US3801261A

US3801261A - Opti-netic flare

Info

Publication number: US3801261A
Application number: US00248066A
Authority: US
Inventors: R Reed; R Schwartz
Original assignee: John Zink Co
Current assignee: KGI Inc
Priority date: 1972-04-27
Filing date: 1972-04-27
Publication date: 1974-04-02
Anticipated expiration: 1991-04-02

Abstract

This invention describes an improved apparatus for the smokeless flare burning hydrocarbon gases. The improvement results from the improved use of steam energy to provide increased turbulence of the air, steam and the hydrocarbons that are to be burned and to provide an intense high temperature burning zone to ensure that any free carbon that is formed is completely consumed. The steam is supplied through a plurality of nozzles which are placed circumferentially around the top of the flare and are directed generally inwardly toward the vertical stream of gases that are issuing from the tip of the flare. Relationships are given for the vertical angle of the steam nozzles in relation to their position above the tip of the flare.

Description

United States Patent 1 1 Reed et al.

[ OPTI-NETIC FLARE [75] Inventors: Robert D. Reed; Robert E.

Schwartz, both of Tulsa, Okla.

[73] Assignee: John Zink Company, Tulsa, Okla.

[22] Filed: Apr. 27, 1972 21 Appl. NO.Z 248,066

FOREIGN PATENTS OR APPLICATIONS Great Britain... 431/4 1451 'Apr-.2, 1974 Primary Examiner-William F. ODea Assistant Examiner-William C. Anderson Attorney, Agent, or FirmHead & Johnson [57] ABSTRACT This invention describes an improved apparatus for the smokeless flare burning hydrocarbon gases. The improvement results from the improved use of steam energy to provide increased turbulence of the air, steam and the hydrocarbons that are to be burned and to provide an intense high temperature burning zone to ensure that any free carbon that is formed is completely consumed. The steam is supplied through a plurality of nozzles which are placed circumferentially around the top of the flare and are directed generally inwardly toward the vertical stream of gases that are issuing from the tip of the flare. Relationships are given for the vertical angle of the steam nozzles in relation to their position above the tip of the flare.

8 Claims, 8 Drawing Figures OPTl-NETIC FLARE BACKGROUND OF THE INVENTION The basic concept in this invention is significant enhancement of two of the Three Ts which are fundamental for either combustion or chemical reaction, but specially related to smokeless flare burning. The Three T5 are Turbulence, Temperature, and Time. Temperature and Turbulence determine Time for either burning or reaction since burning involves chemical reaction. The equations of Arrhenius relate to speed of reaction as a function of temperature. Turbulence, which is resultant from energy speeds temperature elevation and varies directly as the relative energy. In gaseous flow, energy resulting from such flow is MV /2, i.e., with constant mass, energy will vary as the square of the velocity thus velocity preservation up to a point of utilization enhances turbulence. With enhanced turbulence, reaction is speeded and if the reaction is exothermic (heat productive) temperature level is increased in reference to the speed-of-reaction increase.

As related to smokeless burning of flared hydrocarbons, the time factor is significant in avoiding smoke production because, if the slow-burning carbon (as a solid) can be held within a high-temperature zone long enough, there is complete burning of the carbon and avoidance of smoke production. In the arts of smoke suppression for burning hydrocarbons in flares, a number of chemical reactions are involved and they may be considered as:

1. Direct oxidation of hydrocarbon 2. Dissociation of hydrocarbons to H and C (smoke productive) 3. Water-gas shift reactions of C H 4. Reformation of hydrocarbon with water-vapor to These reactive conditions are either exothermic or endothermic. Where reaction is involved, greater turbulence or greater temperature speeds reaction, takes less time for complete reaction, and if the conditions of temperature/turbulence are right there is complete burning and avoidance of smoke since smoke (carbon) is a product of incomplete burning of hydrocarbons.

In the flare-burning of hydrocarbonsthe state of burning is in the open air at an elevated point, typically, where the potential for heat-loss in radiation, and in wind-rain cooling makes it imperative to establish the highest possible flame temperature within a very small fraction of a second after emergence of the hydrocarbon for burning. In the prior art, such as U.S. Pat. Nos. 2,779,399 and 3,134,424, steam has been injected to the burning zone immediately downstream of the point at which the gases emerge for burning with the steam injection pressure typically 100 lbs. gauge (1 14.7 absolute). In the prior art there has not been proper utilization of the steam flow energy because the points from which the steam emerges, for directed travel into the burning zone, are considerably radially outward from the boundary of the hydrocarbon stream emerging for burning. Thus the streams must travel a significant distance before their turbulence potential can be realized, and there is a great loss of energy before the energy is utilized, preferentially.

In flow of gases from an orifice or port, and instantly upon emergence, the flowing gases possess latent kinetic energy which is velocity-established. The flow velocity is a function of the ratio of upstream absolute pressure to downstream absolute pressure. When the i upstream pressure (absolute) is twice the downstream pressure (absolute) the flow velocityfor the gas becomes critical or sonic, as it passes the orifice restriction. Since the velocity as it passes the orifice restriction, becomes critical it is impossible to further accelerate the gas flow at that point. But if the ratio of absolute pressures exceeds two (as above) the flow becomes supersonic or supercritical downstream of the port or orifice because of a resultant increase in mass at critical velocity. This results in velocity increase as the additional mass or density (already at critical velocity) further expands. Examples of this are turbinenozzles for steam and rocket nozzles for supersonic or supercritical energy utilization. Alittle appreciated fact is that the supercritical flow effect exists immediately downstream of any flow orifice or port. Due to the fact that in prior steam injection flare burning apparatus the supercritical expansion is not confined or directed, only part of the supercritical energy is useful in the directed area downstream of the orifice or port.

The radial location of the stream injection orifice or orifices as spaced from the border of flared gases is a critical factor as to energy delivery for turbulence as the flared gases subsequently burn. This factor is predicated on research-supported data that, in forward movement downstream of the orifice, substantially percent of the orifice-stream energy will have been spent in a travel distance approximately equal to nine orifice diameters (Masters Thesis, Fluid Flow, U. Of Tulsa, Richard Martin). Thus if the orifice has a diameter of three-eighths inch, within the forward gas movement of 3 inches, 90 percent of the gas stream energy will have been spent. Turbulence is proportional to energy and therefore, in this case, only 10 percent of the kinetic energy is useful. From this the conclusion might be drawn that, in point of energy-turbulence potential, the orifice should be located immediately adjacent to the border of the gas stream and, if turbulence alone is considered, this is true. But since the end-purpose of turbulence is to promote reaction/temperature, the components for the preferred reaction/temperature must be present as the state of turbulence is created in order to promote rise in temperature. 7 i

In the case of steam injection alone, the potential reaction would be only the endothermic reforming condition and without adequate temperature level this reaction cannot occur to an appreciable degree. Therefore to cause generation of adequate heat the steam-stream must draw in air for the exothermic direct oxidation of hydrocarbon as the condition of turbulence exists. Thus it is preferable that; of the steam-stream energy, more nearly 50 percent be spent for turbulent energy and 50 percent spent for air induction. The steam orifice must be spaced radially outward from the border of the gas stream a limited distance to permit access of air to the vicinity of the issuing steam-stream where the pressure immediately adjacent to the orifice is less than 14.7 lbs. absolute. Preferred spacing radially outward from the border of the flared-gas stream is that spacing which will cause flow energy utilization in a preferred manner but there may be variation in gas flow boundary definition according to the flow characteristics of the device from which the flared gases flow.

In some cases, where the problem of smoke suppression is particularly demanding, it is desirable to cause steam-air injection in a flow direction which is horizontal, rather than in a direction which is above the horizontal in some angular relationship with the horizontal which is typical of the art of U.S. Pat. Nos. 2,779,399 and 3,134,424. I

SUMMARY OF THE INVENTION It is a principal object of this invention to provide a flare system, a system for flaring hydrocarbon gases in which steam is utilized to provide highly turbulent mixing of the flare gas and air plus steam in order to get complete combustion of carbon.

These and other objects of the invention are realized and the limitations of the prior art devices are overcome in this invention in its broadest aspects by utilizing a plurality of steam jets which are directed generally inwardly into the column of hydrocarbon gases is suing from the tip of a flare stack. The particular advantages of the invention lie in the design of the norzles which are such as to confine, conserve and direct the supercritical steam energy, and to obtain a maximum team velocity which entrains air into and mixes in a turbulent manner with the vertically rising column of hydrocarbon' dump gases. A large diameter supply conduit and circular header is provided near the tip of the flare stack and surrounding it from this a plurality of vertical riser pipes are provided which are spaced radiallyoutwardly from the tip of the flare stack and are directed inwardly and upwardly at appropriate angles into the stream of gas issuing from the tip of the flare.

The particular advantages of the nozzle over the orifice is that whereas the orifice provides opportunity for the steam stream to expand in almost a hemispherical manner, the nozzle will confine and direct the stream and so conserve itsene'rgy. Two important types of steam nozzles are described which are efficient in the utilization and conversion of the steam energy into high velocity, supercritical, steam jets which are used to provide a turbulentmixing of the gases with air and hence achieve the basic Three Ts of smokeless burning.

BRIEFDESCRIPTION or THE DRAWINGS This and other objects of theinventio'n and a better understanding of the principles and details of the invention will be evident from the following description taken in conjunction with the appended drawings in which:

FIGS. 1 and 2 show respective plan and partial sectional elevation views of the apparatus of this invention.

FIGS. 3A, 3B and 3C show three different types of steam nozzles which can be used to accomplish the objectives of this invention.

FIGS. 4A, 4B and 4C illustrate the geometry of the positioning and directing the steam nozzles in accordance with this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIGS; 1 and 2 the numeral indicates generallyithe flare stack tip construction while numeral 12 indicates generally the manifold and riser types that supply steam into the burning gases. The flare stack is indicated generally as a vertical tubular column 16 to rounds the stack near its tip. This is a large diameter pipe and is supplied from a steam source via vertical supply pipe 25, also of larger diameter so that under the flow conditions from the steam source (e.g., boiler) and the header 24 there is minimal pressure loss. Similarly, fairly large diameter vertical riser pipes 26 are provided, usually a plurality of them, angularly spaced around the header pipe 24. These rise vertically to a point above the tip of the flare stack and then are bent inward, at an angle to the vertical which is a function of the position of the tip of the nozzle radially outward from the flared gas stream and the vertical distance above the tip as will be explained in connection with FIGS. 4A, 4B and 4C.

Consider next FIGS. 3A, 3B and-3C. As has been discussed previously, the importance of conserving the velocity energy of the steam and converting it efficiently into supercritical steam discharge velocity at the outlet of the nozzle is extremely important in obtaining the maximum air injection and turbulence in the burning area. The ideal type of nozzle is shown in FIGS. 3A which includes an entry section 34, a neck section 36, and an expander section 38, which is slowly diverging or tapering outwardly from the neck section 36 leading to the outlet of the nozzle at 40.

Ideally the steam nozzle design to which this invention is directed is one in which the ratio of the upstream pressure P to the downstream pressure I (all pressures being absolute) is greater than two. As such, in the nozzle, the velocity flow in the area of the neck 36 is critical or sonic while in the confined expander section 38 the tlow is one of added acceleration because of supplemental expansion downstream of 36 to achieve a directed supercritical flow velocity at P This steam energy accomplishes the objects of drawing additional combustion air into the burning flare and creates therewith turbulence and mixing for more efficient smokeless combustion. The expanding included angle of the expansion section of the nozzle 38 is generally at a solid angle of 7 to 14.

It has been found that in place of the nozzle shown in FIG. 3A, which when properly designed is the most efficient, a very satisfactory substitute for that nozzle is shown in FIG. 3B. This comprises a cylindrical block of metal 42 in which is bored an axial opening 44 at one end 43 and an axial opening 48 at the outlet end 47 of larger diameter. The opening 44 corresponds to the neck 36 of the nozzle of FIG. 3A and the expansion section corresponds to the larger diameter portion 48. The diameter of the neck portion is D, and the corresponding length is indicated at X. The expansion section is indicated of length Z and its diameter is indicated as Y.

Each of the dimensions X, Y & Z can have a limited range for optimum conditions. for example X can be in the range of 0.5D to 2D. Y can be in the range of 1.05D to 1.50D and Z can be in the range of 0.2D to 0.6OD.

A third type of nozzle which comprises simply an orifice or port is illustrated in FIG. 3C. Here the steam pipe 28 has an orifice plate 50 with a central opening or port 52. This nozzle simply permits steam discharge noncritical service and is thus limited. The position of the nozzle with respect to the column of gas is very important. On the consideration of velocity alone the nozzle should be close in so that the velocity of the steam will carry as far into the column of rising gas. On the other hand, the nozzle should be out far enough to entrain some air with the steam to provide for combustion. Also, the nozzle should be positioned downstream of the tip of the flare to give the gas some opportunity to partially burn and provide heat to the mixture. Entry of steam and consequent reforming is a cooling reaction.

However, there is some latitute in the position of the nozzle, although the relation between spacings and angle are very important. When the nozzle outlet is placed close to the gas stream, say a distance outward of D where D is the diameter of the nozzle, the angle from the horizontal of the nozzle should be in the range of 50 to 80 and the nozzle placed a short distance, preferably about one inch above the tip edge of the flare 60. This is illustrated in FIG. 4A where the numeral 60 indicates the flare tip and 62 illustrates the rising column of flare gas and the point 64 indicates the position of the outlet of the steam nozzle. As shown in FIG. 4B, if the nozzle is moved radially outwardly to a distance 2D then the nozzle should be raised to a position such as 3 inches above the flare tip, and the angle of the nozzle lowered to the range of 30 to 45. Going still farther outward to a distance, say 4D, the point 64 or the position of the outlet of the nozzle should be raised a distance such as 4 inches, and the angle of the nozzle lowered to the range of to 30. This relationship of angle and position of the nozzle has been determined in its relation to providing a maximum of combustion air and a maximum turbulence for the combustion of the gas. Factors of anticipated maximum wind velocity and the nature of the flare stack must be considered.

Summarizing the embodiment of this invention, it comprises a plurality of steam nozzles designed in accordance with the nozzles of FIG. 3A, 3B or FIG. 3C and positioned in accordance with the dimensions and ranges of angle of FIGS. 4A, 4B and 4C and supplied with steam through large diameter riser and manifold pipes so that there is a minimum reduction of steam pressure between the steam supply or boiler and the nozzles so that the boiler pressure can be utilized to greater efficiency in providing high velocity steam jets to cause extreme turbulence in mixing and smokeless combustion of the flare gases.

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 embodiment 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.

What is claimed:

1. In a flare system for the smokeless combustion of combustible dump gases, having means to flow said dump gases in a flare stack vertically upward to a tip of said stack; means to ignite and maintain burning of said dump gases at or above said tip; a plurality of steam injection nozzlescircumferentially contiguous said tip and directed toward said burning gases; and means to supply steam under pressure to said nozzles; the improvement comprising:

said nozzles'including means to supply said steam therefrom at super-critical velocity.

2. The flare system of claim 1 wherein said direction of flow of said steam is inwardly and upwardly above said tip into said burning gases.

3. The flare system as in claim 1 in which said nozzle includes an insert which comprises a cylinder having an inwardly contracting inlet section, a short neck section and an expansion section.

4. The flare system as in claim 3 in which said expansion section diverges from said neck section at an angle 5. The flare system as in claim 1 in which said nozzle means comprises a cylinder having a neck section of diameter D and length of said neck section in the range of 0.5D-2D and an expansion section of diameter in the range of 1.05D to 1.5D and length of said expansion section in the range of 0.2D to 0.6D.

6. The flare system as in claim 1 in which the outlet of each of said nozzles is positioned radially outward from the circumference of the rising gas stream a dis tance D where D is the diameter of the neck section of said nozzles, and approximately 1 inches above the tip of the flare, and at an angle of 50 to above the horizontal.

7. The flare system as in claim 1 in which the outlet of said nozzles are positioned radially outward from the circumference of the rising gas stream a distance 2D where D is the diameter of the neck section of said nozzles, and approximately 2 inches above the tip of the flare, and at an angle of 30 45 above the horizontal.

zontal.

Claims

1. In a flare system for the smokeless combustion of combustible dump gases, having means to flow said dump gases in a flare stack vertically upward to a tip of said stack; means to ignite and maintain burning of said dump gases at or above said tip; a plurality of steam injection nozzles circumferentially contiguous said tip and directed toward said burning gases; and means to supply steam under pressure to said nozzles; the improvement comprising: said nozzles including means to supply said steam therefrom at super-critical velocity.

4. The flare system as in claim 3 in which said expansion section diverges from said neck section at an angle of 7*-14*.

5. The flare system as in claim 1 in which said nozzle means comprises a cylinder having a neck section of diameter D and length of said neck section in the range of 0.5D-2D and an expansion section of diameter in the range of 1.05D to 1.5D and length of said expansion section in the range of 0.2D to 0.6D.

6. The flare system as in claim 1 in which the outlet of each of said nozzles is positioned radially outward from the circumference of the rising gas stream a distance D where D is the diameter oF the neck section of said nozzles, and approximately 1 inches above the tip of the flare, and at an angle of 50* to 80* above the horizontal.

7. The flare system as in claim 1 in which the outlet of said nozzles are positioned radially outward from the circumference of the rising gas stream a distance 2D where D is the diameter of the neck section of said nozzles, and approximately 2 inches above the tip of the flare, and at an angle of 30* - 45* above the horizontal.

8. The flare system as in claim 1 in which the outlet of said nozzles are positioned radially outward from the circumference of the rising gas stream a distance 4D and where D is the diameter of the neck section of said nozzles, and approximately 4 inches above the tip of the flare, and at an angle of 20* to 30* above the horizontal.