Abstract:
An ignition assembly for use in pilots for flaring, incineration, and process burner applications, includes a hot surface igniter assembly specifically located in the pilot head or combustion chamber of a flame front ignition system for providing a pilot ignition source. The pilot head is positioned proximally to the exhaust exit of a flare gas stack. The hot surface ignition assembly is positioned proximally to the pilot head. The hot surface ignition assembly passes electric current through a ceramic-insulated element in order to produce heat by induction sufficient to ignite said pilot gas. A thermocouple, or other form of flame sensor, is provided for detecting and a sensing the existence of pilot flame and for controlling the ignition sequence.

Description:
PRIORITY STATEMENT UNDER 35 U.S.C. §119 &amp; 37 C.F.R. §1.78    
       [0001]    This non-provisional application claims priority based upon prior U.S. Provisional Patent Application Ser. No. 61/407,728 filed Oct. 27, 2011 in the name of Trace Cody, Case Gornstein, George Hanesworth, Michael Hainsworth, Michael Hamlin, Alejandro Lago, Colby Nuse, Matthew Phelps and Mark Thatcher entitled “Hot Surface Ignition Assembly for Use in Pilots for Flaring, Incineration, and Process Burners,” the disclosure of which is incorporated herein in its entirety by reference as if fully set forth herein. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to devices for igniting combustible waste gases, and more particularly, to a spark-less pilot igniter which uses induction heating to ignite combustible gas in an ignition system. 
       BACKGROUND OF THE INVENTION 
       [0003]    In the field of waste gas management, combusting gases has been commonly used as a means of reducing the environmental and operational hazards associated with the release of these gases to atmosphere. Gases may need to be combusted in a variety of industries, and for a large number of reasons. In chemical and oil refining, plant upsets or emergency shut downs require the blow down of all plant gases to atmosphere, and flares are used to convert these gases into less harmful combustion byproducts. 
         [0004]    Regardless of the source of waste gas, the most commonly employed means of disposing of waste gases is generally by elevated flare stacks. The safety and effectiveness of disposing waste gas in an elevated flare is dependent on the ignition of these gases either through a continuous or intermittent pilot, or with constant or intermittent electric ignition. The present means of igniting waste gases at the end of a flare stack is with a constant burning pilot. Since a pilot uses natural gas or propane which is becoming more costly, a method of igniting either the pilot or a direct ignition of the flare gases by the use of an electrical ignitor is advantageous. The present method of ignition of a pilot at the top of a stack is mixing natural gas, propane, or other fuel gas and air at the ground level and igniting it and forcing this ignited gas up a long tube to a pilot at the top of the stack. This method, however, is not a positive method of ignition. 
         [0005]    Other methods for igniting flare stack gases have been proposed and run the gamut from sending personnel up the stack to light the gas, to shooting fiery arrows across the top of the stack from ground level. It has been found, however, that these methods are at best ineffective and dangerous. It has also been proposed to employ electrical means for igniting flare stack gases. However, electrical ignitors that have been used in the past have utilized single ignitor tips and have encountered the drawback in that severe shorting occurs in bad weather or with the buildup of carbon material resulting from gas burning, with the result that no sparking occurs. Another problem with previous electric-type flare stack gas ignitors has been their inaccessible location. Thus, many have been mounted in a permanent fashion in order to render replacement difficult if not impossible, while others have been secured interiorly of the stack itself making repair and replacement hazardous. 
         [0006]    There is a need, therefore, for an improved method and system for igniting combustible waste gas. 
       SUMMARY OF THE INVENTION 
       [0007]    According to one aspect of the invention, there is provided apparatus and method for igniting waste gases and, more particularly waste gases resulting from the operation of chemical plants, refineries, pipelines, and oil field production units. 
         [0008]    In one embodiment, an apparatus is provided for igniting waste gases flowing from an exhaust exit of a flare gas stack. A pilot head is positioned proximally to the exhaust exit, wherein combustible pilot gas flows through the pilot head. A hot surface ignition assembly is positioned proximally to the pilot head, wherein the hot surface assembly passes electric current through a ceramic-insulated element in order to produce heat by induction sufficient to ignite the pilot gas. The hot surface ignition assembly can operate at or above temperatures of 2,100° F. 
         [0009]    In some embodiments of the present invention, the combustible pilot gas is a different composition than the gas flowing through the flare gas stack. In yet other embodiments, the combustible pilot gas is the same composition as the gas flowing through the flare gas stack. 
         [0010]    It may be desirable in certain embodiments to include a thermocouple positioned proximally to the pilot head, wherein the thermocouple is able to sense heat from combusting pilot gas and, upon sensing the heat, reducing or eliminating the electric current passing through the ceramic-insulated element. The thermocouple is also able to sense the absence of heat from combusting pilot gas and, upon sensing the absence of heat, again passing said electric current through said ceramic-insulated element. 
         [0011]    The foregoing has outlined rather broadly certain aspects of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures or processes for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0012]    For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: 
           [0013]      FIG. 1  is a side view of a pipe flare tip with a pilot incorporating one embodiment of the hot surface igniter of the present invention; 
           [0014]      FIG. 2  is a perspective view of a pilot as shown in  FIG. 1 , incorporating one embodiment of the hot surface igniter of the present invention; 
           [0015]      FIG. 3  is a side view of a pilot as shown in  FIG. 1  and  FIG. 2 ; 
           [0016]      FIG. 4  is a perspective view of a flame front combustion chamber incorporating one embodiment of the hot surface igniter of the present invention; 
           [0017]      FIG. 5  is a side view of a flame front combustion chamber as shown in  FIG. 4 ; 
           [0018]      FIG. 6 . is a side view of a flare tip combustion chamber mounted on a flare tip to ignite process gas and using one embodiment of the hot surface igniter of the present invention; 
           [0019]      FIG. 7  is a perspective view of a flare tip combustion chamber hot surface igniter as shown in  FIG. 6 ; 
           [0020]      FIG. 8  is a perspective view of a flare tip combustion chamber hot surface igniter assembly as in  FIG. 6  and  FIG. 7  and 
           [0021]      FIG. 9  is a side view of a flare tip combustion chamber hot surface igniter assembly with a partial cross-sectional cutaway view of the internal wiring connection and tip. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0022]    The present invention is directed to improved methods of igniting waste gas. The configuration and use of the presently preferred embodiments are discussed in detail below. It should be appreciated, however, that the present invention provides many applicable inventive concepts that can be embodied in a wide variety of contexts other than traditional waste gas combustion. Accordingly, the specific embodiments discussed are merely illustrative of specific ways to make and use the invention, and do not limit the scope of the invention. 
         [0023]    The present invention relates generally to the ignition of gases that are combustible. More particularly, the present invention relates to an ignition assembly and its associated controls for the ignition of a pilot gas stream intended to ignite combustible gases resulting from the operation of chemical plants, refineries, pipelines, and oil field production units. 
         [0024]    Many chemical plants, refineries, pipelines, loading docks, oilfield production units, off-shore drilling platforms, and numerous other operations generate waste gases which must be disposed of either continuously or intermittently through flaring, thermal oxidation, or other means of process combustion and must be ignited so that the gases are disposed of safely and effectively. Often these waste gases are process byproducts that are continuously produced at a relatively constant volumetric flow rate. In other instances, because of upsets or interruptions in plant operations, large quantities of gases such as feed materials, intermediates, or products, must be disposed of quickly to prevent explosions and/or hazardous conditions from occurring in the plant. 
         [0025]    Flaring is a combustion control process in which volatile organic compounds (VOCs) are piped to a remote, usually elevated, location and burned in an open flame in the open air using a specially designed burner tip, auxiliary fuel, and steam or air to promote mixing for VOC destruction. The degree to which combustion is completed is governed by flame temperature, amount of time in the combustion zone, turbulence in the mixing of the components to complete the oxidation reaction, and available oxygen for free radical formation. The combustion is considered complete if all VOCs are converted to carbon dioxide and water. Incomplete combustion results in some of the VOC being unaltered or converted to other organic compounds such as aldehydes or acids. 
         [0026]    Elevating the flare can prevent potentially dangerous conditions at ground level where the open flame is located near a process unit and the products of combustion can be dispersed above working areas to reduce the effects of noise, heat, smoke, and objectionable odors. However, when the flare is elevated, the process of igniting the flare is considerably more complicated. While some flares may have one or more continuously burning pilot flames, others save gas by only igniting pilot flames in preparation for use. Even with flares that have continuously burning pilots, the pilots can be blown out by wind and gas leakage and/or waste gas is occasionally released to an unlit flare. All of these situations result in methane, volatile organic compounds (VOC) and hazardous air pollutant (HAP) emissions to the atmosphere. 
         [0027]    Referring now to  FIG. 1 , in which a pipe flare tip  1  is shown with a pilot assembly  2  mounted to it by means of an upper mounting bracket  9  and a lower mounting bracket  10 . The flare tip  1 , or burner tip, is designed to give environmentally acceptable combustion of the vent gas over the flare system&#39;s capacity range. The maximum and minimum capacity of a flare to burn a flared gas with a stable flame is a function of tip design. In designing a flare tip, consideration is given to flame stability, ignition reliability, and noise suppression. Many flare tips are known in the art although they are often proprietary in design. The flare structure, pilot gas piping, and other upstream components have not been shown for clarity, since they are common amongst all flare systems and known to those familiar with the art. 
         [0028]    Referring now to  FIG. 2  and  FIG. 3 , which illustrate one embodiment of a pilot assembly  2  with more clarity. A pilot head  3  is affixed to the top of pilot body  5 . The pilot assembly  2  is secured to a supporting member (not shown) by means of a pilot gas connection flange  13 . In this embodiment of the pilot assembly  2 , the pilot gas will first pass through a Y-strainer  12  in order to remove any debris from the gas stream. The gas then goes through an inspiratory  11  which may, for example, rely on a venturi effect to mix ambient air into the pilot gas stream, thereby creating a combustible mixture. This combustible mixture is delivered to the pilot head  3  by means of the pilot body  5 . The hot surface ignition assembly, or HSI assembly  4 , is affixed to the pilot head  3  by, for example, a threaded or welded fitting, but may be affixed thereto by any means known in the art. The HSI assembly  4  is a device that passes electric current through a ceramic-insulated element in order to produce heat by induction. 
         [0029]    When the combustible mixture enters the pilot head  3 , the HSI assembly  4  provides a source of ignition. In some embodiments, the HSI assembly  4  will operate at a temperature in excess of 2,100° F. to cause ignition of the combustible pilot gas passing through pilot body  5 . Once the pilot gas is ignited, a strong and stable flame continually exits the pilot head  3 . A thermocouple  6  is connected to the pilot head  3  by means of a thermowell (not shown). In some embodiments, the thermocouple  6  will sense the heat from the flame and send a signal through the thermocouple junction box  7  to a control system. The control system is not shown since these control systems are common in the industry and known to those familiar with the art. Once the control system receives confirmation of the flame via the thermocouple junction box  7 , the power to the HSI assembly  4  will be stopped, the HSI assembly  4  will cool, and the pilot flame will continue to burn. In the event that the pilot flame is extinguished, the thermocouple  6  will send a signal that will cause the control system to turn the HSI assembly  4  on again, and within seconds it will be hot enough to reignite the combustible pilot gas, and the cycle continues. 
         [0030]    The HSI assembly  4  is built to be a drop-in replacement for existing sparking technology. As with spark rods in the prior art, the HSI assembly will be supported by means of HSI support brackets  14 . At the base of the HSI assembly is an HSI junction box  8  which provides the means of connecting the HSI assembly  4  to the power source via the HSI power connection  15 . 
         [0031]    Now referring to  FIG. 4  and  FIG. 5 , which illustrate another embodiment of the present invention. In this embodiment, a fire ball (also known in the art as a flame front) that will be used to ignite a pilot is generated in a combustion chamber  3 . The systems in which these are used are commonly called flame front generators, and the entire valve train is not shown since they are typical and understood by those familiar with the art. In this embodiment, ignition gas is introduced to the combustion chamber  3  by means of the ignition gas inlet  16 . This gas is used to induce air into the ignition air inlet  17 . In variations of this equipment, ignition air may be provided by means of a compressed air line in lieu of the air inspirator  17  shown in  FIG. 4  and  FIG. 5 . 
         [0032]    In the embodiment shown, the ignition gas is mixed with the ignition air in the combustion chamber throat  18  by means of turbulence. After leaving the combustion chamber throat  18 , the combustible gas passes into the combustion chamber body  19 , inside of which is installed an HSI element  24 . This element, upon initiation by the controls system, will rapidly heat to a temperature in excess of 2,100° F., causing ignition of the combustible mixture present in the combustion chamber body  19 . The combustion initiates a flame front which can then pass through the combustion chamber exit port  25  to continue through a pipe until it exits and ignites a flare or pilot. The items downstream of the exit port are not shown since they are understood by those familiar with the art. In the prior art, the flame front was initiated by means of a high voltage spark which would be installed in the ignition port  21 . In the present invention, the sparking contacts of the prior art are replaced with a hot surface igniter, which consists of a ceramic body  22 , an induction heating element  21 , and a power connection  23 . The controls system (not shown) connects to the power connection  23  and provides a simple on/off signal. Since the device is entirely enclosed, a sight glass  20  is provided so the operator may have visual confirmation of the status of the HSI element  24 . The HSI element  24  may be inserted, for example, by means of a threaded connection in the ignition port  21  for ease of servicing. 
         [0033]    Referring now to  FIG. 6 , in which process gas flows through the flare tip  26  to be combusted once it exits into the atmosphere. In this embodiment of the present invention, a process gas ignitor assembly  27  is shown mounted to the flare tip  26  and the ignitor head  29  is inserted into the combustion chamber  28  that is filled with re-directed process gas by means of the process gas diverter  33  which extends into the flare tip. This arrangement allows for reliable flaring without the use of pilot gas, a practice commonly referred to as ‘zero-flaring.’ Referring now to  FIG. 7-9 , the HSI junction box  31  is electrically connected to a controller located at grade that can be powered by a range of both AC and DC power sources. The electrical details are not shown for the sake of clarity, since they are conventional and well known to the skilled in the art. Power is transmitted by a high temperature power cable  42  that is electrically isolated within the ignitor body  30 . The ignitor body  30  is affixed to the ignitor head  29  in which the high temperature power cable  42  is connected to the HSI power connection  41 . In this embodiment, a conventional nut and screw connection assembly is depicted for the sake of clarity, however, other means of connectivity are often used. In some embodiments, the HSI power connection  41  is electrically isolated from the ignitor head  29  by means of a high-strength, heat resistant ceramic insulator  40 . The HSI power connection  41  transmits power to the HSI assembly  35  depicted in  FIG. 8 . The HSI assembly is comprised of the HSI body  39  and the ceramic insulator  40 , depicted in  FIG. 9 , which is protected by an impact guard  36 . In reference to  FIG. 6 , the HSI element (not shown for the sake of clarity) located at the end of the ignitor head  29  is inserted into an opening located on the combustion chamber  28 , in which gas is diverted as aforementioned. Once the combustible process gas reaches the high-temperature HSI element (again, not shown for clarity) combustion occurs and a pilot flame then cross-lights the main process gas flow through the flare tip  26 . 
         [0034]    While the present system and method has been disclosed according to the preferred embodiment of the invention, those of ordinary skill in the art will understand that other embodiments have also been enabled. Even though the foregoing discussion has focused on particular embodiments, it is understood that other configurations are contemplated. In particular, even though the expressions “in one embodiment” or “in another embodiment” are used herein, these phrases are meant to generally reference embodiment possibilities and are not intended to limit the invention to those particular embodiment configurations. These terms may reference the same or different embodiments, and unless indicated otherwise, are combinable into aggregate embodiments. The terms “a”, “an” and “the” mean “one or more” unless expressly specified otherwise. The term “connected” means “communicatively connected” unless otherwise defined. 
         [0035]    When a single embodiment is described herein, it will be readily apparent that more than one embodiment may be used in place of a single embodiment. Similarly, where more than one embodiment is described herein, it will be readily apparent that a single embodiment may be substituted for that one device. 
         [0036]    In light of the wide variety of devices for igniting combustible waste gases known in the art, the detailed embodiments are intended to be illustrative only and should not be taken as limiting the scope of the invention. Rather, what is claimed as the invention is all such modifications as may come within the spirit and scope of the following claims and equivalents thereto. 
         [0037]    None of the description in this specification should be read as implying that any particular element, step or function is an essential element which must be included in the claim scope. The scope of the patented subject matter is defined only by the allowed claims and their equivalents. Unless explicitly recited, other aspects of the present invention as described in this specification do not limit the scope of the claims.