MULTI-FUEL TURBINE COMBUSTOR, MULTI-FUEL TURBINE COMPRISING SUCH A COMBUSTOR AND CORRESPONDING METHOD

Abstract

Combustor (50) for use in a turbine (100). The combustor (50) comprising a multiple fuel atomizers (10) which has a gas inlet for feeding gaseous fuel as first combustible into an inlet zone of the atomizer, an air inlet for feeding compressed air into the inlet zone, and an orifice for injecting a liquid fuel as second combustible into the inlet zone. The atomizer comprises a diffuser for emitting a gas stream at an exit side. The atomizer (10) is arranged with respect to a combustion chamber of the combustor (50) so that the exit side of the diffuser points in a tangential direction relative to the combustion chamber. The combustor (50) comprises an outlet duct (51) for discharging an exhaust gas produced by a combustion process of the gas stream inside the combustion chamber. The exhaust gas drives a turbine (63).

Description

TECHNICAL FIELD

The present invention relates to multi fuel gas turbine combustors and multi-fuel turbines comprising such a combustors. The present invention also relates to a method of combustion within a reverse flow annular combustor.

BACKGROUND OF THE INVENTION

A number of technologies are emerging which are designed in order to efficiently generate electricity. Some of them are combustion based systems where a combustible fluid (herein referred to as fuel) is oxidized.

There is a particular need for gas turbines which are designed to combust gas.

SUMMARY OF THE INVENTION

The objective of the present invention is thus to find a combustor layout and a multi-fuel gas turbine set-up which can be switched between at least two different combustible fuels, one in liquid and one in gaseous form.

According to the invention, a combustor for use in a turbine is provided. The combustor comprises multiple fuel air blast atomizers which can be operated at least on a liquid fuel and on a gaseous fuel. Each air blast atomizer comprises a gas inlet for feeding a gaseous fuel as first combustible into an inlet zone of the air blast atomizer, an air inlet for feeding compressed air into the inlet zone, and an orifice for injecting the liquid fuel as second combustible into the inlet zone or into an area close to the inlet zone. The air blast atomizer further comprises a diffuser for emitting a gas stream at an exit side into a primary combustor zone of a combustion chamber. This gas stream comprises the gaseous fuel, the compressed air and the liquid fuel. The combustor comprises a combustion chamber. The air blast atomizer is arranged with respect to the combustion chamber of the combustor so that the exit side of the diffuser points in a tangential direction relative to the combustion chamber to create a main vortex flow. The combustor further comprises an outlet duct for discharging an exhaust gas produced by a combustion process of the gas stream inside said combustion chamber.

An air blast atomizer for the purposes of the present invention is using kinetic energy of air to atomize liquid fuel and to decrease the time which is needed for the vaporization.

Preferrably, the air blast atomizer is arranged with respect to the combustion chamber of the combustor so that the gas stream is tangentially discharged via the exit side of said diffuser into the combustion chamber where due to this form of directed discharging a vortex is established and maintained.

According to the invention, a multi-fuel gas turbine is provided as a fuel-burning device which is designed to burn multiple types of fuels in its operation. The multi-fuel turbine comprises a central exit duct and a reverse flow annular combustor.

Preferred embodiments of the invention are characterized by an overall arrangement where the exit side of the combustor is pointing into a direction essentially opposite to a major flow direction of the exit duct (called reverse flow arrangement).

The invention offers several advantages. The combustion chamber of the invention is working properly during the critical start phase of the gas turbine. Also during regular operation the system reaches a stable and very reliable state. The switching from a liquid fuel to a gaseous fuel or vice versa takes place without any noticeable interruption, which means that the response time is very low. The measured combustion chamber efficiency is very high (it was measured to be about 0.98 at main regime) on maximum load and on partial load. The emission characteristics are excellent as compared to other gas turbines. In particular the NOx emissions are quite low on maximum load and on partial load.

It is another advantage of the invention, that a multi-fuel turbine generator set could be powered by various combustibles according to the actual need or taking into consideration the availability of resources (such as LNG, diesel fuel, palm oil or syngas).

Further advantages will become apparent from the detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

Further characteristics and advantages of the invention will in the following be described in detail by means of the description and by making reference to the drawings.

FIG. 1A shows a cross-section of a multi-fuel turbine, according to the present invention;

FIG. 1B shows a magnified cross-section of a part of the multi-fuel turbine of FIG. 1A;

FIG. 1C shows another magnified cross-section of a part of the multi-fuel turbine of FIG. 1A;

FIG. 1D shows rear view of the multi-fuel turbine of FIG. 1A;

FIG. 2A shows a cross-section of an air-blast atomizer, according to the present invention;

FIG. 2B shows a cross-section of the diffuser shape of the air-blast atomizer of FIG. 2A.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Terms are herein used which also find use in relevant publications and patents. It is noted however, that the use of these terms shall merely serve a better comprehension. The inventive idea and the scope of the patent claims shall not be limited in their interpretation by the specific selection of the terms. The invention can be transferred without further ado to other systems of terminology.

A first embodiment of the invention is now described in connection with the FIGS. 1A through 1D and FIG. 2.

The invention concerns a multi-fuel turbine 100 which has a reverse flow annular combustor. Reverse flow annular combustor turbines in various configurations are known in the art. In general terms, a reverse flow annular combustor turbine 100 comprises one reverse flow annular combustor arranged around the periphery of a (central) exit duct 30. In connection with FIGS. 1A-1D an embodiment is described which comprises twelve air blast atomizers 10 in a reverse flow annular combustion chamber 50. The annular combustion chamber 50 is arranged next to a radial inflow turbine 63, as illustrated in FIG. 1A.

As indicated above, the turbine 100 comprises a central exit duct 30 which typically has a funnel shape, a cylindrical shape or the shape of a truncated cone. The exit duct 30 may also comprise various sections for instance with an upstream truncated cone-shaped portion followed by a downstream cylindrical portion, like the exit duct 30 of FIG. 1A. The arrow EG (EG schematically represents the exhaust gases flow) in FIG. 1A points in the downstream direction. The central exit diffuser duct 30 is symmetric with respect to a longitudinal axis LA2.

According to the invention, a reverse flow annular combustor 50 with air blast atomizers 10 is positioned in a annular arrangement around the central exit duct 30. The combustor 50 is sitting outside of the exit duct 30. The reverse flow annular combustor 50 is supplied/powered by several air-blast atomizers 10.

Details of a preferred embodiment of an air-blast atomizer 10 are shown in FIG. 2A. The air-blast atomizer 10 of FIG. 2A can be employed in all embodiments of the invention.

According to the invention, all embodiments comprise multi-fuel air-blast atomizers 10 which are designed in order to be feedable by a liquid fuel LF and a gaseous fuel GF. The inventive turbine 100 comprises multiple (preferrably four and more) multi-fuel air-blast atomizers 10.

All embodiments of a multi-fuel air-blast atomizer 10 of the invention comprise a diffuser 11 with an exit side 12 and an inlet side or zone 13, as shown in FIG. 2A.

The diffuser 11 has a rotationally symmetric shape with a first large diameter area A1 serving as the inlet zone 13, followed by a second area A2 with constriction of diameter and a third area A3 with a diameter expanding towards the exit side 12. The shape of the diffuser 11 of FIG. 2A is depicted in FIG. 2B. FIG. 2B shows the shape of a preferred diffuser 11.

In other words, the diffuser 11 has a rotationally symmetric shape with respect to a longitudinal axis LA1. The shape is derived from an hourglass shape where an area A2 with constriction separates the inlet zone 13 from a funnel shaped area A3, and wherein the funnel shaped area A3 opens out into the exit side 12.

There is an orifice 14 which is designed for the injection of the liquid fuel LF. The orifice 14 is typically placed at the circumference of the wall enclosing/defining the diffuser 11 of the air-blast vaporizer 10. Preferably, the orifice 14 is oriented in a radial direction with respect to the central longitudinal axis LA1 of the air-blast atomizer 10. Each atomizer 10 further has a gas inlet 15 which is designed for the injection of the gaseous fuel GF. Preferably, the gas inlet 15 of all embodiments is co-axially arranged with respect to the longitudinal axis LA1. In preferred embodiments of the invention, the gas inlet 15 enters the diffuser 11 at the back side so that the gaseous fuel GF is streaming right into the center of the inlet side or zone 13. An air inlet 16 is provided, which is designed for the intake of compressed air (provided by an upstream portion 66 of the turbine 63, cf. FIG. 1A). The embodiment of FIG. 2A shows an air inlet 16 which takes in air at the circumference and which redirects the air in a direction which is essentially parallel to the longitudinal axis LA1. At the inlet side or zone 13 the gaseous fuel GF and the compressed air are mixed automatically. A short distance downstream from the gas inlet 15 the orifice 14 is spraying the liquid fuel LF into the diffuser 11, if both kinds of fuels GF and LF are used at the same time. The orifice 14 is located near the second area A2 with constriction of diameter or right at the second area A2.

For the purposes of the present description and claims, a multi-fuel air-blast atomizer 10 is a device which takes in gaseous fuel GF and/or liquid fuel LF and compressed air, mixes these constituents and releases them through the exit side 12 into the combustor 50 so that an efficient combustion process can be initiated and maintained in the combustor 50.

Generally speaking, the orifice 14, the gas inlet 15, and the air inlet 16 of all embodiments are positioned at or close to the inlet side or zone 13 of the air-blast atomizer 10 so as to produce a high-pressure gas stream GS. This high-pressure gas stream GS exits the diffuser 11 via the exit side 12, as schematically illustrated in FIG. 2A. This high-pressure gas stream GS typically is a sub-sonic two phase gas stream. The flow of this gas stream GS is subsonic, which means that is has a Mach number smaller than one, because one has to decrease the velocities in the combustion chamber. The flow of this gas stream GS is two-phase because it consists of air and gaseous fuel GF, or air and liquid fuel LF, or air and gaseous fuel GF plus liquid fuel LF, if both kinds of fuel GF and LF are employed at the same time.

According to the invention, each of the air-blast atomizers 10 is tangentially arranged with respect to the reverse flow annular combustor 50, as can be seen in FIGS. 1B and 1C. The tangential arrangement is essential since it causes a vortex stream inside the combustor 50 for main stabilization in the primary combustor zone PCZ (in FIGS. 1B and 1C the position/dimension of the primary combustor zone PCZ is depicted schematically by means of a simple oval). The primary combustor zone PCZ is a region of the reverse flow annular combustor 50 which is located downstream of the air-blast atomizer(s) 10. A so-called dilution region DR follows downstream of the primary combustor zone PCZ (in FIGS. 1B and 1C the position/dimension of the dilution region DR is depicted schematically). The vortex is established and maintained by the tangential arrangement of the diffuser 11 which injects the two phase gas stream GS tangentially into the chamber of the combustor 50.

An igniter 53 is preferrably positioned inside the reverse flow annular combustor 50 so as to be able to ignite the primary combustor zone PCZ. A preferred position of the igniter 53 is indicated in FIG. 1A by means of the symbol

Practically, the vortex formed by the airblast injector 20 in combustor 50 produces or serves as main stabilization stream. The vortex in the combustor 50 is crucial for a flame stabilization in the combustor's primary zone. The stabilization process of the reverse flow annular combustor 50 is designed so that the vortex is established and maintained by the special arrangement and orientation of the air-blast atomizers 10.

Preferably, all embodiments of the invention employ a gas inlet 15 which, together with the air pressed into the air-blast atomizer 10, form a high-speed subsonic gas stream GS.

FIG. 1D show a rear view where all twelve air-blast atomizers 10 are visible. This Figure shows that all atomizers 10 have the same radial distance with respect to the longitudinal axis LA2. One can also see the gas fuel pipes 102 which here comprise a common ring-shaped pipe. The liquid fuel pipes 101 are hidden behind the gas fuel pipes 102.

It is one problem of a multi-fuel turbine 100, that each type of fuel has a different fuel mass flow. In order to ensure an identical fuel heat input (which is essential for a stable operation of the multi-fuel turbine 100 or the multi-fuel turbine generator set, respectively), the flow of the gaseous fuel GF has to be stronger when processing flare gas than in case of syngas serving as gaseous fuel GF, for instance. The flows of a liquid fuel LF and a gaseous fuel GF have to be adjusted following the same principle so that the effective fuel mass flow is maintained. The control unit CU of the multi-fuel turbine 100 or the multi-fuel turbine generator set controls the actual state and intervenes, if required.

The invention employs a non-premixed combustion scheme. This means that neither the compressed air and the gaseous nor the liquid fuel(s) are mixed before they enter the diffuser 11 of the air-blast vaporizer 10. This is of particular advantage regarding the processing of syngas, since the hydrogen contained in the syngas might cause a flashback if it is pre-mixed with (hot) air before it reaches the inlet side or zone 13 of the diffuser 11. A non-premixed combustion scheme is also advantageous if for instance liquid hydrogen is employed as liquid fuel LF.

In all preferred embodiments of the invention, the mixing of the gaseous fuel GF (e.g. syngas) and the (hot) air takes place in the inlet side or zone 13 of the diffuser 11. Then further compressed (hot) air is mixed after the two phase gas stream GS has left the air-blast atomizers 10 and before it enters the central exit duct 30. Further compressed (hot) air might be fed in via optional air inlets 52 (cf. FIG. 1C). Preferably, in all embodiments of the invention, more than 50% of the air mass flow is injected through optional air inlets 52 into the combustion chamber 50.

The multi-fuel turbine 100 may further comprise a compressor housing 61 with air slots 62. This compressor housing 61 is located at the upstream side of the central exit duct 30. Between the compressor housing 61 and the exit duct 30 there is a compressor diffuser vane 105 which diffuses the compressed hot air and guides it through air channels 65.1, 65.2 into the reverse flow annular combustor 50 (this is done via optional air inlets 52, one of which is visible in FIG. 1C) and to the air inlets 16 of the air-blast atomizers 10. Inside the compressor 60 there is a power transmission shaft 107 (and other rotating parts) which is co-axially arranged with respect to the longitudinal axis LA2. The power transmission shaft 107 rotates around the longitudinal axis LA2. The actual turbine 63 sits at the downstream end of the shaft 107. The radial inflow turbine 63 has a number of curved blades (not visible in the cross-sections) which are arranged so that exhaust gas, redirected by outlet ducts 51, interacts with these blades and causes a rotation of the turbine 63. The turbine 63 also has a number of curved air blades (not visible in the cross-sections) in an upstream portion 66 of the turbine 63 arranged so that air sucked in via the air slots 62 is compressed by these air blades.

There is a exit duct pipe connection 64 for mechanically connecting the compressor 60 to the exit duct 30.

The reverse flow annular combustor 50 is placed around the exit duct 30 and the whole arrangement sits outside the exit duct 30 and inside an outer combustor housing 104. The outer combustor housing 104 typically has a annular shape.

In the following sections further details are addressed.

A gas turbine is a type of internal combustion engine. It has at least one downstream turbine (here the turbine 63) following after a combustion chamber 50.

According to the invention, energy is added to the two phase gas streams GS which are fed via several air-blast atomizers 10 tangentially into the reverse flow annular combustion chamber 50. Here (liquid and/or gaseous) fuel mixed with air is ignited and combusted. That is, in the reverse flow annular combustion chamber 50 the two phase gas streams GS provided by the air-blast atomizers 10 are ignited and combusted so as to produce a high pressure gas stream and the temperature is increased due to the internal combustion processes. The (reaction) products of the combustion is forced via cambered outlet ducts 51 into the radial inflow turbine 63 downstream of the combustor 50. The high velocity of the high pressure, hot exhaust gas flow is directed over the blades of the turbine 63. The turbine 63 spins around the longitudinal axis LA2 and drives a mechanical output (e.g. the shaft 107). Simply phrased, the energy imposed upon the turbine 63 is taken from the reduction in the temperature and pressure of the exhaust gas produced by the reverse flow annular combustion chamber 50. The exhaust gases EG is guided along the blades of the turbine 63 and through the jet pipe 30 into a direction parallel to the longitudinal axis LA2. In FIG. 1A the exhaust gas EG is schematically represented by an arrow which points in the downstream direction.

In the most preferred embodiments of the invention, air is accelerated in either a compressor (e.g. in a centrifugal compressor 60 or in an axial compressor), before the air is fed into the gas inlets 16 of the air-blast atomizers 10. When guided through the inlets 15, 16 and the orifice 14, the pressure and temperature of the air and other gas flow(s) increase(s). Then the two phase gas streams GS pass from the diffusers 11 into the reverse flow annular combustion chamber 50 where the temperature increases further due to the combustion processes and the specific volume of the gases increases, i.e. the gases are caused to expand. This increased volume of gases is (re-)directed via the outlet duct 51 onto the turbine blades of the turbine 63 or it is expanded and accelerated by means of nozzles before the inherent kinetic energy is extracted by the turbine 63.

The gas stream inside the reverse flow annular combustion chamber 50 is caused to form a vortex stream due to the specific arrangement of the air-blast atomizers 10. The vortex stream causes a high level of mixture of the gas “components” which in turn increases the performance of the combustion. It is a further advantage of the vortex operation that the walls of the combustion chamber 50 do not get as hot as they would in a conventional combustion chamber.

Depending on the implementation of the invention, the reverse flow annular combustion chamber 50 can be operated without the need of a cooling device since the walls remain relatively cool. The compressed air, which is fed via the channels 65.1, 65.2 to the combustor 50, is streaming along the walls of the combustion chamber 50 and thus provides for a cooling effect.

The above described operation is initiated using liquid fuel LF or gas fuel GF. Once started, an operator by manual intervention or the control unit CU can choose the most favorable fuel and switch over the operation at anytime. The switching can be done by means of control lines 71, 71, as schematically illustrated in FIG. 3. These control lines 71, 71 interact with actuators 72, 73 (e.g. valves and/or pumps).

Afterwards, an operator or the control unit CU can for instance select the most inexpensive fuel in accordance with seasonal and other fluctuations or the fuel which causes the least emissions (e.g. reduced NOx emissions).

In preferred embodiments of the invention, a multi-fuel turbine generator set is provided which is designed in order to be operated with two different types of fuels, namely with a gaseous fuel GF and a liquid fuel LF.

In preferred embodiments of the invention, the multi-fuel turbine generator set is designed in order to burn gasoline, kerosene, diesel oil, palm oil, liquefied natural gas, or liquefied hydrogen as liquid fuel LF and syngas (a mixture of H₂ and CO), natural gas, or flare gas as gaseous fuel GF. The syngas could be provided by a waste disposal reactor, for instance. The flare gas could be provided by an oil platform where so far the flare gas is typically flared.

If a liquid fuel LF is processed together with syngas, the liquid fuel LF is injected through small orifices 14 (one orifice 14 per air-blast atomizer 10), into the inlet side or zone 13 (into area A1 or A2) of the respective air-blast atomizer 10. The injected liquid fuel LF is merged with a subsonic gas stream GS comprising syngas and compressed air. This subsonic gas stream GS is then injected tangentially into the reverse flow annular combustion chamber 50.

There might be an electric cabinet or control cabinet (not shown) which comprises switches, high-power semiconductor elements, fuses and the like. The control unit CU (see FIG. 1A) might be part of the cabinet or it could be realized as separate unit or building block of the multi-fuel turbine 100.

As mentioned before, there is a gas fuel supply 40 and a liquid fuel supply 41 both of which are in fluid connection with the reverse flow annular combustion chamber 50. The gas fuel supply 40 and the liquid fuel supply 41 are switchable by the control unit CU in order to enable the multi-fuel turbine 100 to be operated by gaseous fuel GF and/or by liquid fuel LF. FIG. 1A indicates in a schematic block diagram that there are control lines 70, 71 which enable the control unit CU to switch the flow of the gaseous fuel GF and the flow of the liquid fuel LF. Actuators or valves 72, 73 are employed in order to control the flow of the gaseous fuel GF and the flow of the liquid fuel LF.

While the present invention has been illustrated and described with respect to a particular embodiment thereof, it should be appreciated by those of ordinary skill in the art that various modifications to this invention may be made without departing from the spirit and scope of the present.

Claims

1. A reverse flow annular combustor for use in a turbine, said combustor comprising at least one air-blast atomizer operating on a combustible, wherein the air-blast atomizer is a multiple fuel atomizer which has a gas inlet for feeding gaseous fuel as first combustible into an inlet zone of the atomizer,an air inlet for feeding compressed air into the inlet zone,an orifice for injecting a liquid fuel as second combustible into the inlet zone or into an area close to the inlet zone, anda diffuser for emitting a gas stream at an exit side comprising said gaseous fuel, compressed air and said liquid fuel, said atomizer being arranged with respect to a combustion chamber of said combustor so that the exit side of said diffuser points in a tangential direction relative to said combustion chamber, and wherein said combustor comprises an outlet duct for discharging an exhaust gas produced by a combustion process of said gas stream inside said combustion chamber.

2. The combustor according to claim 1, wherein said diffuser has a rotationally symmetric shape with a first large diameter area serving as the inlet zone, followed by a second area with constriction of diameter and a third area with a diameter expanding towards the exit side.

3. The combustor according to claim 1, wherein said diffuser has a rotationally symmetric shape with an hourglass shape where an area with constriction separates the inlet zone from a funnel shaped area, and wherein the funnel shaped area opens out into the exit side.

4. The combustor according to claim 2, wherein said orifice is positioned at or close to said constriction.

5. The combustor according to claim 1, wherein said gas inlet is co-axially arranged with respect to a longitudinal axis of said atomizer.

6. The combustor according to claim 1, wherein said gas inlet and said air inlet are arranged so that gaseous fuel and said compressed air are clashing in the inlet zone.

7. The combustor according to claim 1, wherein said atomizer is arranged with respect to the combustion chamber of said combustor so that said gas stream is tangentially discharged via the exit side of said diffuser into said combustion chamber where a vortex is established.

8. The combustor according to claim 1, wherein said combustor comprising a plurality of atomizers, these atomizers being arranged on a common circle.

9. A multi-fuel turbine comprising a central exit duct pipe and a reverse flow annular combustor in accordance with claim 1, said combustors being arranged at the outside of said exit duct pipe so that the exhaust gas discharged by the reverse flow annular combustor is streaming into a direction essentially opposite to a major flow direction of said exit duct pipe.

10. The multi-fuel turbine according to claim 9, which comprises a turbine which is co-axially arranged with respect to a longitudinal axis of said exit duct pipe and which further comprises a cambered outlet duct connected to said combustor for redirecting said exhaust gas onto blades of said turbine.

11. The multi-fuel turbine according to claim 10, wherein said turbine comprises an upstream portion with air blades for taking in air and for releasing compressed air.

12. The multi-fuel turbine according to claim 11, comprising air channels arranged so that compressed air released by said upstream portion is guided towards air inlets of said atomizers.

13. The multi-fuel turbine according to claim 9, wherein said reverse flow annular combustor comprises at least one air inlet arranged so as to provide a direct air entry into the combustion chamber of said combustor.

14. The multi-fuel turbine according to claim 9, comprising a control unit connectable to actuators or valves so as to enable the multi-fuel turbine to be fed by said gaseous fuel and/or by said liquid fuel.

15. The multi-fuel turbine according to claim 14, further comprising liquid fuel pipes and gas fuel pipes for feeding said liquid fuel to said orifices of each vaporizer and said gaseous fuel to said gas inlets of each vaporizer.

16. The multi-fuel turbine according to claim 14, comprising a common ring-shaped liquid fuel pipe and a common ring-shaped gas fuel pipe for feeding said liquid fuel to said orifices of each atomizer and said gaseous fuel to said gas inlets of each atomizer.

17. The multi-fuel turbine according to claim 9, further comprising an igniter arranged inside the combustion chamber for igniting and maintaining a combustion of the gas stream in said combustor.

18. A multi-fuel turbine according to claim 17, comprising a gas fuel supply and a liquid fuel supply in fluid connection with the reverse flow annular combustor, said gas fuel supply and said liquid fuel supply being switchable by a control unit in order to enable said multi-fuel turbine to be operated by said gaseous fuel and/or by said liquid fuel.

19. A method of combustion within a reverse flow annular combustor of a gas turbine, comprising the steps: injecting a liquid fuel into an air-blast atomizer and/or injecting a gaseous fuel into an inlet zone of said air-blast atomizer,feeding compressed air into said inlet zone of said air-blast atomizer, so that said fuels and said compressed air are mixed inside said air-blast atomizer and that a gas stream leaves said air-blast atomizer via an exit side and enters a combustion chamber of said reverse flow annular combustor, said exit side of said air-blast atomizer pointing in a tangential direction relative to said reverse flow annular combustor to create a main vortex flow in said combustion chamber,combusting said gas stream in a primary combustor zone of said combustion chamber,discharging an exhaust gas produced by said combusting in said combustion chamber onto blades of a turbine.

20. The method of claim 19, comprising the following step: switching from a first mode of operation where said air-blast atomizer is fed with said liquid fuel and compressed air into a second mode of operation where said air-blast atomizer is fed with said gaseous fuel and compressed air; orswitching from a second mode of operation where said air-blast atomizer is fed with said gaseous fuel and compressed air into a first mode of operation where said air-blast atomizer is fed with said liquid fuel and compressed air.

21. The method of claim 20, wherein said liquid fuel is selected from the group consisting of gasoline, kerosene, diesel oil, palm oil, liquefied natural gas, liquefied hydrogen.

22. The method of claim 20, wherein said gaseous fuel is selected from the group consisting of syngas, natural gas, flare gas.