EP1446610A1 - Method of combustion, in particular methods for the production of electrical current and/or heat - Google Patents

Abstract

The invention relates to a method, in particular to a method for the generation of electrical current and/or heat, whereby a gas mixture of oxygen, fuel and essentially nitrogen-free inert gas is formed and burnt in a burner (3). The combustion is embodied as a flameless combustion, in order to guarantee a stable combustion, even with relatively high proportion of inert gas.

Description

Combustion process, in particular for processes for generating electrical current and / or heat

Technical field

The invention relates to a combustion method, in particular for a method for generating electrical power and / or heat, with the features of the preamble of claim 1. The invention also relates to a combustion method working with flameless combustion with the features of the preamble of claim 2. Des the invention further relates to a plant, in particular a gas turbine plant, for carrying out such combustion processes, and to a special use of a combustion process which works with flameless combustion.

State of the art

WO 98/55208 discloses a combustion process for a process for generating electrical current and / or heat, in which a gas mixture of oxygen, fuel and essentially nitrogen-free inert gas is formed and burned in a burner. The inert gas is formed by the combustion exhaust gases of the burner, and this inherently nitrogen-free exhaust gas can contain negligible parasitic nitrogen components via the burned fuel. The oxygen for the gas mixture is provided with the aid of an oxygen transport membrane, which is preferably heated and compressed air is applied to a barrier side. On its barrier side, this membrane extracts oxygen from the air there, transports it to a passage side of the membrane and releases it there. With the help of a purge gas, the oxygen can be removed on the passage side. The combustion exhaust gas from the burner, which can be additionally heated by combustion with fuel, is expediently used as the purge gas. Certain embodiments of such membranes are known as MCM (mixed conducting membrane).

In such a combustion process - apart from parasitic nitrogen components in the fuel - no nitrogen is involved, so that the resulting exhaust gases essentially only contain CO ₂ and H ₂ O in the form of water vapor. By condensing out the water vapor, the CO _{2 can be} separated and disposed of relatively easily. Since there are basically no harmful emissions in such a combustion process, one can also speak of a zero emission process here.

In order to increase the performance of an oxygen transport membrane, a relatively high volume flow of purge gas is required. With these advantageous large amounts of purge gas, however, an exhaust gas / oxygen mixture results, the oxygen content of which is so low that it is only very weakly reactive. Conventional combustion processes, in particular combustion processes using a diffusion flame, can no longer be used. For example, the volume of the gas mixture of oxygen diluted with flushing gas and added fuel can be composed as follows: 2.5% CH, 5% O ₂ , 27.5% CO _2, 65% H ₂ O. The temperature of this gas mixture is usually between 600 and 900 ° C. Under these conditions, existing lean premix burners and catalytic burners have a reactivity that is lower than that of conventional fuel / air mixtures at the same temperatures. This leads to long ignition delay times, a reduced flame speed and tighter lean extinguishing limits. In addition, the operating parameters are also deteriorated in that the achievable temperature of the combustion gases is significantly reduced and is, for example, only around 1200 ° C. Due to these conditions, conventional combustion The process can not be used satisfactorily for stable combustion of such a weakly reactive gas mixture.

When integrating a burner into a heat exchanger and / or into an oxygen separation device working with an oxygen transport membrane or if the burner feeds its combustion exhaust gases directly into a heat exchanger or such an oxygen separation device, further problems arise because the operation of such heat exchangers or Oxygen separators are only optimal in terms of heat transfer and thermal stress if the temperature distribution is as uniform as possible. In conventional combustion processes, however, there are usually non-uniform temperature distributions.

EP 0 463 218 A1 discloses a method for burning fuel in a combustion chamber, in which fuel is oxidized with preferably preheated combustion air in the presence of recirculated combustion exhaust gases. When air is burned, thermal NO _x is always formed, the NO _x formation increasing sharply with increasing flame temperature. To reduce the NO _x emissions, the known method proposes to oxidize the fuel with extremely high combustion exhaust gas recirculation essentially without flames and without pulsations. This is achieved in that combustion exhaust gases, from which useful heat previously removed from the system was previously extracted, are mixed with the preheated combustion air in a combustion exhaust gas recirculation ratio greater than or equal to 2, the exhaust gas recirculation ratio being the ratio of the mass flows of the recirculated combustion exhaust gas and of the supplied combustion air is defined, this exhaust gas-air mixture being maintained at a temperature which is higher than the ignition temperature, and the exhaust gas / air mixture is then brought together with the fuel to form an oxidation zone, in which essentially one flameless and pulsation-free oxidation takes place in the combustion chamber. With this known method, the NO _x emissions during the combustion of air can be estimated to be reduced by a factor of 10. Presentation of the invention

The present invention is concerned with the problem of demonstrating satisfactorily functional possibilities for the combustion of weakly reactive and nitrogen-free gas mixtures.

This problem is solved by the subject matter of the independent claims. Advantageous embodiments are given in the dependent claims.

The invention is based on the general idea of using the flameless combustion known for reducing the NO _x emissions for the combustion of a nitrogen-free gas mixture. It is easy to see that the application of a method known for reducing the NO _x emissions, which works with flameless combustion, in a nitrogen-free and thus without NO _x emissions combustion method is obviously motivation-free, since the nitrogen-free combustion method with regard to its NO _x emission values cannot be improved. The invention now makes use of the knowledge that a combustion process using flameless combustion is particularly suitable for the combustion of weakly reactive gas mixtures. By coupling a nitrogen-free combustion process with a flameless combustion process according to the invention, the performance of the nitrogen-free combustion process can be significantly improved if a weakly reactive gas mixture is to be burned, in particular if the oxygen in the gas mixture to be burned is added using an oxygen transport membrane a larger amount of purge gas is obtained. The invention achieves a synergy effect which was not to be expected in this way, since the known combustion process which works with flameless combustion expressly serves to reduce the NO _x emissions, but which it does not do at all with a nitrogen-free combustion process from which the invention is based gives. To that extent, the present invention uses the flameless combustion method of combustion to another Purpose. This is because the use of flameless combustion enables reliable and stable combustion of a weakly reactive gas mixture in a nitrogen-free combustion process.

Further important features and advantages of the invention result from the subclaims, from the drawings and from the associated description of the figures with reference to the drawings.

Brief description of the drawings

Preferred exemplary embodiments of the invention are shown in the drawings and are explained in more detail in the following description, the same reference symbols referring to the same or functionally identical or similar features. Each shows schematically

1 is a very simplified schematic diagram of a device according to the invention,

2 ^'is a greatly simplified schematic diagram of a burner for a device according to FIGS. 1 and

Fig. 3 is a view as in Fig. 2, but in another embodiment.

Ways of Carrying Out the Invention

1, a device or system 1 according to the invention has a mixture formation device 2 and a burner 3. The mixture formation device 2 comprises an oxygen separation device 4, which is equipped with an oxygen transport membrane 5. According to FIG. 1, the membrane 5 has a blocking side 6 at the top and a passage side 7 according to FIG. 1 at the bottom the barrier side 6, the membrane 5 is supplied with an oxygen-containing gas Ai, for example air. Oxygen (O ₂ ) is then transported on the membrane 5 in accordance with an arrow 8, which is removed from the barrier side 6 of the membrane 5 and transported on its passage side 7. In the oxygen separation device 4, the oxygen content of the gas Ai supplied on the blocking side 6 is accordingly reduced; Accordingly, the gas located in the oxygen separation device 4 is marked with A in FIG. 1. Gas A _{2, which has a} reduced oxygen content, then emerges from the oxygen separation device 4.

In order to increase the performance of the membrane 5, its passage side 7 is charged with an inert purge gas GER, which transports the oxygen out of the oxygen separation device 4. In the present case, the purge gas GER is formed by externally recirculated exhaust gas, which is taken from an exhaust line 9 after the burner 3.

Advantageously, the oxygen separation device 4 can also be designed as a heat exchanger. In this way, the temperature of the supplied oxygen-containing gas Ai can be increased to improve the performance of the oxygen separation device 4.

The oxygen-enriched, externally recirculated exhaust gas is fed to the burner 3 via a line 10. A pump 11 or turbine or blower or the like can be used in line 10 to drive this gas mixture of oxygen and externally recirculated exhaust gas. be arranged.

Furthermore, a fuel injection device 12 is provided, which can form part of both the mixture formation device 2 and the burner 3. In the present case, a fuel line 13 supplies fuel F to the burner 3. As already mentioned above, the burner 3 is equipped with an external exhaust gas recirculation 14, which takes a part of the combustion exhaust gases downstream of the burner 3 via a return line 15 branching off from the exhaust line 9 and ultimately admixes it again in front of the burner 3. In the case shown here, the serve externally recirculated exhaust gases GER for flushing the membrane 5. Furthermore, the burner 3 here is equipped with an internal exhaust gas recirculation 16, in which a part of the exhaust gases remains in a combustion chamber of the burner 3, which is not shown in FIG. 1. This with G | Internally recirculated exhaust gases designated _R mix in the combustion chamber with the other gas components supplied to the burner 3 so as to form the desired gas mixture which has a relatively high exhaust gas recirculation rate (external and / or internal). The internal exhaust gas recirculation is also symbolized by arrows 17 in FIG. 1.

As can be seen from the diagram shown in FIG. 1, the combustion process which can be carried out with the system 1 works without nitrogen, so that the combustion exhaust gases generated by the burner 3 contain no or only parasitic NO _x components which originate from the fuel. The exhaust gas Gs essentially contains only CO ₂ and vaporous water (H ₂ O).

According to the invention, the burner 3 is designed to carry out flameless combustion. For this purpose, the mixture formation device 2 is designed such that it only brings together the oxidizer O _x together with the externally recirculated exhaust gases GER and the fuel F in the burner 3 in order to produce the gas mixture to be burned. Furthermore, a corresponding interaction of the mixture-forming device 2 and the burner 3 ensures that the finished gas mixture, which in the embodiment shown in FIG. 1 is only formed by mixing the internally recirculated exhaust gas quantity GIR, has a temperature which is above the self-ignition temperature of this gas mixture. Under these conditions, the desired flameless combustion can be implemented in burner 3. It is particularly advantageous here that such flameless combustion can also proceed with sufficient stability if the gas mixture to be burned has a very low oxygen content, that is to say a very weak reactivity. This is particularly the case if a relatively large amount of purge gas is used to remove the oxygen, that is to say a relatively high external exhaust gas recirculation rate, in order to increase the performance of the oxygen separation device 4. It is entirely possible that the external exhaust gas recirculation rate is selected to be so large that internal exhaust gas recirculation can be dispensed with more or less or that the internal exhaust gas recirculation can be kept very low.

It has been shown that reliable flameless combustion can be achieved if the volume ratio of inert gas in the gas mixture, i.e. externally recirculated exhaust gas GER and internally recirculated exhaust gas GIR, ZU fuel F and oxygen O _{x is} greater than 2, in particular greater than 3.

According to FIG. 2, according to a special embodiment, the burner 3 can have a pre-combustion chamber 18 and a main combustion chamber 20 arranged downstream of the flow direction of the burner 3 symbolized by an arrow 19. The burner 3 is expediently rotationally symmetrical with respect to an axis of symmetry 21.

In the embodiment according to FIG. 2, the fuel injection device 12 is configured such that first injection nozzles 22 in the pre-combustion chamber 18 enable fuel to be pre-injected. Furthermore, second injection nozzles 23 are provided, which allow a main injection of fuel in the main combustion chamber 20. In the pre-combustion chamber 18, a mixing device 24, a catalyst device 25 and a swirling device 26 are arranged one behind the other in the flow direction 19.

The burner 3 according to FIG. 2 works as follows:

The pre-combustion chamber 18 is supplied with oxygen O _x , which can be diluted more or less with externally recirculated exhaust gas GER, so that an oxygen-exhaust gas mixture O _x + G _E R is then supplied. A relatively small amount of fuel is injected via the first injection nozzles 22. The individual components are mixed thoroughly in the mixing device 24. A catalytically initiated takes place in the catalyst device 25, which contains a corresponding catalyst or stabilized combustion of the fuel F, whereby only a part of the amount of oxygen supplied is consumed. In particular, it is possible to pass only a partial flow through the catalyst device 25, as a result of which a complete combustion of the oxygen can also be achieved in this partial flow.

The temperature increase of the gas mixture supplied to the main combustion chamber 20 can be achieved by the catalytic combustion. Due to the catalytic combustion in the pre-combustion chamber 18, the exhaust gas quantity and thus the exhaust gas concentration can be increased quasi internally, which makes it possible to reduce the externally recirculated exhaust gas quantity GER ZU. Since a high external exhaust gas recirculation rate leads to high pressure losses, which have to be compensated for by corresponding pump power, the overall efficiency of the turbine process can be improved by the internal catalytic exhaust gas generation proposed here.

When flowing through the swirling device 26, a desired flow or swirl behavior can be forced onto the gas flow. Further fuel F is then added in the main combustion chamber 20 via the second injection nozzles 23, the desired gas mixture then forming, the temperature of which is above the self-ignition temperature of this gas mixture. Depending on the external exhaust gas recirculation rate, this mixture formation may require an internal exhaust gas recirculation, which can be generated here by means of suitable, aerodynamically operating exhaust gas guiding devices. In the exemplary embodiment shown, such an exhaust gas guiding device is formed by a cross-sectional widening 27 at the transition from the pre-combustion chamber 18 into the main combustion chamber 20, which initiates an annular vortex roller symbolized by an arrow 28. The exhaust gas guiding device thus formed causes a backflow of part of the exhaust gases against the flow direction 19 of the burner 3 through the vortex 28, so that this portion of the exhaust gases remains in the main combustion chamber 20. The annular swirl roller shown in the vicinity of the axis of symmetry 21 and designated by 29 can be, for example, by the swirling device 26, in particular in connection with the cross-sectional expansion 27. This swirl roller 29 also supports the internal exhaust gas recirculation.

By a suitable choice of the flow velocities, the turbulence and in particular the internal exhaust gas recirculation, relatively long dwell times for the gas to be burned can be achieved in the burner 3, whereby a complete combustion of the injected fuel can be ensured.

This recirculation due to the vortices 28 and 29 also supports the mixing of the internally recirculated exhaust gases with the gas mixture introduced into the main combustion chamber 20, as a result of which, for example, heating of the combustible mixture and stabilization of the reactions can also be achieved. Accordingly, the catalyst device 25, which leads to an increase in temperature in the mixture, is not absolutely necessary, but can e.g. in the partial load range.

3, in a particular embodiment, the fuel injection device 12 can have a lance 30 which extends coaxially with the axis of symmetry 21. This lance 30 has first injection nozzles 31 assigned to the pre-combustion chamber 18 and second injection nozzles 32 assigned to the main combustion chamber 20. With the aid of such a lance 30, a particularly homogeneous distribution of the injected fuel quantity can be achieved in the main combustion chamber 20, whereby the formation of flameless combustion is facilitated.

It is clear that the injection nozzles 22, 23, 31 and 32 are preferably distributed in a rotationally symmetrical manner with respect to the axis of symmetry 21, it being possible for more than the two exemplified nozzles to be provided for each type of nozzle.

The flameless combustion in the main combustion chamber 20 results in a combustion which is homogeneously distributed over the entire main combustion chamber 20 and which runs freely. The flameless combustion thus produces a homogeneous temperature distribution over the entire main combustion chamber 20, which considerably simplifies the integration of the burner 3 into a heat exchanger and / or into an oxygen separation device 4 and a direct attachment of the burner 3 to a heat exchanger and / or an oxygen separation device 4 ,

Since a single ignition point within the combustion chamber can no longer be located in flameless combustion, the risk of a flashback is reduced.

While in the embodiments shown in FIGS. 1 to 3, pure fuel is always introduced into the burner 3 or into the main combustion chamber 20, in another embodiment a mixture of fuel and inert gas, e.g. externally recirculated exhaust gas can be used. In contrast to the illustrated embodiments, it is also possible, instead of a mixture of oxygen and inert gas, to supply the oxygen essentially in pure form to the burner 3 or the main combustion chamber 20. Essentially pure oxygen can, for example, be produced cryogenically.

In one embodiment, in which the mixture formation device 2 introduces substantially pure oxygen into the main combustion chamber 20, this takes place in order to achieve the desired gas mixture at a point in the vicinity of which the fuel injection also takes place. An internal exhaust gas recirculation with a relatively high recirculation rate then serves to form the desired gas mixture.

If pure oxygen is available and is introduced into the main combustion chamber 20 in the vicinity of the fuel injection, the flameless combustion reaction can be initiated relatively stably due to the locally elevated temperatures. In this respect, the catalyst device 25 can be omitted in such an embodiment. It is also possible to introduce oxygen both into the pre-combustion chamber 18 and into the main combustion chamber 20, whereby on the one hand catalytic preheating of the supplied gas mixture can be achieved and on the other hand a more stable flameless combustion can be achieved. The latter embodiment is particularly advantageous when the burner 3 is under partial load.

It is clear that the exhaust gases Gs generated by the burner 3, for example. can be used in a gas turbine plant for generating electrical current.

LIST OF REFERENCE NUMBERS

1 facility

2 mixture formation device

3 burners

4 oxygen separator

5 oxygen transport membrane

6 blocking side of 5

7 passage side of 5

8 oxygen transport

9 exhaust line

10 line

11 pump

12 fuel injector

13 fuel line

14 external exhaust gas recirculation

15 return line

16 internal exhaust gas recirculation

17 arrow

18 pre-combustion chamber

19 Flow direction 0 main combustion chamber Axis of symmetry first injector second injector

mixing equipment

catalyst device

swirling

Cross-sectional widening

eddy roll

eddy roll

Lance first injector second injector

Claims

claims 1. Combustion process, in particular for a process for generating electrical current and / or heat, in which a gas mixture of oxygen, fuel and essentially nitrogen-free inert gas is formed and burned in a burner (3), characterized in that the combustion as flameless combustion is designed. 2. Flameless combustion combustion process, in particular for a process for generating electrical current and / or heat, in which a gas mixture of oxidizer, fuel and inert gas is burned in a burner (3), characterized in that essentially as an oxidizer pure oxygen or a mixture of essentially pure oxygen and essentially nitrogen-free inert gas is used, and that an essentially nitrogen-free inert gas is used as the inert gas. 3. The method according to claim 1 or 2, characterized in that the temperature of the gas mixture is above the self-ignition temperature of the gas mixture, the admixture of oxygen or a mixture of oxygen and inert gas and / or the admixture of fuel or a mixture of fuel and inert gas only in the burner (3). 4. The method according to any one of claims 1 to 3, characterized in that the inert gas is a mixture of inert gases. 5. The method according to any one of claims 1 to 4, characterized in that in the gas mixture a volume ratio of inert gas to fuel and oxygen is greater than 1, 5, in particular 2.5. 6. The method according to any one of claims 1 to 5, characterized in that the inert gas is formed from an exhaust gas formed during the combustion of the gas mixture. 7. The method according to claim 6, characterized in that the admixture of the exhaust gas to the oxygen and / or to the fuel by an internal exhaust gas recirculation (16), in which a part of the exhaust gases remains in a combustion chamber (20) of the burner (3), and / or by an external exhaust gas recirculation (14), in which a part of the exhaust gases are removed after the burner (3) and is returned to the burner (3). 8. The method according to any one of claims 1 to 7, characterized in that substantially pure oxygen is used to form the gas mixture cryogenically produced. 9. The method according to any one of claims 1 to 8, characterized in that a mixture of essentially pure oxygen and inert gas is used to form the gas mixture, which is formed in that an oxygen transport membrane (5) from one Oxygen-containing gas mixture (A1) arranged on a barrier side (6) of the membrane (5) removes oxygen and transports it to a passage side (7) of the membrane (5), where the oxygen is removed with the inert gas used as the purge gas. 10. The method according to any one of claims 1 to 9, characterized in that in order to form the gas mixture, the fuel or a mixture of fuel and inert gas with respect to a flow direction (19) of the burner (3) at at least two points (22, 23; 31, 32) is mixed in the burner (3). 11. The method according to any one of claims 1 to 10, characterized in that to increase the mixture temperature in the burner (3) and / or to increase the exhaust gas content in the gas mixture in front of a main combustion chamber (20) a catalytically initiated and / or stabilized pre-combustion of a portion of the Oxygen and a subset of the fuel is carried out. 12. Plant, in particular gas turbine plant, for carrying out a method according to one of claims 1 to 11, with a mixture formation device (2) for forming a substantially nitrogen-free gas mixture of oxidizer, fuel and inert gas and with a burner (3 ), the mixture formation device (2) only in the burner (3) brings oxygen and fuel together, such that the finished gas mixture has a temperature which is above the self-ignition temperature of the gas mixture. 13. Plant according to claim 12, characterized in that an exhaust gas recirculation (14, 16) is provided and that the inert gas is formed by the exhaust gas formed during the combustion of the gas mixture. 14. Plant according to claim 13, characterized in that the exhaust gas recirculation an internal exhaust gas recirculation (16), in which a part of the exhaust gases remains in a combustion chamber (20) of the burner (3), and / or an external exhaust gas recirculation (14) which removes part of the exhaust gases after the burner (3) and recycled before the burner (3). 15. Plant according to claim 14, characterized in that the internal exhaust gas recirculation (16) has a swirling device (26) which a gas flow of oxygen or a mixture of oxygen and exhaust gas before or when it enters a combustion chamber (20) of the burner (3) swirled. 16. Plant according to claim 14 or 15, characterized in that the internal exhaust gas recirculation (16) in a combustion chamber (20) of the burner (3) has an exhaust gas guide device, e.g. in the form of a cross-sectional widening (27), which causes or supports a backflow of part of the exhaust gases within the combustion chamber (20) against the flow direction (19) of the burner (3). 17. Plant according to one of claims 12 to 16, characterized in that a fuel injection device (12) is provided with the fuel both in an upstream pre-combustion chamber (18) of the burner (3) and in a downstream main combustion chamber (20) of the burner (3) can be introduced. 18. Plant according to claim 17, characterized in that the fuel injection device (12) has a lance (30) which extends centrally in the pre-combustion chamber (18) and in the main combustion chamber (20) and the pre-combustion chamber (18) assigned injection nozzles (31) and the main combustion chamber (20) assigned injection nozzles (32) through which the fuel is introduced into the pre-combustion chamber (18) or into the main combustion chamber (20). 19. Plant according to claim 17 or 18, characterized in that a catalyst or a catalyst device (25) containing a catalyst is arranged in the pre-combustion chamber (18), through which the fuel is introduced into the pre-combustion chamber (18) in the pre-combustion chamber (18 ) introduced oxygen burns at least partially. 20. Plant according to one of claims 12 to 19, characterized in that the mixture formation device (2) has an oxygen separation device (4) with an oxygen transport membrane (5), which consists of a on a barrier side (6) of the membrane (5 ) arranged oxygen-containing gas mixture takes oxygen and transports it to a passage side (7) of the membrane (5), where the oxygen is removed with a purge gas, the exhaust gas from an external exhaust gas recirculation system (14) being used as the purge gas. 21. Plant according to one of claims 12 to 19, characterized in that the mixture formation device (2) introduces substantially pure oxygen into a combustion chamber (20) of the burner (3) in the vicinity of a point at which the fuel or a mixture is made Fuel and inert gas are introduced into the combustion chamber (20), an internal exhaust gas recirculation (16), in which part of the exhaust gases remain in the combustion chamber (20), which supplies the inert gas which is missing for the formation of the gas mixture. 22. Use of a combustion process which works with flameless combustion, in particular for a process for generating electric current and / or heat, for burning an essentially nitrogen-free gas mixture formed from oxidizer, fuel and inert gas.