US2976922A - Flare - Google Patents

Description

March 28, 1961 D. J. BERGMAN FLARE Filed April 29, 1959 INVENTOR Donald J. Bergman zzm g A TTOR/VEYS United States Patient -C FLARE Donald J. Bergman, Kenilworth, Ill., assignor to Universal Oil Products Company, Des Plaines, 111., acorporation of Delaware Filed Apr. 29, 1959, s... No. 809,793 3 Claims. 01. 158-99) This application is a continuation-in-part of copending application Serial No. 649,824, fi1ed April 1, 1957, now abandoned. This invention relates to a gas flare stack which is'modified to overcome diflilculties presently associated with flare stacks.

Flare stacks are widely employed in industries where a combustible waste gas is produced. Theyare commonly used in petroleum refineries and in conjunction with coke ovens and steel mills. Flares usually are quite simple structures, comprising merely a cylindrical metal stack placed, for purposes of safety, remotefrom the process which produces the combustible waste gas and having an igniter at the discharge end thereof to insure that the waste gases are burned.

In operation, the combustible waste gases are passed to the flare and upwardly therethrough and are ignited at the discharge end thereof causing the combustible gases to be..dissipated harmlessly into the atmosphere :as combustion products;

It has been found that under certain wind conditions the flames issuing from the top of the flare stack are sucked down along the sides thereof. When wind velocities are low, the flames pass upwardly from the stack and it operates cool; however at higher wind velocities, the flames are sucked down alongside of the stack, causing heat damage and oxidation to the stack thereby severely reducing its life and possibly creating a dangerous condition wherein burning may take place within the confined portion of the stack due to air passing into the stack through holes burned through its side.

It is an object of this invention to construct a flare stack in a unique manner which causes the flames issuing from it always to pass upwardly or horizontally from the discharge end thereof. In other words, it is an object of this invention to prevent flames from a flare from being sucked down behind the flare stack and thereby causing the harmful eifects heretofore described.

It is an embodiment of this invention to provide a flare comprising a vertical stack having a plurality of perforated vertical .vanes connected along a vertical edge thereof to and extending outwardly from the upper portion of the stack, said vanes being spaced around the external periphery of the stack and extending downwardly from substantially the top of the stack a distance equal to at least three times the diameter of the stack.

The sucking down of flames around a flare stack has.

been observed to be most pronounced on Windy days. It has been accordingly proposed as an explanation for this action that the stack portion of the flare in a flowing air stream, that is, the wind, acts as an air foil which produces local relatively high velocity streams of air adjacent to the surface of the stack within the larger body of a relatively lower velocity stream of air. These local high velocity streams are at lower static pressure because of the known energy relationships of pressure and velocity head and therefore, cause an air flow from a lower velocity higher pressure zone into the relatively higher velocity lower pressure area. The flow of air into this low presp I C Patented Mar. 28,19 1

sure area causes the air above the stack as well as the flames issuing from the flare to be sucked down along the stack. 1

It has been found that the use of the perforated vertical vanes of this invention completely eliminates the problem. The vertical vanes of this invention placed at ,the upper portion of the stack provide a resistance in the path of the local high velocity streams thereby reducing their velocity and eliminating the diminished pressure head which results when the vanes are not there. Furthermore, a properly designed flare stack constructed in accordance with this invention will break up the high velocity air streams into a zone of many smaller disturbances or vortices of air adjacent to the stack, which actually repel the flames away from the sides of the stack.

The vanes are preferably perforated flat metal sheets which are connected along their vertical edges to the side of the stack at or slightly below the top thereof. The vanes may be punched with holes or may contain slots or any other shape of perforation. They may also be perforated so that there is greater open area in the portion of the vane most remote from the stack, thus providing less resistance to flow in the air stream farther from the 'stack. The perforated area preferably ranges from about diameter) and the preferred width is from about 0.10 to about 0.30 stack diameter. Similarly, the length of the vanes may be from about 3 stack diameters for large stacks to about 15 stack diameters for small stacks. It is, however, within the scope of this invention to provide vanes having dimensions in excess of those stated hereinabove; for example, the vanes may extend the full vertical length of the stack and may be 0.75 stack diameter or more in width. But such construction will not appreciably increase the aerodynamic effectiveness of the vanes and will obviously impose excessively large windloading on the stack as well was making the cost of construction prohibitively high. From a practical standpoint, the above cited dimensional ranges of the vanes result in a low-cost stack which effectively eliminates the sucking down of the flame without subjecting the stack to any materially increased windload. Although flare stacks are most commonly and economically fabricated with cylindrical pipe, the vanes are equally effective when used in conjunction with stacks having an oval, square, or rectangular crosssection. The term diameter? as used herein, when applied to stacks having a non-circular cross-section, is defined as the projected width of the cross-section, that is, the length of the side of the cross-section adjacent the side to which the vane referred to said diameter is attached. The vanes may extend downwardly from the very top of the stack or they may start several inches below the top and still exert their beneficial influence. It is preferred to employ at least four vanes which are regularly spaced around the diameter of the stack, however, more or less vanes may be employed and their spacing may be altered when prevailing winds make protection in certain directions unnecessary.

The accompanying drawing is presented to illustrate further the construction and utility of this invention and is intended to be illustrative rather than limiting upon the broad scope of the invention. The drawing represents the upper portion of a flare stack assembled with the vanes which work in combination with it.

In the drawing, 1 represents a stack which is suitable for use as a flare. The stack may be constructed of any suitable material such as iron, steel, brick, stone, etc. and it may be cylindrical as herein shown or have a non-circular or irregular cross-section as described above. The waste gases which may be, for example, refinery waste gases consisting primarily of hydrogen, methane, ethane and propane pass upwardly through the stack in a relatively cool condition and as they issue from the top of the stack they are ignited by igniter 4 which may consist of a gas burning pilot light, an electric spark plug or any other suitable ignition means. Around the periphery of the upper portion of stack 1 are spaced, in this embodiment, six regularly spaced, vertically elongated vanes 2 which are perforated with round holes 3. Vanes 2 are connected as close to the top of stack 1 as practical; alternatively, the vanes may be mounted several inches below the top of the stack. The vanes are connected along their vertical edges to stack 1 by any suitable means such as by welding, bolting, riveting or with clips. A sealed connection to the stack is not necessary since the presence of the vanes will preclude high velocity streams at the surface of the stack; however, spaces of more than an inch between the vanes and the stack may result in a local high velocity stream and a spacing in excess of about one inch should therefore be avoided. By fastening the vanes along the Vertical edges thereof directly to the surface of the stack in the manner described, any such tendency to produce local high velocity air streams is eliminated.

As a specific embodiment of this invention, a flare stack for burning the waste gases from a petroleum catalytic cracking unit consists of 12 inch diameter steel pipe 100 feet high with an electric spark plug igniter at the exit thereof. This stack is equipped with four vanes extending downwardly from the very top thereof and regularly spaced around the periphery thereof. These vanes are 3 inches wide and 12 feet long and are drilled with sufficient regularly spaced /2 inch holes to provide open area. With the stack so equipped, the sucking down of flames is eliminated during the operation of the flare.

As another example of this invention, a main flare stack for burning the waste gases from a number of refinery process units consists of a 6 foot diameter pipe feet high with ignition means positioned at the discharge thereof. This stack is provided with eight vanes extending downwardly from a line 4" below the very top of the stack and regularly spaced around the periphery thereof. These vanes are 9" wide and 30 feet long and are drilled with sufficient regularly spaced inch holes to provide approximately 30% open area.

From the foregoing, it may be seen that this invention, through a simple, inexpensive and permanent means, prevents the costly and dangerous sucking down of flames issuing from a flare stack.

I claim as my invention:

1. A flare comprising a vertical stack, ignition means at the upper discharge end of the stack, and a plurality of perforated Vertical vanes connected along a vertical edge thereof to and extending outwardly from the upper portion of the stack, said vanes being spaced around the external periphery of the stack and extending downwardly from substantially the top of the stack a distance equal to at least three times the diameter of the stack.

2. The flare of claim 1 further characterized in that said perforated vanes extend outwardly from the upper portion of said stack a distance equal to at least 0.05 diameter of said stack.

3. The flare of claim 1 further characterized in that it comprises at least four regularly spaced vanes.

References Cited in the file of this patent UNITED STATES PATENTS

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