Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23D—BURNERS
  • F23D17/00—Burners for combustion conjointly or alternatively of gaseous or liquid or pulverulent fuel
  • F23D17/002—Burners for combustion conjointly or alternatively of gaseous or liquid or pulverulent fuel gaseous or liquid fuel
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23C—METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN  A CARRIER GAS OR AIR 
  • F23C7/00—Combustion apparatus characterised by arrangements for air supply
  • F23C7/002—Combustion apparatus characterised by arrangements for air supply the air being submitted to a rotary or spinning motion
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23D—BURNERS
  • F23D11/00—Burners using a direct spraying action of liquid droplets or vaporised liquid into the combustion space
  • F23D11/10—Burners using a direct spraying action of liquid droplets or vaporised liquid into the combustion space the spraying being induced by a gaseous medium, e.g. water vapour
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23R—GENERATING COMBUSTION PRODUCTS OF HIGH PRESSURE OR HIGH VELOCITY, e.g. GAS-TURBINE COMBUSTION CHAMBERS
  • F23R3/00—Continuous combustion chambers using liquid or gaseous fuel
  • F23R3/02—Continuous combustion chambers using liquid or gaseous fuel characterised by the air-flow or gas-flow configuration
  • F23R3/04—Air inlet arrangements
  • F23R3/10—Air inlet arrangements for primary air
  • F23R3/12—Air inlet arrangements for primary air inducing a vortex
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23R—GENERATING COMBUSTION PRODUCTS OF HIGH PRESSURE OR HIGH VELOCITY, e.g. GAS-TURBINE COMBUSTION CHAMBERS
  • F23R3/00—Continuous combustion chambers using liquid or gaseous fuel
  • F23R3/28—Continuous combustion chambers using liquid or gaseous fuel characterised by the fuel supply
  • F23R3/286—Continuous combustion chambers using liquid or gaseous fuel characterised by the fuel supply having fuel-air premixing devices
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23C—METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN  A CARRIER GAS OR AIR 
  • F23C2900/00—Special features of, or arrangements for combustion apparatus using fluid fuels or solid fuels suspended in air; Combustion processes therefor
  • F23C2900/07002—Premix burners with air inlet slots obtained between offset curved wall surfaces, e.g. double cone burners
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23D—BURNERS
  • F23D2900/00—Special features of, or arrangements for burners using fluid fuels or solid fuels suspended in a carrier gas
  • F23D2900/11101—Pulverising gas flow impinging on fuel from pre-filming surface, e.g. lip atomizers

Definitions

• the present invention relates to a method and a fuel atomizer for atomizing a liquid fuel in a burner for gaseous and liquid fuel, wherein the burner develops low NO ⁇ emissions during dry combustion.
• the combustion of a lean fuel mixture reduces the NO ⁇ mixture in two ways. First of all, the burner operates under leaner conditions, which reduces the combustion temperature and the NO x formation. Secondly, fuel and air are efficiently mixed prior to com- bustion such that the local fuel-air mixture becomes more uniform, which results in a significant reduction of the NO x formation.
• Burners using the method of dry combustion are referred to as dry low-NO x burners.
• the principal fuels for gas turbines are natural gas and oil. It is desirable to be able to use for the same burner both gas and liquid fuel.
• the principal fuel of the burner is gas whereas liquid fuel is used as standby fuel. Since the burner of the gas turbine is designed for two types of fuel, the operation would be continued with oil, for example diesel oil, if the gas supply were to be interrupted.
• the fuel atomizer for liquid fuel is arranged separately from the fuel atomizer for gaseous fuel.
• a type of burner which is used for gas turbines and which provides low NO x emissions are burners based on the principle of vortex collapse.
• Such a type of burner is known under the term EV (Environmental) burner and is shown, for example, in the journal Modern Power Systems. Vol. 12. No. 5, May 1992, in an article entitled “Annular combustor will boost Deeside efficiency", pages 49-57.
• the EV burner also constitutes the prior art according to EP 0321809 Bl.
• Figure 1 in this patent shows an EV burner. This known burner is schematically shown in Figure 1 in the present application and is here designated 1.
• the burner is intended for liquid and gaseous fuel, the fuel being mixed in the burner with a combustion gas, preferably air 8.
• the liquid burner is supplied here without being premixed in a premixing zone prior to combustion.
• the EV burner 1 is largely designed as a conical shell 2 and 3, the cone being cut into halves in an axial section. This, of course, does not exclude that the cone may be cut into halves more than twice.
• Two cone halves 2 and 3, respectively, are moved in relation to each other in the radial direction. This results in the occurrence of two gaps 4 and 5 on either side of the cone, that is, along two opposite generatrices 6 and 7, respectively, of the cone.
• Air 8 is supplied to the cone from outside at the gaps 4 and 5 and flows inside the cone towards an outlet 12 at the widest part of the cone.
• Liquid fuel is supplied at the tip of the cone via a fuel injector 13 and gaseous fuel is supplied via a nozzle 9 arranged along the gaps 4 and 5. Because of the conical shape of the burner 1, a strong vortex of the fuel and the air is generated, the fuel and the air flowing towards the outlet 12 of the cone. At the outlet 12 of the cone, where the well-defined area increase suddenly ceases, the vortex collapses. Because of the intense mixing which takes place between the fuel and the air both in the generated vortex and in the powerful turbulence in the collapsed vortex, the local fuel-air mixture is uniform.
• the problem with the above-mentioned type of EV burner for both liquid and gaseous fuel is to attain a local uniform and lean fuel-air ratio in the mixture in order to attain a low value of the NO x emissions from the burner when liquid fuel is used.
• a further problem with the above-mentioned burner is that droplets of the liquid fuel which is supplied to the fuel mixture are too large.
• the large droplets have no time to evaporate completely before reaching the combustion zone, which means that a local uniform fuel-air ratio is not obtained.
• Still another problem to overcome is the location of the fuel atomizer in the burner for optimum distribution of the fuel in the burner, with a minimum risk of coking and a reduced risk of adhesion of the fuel to the shell surfaces.
• the present invention aims to solve the problems described above and comprises the features which are described in the characterizing part of a method according to claim 1 and of a fuel atomizer according to claim 5.
• the invention comprises a method for atomizing a liquid fuel in a burner for gaseous and liquid fuel, wherein the fuel is mixed with an air flow to a fuel mixture for combustion.
• the method of atomizing comprises arranging in the burner at least one straight fuel atomizer for injecting a fuel film for atomization.
• straight is meant that the nozzles of the fuel atomizer are placed on a straight line, that is to say, the nozzle is not, for example, circular.
• the atomization of the straight fuel film gives a high air-fuel ratio.
• the method comprises arranging a surplus fuel conduit for the liquid fuel to the fuel atomizer such that the fuel supplied to the fuel atomizer does not have time to be heated to such an extent that there is a risk of coking of the fuel. In the surplus fuel conduit, moderately heated fuel runs back to a service tank, possible via a cooler.
• the invention comprises a fuel atomizer for injec ⁇ ting the liquid fuel into a burner for gaseous and liquid fuel, wherein the fuel is mixed with a gas, preferably air, to a fuel mixture for combustion.
• the fuel atomizer comprises a body with a suitable design from the point of view of flow conditions, in order not to disturb the air flow or form any resistance to the air flow into the burner.
• the body compri ⁇ ses a fuel channel, an inlet, a discharge, at least one out ⁇ let, and a nozzle.
• the nozzle of the fuel atomizer is com- prised by an outer and an inner lip, whereby by outer and inner lip, respectively, are meant the positions of the lips in relation to the axis of the burner in the present inven ⁇ tion.
• the nozzle is a straight spraying nozzle for distri ⁇ bution of the fuel film.
• straight is meant that the opening of the spraying nozzle lies on a straight line.
• At least one outlet is arranged from the fuel chamber out into the nozzle. The outlet conducts the fuel from the fuel chamber out between the outer and the inner lip where a thin fuel film is formed on the inner lip.
• the inner lip releases the fuel film by the air flow in the burner passing the lips pulling along with it the film out into the air flow. In this way, the fuel is distributed and atomized in very small drop ⁇ lets - a process known as atomization - in the air flow and is evaporated because of the high air temperature prevailing.
• the outer lip is shorter than the inner lip and acts as pro ⁇ tection for the fuel film on the inner lip.
• Both the method and the fuel atomizer are used for a burner of the EV burner type, which, of course, does not exclude that the method and the fuel atomizer may be used for other types of burners as well.
• the EV burner is based on the principle of vortex collapse and comprises at least two parts of a conical shell. The parts are moved relative to each other in the radial direction so as to form at least two gaps along at least two opposite generatrices.
• the fuel atomizer for the liquid fuel and the surplus fuel conduit are arranged along the gaps.
• the fuel atomizer and the method of the invention for atomi ⁇ zing the fuel cause the liquid fuel to be distributed ato- mized in very small droplets in the air flow, which results in the droplets being evaporated completely before combustion is performed. This results in a local uniform and high air- fuel ratio in the fuel mixture, more than twice the ratio prevailing in conventional circular spraying nozzles.
• the air-fuel ratio is of the order of magnitude of 10 or more, by ratio being meant mass ratio.
• the fuel atomizer or fuel atomizers is or are arranged on the inner conical part along the above-mentioned gaps which extend along at least some of the generatrices of the cone such that the fuel atomizer distributes the fuel in the direction of the air flow tangentially to the shell of the cone.
• the fuel atomizer is arranged along the respective gap and extends from the opening of the cone towards the tip of the cone but not all the way to the tip of the cone so as to reduce the risk of fuel adhering to the surface of the shell.
• the fuel atomizer may consist of one single long nozzle or several smaller nozzles arranged one after the other along the respective gap. Normally, a fuel atomizer is arranged at each gap arranged along the generatrices of the cone parts.
• the air speed around the fuel atomizer is greater on the side of the fuel atomizer facing away from the centre of the cone than on the side facing the centre of the cone. This means that the air flow which pulls along with it the fuel film from the upper side of the inner lip is greater than the air flow on the lower side of the inner lip.
• the above-mentioned method and fuel atomizer permit the method with dry combustion developing low N0 X emissions to be applied with a good result during combustion of liquid fuel, and the disadvantages of water injection into the burner are avoided.
• the straight fuel atomizer is located somewhere in the actual air flow through the respec- tive gap such that the air flow flows on both sides of the fuel atomizer.
• Figure 1 shows an EV burner according to the prior art.
• Figure 2 shows a section A-A of Figure 1 of an EV burner with a fuel atomizer arranged according to the invention.
• Figure 3 shows a fuel atomizer according to the invention arranged in an EV burner seen from above according to section B-B in Figure 2.
• Figure 4 shows a fuel atomizer arranged in a gap between two shell parts.
• Figure 5 shows a fuel atomizer mounted together with the gas nozzle at the inlet of a gap.
• An EV burner 1 according to Figure 1 comprises two conical shell parts 2 and 3 which are arranged and displaced relative to each other in the radial direction so as to form the gaps 4 and 5 along two generatrices 6 and 7 on the shell of the cone.
• a fuel atomizer 21, see Figures 2 and 3 is associated with the inner conical shell part 3 , along the generatrix 6 thereof, at the interior of the gap 5.
• a fuel atomizer 21 is arranged along the gap 4. Since the EV burner 1 is symmetrical, the invention is described at one of the gaps 5 only in the embodiment.
• a gas nozzle 9 for supply ⁇ ing gaseous fuel 11 to the EV burner is associated with the outer conical shell part 2 at the gap 5.
• FIGS 2 and 3 show the fuel atomizer 21 arranged along a gap 5 in an EV burner 1.
• the fuel atomizer 21 comprises a body 22.
• the body 22 comprises a fuel chamber 23, an inlet 24, a discharge 25, at least one outlet 26, and a nozzle 27.
• the nozzle 27 comprises an outer lip 28 and an inner lip 29.
• the outer lip 28 is arranged opposite to the inner lip 29, and the outer lip 28 is shorter than the inner lip 29.
• the lips 28 and 29 are arranged along a straight line 33, which results in the fuel atomizer 21 being a straight fuel atomi ⁇ zer.
• a volume of liquid fuel larger than what the fuel atomizer 21 can distribute is supplied to the fuel chamber 23 via the inlet 24 and the superfluous fuel is conducted from the fuel chamber 23 via the discharge 25.
• the outlets 26 conduct the fuel from the fuel chamber 23 out into the nozzle 27.
• the fuel is distributed in very small droplets 32 in the air flow and is evaporated in the vortex zone z of the burner, which zone is defined as the space to which the fuel mixture is passed after passage through any of the gaps 4, 5 and up to the very combustion zone at the outlet 12 of the burner. Since the speed of the air flow F is greater on the upper side 30 of the inner lip 29 than on the lower side 31 thereof, while at the same time the air flow F must follow the curved wall 2, the droplets 32 are deflected in a path towards the interior of the axis of the cone.
• the fuel mixture is set in a vortex motion in the vortex zone z while at the same time the mixture flows along the axis of the burner towards the burner outlet 12.
• the vortex zone exhibits an increasing cross section towards the outlet 12.
• the straight fuel atomizer is placed in the gap 4 itself as shown in Figure 4, or is integrated with the gas nozzle 9 according to Figure 5.
• the fuel atomizer 21 arranged at the gap 4 is designed in a manner corresponding to that of the fuel atomizer described above.
• the fuel atomizer 21 may, of course, be arranged in a number greater than two, for example when more than two gaps 4, 5 occur in a burner.

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Cited By (13)

Citations (6)

• 1993
  • 1993-12-17 SE SE9304194A patent/SE9304194L/sv not_active Application Discontinuation
• 1994
  • 1994-12-16 WO PCT/SE1994/001213 patent/WO1995016881A1/en active Application Filing

Patent Citations (6)

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