US3817695A - Airductor flare - Google Patents

Abstract

This invention describes an improved flare stack system for burning dump gases, in which air is induced into the main body of the vertically rising gas column by means of radial transverse obstructions, such as bars or strips, which cause a deflection of the uprising gas and a pressure drop due to the obstruction, which induces air radially inwardly, which mixes with the rising gas. This particularly advantageous structural system for air induction can be supplemented by the use of radial steam jets or steam pipes in conjunction with the radial strips.

Description

United States Patent [191 Reed et al.

[ June 18, 1974 AIRDUCTOR FLARE Robert D. Reed; Robert E. I Schwartz, both of Tulsa, Okla.

John Zink Company, Tulsa, Okla.

June 13, 1972 Inventors:

Assignee:

Filed:

Appl. No.:

US. Cl 431/202, 431/4, 431/347,

431/350 Int. Cl. F23d Field of Search 431/4, 202, 347, 350, 278

References Cited UNITED STATES PATENTS 5/1964 Zink et a1. 431/202 11/1970 Zink et a1. 431/202 1/1971 Proctor 431/202 Alf? 3,697,231 10/1972 Reed 431/202 Primary Examiner-Carroll B. Dority, Jr. Attorney, Agent, or Firm-l-1ead & Johnson [57] ABSTRACT 8 Claims, 15 Drawing Figures All? mmmmwu 3.8171695 SHEET 10$ 3 Alf? STEAM PAIEmEnJum m4 118173395 saw 30! a AIRDUCTOR FLARE BACKGROUND OF THE INVENTION This invention lies in the field of the design of flare stacks for the burning of dump hydrocarbon gases. More particularly, this invention lies in the field of apparatus for improving the air induction into and the turbulent mixing of the induced air with the rising gases to promote intimate mixing and combustion within the body of the column of gas.

In the prior art it has been customary to provide a more or less solid cylindrical rising volume of hydrocarbon gas which is to be burned in a smokeless manner. Various means have been provided, particularly the use of high velocity steam jets directed into the gas stream to induce air into the body of this rising gas column and to create turbulent mixing of the steam, gas and air. Of course, there is the additional advantage of the increase in weight ratio of hydrogen to carbon by the reforming action of the steam because of abrupt turbulenceinduced temperature rise in the mixture zone.

It is well known in the art of smokeless flaring, that the tendency for smoke production in flare burning of gases is a function of the weight ratio of hydrogen to carbon. In the case of methane, for example, for which the hydrogen to carbon ratio (I-I/C) is 0.33, there is very small tendency to smoke in the normal flaring operation. Ethane has a lower H/C ratio, equal to 0.25 and ethane produces appreciable smoke as it burns. Going to lower hydrogen to carbon ratio hydrocarbons, propane has an I-I/C ratio equal to 0.222 and smokes more strongly. Butane which has an l-I/C ratio of 0.208 smokes still more strongly, and so on.

Experience has shown that when the average H/C ratio of the flare gases is less than 0.30 there is a tendency for smoke production in the flare burning of gases, and according to the present state of the art, steam or other smoke suppressant injection is required to avoid smoking.

SUMMARY OF THE INVENTION In this invention means are provided to utilize the kinetic energy of the uprising column of gas to provide added turbulence plus air induction into the body of the gas stream. This is done by inserting into the column of rising gas, bars, strips, plates or other obstructions which cover a portion of the cross section of the flare stack. These are preferably positioned in a radial manner so that the solid cylinder of rising gas is broken up into a plurality of adjacent and pie-shaped sectors of rising gas with distinct spaces or voids between each. These rise up through the spaces between the obstructions. The obstructions can be simple strips placed with their flat side perpendicular to the rising gas stream or they can be shaped in such a way as to cause the rising gas to be displaced sideways around the obstruction. By thus confining the rising gas to a smaller cross section, there will be a higher velocity of gas flow in these sectors than in the cylindrical column below because of area reduction and there will be a reduction of pressure immediately downstream of (that is, above) the obstruction proportional to the square of the increased velocity. If these obstructions are now placed in a radial manner, this lower pressure will cause atmospheric air to flow in radially over the tops of these obstructions and then to spread sideways into the rising sectors of gas and to be intermixed with the gas and to provide the air needed for the combustion. By the use of the mechanical expedients disclosed it has been observed that smoke suppression is less difficult and smoke suppression is improved in any flare-burning of smoke-prone gases.

In addition, it is possible to add means for bringing in steam as a smoke suppressant in the form of a plurality of radially disposed jets, which because of their high velocity cause air induction to the steam jet, thence into the gas columns, which air induction is in addition to that caused by the obstructions and the energy of the rising gas column. The combined advantages of both the structure and the use of steam is provided in an effective manner.

BRIEF DESCRIPTION OF THE DRAWINGS It is a principal object of this invention to provide a structure for a flare stack in which the kinetic energy of the rising gas column is utilized to provide air induction into the interior of the column of rising gas, so as to promote mixing of air and gas, and thus to promote the more rapid and higher temperature combustion of the gas.

This and other objects are realized and the limitations of the prior art are overcome in the present invention which is illustrated with the attached drawings, in which:

FIGS. 1, 2 and 3 illustrate views of a first embodiment of this invention in which the kinetic energy of the gas alone is utilized to provide the air induction.

FIGS. 4, 5, 6, 6A and 6B illustrate a second embodiment which provides the features of the first embodiment with the addition of a plurality of circumferential steam jets which act to provide air induction into the rising column of gas and also to provide the smoke suppressant action.

FIGS. 7, 8, 9, l0, and 11 show a third embodiment in which in addition to the second embodiment there are provided radial tubes carrying steam. These are placed directly on top of the obstructions of the first embodiment and have a plurality of openings in a horizontal direction to which steam is injected horizontally into the various sectors of the gas column.

FIGS. 12 and 13 illustrate a fourth embodiment in which steam pipes are used in conjunction with the-radial obstructions. However, the steam for these pipes is introduced through a vertical axial steam pipe which rises along the axis of the flare stack and carries a plurality of radial arms.

DESCRIPTION OF THE PREFERRED EMBODIMENT Refer now to FIGS. 1, 2 and 3. FIG. 1 is a plan view of the top of a flare stack modified in accordance with this invention. FIG. 2 illustrates a vertical diametrical section through the stack of FIG. 1. The stack is generally indicated by the numeral 10 and the obstruction structure by the numeral 12.

As shown in FIG. I, there are six radial bars, or straps, which as shown in FIG. 3, are arranged with their flat surface in a horizontal'plane. While six bars are shown, FIG. 4 shows that four may be used so that it is clear that any desired number of bars, obstructions or dividers can be used. The larger the diameter of the flare stack, in general, the more radial arms, the intent being to break up' the rising solid cylindrical column of gas into a plurality of sectors with intervening air spaced immediately above the obstructions. Due to the velocity of the gas, it is compressed from the cylindrical diameter, below the bars, to a lesser space, which corresponds to the sum total of cross section of the sectors, such as 21. This reduction in cross section provides a higher velocity and therefore there is a lower pressure in the space immediately above, that is, downstream of, the bars 18. This crowding of the gas into the sector space is shown in FIG. 3 where the arrows labeled 22 are shown rising under the bar 18 and spreading out 23 and crowding to the side of the bar in the spaces 21. Because of the lower pressure on top of the bars 18, there will be a radial air flow, as shown by the arrows 24, from the outside of the stack along the tops of the bars and then in a sideways manner as shown by the arrows 26, directly into the rising gas columns.

By this means air is induced from the outside of the stack into the central portion of the gas column. Combustion can therefore proceed throughout the entire cross section of the gas column while providing increased heat and turbulence to promote the rapid and smokeless combustion.

It has been determined by experiment that this use of obstructive bars or strips improves air induction into the column of gas sufficiently so that smoke production for any smoke-prone gas is reduced without the use of any other means of smoke suppression.

The framework of radial bars 18 are tied together preferably by a plate 19 which itself acts as an obstruction. They are supported at their outer ends by means which are welded or bolted to the wall 14 or the tip 16 of the flare.

There are three other embodiments of this invention which become increasingly more involved in the use and application of steam as a smoke suppressant. For example, FIGS. 4, 5, 6, 6A and 6B show a second embodiment in which there are provided the radial bars 18, central plate 19, a plurality of sectors 21 as in the case of FIGS. 1, 2, and 3. However, in addition, there are provided in FIGS. 4 and a circular manifold 34 around the outside of the stack with a plurality of riser pipes 36 each of which has at least one or more inwardly facing openings such as 37. This is shown in more detail in FIG. 6. The steam rises as shown by arrow 38 from the manifold through the pipes 36 and issues in a more or less horizontal radial direction as shown by arrow 39. This high velocity jet of steam radially flowing into the column of gas will induce air in accordance with the arrows 40 so that in addition to the beneficial effects of the structure 12 of FIG. 2 there will be additional air induction by the steam resulting from this plurality of radial jets.

FIGS. 6A and 6B illustrate that there may be more than a single inwardly facing opening. The idea is, as shown in FIG. 4, that for those risers which are in line with the bars 18 it is desirable to have one jet facing radially inward over the bar and other jets such as 42 and 43 which are directed more or less into the volume of the sectors 21. At a point on the circumferences intermediate the radial obstructions 18 the jet can be a single one which is directed radially inward such as 41, since it goes then directly into the volume of the sector, inducing air according to arrows 45 to follow it and to be turbulently mixed with the gas. Whereas, FIGS. 1 and 3 show that air is induced along the top surface of the obstructions l8 and flow sideways as shown by the arrows 26, the same will apply under the jets 41 so that there will be introduced-along the boundaries of the sectors air and steam which will beneficially contact the faces of the rising sectors of gas.

In FIGS. 7, 8, 9, 10 and 11 there is shown a third embodiment, which in addition to the obstructions l2 and the plurality of risers and steam jets indicated generally by the numeral 29 of FIG. 4, there is added a still further supply of steam to the gas, by a corresponding plurality of steam jets. This is provided by having as part of the steam system a plurality of horizontal pipes 50 coming from the riser 51. The steam pipes 50 are placed in line with the obstructions 54 and carry a plurality of openings on each side of the pipes so that there will be a plurality of steam streams 56 as shown in FIG. 7. Similarly, as in the previous embodiment, there will be air induced in accordance with the arrows 58 which will flow in along and below the steam pipe and over the arms 54, and will move in a lateral direction in accordance with the arrows 56 into the sectors 21.

FIG. 10 illustrates that the steam pipe 50 which moves radially inward from the manifold riser has an orifice 62 in its end, which provides further turbulence in the central portion of the column. The pipes 50 are welded to the plates 54 which provide the principal obstruction and air induction described in connection with FIG. 1. Referring back to FIG. 5, the tip 16 of the flare stack is formed in a characteristic shape with a plurality of openings such as 27 and 28 which are shown in FIGS. 4 and 5. These direct a plurality of streams of gas upward into the air gas boundary causing air induction into the outer wall of the sectors and improving the turbulence and mixing along the outer surface. This is shown also in the plane view of FIG. 7. While this has been customary in prior art systems, they still do not provide the air induction into the center of the column which is a problem to which this invention is directed, and which it has measurably improved.

FIG. 9 shows a slight modification of the obstruction arm 54 by the use of a pair of cylindrical segments 65 which are welded to the bottom of the strip or bar 54 and providing means of guiding the steam flow in accordance with arrows 62 and 63 to improve the velocity of the gas as it passes the bar and therefore improve the pressure lowering required to induce the air.

Referring now to FIGS. 12 and 13 this fourth embodiment is similar to the third embodiment of FIGS. 7 to 11 except that the horizontal steam pipes 71 are now fed with steam from a central vertical axial steam pipe 72 which is closed off at the top by the plate 74 and which has openings 76 feeding steam into the radial pipes 71. Each of these pipes has a plurality of horizontal openings 78 through which steam flows in accordance with the arrows 79. The circular manifold 34 may still be provided to feed steam to the risers 36 as shown in FIG. 5, or the steam pipes 71 may be used without the circular manifold. The steam pipes 71 rest upon the strips or bars as in the other embodiments and the flow of gas, steam and air is in accordance with FIG. 9.

The principal invention lies in the use of the obstruction system, which utilizes the kinetic energy of the rising gas column to provide air induction into the body of the gas column. However, because of limitations even to this improvement, the use of steam as a smoke suppressant may still be required and the methods of utilization of the steam are shown in the second, third,

and fourth embodiments, the second using simply the plurality of risers and radially directed jets. The third and fourth use, in addition, steam pipes placed on the top of the obstruction bars and having horizontal jets directed into the sides of the sectors of the columns of gas. The difference between the third and fourth embodiments are in the manner of feeding steam into these radial steam pipes.

While the invention has been described with a certain degree of particularity, it is manifest that many changes may be made in the details of construction and the arrangement of components. It is understood that the invention is not to be limited to the specific embodiments set forth herein by way of exemplifying the invention, but the invention is to be limited only by the scope of the attached claim or claims, including the full range of equivalency to which each element or step thereof is entitled.

We claim:

1. In a flare stack system for the smokeless combustion of hydrocarbon gas, including a vertical cylindrical stack and means for providing a rising column of said gas inside said stack, the improvement comprising:

at least one flat strip extending horizontally from the outer periphery of said stack across at least a portion of the discharge exit of said stack to divide the cross sectional area of said rising column of gas and to cause a lower pressure over said strip and thus induce combustion supporting air from the outer periphery of said stack along the top of said strip means comprises a circumferential steam manifold and a plurality of riser pipes circumferentially spaced and connected to said steam jet.

6. The flare stack system as in claim 4 including a plurality of radial directed steam pipes on top of said radial members, with a plurality of horizontal orifices in said pipes, and including means to supply steam to said plurality of steam pipes.

7. The flare stack system as in claim 6 in which said means to supply steam to said radial steam pipes, comprise a circumferential steam manifold, said radial pipes connected to said manifold.

8. The flare stack system as in claim 6 in which said means to supply steam comprise a vertical steam line along the axis of said stack, said radial steam pipes connected to said steam line.

Claims (8)

1. In a flare stack system for the smokeless combustion of hydrocarbon gas, including a vertical cylindrical stack and means for providing a rising column of said gas inside said stack, the improvement comprising: at least one flat strip extending horizonTally from the outer periphery of said stack across at least a portion of the discharge exit of said stack to divide the cross sectional area of said rising column of gas and to cause a lower pressure over said strip and thus induce combustion supporting air from the outer periphery of said stack along the top of said strip into said rising columns of gas.

2. The flare stack system as in claim 1 in which said strip comprises a flat bar with a triangular cylindrical form the apex of which is directed upstream of said rising gas.

3. The flare stack system as in claim 1 in which said strip includes a plurality of radially directed members attached to a central member.

4. The flare stack system as in claim 1 and including means to provide a steam jet directed inwardly above each said strip.

5. The flare stack system as in claim 6 in which said means comprises a circumferential steam manifold and a plurality of riser pipes circumferentially spaced and connected to said steam jet.

6. The flare stack system as in claim 4 including a plurality of radial directed steam pipes on top of said radial members, with a plurality of horizontal orifices in said pipes, and including means to supply steam to said plurality of steam pipes.

7. The flare stack system as in claim 6 in which said means to supply steam to said radial steam pipes, comprise a circumferential steam manifold, said radial pipes connected to said manifold.

8. The flare stack system as in claim 6 in which said means to supply steam comprise a vertical steam line along the axis of said stack, said radial steam pipes connected to said steam line.

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