GB2136555A - Improvements in flares - Google Patents

Abstract

A flare tip assembly has a frusto-conical hollow body 10 surrounded at its lower region by a shroud 12 to form an upstanding gap 13. Waste gas rises through this gap and clings to the exterior surface 15 of the body 10. Air is induced to flow upwardly and mixes with the rising gas for combustion above the body 10. Swirling gas also passes upwardly through the body 10. <IMAGE>

Description

SPECIFICATION Improvements in or relating to flares The present invention relates in general to flares used to dispose of dump or waste gas. As is known it is desirable to burn offwaste gas particularly in oil production installations without undue smoke and noise. Flares designed to achieve this often employ a narrowgapwhich is preciselyshapedand dimensioned to induceairflow by creating the Coanda effect. Prior constructions suffer from certain disadvantages and a general object of this invention is to provide an improved assembly for use in the disposal of gas.

An assembly constructed in accordance with the invention has a main hollow body ortip structure which preferably has a frusto-conical external profile or a similar shape as is known per se. In accordance withthe invention,ashroudsurrounds or partly surrounds the lower region ofthe main body and establishes a simple non-Coanda gap between the exterior surface ofthe main body and the interior of the shroud. Gasfor disposal is passed into the shroud and emerges directly upwardly through the gap to flow overthe exterior ofthe main body. This wall-discharged jet induces ambient airto rise with the gas and this air becomes mixed with the gasto support and sustain combustion.

Atubular member or conduitcan introduce the gas to the interior ofthe shroud. The gas can however be split and some of the gas mayflowthrough the gap as aforesaid while the remainder may pass up through the main bodyto meet the exterior gas/air mixture.

Alternatively one source of gas may supply gas partly orsolelyto the interior ofthe shroud and thence to the gap while anothersource of gas usually at lower pressure would pass through the main body. The lower pressure gas emerging from the the main body, or from a tubular membertherein, would then mix with the air and higher pressure gas above the main body.

Diverters, e.g. in the form of inclined webs, may be provided in the main bodyto impart swirl to gas passing therethrough.

A preferred embodiment of the invention takes the form ofaflaretip assembly composed of a hollow upstanding frusto-conical tip structure, a frustoconical shroud inverted in relation to the tip structure disposed at or nearthe lower inlet region ofthe tip structureto define therewith an upwardly-extending gap or slot communicating with the interior ofthe shroud and leading to the exterior surface of the tip structure and means for passing waste gas into the interior of the shroud from whencethe gas passes smoothly to the exteriorvia the gap or slot predomi- nantly in an upward direction and without drastic change in direction and entrains airto move to the top ofthe tip structure and mix with the gas which tends to cling to the exterior surface of the tip structure. Gas also passes through the tip structure to emerge from its upper outlet and means can be provided in the tip structure to impart swirl tothe rising gas. An upstanding pipe coaxial with the tip structure and the shroud may supportthe tip structure and shroud and pass gas thereto ortherethrough.

The invention may be understood more readily, and various other aspects and features ofthe invention may become apparent, from consideration of the following description.

Embodiments ofthe invention will now be described, by way of examples only, with reference to the accompanying drawings, wherein : Figure lisa schematic representation of a flare stack tip assembly constructed in accordance with the invention; and Figure 2 is a schematic representation of a further flare stack assembly constructed in accordance with the invention.

Figure 1,which is partly broken away to showthe interior details, depicts a burnerorflareassembly which is primarily intended for installation atthetop of an elevated flare stack. The assembly is composed of a main body ortip structure 10 of frusto-conical profile with an external shape resembling a tulip. The tip structre 10 is superimposed on a tubular member 11 and a shroud 12surroundsthe lower region ofthe tip structure 10 and the upper part of the tubular member 11. A simple non-Coanda continuous annular gap 13 is established between the interior ofthe shroud 12 and the exterior surface 15 of the tip structure 10. Means, such as a plurality ofthe bores 18, in the tubular member 11 establish communication between the interior of the shroud 12 and the member 11.Webs 14 are disposed within the lower region of the structure 10 so as to incline in relation to the main longitudinal axis A-A. The exterior surface 15 ofthetip structure 10 is provided by a refractory lining 16 although this is optional. A preferred form of refractory material is a "needled" refractory material i.e. a refractory material containing particles or needles of stainless steel to resist fracturing.

During use, high-pressure gas for disposal is passed upthrough the tubular member 11 as indicated bythe arrows with filled-in heads. A proportion of this high pressure gas passes outthrough the bores 18 into the interior of the chamber 12 and thence upwardly through the gap 13 to pass overthe exterior surface 15 of the tip structure 10. The passage of the high pressure gas tends to induce air to flow upwardly as indicated by open-head arrows. The induced airtends to hold the high pressure gas in contact with the exterior surface 15 of the tip structure 10.The remaining proportion of the high pressure gas passes upthrough thetubular member 11 and insidethetip structure 1 Otto merge with the exterior air/gas mixture atthe top of the structure 10. This gas is diverted by the webs 1 4to assume a swirling motion which assists in intimate mixing of the air and gas generally above the tip structure 10.

A modified construction is shown in Figure 2 and for convenience utilises the same reference numerals as in Figure 1. In constrastto the Figure 1 construction, the tubular member 11 is extended up through the tip structure 10 and serves solelyto convey a low pressure gas to the region above the tip structure 10.

The path ofthe low pressure gas is shown as part filled and part open headed arrows. Afurthertubular member 17 communicates with the interior ofthe shroud 12 and serves to introduce the high pressure gas therein as in the Figure 1. Some of the high pressure gas emerges through the gap 13to entrain air as before while the remainder of this gas flows up through the structure 10 and swirls aroundthe member 11. The external high-pressure gas and air mixture then meets the outflowing low and high pressure gases atthetop of the structure.

In both constructions one or more pilot burners (not shown) would serve to initiate combustion.

It is significantthatthe gas emerging through the gap 13 essentially does not change direction butflows smoothly upwards. This reduces noise and the assembly is less affected by wind. Good mixing is ensured and combustion with low luminosity can be established.

Claims (10)

1. For use in flare; an assembly comprising a main body intended to form a tip structure for the flare and a shroud at least partly surrounding a lower region of the main body to establish a non-Coanda gap between the extrior ofthe main body and the interior ofthe shroud; the arrangement being such that during use waste gas for disposal is passed into the shroud to emerge and flow upwardly through the gap to flow overthe exterior ofthe main body and induce ambient airto rise with the gas and to mixtherewith.

2. An assemblyaccording to claim 1, and further comprising a tubular memberfor introducing the waste gas into the shroud.

3. An assembly according to claim 1, and further comprising means for diverting the waste gas so that part ofthewaste gas flows upwardly th rough the main body and the remainder ofthe waste gas flowthrough the gap as aforesaid.

4. An assembly according to claim 2, wherein the tubular member leads to the interior of the main body and is apertured within the shroud so that part ofthe waste gas flows upwardly through the main body and the remainder ofthe waste gas flowth rough the gap as aforesaid.

5. An assembly according to claim 1 wherein the gas passed into the shroud is from a first source and a tubular member leads at least partly through the main body and serves to introduce gas from a second source to the assembly for discharge from the top of the hollow body, the first source being at a higher pressure than the second source.

6. Aflaretip assembly composed of a hollow upstanding frusto-conical tip structure, a frusto conical shroud inverted in relation to the tip structure disposed at or nearthe lower inlet region ofthe tip structure to define therewith an upwardly-extending gap or slot communicating with the interior of the shroud andleadingtotheexteriorsurfaceofthetip structure and means for passing waste gas into the interior of the shroud from whence the gas passes smoothly to the exterior via the gap orslot predominantly in an upward direction and without drastic change in direction and entrainsairto move to the top ofthe tip structure and mix with the gas which tends to cling to the exteriorsurface ofthetipstructure.

7. An assembly according to claim 6, andfurther comprising an upstanding pipe coaxial withthetíp structure and the shroud which supports at least the tip structure and passes gas thereto orthernthrough

8. An assembly according to any one of claims 1. to 7, andfurther comprising means for imparting swirl to; gas passing through the main body ortip-structu re.

9. An assembly according to claim 8, wherein the swirl-imparting means takes the form of inclined webs in the main body ortip structure

10. An assembly substantially as described with reference to, and as illustrated in, Figures 1 to 2 ofthe accompanying drawings.