Abstract:
A system for environmentally acceptably disposing of BTEX and/or VOC containing off gases, including entrained vapors and liquids that originate from gas processing equipment including a flare stack communicating at an upper end with the atmosphere, a steam cup supported within the flare stack, a gas inlet extending into the flare stack and into the steam cup and serving to convey off gasses into the flare stack and collect any entrained liquid carried by the off gasses and a burner positioned within the flare stack below the steam cup and connected to receive and burn a combustion gas/air mixture, heat produced by the burner serving to vaporize any entrained liquid collected in the steam cup and to combust any BTEX and/or VOC components of the off gasses and vaporized liquid into inert oxidized states that pass out the flare stack upper end.

Description:
REFERENCE TO PENDING APPLICATIONS 
     This application is based upon U.S. Provisional Patent Application No. 60/166,628 filed Nov. 19, 1999 entitled, “FLARE STACK FOR NATURAL GAS DEHYDRATORS”. 
    
    
     REFERENCE TO MICROFICHE APPENDIX 
     This application is not referenced in any microfiche appendix. 
     BACKGROUND OF THE INVENTION 
     Previously issued United States Patents that provide background information concerning the technology to which this invention is directed include the following: 
     
       
         
               
               
               
             
           
               
                   
               
               
                 PATENT NO. 
                 INVENTOR 
                 TITLE 
               
               
                   
               
             
             
               
                 2,725,337 
                 Laurence et al. 
                 Method and Apparatus for 
               
               
                   
                   
                 Low Temperature 
               
               
                   
                   
                 Separation and 
               
               
                   
                   
                 Stabilization of Liquid 
               
               
                   
                   
                 Hydrocarbons from High 
               
               
                   
                   
                 Pressure Natural Gas 
               
               
                 3,395,512 
                 Finney et al. 
                 Method and Means for 
               
               
                   
                   
                 Cooling and Cleaning Hot 
               
               
                   
                   
                 Converter Gases 
               
               
                 3,904,351 
                 Smith et al. 
                 Combustor and Method of 
               
               
                   
                   
                 Eliminating Odors Using 
               
               
                   
                   
                 the Same 
               
               
                 3,932,111 
                 Liknes et al. 
                 Apparatus for Incinerating 
               
               
                   
                   
                 Combustible Wastes 
               
               
                 4,003,722 
                 Holter 
                 Process and Arrangement 
               
               
                   
                   
                 for the Removal of 
               
               
                   
                   
                 Impurities From Gases 
               
               
                 4,162,145 
                 Alleman 
                 Regeneration of Liquid 
               
               
                   
                   
                 Absorbents 
               
               
                 4,182,659 
                 Anwar et al. 
                 Method of Concentrating a 
               
               
                   
                   
                 Water-Containing Glycol 
               
               
                 4,227,897 
                 Reed 
                 Apparatus for Recovery of 
               
               
                   
                   
                 Flared Condensible 
               
               
                   
                   
                 Vapors 
               
               
                 4,237,620 
                 Black 
                 Contactor 
               
               
                 4,280,867 
                 Hodgson 
                 Glycol Regeneration 
               
               
                 4,494,967 
                 Barth 
                 Process for the Removal 
               
               
                   
                   
                 of Impurities from a Gas 
               
               
                   
                   
                 Stream Containing Solvent 
               
               
                   
                   
                 Vapors 
               
               
                 4,597,733 
                 Dean et al. 
                 Gas Heating System for 
               
               
                   
                   
                 Dehydrators and Like 
               
               
                 4,676,806 
                 Dean et al. 
                 Temperature Sensitive 
               
               
                   
                   
                 Control System for Liquid 
               
               
                   
                   
                 Motor and Pump in a 
               
               
                   
                   
                 Natural Gas Dehydration 
               
               
                   
                   
                 System 
               
               
                 4,702,898 
                 Grover 
                 Process for the Removal 
               
               
                   
                   
                 of Acid Gases from Gas 
               
               
                   
                   
                 Mixtures 
               
               
                 4,714,032 
                 Dickinson 
                 Pollution-Free Pressurized 
               
               
                   
                   
                 Combustion Utilizing a 
               
               
                   
                   
                 Controlled Concentration 
               
               
                   
                   
                 of Water Vapor 
               
               
                 4,717,408 
                 Hopewell 
                 Process for Prevention of 
               
               
                   
                   
                 Water Build-Up in 
               
               
                   
                   
                 Cryogenic Distillation 
               
               
                   
                   
                 column 
               
               
                 4,983,364 
                 Buck et al. 
                 Multi-Mode Combustor 
               
               
                 5,163,981 
                 Choi 
                 Method and Apparatus for 
               
               
                   
                   
                 Controlling Discharge of 
               
               
                   
                   
                 Pollutants from Natural 
               
               
                   
                   
                 Gas Dehydrators 
               
               
                 5,221,523 
                 Miles et al. 
                 Contaminant Control 
               
               
                   
                   
                 System for Natural Gas 
               
               
                   
                   
                 Dehydration 
               
               
                 5,261,225 
                 Dickinson 
                 Pressurized Wet 
               
               
                   
                   
                 Combustion at Increased 
               
               
                   
                   
                 Temperature 
               
               
                 5,346,537 
                 Lowell 
                 Method and System for 
               
               
                   
                   
                 Controlling Emissions 
               
               
                 5,514,305 
                 Ebeling 
                 Bubble Tray 
               
               
                 5,520,723 
                 Jones, Jr. 
                 Method and System for 
               
               
                   
                   
                 Reducing Air Pollution 
               
               
                   
                   
                 from Natural Gas 
               
               
                   
                   
                 Dehydrators 
               
               
                 5,536,303 
                 Ebeling 
                 Method of Low 
               
               
                   
                   
                 Temperature 
               
               
                   
                   
                 Regeneration of Glycol 
               
               
                   
                   
                 Used for Dehydrating 
               
               
                   
                   
                 Natural Gas 
               
               
                 5,664,426 
                 Lu 
                 Regenerative Gas 
               
               
                   
                   
                 Dehydrator 
               
               
                 5,665,144 
                 Hill et al. 
                 Method and Apparatus 
               
               
                   
                   
                 Utilizing Hydrocarbon 
               
               
                   
                   
                 Pollutants from Glycol 
               
               
                   
                   
                 Dehydrators 
               
               
                 5,766,313 
                 Heath 
                 Hydrocarbon Recovery 
               
               
                   
                   
                 System 
               
               
                 5,882,486 
                 Moore, Jr. 
                 Glycol Refining 
               
               
                   
               
             
          
         
       
     
     Hodgson, U.S. Pat. No. 4,280,867, discloses a reboiler used to heat wet glycol and water vapor is discharged. The dehydrated glycol then flows through a stripping column where glycol comes into contact with dry flue gas generated by a catalytic burner. 
     Anwar et al., U.S. Pat. No. 4,182,659, provides a system where wet glycol is initially drawn off into an expansion chamber where part of the hydrocarbon gases separate out, are drawn off and may be re-used as heating gas. The glycol is then heated to remove the majority of the water which is vented to the atmosphere. Finally, then glycol is heated at sub-atmospheric pressure (vacuum) to further purify it. 
     Holter, U.S. Pat. No. 4,003,722, discloses a system where gas may be purified by cleansing fluid. The cleansing fluid may be admitted from a flow circuit into an evaporator causing the impurities to be evaporated by heating. The impurities liberated in the evaporator are conveyed to a burner or combustion chamber and combusted. 
     The other previously issued patents provide information as to the state of the art of glycol dehydration of natural gas. 
     Accordingly, it is a principal object and purpose of the present invention to provide a system for control and disposal on contaminants released by natural gas dehydration processes. 
     It is further an object and a purpose of the present invention to provide a system for control and disposal of contaminants released in the glycol regeneration process wherein the contaminants are incinerated to reduce them to non-pollutant states. 
     It is further an object and a purpose of the present invention to provide a system for control and disposal of contaminants released in the glycol regeneration process which will not add undo back pressure to the reboiler. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention relates to a system for use to incinerate contaminants released in the regeneration or reconcentration of glycol, or similar liquid desiccant, employed in the process of dehydration of natural gas. 
     Natural gas processing usually includes removal of contaminants in order to produce a transportable natural gas product. One of the major contaminants removed from natural gas is water, either in the gaseous state or in condensed form. Other contaminants present in smaller quantities are BTEX and VOCs and other pollutants. 
     Most large volume dehydration units are of the glycol type. Glycol is a preferred liquid desiccant because it has a relatively high boiling point, is thermally stable and does not oxidize in normal use. The glycol used is normally of one of three kinds: ethylene, diethylene, or triethylene, with triethylene being the most frequently used at the present time. Water, including other pollutants in natural gas, is absorbed by contact with the glycol. 
     A typical dehydration facility includes an inlet gas scrubber and a separator where liquid accumulations that are easily separated are removed. The natural gas is then directed to a gas contractor where the glycol comes into contact with the gas, a majority of any entrained water and the water vapor being absorbed by the glycol producing what is known as “wet glycol”. The dehydrated natural gas leaves the contractor tower where it is directed to be transported for use as fuel or raw material for the chemical industry. The wet glycol is directed from the contractor tower to a reconcentrator or reboiler column. 
     In the reboiler column the wet saturated glycol is heated to a temperature of between 380° to 400° Fahrenheit to boil off the water. The reboiler is usually maintained at the lowest possible pressure so that the water solubility of glycol is not increased. The vaporized water, along with the contaminants not removed with the skimming and filtration process, have, in the past, been vented to the atmosphere. Venting the contaminants to the atmosphere is becoming an increasing environmental problem. These odorous vapors emitted from the reboiler create uncomfortable living conditions and health concerns for local residents and workers. 
     New environmental laws have mandated a great reduction in the amount of pollutants that can be emitted from natural gas dehydrators. These pollutants consist primarily of BTEX and VOCs, and are absorbed from the gas stream by the glycol. Also, some natural gas becomes dissolved in the glycol, and since the function of a dehydrator is to remove water vapor from the gas stream, the glycol will also contain water. The glycol regeneration process utilizes a reboiler to heat the glycol and drive off the water, but the process also liberates the pollutants that are dissolved in the glycol. Current technology to control emissions consists of two methods: 1) The stream from the still column&#39;s outlet is condensed. The waste gas is flared and the liquid is trucked to disposal. Or, 2) The stream from the still column&#39;s outlet is condensed and the waste gas is compressed and injected into a gas sales line, the liquid, once again, being trucked to disposal. Obviously, the problem with both systems is dealing with the disposal of the BTEX and/or VOCs laden water. It is to this problem that the present invention is directed. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an elevational view, shown partially cut away, of a flare stack that employs the principles of this invention, the flare stack being used with natural gas dehydration systems. 
     FIG. 2 is an enlarged elevational view of the flame cup as used in the flare stack of FIG.  1 . 
     FIG. 3 is a top plan view of the flame cup of FIG.  2 . 
     FIG. 4 is a bottom view of the heat shield as used as a part of the flame cup. 
     FIG. 5 is a cross-sectional view showing the use of turbulator blades within the flame cup as an alternate embodiment. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring first to FIG. 1, the system of this invention for use with a natural gas dehydrator is shown. When natural gas is extracted from a subterranean formation it flows to the earth&#39;s surface by formation pressure. At the well site, the gas is collected. Natural gas contains essentially hydrocarbons but it inevitably includes, entrained within it, water that is usually in the form of vapor, a portion of which readily condenses into liquid when cooler temperatures are encountered along with decreased vapor pressure at the earth&#39;s surface. In addition to water, natural gas frequently includes other pollutants such as BTEX and VOCs. 
     Entrained water is a problem to the transportation, storage and use of natural gas. Accordingly, in the petroleum industry it is customary to extract as much as possible of entrained water before the natural gas is passed to a pipeline for transportation to an area where it is stored or used. Entrained water causes several problems in pipeline and process equipment including corrosion. Further, water tends to collect in low places in a pipeline and, if subfreezing temperatures are encountered, becomes ice or a solid to a point that the flow through a line can be severely restricted or blocked. 
     The most common means employed in the petroleum industry to extract water from natural gas is by the use of liquid dehydrators. In this process the natural gas is conducted into a vessel in which it is intimately mixed with a liquid desiccant. The most commonly used liquid desiccant is a glycol, either ethylene, diethylene, triethyline or mixtures thereof. Glycol makes an ideal liquid desiccant for natural gas because it is relatively inexpensive, has a relatively high boiling point, does not easily oxidize and is recyclable. After natural gas has been intimately exposed to glycol and the water carried in the natural gas has been absorbed by the glycol, the dried gas is separated from the glycol and passed to a pipeline for storage or use. The glycol (referred to as “wet glycol”), to be reused for drying additional natural gas must be treated to extract the entrained water. This is accomplished by heating the wet glycol to a temperature above the boiling point of water, to boil off the water without boiling the glycol so that the glycol remains in liquid state and the water is converted to a vapor state. In the past, the vapor that was created when water was boiled off of wet glycol was simply vented to the atmosphere. If the vapor is one-hundred percent water, that is pure water, the venting of the water vapor to the atmosphere is not harmful to the environment. However, inevitably, the vapor passing from a glycol regenerator includes other contaminants and pollutants particularly BTEX and VOCs. Environmental laws enacted in recent years have mandated that the discharge of these pollutants to the atmosphere should to be eliminated or at least substantially reduced. It is the object of the processes illustrated in FIG. 1 to accomplish this result. 
     The vapor or gas discharge from a glycol regenerator is fed to an inlet  10 , through a vacuum/vent relief valve  12 , and an inline flame arrestor  14 , an emergency shut down valve  16  (an optional element) and through an injector tube  18  into the interior of a combustion tower  20 . The combustion tower  20  is preferably formed of metal, such as carbon steel and may have a diameter, as an example, of about thirty inches and an overall height of, by example, twenty-four feet. Combustion tower  20  rests on a base  22  and has, at its upper end  24 , a vent screen  26  and a top cover  28 . 
     Centrally positioned within air injection tube  18  is a smaller diameter air injection tube  30  having on its inner end a diffuser  32  and on its outer end, exteriorally of air injection tube  18 , a flame arrestor  34 . Thus injection tube  18  provides means for introducing the off gas from a glycol dehydrator flowing into the system through inlet  10  and admixing therewith secondary air as drawn into the system through flame arrestor  34 . The inner end of injection tube  18  connects with a steam cup generally indicated by the numeral  36  that will be described in detail subsequently. 
     Centrally positioned within combustion tower  20  is a reduced diameter tower liner  38  that preferably is a metal, such as steel, and more particularly, preferably stainless steel. Liner  38  receives, in the lower end portion thereof the steam cup  36  and the top end  40  of liner  38  is substantially coincident with the upper end  24  of combustion tower  20 . The bottom  42  of liner  38  is spaced above the tower base  22 . Liner  38  provides an annular area  44  between it and tower  20 . 
     Positioned within the lower interior of combustion tower  20  is a burner  46  connected by piping  48  to a fuel gas inlet  50 . Fuel gas supplied to inlet  50  is generally gas that has been dissolved in the glycol employed for the dehydration process, the gas leaving the glycol when a pressure cut is taken in the glycol/gas separator forming a part of the dehydrator (not shown). This gas is considered waste gas and in the past has been vented to the atmosphere or burned in the reboiler to heat spent glycol as a part of the glycol regeneration process. The waste gas from the dehydration system can be supplemented as necessary by gas from other sources including commercially available clean, dehydrated gas. 
     The flame that is generated by burner  46  is best ignited from pilot light burner  52 . A gas source is connected to pilot light inlet  54  that connects to pilot light burner  52  by means of piping  56 . The pilot light gas is fed through a venturi  58  which draws pilot light combustion air through a pipe  60  that communicates with the atmosphere through pilot light flame arrestor  62 . 
     Normally, pilot light burner  52  maintains a small pilot light flame continuously. Pilot light burner  52  may be manually lit through a closable opening formed in combustion tower  20  or, as illustrated, a pilot light ignitor  64  operated by a control  66  external of combustion tower  20  is provided. Ignitor  66  is typically designed to supply an electric spark for the purpose of lighting pilot light burner  52 . 
     Positioned within the lower interior of combustion tower  20 , also within the lower interior of tower liner  38 , is a device referred to as a steam cup generally indicated by the numeral  36 . The steam cup is illustrated in greater detail in FIGS. 2-4 and reference is now made specifically to FIGS. 2 and 3. The steam cup includes a cylindrical housing  70 , made of metal and preferably a metal that resists heat, such as stainless steel. The top end  72  of cylindrical housing  70  is partially closed by a top deflector shield  74 , a plan view of which is seen in FIG.  3 . Top deflector shield  74  is semi-toroidal to deflect gases entering steam cup  36  from injector tube  18 . 
     Received coaxially within cylindrical housing  70  is a flame chamber cylinder  78  formed of metal, and preferably of stainless steel or the like that resists heat. Spaced apart openings  80  are formed in the flame cylinder upper portion. Flame cylinder  78  forms an annular area  82  between its external cylindrical surface and the internal surface of cylindrical housing  70 . Openings  80  provide communication between annular area  82  and the interior of flame chamber cylinder  78  that is open at the top so that the interior of flame chamber cylinder  78  communicates directly with the interior of tower liner  38 . 
     Attached to the bottom of both cylindrical housing  70  and flame chamber cylinder  78  is a bottom ring  84 . The external circumferential edge  86  of bottom ring  84  is secured, such as by welding, to the bottom external circumferential edge of cylindrical housing  70  while the internal circumferential edge  88  of bottom ring  84  is attached, such as by welding to the lower circumferential edge of flame chamber cylinder  78 . 
     Positioned within the lower portion of annular area  82  within the steam cup is a toroidal cup-shaped member forming a liquid retention cup  90 . The cup is toroidal in shape having an inner circumferential diameter greater than the external diameter of flame chamber cylinder  78  and an outer circumferential diameter less than the internal diameter of cylindrical housing  70 . The liquid retention cup sits within annular area  82 , resting on bottom ring  84 . 
     The steam cup cylindrical housing  70  has a large diameter opening  92  in the sidewall thereof that receives injection tube  18  which extends slightly within annular area  82  within the steam cup  36  so that the edge thereof extends over the interior of liquid retention cup  90 . Any liquids, such as condensed water that pass into the interior of combustion tower  20  and thereby into the interior of steam cup  36 , are deposited within liquid retainer cup  90 . The liquids are held in position in close proximity to the flame produced by burner  46  (as seen in FIG. 1) so that heat from the burner evaporates any liquids that are deposited into the liquid retention cup  90 . 
     In the preferred arrangement liquid retention cup  90  includes an integral upwardly extending flash shield portion  94 , the flash shield being of an arcuate configuration and covering an arch sufficient to stand between the inner end of injection tube  18  and flame chamber cylinder  78 . The function of the flash shield  84  is to divert fluids and gases passing into the flame cup from direct impingement on flame chamber cylinder  78  and to help distribute the gases around the entire annular area  82 . 
     Positioned below bottom ring  84  of steam cup  36  is a toroidal heat shield  96 . Heat shield  96  has a large diameter opening  98  therethrough just slightly smaller in diameter than the interior diameter of flame chamber cylinder  78 . Affixed to heat shield  96  at the internal circumferential edge of opening  98  is a short length upstanding tubular heat shield  100  that is open at its top and bottom. The short length tubular heat shield  100  and the toroidal heat shield  96  are welded together to form as an integral member and are made of metal to protect steam cup  68  from the direct intense heat of burner  46 . The material of which the flat toroidal heat shield  96  and the short length tubular heat shield  100  are formed is such as stainless steel and may be of metal that is of thickness greater than the metal employed for forming cylindrical housing  70  and flame chamber cylinder  78 . 
     The actual geometrical arrangement of steam cup  36  can vary considerably without departing from its basic and important function. For example, top deflector shield  74  can be eliminated without significantly changing the structure or the utility of the steam cup. 
     The method of supporting the heat shield formed of components  96  and  100  can vary such as by the use of clips (not shown) that extend externally of cylindrical housing  70  to be secured to cylindrical housing top edge  72 . Another way is to provide short length bolts (not shown) extending from steam cup bottom ring  84  that are loosely received in openings formed in the flat toroidal heat shield  96 . Heads on such bolts below heat shield  96  support the heat shield so that it is free to contract and expand without affecting the steam cup itself but at the same time provide protection against the direct intense heat of burner  46 . 
     Returning to FIG. 1, openings are formed in the lower portion of combustion tower  20 , spaced above the base  22 , each opening being provided with a conduit  102 . Each conduit  102  communicates with a primary flame arrestor  104 . This permits combustion air to flow freely into the lower interior of combustion tower  20 , the air being drawn upward by convection as a result of heat from burner  46 . Some of the air being drawn through conduits  102  and flame arrestors  104  passes upwardly in the annular area  44  externally of the tower liner  38  and a portion of the air drawn through the primary flame arrestors  104  passes upwardly interiorially of tower liner  38 . Some of the air flowing through primary flame arrestors  104  and conduits  102  serves to support combustion of the fuel injected through fuel inlet  50  to burner  46 . 
     It is important that the system be constructed and operated in such a way that the possibility of igniting ambient gas that might inadvertently surround the flare stack be prevented. Therefore the temperature of the external surface of all portions of combustion tower  20  must, at all times, be below the ignition temperature of a natural gas/air mixture. If necessary, supplemental air may be introduced into annular area  44  by annular area flame arrestors  106  that may be positioned as required among the external sidewall of combustion tower  20 . The sole function of flame arrestors  106  is to provide a cooling effect since air passing through annular area flame arrestors is not employed in the combustion process produced by burner  46 . 
     To increase the effectiveness of the contact of steam passing into the tower and into steam cup  36  with hot gasses produced by burner  46 , turbulator blades  108  may be positioned within flame chamber cylinder  78  as seen in FIG.  5 . The particular configuration of turbulator blades  108  is not important as long as turbulence is produced to more thoroughly heat the incoming steam. 
     When a reboiler (glycol regenerator) is employed to regenerate glycol or other liquid desiccant employed in dehydration of natural gas, the steam, along with any entrained liquids, is passed from the reboiler through the steam inlet  10  and flows through air injection tube  30  into the interior of combustion tower  20  and tower liner  38  and into the interior of steam cup  36 . The flow of steam draws supplemental air through flame arrestor  34  so that a mixture of steam and air is passed into the opening  92  in the external sidewall of the steam cup  36 . A flame is produced by fuel supplied at fuel inlet  50  to burner  46 , the flame being located immediately below steam cup  36 . Any liquid components of the vapor or gases passing into the interior of the steam cup are collected in liquid retention cup  90  contained within the steam cup. Liquid collected in retention cup  90  is subjected to intense heat and is vaporized and combusted to thereby convert any BTEX or VOCs into oxidized compositions that are safe to the environment. At the same time, any combustible components are burned. These combusted and oxidized components are passed upwardly within tower liner  38  and discharged through vent screen  26  to the atmosphere. The length of the tower is such as to provide positive movement of combustion air within the tower and past the steam cup and particularly past burner  46  to insure full combustion and oxidation of all components. The result is that all the biologically unacceptable components of steam discharged from a glycol generator, or other liquid desiccant regenerator used to extract water from natural gas, is reduced to an environmentally acceptable state before discharge into the atmosphere. The system avoids the problems and expense of separately disposing of this biological unacceptable waste. 
     The claims and the specification describe the invention presented and the terms that are employed in the claims draw their meaning from the use of such terms in the specification. The same terms employed in the prior art may be broader in meaning than specifically employed herein. Whenever there is a question between the broader definition of such terms used in the prior art and the more specific use of the terms herein, the more specific meaning is meant. 
     While the invention has been described with a certain degree of particularity, it is manifest that many changes may be made in the details of construction and the arrangement of components without departing from the spirit and scope of this disclosure. 
     It is understood that the invention is not limited to the embodiments set forth herein for purposes of exemplification, but is to be limited only by the scope of the attached claim or claims, including the full range of equivalency to which each element thereof is entitled.