Patent Application
20070183952
The present invention relates to the catalytic treatment of exhaust gases. More specifically, the present invention relates to an apparatus for the catalytic treatment of exhaust gases.
Many industrial processing schemes involve the heating of raw materials to enable mold castings (e.g., plastics), thin film fabrication (e.g., microelectronics), and extrusion (e.g., filter materials) as the first step in product manufacturing, to name just a few. The heating of polymeric and other man-made materials can liberate volatile organic compounds (VOCs). VOCs may be harmful to the environment. Of particular concern is the emission of formaldehyde, which has been the subject of investigation and regulation by the U.S. Environmental Protection Agency.
Existing technologies for the remediation of formaldehyde from industrial smoke stack effluent streams include water misting and total combustion furnace technologies. In the former method, the emission stream is subjected to a water mist, which serves to condense formaldehyde and other VOCs. The formaldehyde and VOCs are captured in the collected water. The formaldehyde-contaminated water is then recovered and shipped to chemical processing facilities where the formaldehyde is removed from the water and destroyed by conventional means. This is a time-consuming and costly process that exhibits insufficient capacity to remove formaldehyde at levels encountered in the heating of many classes of industrial-use resin materials. Total combustion furnaces do not suffer the limitations of water-misting technologies; however, they are very costly to procure, integrate, and maintain for the purpose of reducing VOC emissions, specifically formaldehyde emissions in industrial processing facilities.
NASA low-temperature oxidation catalyst (LTOC) technology was originally developed for space-based carbon dioxide (CO2) laser systems, and has subsequently been adapted to effect catalytic oxidation of carbon monoxide (CO) and VOC species (e.g., hydrocarbons, aldehydes, and keytones) to CO2 and water, and to reduce nitrogen oxide species (NOx) to molecular nitrogen and (N2) and oxygen (O2). Moreover, the LTOC technology has been adapted for use in environments ranging from the cold vacuum of space to the extremely high temperature and pressure conditions of internal combustion engines. The existing application heritage of the LTOC supports the integration of this technology for formaldehyde remediation for conditions extending over several decades of pressure and temperature.
Recently, a catalyst for the oxidation of volatile organic compounds has been developed. U.S. Pat. No. 6,132,694, issued to Wood, et al., discloses a process for oxidizing volatile organic compounds to carbon dioxide and water with the minimal addition of energy, which is hereby incorporated herein by reference as if set forth in its entirety. In the disclosed process, a mixture of the volatile organic compound and an oxidizing agent (e.g., ambient air containing the volatile organic compound) is exposed to a catalyst which includes a noble metal dispersed on a metal oxide which possesses more than ones oxidation state. Especially good results are obtained when the noble metal is platinum, and the metal oxide which possesses more than one oxidation state is tin oxide. A promoter (i.e., a small amount of an oxide of a transition series metal) may be used in association with the tin oxide to provide very beneficial results.
Additional oxidation catalysts, and methods for making same, which could potentially be used in or with at least one embodiment of the instant invention, can be found in U.S. Pat. No. 4,855,274 entitled “Process for Making a Noble Metal Oxide Catalyst”; U.S. Pat. No. 4,829,035 entitled “Reactivation Of A Tin Oxide-Containing Catalyst”; U.S. Pat. No. 4,912,082 entitled “Catalyst For Carbon Monoxide Oxidation”; U.S. Pat. No. 4,991,181 entitled “Catalyst For Carbon Monoxide Oxidation”; U.S. Pat. No. 5,585,083 entitled “Catalytic Process For Formaldehyde Oxidation”; U.S. Pat. No. 5,948,965 entitled “Solid State Carbon Monoxide Sensor”; and U.S. Pat. No. 6,132,694 entitled “Catalyst for Oxidation of Volatile Organic Compounds.” These patents are hereby incorporated herein by reference as if set forth in their entirety. Likewise, the following U.S. Patent Applications have been filed for other catalysts and methods that could potentially be used in or with at least one embodiment of the present invention, namely U.S. patent application Ser. No. 09/607,211 entitled “Process for Coating Substrates With Catalyst Materials,” filed on Jun. 30, 2000; Ser. No. 10/056,845 entitled “Methodology for the Effective Stabilization of Tin-Oxide-Based Oxidation/Reduction Catalysts,” filed on Jan. 22, 2002; Ser. No. 10/342,660 entitled “Ruthenium Stabilization For Improved Oxidation/Reduction Catalyst Systems,” filed on Jan. 13, 2003; and Ser. No. 10/601,801 entitled “Method For The Detection Of Volatile Organic Compounds Using A Catalytic Oxidation Sensor,” filed on Jun. 20, 2003. These U.S. Patent Applications are also hereby incorporated herein by reference as if set forth in their entirety.
Thus, there is a need to develop a chemical oxidation system to supplant the current state-of-the-art in pollutant emission remediation by offering a more efficient and cost effective alternative. Therefore, it would be advantageous to provide an exhaust gas treatment system that can incorporate an appropriate catalyst, such as the NASA LTOC technology.
In view of the insufficiencies discussed above, it is an object of the present invention to apply LTOC technology to the treatment of exhaust gas emissions. It is a further object of the present invention to provide an exhaust gas treatment system that can be easily and cost-efficiently integrated into industrial processing facilities. Furthermore, the present invention will enable industry to comply with U.S. Environmental Protection Agency mandates on formaldehyde and other VOC emissions at significantly lower cost than previous approaches.
Generally, the present invention is an exhaust gas treatment system that provides tremendous flexibility to facilitate integration. The present invention also lends itself to various configurations and scales. The apparatus of the present invention can be plumbed inline with the emission ductwork that typically culminates at a smoke stack interface, known in the art and common to industrial facilities. This allows the present invention to be installed in a new facility or as an upgrade to an existing facility.
In various embodiments, the present invention is comprised of the following primary components: an exhaust gas inlet section, an optional oxygen enrichment system, a plurality of catalyst holding arms, and an exhaust gas outlet section. The exhaust gas inlet and outlet sections can be designed to mate to existing exhaust gas plumbing systems for industrial facilities.
Downstream of the exhaust gas inlet section is the optional oxygen enrichment system that increases the oxygen concentration of the pollutant exhaust gas stream. The oxygen enrichment system contributes to optimizing catalytic performance by maintaining an excess amount of oxygen in the exhaust gas stream and imparting greater turbulence to the exhaust gas stream. The oxygen enrichment system can be an active or passive system. For example, the oxygen enrichment system may contain a plurality of passive oxygen enrichment ports.
lnside the plurality of catalyst holding arms, the catalytic oxidation of carbon monoxide, formaldehyde, and/or other VOCs can occur, additionally the reduction of nitrogen oxide species might also take place. Disposed within each catalyst holding arm is at least one catalyst coated substrate, for example, the NASA LTOC technology. Optionally, each catalyst holding arm can be selectively closed off using upstream and downstream isolation valves. The design of the plurality of catalyst holding arms also can increase catalytic efficiency by controlling the exhaust gas stream volumetric flow rate through each catalytic substrate. Additionally, the exterior of each catalyst holding arm can be covered with a thermal control means, such as heater tape, or similar device, to allow thermal control of the catalytic substrate.
The catalyst substrates are coated with a catalyst formulation optimized for the specific environmental conditions to be encountered. In one embodiment, formaldehyde and other VOCs in the exhaust gas stream are oxidized to CO2 and water at the catalyst substrate surface, and are subsequently displaced by new pollutant molecules, thereby replenishing the catalytically active catalyst substrate surface. The formaldehyde and reactive VOCs can be oxidized completely to CO2 and water. The catalytic substrate can be, for example, catalyst coated bricks, particles, beads, fabrics, or filter materials.
Longevity and durability of the catalyst substrates can be increased by the inclusion of an optional filter upstream of the catalyst substrates. Upstream and downstream of the filter, there can be upstream and downstream filter cut-off valves.
Other features and advantages of the invention will be apparent from the following detailed description taken in conjunction with the following drawings, wherein like reference numerals represent like features.
While this invention is susceptible of embodiments in many different forms, there are, shown in the drawings and will herein be described in detail, specific embodiments of the invention with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the broad aspect of the invention to the embodiments illustrated.
Generally, the present invention is an exhaust gas treatment system 100. The system 100 provides tremendous flexibility to facilitate integration. Additionally, the present invention lends itself to various configurations and scales ranging from sub-one-inch to several feet or more. The present invention is comprised of the following primary components, shown in
The present invention can be plumbed inline with the emission ductwork that typically culminates at a smoke stack interface, known in the art and common to industrial facilities. The exhaust gas inlet section 110 can be designed to mate to existing exhaust gas plumbing systems for industrial facilities. This allows the present invention to be installed in a new facility or as an upgrade to an existing facility.
Downstream of the exhaust gas inlet section 110 is the optional oxygen enrichment system 120. The optional oxygen enrichment system 120 increases the oxygen concentration of the pollutant exhaust gas stream. The oxygen enrichment system 120 maintains an excess amount of oxygen in the exhaust gas stream to enhance the catalytic oxidation of carbon monoxide, formaldehyde, and other VOCs. The oxygen enrichment system 120 also imparts greater turbulence to the exhaust gas stream which increases the residence time of each pollutant molecule at the catalyst/air interface. Thus, the oxygen enrichment system 120 contributes two-fold to optimizing catalytic performance of the present invention. In oxygen rich environments or for exhaust gas streams having sufficient turbulence, the apparatus of the present invention may still be operable and the optional oxygen enrichment system 120 may not be required.
One embodiment of the oxygen enrichment system 120 comprises a plurality of oxygen enrichment ports 150 located downstream of the exhaust gas inlet section. The oxygen enrichment system 120 can be an active or passive system. An active system can pump air or oxygen into the exhaust gas stream. A passive injection system can allow the influx of air or oxygen using the moving exhaust gas stream to draw air or oxygen into the exhaust gas stream.
In this embodiment, inside the plurality of catalyst holding arms 130, the catalytic oxidation of formaldehyde and other VOCs occurs. Disposed within each catalyst holding arm 130 is at least one catalyst coated substrate 160, for example, as shown in
As shown, the plurality of catalyst holding arms 130 are approximately equal in length and aligned in the same general direction. In practice, the plurality of catalyst holding arms 130 can vary in length and alignment. Generally, the exhaust gas stream flow through the holding arms 130 is referred to as being parallel, which can be parallel in the geometric sense, but more appropriately, and as intended herein, is parallel in the fluid dynamic or electrical circuit sense. That is, the exhaust gas stream through the apparatus 100 is separated from a single stream into a plurality of exhaust gas streams, wherein each gas stream of the plurality of gas streams flows through a separate catalyst holding arm 130. Further, the plurality of catalyst holding arms 130 need not be geometrically parallel and can include bends or turns in the plumbing. Thus, the term “parallel,” as used herein means parallel in the fluid dynamic sense and not necessarily geometrically parallel.
The design of the plurality of catalyst holding arms 130 also can increase catalytic efficiency. The exhaust gas stream volumetric flow rate, and hence the pollutant residence time at the catalyst substrate 160, can be affected by designing a system in which the combined cross sectional area of the catalyst holding arms 130 is greater than the cross sectional area of the exhaust gas inlet section 110. For example a one-foot diameter exhaust gas inlet section 130 diverging into six 0.5-foot catalyst holding arms 130 would effect a 3-to-1 reduction in the exhaust gas stream volumetric flow rate at the catalyst substrate 160, potentially resulting in a three-fold increase in catalytic efficiency. Additionally, the exterior of each catalyst holding arm 130 can be covered with a thermal control means, either active or passive (not shown), such as heater tape, or similar device, to allow thermal control of the catalytic substrate 160. This further enhances catalytic efficiency, including formaldehyde destruction performance, particularly in cold climates.
The catalyst substrates 160 are coated with a catalyst formulation optimized for the specific environmental conditions (e.g., pressure, temperature, flow rate, pollutant concentration, etc.) to be encountered. Carbon monoxide, formaldehyde, and other VOCs in the exhaust gas stream are oxidized to CO2 and water at the catalyst substrate 160 surface, and are subsequently displaced by new pollutant molecules, thereby replenishing the catalytically active catalyst substrate 160 surface. The carbon monoxide, formaldehyde, and reactive VOCs can be oxidized completely to CO2 and water.
In one embodiment, the catalytic substrate 160 is a catalyst coated ceramic brick 190, shown in
In addition to catalyst coated bricks 190, the catalyst substrate 160 can comprise a variety of materials, for example, the substrate can also be catalyst coated particles (e.g., silica, alumina) or beads, fabrics, or filter materials, not shown. As such, the present invention exhibits tremendous packaging flexibility that can contribute favorably to its successful integration into new and existing facilities.
Longevity and durability of the catalyst substrates 160 will be highly application dependent and driven by the concentration of catalytic poisons, such as sulfur, and particulate matter, such as oil and grease, in the exhaust gas stream. Many industrial facilities incorporate particulate filters prior to exhausting the emission into the environment, thereby mitigating the risk of catalytic poisoning. Additional filtering within the present invention would further reduce the potential for catalytic poisoning and extend the longevity of the replaceable catalyst substrates 160.
For some applications, existing techniques that are currently commercially available can be applied to refresh degraded catalyst substrates 160, further reducing the maintenance cost of the present invention.
After passing through the plurality of catalyst holding arms 130, the plurality of exhaust gas streams are recombined in the exhaust gas exit section 140. As was the case with the exhaust gas inlet section 110, the exhaust gas exit section 140 can be designed to mate to existing exhaust gas plumbing systems for industrial facilities, thereby allowing the present invention to be installed in a new facility or as an upgrade to an existing facility. Alternately, each of the plurality of catalyst holding arms can be plumbed directly to the smoke stack of the facility.
Although only a few exemplary embodiments of this invention have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention as defined in the following claims. In the claims, means-plus-function and step-plus-function clauses are intended to cover the structures or acts described herein as performing the recited function and not only structural equivalents, but also equivalent structures.
The invention described herein was made in the performance of work under a NASA contract and by employees of the United States Government and is subject to the provisions of Public Law 96-517 (35 U.S.C. §202) and may be manufactured and used by or for the Government for governmental purposes without the payment of any royalties thereon or therefor. In accordance with 35 U.S.C. §202, the contractor elected not to retain title.
