METHOD AND BURNER APPARATUS FOR FLARING WASTE GASES

Abstract: A method and burner apparatus for flaring insert vitiated waste gases in an efficient stable manner, in which a first tubular member (12) discharges waste gases from its discharge end (32) and a second tubular member (40) is positioned around at least the discharge end portion of the first tubular member to define a discharge space (42) therebetween. A burner (50) is disposed within the discharge space (42) and is supplied with fuel gas via a conduit (54). Combustion air is supplied to the discharge space (42) from a source (16) via a duct (18,44) and is mixed with fuel gas discharged from the burner (50). The mixture is ignited and discharged from the discharge space (42) and burned in a stable envelope around discharged waste gases, a portion of which are heated by the burning fuel gas and air, ignited and burned thereby providing a source of heat and ignition to the remaining gases which are burned in an efficient manner.

Description: The present invention relates to a method and flare burner apparatus for flaring gases, such as vitiated waste gases. Flare burner apparatus are commonly utilized for disposing of waste gases, both continuously and intermittently and usually include continuously burning pilot flames for igniting and maintaining the burning of the waste gases. When the flared waste gases contain inert gases in high quantities i.e. the waste gases have heating values below about 11.175 x 10⁶ J/m³ when burned, problems have been encountered, because the burning of such inert vitiated waste gases can be inefficient and/or unstable and in windy environments the flames can be blown out. Examples of particularly difficult inert vitiated waste gases are those containing high concentrations of carbon dioxide such as steel mill blast furnace residue gas and the gases produced in subterranean formation carbon dioxide secondary recovery processes. Such inert vitiated waste gases have hitherto been flared in conventional flare burner apparatus by combining fuel gas with the waste gases, to form a relatively high calorific value gas mixture, which is then conducted to the burner apparatus. Because this technique requires high quantities of fuel gas and is expensive to carry out, various forms of special flare burner apparatus have been developed which burn a separate stream of a fuel and air mixture at the burner apparatus to heat a portion of the waste gases to the temperature required for ignition and burning thereof. While such apparatus have been developed and used successfully, they are generally limited in size and capacity, because the higher the quantity of inert vitiated waste gases to be burned, the more auxiliary fuel and air mixture required and the more expensive the flare burner apparatus. Other forms of apparatus have included means for discharging auxiliary fuel gas into the atmosphere around and/or into the waste gases, whereby the fuel gas mixes with atmospheric air, is ignited and burned thereby raising the temperature of a portion of the waste gases to the ignition temperature thereof. While this type of flare burner can be used successfully, the burning of the fuel gas and waste gases using such a burner in a windy environment may sometimes result in a unstable and/or inefficient burning. A variety of air assisted flare burner apparatus, wherein combustion air is forced through or around the burner by one or more air blowers have been developed (see for example US-A-4,457,696) but are ineffective for flaring inert vitiated waste gases in that the gases are diluted and cooled by the air and consequently, do not reach the temperature at which ignition will occur. According to the present invention there is provided burner apparatus for flaring waste gases comprising a first tubular member having an inlet end a discharge end for discharging waste gases; a second tubular member positioned around at least the discharge end portion of said first tubular member whereby a discharge space is provided between said first and second tubular members around and adjacent said discharge end of said first tubular member; burner means disposed within said discharge space for discharging and igniting fuel gas therein; a fuel gas conduit for supplying fuel gas to said burner means; a combustion air conduit connecting a source of combustion air to said discharge space, whereby combustion air supplied to said discharge space may be mixed with fuel discharged from said burner means, to form a mixture which may be ignited and burned in a stable envelope around waste gases discharged from said first tubular member, to heat a portion of said waste gases to the ignition temperature thereof, ignited and burned thereby providing heat and ignition to the remaining waste gases. According to another aspect of the invention there is provided a method of flaring waste gases, said method comprising the steps of discharging said waste gases into the atmosphere, discharging combustion air into the atmosphere in an envelope around said waste gases and discharging and igniting fuel gas within said envelope of combustion air so that said fuel gas mixes with, and is burned in, said combustion air and a stable envelope of burning gases is formed around said waste gases, whereby a portion of said waste gases is heated to the ignition temperature thereof, ignited and burned, thereby providing heat and ignition to the remaining waste gases. In order that the invention may more readily be understood, the following description is given, merely by way of example, reference being made to the accompanying drawings, in which:- Figure 1 is a side, partly sectional view of one form of flare burner apparatus of the present invention; Figure 2 is a cross-sectional view taken along line 2-2 of Figure 1; Figure 3 is a cross-sectional view taken along line 3-3 of Figure 1; Figure 4 is an enlarged view of a portion of the apparatus of Figure 1; Figure 5 is a top view of the apparatus of Figure 4; Figure 6 is an enlarged view similar to Figure 4, but showing an alternative form of apparatus of the invention; Figure 7 is a view similar to Figure 6 showing a third form of apparatus of the invention; Figure 8 is a view similar to Figure 6 showing a fourth form of apparatus of the invention; Figure 9 is a side, partly sectional view of a fifth form of flare burner apparatus of the present invention; Figure 10 is a cross-sectional view taken along line 10-10 of Figure 9; Figure 11 is a side partly sectional view similar to Figure 9 showing a sixth form of flare burner apparatus of the invention; and Figure 12 is a side, partly sectional view similar to Figure 9 showing a seventh form of flare burner apparatus of the present invention. Referring now to the Figures 1-5, flare burner apparatus 10 is shown connected to an upstanding waste gas stack or conduit 12 which is in turn connected to a conduit 14, which conducts a stream of waste gas from a source thereof to the conduit 12. A combustion air blower 16 is connected to a conduit 44 of the apparatus 10 by a conduit 18 and burner fuel gas is connected to a conduit 54 of the apparatus 10 by a conduit 20. Pilot fuel gas is conducted to gas-air mixers 22 and the mixture produced is conducted to conduits 72 and pilot burner apparatus 70 of the apparatus 10 by conduits 26. As best shown in Figures 1-3, the apparatus 10 comprises a first tubular member 30, preferably cylindrical, having a discharge end 32 and an inlet end 34. The inlet end 34 of the tubular member 30 includes a flange connected to a complementary flange on conduit 12. Positioned around at least the discharge end portion of the tubular member 30 and attached thereto by an annular closing wall 36 is a second tubular member 40, preferably also cylindrical in shape. The first and second tubular members 30 and 40 provide a discharge space 42 therebetween positioned around and adjacent the discharge end 32 of the first tubular member 30. While the discharge ends of the tubular members 30 and 40 are shown in the drawings to lie in the same plane, it is to be understood that the ends can be positioned at different elevations relative to each other. The conduit 44 is sealingly attached to the wall 36 over an opening therein so that a stream of combustion air produced by the air blower 16 is conducted to the discharge space 42 and discharged therefrom around the discharge end 32 of the tubular member 30. Disposed within the annular discharge space 42 above the conduit 44 is a diverting plate 46. The diverting plate 46 can cover a 360° or less segment of the annular space 42 (a 90° segment plate being shown) and contains perforations of a number and size such that the stream of air conducted to the space 42 by the conduit 44 is distributed within the space 42 and the air is discharged therefrom in the form of an annular envelope of relatively constant velocity. Located within the discharge space 42 is a burner 50, connected to conduit 54. The burner can include multiple burner tips or nozzles, but preferably is a continuous annular conduit of square, rectangular or round shape centred about the tubular member 30 by a plurality of lugs 52. As best shown in Figures 4 and 5, the burner 50 includes a plurality of ignition orifices 56 formed its side facing the tubular member 40 and a plurality of primary fuel gas discharge orifices 58 formed in its top. Fuel gas is discharged both laterally through ignition orifices 56 into an ignition zone and also through primary discharge orifices 58 substantially in the direction of discharge of the waste gases from the first tubular member 30. Attached to the radially outer side of the burner 50, upstream of the ignition orifices 56, is an ignition zone shield 60. The shield 60 includes a plurality of openings 62 for the passage of a portion of the air therethrough, and baffles 64 are optionally attached to the periphery of the shield 60 at points opposite the ignition orifices 56 to divert fuel gas discharged from the orifices 56. The shield 60 can also optionally include slots (not shown) therein for providing air passage and allowing for thermal expansion. Optionally attached to the first tubular member 30 at the discharge end 32 thereof is a flame retention device 66, which has a plurality of openings 68 therein, through which portions of the waste gases flow and are ignited and burned adjacent the device to retain a waste gas ignition flame adjacent the discharge end 32 of the tubular member 30. As shown in Figures 1-3, three pilot burners 70 are attached at the discharge end of the apparatus for initially igniting the fuel gas discharged from the burner 50 and/or waste gas discharged from the discharge end 32 of the tubular member 30. In operation of the apparatus 10, a stream of inert vitiated waste gases to be flared is caused to flow by way of the conduits 14 and 12 through the first tubular member 30. Simultaneously, a stream of combustion air produced by the air blower 16 flows through the conduits 18 and 44 into the discharge space 42. The diverting baffle 46 causes the air to be distributed within the discharge space 42 and then to be discharged in an annular envelope of relatively constant velocity around the waste gases discharged from the discharge end 32 of the tubular member 30. Fuel gas supplied to the burner 50 is discharged from burner 50 by way of the orifices 56 and 58. The fuel gas discharged through ignition orifices 56 enters the ignition zone shielded by the shield 60, is initially ignited by the pilot burners 70, mixes with air flowing into the ignition zone by way of the openings 62 in the shield 60 and is continuously burned in the ignition zone. The fuel gas discharged through primary discharge orifices 58 is ignited by the burning gases in the ignition zone and/or the pilots 70, is mixed with combustion air flowing through the discharge space 42 and is burned in a stable envelope around the stream of waste gases discharged from the tubular member 30. This envelope causes a portion of the waste gases to be heated to the ignition temperature thereof and then to be ignited and burned, thereby providing heat and ignition to the remaining waste gases. The rates of combustion air and auxiliary fuel gas discharged from the space 42 are adjusted, whereby the fuel gas is burned efficiently and the flames produced are highly stable in windy environments. While the apparatus 10 is particularly suitable for flaring inert vitiated waste gases, other waste gases including those having intermediate and high heating values can also be efficiently flared using the method and apparatus of this invention. Figures 6, 7 and 8 show various modifications of the burner 50, ignition shield 60 and discharge space 42. In Figure 6, the ignition discharge orifices 56 in the side of the burner 50 are facing the tubular member 30, with the ignition zone shield 60 being positioned between the burner 50 and the tubular member 30. In addition, in order to direct the envelope of burning gases produced towards the waste gases discharged from the tubular member 30, the primary fuel gas discharge orifices 58 of the burner 50 can be inclined towards the discharge end 32 of the tubular member 30. In applications where it is desirable to provide extra stability to the flames produced by the flare burner, where large volumes of waste gases are being flared, or for other reason, both the air and fuel gas discharged from the discharge space 42 can be caused to flow inwardly towards the waste gases by inclining both the burner 50 and tubular member 40 inwardly as shown in Figure 7. In Figure 8, both the tubular member 40 and tubular member 30 are inclined inwardly at the discharge end 32 for the same purpose. In addition, the burner 50 is of circular cross-sectional shape and ignition shields 60 are provided on opposite sides thereof. The flare burner 80 shown in Figures 9 and 10 is particularly suitable for flaring high flow rates of inert vitiated waste gases and is identical to flare burner 10, except that it includes a baffle member disposed within the discharge end portion of the first tubular member and an optional fuel gas injector ring disposed externally of the discharge end of the second tubular member. More specifically, the flare burner 80 includes first and second tubular members 82 and 84, forming a discharge space 86 therebetween. A burner 88 and ignition zone shield 90 are disposed in the discharge space 86, the burner 88 being connected to a source of fuel gas by a conduit 92. A conduit 94 is sealingly connected to the discharge space 86 and to a source of combustion air and pilot burners 96 are provided connected to sources of fuel and air mixtures by conduits 98 disposed within the tubular member 84. Located within the discharge end portion of the tubular member 82 and positioned coaxially therewith is a preferably cylindrical baffle member 100 which is substantially closed at both ends. The baffle member 100 is attached within the tubular member 82 by a plurality of lugs 102 and functions to discharge the waste gases in an annulus, to bring them closer to the envelope of burning auxiliary fuel gas, thereby increasing the exposure of the waste gases to the fuel gas being burned and accelerating their ignition and burning. Optionally, in order to provide additional fuel gas for mixing with air and burning in the envelope of burning gases surrounding the discharged waste gases, a fuel gas injector ring 120 may be located externally of the discharge end of the tubular member 84 and attached thereto by lugs 122. A plurality of upstanding fuel injector nozzles 124 or equivalent orifices are provided on the ring 120, which is connected via a conduit 126 to a source of fuel gas. As shown in Figure 9, the fuel injector nozzles 124 are preferably inclined towards the interior of the burner 80, so that fuel gas discharged from the nozzles 124 is injected into the envelope of burning fuel gas and air adjacent the discharge end of the burner 80. If the high flow rate and/or burning properties of the waste gases require even more heating, additional auxiliary fuel gas can be combined with the waste gases, preferably in an annular pattern, as this is found to accelerate the burning of the waste gases. As shown in Figure 11, this can be accomplished in the burner 80 by providing a plurality of discharge orifices 104 in the sides of the baffle member 100 and connecting the interior of the member 100 to a source of fuel gas by a conduit 106. To prevent this fuel gas from being immediately dispersed in the waste gases and to promote the burning thereof in an annular pattern, shields 108 can be utilized adjacent the orifices 104. In the modification of Figure 12, a plurality of fuel gas discharge orifices 110 are disposed in the sides of the first tubular member 82 shielded by shield 112. A fuel gas bustle is attached over the orifices 110 within the discharge space 86 and the bustle is connected by a conduit 116 to a source of fuel gas. The method of use of the apparatus of the present invention is illustrated in the following example. EXAMPLE A flare burner apparatus 10 is attached ot a 40.6 cm by 3.05 cm high conduit which conducts inert vitiated waste gases at a rate of 2550 m³/hr and at a temperature of -23°C to the burner. The first tubular member 30 of the apparatus 10 is about 40.6 cms in diameter and the second tubular member 40 is about 55.9 cm in diameter. The burner 50 is formed of 1.3 cm rectangular tubing and includes 15 ignition orifices 56 and 30 primary discharge orifices 58. The waste gases have a heating value of about 7.08 x 10⁶J/m³. About 850 m³/hr of combustion air is supplied to and discharged from the discharge space 42 of the burner 10 and 57m³/hr of natural gas is conducted to the burner 50 and discharged therefrom. The natural gas is burned in a stable envelope of burning gases around the waste gases and a portion of the waste gases is heated to ignition temperature, ignited and efficiently burned thereby providing heat and ignition to the remaining waste gases.

Claims: 1. Burner apparatus for flaring waste gases comprising a first tubular member (30,82) having an inlet end (34) a discharge end (32) for discharging waste gases; a second tubular member (40,84) positioned around at least the discharge end portion of said first tubular member whereby a discharge space (42,86) is provided between said first and second tubular members around and adjacent said discharge end of said first tubular member; burner means (50,88) disposed adjacent said discharge end, a fuel gas conduit for supplying fuel gas to said burner means; and a combustion air conduit connecting a source of combustion air to said discharge space, characterised in that said burner means (50,88) is located in said discharge space (42,86) whereby combustion air supplied to said discharge space may be mixed with fuel discharged from said burner means, to form a mixture which may be ignited and burned in a stable envelope around waste gases discharged from said first tubular member, to heat a portion of said waste gases to the ignition temperature thereof, ignited and burned thereby providing heat and ignition to the remaining waste gases. 2. Apparatus according to claim 1, characterised in that said second tubular member (40,84) completely surrounds said first tubular member (30,82), so that said discharge space (42,86) is annular. 3. Apparatus according to claim 1 or 2 characterised in that said burner means (50,88) comprise a conduit disposed in said discharge space in a plane substantially parallel with the plane of said discharge end (32) of said first tubular member, said conduit including a plurality of fuel gas discharge orifices (56,58) disposed therein. 4. Apparatus according to claim 3, characterised in that said fuel gas discharge orifices comprise ignition orifices (56) for discharging fuel gas into an ignition zone adjacent said conduit and primary discharge orifices (58) for discharging fuel gas substantially in the direction of discharge of said waste gases from said first tubular member. 5. Apparatus according to claim 4, characterised in that a perforated ignition zone shield is positioned adjacent said conduit upstream of the ignition orifices therein. 6. Apparatus according to any preceding claim, characterised in that flame retention means (66) are attached to the discharge end of said first tubular member. 7. Apparatus according to any preceding claim, characterised in that a baffle member (100) is disposed within said discharge end (32) of said first tubular member to cause the waste gases discharged as an annulus from said tubular member. 8. Apparatus according to claim 7, characterised in that said baffle (100) comprises a cylindrical member substantially closed at both ends positioned coaxially within said first tubular member. 9. Apparatus according to any preceding claim, characterised in that at least one fuel injector nozzle, connected to a source of fuel gas, is positioned adjacent said second tubular member for injecting additional fuel gas into said annular envelope of burning fuel gas and air. 10. Apparatus according to claim 8 or 9, characterised in that said substantially closed cylindrical member (100) includes at least one fuel gas discharge orifice (104) disposed therein for discharging fuel gas into said waste gases and a conduit (106) connected to said substantially closed cylindrical member for connecting the interior of said member to a source of fuel gas. 11. Apparatus according to any preceding claim, characterised in that at least one fuel gas discharge orifice (110) is disposed therein for discharging fuel gas into said waste gases, a fuel gas bustle (114) is attached to said first tubular member over said fuel gas discharge orifice therein and a feed conduit (116) is connected to said fuel gas bustle for supplying fuel gas to the interior of said bustle. 12. A method of flaring waste gases, said method comprising the steps of discharging said waste gases into the atmosphere and discharging combustion air and additional fuel into the atmosphere, characterised in that said combustion air is discharged in an envelope around said waste gases and in that said fuel gas is discharged and ignited within said envelope of combustion air so that said fuel gas mixes with and is burned in said combustion air and a stable envelope of burning gases is formed around said waste gases whereby a portion of said waste gases is heated to the ignition temperature thereof, ignited and burned thereby providing heat and ignition to the remaining waste gases. 13. A method according to claim 12, characterised in that said envelope of combustion air is annular in cross-section and said fuel gas is discharged therein in an annular pattern. 14. A method according to claim 13, characterised in that said waste gases are formed into an annular shape in cross-section with and adjacent to said annular envelope of burning gases. 15. A method according to claim 12, 13 or 14, characterised in that additional fuel gas is discharged in an annular pattern within said waste gases whereby said fuel gas is ignited by said envelope of burning gases, mixes with air and burns downstream of said envelope to facilitate the heating, igniting and burning of said waste gases. 16. A method according to claim 12, 14 or 15 characterised in that additional fuel gas is injected into said envelope of burning gases from at least one location external to said envelope.

Inventors: NOBLE, ROGER K., SCHWARTZ, ROBERT E.
Applicants: JOHN ZINK COMPANY
Application year: 1986
Main classification: F23G7
IPC codes: F23G7