EP2251601A2

EP2251601A2 - Air flare apparatus and method

Info

Publication number: EP2251601A2
Application number: EP10250914A
Authority: EP
Inventors: Roger L. Poe; Joseph Colannino; Jianhui Hong; Robert E. Schwartz
Original assignee: John Zink Co LLC
Current assignee: John Zink Co LLC
Priority date: 2009-05-12
Filing date: 2010-05-12
Publication date: 2010-11-17
Also published as: CN101886812A; SG166728A1; TW201102588A; KR101255883B1; AR079587A1; KR20100122458A; AU2010201853B2; US20100291492A1; BRPI1001922A2; JP2010286230A; CA2700957C; MX2010004321A; CA2700957A1; AU2010201853A1

Abstract

A flare apparatus for discharging and burning flare gas in the atmosphere is provided. The flare tip includes a flare gas conduit having a flare gas discharge opening and a combustion air conduit having a combustion air discharge opening. All of the flare gas to be flared is discharged through the flare gas discharge opening into a unified column of air discharged through the combustion air discharge opening. The flare gas discharge opening and the combustion air discharge opening are positioned with respect to one another such that flare gas discharged from the flare gas discharge opening is discharged inwardly into combustion air that is discharged from the combustion air discharge opening and admixed therewith. Essentially all of the discharged flare gas is admixed with discharged combustion air or external atmospheric air outside of the flare apparatus thereby preventing internal burning. A method of flaring a mixture of flare gas and combustion air is also provided.

Description

Gas flares are commonly located at production facilities, refineries, processing plants and the like for disposing of flammable waste gases and other flammable gas streams that are diverted due to venting requirements, shut-downs, upsets and/or emergencies. Such flares are often required to operate in a smokeless manner, which has been achieved by making sure that the flammable gas to be discharged and burned ("flare gas") is admixed with enough air to sufficiently oxidize the gas. A typical flare apparatus includes a flare stack, which can extend high above the ground, and a flare tip mounted on the flare stack.
In an air-assist flare, one or more blowers are used to blow air up through the flare stack. In a steam-assist flare, steam is used to provide the necessary motive force and entrainment energy to augment air from around the flare apparatus. Some flares utilize both forced air and steam to achieve the desired result.
In addition to being designed and operated in a manner that eliminates or significantly reduces smoke, flares need to be designed and operated such that internal burning is avoided. Internal burning, that is the burning of portions of the flare gas and air within the flare tip and other structure, can cause the flare apparatus to have a relatively short service life. Repairing and/or replacing the flare apparatus or parts thereof is expensive and can result in costly interruptions of the corresponding facility or plant.
In an air-assist flare tip, air is blown in by a blower or a fan through the bottom of the flare tip. The stoichiometric amount of air needed to achieve the desired degree of combustion varies depending on the application. As a result, the number of blowers or fans and the horsepower thereof varies from flare to flare. The flow rate of the flare gas varies depending on what is causing the flare gas to be discharged. Typically, only a relatively small percentage of the total flammable gas generated or used in the facility or plant is vented at any given time. On the other hand, in many applications, a flare apparatus needs to be designed to accommodate a total shut-down of the plant or facility, requiring a high volume of flammable gas to be vented within a relatively short amount of time. Thus, many flares are designed and include the number and size of blowers necessary to accommodate a relatively high flow rate of flare gas.
In a typical flare tip, the air and the flare gas are generally coaxially discharged into the atmosphere. Such a flare tip relies on turbulence and diffusion to mix the air and gas sufficiently for a stable combustion process. Unfortunately, such a mixing system may not be as efficient as possible in all applications. External atmospheric air on the outside of the flare gas stream can be inhibited from mixing with the flare gas due to the wind and other factors.
In some flares, flare gas is injected into the interior of the combustion air stream that is discharged from the flare tip to break up the discharged combustion air into several specific portions. Flare gas is also annularly injected around the discharged combustion air/flare gas stream. This approach is effective in that it imparts flare gas directly to the interior of the flame envelope adjacent to the flare tip. A premixed or aerated stream is created immediately adjacent to the outlet of the flare tip and within the interior of the flame envelope. However, in accordance with the present invention, it has been discovered that, in some scenarios, the flare gas or flame envelope can appreciably cap or inhibit the flow of the premixed or aerated stream early on in the mixing process. This can minimize the amount of discharged combustion air that can be admixed into the flame envelope further away from the discharge end of the flare tip.
It may also be possible to pre-mix the flare gas and combustion air within the flare apparatus before the gas and air are discharged from the flare apparatus and ignited. However, in certain applications, this approach can lead to internal burning and significantly shorten the service life of the flare tip.
In accordance with the present invention, a flare apparatus for discharging and burning flare gas in the atmosphere is provided. An improved flare tip is provided for use in association with the inventive flare apparatus. A method of flaring a mixture of flare gas and combustion air in a flare apparatus without pre-mixing a significant portion of the flare gas with the combustion air within the flare apparatus prior to discharging the flare gas and combustion air from the flare apparatus is also provided.
The inventive flare tip comprises a flare gas conduit, and a combustion air conduit associated with the flare gas conduit. The flare gas conduit includes a first end, a second end and a side wall connecting the first end to the second end, wherein the flare gas conduit is adapted to be fluidly connected to a source of flare gas, and the second end of the flare gas conduit defines a flare gas discharge opening. The flare gas conduit and the flare gas discharge opening are of a size sufficient to allow all of the flare gas that is to be discharged and burned by the flare apparatus to be discharged through the flare gas discharge opening. The combustion air conduit includes a first end, a second end and a side wall connecting the first end to the second end, wherein said combustion air conduit is adapted to be fluidly connected to a source of combustion air, and said second end of said combustion air conduit defines a combustion air discharge opening. The combustion air conduit has a structure that causes a unified column of combustion air to be discharged through the combustion air discharge opening.
The flare gas discharge opening and the combustion air discharge opening of the inventive flare apparatus are positioned with respect to one another such that essentially all of the flare gas to be discharged and burned by the flare apparatus can be discharged through the flare gas discharge opening inwardly into the column of combustion air discharged from the combustion air discharge opening and such that essentially all of the discharged flare gas can be admixed with discharged combustion air or external atmospheric air outside of the combustion air conduit and the flare gas conduit.
The inventive method comprises the following steps:

(a) a unified column of combustion air is discharged into the atmosphere from the flare apparatus;
(b) essentially all of the flare gas to be flared by the flare apparatus is discharged into the atmosphere from the flare apparatus and inwardly into the discharged column of combustion air such that essentially all of the discharged flare gas is admixed with discharged combustion air and external atmospheric air outside of the flare apparatus; and
(c) the mixture of discharged flare gas, discharged combustion air and external atmospheric air is ignited.

In accordance with a first aspect of the invention, there is provided a flare tip for use in association with a flare apparatus for discharging and burning flare gas in the atmosphere comprising: a flare gas conduit including a first end, a second end and a side wall connecting said first end to said second end, wherein said flare gas conduit is adapted to be fluidly connected to a source of flare gas and said second end of said flare gas conduit defines a flare gas discharge opening, said flare gas conduit and said flare gas discharge opening being of a size sufficient to allow all of the flare gas that is to be discharged and burned by said flare apparatus to be discharged through said flare gas discharge opening; and a combustion air conduit associated with said flare gas conduit, said combustion air conduit including a first end, a second end and a side wall connecting said first end to said second end, wherein said combustion air conduit is adapted to be fluidly connected to a source of combustion air, and said second end of said combustion air conduit defines a combustion air discharge opening, said combustion air conduit having a structure that causes a unified column of combustion air to be discharged through said combustion air discharge opening, said flare gas discharge opening and said combustion air discharge opening being positioned with respect to one another such that essentially all of the flare gas to be discharged and burned by said flare apparatus can be discharged through said flare gas discharge opening inwardly into the column of combustion air discharged from said combustion air discharge opening and such that essentially all of the discharged flare gas can be admixed with discharged combustion air or external atmospheric air outside of said combustion air conduit and said flare gas conduit.
Optionally, said combustion air conduit is positioned at least partially within said flare gas conduit, and wherein said flare gas discharge opening and said combustion air discharge opening are positioned with respect to one another such that essentially all of the flare gas to be discharged and burned by said flare apparatus can be discharged through said flare gas discharge opening around and inwardly into the column of combustion air discharged from said combustion air discharge opening.
Optionally, the height of said combustion air conduit is equal to, greater than, or less than the height of said flare gas conduit, and wherein if the height of said combustion air conduit is less than the height of said flare gas conduit, the ratio of the difference between the heights of said combustion air conduit and said flare gas conduit to the hydraulic diameter of said combustion air conduit is no greater than 0.05.
Optionally, the height of said combustion air conduit is equal to, greater than, or less than the height of said flare gas conduit, and wherein in the event that the height of said combustion air conduit is less than the height of said flare gas conduit, the ratio of the difference between the heights of said combustion air conduit and said flare gas conduit to the hydraulic diameter of said combustion air conduit is no greater than 0.02.
Optionally, the height of said combustion air conduit is equal to or greater than the height of said flare gas conduit.
Optionally, the height of said combustion air conduit is greater than the height of said flare gas conduit, and wherein the ratio of the difference between the heights of said combustion air conduit and said flare gas conduit to the hydraulic diameter of said combustion air conduit is approximately 0.01.
Optionally, said side wall of said flare gas conduit includes a portion adjacent to said flare gas discharge opening that tapers inwardly toward the vertical central axis of said combustion air conduit.
Optionally, said portion of said side wall of said flare gas conduit adjacent to said flare gas discharge opening tapers inwardly toward the vertical central axis of said combustion air conduit at an angle in the range of from about 10° to about 90°.
Optionally, said portion of said side wall of said flare gas conduit adjacent to said flare gas discharge opening tapers inwardly toward the vertical central axis of said combustion air conduit at an angle in the range of from about 25° to about 45°.
Optionally, said portion of said side wall of said flare gas conduit adjacent to said flare gas discharge opening tapers inwardly toward the vertical central axis of said combustion air conduit at an angle of about 35°.
Optionally, said side wall of said combustion air conduit includes a portion adjacent to said combustion air discharge opening that tapers inwardly toward the vertical central axis of said combustion air conduit.
Optionally, said flare gas conduit and said combustion air conduit each have circular cross-sections, and said combustion air conduit is at least partially concentrically disposed within said flare gas conduit.
Optionally, the height of said combustion air conduit is equal to, greater than, or less than the height of said flare gas conduit, and wherein if the height of said combustion air conduit is less than the height of said flare gas conduit, the ratio of the difference between the heights of said combustion air conduit and said flare gas conduit to the diameter of said combustion air conduit is no greater than 0.05.
Optionally, said flare gas conduit further comprises: an inlet adapted to be fluidly connected to a source of flare gas; and a flow distribution member attached within said flare gas conduit.
Optionally, said flow distribution member is an annular plate disposed within said flare gas conduit.
Optionally, said flare gas conduit includes at least one inlet adapted to be fluidly connected to a source of flare gas and to inject flare gas into said flare gas conduit at an angle with respect to the vertical central axis of said flare gas conduit.
Optionally, said flare gas conduit includes at least two inlets, each inlet adapted to be fluidly connected to a source of flare gas and to inject flare gas into said flare gas conduit at an angle with respect to the vertical central axis of said flare gas conduit.
In a second aspect, the invention comprises a flare tip for use in association with a flare apparatus for discharging and burning flare gas in the atmosphere comprising: a flare gas conduit including a first end, a second end and a side wall connecting said first end to said second end, wherein said flare gas conduit is adapted to be fluidly connected to a source of flare gas and said second end of said flare gas conduit defines a flare gas discharge opening, said flare gas conduit and said flare gas discharge opening being of a size sufficient to allow all of the flare gas that is to be discharged and burned by said flare apparatus to be discharged through said flare gas discharge opening; and a combustion air conduit positioned at least partially within said flare gas conduit, said combustion air conduit including a first end, a second end and a side wall connecting said first end to said second end, wherein said combustion air conduit is adapted to be fluidly connected to a source of combustion air, and said second end of said combustion air conduit defines a combustion air discharge opening, said combustion air conduit having a structure that causes a unified column of combustion air to be discharged through said combustion air discharge opening, said flare gas discharge opening and said combustion air discharge opening being positioned with respect to one another such that essentially all of the flare gas to be discharged and burned by said flare apparatus can be discharged through said flare gas discharge opening around and inwardly into the column of combustion air discharged from said combustion air discharge opening and such that essentially all of the discharged flare gas can be admixed with discharged combustion air or external atmospheric air outside of said combustion air conduit and said flare gas conduit.
Optionally, the height of said combustion air conduit is equal to, greater than, or less than the height of said flare gas conduit, and wherein if the height of said combustion air conduit is less than the height of said flare gas conduit, the ratio of the difference between the heights of said combustion air conduit and said flare gas conduit to the hydraulic diameter of said combustion air conduit is no greater than 0.05.
Optionally, the height of said combustion air conduit is equal to, greater than, or less than the height of said flare gas conduit, and wherein in the event that the height of said combustion air conduit is less than the height of said flare gas conduit, the ratio of the difference between the heights of said combustion air conduit and said flare gas conduit to the hydraulic diameter of said combustion air conduit is no greater than 0.02.
Optionally, the height of said combustion air conduit is equal to or greater than the height of said flare gas conduit.
Optionally, the height of said combustion air conduit is greater than the height of said flare gas conduit, and wherein the ratio of the difference between the heights of said combustion air conduit and said flare gas conduit to the hydraulic diameter of said combustion air conduit is approximately 0.01.
Optionally, said side wall of said flare gas conduit includes a portion adjacent to said flare gas discharge opening that tapers inwardly toward the vertical central axis of said combustion air conduit.
Optionally, said portion of said side wall of said flare gas conduit adjacent to said flare gas discharge opening tapers inwardly toward the vertical central axis of said combustion air conduit at an angle in the range of from about 10° to about 90°.
Optionally, said portion of said side wall of said flare gas conduit adjacent to said flare gas discharge opening tapers inwardly toward the vertical central axis of said combustion air conduit at an angle in the range of from about 25° to about 45°.
Optionally, said portion of said side wall of said flare gas conduit adjacent to said flare gas discharge opening tapers inwardly toward the vertical central axis of said combustion air conduit at an angle of about 35°.
Optionally, said side wall of said combustion air conduit includes a portion adjacent to said combustion air discharge opening that tapers inwardly toward the vertical central axis of said combustion air conduit.
Optionally, said flare gas conduit and said combustion air conduit each have circular cross-sections, and said combustion air conduit is at least partially concentrically disposed within said flare gas conduit.
Optionally, the height of said combustion air conduit is equal to, greater than, or less than the height of said flare gas conduit, and wherein if the height of said combustion air conduit is less than the height of said flare gas conduit, the ratio of the difference between the heights of said combustion air conduit and said flare gas conduit to the diameter of said combustion air conduit is no greater than 0.05.
Optionally, said flare gas conduit further comprises: an inlet adapted to be fluidly connected to a source of flare gas; and a flow distribution member attached within said flare gas conduit.
Optionally, said flow distribution member is an annular plate disposed within said flare gas conduit.
Optionally, said flare gas conduit includes at least one inlet adapted to be fluidly connected to a source of flare gas and to inject flare gas into said flare gas conduit at an angle with respect to the vertical central axis of said flare gas conduit.
Optionally, said flare gas conduit includes at least two inlets, each inlet adapted to be fluidly connected to a source of flare gas and to inject flare gas into said flare gas conduit at an angle with respect to the vertical central axis of said flare gas conduit.
In a third aspect, the invention comprises a method of flaring a mixture of flare gas and combustion air in a flare apparatus without pre-mixing a significant portion of the flare gas with the combustion air within the flare apparatus prior to discharging the flare gas and combustion air from the flare apparatus, comprising:

(a) discharging a unified column of combustion air into the atmosphere from the flare apparatus;
(b) discharging essentially all of the flare gas to be flared by the flare apparatus into the atmosphere from the flare apparatus and inwardly into the discharged column of combustion air such that essentially all of the discharged flare gas is admixed with discharged combustion air or external atmospheric air outside of the flare apparatus; and
(c) igniting the mixture of discharged flare gas, discharged combustion air and external atmospheric air.

Optionally, all of the flare gas to be flared by the flare apparatus is discharged into the atmosphere from the flare apparatus and inwardly into the discharged column of combustion air.
Optionally, the combustion air is discharged into the atmosphere from the flare apparatus at a radial velocity less than the radial velocity at which the flare gas is discharged into the atmosphere from said flare apparatus.
Optionally, the combustion air is discharged into the atmosphere from the flare apparatus at an axial velocity of at least 50 feet per second.
Optionally, the combustion air is discharged into the atmosphere from the flare apparatus at an axial velocity in the range of from about 50 feet per second to about 200 feet per second.
Optionally, the combustion air is discharged into the atmosphere from the flare apparatus at an axial velocity in the range of from about 120 feet per second to about 150 feet per second.
Optionally, the combustion air is discharged into the atmosphere from the flare apparatus at an axial velocity of about 150 feet per second.
Optionally, essentially all of the flare gas to be flared by the flare apparatus is discharged into the atmosphere from the flare apparatus around the discharged column of combustion air and inwardly into the discharged column of combustion air.
Optionally, essentially all of the flare gas to be flared by the flare apparatus is discharged into the atmosphere from the flare apparatus inwardly into the discharged combustion air at an angle in the range of from about 10° to about 90°.
Optionally, essentially all of the flare gas to be flared by the flare apparatus is discharged into the atmosphere from the flare apparatus inwardly into the discharged combustion air at an angle in the range of from about 25° to about 45°.
Optionally, essentially all of the flare gas to be flared by the flare apparatus is discharged into the atmosphere from the flare apparatus inwardly into the discharged combustion air at an angle of about 35°.
Optionally, all of the flare gas to be flared by the flare apparatus is discharged into the atmosphere from the flare apparatus around the discharged column of combustion air and inwardly into the discharged column of combustion air.
Optionally, the method further comprises reducing the static pressure of a portion of the admixture of discharged flare gas, discharged combustion air and/or external atmospheric air adjacent to the flare apparatus.
Optionally, the static pressure of a portion of the admixture of discharged flare gas, discharged combustion air and/or external atmospheric air adjacent to the flare apparatus is reduced by creating a low pressure zone in the area of said combustion air discharge opening.
Optionally, a low pressure zone is created adjacent to the flare apparatus by causing the flare gas to be discharged from the flare apparatus in a swirling annular pattern around the discharged combustion air.
Optionally, the method further comprises blowing combustion air into the flare apparatus.
The objects, features and advantages of the present invention will be readily apparent to those skilled in the art upon a reading of the following detailed description. The invention will be further described, by way of non-limitative example only, with reference to the accompanying drawings, in which:
FIG. 1 is a front sectional view of a prior art flare apparatus.
FIG. 2 is a cross-sectional view taken along the line 2-2 of FIG. 1.
FIG. 3 is a front elevated view of one configuration of the inventive flare apparatus.
FIG. 4A is a perspective view of the flare tip of the flare apparatus illustrated by FIG. 3.
FIG. 4B is a front sectional view of the flare apparatus shown by FIG. 4A.
FIG. 4C is a cross-sectional view taken along the line 4C-4C of FIG. 4B..
FIG. 4D is a cross-sectional view taken along the line 4D-4D of FIG. 4B.
FIG. 4E is an enlarged detail view of a portion of the flare apparatus illustrated by FIGS. 4A-4D illustrating the difference between the heights of the combustion air conduit and the flare gas conduit and the hydraulic diameter of the combustion air conduit.
FIGS. 5A and 5B are front sectional views illustrating additional configurations of the inventive flare apparatus.
FIG. 6A is a front sectional view illustrating another configuration of the inventive flare apparatus.
FIG. 6B is an enlarged detail view of a portion of the flare apparatus illustrated by FIG. 6A.
FIG. 7A is a front sectional view illustrating another configuration of the inventive flare apparatus.
FIG. 7B is an enlarged detail view of a portion of the flare apparatus illustrated by FIG. 7A.
FIG. 8A is a front sectional view of the flare apparatus illustrated by FIGS. 4A-4E illustrating how the flare gas can be swirled.
FIG. 8B is a cross-sectional view taken along the line 8B-8B of FIG. 8A.
FIGS. 9A-9C further illustrate a 3D coordinate system that can be utilized in connection with the inventive flare apparatus to describe the flow mechanisms associated therewith.
FIG. 10A is a front sectional view illustrating another embodiment of the inventive flare apparatus.
FIG. 10B is cross-sectional view taken along the line 10B-10B of FIG. 10A.
FIG. 11 is a perspective view illustrating yet another embodiment of the inventive flare apparatus.
FIGS. 12 and 13 illustrate some alternative configurations of the inventive flare apparatus.
FIG. 14A illustrates a flame pattern created by the inventive flare apparatus.
FIG. 14B illustrates the flare gas volume fraction contours estimated by a computational fluid dynamic simulation on the inventive flare apparatus.
Referring now to the drawings, and particularly to FIGS. 1 and 2, an example of a flare apparatus used heretofore is illustrated and generally designated by the numeral 10. As shown by FIG. 1, a flare tip 12 is attached to the top end of a flare stack 14 and to a flammable gas conduit 16 which extends through the flare stack 14 for conducting a stream of flammable gas to the flare tip 12. A pilot assembly 18 is attached to the flare apparatus 10 for igniting the admixture of flammable gas and air discharged from the flare apparatus.
The prior art flare apparatus 10 is comprised of an outer tubular member 20 having a discharge end 22. A combustion air blower 24 is attached to the flare stack 14. As indicated by the arrows 23, the blower 24 causes air to travel upwardly through the flare stack 14 and into and through the flare tip 12. A first inner tubular member 26 having a discharge end 28 is positioned within the outer tubular member 20 and forms an annular air discharge space 30 between the first inner tubular member and the outer tubular member. A second inner tubular member 32 having a discharge end 34 is positioned within the first inner tubular member 26. The second inner tubular member 32 forms an annular flammable gas discharge space 36 between the second inner tubular member and the first inner tubular member 26. The flammable gas discharge space 36 is provided immediately adjacent to the annular air discharge space 30. The second inner tubular member 32 also includes an interior space 38 which preferably serves as an additional air discharge space 40. A plurality of air deflectors 42 and 44 are disposed within the annular air discharge space 30 and the air discharge space 40.
As indicated by the arrows 46, the flammable gas is discharged from the flammable gas discharge space 36 into the atmosphere in an annular straight out pattern, that is, in a direction generally parallel to the central vertical axis (the longitudinal axis) 47 of the flare apparatus 10. The deflectors 42 and 44 cause the air discharged from the air discharge spaces 30 and 40 to swirl immediately adjacent to the flammable gas which prevents the discharged air as well as ambient air from ingressing into and mixing with flammable gas inside of the flare apparatus, thereby preventing burning therein.
The prior art flare apparatus shown by FIGS. 1 and 2 of the drawings is described and illustrated in U.S. Patent No. 5,846,068, which issued on December 8, 1998 and is incorporated by reference herein. Although such a flare apparatus is effective in many applications, a different or supplemental mixing mechanism may be desirable.
In accordance with the invention, rapid mixing of the flare gas and air outside of the flare apparatus can be achieved in a highly efficient manner. The mixing approach utilized allows the flare gas and combustion air to be effectively and efficiently admixed without premixing a significant portion of flare gas and combustion air within the flare apparatus prior to discharging the gas and air therefrom.
Referring now to FIG. 3, the inventive flare apparatus for discharging and burning flare gas in the atmosphere is illustrated and generally designated by the reference number 50. The flare apparatus 50 includes a flare base 52, a flare stack 54, a flare tip 56, a flare gas delivery conduit 58, a pilot assembly 60, and a combustion air blower 62.
The flare base 52 includes a base platform 70 and a plurality of base arms 72 extending therefrom. The base platform 70 can be attached to the ground or some other structure (not shown). The base arms 72 are attached to the flare stack 54 and hold the flare stack off the ground in order to allow air to be inducted directly through the bottom of the flare stack.
The flare stack 54 is a conduit having a circular cross-section. The flare stack includes a first end 74, a second end 76 and a side wall 77 connecting the first end to the second end. Combustion air is conducted through the first end 74 into the interior 78 of the flare stack 54 and through the interior of the flare stack to the interior 80 of the flare tip 56. A conventional connecting flange 79 is attached to the second end 76 of the flare stack 54.
The combustion air blower is mounted within the interior 78 of the flare stack 54 adjacent to the first end 74 thereof. The blower forces external air from the atmosphere 81 around the first end 74 of the flare stack 54 into and through the interior 78 of the flare stack 54 and into and through the interior 80 of the flare tip 56.
The flare gas delivery conduit 58 is also a conduit having a circular cross-section. The flare gas delivery conduit 58 includes a first end 82 directly or indirectly attached to the source of the flare gas to be vented by the flare apparatus 50 (not shown) and a second end 84 attached to the flare tip 56. Flare gas is conducted through the interior 87 of the flare gas delivery conduit 58 to the flare tip 56. As used herein and in the appended claims, "flare gas" refers to the flammable gas to be discharged and burned by the flare apparatus 50.
The pilot assembly 60 includes a pilot fuel conduit 88 attached to the flare apparatus 50, a conventional pilot gas-air mixer 90 associated with the pilot fuel conduit, and a pilot burner 92. Pilot fuel is conducted from a source thereof (not shown) through the conduit 88 (conduit 88a) to the mixer 90. The mixer 90 mixes the pilot fuel with air. The mixture of pilot fuel and air is conducted from the mixer 90 through the conduit 88 (conduit 88b) to the pilot burner 92. A pilot ignitor (not shown) is connected to an ignition conduit 94 which is attached to the flare apparatus 50 for generating an ignition flame (not shown). The ignition flame is conducted to the pilot burner 92 through the ignition conduit 94. While only one pilot assembly 60 is illustrated by FIG. 3, it will be understood by those skilled in the art that two or more of such assemblies can be utilized depending on the quantity of gas to be flared and other factors.
Referring now to FIGS. 4A though 4E, the flare tip 56 includes a flare gas conduit 100, and a combustion air conduit 102. The flare tip 56, flare gas conduit 100 and combustion air conduit 102 include vertical central axes 103, 104 and 105, respectively. The vertical central axes 103, 104 and 105 are also each the longitudinal axes of the respective conduit. Except for the embodiment illustrated by FIG. 11, the vertical central axes (longitudinal axes) 103, 104 and 105 of the flare apparatus 50, flare gas conduit 100 and combustion air conduit 102 are the same. The flare gas conduit 100 also includes a vertical outside axis 107, which is generally parallel to the vertical central axis 104. Similarly, the combustion air conduit 102 also includes a vertical outside axis 109, which is generally parallel to the vertical central axis 105. As used herein and in the appended claims, terms of orientation used in connection with the flare apparatus 50 such as "vertical" and "horizontal" are based on the orientation of the flare apparatus as illustrated by the drawings.
The flare gas conduit 100 has a circular cross-section and includes an interior 106, a first end 108, a second end 110 and a side wall 112 connecting the first end of the flare gas conduit to the second end thereof. The second end 110 of the flare gas conduit 100 defines a flare gas discharge opening 114. The flare gas conduit 100 and the flare gas discharge opening 114 are of a size sufficient to allow all of the flare gas that is to be discharged and burned by the flare apparatus 50 to be discharged through the flare gas discharge opening. A portion 115 of the side wall 112 that is adjacent to the flare gas discharge opening 114 tapers inwardly toward the vertical central axis 105 of the combustion air conduit 102. The side wall 112 of the flare gas conduit 100 includes an opening 116 therein. The second end 84 of the flare gas delivery conduit 58 is attached to the side wall 112 of the flare gas conduit 100 over the opening 116 in the side wall thereby allowing flare gas to be conducted from the interior 87 of the flare gas delivery conduit to the interior 106 of the flare gas conduit. The first end 108 of the flare gas conduit 100 includes a bottom wall 118 having an opening 120 therein.
The combustion air conduit 102 has a circular cross-section and includes an interior 126, a first end 128, a second end 130 and a side wall 132 connecting the first end of the flare gas conduit to the second end thereof. The second end 130 of the combustion air conduit 102 defines a combustion air discharge opening 134. The combustion air conduit 102 has a structure that causes a unified column of combustion air 133 to be discharged through the combustion air discharge opening 134. As used herein and in the appended claims, a unified column of combustion air means a stream or column of combustion air that does not include a significant amount of flare gas therein (that is, a stream or column of combustion air that does not include an amount of flare gas therein that would have been sufficient to form a flammable mixture of combustion air and flare gas within the flare apparatus prior to being discharged from the flare apparatus). A significant amount of flare gas (that is, an amount of flare gas that is or would be sufficient to create a flammable mixture of combustion air and flare gas within the combustion air conduit 102) is not admixed with the combustion air in the combustion air conduit 102 or injected from within the combustion air conduit 102 directly into the interior of the column of combustion air discharged through the combustion air discharge opening 134. Preferably, no flare gas is admixed with the combustion air in the combustion air conduit 102 or injected from within the combustion air conduit 102 directly into the interior of the column of combustion air discharged through the combustion air discharge opening 134.
A portion 135 of the side wall 132 that is adjacent to the combustion air discharge opening 134 tapers inwardly toward the vertical central axis 105 of the combustion air conduit 102 and the vertical central axis 103 of the overall flare tip 56. The first end 128 of the combustion air conduit 102 includes a flange 136 attached thereto, which is complementary to the flange 79 attached to the second end 76 of the flare stack 54. The flange 136 is connected to - the flange 79 to sealingly connect the first end 128 of the combustion air conduit 102 to the second end 76 of the flare stack 54 such that the interior 126 of the combustion air conduit is in fluid communication with the interior 78 of the flare stack.
The combustion air conduit 102 is positioned within the flare gas conduit 100 such that the second end 130 of the combustion air conduit extends slightly beyond the second end 110 of the flare gas conduit. In other words, the height of the combustion air conduit 102 is slightly greater than the height of the flare gas conduit 100. As used herein and in the appended claims, the "height" of the flare gas conduit 100, combustion air conduit 102 or any other component means the extent to which the conduit extends into the atmosphere 81 along the vertical central axis 103 of the flare tip 56. The combustion air conduit 102 does not extend all the way into the flare gas conduit 100. Specifically, the combustion air conduit extends through the opening 120 in the bottom wall 118 of the flare gas conduit 100 such that the first end 128 of the combustion air conduit is positioned below the first end 108 of the flare gas conduit. The combustion air conduit 102 is at least partially concentrically disposed within the flare gas conduit 100.
Due to the positioning of the combustion air conduit 102 within the flare gas conduit 100, an annular flare gas discharge space 140 extends around the combustion air conduit within the interior 106 of the flare gas conduit. The interior 126 of the combustion air conduit 102 serves as a combustion air discharge space 142. A gasket 146 is included in or adjacent to the edge 147 of the opening 120 in the bottom wall 118 of the flare gas conduit 100 to form a seal between the side wall 132 and the edge 147 of the opening 120 to prevent flare gas from leaking therethrough.
As shown by arrows 150 in FIGS. 4A and 4B (and also FIGS. 8A, 11 and 14B, discussed below), the unified column of combustion air 133 is conducted through the combustion air discharge space 142 (the interior 126) of the combustion air conduit 102 and discharged into the atmosphere 81 through the combustion air discharge opening 134 thereof. A central portion of combustion air 152 within the combustion air discharge space 142 (the interior 126) is axially discharged from the combustion air discharge opening 134. An outer, annular portion of combustion air 154 within the combustion air discharge space 142 (the interior 126) is directed inwardly toward the central portion of combustion air 152 by the inwardly tapered portion 135 of the side wall 132 that is adjacent to the combustion air discharge opening 134. As discussed further below, although the column of combustion air is a unified column of combustion air at the point of discharge into the atmosphere 81 through the combustion air discharge opening 134, it does not necessarily remain unified once it is discharged through the combustion air discharge opening due to the mixture of flare gas from the flare gas discharge opening 114 therewith. The column of combustion air 133, although not necessarily a unified column of combustion air after being discharged through the combustion air discharge opening 134, penetrates upwardly through the flame until the combustion air is consumed.
Essentially all of the flare gas to be discharged and burned by the flare apparatus 50 is conducted through the annular flare gas discharge space 140 (the interior 106) of the flare gas conduit 100 and discharged into the atmosphere 81 through the flare gas discharge opening 114 of the flare gas conduit as a stream of flare gas 162. As used herein and in the appended claims, "essentially all" of the discharged flare gas means all of the flare gas to be discharged and burned by the flare apparatus 50 except for an insignificant portion thereof (that is, all of the flare gas to be discharged and burned by the flare apparatus 50 except for possibly an amount of flare gas that would not be sufficient to create a flammable mixture of combustion air and flare gas within the combustion air conduit 102). In other words, any of the flare gas to be discharged and burned by the flare apparatus 50 that is admixed with combustion air within the combustion air conduit 102 is not sufficient to form a flammable mixture within the combustion air conduit. Preferably, and as shown by the arrows 160 in the drawings, all (100%) of the flare gas to be discharged and burned by the flare apparatus 50 is conducted through the annular flare gas discharge space 140 (the interior 106) of the flare gas conduit 100 and discharged into the atmosphere 81 through the flare gas discharge opening 114 of the flare gas conduit as a stream of flare gas 162.
Due to the positioning of the flare gas discharge opening 114 and the combustion air discharge opening 134 with respect to one another and the inwardly tapered portion 115 of the side wall 112 of the flare gas conduit 100, the flare gas stream 162 is discharged through the flare gas discharge opening 114 around and inwardly (toward the vertical central axis 105 of the combustion air conduit 102) into the column of combustion air 133 discharged through the combustion air discharge opening 134 of the combustion air conduit 102. As used herein and in the appended claims, "around" the column of combustion air 133 discharged through the combustion air discharge opening 134 means completely encircling the column of combustion air, partially encircling the column of combustion air or intermittently encircling the column of combustion air. As shown, the flare gas stream 162 is preferably discharged through the flare gas discharge opening 114 in an annular pattern completely around the column of combustion air 133 discharged from the combustion air discharge opening 134.
Due to the positioning of the flare gas discharge opening 114 and the combustion air discharge opening 134 with respect to one another, the flare gas stream 162 is discharged through the flare gas discharge opening 114 around and inwardly into the column of combustion air 133 discharged through the combustion air discharge opening 134 in a manner that causes discharged flare gas to be mixed with discharged combustion air. Due to the positioning of the flare gas discharge opening 114 and the combustion air discharge opening 134 with respect to one another, essentially all of the discharged flare gas (that is, all of the flare gas discharged by the flare apparatus 50 except for possibly an amount of flare gas that would not be sufficient to create a flammable mixture of combustion air and flare gas within the combustion air conduit 102) is admixed with either discharged combustion air or external atmospheric air outside of the combustion air conduit 102 and the flare gas conduit 100. The flare gas to be discharged and burned by the flare apparatus 50 and the combustion air are sufficiently admixed together without premixing a significant portion of the flare gas (that is, an amount of flare gas sufficient to form a flammable mixture) with the combustion air within the flare apparatus (e.g., within the combustion air conduit 102 or the flare gas conduit 100) prior to discharging the flare gas and combustion air from the flare apparatus. The outer perimeter of the discharge end of the flare tip 56 is used as a mixing point of air and gas. In this way, internal burning and flash back, for example, can be minimized or avoided.
Due to the fact that the flare gas is discharged from the flare gas discharge opening 114 inwardly (toward the vertical central axis 105 of the combustion air conduit 102) into the column of combustion air 133 discharged from the combustion air discharge opening 134 of the combustion air conduit 102, a large portion (preferably the bulk) of the discharged flare gas stream 162 penetrates into the column of combustion air 133. This causes the discharged flare gas stream 162 to be broken apart or chopped up by the discharged combustion air stream or column 133, which promotes rapid and efficient mixing of essentially all of the discharged flare gas with discharged combustion air or external atmospheric air outside of the combustion air conduit. As used herein and in the appended claims, external atmospheric air means air from the atmosphere around the flare gas discharge opening 114 and combustion air discharge opening 134. By causing the mixing process to occur outside of the combustion air conduit 102 and the flare gas conduit 100, the flare gas stream is exposed on one side to the combustion air discharged from the combustion air discharge opening 134 and on the other side to external air from the atmosphere 81. Two distinct air mixing surfaces are provided with respect to the flare gas. This in effect approximately doubles the gas and air interfacial area as the annular gas flow now has air at both its inner and outer surfaces of interface. External air is drawn into the discharged flare gas and combustion air streams. The velocity of the discharged flare gas stream 162 helps draw air into the mix. A great deal of air is available at the points of discharge and mixing. As a result, a very rapid and efficient mixing process occurs.
The mass of the unified column of combustion air 133 discharged through the combustion air discharge opening 134 of the combustion air conduit 102 is sufficient to cause a large portion of the column of combustion air to penetrate upwardly through at least the portion of discharged flare gas that it initially encounters. As a result, the discharged combustion air is not easily capped early on by the flare gas thereby allowing a significant amount of discharged combustion air to be delivered to and admixed with flare gas further away from the discharge end of the flare tip.
The second end 130 of the combustion air conduit 102 is generally adjacent to the second end 110 of the flare gas conduit 100. The height of the combustion air conduit 102 can be equal to, greater than, or less than the height of the flare gas conduit 100. However, in order to assure that a significant portion of the flare gas is not admixed with the combustion air within the flare apparatus 50 prior to discharging the flare gas and combustion air from the flare apparatus, the height of the flare gas conduit 100 with respect to the height of the combustion air conduit 102 is limited. Specifically, if the height of the combustion air conduit 102 is less than the height of the flare gas conduit 100, the ratio of the difference between the heights of the combustion air conduit and the flare gas conduit to the hydraulic diameter of the combustion air conduit is no greater than 0.05. Preferably, in the event that the height of the combustion air conduit 102 is less than the height of the flare gas conduit 100, the ratio of the difference between the heights of the combustion air conduit and flare gas conduit to the hydraulic diameter of the combustion air conduit is no greater than 0.02. More preferably, the height of the combustion air conduit 102 is equal to or greater than the height of the flare gas conduit 100. Most preferably, the height of the combustion air conduit 102 is greater than the height of the flare gas conduit 100 and the ratio of the difference between the heights of the combustion air conduit and flare gas conduit to the hydraulic diameter of the combustion air conduit is approximately 0.01. As used herein and in the appended claims, the hydraulic diameter of the combustion air conduit 102 is defined by four times the cross-sectional area of the combustion air conduit divided by the wetted perimeter of the combustion air conduit, that is, the perimeter of the combustion air discharge opening 134. In the event that the combustion air conduit has a circular cross-section, as shown by FIGS. 4A - 4E, the hydraulic diameter equates to the diameter of the combustion air conduit.
As shown by FIGS. 4A, 4B and 4E, the height of the combustion air conduit 102 of the illustrated flare apparatus 50 is slightly greater than the height of the flare gas conduit 100 of the flare apparatus, that is, the combustion air conduit extends slightly further into the atmosphere 81 along the vertical central axis 104 of the flare apparatus than the flare gas conduit extends into the atmosphere along the vertical central axis of the flare apparatus. Referring specifically to FIG. 4E, the ratio of the difference between the heights of the combustion air conduit and the flare gas conduit to the hydraulic diameter of the combustion air conduit in the illustrated flare apparatus 50 will be described. Assuming that the difference between the heights of the combustion air conduit 102 and the flare gas conduit 100, shown by "L" in FIG. 4E, is 0.375 inches, and that the hydraulic diameter of the combustion air conduit, represented by "D" in FIG. 4E, is 29.625 inches, the ratio of the difference between the heights of the combustion air conduit and the flare gas conduit to the hydraulic diameter of the combustion air conduit is approximately 0.01. The relative heights of the combustion air conduit 102 and flare gas conduit 100 can be varied within the parameters discussed above.
The portion 115 of the side wall 112 of the flare gas conduit 100 adjacent to the flare gas discharge opening 114 preferably tapers inwardly from the vertical outside axis 107 of the flare gas conduit toward the vertical central axis 105 of the combustion air conduit 102 at an angle, shown by the drawings as the angle alpha (α), in the range of from about 10° to about 90°. The angle alpha (a) is more preferably in the range of from about 25° to about 45°. A greater degree of mixing can occur when the angle alpha (α) is about 25° or higher. An angle alpha (α) of about 45° or less helps assure operation of the flare without backflow in the event combustion air cannot be forced into the flare tip, for example, in the event of a power loss. Backflow can create an undesirable and dangerous condition of unburned flammable gases at ground level. In the embodiment illustrated by FIGS. 4A-4E, and as best shown by FIG. 4B, the angle alpha (α) is about 35°. The angle alpha (α), as shown by the drawings, generally corresponds to the angle at which the flare gas is discharged into the atmosphere 81 from the flare gas discharge opening 114 inwardly into the combustion air discharged from the combustion air discharge opening 134.
The portion 135 of the side wall 132 of the combustion air conduit 102 adjacent to the combustion air discharge opening 134 preferably tapers inwardly from the vertical outside axis 109 of the combustion air conduit toward the vertical central axis 105 of the combustion air conduit at an angle, shown by the drawings as the angle beta (β), in the range of from about 10° to about 90°. More preferably, the angle beta (β) is within about 15° of the angle alpha (α), and less than about 45°. In the embodiment illustrated by FIGS. 4A-4E, and as best shown by FIG. 4B, the angle beta (β) is about 35°. The angle beta (β), as shown by the drawings, generally corresponds to the angle at which the outer, annular portion of combustion air 154 is discharged into the atmosphere 81 from the combustion air discharge opening 134. The purpose for tapering the portion 135 of the side wall 132 inwardly toward the vertical central axis 105 of the combustion air conduit 102 is to aid mixing of the fuel and air. A vena contracta may be created that to some extent helps induce flare gas into the column of combustion air.
In the configuration illustrated by FIGS. 3-7B, a single flare gas delivery conduit 58 is utilized to deliver flare gas to be vented by the flare apparatus 50 to the flare tip 56. Flare gas is conducted through the interior 87 of the flare gas delivery conduit 58 through the opening 116 in the side wall 112 of the flare gas conduit and into the annular flare gas discharge space 140. In order to assure that the flare gas is fairly evenly distributed throughout the annular flare gas discharge space 140 before it is discharged into the atmosphere through the flare gas discharge opening 114, the flare gas conduit 100 further comprises a flow distribution member 170. In the embodiment illustrated by the drawings, the flow distribution member 170 is an annular plate 172 that is attached to the outside 174 of the side wall 132 of the combustion air conduit 102. The annular plate 172 is preferably attached to the side wall 132 of the combustion air conduit 102 and positioned within the annular flare gas discharge space 140 adjacent to the top 176 of the opening 116 in the side wall 112 of the flare gas conduit 100. The annular plate 172 extends perpendicularly from the side wall 132 of the combustion air conduit 102 about half way into the annular flare gas discharge space 140 thereby leaving a space 178 between the outermost edge 180 of the annular plate 172 and the inside 182 of the side wall 112 of the flare gas conduit 100. Thus, when flare gas is conducted by the flare gas delivery conduit 58 through the opening 116 in the side wall 112 of the flare gas conduit 100 into the annular flare gas discharge space 140, the annular plate 172 helps distribute the flare gas around the combustion air conduit 102 throughout the annular flare gas discharge space. The distributed flare gas passes through the annular space 178 between the outermost edge 180 of the annular plate 172 and the side wall 112 of the combustion air conduit 102 and ultimately through the flare gas discharge opening 114 into the atmosphere.
Referring now to FIGS. 5A, 5B, 6A, 6B, 7A and 7B, various configurations of the flare gas conduit 100 and combustion air conduit 102 will be described.
FIGS. 5A and 5B illustrate variations in the height of the flare gas conduit 100 with respect to the height of the combustion air conduit 102 when the height of the combustion air conduit 102 is less than the height of the flare gas conduit 100. In FIG. 5, the ratio of the difference between the heights of the combustion air conduit and flare gas conduit 100 to the hydraulic diameter of the combustion air conduit is approximately 0.05. In FIG. 5B, the ratio of the difference between the heights of the combustion air conduit 102 and the flare gas conduit 100 to the hydraulic diameter of the combustion air conduit 102 is approximately 0.02. For example, in the configuration shown by FIG. 5A, the difference between the heights of the combustion air conduit 102 and the flare gas conduit 100, shown by "L" in FIG. 5A, is 1.5 inches, and the hydraulic diameter of the combustion air conduit 102, represented by "D" in FIG. 5A, is 29.625 inches. In the configuration shown by FIG. 5B, the difference between the heights of the combustion air conduit 102 and flare gas conduit 100, shown by "L" in FIG. 5B, is 0.5 inches and the hydraulic diameter of the combustion air conduit, represented by "D" in FIG. 5B, is 29.625 inches. In both the configuration shown by FIG. 5A and the configuration shown by FIG. 5B, the relative heights of the combustion air conduit 102 and flare gas conduit 100 are not such that a significant portion of the flare gas is admixed with the combustion air within the flare apparatus 50 prior to discharging the flare gas and combustion air from the flare apparatus 50.
Also, the horizontal distance between the inside 182 of the side wall 112 of the flare gas conduit 100 and the outside 174 of the side wall 132 of the combustion air conduit 102, that is, the width 186 of the annular flare gas discharge space 140, can be varied. Decreasing the width 186 may allow the performance of the flare apparatus 50 to be optimized for smokeless capacity. Increasing the width 186 may allow for more hydraulic capacity.
FIGS. 6A, 6B, 7A and 7B illustrate how the angle alpha (α) and the angle beta (β) can vary. In the configuration shown by FIGS. 6A and 6B, the angle alpha is 75°, and the angle beta is 75°. As best illustrated by FIG. 6B, in the configuration shown by FIGS. 6A and 6B, the height of the combustion air conduit 102 is less than the height of the flare gas conduit 100. The ratio of the differences between the heights of the combustion air conduit 102 and the flare gas conduit 100 to the diameter of the combustion air conduit 102 is approximately 0.01.
FIGS. 7A and 7B illustrate a configuration wherein the angle alpha (α) is 20° and the angle beta (β) is 20°. Again, as best shown by 7B, the height of the combustion air conduit 102 is greater than the height of the flare gas conduit 100. The ratio of the difference between the heights of the combustion air conduit 102 and the flare gas conduit 100 to the diameter of the combustion air conduit 102 is approximately 0.01.
Referring now to FIGS. 8A and 8B, another configuration of the flare apparatus 50 is illustrated and will be described. In this configuration, the flare gas is injected into the flare gas conduit 100 at an angle with respect to the vertical central axis 104 of the flare gas conduit 100 in order to impart radial velocity to the flare gas and cause the flare gas to swirl within the annular flare gas discharge space 140 and be discharged from the flare gas discharge opening 114 in a swirling pattern. Discharging the flare gas from the flare gas discharge opening 114 in a swirling pattern causes the flare gas to swirl around and into the combustion air column 133 discharged through the combustion air discharge opening 134. The swirling flare gas has both axial velocity, radial velocity and tangential velocity.
In the configuration shown by FIGS. 8A and 8B, the side wall 112 of the flare gas conduit 100 includes a pair of tangential inlets 190, each extending outwardly from the sidewall 112 of the flare gas conduit 100. Each inlet 190 includes a flange 192 attached thereto. Separate flare gas delivery conduits 58 (not shown) can be used in connection with each inlet 190. Specifically, the second end 84 of each flare gas delivery conduit 58 can include a flange attached thereto which is attached to the flange 192 of the corresponding inlet 190 to fluidly connect the flare gas delivery conduit to the annular flare gas discharge space 140. As illustrated, the angle with respect to the vertical central axis 104 of the flare gas conduit 100 at which the flare gas is injected into the flare gas conduit through the inlets 190 is approximately 90°. Imparting tangential velocity to the flare gas within the annular flare gas discharge space 140 and causing the flare gas to swirl therein creates a low pressure zone immediately above the combustion air discharge opening 134 which reduces the static pressure above the combustion air discharge opening. The low pressure zone encourages mixing by causing combustion air from the atmosphere and combustion air from the combustion air discharge to flow toward the low pressure zone. Such mixing improves the smokeless performance of the inventive flare apparatus. Only one inlet or more than two inlets 190 can be used if desired. The combustion air from the combustion air discharge can be swirled as well. For example, helical flights or passages known as swirl vanes may be added to either the flare gas conduit 100 or combustion air conduit 102 to impart swirl to the respective streams flowing therethrough. The air alone may be swirled, the flare gas alone may be swirled, or both the air and flare gas may be swirled. In the latter case, the air and flare gas may be swirled in like directions or opposing directions. Opposing swirl would result if one stream were swirled in a clockwise direction and the other were swirled in a counter-clockwise direction.
Referring specifically to FIGS. 4A and 9A, 9B and 9C, the mixing and swirling mechanisms described above will be further described. FIGS. 4A, 9A, 9B and 9C illustrate a 3-D coordinate system corresponding to the inventive flare apparatus 50 and showing certain flow vectors associated therewith. As illustrated, the inventive flare apparatus 50 includes an axial coordinate (flow component) 200, a radial coordinate (flow component) 202 and a tangential coordinate (flow component) 204. These coordinates (hereinafter referred to as "flow components") are best illustrated by FIG. 9A. The axial flow component 200 coincides with the vertical central axes 103, 104 and 105 of the overall flare apparatus, the flare gas conduit 100 and the combustion air conduit 102, respectively. The radial flow component 202 extends toward the vertical central axes 103, 104 and 105 and normal to them, that is, its extension making a 90° angle to the vertical central axes 103, 104 and 105. The tangential flow component 204 is directed from the perimeter of the combustion air discharge opening 134 at 90° to the radial component. These three components are sufficient to describe motion in any direction in three dimensions and are related to the coordinate system generally known to those skilled in the art as the "cylindrical coordinate" system.
FIG. 9A illustrates decomposition of a three-dimensional flow vector 210 into the axial, radial and tangential flow components 200, 202 and 204, respectively, in connection with the flare apparatus 50. As shown, the flow vector 210 is offset from the vertical central axis 103 of the flare apparatus 50 as a result of the tangential component. Alternatively and equivalently, if the axial, radial and tangential flow components are imposed at the point of origin shown for vector 210, the vector 210 would result.
In order for the discharged flare gas stream 162 to be directed into the combustion air stream or column 133 discharged by the inventive flare apparatus, the discharged flare gas includes a radial flow component. The combustion air is discharged from the combustion air discharge opening 134 in a straight out pattern along the vertical central axis 104 and axial flow component 200, and except for the relatively small outer annular portion 154, there is essentially no radial component in the flow of the combustion air. As a result of the radial component in the flow of flare gas discharged from the flare gas discharge opening 114, the discharged flare gas will be directed into the combustion air stream or column 133 discharged from the combustion air discharge opening 134 and admixed therewith.
By way of further illustration, when the flow direction of the discharged flare gas is not perfectly aligned with the vertical central axis 104 of the flare gas conduit 100, a tangential component exists. If a sufficient portion of flare gas possesses a tangential component at the periphery of the combustion air discharge, a swirling flow pattern is created. FIG. 9C shows the swirl that results when the drawn vector 212 is symmetric about the circumference (typical). For illustration purposes, only six vectors 212 are shown. As shown, swirl results as a consequence of the tangential components even though the flow is largely axial, to a lesser degree radial, and to an even lesser degree tangential (as shown by the size of each component vector in FIG. 9A). In short, the greater radial component of the discharged flare gas compared to the radial component, if any, of the discharged combustion air causes the discharged flare gas to be directed into the discharged combustion air, and the difference in the tangential component provides the swirl whether or not these components are superimposed on an axial flow. Since the flow of combustion air through the combustion air discharge opening 134 has mostly axial flow, even a modest radial component in the discharged flare gas will initiate mixing, and tangential components will create swirl in direct proportion to the strength of each.
Referring now to FIGS. 10A and 10B, an alternative configuration of the flare apparatus 50 is illustrated. In this configuration, instead of circular cross-sections, the flare gas conduit 100 and combustion air conduit 102 each have a square cross-section. The combustion air conduit 102 is at least partially disposed within the flare gas conduit 100 such that the vertical central axes 103 and 104 of the conduits overlap. In calculating the ratio of the difference between the heights of the combustion air conduit 102 and flare gas conduit 100, the hydraulic diameter, as opposed to the diameter, of the combustion air conduit is utilized. The term "hydraulic diameter" is defined above. In addition to circular and square cross-sections, the flare gas conduit 100 and combustion air conduit 102 of the flare apparatus 50 can have other cross-sectional shapes as well.
In the configurations of the flare apparatus 50 described above, the combustion air conduit 102 is at least partially disposed within the flare gas conduit 100 creating, for example, an annular or square flare gas discharge space 140 between the combustion air conduit and the flare gas conduit. However, additional configurations of the flare apparatus can be utilized. For example, as shown by FIG. 11, the combustion air conduit 102 and flare gas conduit 100 of the flare apparatus 50 can have a linear configuration.
As shown by FIG. 11, the flare gas conduit 100 and combustion air conduit 102 each have a rectangular cross-section. The combustion air conduit 102 is attached to the flare gas conduit 100 and positioned directly adjacent thereto. The back 220 of side wall 112 of the flare gas conduit 100 includes a portion 222 adjacent to the flare gas discharge opening 114 that tapers inwardly toward the vertical central plane 223 of the flare gas conduit. As in the configurations described above, the flare gas discharge opening 114 and combustion air discharge opening 134 are positioned with respect to one another such that essentially all (preferably all) of the flare gas to be discharged and burned by the flare apparatus can be discharged through the flare gas discharge opening inwardly into the column of combustion air 133 that is discharged from the combustion air discharge opening and admixed therewith. The flare gas discharge opening 114 and combustion air discharge opening 134 are positioned with respect to one another such that essentially all (preferably all) of the discharged flare gas is admixed with discharged combustion air or external atmospheric air outside of the combustion air conduit 102 and the flare gas conduit 100. The portion 222 of the side wall 112 of the flare gas conduit 100 adjacent to the flare gas discharge opening 114 preferably tapers inwardly toward the vertical central axis 105 of the combustion air conduit 102 at an angle in the range of from about 10° to about 90°, preferably in the range of from about 25° to about 45°.
FIGS. 12 and 13 illustrate alternative configurations of the overall flare apparatus 50. The flare tip 56 of the flare apparatus 50 illustrated by FIGS. 12 and 13 has the same configuration as the flare tip illustrated by FIGS. 3 and 4A-4E of the drawings. However, in the configuration shown by FIG. 12, the first end 74 of the flare stack 54 includes dual inlets 228A and 228B, each with a combustion air blower 62 positioned therein. This allows, for example, one of the blowers to operate at a low standby while the other blower is switched off, thus reducing the total standby combustion air blower horsepower associated with the flare apparatus 50.
In FIG. 13, the flare gas delivery conduit 58 includes a section having a different configuration. In this configuration, a lower portion 230 of the flare gas delivery conduit 58 extends around and encases the flare stack 54; that is, the flare stack 54 is at least partially positioned within the flare gas delivery conduit 58 creating an annular flare gas delivery space 232 between the outside 234 of the flare stack 54 and the inside 236 of the flare gas delivery conduit. The lower portion 230 of the flare gas delivery conduit 58 includes a first end 238, a second end 240 and a side wall 242 connecting the first end to the second end. The second end 240 is sealed around the flare stack 54. The side wall 242 includes an opening 244 therein. The first end 238 of the lower portion 230 of the flare gas delivery conduit 58 is fluidly connected to a source of flare gas (not shown).
The flare gas delivery conduit 58 in the configuration shown by FIG. 13 also includes an upper section 246 having a first end 248, a second end 250 and a side wall 252 attaching the first end to the second end. The first end 248 of the upper section 246 of the flare gas delivery conduit 58 is attached to and fluidly communicates with the opening 244 in the side wall 242 of the lower portion 230 of the flare gas delivery conduit 58. The second end 250 of the upper section 246 of the flare gas delivery conduit 58 is attached to and fluidly communicates with the opening 116 in the side wall 112 of the flare gas conduit 100 of the flare apparatus 50. The configuration of the flare gas delivery conduit 58 illustrated by FIG. 13 provides overall stability to the flare apparatus 50 and may have certain structural advantages.
Additional configurations of the flare apparatus can be used and modifications can be made thereto depending upon the specific application. Gas flares can generally be relatively simple or extremely complex depending on the mechanical system within which they must perform. For example, in some applications such as when high molecular weight gases need to be flared, the flare apparatus can include a mechanism for perimeter control, that is, a mechanism that can be used to help keep the flame from being swept away by wind or other external factors. By way of example, steam or air can be injected into the atmosphere from outside of the flare gas conduit 100 to create a perimeter boundary and help contain the admixture of flare gas and combustion air discharged from the flare apparatus. The combustion air conduit 102 and flare gas conduit 100 can be positioned within a third conduit to create a second annular combustion air discharge space and opening for injecting an annular core of combustion air around the discharged flare gas. In another configuration, steam can be injected into the interior of the flare apparatus to induce air into the flare apparatus, that is, steam can be used as a motive force for the air. In another configuration, more than one flare tip 56 can be used. For example, a relatively small flare tip 56 can be provided for flaring a relatively low volume of gas and a relatively large flare tip 56 can be provided for flaring a relatively large volume of gas.
As discussed above, the inventive flare apparatus 50 can be used to flare a mixture of flare gas and combustion air without pre-mixing a significant portion of the flare gas with the combustion air within the flare apparatus prior to discharging the flare gas and combustion air from the flare apparatus. As used herein and in the appended claims, "without pre-mixing a significant portion of the flare gas with the combustion air within the flare apparatus prior to discharging the flare gas and combustion air from the flare apparatus" means that the amount of flare gas, if any, pre-mixed with the combustion air within the flare apparatus prior to discharging the flare gas and combustion air from the flare apparatus is not sufficient to form a flammable mixture within the flare apparatus. Essentially all of the discharged flare gas (that is, all of the discharged flare gas except for possibly an amount of flare gas that would not be sufficient to create a flammable mixture of combustion air and flare gas within the combustion air conduit 102) is admixed with discharged combustion air or external atmospheric air outside of the combustion air conduit and the flare gas conduit 100.
In operation of the flare apparatus 50, combustion air is discharged into the atmosphere 81 through the combustion air discharge opening 134 of the combustion air conduit 102 of the flare apparatus. As stated above and indicated by arrows 150 in FIGS. 4A and 4B (and also by FIGS. 8A, 11 and 14B), a unified column of combustion air 133 is discharged into the atmosphere from the flare apparatus 50. A central portion of air 152 and an outer annular portion of air 154 are discharged into the atmosphere 81 from the combustion air discharge opening 134. Although a large portion of the combustion air column 133 penetrates upwardly, it is soon infused by the annular flare gas discharge stream 162 and may not remain a unified column of combustion air for very long after it is discharged into the atmosphere through the combustion air discharge opening 134.
Essentially all of the flare gas to be discharged and burned (i.e., flared) by the flare apparatus 50 (that is, all of the flare gas to be flared by the flare apparatus except for possibly a portion of flare gas that is not sufficient to form a flammable mixture with the combustion air within the flare apparatus prior to being discharged from the flare apparatus) is discharged into the atmosphere from the flare gas discharge opening 114 around and inwardly into the discharged column of combustion air 133 and admixed therewith. Essentially all of the discharged flare gas (that is, all of the discharged flare gas except for possibly a portion of flare gas that is not sufficient to form a flammable mixture with the combustion air within the flare apparatus prior to being discharged from the flare apparatus) is admixed with discharged combustion air or external atmospheric air outside of the flare apparatus 50. Preferably, all of the flare gas to be flared by the flare apparatus 50 is discharged into the atmosphere from the flare gas discharge opening 114 around and inwardly into the discharged column of combustion air 133 and admixed therewith. Preferably all of the discharged flare gas is admixed with discharged combustion air or external atmospheric air outside of the flare apparatus 50. The mixture of discharged flare gas, discharged combustion air and external atmospheric air is then ignited outside of the flare apparatus 50. The pilot assembly 60 is used to ignite the mixture. Due to the fact that the flare gas is discharged from the flare gas discharge opening 114 inwardly (toward the vertical central axis 105 of the combustion air conduit) into the combustion air discharged from the combustion air discharge opening 134 of the combustion air conduit 102, the discharged flare gas stream 162 penetrates into the discharged combustion air column 133.
The overall velocity and pressure at which the flare gas is discharged from the flare gas discharge opening 114 will vary depending upon the volume of flare gas that needs to be vented and its delivery pressure. For example, the pressure of the flare gas in the flare gas conduit 100 is typically 3 to 4 pounds per square inch but can be greater or lesser than such amount depending on the application. The axial velocity at which the combustion air is discharged into the atmosphere from the flare apparatus 50 can be maintained at a particular level. Preferably, the combustion air is discharged into the atmosphere from the flare apparatus 50 at an axial velocity of at least 50 feet per second. More preferably, the axial velocity at which the combustion air is discharged into the atmosphere 81 from the flare apparatus 50 is in the range of from about 50 feet per second to about 200 feet per second, even more preferably in the range of from about 120 to about 150 feet per second. Most preferably, the combustion air is discharged into the atmosphere from the flare apparatus 50 at an axial velocity of about 150 feet per second.
The flare gas is preferably discharged into the atmosphere from the flare apparatus 50 inwardly into the discharged column of combustion air 133 at an angle in the range of from about 10° to about 90°, more preferably in the range of from about 25° to about 45°. Most preferably, the flare gas is discharged into the atmosphere 81 from the flare apparatus 50 inwardly into the discharged combustion air at an angle of about 35°.
As described above, a unified column of combustion air 133 is discharged into the atmosphere from the flare apparatus. The combustion air is axially discharged into the atmosphere from the flare apparatus 50 except for the outer annular portion of combustion air 154 which is directed inwardly toward the central portion of combustion air 152. The flare gas is discharged into the atmosphere 81 from the flare apparatus 50 around and into the discharged column of combustion air 133. In one configuration, the flare gas is discharged into the atmosphere 81 from the flare apparatus 50 in a swirling, annular pattern around and into the discharged column of combustion air 133. By swirling the flare gas in an annular pattern around and into the discharged column of combustion air 133, a low pressure zone is created above the combustion air discharge opening, thereby reducing the pressure above the combustion air discharge opening.
Referring now to FIG. 14A and 14B, the flame generated by the inventive flare apparatus and in accordance with the inventive method is illustrated. FIG. 14A illustrates the flame pattern generated by the flare apparatus 50 and in accordance with the inventive method. As indicated, the flame is relatively short, straight and smokeless due to the initial rapid mixing at the base of the flame.
FIG. 14B is a sectional view illustrating the volume fraction contours of the flare gas that can be generated by the inventive flare apparatus 50. More specifically, FIG. 14B is a computational fluid dynamic simulation of the mixing of propane with the surrounding fluid that illustrates the degree to which the flare gas can be mixed in with the combustion products and/or external atmospheric air. All of the flare gas can be admixed with combustion air and/or external atmospheric air rapidly and efficiently upon being discharged from the flare gas discharge opening 114. As shown by FIG. 14B, a central column 133 of discharged combustion air is present in the middle of the flame envelope (between the designated concentration zones). The length and width of the column of combustion air 133 will vary depending on process conditions including the type of flare gas to be flared, the discharge rate of the flare gas and ambient conditions such as wind. External atmospheric air 81 is drawn in from around the flame. The contour line designated by reference numeral 260 represents a 50% volume fraction of propane. This contour line occurs close the flare gas discharge opening 114 thereby indicating rapid fuel mixing. Likewise, the contour line 262 represents a 40% volume fraction of propane. The contour line 264 represents a 30% mixture of propane, whereas the contour line 266 represents a 20% mixture of propane. Finally, the contour line 268 represents a 10% mixture of propane.
Thus, the flare gas is rapidly and efficiently admixed with air upon being discharged by the flare apparatus. A lean, well mixed effluent having a solid core of air in the axial center is rapidly formed. In accordance with the invention, it has been discovered that better mixing is achieved by discharging a unified column of combustion air directly into the center of the flame envelope. The overall mixing achieved by discharging a unified column of combustion air directly into the center of the flame envelope is better in many situations than the overall mixing achieved by discharging both combustion air and flare gas into the center of the flame envelope.
The mass of the unified column of combustion air 133 discharged through the combustion air discharge opening 134 of the combustion air conduit 102 is sufficient to cause a large portion of the column of combustion air to penetrate upwardly through at least the portion of discharged flare gas that it initially encounters. This serves to ensure that the central combustion air flow can create a stretched or prolate toroidal geometry with respect to the flare gas. The discharged combustion air is placed in the center of the annular flare gas stream to create an internal mixing surface area. An external surface is also created on the outside of the gas envelope where external atmospheric air is pulled into the flame for mixing. Thus, two distinct mixing surfaces are created for mixing air with the flare gas. The discharged combustion air is not easily capped or encapsulated early on by the flare gas or flame envelope allowing a significant amount of discharged combustion air to be centrally delivered to and admixed with flare gas further away from the discharge end of the flare tip and throughout the length of the flame envelope. By increasing the surface area of the air, the mixing rate of the gas into the air is also increased.
The amount of combustion air that must be provided to achieve a stoichiometric ratio of flare gas and air that will allow complete and smokeless combustion to occur can be substantially less than the amount of combustion air required in connection with other flare apparatuses. For example, the amount of air required for a smokeless flame in a conventional tip is about 30% of stoichiometry when firing propane. The inventive flare apparatus may use, for example, approximately 13% of stoichiometry to accomplish the same task. This significantly reduces both the required air flow and the required power to drive the blower needed to deliver the stream the required air flow.
The inventive flare apparatus and method can be used to efficiently and effectively flare a large volume of flare gas. A large variety of gases can be flared. For example, the inventive flare apparatus is very effective in connection with ethylene plants and other facilities in which low molecular weight (including gases having molecular weights of 40 and under) need to be flared. The inventive flare apparatus and method can be in connection with most types of flares, including ground flares, utility flares, and any other flares in connection with which a well blended or smokeless flame is required.
The inventive flare apparatus is simple in design and easy to fabricate.
In order to further illustrate the invention, the following example is provided.

EXAMPLE

The inventive flare apparatus 50 was operated to smokelessly fire about 84,000 lb/hr of propane with about 34,000 standard cubic feet per minute of air representing about 13% of the theoretically required stoichiometric air requirement for complete combustion of propane. The flame outline shown by Figure 14A was produced. Conventional air flare technology would have required about 30% of the theoretical stoichiometric rate or more than twice as much air. That is, the inventive technology required about half of the customary airflow to achieve smokeless operation.
Thus, the present invention is well adapted to carry out the objects and attain the ends and advantages mentioned as well as those which are inherent therein.

Claims

A flare tip for use in association with a flare apparatus for discharging and burning flare gas in the atmosphere comprising:
a flare gas conduit including a first end, a second end and a side wall connecting said first end to said second end, wherein said flare gas conduit is adapted to be fluidly connected to a source of flare gas and said second end of said flare gas conduit defines a flare gas discharge opening, said flare gas conduit and said flare gas discharge opening being of a size sufficient to allow all of the flare gas that is to be discharged and burned by said flare apparatus to be discharged through said flare gas discharge opening; and

a combustion air conduit associated with said flare gas conduit, said combustion air conduit including a first end, a second end and a side wall connecting said first end to said second end, wherein said combustion air conduit is adapted to be fluidly connected to a source of combustion air, and said second end of said combustion air conduit defines a combustion air discharge opening, said combustion air conduit having a structure that causes a unified column of combustion air to be discharged through said combustion air discharge opening,

said flare gas discharge opening and said combustion air discharge opening being positioned with respect to one another such that essentially all of the flare gas to be discharged and burned by said flare apparatus can be discharged through said flare gas discharge opening around and/or inwardly into the column of combustion air discharged from said combustion air discharge opening and such that essentially all of the discharged flare gas can be admixed with discharged combustion air or external atmospheric air outside of said combustion air conduit and said flare gas conduit.
The flare tip of claim 1, wherein said combustion air conduit is positioned at least partially within said flare gas conduit, and wherein said flare gas discharge opening and said combustion air discharge opening are positioned with respect to one another such that essentially all of the flare gas to be discharged and burned by said flare apparatus can be discharged through said flare gas discharge opening around and inwardly into the column of combustion air discharged from said combustion air discharge opening.
The flare tip of claim 1 or 2, wherein any one of the following (a) - (c) applies:
(a) the height of said combustion air conduit is less than the height of said flare gas conduit, and wherein optionally the ratio of the difference between the heights of said combustion air conduit and said flare gas conduit to the hydraulic diameter of said combustion air conduit is no greater than 0.05, preferably no greater than 0.02.

(b) the height of said combustion air conduit is equal to or greater than the height of said flare gas conduit;

(c) the height of said combustion air conduit is greater than the height of said flare gas conduit, and wherein optionally the ratio of the difference between the heights of said combustion air conduit and said flare gas conduit to the hydraulic diameter of said combustion air conduit is approximately 0.01.
The flare tip of any one of claims 1 - 3, wherein said side wall of said flare gas conduit includes a portion adjacent to said flare gas discharge opening that tapers inwardly toward the vertical central axis of said combustion air conduit, preferably at an angle in the range of from about 10° to about 90°, more preferably at an angle in the range of from about 25° to about 45°, still more preferably at an angle of about 35°.
The flare tip of any one of claims 1 - 4, wherein said side wall of said combustion air conduit includes a portion adjacent to said combustion air discharge opening that tapers inwardly toward the vertical central axis of said combustion air conduit.
The flare tip of any one of claims 1 - 5, wherein said flare gas conduit and said combustion air conduit each have circular cross-sections, and said combustion air conduit is at least partially concentrically disposed within said flare gas conduit.
The flare tip of any one of claims 1 - 6 , wherein said flare gas conduit further comprises:
an inlet adapted to be fluidly connected to a source of flare gas; and

a flow distribution member attached within said flare gas conduit, said flow distribution member preferably being an annular plate disposed within said flare gas conduit.
The flare tip of any one of claims 1 - 7, wherein said flare gas conduit includes at least one inlet adapted to be fluidly connected to a source of flare gas and to inject flare gas into said flare gas conduit at an angle with respect to the vertical central axis of said flare gas conduit.
A method of flaring a mixture of flare gas and combustion air in a flare apparatus without pre-mixing a significant portion of the flare gas with the combustion air within the flare apparatus prior to discharging the flare gas and combustion air from the flare apparatus, comprising:
(a) discharging a unified column of combustion air into the atmosphere from the flare apparatus;

(b) discharging essentially all of the flare gas to be flared by the flare apparatus into the atmosphere from the flare apparatus and around and/or inwardly into the discharged column of combustion air such that essentially all of the discharged flare gas is admixed with discharged combustion air or external atmospheric air outside of the flare apparatus; and

(c) igniting the mixture of discharged flare gas, discharged combustion air and external atmospheric air.
The method of claim 9, wherein essentially all of the flare gas to be flared by the flare apparatus is discharged into the atmosphere from the flare apparatus around the discharged column of combustion air and inwardly into the discharged column of combustion air.
The method of claim 9, wherein all of the flare gas to be flared by the flare apparatus is discharged into the atmosphere from the flare apparatus and inwardly into the discharged column of combustion air.
The method of any one of claims 9 - 11, wherein the combustion air is discharged into the atmosphere from the flare apparatus at a radial velocity less than the radial velocity at which the flare gas is discharged into the atmosphere from said flare apparatus.
The method of any one of claims 9 - 12, wherein the combustion air is discharged into the atmosphere from the flare apparatus at an axial velocity of at least 50 feet per second, preferably at an axial velocity in the range of from about 50 feet per second to about 200 feet per second, more preferably at an axial velocity in the range of from about 120 feet per second to about 150 feet per second, still more preferably at an axial velocity of about 150 feet per second.
The method of any one of claims 9 - 13, wherein essentially all of the flare gas to be flared by the flare apparatus is discharged into the atmosphere from the flare apparatus inwardly into the discharged combustion air at an angle in the range of from about 10° to about 90°, preferably at an angle in the range of from about 25° to about 45°, more preferably at an angle of about 35°.
The method of any one of claims 9 - 14, further comprising reducing the static pressure of a portion of the admixture of discharged flare gas, discharged combustion air and/or external atmospheric air adjacent to the flare apparatus, optionally wherein the static pressure of a portion of the admixture of discharged flare gas, discharged combustion air and/or external atmospheric air adjacent to the flare apparatus is reduced by creating a low pressure zone in the area of said combustion air discharge opening, optionally wherein said low pressure zone is created adjacent to the flare apparatus by causing the flare gas to be discharged from the flare apparatus in a swirling annular pattern around the discharged combustion air.