Method for combusting a fuel, and combustion device

Abstract

A method for determining fatigue lifetime consumption of an engine component, by defining a reference thermal load cycle, the reference thermal load cycle being characterized by a reference load cycle amplitude and a reference load cycle time, and determining a reference load cycle lifetime consumption. The method includes measuring a temperature of the engine component, determining a thermal load cycle based upon the temperature measurement, determining a load cycle amplitude, determining a load cycle time, relating the load cycle time to the reference load cycle time, thereby determining a load cycle time factor, relating the load cycle amplitude to the reference load cycle amplitude, thereby determining a load cycle amplitude factor, combining the load cycle time factor and the load cycle amplitude factor into a combined load cycle factor for determining a load cycle lifetime consumption.

Claims

1. A method for combusting a fuel, the method comprising: providing a first oxidizer mass flow; providing a second oxidizer mass flow; discharging a fuel mass flow into the first oxidizer mass flow thereby providing a fuel/oxidizer mass flow; apportioning the fuel mass flow such as to achieve an overstoichiometric ratio of the fuel mass flow related to the first oxidizer mass flow; initiating a combustion of the fuel mass flow with the first oxidizer mass flow, thereby generating a flow of combustion products, wherein the flow of combustion products includes residual combustible components; providing the flow of combustion products to at least one first duct of a heat exchange appliance; providing the second oxidizer mass flow to at least one second duct of the heat exchange appliance, whereby the flow of combustion products is provided in a heat exchange relationship with the second oxidizer mass flow through the heat exchange appliance exchanging heat between the flow of combustion products and the second oxidizer mass flow, thereby heating the second oxidizer mass flow and cooling the flow of combustion products; discharging the flow of combustion products from the at least one first duct of the heat exchange appliance at a downstream end of the heat exchange appliance; discharging the second oxidizer mass flow from the second duct of the heat exchange appliance at a downstream end of the heat exchange appliance; combusting the residual combustible components provided in the flow of combustion products in a presence of the second oxidizer mass flow; discharging the flow of combustion products and the second oxidizer mass flow such as to avoid intermixing of the flow of combustion products and the second oxidizer mass flow, thus providing an interface between the second oxidizer mass flow and the flow of combustion products downstream of the heat exchange appliance; and combusting the residual combustible components provided in the flow of combustion products at the interface between the second oxidizer mass flow and the flow of combustion products.

2. The method according to claim 1, comprising: apportioning the fuel mass flow and the first and second oxidizer mass flows such that an overstoichiometric fuel/air ratio is achieved when relating the fuel mass flow to the first oxidizer mass flow, and an understoichiometric fuel/air ratio is achieved when relating the fuel mass flow to the combined first and second oxidizer mass flows.

3. A method for combusting a fuel, the method comprising: providing a first oxidizer mass flow; providing a second oxidizer mass flow; discharging a fuel mass flow into the first oxidizer mass flow thereby providing a fuel/oxidizer mass flow; apportioning the fuel mass flow such as to achieve an overstoichiometric ratio of the fuel mass flow related to the first oxidizer mass flow; initiating a combustion of the fuel mass flow with the first oxidizer mass flow, thereby generating a flow of combustion products, wherein the flow of combustion products includes residual combustible components; providing the flow of combustion products to at least one first duct of a heat exchange appliance; providing the second oxidizer mass flow to at least one second duct of the heat exchange appliance, whereby the flow of combustion products is provided in a heat exchange relationship with the second oxidizer mass flow through the heat exchange appliance; exchanging heat between the flow of combustion products and the second oxidizer mass flow, thereby heating the second oxidizer mass flow and cooling the flow of combustion products; discharging the flow of combustion products from the at least one first duct of the heat exchange appliance at a downstream end of the heat exchange appliance; discharging the second oxidizer mass flow from the second duct of the heat exchange appliance at a downstream end of the heat exchange appliance; combusting the residual combustible components provided in the flow of combustion products in a presence of the second oxidizer mass flow; and wherein the second oxidizer mass flow exceeds the first oxidizer mass flow.

4. The method according to claim 3, comprising: controlling the first oxidizer mass flow in order to control a ratio of the fuel mass flow to the first oxidizer mass flow.

5. The method according to claim 3, comprising: adding a second fuel mass flow to the second oxidizer mass flow, thereby providing a second fuel/oxidizer flow, wherein the second fuel mass flow is added upstream a downstream end of the heat exchange appliance or upstream the heat exchange appliance.

6. The method according to claim 5, comprising: apportioning the second fuel mass flow such as to achieve an understoichiometric fuel/oxidizer ratio for both the fuel/oxidizer ratio of the second fuel/oxidizer flow as well as for a combined fuel/oxidizer mass flow ratio of a combined fuel mass flow which includes the fuel mass flow added to the first oxidizer mass flow and the second fuel mass flow, related to a combined oxidizer mass flow including the first oxidizer mass flow and the second oxidizer mass flow.

7. The method according to claim 5, comprising: performing an addition of the second fuel mass flow such as to provide a lean premixed second fuel/oxidizer flow at the downstream end of the heat exchange appliance.

8. The method of claim 3, wherein the second oxidizer mass flow is 4 to 20 times the first oxidizer mass flow.

9. The method of claim 3, wherein the second oxidizer mass flow is at least 10 times the first oxidizer mass flow.

10. The method of claim 3, wherein an equivalence ratio of the fuel mass flow to the first oxidizer mass flow is between 1.5 and 3.

11. The method of claim 3, comprising: discharging the flow of combustion products and the second oxidizer mass flow such as to avoid intermixing of the flow of combustion products and the second oxidizer mass flow, thus providing an interface between the second oxidizer mass flow and the flow of combustion products downstream the heat exchange appliance; and combusting the residual combustible components provided in the flow of combustion products at the interface between the second oxidizer mass flow and the flow of combustion products.

12. The method of claim 3, comprising: apportioning the fuel mass flow and the first and second oxidizer mass flows such that an overstoichiometric fuel/air ratio is achieved when relating the fuel mass flow to the first oxidizer mass flow, and an understoichiometric fuel/air ratio is achieved when relating the fuel mass flow to the combined first and second oxidizer mass flows.

13. A combustion device for combusting a fuel, the combustion device comprising: means for providing a first fluid flow; fuel discharge means for discharging a fuel flow into the first fluid flow; a first combustion zone adapted and configured to stabilize a flame and being disposed downstream the fuel discharge means and being in fluid communication with the means for providing the first fluid flow at an upstream end of the first combustion zone; a heat exchange appliance, said heat exchange compliance having at least one first duct and at least one second duct and the heat exchange appliance being configured to enable an exchange of heat between a fluid provided in the at least one first duct that comprises combustion products having residual combustible components and a fluid provided in the at least one second duct, the at least one first duct of the heat exchange appliance, at an upstream end thereof being in fluid communication with the first combustion zone at a downstream end of the combustion zone; a means for providing a second fluid flow to an upstream end of the at least one second duct of the heat exchange appliance; and a second combustion zone being provided downstream the heat exchange appliance, wherein the at least one first duct and the at least one second duct are provided in fluid communication with the second combustion zone at a downstream end of the respective duct; the second combustion zone configured so that a flow of the combustion products and the second fluid flow are discharged so as to avoid intermixing of the flow of combustion products and the second fluid flow to provide an interface between the second fluid flow and the flow of combustion products downstream of the heat exchange appliance to combust the residual combustible components at the interface between the second fluid flow and the flow of combustion products.

14. The combustion device according to claim 13, wherein the at least one first duct and the at least one second duct are at least at a downstream end of the respective duct arranged parallel to each other such as to avoid intermixing of a flow of the fluid provided in the at least one first duct and the flow of the fluid provided in the at least one second duct upon being discharged from the ducts.

15. The combustion device according to claim 13, wherein the heat exchange appliance comprises: a heat pipe.

16. The combustion device according to claim 13, comprising: at least one control means for controlling at least one of a mass flow of the fluid provided in the at least one first duct and/or a mass flow of the fluid provided in the at least one second duct.

17. The combustion device according to claim 13, comprising: at least one second fuel discharge means provided and configured to discharge a second fuel into the fluid provided in the at least one second duct.

18. The combustion device according to claim 17, wherein the at least one second fuel discharge means and the means for providing the second fluid flow are provided, adapted and configured to provide a premixed flow of the fluid provided in the at least one second duct and the second fuel at the downstream end of the heat appliance device.

19. A gas turbine engine comprising: gas turbine; and at least one combustion chamber having a combustion device according to claim 13.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The subject matter of the present disclosure is now to be explained in more detail by means of selected exemplary embodiments shown in the accompanying drawings. The figures show

(2) FIG. 1 a first exemplary embodiment of a combustion device according to the present disclosure, in which a method as disclosed above is performed;

(3) FIG. 2 a cross sectional view of the heat exchange appliance of the combustion device of FIG. 1;

(4) FIG. 3 a second exemplary embodiment of a combustion device according to the present disclosure, in which a method as disclosed above is performed;

(5) FIG. 4 a cross sectional view of the heat exchange appliance of the combustion device of FIG. 3, and

(6) FIG. 5 a third exemplary embodiment of a combustion device according to the present disclosure comprising heat pipes, in which a method as disclosed above is performed.

(7) It is understood that the drawings are highly schematic, and details not required for instruction purposes may have been omitted for the ease of understanding and depiction. It is further understood that the drawings show only selected, illustrative embodiments, and embodiments not shown may still be well within the scope of the herein disclosed and/or claimed subject matter.

EXEMPLARY MODES OF CARRYING OUT THE TEACHING OF THE PRESENT DISCLOSURE

(8) FIG. 1 shows a first exemplary embodiment of a combustion device as lined out above, and illustrating an exemplary mode of performing a method as herein disclosed. Combustion device 1 comprises front burner 11 and first combustion zone 12 disposed downstream thereof. A first fluid flow, or first oxidizer mass flow 51, is provided to front burner 11 through an appropriate means. The specific implementation of said means is not relevant to the present explanations. First oxidizer mass flow 51 may for instance be a portion of a compressed air mass flow provided by a compressor in a gas turbine engine. First oxidizer mass flow 51 is guided, for instance, through swirl generating means 110. A fuel mass flow 52 is discharged into first oxidizer mass flow 51. A combined flow of first oxidizer mass flow 51 and fuel mass flow 52 enters first combustion zone 12. First combustion zone 12 is in this instance provided as a cross sectional jump. Generally, suitable means are provided to allow stabilization of a flame 53 in first combustion zone 12. Any suitable means the skilled person is familiar with may be provided. Fuel mass flow 52 is combusted in first oxidizer mass flow 51 in flame 53. Front burner 11 and first combustion zone 12 may be provided to provide flame 53 as a diffusion flame, a premix flame, or any hybrid type thereof. Fuel mass flow 52 and first oxidizer mass flow 51 are apportioned such as to provide an overstoichiometric fuel/oxidizer ratio. That is, the mass flow of oxidizing agent in first oxidizer mass flow 51, i.e. for instance the mass flow of oxygen provided in an air mass flow, is insufficient to completely burn fuel mass flow 52. Accordingly, a peak combustion temperature in flame 53 is significantly lower than a stoichiometric combustion temperature. Thus, and due to the lack of oxidizing agent, the thermally induced formation of pollutants, such for instance thermally induced nitric oxides formation, is significantly reduced when compared to a combustion under stoichiometric conditions, or even in a combustion with a surplus of oxidizing agent. The reasons are, as will be readily appreciated, the lower temperatures for initiating thermally induced nitrogen oxidation, arid the lack of oxidizing agent available for the formation of nitric oxides. Combustion products 54 from the combustion of fuel mass flow 52 in first oxidizer mass flow 51 thus comprise residual combustible components, such as, in the case of the combustion of hydrocarbons, unburnt or incompletely burnt hydrocarbons and carbon monoxide, and/or other residual combustibles. Downstream of first combustion zone 12 heat exchange appliance 13 is provided. As is illustrated in connection with FIG. 2, showing a cross section along A-A in FIG. 1, heat exchange appliance 13 in the present example comprises a core 130, first ducts 131 of the heat exchange appliance, and second ducts 132 of the heat exchange appliance. Walls separating first ducts 131 and second ducts 132 are convoluted or lobed to enlarge the heat exchange surface between fluids provided in first and second ducts. As is known to the skilled person, the walls may further comprise structures to further enhance heat transfer. Ducts 131, 132 may extend spirally or otherwise wound around core 130. First combustion zone 12 is in fluid communication with first ducts 131 at an upstream end of the heat exchange appliance and receives the flow of combustion products 54 from first combustion zone 12. A second oxidizer mass flow 55 is provided to second ducts 132 of heat exchange appliance 13 at an upstream end thereof. First and second oxidizer mass flows 51, 55 may be mass flows of a common oxidizer mass flow, such as for instance a compressed air mass flow provided by a compressor of a gas turbine engine. Second oxidizer mass flow 55 will generally be larger than first oxidizer mass flow 51. A combined fuel/oxidizer mass flow in combustion device 1 may be understoichiometric, that is, provide an oxidizing agent surplus, as will be lined out below. Second oxidizer mass flow 55 and the flow of combustion products 54 flow through the respective ducts in heat exchange appliance 13 in a heat exchange relationship. Generally, due to the combustion in first combustion stage 12, the temperature of combustion products 54 may be assumed to be higher than the temperature of the second oxidizer mass flow 55. Accordingly, the flow of combustion products 54 will cool down and the second oxidizer mass flow 55 will heat up in heat exchange appliance 13. At a downstream end of heat exchange appliance 13 the heated second oxidizer mass flow and the cooled flow of combustion products are discharged from the ducts of the heat exchange appliance at a downstream end of the heat exchange appliance, and into a second combustion zone 14 disposed at a downstream end of heat exchange appliance 13. The flow of combustion products 54 and the second oxidizer mass flow 55 are discharged at least essentially without crosswise, mutually penetrating, velocity components, or at least largely parallel to each other. Thus, rapid large scale intermixing of the flows is avoided. The discharged flows form the heat exchange appliance form an interface layer between them. The residual combustible components comprised in the flow of combustion products 54 are combusted with oxidizing agent from the second oxidizer mass flow at the flow interfaces between the discharged cooled combustion products and the discharged heated second oxidizer mass flow in flames 56. Flames 56 are essentially located downstream first ducts 131. Said combustion, due to the lack of intermixing between the fluids discharged from heat exchange appliance 13, takes place in a diffusion combustion mode, providing for a superior combustion stability even at overall lean, strongly understoichiometric conditions. Due to the surplus of oxidizer provided in the second oxidizer mass flow not ail the oxidizer provided in the second oxidizer mass flow will participate in the combustion process in flames 56. In fact, as will be lined out below, only a minor fraction of the second oxidizer mass flow will participate in the combustion in flames 56. The heat from the combustion in first combustion zone 12 has however been dispersed from the flow of combustion products to the sum of the mass flow of combustion products plus the second oxidizer mass flow. Thus, part of the heat from the combustion in first combustion zone 12 is provided in fluid which does not participate in the combustion in flames 56. In turn, not all the heat form the combustion of fuel mass flow 52 is present in the combustion in flames 56 in the second combustion zone 14. In turn, although flames 56 are diffusion flames, thus locally combusting at stoichiometric conditions, the peak temperature in flames 56 is reduced when compared to the combustion of fuel mass flow 52 in a diffusion combustion mode in one single step. Consequently, the combined thermally induced formation of nitric oxides in flames 53 and 56, or in first and second combustion zones 12 and 14, respectively, is significantly reduced when compared to a diffusion combustion in one single stage, while still providing the superior combustion stability and part load operation behavior of a diffusion flame.

(9) Second oxidizer mass flow 55 may be typically 4 to 20 times the first oxidizer mass flow, and in more specific instances at least approximately 10 times the first oxidizer mass flow. The equivalence ratio of the fuel mass flow related to the first oxidizer mass flow may be larger than or equal to 1.5 and smaller than or equal to 3, and in particular may be larger than or equal to 1.8 and smaller than or equal to 2.5, and may in a specific instance be at least approximately 2, or about 2. In order to maintain the equivalence ratio in first combustion stage 12 in said range over a large load range of the combustion device, that is a large range of fuel mass flow 52, it is conceivable to control first oxidizer mass flow 51. The overall equivalence ratio, resulting when relating fuel mass flow 52 to the sum of the first and second oxidizer mass flow, may consequently be 0.5 or less, and, depending on the state of operation, 0.25 or less. Consequently, at least 50% of second oxidizer mass flow 55 will not participate in the combustion, and consequently a significant share of the heat released form combustion and transferred to second oxidizer mass flow 55 in heat exchange appliance 13 is not present in the flame, resulting in the lower peak flame temperature mentioned above. It may be said that the diffusion flames downstream of heat exchange appliance 13 are cooled in transferring heat released in first combustion zone 12 to second oxidizer mass flow 55 in heat exchange appliance 13.

(10) A further embodiment of a combustion device according to the present disclosure, and suitable for carrying out the method as disclosed above, is illustrated in connection with FIGS. 3 and 4. In substance, the combustion device differs from the one lined out in connection with FIGS. 1 and 2 in a different embodiment of heat exchange appliance 13. FIG. 4, which is a section along B-B of FIG. 3, illustrates a heat exchange appliance 13 which is provided with a first, inner duct 131 and a second, outer duct 132. The flow of combustion products 54 from first combustion zone is provided through inner duct 131, and flows through first, inner duct 131 in a heat exchange relationship with a second oxidizer mass flow 65 which is provided through second, outer duct 132. As in the example provided above, the walls separating first duct 131 from second duct 132 are convoluted or lobed to enhance the heat exchange surface. First duct 131 exhibits a generally star-shaped cross section. Again, further elements further enhancing heat transfer between the walls and a fluid flowing along the wall may be provided in a manner known to the skilled person. Also, as in the example provided above, a fuel mass flow 52 and a first oxidizer mass flow are apportioned such as to provide a rich, overstoichiometric combustion in first combustion zone 12. Combustion products 54 thus comprise, as in the example provided above, residual combustibles. While flowing through heat exchange appliance 13, the flow of combustion products 54 is cooled down, while the second oxidizer mass flow 55 is heated. When heated second oxidizer mass flow 55 and combustion products 54 are discharged into second combustion zone 14 at a downstream end of heat exchange appliance 13, again rapid intermixing of the flows is avoided. The combustible residuals comprised in the flow of combustion products 54 are combusted in a diffusion flame 56 at an interface between the discharged combustion products and the discharged second oxidizer mass flow. It will be appreciated that a single generally star-shaped diffusion flame 56 will result in second combustion zone 56. It may be assumed that the heat exchange appliance shown in the embodiment of FIGS. 3 and 4 yields a lower total pressure loss when compared to that of the embodiment of FIGS. 1 and 2. However, the heat exchange surface per unit length of heat exchange appliance 13 is smaller when compared to the embodiment of FIGS. 1 and 2. Moreover, the fluid interface between the discharged flow of combustion products and the discharged second oxidizer mass flow in second combustion zone 14 may be smaller at a comparable flow cross section. Hence, a larger distance may be required in second combustion zone 14 to provide a complete burn-out of the combustible residuals comprised in the flow of combustion products. These facts need to be considered when designing the combustion device.

(11) In a further embodiment shown in connection with FIG. 5 a further embodiment of a heat exchange appliance is shown. A first duct 131 of heat exchange appliance 13, to which the flow of combustion products 54 from first combustion zone 12 is provided, and a second duct 132 of heat exchange appliance 13, to which the second oxidizer mass flow is provided, are separated by a wall 15. Second duct 132 may in particular be provided as an annular duct. Heat exchange, however, is not primarily effected by heat conduction through wall 15, but makes use of heat pipe technology, which is generally known to the skilled person. Heat pipes 16 are provided extending from within first duct 131 to within second duct 132, thus enabling the transfer of heat from the flow of combustion products to the second oxidizer mass flow. Second fuel discharge devices 17 are provided in the second oxidizer mass flow and are provided to discharge a second fuel mass flow 57 into second oxidizer mass flow 55. Second fuel discharge devices 17 are arranged and configured to disperse second fuel 57 as finely and uniform into second oxidizer mass flow 55 as possible. At least the sections of heat pipes 16 which extend within second duct 132 are provided as a swirler and/or vortex generating device, such that the second fuel mass flow 57 becomes uniformly admixed with second oxidizer mass flow 55, and a vortex flow is generated in second duct 132. At the transition location from heat exchange appliance 13 to second combustion zone 14 a cross sectional jump is provided. The vortex flow emanating from second duct 132 bursts open and provides a flame stabilization region. Further, as in the examples provided above, a diffusion flame 56, combusting the residuals combustibles in the flow of combustion products 54, is formed at a fluid interface between the second oxidizer mass flow and the flow of combustion products. Second fuel mass flow 57, which is provided in a premixed vortex flow with second oxidizer mass flow 55, is combusted in a premix flame 58 which is induced by the vortex breakdown upon discharge of the premix vortex flow from heat exchange appliance 13, or second duct 132 thereof, respectively, and into second combustion zone 14, and further due to the cross sectional jump at the transition from heat exchange appliance 13 to second combustion zone 14. Premix flame 58 is supported and stabilized, in particular at low equivalence ratios of the premixed fuel/oxidizer mixture, by diffusion flame 56.

(12) It will be appreciated that the combustion devices as lined out in connection with FIGS. 1 through 4 may, in the manner of the device of FIG. 5, be equipped with fuel discharge devices provided for discharging a fuel into the second oxidizer mass flow, and may accordingly be operated with a premix flame in the second combustion zone from a premixed fuel/oxidizer flow from the second oxidizer mass flow and a second fuel mass flow discharged therein, and further with a diffusion flame wherein combustible residuals in the combustion products from the first combustion zone are combusted with oxidizing agent from the second oxidizer mass flow. Any combustion device of the type herein disclosed, and the lined out combustion method, may be used as a piloting stage for a premix burner, for instance, but not limited to, a premix burner of the type initially mentioned. It will be readily appreciated that in one instance the combustion process, or the combustion device, respectively, including, in case a second fuel mass flow is discharged into the second oxidizer mass flow, the premix flame therefrom, may serve as the piloting stage supporting the premix combustion of the premix burner, at least at low premix burner fuel/oxidizer mass flow ratios. In other instances, the second oxidizer mass flow may be provided as the oxidizer mass flow of a main premix burner, and the diffusion flame combusting the combustible residuals from the first combustion stage may serve as the supporting piloting stage. As will further be readily appreciated, the method and combustion device herein disclosed allow for providing a supporting piloting operation of a premix burner with significantly lower nitric oxides emissions penalties when compared to a piloting diffusion combustion of a piloting fuel mass flow in one single stage.

(13) While the subject matter of the disclosure has been explained by means of exemplary embodiments, it is understood that these are in no way intended to limit the scope of the claimed invention. It will be appreciated that the claims cover embodiments not explicitly shown or disclosed herein, and embodiments deviating from those disclosed in the exemplary modes of carrying out the teaching of the present disclosure will still be covered by the claims.

LIST OF REFERENCE NUMERALS

(14) 1 combustion device

(15) 11 front burner

(16) 12 first combustion zone

(17) 13 heat exchange appliance

(18) 14 second combustion zone

(19) 15 wall

(20) 16 heat pipe

(21) 17 second fuel discharge device

(22) 51 first fluid flow, first oxidizer mass flow

(23) 52 fuel mass flow

(24) 53 flame

(25) 54 combustion products, flow of combustion products

(26) 55 second oxidizer mass flow

(27) 56 flame, diffusion flame

(28) 57 second fuel, second fuel mass flow

(29) 58 flame, premix flame

(30) 110 swirl generating means

(31) 130 core of heat exchange appliance

(32) 131 first duct of heat exchange appliance

(33) 132 second duct of heat exchange appliance