Method for determining the distribution of a total airflow in a combustion chamber system and combustion chamber system

Abstract

The invention relates to a method and a combustion chamber system (1) for determining the division of a total airflow (30) in a combustion chamber system (1) of a gas turbine arrangement, wherein, when the combustion chamber system (1) is in combustion operation, the total airflow (30) is divided into at least two airflows of specific quantities, which are supplied to a combustion chamber (16) of the combustion chamber system (1) or to the combustion chamber (16) and an exhaust gas tract (20) adjacent to the combustion chamber (16) via different supply paths for different purposes,One of the air streams is supplied as combustion air stream (30) via a supply path in the form of a supply device (24) for combustion in a combustion chamber (18) of the combustion chamber (16) with supplied fuel in a first burner stage, and a significant pressure loss occurs in at least one first supply path of a first air stream when the corresponding air streams flow through the supply paths. A precise design of the air stream distribution can be achieved by determining a differential pressure within the first supply path and determining the quantity of the corresponding air stream from the differential pressure.

Description

[0001] The invention relates to a method for determining the distribution of a total airflow in a combustion chamber system of a gas turbine arrangement, in which, when the combustion chamber system is in combustion operation, the total airflow is divided into at least two airflows of specific quantities, which are supplied to a combustion chamber of the combustion chamber system or the combustion chamber and to an exhaust gas tract adjacent to the combustion chamber via different supply paths for different purposes, one of the airflows is added as a combustion airflow via a supply path in the configuration of a supply device for combustion in a combustion chamber of the combustion chamber with supplied fuel in a first burner stage, and a significant pressure loss is caused in at least one first supply path of a first airflow when the corresponding airflows flow through the supply paths.

[0002] In combustion chamber systems, such as those used today in connection with gas turbines, several air streams are often supplied to the combustion chamber for different purposes. These air streams may contain additional components, such as externally recirculated exhaust gas or process gas components. For example, in addition to a combustion air stream for the first (main) stage of a burner, another air stream is sometimes used as cooling and / or mixing air, which is supplied to the exhaust gas downstream of the combustion zone, and / or as combustion air for at least one further burner stage, such as a pilot stage. The distribution is usually determined by the geometry; that is, a total air stream is initially supplied to the combustion chamber, and the design of the individual supply paths for the individual air mass flows determines the distribution of the individual air stream components or volume flows.These are designed – for example with the help of computer simulations – so that a desired distribution results due to the pressure losses in the supply paths.

[0003] For the design of a combustion chamber system that operates with the lowest possible emissions, the precise definition and knowledge of the individual airflows are of paramount importance. Since the actual airflow distribution can deviate from that determined by computer simulation, the actual distribution is usually also determined in the laboratory when developing a new combustion chamber geometry. Direct measurement of the actual airflow distribution during operation is only possible with considerable effort and limitations (additional pressure losses due to the measuring equipment) in combustion chamber systems because of the inherently high temperatures and pressures (e.g., in micro gas turbines due to compression and, if applicable, recuperation before addition to the combustion chamber).Therefore, the air distribution is decoupled by closing individual supply paths, and in this way, information about the airflow distribution is obtained based on the pressure loss distribution across the combustion chamber (starting from the air plenum before the distribution). However, these tests are only possible with limited accuracy. One inaccuracy lies, for example, in the fact that these tests are carried out without a combustion reaction, even though combustion influences the back pressure and thus the airflow distribution. Consequently, adjustments to the supply paths, such as mixing air bores, are often necessary after commissioning a new combustion chamber system in order to operate the combustion chamber system optimally with regard to pollutant emissions, even under partial load. Thus, the optimal air distribution can only be achieved through iterative variations in the supply paths, such as the mixing air bores.Changes in air distribution during operation due to defective components or altered gap dimensions caused by thermal expansion can only be determined indirectly, for example, using any existing temperature measuring points or exhaust gas analysis. Undetected changes / damage can, in the worst case, lead to consequential damage to the combustion chamber and / or hot streaks at the combustion chamber outlet, which can negatively affect the service life and efficiency of the downstream turbine.

[0004] German patent application DE 10 2012 017 065 A1 describes a method for operating a lean-burn premix burner of an aircraft gas turbine. In this method, three combustion air streams—primary support air, secondary air, and air from a main burner—are supplied to a combustion chamber via a concentric main air supply and an external air supply. At least the primary support air and the main air are swirled by means of swirl elements.

[0005] German patent application DE 10 2008 047 504 A1 discloses a device for measuring the exhaust gas recirculation flow of an internal combustion engine in an exhaust gas recirculation line. The mass flow rate of the exhaust gas recirculation is measured using a differential pressure sensor based on the Venturi principle in a constricted area of ​​the exhaust gas recirculation line.

[0006] German patent application DE 298 19 201 U1 describes a control device for regulating the speed of a combustion air blower for a burner in a combustion plant. The control is based on measuring a pressure difference between a first measuring point upstream of a throttling device and a pressure in the combustion chamber.

[0007] The publication DE 699 29 282 T2 shows a combustion chamber design for a gas turbine engine with a tubular combustion chamber in which different combustion zones are formed in different sections, namely a primary combustion zone, a secondary combustion zone and a tertiary combustion zone.

[0008] The invention is based on the objective of providing a method with which the division of a total airflow in a combustion chamber system can be determined with improved accuracy, as well as a corresponding combustion chamber system.

[0009] This problem is solved for the method with the features of claim 1 and for the combustion chamber system with the features of claim 15.

[0010] According to claim 1, a differential pressure is determined within the first supply path, and the volume of the corresponding airflow is calculated from this differential pressure. This involves determining the (statistically) significant, i.e., measurably detectable, pressure loss caused in the first supply path. The inventors utilize the effect that the pressure loss—at a given temperature and pressure—depends on the volume of air. Since the first airflow within the first supply path is separated from the other airflows, the determined differential pressure is essentially induced by the pressure loss caused by the first airflow. In this way, the determined differential pressure can be assigned to a first airflow with good accuracy. Knowing this airflow improves the ability to predict the distribution of the airflows and simplifies the design for low-emission combustion.

[0011] In a preferred embodiment of the method, the differential pressure between at least one pressure measuring point in an inlet area and at least one pressure measuring point in an outlet area within the supply path, between which the significant pressure loss occurs, is determined. The differential pressure can be determined with good accuracy using such pressure measuring points. Advantageously, the pressure measuring points can be positioned at a certain distance (e.g., one or a few millimeters) from the inlet and / or outlet in or out of the supply path. In the inlet area, this offers the advantage that the flow in the supply path becomes more uniform after a certain inflow distance, allowing for a more precise measurement.A gap in the outlet area can be advantageous in that it maintains a certain distance from the combustion chamber, thereby reducing the thermal stress on the pressure measuring point (and any connected sensor). The sensor can, for example, be positioned outside a pressure housing and connected to the pressure measuring point on the combustion chamber via a connecting line. It can be useful to design the pressure measuring point to be closable, for example with a screw cap, when no measurement is required.

[0012] In a preferred embodiment, the combustion chamber is first supplied with a total airflow of a defined quantity, pressure, and temperature—preferably relevant for combustion (with respect to the first airflow)—during a calibration process, preferably on a test bench, without the addition of fuel. Only the first supply path is open, while the others are closed. The differential pressure in the first supply path is then determined. In this way, the quantity of the first airflow at a given pressure and temperature can be correlated with a determined differential pressure. This allows the corresponding quantity of the first airflow to be determined with good accuracy, optionally even during combustion. Thus, the measured differential pressure and the first airflow are correlated.

[0013] Preferably, the first step is repeated with several different defined quantities to generate an airflow-differential pressure characteristic curve, preferably at several different air temperatures and / or pressures relevant to combustion operation. This allows for a wide range of application of the inventive method across various operating ranges in the combustion operation of the combustion chamber system, thereby achieving good accuracy in quantity determination during design or verification. If the total airflow is divided into two airflows, the quantity of a second airflow, and thus the division between the first and second airflows, can be determined by knowing the total airflow, which is relatively easy to ascertain even during combustion operation, and the quantity of the first airflow determined via the differential pressure.

[0014] If, in a second step during the calibration process, the combustion chamber is supplied with a total airflow of a defined quantity relevant to the combustion process (preferably the sum of the first and second airflows), with air temperature and pressure corresponding to the first step, with the first supply path and a second supply path open, and with the differential pressure of the first supply path being determined, a correlation can also be established between the determined first airflow and a second airflow. In this way, the application range of the method can be extended to multiple airflows.

[0015] The relationship can be established particularly advantageously by determining the quantity of the second airflow as a function of the quantity of the first airflow from the characteristic curve(s) determined in the first step and the quantity of the total airflow, preferably at several air temperatures and / or pressures according to the characteristic curve(s) from the first step.

[0016] It is particularly advantageous to carry out the second step if the combustion chamber is designed for operation with at least three air streams. This allows the accuracy of the design to be increased compared to methods known from the prior art, even for combustion chamber systems with at least three air streams.

[0017] Advantageously, the distribution of the total airflow can now be determined during combustion operation, at least by incorporating the characteristic curve determined from the first step of the calibration operation. If two airflows are present, the distribution essentially results from the known total airflow and the quantity of the first airflow, determined via the differential pressure. If three airflows are present, the relationship between the quantity of the first airflow and a second airflow is preferably also considered, so that a third airflow can also be inferred.

[0018] The method is particularly advantageous when the first airflow is formed by the combustion airflow. The combustion airflow is preferably that of a first (main) stage of the burner in the combustion chamber system. Knowledge of this airflow is especially important for the design of a low-emission combustion chamber system. If this airflow is determined via the differential pressure as described, a crucial airflow for the low-emission operation of the combustion chamber system is already known.

[0019] Preferably, the combustion air flow is supplied to the combustion chamber via a supply device located at an inlet-side end face of the combustion chamber and at least one supply nozzle. In such combustion chamber systems, for example, systems with circumferential supply openings designed for flameless oxidation, but also for other combustion modes in which individual flames are formed, a significant pressure drop across the supply nozzle(s) often occurs due to the system design. This pressure drop can be advantageously utilized here without having to generate a pressure drop that might not otherwise exist and would impair the overall efficiency.

[0020] A particularly measurable pressure loss or differential pressure occurs when the combustion air flows through a cross-sectional constriction within the supply nozzle.

[0021] The method is advantageously applicable when the fuel is added upstream of the inlet to the combustion chamber into the combustion air stream for at least partial premixing of combustion air and fuel, or separately from the inlet-side end face into the combustion chamber.

[0022] Furthermore, the method is advantageously applicable if the second or third airflow is formed by a combustion airflow of a second burner stage, in particular a pilot burner.

[0023] Another advantageous application arises when the second or third airflow is formed from a mixed airflow added to the exhaust gas flow downstream of a combustion zone.

[0024] It is also possible that the first airflow is formed by the mixed airflow or by the combustion airflow of a further burner stage if a significant pressure loss occurs within their supply paths.

[0025] In the combustion chamber system according to claim 15, it is provided that within the first supply path at least one pressure measuring point in an inlet area and at least one pressure measuring point in an outlet area, between which the significant pressure loss occurs, are provided to determine a differential pressure from which the quantity of the corresponding airflow can be determined.

[0026] Preferably, the feed device is arranged on an inlet-side end face of the combustion chamber and has at least one feed nozzle, in particular one with a cross-sectional constriction in the flow path. The end face can lie in a plane perpendicular to a central longitudinal axis or have another shape, e.g., tapering conically against the flow direction. The feed nozzles can, for example, be aligned parallel to a central longitudinal axis of the combustion chamber or point outwards with an additional radial directional component.

[0027] The invention will now be explained in more detail using exemplary embodiments and with reference to the drawings. The drawings show: Fig. 1 A schematic representation of a combustion chamber system in which three air streams, divided from a total air stream, are added to a combustion chamber, Fig. 2A-C each show a schematic representation of a burner head with feed nozzles in different design variants, Fig. 3A, B a first process step and the resulting relationship between a measured pressure loss and a combustion air flow and Fig. 4A, B a further process step and the resulting relationship between a combustion air flow and an air flow of a pilot stage.

[0028] Fig. Figure 1 shows a schematic representation of a combustion chamber system 1 with a combustion chamber 16 extending along a central longitudinal axis M. A burner head 12 is assigned to the combustion chamber 16 at an inlet-side end face 13 for supplying combustion air and fuel into a combustion chamber 18, which is enclosed by a circumferential wall 14 of the combustion chamber 16. Openings 38 are provided around the perimeter of the circumferential wall 14 in a downstream end region of the combustion chamber 16, near an outlet region 19 located opposite the end face 13. The outlet region 19 opens into an exhaust gas tract 20, downstream of which, for example, a turbine is arranged (not shown here).

[0029] Upstream of the burner head 12, an air plenum 10 is assigned to the combustion chamber system 1, through which a total airflow 30 is supplied to the combustion chamber 16. At the combustion chamber 16, the total airflow 30 is divided into three airflows, which are supplied to the combustion chamber 16 for different purposes via respective supply paths. Specifically, these are a combustion airflow 32, which is supplied to the combustion chamber 18 via a supply device 24 of the burner head 12, here with supply nozzles 22, together with fuel (not shown here). The supply device 24, together with a fuel supply device (not shown here), is assigned to a main stage of a burner of the combustion chamber system 1. The fuel can be added to the combustion chamber 18, for example, via at least one of the supply nozzles 22, or also via separate supply paths.A further airflow, designated as pilot airflow 34, is supplied to a second burner stage, in this case a pilot stage 26 located centrally in the front face 13, together with pilot fuel, and fed into the combustion chamber 18. In this design, the supply nozzles 22 are arranged around the pilot stage 26, in particular in an annular configuration. A third airflow, a mixed airflow 36, is branched off from the total airflow 30. This is fed via a mixing air duct 28, which forms the supply path between the circumferential wall 14 and a pressure housing wall 29, to the openings 38. During operation, the mixed airflow 36 is blended with the exhaust gas downstream of a combustion zone, thus cooling it. The mixed airflow 36 also serves for the convective cooling of the circumferential wall 14. Alternatively, the airflow could be divided into only two airflows, in which case, for example, neither a mixed airflow 36 nor a pilot airflow 34 could be provided.

[0030] The distribution of the quantities of the three air streams can be determined using the method according to the invention, as shown below. To carry out the method, a pressure loss 40 within one of the supply paths, in this case within the supply nozzle 22, is determined. For this purpose, as Fig. Figures 2A to 2C show two pressure measuring points in at least one of the supply nozzles 22, namely a first pressure measuring point 42 in an inlet area 22.1 of the combustion air into the supply nozzle 22 and a second pressure measuring point 44 in an outlet area 22.2 of the supply nozzle 22, between which a differential pressure is measured. The pressure drops between the two pressure measuring points 42, 44, particularly at a cross-sectional constriction within the supply nozzle 22.

[0031] In the Fig. 2A to 2C are different variants of the supply nozzles 22 or their cross-sectional constrictions shown as examples (without fuel supply device). Fig. Figure 2A shows a conical shape of the area, leading to a narrowing of the cross-section between the inlet area 22.1 and the outlet area 22.2. Fig. 2B is the cross-sectional narrowing in the form of a cross-sectional step at an axial position. In Fig. 2C, the cross-sectional narrowing is achieved by a continuously curved wall profile in the feed nozzle 22.

[0032] The first step of the inventive method is in the Fig. 3A and Fig. Figure 3B shows that initially only the first supply path, here the supply device 24 with the supply nozzles 22 of the burner main stage, is open, and the two other supply paths (via the pilot burner 26 and the mixing air duct 28) are closed (indicated with respect to pilot burner 26 in Figure 3B). Fig. 3A, due to the lack of a pilot airflow 34). In a calibration operation on a test bench, the combustion chamber 16 is supplied with a total airflow 30 of a defined quantity without the addition of fuel. The quantity, air temperature, and pressure preferably correspond to the conditions that exist during combustion operation via the supply nozzles 22. The differential pressure between the two pressure measuring points 42, 44 is determined and assigned to the defined air quantity. In order to be able to establish a correlation between combustion airflow and differential pressure over a large operating range, this step is repeated, preferably with several different defined air quantities and with several different pressures and temperatures relevant for combustion operation. Fig. Figure 3B shows the relationship between the determined pressure loss 40 and the quantity of combustion air flow 32 in a first characteristic curve 46 for a given temperature and pressure. In this way, the quantity of combustion air flow 32 can be determined from a determined differential pressure over a wide operating range in real-world operation.

[0033] If only two partial airflows are present, this procedure is sufficient to determine a second airflow and thus the division of the total airflow 30, given knowledge of the total airflow 30 and, with the described procedure step, also of the combustion airflow 32.

[0034] Subsequently, in a further process step within the calibration operation, in addition to the first feed path, here the feed nozzles 22, a second feed path, in this case via the pilot stage 26, is opened (see Fig. 4A, pilot airflow 34 indicated by the highlighted arrow). Now, a total airflow 30, corresponding to a realistic sum of the two partial airflows during combustion, is added at an air temperature and pressure investigated in the first step, and the differential pressure in the supply nozzle 22 is determined. This is preferably repeated for several air volumes, air temperatures, and pressures relevant to combustion in order to obtain a characteristic curve. Advantageously, the pressures and temperatures correspond to those from the first step. Subsequently, using the results from the first step, the respective combustion airflows 32 can first be determined from the measured differential pressures. From these, the respective pilot airflows 34 can in turn be determined from the difference between the total airflow 30 and the combustion airflow 32. Fig.Figure 4B shows in a second characteristic curve 48 an exemplary relationship resulting from this between the quantity of the combustion air flow 32 and the pilot air flow 34. It would also be possible to use the mixed air flow 36 as the second air flow instead of the pilot air flow 34.

[0035] From the two known airflows, the mixed airflow 36 can now also be determined as a third airflow. Although the distribution between combustion airflow 32 and pilot airflow 34 may change when the third supply path for the mixed airflow 36 is additionally opened, the method according to the invention nevertheless achieves greater accuracy than methods known in the prior art. In particular, the combustion airflow 32, which plays a significant role in a stable and low-emission combustion process, can be determined with good accuracy.

[0036] The described method can be advantageously applied to the design of new combustion chamber systems 1, or to the verification of a combustion chamber system 1 already in operation. The determination of the airflow and / or the distribution of the airflows can be carried out following the calibration operation during combustion operation, either once or during special operation, e.g., for the design or verification of a combustion chamber system 1, or even during actual operation. In the latter case, a device for differential pressure measurement with a corresponding pressure sensor would be required to transmit the measured values ​​to a control system for the combustion chamber system 1 or a gas turbine. In particular, the method can also be advantageously applied to a micro gas turbine, since such a system is compact and relatively easily accessible.The combustion chamber 16 could also be occasionally examined on a test bench for maintenance purposes, during which the procedure could be carried out. In general, it may be advantageous to provide the existing pressure measuring points 42, 44 with a seal, for example with a screw cover, so that they can be closed when not in use.

[0037] In principle, two pressure measuring points 42, 44 in a supply path are sufficient to determine the differential pressure. However, it is also possible, for example in the present supply device 24, to have two pressure measuring points 42, 44 in each of several supply nozzles 22. These can be coupled during measurement to obtain an average differential pressure. Parallel individual measurements at several pressure measuring points 42, 44 are also conceivable, allowing for comparison. In this case, an average differential pressure can also be obtained from several parallel differential pressure measurements.

[0038] The method according to the invention provides a simplified and accurate design and / or verification option for low-emission combustion chamber systems 1, as well as a combustion chamber system 1 that allows the implementation of this method.

Claims

[1] Method for determining the distribution of a total air flow (30) in a combustion chamber system (1) of a gas turbine arrangement, in which - when the combustion chamber system (1) is in combustion operation, the total air flow (30) is divided into at least two air flows of specific quantities, which are supplied to a combustion chamber (16) of the combustion chamber system (1) or to the combustion chamber and an exhaust tract (20) adjacent to the combustion chamber (16) via different supply paths for different purposes, - one of the air streams is added as a combustion air stream (32) via a supply path in the form of a supply device (24) for combustion in a combustion chamber (18) of the combustion chamber (16) with supplied fuel in a first burner stage and - a significant pressure loss is caused in at least one first supply path of a first air stream when the corresponding air streams flow through the supply paths, and - a differential pressure is determined within the first supply path and the quantity of the corresponding air flow is determined from the differential pressure. [2] Method according to claim 1, characterized by that the differential pressure is determined between at least one pressure measuring point (42) in an inlet region and at least one pressure measuring point (44) in an outlet region within the supply path, between which the significant pressure loss occurs. [3] Method according to claim 1 or 2, characterized by that initially, in a calibration operation without addition of fuel, in a first step the combustion chamber (16) is subjected to a total air flow (30) of a defined quantity, pressure and air temperature preferably relevant for the combustion operation, wherein only the first supply path is opened and the others are closed and wherein the differential pressure in the first supply path is determined. [4] Method according to claim 3, characterized by that the first step is repeated with several different defined quantities to create an air flow rate-differential pressure characteristic curve (46), preferably at several different air temperatures and / or pressures relevant for the combustion operation. [5] Method according to claim 3 or 4, characterized by that within the calibration operation, in a second step, the combustion chamber (16) is subjected to a total air flow of a defined quantity relevant for the combustion operation, with air temperature and pressure corresponding to the first step, wherein the first supply path and a second supply path are open, and wherein the differential pressure of the first supply path is determined. [6] Method according to claim 5, characterized bythat the quantity of the second air flow is determined from the characteristic curve(s) (46) determined from the first step and the quantity of the total air flow (30) as a function of the quantity of the first air flow, preferably at several air temperatures and / or pressures corresponding to the characteristic curve(s) (46) from the first step. [7] Method according to one of claims 5 or 6, characterized by that the second step is carried out when the combustion chamber (16) is designed to operate with at least three air streams. [8] Method according to one of claims 4 to 7, characterized by that during combustion operation, the distribution of the total air flow (30) is determined at least taking into account the characteristic curve (46) determined from the first step of the calibration operation. [9] Method according to one of the preceding claims, characterized by that the first air flow is formed by the combustion air flow (32). [10] Method according to one of the preceding claims, characterized by that the combustion air flow (32) is fed into the combustion chamber (18) via the supply device (24) arranged on an inlet-side end face (13) of the combustion chamber (16) via at least one supply nozzle (22). [11] Method according to claim 10, characterized by that the combustion air flows through a cross-sectional constriction within the supply nozzle (22). [12] Method according to one of claims 10 or 11, characterized by that the fuel is added upstream of the inlet into the combustion chamber (16) into the combustion air flow (32) for at least partial premixing of combustion air and fuel or separately from the inlet-side end face (13) into the combustion chamber (16). [13] Method according to one of the preceding claims, characterized bythat the second or third air flow is formed by a combustion air flow of a second burner stage, in particular a pilot burner. [14] Method according to one of the preceding claims, characterized by that the second or third air flow is formed by a mixed air flow (36) added to the exhaust gas flow downstream of a combustion zone. [15] Combustion chamber system (1) for applying the method according to one of the preceding claims, with a combustion chamber (16), a combustion chamber (18) enclosed by a peripheral wall (14) of the combustion chamber (16) and at least one fuel supply device, wherein at least two supply paths are assigned to the combustion chamber system (1) for supplying at least two air flows divided from a total air flow (30) for different purposes, wherein one of the supply paths is designed as a supply device for a combustion air flow (32) of a first burner stage formed by one of the air flows, and wherein at least a first of the supply paths is designed such that a significant pressure loss occurs when the corresponding first air flow flows through the supply path, characterized by , that within the first supply path, at least one pressure measuring point (42) in an inlet region (22.1) and at least one pressure measuring point (44) in an outlet region (22.2), between which the significant pressure loss occurs, are provided for determining a differential pressure from which the quantity of the corresponding air flow can be determined. [16] Combustion chamber system (1) according to claim 15, characterized bythat the supply device (24) is arranged on an inlet-side end face (13) of the combustion chamber (16) and has at least one supply nozzle (22), in particular having a cross-sectional constriction in the flow path.

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