22 days with 5 scfm of contaminated air flowing to the FTO system and the reactor temperature maintained at 1600 oF.

Capital and Operating Costs

The total capital cost of the FTO for the Savannah River demonstration was $50,000.  This $50,000 capital cost was for an electrically heated, 5 scfm unit without an integrated caustic scrubber.   A larger, more typical 400-scfm, gas-heated FTO is estimated to have a capital cost of $160,000.  Total operating costs vary from $1 to $20 per pound of solvent treated for competing and baseline technologies, as compared with the estimated $0.72 per pound for the FTO system.  Included in the total operating costs are capital recovery, energy, labor and maintenance costs.  The vendor reports that typical, thermal catalytic technologies cost between $1.65 and $2.35 per pound of CVOC destroyed.  Direct thermal destruction systems as compared to thermal catalytic techniques will typically require about twice as much energy. 

Data Gaps Identified

·         There are two different operating temperatures listed in the report for the thermal reaction zone.  One states 1400 to 1700 oF , while the other states 1600 to 1850 oF.  This may be compound dependent and determined by pilot-tests, with the more recalcitrant compounds requiring higher temperature range operation as evident in the data presented for PCE.

 

Vendor

Bob Wilbourn

Thermatrix, Inc.

(615)-5539-9603

 

U.S. DOE, (1995), Flameless Thermal Oxidation at the M Area, Savannah River Site, Aiken, South Carolina, in Cooperation with the U.S. Department of Energy Oak Ridge Operations, Case Study, U.S. DOE, Office of Technology Development, September.