GB2304180A - Flare head - Google Patents

Abstract

A flare head for the burning of waste combustible gas has a diffuser section 12 arranged for connection to a flare stack, to receive gas from the stack. A flare tip 17 of reducing cross-section is arranged downstream of the diffuser section 12, with an orifice plate 15 disposed between the diffuser section 12 and the flare tip 17. The orifice plate 15 has a plurality of through-holes 23 each of which is of greater cross-sectional area at the flare tip end of the hole than at the diffuser end thereof, a respective sealing ball 24 being located in each hole 23. A mesh 16 is laid over the tip side of the plate 15, to retain the balls 24 in their respective holes 23. The number of hoes 23 can be selected to ensure gas passing through the flare head becomes highly turbulent so as to ensure optimum combustion thereof.

Description

FLARE HEAD This invention relates to a flare head suitable for the burning of waste combustible gases.

The extraction of oil or gas from underground reserves very often produces waste combustible gases which are most conveniently disposed of by burning in air. Also, for safety reasons, it may be necessary to vent combustible gases to atmosphere, to relieve pressures which otherwise might become dangerous. In either case, it is the usual practice to direct such gases to a relatively long pipe known as a flare stack, leading away from the production site, the gases being burnt at the remote end of the flare stack, as they escape to atmosphere.

In order to ensure reliable burning of the gases at the remote end of the flare stack, it is usual to fit to that stack a flare head which is adapted to promote the burning with a minimum likelihood of a flame front travelling back down the flare stack to the production site. There have been various proposals for flare heads, intended for use at the remote end of a flare stack: one such example is described in GB2216250. The flare head there described includes an adjustable conical member whereby the exit orifice may be adjusted so as to be suitable for the particular conditions prevailing - primarily the volume of the gas fed to the flare stack and the pressure of that gas.

However, after an extended period of use, the hostile environment at the flare head tends to seize the movable components and so the advantage of having an adjustable flare head is lost, notwithstanding the higher cost of such a flare head as compared to the provision of a conventional non-adjustable flare head.

It is a principal aim of the present invention to provide a flare head which, whilst not being adjustable in itself, may readily be modified to suit different conditions of use whilst at the same time giving combustion-promoting conditions to ensure reliable burning of waste gases.

According to the present invention, there is provided a flare head for a flare stack to permit the burning of waste combustible gas, which flare head comprises a diffuser section arranged for connection to a flare stack to receive gas therefrom, a flare tip of reducing cross-section mounted downstream of the diffuser, and an orifice plate assembly arranged between the diffuser and the flare tip, the orifice plate assembly comprising an orifice plate having a plurality of holes formed therein, the flare tip end of each hole having a greater cross-sectional area than the diffuser end of the hole, a plurality of metallic sealing members located one in each hole respectively, each sealing member being of a greater size than the diffuser end of the hole, and means on the flare tip side of the orifice plate to retain each sealing member in its respective hole.

The flare head of the present invention may be adapted to suit the circumstances prevailing at a given site by employing an orifice plate having a suitable number of holes formed therein, with each hole being of a suitable size having regard to the gas volume flow rate and pressure. If a flow rate greater than that anticipated for a particular orifice plate is to be accommodated, further holes may be drilled into the orifice plate, each such hole then being furnished with a suitable sealing member. If however a lesser flow rate is anticipated, then the holes in a given orifice plate may be plugged, or in the alternative the orifice plate may be removed and substituted by another having a lesser number of holes. Either way, the flare head of this invention may readily be adapted to suit the circumstances prevailing for the time being at a given site.

The presence of the sealing members in the holes of the orifice plate, and which may close off those holes, serves to prevent blow-back, in the event that there is a sudden reduction in gas pressure, upstream of the orifice plate. However, so long as normal conditions prevail, the sealing members may lift from their respective sealing positions, to allow gas flow into the flare tip for combustion.

Preferably, each hole in the orifice plate is of a circular cross sectional shape and conveniently comprises a through-hole counter-bored from the flare tip side of the plate.

Each sealing member may be in the form of a spherical ball, or possibly a member of some other shape but having a conical surface which is engageable with a wall of the orifice plate defining the associated hole. The diameter of the hole itself may taper from the flare tip end thereof to the diffuser end of the hole, or in the alternative a shoulder may be formed within the hole against which shoulder the sealing member may seat.

The sealing members, which should be heat resistant and so metallic, are preferably retained in their respective holes by a mesh laid over the flare tip side of the orifice plate, the pitch of the mesh being such that a part thereof will overlie each hole, whereby the retention of all of the sealing members may be assured. Another possibility is to arrange all of the holes on one or more common pitch circles and then to provide for each such pitch circle a ring centred thereon and overlying the holes of that circle. The or each ring may be releasably connected to the plate, to allow for maintenance.

Preferably, a tubular windshield is mounted on the outlet end of the flare tip, with the flare tip outlet within the windshield. Such a windshield may serve to protect the flame at the flare tip from strong cross winds, so reducing the likelihood of the flame being extinguished.

An igniter may be mounted adjacent the flare head, in order to ignite gas passing therethrough. Such an igniter may be mounted externally of the flare head, adjacent the exit therefrom.

By way of example only, certain specific embodiments of flare head constructed and arranged in accordance with the present invention will now be described in detail, reference being made to the accompanying drawings, in which: Figure 1 is a vertical sectional view through a first embodiment of flare head; Figure 2 is a plan view on an orifice plate usable in conjunction with the flare head of Figure 1; Figure 3 is a vertical sectional view through the orifice plate of Figure 2; Figure 4 is a plan view on an alternative form of orifice plate; and Figure 5 is a diagrammatic elevation of a flare stack, flare head and igniter assembly.

Referring initially to Figure 1, there is shown a first embodiment of flare head arranged in accordance with the present invention and it can be seen that this comprises a gas inlet pipe section 10 provided with a flange 11 at its lower end, which flange is adapted for bolting to the upper end of a conventional gas discharge flare stack from, for example, an oil production rig. At its upper end, the inlet pipe 10 is connected to a diffuser 12, which terminates in a parallel section 13 having a flange 14 secured therearound. Let into the parallel section 13 is an orifice plate 15, to be described in more detail below, and overlying that orifice plate 15 is a mesh 16.

A flare tip 17 is fitted to the diffuser 12, that flare tip 17 including a flange 18 which mates with flange 14, bolts (not shown) passing through the registering holes of the two flanges, to clamp the flare tip 17 to the diffuser 12. Internally, the flare tip 17 includes a shoulder 19, which shoulder bears on the mesh 16 so as to locate both that mesh and the orifice plate 15 in position, in the diffuser 12.

The flare tip 17 terminates at its upper end in a relatively small diameter exit nozzle 20, located within a tubular windshield 21. The windshield is mounted on the flare tip 17 and includes openings 22, through which combustion air may pass to permit burning of the gas passing through the orifice plate 15.

The orifice plate 15 is provided with a plurality of bores 23, each of which is counter-bored part-way along its length. In each counter-bore, there is located a steel ball 24, which seats on the shoulder between the associated bore 23 and its counter-bore; in this way, each ball and its bore in effect form a oneway valve through the orifice plate 15. The mesh 16 serves to maintain each ball 24 in its counter-bore, whilst allowing the free passage of gas therethrough.

Figure 2 shows an alternative orifice plate 25, wherein there are provided only eight holes 23, each of which has a ball 24 mounted therein. In Figure 2, the mesh 16 has been omitted for clarity, but that mesh is shown in greater detail in Figure 3, along with the profile of the bore and counter-bore, through the orifice plate. As can be seen, there is a conical shoulder 26 between a bore 23 and its counter-bore 27, which conical shoulder 26 allows for better seating of the ball 24. The mesh takes the form of a multi-layer gauze, though it would be possible for other designs of mesh to be employed.

Figure 4 shows a further alternative orifice plate 28. This orifice plate has thirty-four through-holes 23, each of which is fitted with an associated ball 24.

Clearly, the gas throughput for the orifice plate of Figure 4 is very much higher than that of orifice plate 25, of Figure 2.

Instead of the use of mesh, as shown in Figures 1 and 3, metal rings as shown diagrammatically at 29 in Figure 4 may instead be employed to maintain the balls in their respective bores. Such metal rings may be secured to the orifice plate 28 in any convenient manner - for example, by passing bolts through bores formed in the rings, which bolts are threaded into tapped holes formed in the orifice plate 28.

All of the components of the flare heads described above are preferably made of stainless steel, in order to give durability and corrosion resistance, despite the hot hostile atmosphere to which the head is exposed.

In use, gas rising up the flare stack (not shown) enters the inlet pipe 10 and then is expanded in the diffuser 12. The gas pressure forces the gas through the holes 23 and the configuration of those holes should be such that the gas is compressed whilst its velocity rises, to slightly below sonic velocity. The increase in the pressure lifts each ball to open each non-return valve to an extent sufficient to regulate the gas flow, so as thereby to give a consistent velocity ensuring efficient combustion. Once the gas escapes into the flare tip 17, it is in a highly turbulent state before being discharged out of the exit nozzle 20 for mixing with air within the windshield 21, combustion taking place at the exit nozzle 20. As the flame is in effect created within the windshield 21, that flame displays a high degree of resistance to extinguishing by, for example, strong cross winds.

Referring now to Figure 5, there is shown a complete assembly of flare head of this invention together with a flare stack 30 receiving waste combustible gas from an underground pipe 31. A tapping 32 on that pipe feeds gas to an igniter system 33. The gas is ignited within an ignition zone 34 by means of a spark electrode assembly, the resultant flame then travelling along flame pipe 35 to a pilot nozzle 36 disposed closely adjacent the outlet from the windshield 37 of the flare head.

Claims (13)

1. A flare head for a flare stack to permit the burning of waste combustible gas, which flare head comprises a diffuser section arranged for connection to a flare stack to receive gas therefrom, a flare tip of reducing cross-section mounted downstream of the diffuser, and an orifice plate assembly arranged between the diffuser and the flare tip, the orifice plate assembly comprising an orifice plate having a plurality of holes formed therein, the flare tip end of each hole having a greater cross-sectional area than the diffuser end of the hole, a plurality of metallic sealing members located one in each hole respectively, each sealing member being of a greater size than the diffuser end of the hole, and means on the flare tip side of the orifice plate to retain each sealing member in its respective hole.

2. A flare head as claimed in claim 1, wherein each hole in the orifice plate is of circular crosssectional shape.

3. A flare head as claimed in claim 2, wherein each hole in the orifice plate comprises a through-hole counter-bored from the flare tip side of the plate.

4. A flare head as claimed in any of the preceding claims, wherein each said sealing member comprises a spherical ball.

5. A flare head as claimed in any of claims 1 to 3, wherein each said sealing member has a conical surface engageable with a wall of the orifice plate defining the associated hole.

6. A flare head as claimed in any of the preceding claims, wherein said retaining means comprises a mesh laid over the flare tip side of the orifice plate.

7. A flare head as claimed in any of the preceding claims, wherein at least one group of the holes is formed on a common pitch circle, and the retaining means comprises a ring centred on the pitch circle centre and overlying the holes, the ring being releasably connected to the plate.

8. A flare head as claimed in any of the preceding claims, wherein the orifice plate assembly is arranged between the diffuser and the flare tip such that the assembly may be removed and replaced by another of a different rating.

9. A flare head as claimed in any of the preceding claims, wherein a tubular wind shield is mounted on the outlet end of the flare tip, with the outlet within the wind shield.

10. A flare head as claimed in any of the preceding claims, wherein the adjacent ends of the diffuser and the flare tip are provided with surrounding flanges, the flanges being connected together with the orifice plate assembly clamped therebetween.

11. A flare head as claimed in claim 8, wherein screw-threaded fasteners are used to connect together the two flanges.

12. A flare head as claimed in any of the preceding claims, and including an igniter assembly arranged to lie externally but alongside the flare head, whereby gas passing through the orifice plate may be ignited thereby.

13. A flare head as claimed in claim 1 and substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.