EP1144915B1 - Burner-type apparatus and fuel combustion method - Google Patents

Description

An apparatus and method allowing better gas combustion containing in particular hydrocarbons. These devices and process can be used, for example, in torches from an oil refinery or on the fields of oil and gas production, for burning gases waste or gaseous emissions without emissions unburnt hydrocarbons.

STATE OF THE ART

Oil processing in a refinery results the production of waste gases and gaseous emissions, whose elimination by combustion in gas burning, called "torches" or "gas flares" in the profession, can cause emissions toxic and smelly, fumes or noise, harmful to the environment.

These nuisances, and in particular those caused by the incomplete combustion of gases, for example rich in hydrogen sulphide (H ₂ S), generally appear, when the quantity of air necessary for perfect combustion is insufficient, that is to say when the ratio between the flow rate of gas to be burned and the air flow rate required for combustion is less than the stoichiometric ratio, and when the three conditions necessary for optimal combustion, called "the three T", namely the T emperature of the flame, the T emps of air / gas mixture before burning and the T urbulence applied to this mixture, are insufficiently filled.

This is generally due to the fact that the excess gas to be burned has a relatively low pressure and a high flow rate of up to 10 000 000 Nm ³ / day, consecutive for example, to a malfunction on a refining unit of the petroleum or at an oil or gas production site. Since the pressure of the gas to be burnt remains generally low, this does not allow aeration of the flame sufficiently activated by the pressure of the gas leaving the torch supply tube. Since the fuel-oxidant mixture in the combustion zone becomes deficient in the amount of air necessary for perfect combustion, an external supply of oxidant is therefore necessary by any means available in the art to improve the combustion of the gas.

So far, devices have been used injection fueled, for example, by steam passing through injectors, or other working fluids such than air or gas, which induce air and turbulence necessary for combustion. However, these devices have low yields, which requires the use of large quantities of fluids to compensate for their lack efficiency.

• une émission importante de bruit, due au passage de la vapeur d'eau dans les tubes et les injecteurs ;
• un refroidissement de la flamme, qui ne permet pas d'assurer les conditions correctes de combustion des gaz, par exemple les gaz acides comme H₂S, pour lequel la température de 700°C requise pour sa complète oxydation n'est, dans ces conditions, pas atteinte, produisant ainsi des émissions toxiques et malodorantes ;
• un bilan énergétique du site pouvant être déficitaire, car dépendant de la production de la vapeur d'eau.

This results in a refinery, in the case for example of the use of water vapor as a working fluid, a high consumption having the effects:

• a significant emission of noise, due to the passage of water vapor through the tubes and the injectors;
• a cooling of the flame, which does not make it possible to ensure the correct conditions for combustion of the gases, for example the acid gases such as H ₂ S, for which the temperature of 700 ° C. required for its complete oxidation is not, in these conditions, not reached, thus producing toxic and smelly emissions;
• an energy balance of the site can be in deficit, because dependent on the production of water vapor.

On the oil and gas production fields, there usually has no steam available and the pressure of the gas to be burned is too low to be usable as a fuel-oxidizer mixture energy source sufficient. Therefore, the combustion of discharges, which are gases rich in hydrocarbons and sometimes into liquid hydrocarbons called condensates, becomes incomplete and usually accompanied by thick smoke black.

GB 1,323,674 describes an apparatus of the flare type, supplied with combustible gas by at least one tube gas inlet to burn. The end of the tube is surrounded of a plurality of devices arranged around it and each comprising a venturi and a supply of motor fluid.

FR 573 059 A describes a blowing device in which we use a pressurized fluid to drive a other fluid and give it speed. A plurality of motor fluid supply tubes are arranged with substantially annularly around the axis of at least one venturi, in view of sucking the second fluid before injection in a combustion zone.

US 1,443,315 A and US 3,554,681 also describe devices in which injection devices of a first gas arranged in a ring at the entrance of a venturi cause a second gas in it.

Torch manufacturers have also considered solution which consists in bringing air into the zone of combustion by means of power fan groups high, arranged for example under the torch, and to stagger the gas distribution using automatic valves controlled by complex instrumentation. This solution is difficult to apply because of the cost investment and high operating costs, and more it is made unreliable by the installation of fans under the flame in a warm atmosphere and corrosive, and also raises safety concerns due to possible fallout from liquid hydrocarbons easily flammable on hot fans.

The Applicant therefore carried out research with a view to to find solutions that are, at the same time, technically satisfactory, simple, reliable and whose corresponding investment cost is low, in refinery as on a production site, to obtain smoke-free combustion of a gas which may contain liquid hydrocarbons.

SUMMARY OF THE INVENTION

• en ce que l'extrémité dudit tube est entourée d'une pluralité de dispositifs disposés autour de cette extrémité, composés chacun d'un venturi et d'une alimentation en fluide moteur ;
• en ce que chacun des dispositifs comporte une pluralité de tubes disposés de façon sensiblement annulaire autour de l'axe AA du venturi ;
• et en ce que l'ensemble des tubes de chaque dispositif, qui injectent le fluide moteur dans le venturi, divergent les uns des autres en formant un angle α avec l'axe AA du venturi, supérieur à 3° et, de préférence, sensiblement égal à celui que forme le divergent avec ledit axe.

The Applicant has thus succeeded in developing an apparatus of the gas flare type, to facilitate the combustion of combustible gases in the atmosphere, comprising a combustion zone supplied with at least one combustible gas by at least one inlet tube of gas to be burned, characterized:

• in that the end of said tube is surrounded by a plurality of devices arranged around this end, each composed of a venturi and a supply of working fluid;
• in that each of the devices comprises a plurality of tubes arranged substantially annularly around the axis AA of the venturi;
• and in that the set of tubes of each device, which inject the working fluid into the venturi, diverge from each other by forming an angle α with the axis AA of the venturi, greater than 3 ° and, preferably, substantially equal to that formed by the divergent with said axis.

This device has the major advantage of allowing smokeless combustion even when the gas pressure is low and high throughput, and that it contains liquid hydrocarbons.

The invention also relates to the use of the apparatus defined above to facilitate the combustion in the atmosphere of a combustible gas supplying the gas inlet tube, while the tubes of the supply devices of the working fluid are supplied by a fluid chosen from the group consisting of air, air enriched with oxygen, water vapor or a combustible gas, this use being characterized in that the pressure of the working fluid is between 0.5 and 6.10 ⁵ Pa and, preferably, between 1 and 3.10 ⁵ Pa, and in that each tube transports between 1% and 33% and, preferably, between 5% and 33% of this working fluid.

This use eliminates the need for fans and noise from passing a fluid such as water vapor in injectors.

In addition to complete smoke-free combustion, the apparatus according to the invention allows, on the one hand, to reduce the consumption of engine fluid, for example the water vapor, and on the other hand to increase the reliability of installation by the absence of moving parts, such that fans, to have an implementation process easy, and offer installation costs and relatively weak operational.

Other advantages and features of the device and of the method according to the invention will emerge from the rest of the present description, in which reference will be made to Figures 1 to 3 of the accompanying drawings, which have no limiting character.

SUMMARY DESCRIPTION OF FIGURES

Figure 1 shows schematically an apparatus according to the invention, in front view and in section;

Figure 2 is a detailed schematic view of one of the devices of FIG. 1, in front view and in chopped off ;

Figure 3 illustrates a particular use of the invention for burning acid gases such as hydrogen sulfide.

DETAILED DESCRIPTION OF THE INVENTION Apparatus according to the invention

The combustion apparatus according to the invention is shown in Figure 1 as it can be installed on the top of a gas flare.

It has a combustion zone 1, with an inlet of combustible gas constituted by a tube 2 of gas to burn. Around the end of this gas inlet tube to burn 2 are arranged substantially annularly a plurality of devices 3 for supplying working fluid under pressure.

As can be seen in Figure 1, the devices 3 are inclined towards the combustion zone, i.e. towards the axis BB of tube 2, their axes of symmetry AA forming an angle β with the axis of symmetry BB of the tube 2 of arrival of the gas to be burned between 1 ° and 70 °, and preferably between 5 ° and 60 °.

Figure 2 illustrates an embodiment of a device 3. The latter consists of an arrival of working fluid 4, at the outlet of which is placed a body forming venturi 5, itself made up of a part tapered lower 6, generally called "converging", and which is extended by a part cylindrical 7 called "neck", the latter being extended by an upper frustoconical part 8 called "divergent".

The supply of engine fluid 4 of each of the venturis 5, from the supply tube 13, comprises a central tube 9, which is usually of section transverse annular and arranged substantially coaxially to the axis AA of the venturi 5. The central tube 9 extends from outside, passing through converging 6, to a point located in the venturi 5, generally at the level of the junction of convergent 6 and neck 7.

A plurality of tubes 10 is advantageously provided around the central tube 9. The arrangement of these tubes 10 is generally regular and annular, the tubes 10 may be arranged in at least one ring, the center is located on the axis AA of the venturi body.

Preferably, the tubes 10 and the central tube 9 are identical to each other, have a cross section generally circular and are arranged in an annular manner, following at least one crown whose center is located on the axis AA of the venturi.

The number of tubes 10 is calculated according to the flow air required for combustion and the internal diameter of the venturi body.

Advantageously, all of the feed tubes 13 are connected to the same source of pressurized working fluid.

Preferably, at least the tubes 10 so arranged substantially annular around the axis AA of the venturi 5 and located furthest from this axis inject the motive fluid in the venturi at an angle α, formed with the axis AA of the venturi 5, greater than 3 °, and preference substantially equal to that formed by the divergent 8 with said axis. Their lower part 12 can be cylindrical and substantially parallel to the axis AA of the venturi 5, while, as can be seen in FIG. 2, the angle of inclination α of their upper part 11 by relation to the axis AA is substantially equal to the angle of inclination of the diverging 8 with respect to this same axis AA.

In a variant of the invention not shown in the figures, the axes of the tubes 10 can form with the axis AA of the venturi 5 an angle substantially equal to that that forms the divergent with the axis of said venturi.

The tubes 10 all generally enter the venturi 5 of the same depth, which can be the same or less than the penetration depth of the central tube 9 in the venturi 5.

According to a variant (not shown in the figures), the central tube 9 is replaced by a second plurality of tubes arranged annularly around the axis AA, of so that they are surrounded by the tubes 10.

As indicated above, in the same device, the tubes 10 as well as the central tube 9 (or the plurality of tubes which replace it) may be identical others have a cross section overall circular and are preferably all connected to the tube power supply 13, itself being connected to a source of motor fluid. They are sized so that they transport between 1% and 33% of the working fluid and, from preferably between 5% and 33% of said fluid.

Advantageously, the devices 3 arranged so annular around the end of the gas inlet tube 2 to burn are all identical.

A variant of the invention can also be used, as shown in this figure 3, for burning gases requiring a high combustion temperature, for example hydrogen sulfide, whose temperature oxidation is greater than 700 ° C.

As can be seen in Figure 3, the area of combustion 1 is covered by a venturi body 15, into which the gas to be burned is injected via of tube 2, said body making it possible to maintain a higher temperature and residence time while preserving the flame from external disturbances. According to the invention, a plurality of devices is arranged annularly around the end of the tube 2 for supplying the gas to be burned, so that the motor fluid exiting from each of the diverging the plurality of devices is injected into the body forming venturi 15, thereby improving the combustion of the gas to be burned.

Method according to the invention

According to the invention, to improve the combustion of gases by additional supply of oxidizer, medium of fluid the arrival of motor fluid 4 of each devices 3.

As the working fluid, air, air enriched with oxygen, a gas which is itself combustible or steam is generally used. The pressure of the working fluid is usually between 0.5 and 6.10 ⁵ Pa (0.5 to 6 bars) and, preferably, between 1 and 3.10 ⁵ Pa (1 to 3 bars).

There is therefore no combustion inside 3 devices, because these simply have role of improving the combustion of combustible gases, by causing increased oxidant induction (air) and turbulence favoring the mixing between the fuel and oxidizer.

During the operation of the apparatus according to the invention (see figure 1), the combustible gas is introduced coaxially in combustion zone 1 according to the arrows G. Combustion occurs in the area of combustion 1. It is favored by devices 3, which, thanks to the introduction of a working fluid, alone or in mixture, following the arrows H, cause air to through the venturi 5, following the arrows I. This air driven spring by the divergent 8 of the device concerned and then comes to improve the combustion of gases.

Thus, the use of the devices 3 therefore allows a complete combustion of a gas containing a hydrocarbon, a mixture of hydrocarbons, an acid gas or a mixture of these gas, thanks to a high air entrainment with low amount of working fluid. This results in a noise reduction, compared to existing torches, where air induction is carried out using tubes classics supplied with water vapor in the area combustion. Indeed, as the noise is due to the trigger of the working fluid in the tubes, the use of a less amount of working fluid leads to a reduction in noise.

The Applicant has found, during tests it has that the use of the device according to the invention requires a flow rate of the steam necessary for ensure smoke-free combustion, which is 14 times lower than the flow required by conventional torches for obtaining the same result.

The apparatus according to the invention also has the advantage of be easily achievable on a platform, shortly, by simply fitting out a torch classic, which only causes a short stop the operation of the refining unit, or on a site oil or gas production. Operating losses are therefore minimal.

Claims (11)

1. An apparatus of gas-flare stack type, to facilitate the combustion of combustible gases in the atmosphere, comprising a combustion zone (1) supplied with at least one combustible gas through at least one inlet tube (2) for gas to be burnt, the end of said tube being surrounded by a plurality of devices (3) arranged around said end, each of said devices comprising a venturi tube (5) and a supply of motive fluid (4);
   characterised in that each of the devices (3) comprises a plurality of tubes (10) arranged in a substantially annular manner around the axis AA of the venturi tube (5);

   and in that all the tubes (10) of each device (3), which inject motive fluid into the venturi tube (5), diverge from one another to form an angle α with the axis A-A of the venturi tube (5) which is greater than 3° and, preferably, substantially equal to that which the divergent section (8) of said venturi tube forms with said axis.
2. An apparatus according to claim 1, characterised in that the devices (3) are arranged in a substantially symmetrical manner and preferably annularly around the end of the inlet tube (2) for the gas to be burnt.
3. An apparatus according to either one of claims 1 and 2, characterised in that the axis AA of the venturi tube (5) of each device (3) forms with the axis BB of the inlet tube (2) for the gas to be burnt an angle β of between 1° and 70° and, preferably, between 5° and 60°.
4. An apparatus according to any one of the preceding claims, characterised in that the supply tubes (13) for all the devices (3) are connected to the same source of motive fluid under pressure.
5. An apparatus according to any one of the preceding claims, characterised in that each of the tubes (10) of each device (3) disposed in a substantially annular manner around the end of the inlet tube (2) for the gas to be burnt is of such a size that it can convey between 1 % and 33 % and, preferably, between 5 % and 33 % of the motive fluid.
6. An apparatus according to any one of the preceding claims, characterised in that the inlet of motive fluid (4) for each device (3) comprises a central tube (9) and a plurality of tubes (10) disposed in an annular manner around the axis AA of the venturi (5).
7. An apparatus according to any one of the preceding claims, characterised in that the inlet of motive fluid (4) comprises two sets of tubes arranged respectively in an annular manner around the axis AA of the venturi tube (5).
8. An apparatus according to any one of the preceding claims, characterised in that the tubes (10) of one device (3) are all identical to one another and are overall of circular cross-section.
9. An apparatus according to any one of the preceding claims, characterised in that the tubes (10) are arranged in an annular manner along at least one ring, the centre of which is situated on the axis AA of the venturi tube (5).
10. An apparatus according to any one of the preceding claims, characterised in that the combustion zone (1) is surrounded by a venturi tube (15) disposed downstream of the devices (3).
11. Use of an apparatus according to any one of claims 1 to 10 to facilitate the combustion in the atmosphere of a combustible gas supplying the gas-inlet tube (2), while the tubes (13) of the devices (3) for the inlet of motive fluid are supplied with a fluid chosen from the group comprising air, oxygen-enriched air, steam or a combustible gas, characterised in that the pressure of the motive fluid is between 0.5 and 6.10⁵ Pa and, preferably, between 1 and 3.10⁵ Pa, and in that each tube (10) conveys between 1 % and 33 % and, preferably, between 5 % and 33 % of this motive fluid.

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