Abstract:
Methods and apparatus for enhanced destruction of industrial waste gases include coating a high emissivity material onto to at least portions of the vessel walls of a direct fired incinerator, such as a thermal oxidizer, in order to enhance its incineration efficiencies, particularly for the incineration of volatile organic compounds (VOCs).

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application is based on and claims domestic priority benefits under 35 USC §119(e) from, U.S. Provisional Application Ser. No. 60/686,428 filed on Jun. 2, 2005, the entire content of which is expressly incorporated hereinto by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates generally to the incineration of industrial waste gases and, in one aspect, to methods and systems for the enhanced incineration of industrial waste gases containing volatile organic compounds (VOCs).  
       BACKGROUND AND SUMMARY OF THE INVENTION  
       [0003]     Air quality has increasingly become an issue of public concern. As a result of this public concern and governmental regulation, the scientific community has endeavored to reduce the amounts of environmentally toxic industrial waste materials. In this regard, a large part of air pollution is attributable to the release of volatile organic compounds (VOCs) into the atmosphere. As a result, the reduction of the release of VOCs has become an increasingly important part of the overall strategy to improve air quality.  
         [0004]     The most common technique currently in use to control VOC emissions is to incinerate the VOCs in a thermal oxidizer. See in this regard, U.S. Pat. Nos. 5,832,713, 5,527,984 and 6,450,800, the entire content of each being expressly incorporated hereinto by reference. In this regard, the VOCs in the plant air system are typically collected and fed into a mixing chamber of a thermal oxidizer where they are mixed in a burner flame zone with sufficient natural gas to sustain combustion. The combustion chamber may also be provided with stream so as to prolong the residence time therewithin so as to achieve higher conversation rate. Therefore, according to prior proposals in this art, a large combustion and residence chamber is typically required so as to incinerate the VOCs as well as the fuel thereby producing carbon dioxide and water vapor as the primary combustion products. The incineration of the VOCs in a thermal oxidizer is not, however, entirely complete. Thus, thermal oxidizers are typically classified as having a so-called “two-nine” or better destruction capability, meaning that at least 99.0% or greater of the VOCs are incinerated.  
         [0005]     While conventional thermal oxidizers do in fact destroy very substantial amounts of VOCs, there is a constant need to improve the efficiencies of such incineration so as to drive the amount of VOCs that are destroyed even higher than conventionally available. It is towards fulfilling such a need that the present invention is directed.  
         [0006]     Broadly, the present invention is directed to methods and systems for enhanced destruction of industrial waste gases. In especially preferred embodiments, the present invention is directed to methods and systems whereby a high emissivity coating is applied to at least portions of the vessel walls of a direct fired incinerator, such as a thermal oxidizer, in order to enhance its incineration efficiencies, particularly for the incineration of VOCs.  
         [0007]     These and other aspects and advantages will become more apparent after careful consideration is given to the following detailed description of the preferred exemplary embodiments thereof. 
     
    
     BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING  
       [0008]     Reference will hereinafter be made to the accompanying drawing FIGURE which is a schematic cross-sectional elevation view of an exemplary direct fired incinerator to incinerate VOC&#39;s in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0009]     The accompanying FIGURE depicts schematically an exemplary direct fired incinerator  10  that may be employed to incinerate VOC&#39;s in accordance with the present invention. In this regard, the incinerator  10  is provided with vessel walls  10 - 1  and a burner  10 - 2  which is supplied via line  10 - 3  with a combustible fuel (e.g., natural gas). The incinerator  10  is also supplied with VOCs to be incinerated via line  104 . The products of combustion, namely carbon dioxide and water vapor, are removed from the incinerator  10  via flue  10 - 5 .  
         [0010]     According to the present invention, a coating layer  12  formed of a high emissivity (high-E) coating material is applied to the interior walls of a heated process vessel so as to enhance its thermal characteristics. Although accompanying  FIG. 1  schematically depicts the coating layer  12  is formed entirely on the inside of the incinerator walls  10 - 1 , it will be understood by those skilled in this art that the high-E coating material may be applied to one or both of the interior walls associated with the residence chamber or mixing/combustion chamber associated with a conventional thermal oxidizer. The high-E coating material therefore allows the incinerator  10  (e.g., a thermal oxidizer) to achieve a higher degree of conversion and a higher VOC destruction rate. Specifically, the high-E coatings will have a higher surface temperature and a higher heat flux that will therefore result in more complete destruction of the VOCs.  
         [0011]     By way of example, a thermal oxidizer having a conventional two-nine (i.e., 99.0%) VOC destruction rating may have its capabilities increased to at least a three-nine (i.e., 99.9%) VOC destruction rating by employing a coating layer  12  formed of a high-E coating material according to the present invention. As a result, by use of the present invention, industrial sites may improve substantially the VOC destruction capabilities without the significant added capitol costs associated with installation of thermal oxidizers having a greater initial VOC destruction rating.  
         [0012]     As used herein, the emissivity (E) of a material is meant to refer to a unitless number measured on a scale between zero (total energy reflection) and 1.0 (a perfect “black body” capable of total energy absorption and re-radiation). According to the present invention, a relatively high emissivity (high-E) is meant to refer to coating materials having an emissivity at 2000° F. of greater than about 0.70 to about 0.99, and usually between about 0.90 to about 0.99.  
         [0013]     Virtually any commercially available high-E coating material may be employed satisfactorily in the practice of the present invention. For example, the CERAK™ ceramic coating materials commercially available from Cetek Ltd. of Berea, Ohio may be employed, with CERAK™ R371, R360 and R370 each having an emissivity of about 0.92 at 2000° F. being especially preferred.  
         [0014]     Coating thicknesses on the walls  10 - 1  of the incinerator  10  are not critical but will vary in dependence upon the desired resulting thermal flux and/or the particular material forming the coating. Thus, coating thicknesses of from about 1 to about 60 mils may be appropriate for a given process vessel application, with coating densities typically being greater than about 65%, more specifically 80% or greater.  
         [0015]     The high-E coating material may be applied to process vessel walls in any conventional manner during thermal oxidizer shutdown. The high-E coating material may be applied to the process vessel walls via any pressurized spray system while the process vessel is off-line (i.e., is not at its operational temperatures).  
         [0016]     While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.