EP1439349A1 - Combustion method and burner for carrying out the method - Google Patents

Abstract

The combustion process involves burning the fuel-air mixture flowing through a flow channel (13) in a first combustion stage in a catalytic converter (15), downstream of which the fuel is mixed with the exhaust from the converter. In a second stage, this mixture is burned, producing a homogeneous flame (17) by self-ignition. The flame is passed through aerodynamic stabilizing devices (16, 19).

Description

TECHNICAL AREA

The present invention relates to the field of combustion technology. It relates to a combustion process according to the preamble of claim 1 and a burner to carry out the process.

STATE OF THE ART

Catalytic combustion is a process that can be applied to gas turbines to increase the stability of the combustion process and reduce emissions (see, for example, US-B1-6,339,925). Limits in the material load and operating conditions require that the catalysts used convert only a part (typically up to 60%) of the total fuel flowing through the burner. The resulting gas temperature may therefore not be increased enough to burn the fuel remaining at the outlet of the catalyst (a homogeneous mixture of fuel O ₂ , N ₂ , CO, CO ₂ and H ₂ O at temperatures between 600 ° C and 950 ° C) stabilize thermally. Aerodynamic stabilization is therefore necessary.

A simple solution is a sudden expansion downstream from the catalyst to use, with recirculation zones at the corners of the extension effect anchoring (see e.g. US-A-5,626,017). This However, technology only works at higher temperatures at the catalyst outlet. However, if stronger dynamic stabilization is needed, it can through the formation of highly turbulent currents that happen Favor vortex breakdown. In US-A-5,433,596 a double-cone burner according to the prior art is described, which creates such a breakdown of the vertebra. A number of others Configuration as e.g. in US-A-5,588,826 achieve this Aim also. However, such a large swirl requires comparatively complex devices that cause significant pressure drops.

A simplified vortex generator element, also known as a SEV vortex generator is referred to and by reduced pressure losses distinguished has been disclosed in US-A-5,577,378. It has proven to be suitable proven for sequential combustion or combustion with afterburning. The effect of the device is based on an exhaust gas temperature at the outlet of the first burner, which is above the autoignition temperature of the im second burner injected fuel; the combustion chamber for afterburning is a burnerless room with a number of vortex generating elements, the purpose of which is to mix the second stage fuel with the Mix exhaust gas of the first stage before auto-ignition. The degree of Circulation and the shape of the axial velocity profile can be determined by the Choice of the geometric parameters of the vortex generating element (length, Height, flow angle) can be tailored to the needs and can be in In extreme cases, even lead to a free-standing vertebral collapse like him sometimes observed in planes with delta wings at large angles of attack becomes.

In the above US-A-5,626,017 is a combustor for a gas turbine with a two-stage, sequential combustion, in which in the first stage Fuel / air mixture generated in a mixer completely in a catalytic converter is burned. The exhaust gas emerging from the catalytic converter has a comparative one high temperature from 800 ° C to 1100 ° C. Behind the exit of the Vortex generators are arranged on the catalyst, as exemplified in Fig. 1 of the present application. The Vortex generating elements create a turbulent flow into which then fuel is injected downstream. The resulting exhaust gas / fuel mixture then ignites itself and forms a flame front, aerodynamically by means of a step-like cross-sectional expansion in the flow channel is stabilized. The vortex generating elements come exclusively here the function too, the mixing of exhaust gas and injected fuel to transport. The flame front, on the other hand, is stabilized by the Cross-sectional expansion causes.

The situation is different with a two-stage burner configuration, in which the Fuel / air mixture is not completely burned in the first stage, but the exhaust gas from the catalyst contains a portion of unburned fuel and at the same time a significantly reduced outlet temperature (e.g. 600 ° C to 950 ° C) having. Since in this case no additional fuel is injected in the second stage and accordingly not mixed with the exhaust gas from the catalyst must be in terms of flow technology and especially in relation a different situation on the stabilization of the flame front.

PRESENTATION OF THE INVENTION

It is an object of the invention to use a two-stage combustion process Catalyst in the first combustion stage indicate which one is simple and safe is to be carried out and leads to lower pressure losses, as well as a burner to specify to carry out the procedure.

The object is achieved by the entirety of the features of claims 1 and 7. The essence of the invention is in a combustion in which in the second combustion stage of unburned fuel from the first, with a Combustion-equipped combustion stage, which is burned in the second stage to generate aerodynamically stabilized homogeneous flame by the fuel-containing exhaust gas from the catalyst between the outlet the catalyst and the homogeneous flame is passed through devices, which aerodynamically stabilize the homogeneous flame.

According to a preferred embodiment of the invention are considered to be aerodynamic stabilizing devices used vortex generating elements, which are arranged at the outlet of the catalyst.

According to a preferred development of this embodiment, it is considered aerodynamic stabilizing device additionally a step-like extension in Flow channel uses which between the vortex generating elements and the homogeneous flame is arranged.

In particular, the exhaust gas at the outlet of the catalyst contains, in addition to the unburned fuel, O ₂ , N ₂ , CO, CO ₂ and H ₂ O, exits the catalyst at a flow rate of less than or equal to 50 m / s and has a temperature between 600 ° C and 950 ° C.

It is also conceivable that the exhaust gas downstream of the catalyst in one Bypass is added to the fuel passing by on the outside of the catalyst.

Finally, it is conceivable that H ₂ / CO from a fuel-rich catalytic pilot burner is present in the medium flowing through the flow channel.

A preferred embodiment of the burner according to the invention is thereby characterized that additionally downstream of the vortex generating elements a step-like expansion of the flow channel is provided.

Furthermore, it is advantageous if the formation of the vortex generating elements depends on whether the vortex generating elements are mainly a mixture or cause a breakdown of vertebrae.

BRIEF EXPLANATION OF THE FIGURES

Fig. 1

in einer perspektivischen Darstellung ein für die erfindungsgemässe Lösung einsetzbares Wirbelerzeugungselement, wie es aus dem Stand der Technik bei SEV-Brennern (siehe die US-A-5,577,378) bereits bekannt ist;

Fig. 2

im schematisierten Längsschnitt einen Brenner gemäss einem ersten bevorzugten Ausführungsbeispiel der Erfindung; und

Fig. 3

in einer zu Fig. 2 vergleichbaren Darstellung ein zweites bevorzugtes Ausführungsbeispiel für einen erfindungsgemässen Brenner.

The invention will be explained in more detail below on the basis of exemplary embodiments in connection with the drawing. Show it

Fig. 1

a perspective view of a vortex generating element that can be used for the solution according to the invention, as is already known from the prior art for SEV burners (see US Pat. No. 5,577,378);

Fig. 2

in schematic longitudinal section a burner according to a first preferred embodiment of the invention; and

Fig. 3

in a representation comparable to FIG. 2, a second preferred exemplary embodiment for a burner according to the invention.

WAYS OF CARRYING OUT THE INVENTION

• eine ausreichende Flammenstabilisierung unabhängig von der Ausgangstemperatur am Katalysator erreicht wird, so dass ein Betrieb auch möglich ist, wenn die Ausgangstemperatur am Katalysator niedrig ist;
• der Druckabfall minimiert ist; und
• zum Eingang der Turbine hin vergleichmässigte Strömungs- und Temperaturfelder erzeugt werden, die von der verstärkten Mischung der Wirbelströmungen profitieren.

It is proposed to use so-called SEV vortex generators in order to aerodynamically stabilize the homogeneous flames, particularly with regard to the catalytic burner. The result of this method is that:

• sufficient flame stabilization is achieved regardless of the initial temperature at the catalytic converter, so that operation is also possible when the initial temperature at the catalytic converter is low;
• the pressure drop is minimized; and
• At the entrance to the turbine, even flow and temperature fields are generated, which benefit from the increased mixing of the vortex flows.

The use of SEV vortex generation elements is also advantageous because for these elements already extensive experience regarding their interpretation (regarding cooling, fatigue, flame position, pulsations, speed and temperature distributions) are present in high-temperature burners have been made with afterburning, and directly on burners with catalytic Elements can be applied.

The wedge-shaped shown in Fig. 1 and abutting a combustion chamber wall 11 or tetrahedral SEV vortex generating element 10, which in US-A-5,577,378 is particularly suitable for use with the present Solution. The degree of circulation and the shape of the axial velocity profile by suitable choice of parameters (length L, height h, Inlet angle α, and the angle ) derived from these three quantities Desire to be set. Depending on the exact requirements these parameters can be set so that only one mixture (lowest Pressure drop) or a mixture and a collapse of the vertebrae (higher Pressure loss due to the formation of a recirculation zone in the wake) results. In any case, there will be a pair of counter-rotating flow vortices generated.

• Eine minimale Zirkulation wird bei einem Katalysator benötigt, der Abgase mit den höchsten Temperaturen (ungefähr 900-950°C) erzeugt.
• Eine maximal Zirkulation und ein Zusammenbruch der Wirbel ist erforderlich, wenn die Austrittstemperatur am Katalysator am niedrigsten ist (ungefähr 600°C).
• Für den Fall, dass die Zusammensetzung des Katalysator-Abgases ungleichmässig ist, dienen die Wirbelerzeugungselemente dazu, vor der Selbstzündung einen hohen Grad an Vormischung zu erreichen.
• Der Katalysator kann so ausgelegt werden, dass er eine gewisse Menge an Syngas (H₂ und CO) produziert. Die höhere Reaktivität dieser Gase verringert das Ausmass der benötigten aerodynamischen Stabilisierung. Allgemeiner gesagt bestimmt der Brennstoffanteil im Abgas des Katalysators die genaue Anforderung and die aerodynamische Stabilisierung.

2 shows a configuration of a burner 12 with a flow channel 13 extending along an axis 18. A catalyst 15 is arranged in the flow channel 13. The flow 14 of a fuel / air mixture enters the catalytic converter 15 from the left. The fuel is partially burned in the catalytic converter 15. At the outlet of the catalytic converter 15, an exhaust gas stream then emerges which contains, in addition to the unburned fuel, for example O ₂ , N ₂ , CO, CO ₂ and H ₂ O. The composition of the exhaust gas is very even because of the good mixture. The temperatures of the exhaust gas vary between 600 ° C and 950 ° C. The flow velocity is typically less than or equal to 50 m / s. Vortex generating elements 16 of the shape shown in FIG. 1 are arranged downstream of the catalytic converter 15. The vortex generating elements 16 are designed in such a way that there is sufficient aerodynamic stabilization such that a homogeneous flame 17 is stably located in the position shown in FIG. 2. The exact design of the vortex generating elements 16 depends on the operating properties of the catalytic converter 15:

• Minimal circulation is required with a catalytic converter that produces exhaust gases with the highest temperatures (approximately 900-950 ° C).
• Maximum circulation and breakdown of the vortices is required when the catalyst exit temperature is the lowest (approximately 600 ° C).
• In the event that the composition of the catalytic converter exhaust gas is non-uniform, the vortex generating elements serve to achieve a high degree of premixing before the auto-ignition.
• The catalyst can be designed to produce a certain amount of syngas (H ₂ and CO). The higher reactivity of these gases reduces the level of aerodynamic stabilization required. More generally speaking, the proportion of fuel in the exhaust gas of the catalytic converter determines the exact requirement and the aerodynamic stabilization.

In cases where maximum aerodynamic stabilization is desirable is, the vortex generating elements can be designed so that the homogeneous flames are prevented from returning to the elements themselves attach.

In connection with a lean working standard premix burner the gas stream flowing past the SEV vortex generating elements typically an average speed of up to 150 m / s. Despite the very small Pressure loss coefficients ζ with such a configuration result in high speeds with high pressure drops (up to 4%). Burners with catalytic Elements are generally characterized by significantly lower exit speeds characterized by about 50 m / s. The associated pressure loss is less than 2% and therefore represents a significant reduction.

Although the gas mixture exiting the catalyst mixes very well there are burner types in which fuel and / or air are the main catalyst Flow around in the bypass and be mixed in afterwards. The catalyst can also include a pilot burner that produces its own combustion products (e.g. an enriched fuel / air mixture or syngas), which then also is added to the main gas stream. This is an important consideration because the Combustion of inhomogeneous mixtures leads to high local temperatures and thereby increasing emissions. The vortex generating elements are of their nature according to also mixing devices and therefore ensure that the gas mixtures be mixed well before homogeneous combustion.

If the vortex generating elements 16 are sufficiently steep, i.e. if the approach angle is large, they can have recirculation zones in their post-currents cause. The recirculation zones can be undesirable because they become one Anchor the homogeneous flame to the vortex generating elements could. Such anchoring would be significant on the devices cause thermal stress and reduce the service life.

It is known that an expansion in the cross section of the flow channel 13 favors the collapse of the vertebrae. If a vortex generating element for comparatively small values of the circulation, i.e. without a recirculation zone in the immediate post-flow, is designed, a subsequent expansion cause the vortex to collapse further downstream. This poses ensure that the flame is anchored to or in the immediate vicinity of the Vortex generating element can not occur. A corresponding configuration is shown in Fig. 3. The burner 20 shown in FIG. 3 differs differs from the burner 12 shown in FIG. 2 mainly in that between the vortex generating elements 16 and the homogeneous flame 17 one step-like extension 19 is provided in the cross section of the flow channel 13 is. This step-like extension 19 reliably prevents the flame 17 from the elements 16 is anchored and endangered them.

LIST OF REFERENCE NUMBERS

10.16

Vortex generator

11

combustion chamber wall

12, 20

burner

13

flow channel

14

flow

15

catalyst

17

homogeneous flame

18

Axis (burner)

19

extension

Claims (11)

Combustion process, in which in a burner (12, 20) a fuel / air mixture flowing through a flow channel (13) is reacted in a first combustion stage in a catalytic converter (15) and fuel with the exhaust gas downstream of the catalytic converter (15) the catalytic converter (15) is burned together in a second combustion stage to form a homogeneous flame (17) by self-ignition, characterized in that the fuel from the fuel / air mixture is only partially burned in the catalytic converter (15) in the first combustion stage, that the unburned rest of the fuel is burned in the second combustion stage and that the fuel-containing exhaust gas from the catalytic converter (15) is passed between the outlet of the catalytic converter (15) and the homogeneous flame (17) through devices (16, 19), which bring about an aerodynamic stabilization of the homogeneous flame (17). A method according to claim 1, characterized in that vortex generating elements (10, 16) are used as aerodynamically stabilizing devices, which are arranged at the outlet of the catalyst (15). A method according to claim 2, characterized in that a step-like extension (19) in the flow channel (13) is additionally used as the aerodynamically stabilizing device, which is arranged between the vortex generating elements (10, 16) and the homogeneous flame (17). Method according to one of claims 1 to 3, characterized in that the exhaust gas at the outlet of the catalyst (15) contains O ₂ , N ₂ , CO, CO ₂ and H ₂ O in addition to the unburned fuel. Method according to one of claims 1 to 4, characterized in that the exhaust gas emerges from the catalyst (15) at a flow rate of less than or equal to 50 m / s. Method according to one of claims 1 to 5, characterized in that the exhaust gas emerges from the catalyst (15) at a temperature between 600 ° C and 950 ° C. Method according to one of Claims 1 to 6, characterized in that fuel which is conducted past the outside of the catalytic converter (15) past the catalytic converter (15) is added to the exhaust gas. Method according to one of claims 1 to 7, characterized in that H ₂ / CO from a fuel-rich catalytic pilot burner is present in the medium flowing through the flow channel (13). Burner (12, 20) for carrying out the method according to one of claims 1 to 8, with a flow channel (13) in which a catalyst (15) for the catalysis of a fuel / air mixture flowing through the flow channel (13) is arranged , and in which downstream from the catalytic converter (15) means for aerodynamically stabilizing a downstream homogeneous flame (17) are arranged, characterized in that the stabilizing means comprise vortex generating elements (10, 16). Burner according to claim 9, characterized in that a step-like widening (19) of the flow channel (13) is additionally provided downstream of the vortex generating elements (10, 16). Burner according to one of claims 9 or 10, characterized in that the formation of the vortex generating elements (10, 16) depends on whether the vortex generating elements (10, 16) are mainly intended to cause a mixture or a breakdown of vortices.

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