Method of operating a gas turbine power plant with exhaust gas recirculation and corresponding gas turbine power plant

Abstract

The invention relates to a method for operating a gas turbine, in which an oxygen-reduced gas and fresh air are delivered to a compressor of the gas turbine in a radially staged manner, the fresh air being delivered via an outer sector of the inlet cross section in relation to the axis of rotation of the compressor, and the oxygen-reduced gas being delivered via an inner sector of the inlet cross section in relation to the axis of rotation of the compressor. The invention relates, further, to a gas turbine power plant with a gas turbine having a compressor inlet which is followed by the flow duct of the compressor and which is divided into an inner sector and an outer sector, a feed for an oxygen-reduced gas being connected to the inner sector of the compressor inlet, and a fresh air feed being connected to the outer sector of the compressor inlet.

Claims

1. A method for operating a gas turbine having a compressor with an inlet cross section, a combustion chamber and a turbine, said method comprising: delivering an oxygen-reduced gas, which has an oxygen concentration which is lower than an average oxygen concentration of a compressor intake flow, and delivering fresh air to the compressor in a radially staged manner as part of the compressor intake flow, wherein the fresh air is delivered via an outer sector of the inlet cross section in relation to an axis of rotation of the compressor, and the oxygen-reduced gas is delivered via an inner sector of the inlet cross section in relation to the axis of rotation of the compressor, wherein the inner and outer sectors of the inlet cross section are separated by an inlet guide plate, wherein the inlet guide plate is aligned with shroud segments attached to each guide vane and moving blade of the compressor, and wherein the fresh air and the oxygen-reduced gas are delivered into the inlet cross section in a direction normal to an axis of rotation of the compressor.

2. The method as claimed in claim 1, comprising: dividing exhaust gases of the gas turbine into a first exhaust gas flow for recirculation into the compressor intake flow of the gas turbine and into a second exhaust gas flow for discharge into surroundings; and delivering the first exhaust gas flow as the oxygen-reduced gas to the compressor via the inner sector of the inlet cross section.

3. The method as claimed in claim 2, wherein a lean gas is delivered via the inner sector of the inlet cross section of the compressor.

4. The method as claimed in claim 1, wherein at least 95% of the oxygen-reduced gas is guided into the combustion chamber of the gas turbine.

5. The method as claimed in claim 1, wherein the fresh air is introduced into a compressor inlet without being intermixed with the oxygen-reduced gas, and at least part of the fresh air compressed in the compressor is branched off as cooling gas for cooling of hot gas parts.

6. The method as claimed in claim 1, wherein the oxygen-reduced gas is introduced via feeds arranged upstream of a compressor inlet, so as to be distributed in a circumferential direction on a diameter of an intake duct concentrically with respect to the axis of rotation of the compressor.

7. The method as claimed in claim 1, wherein an oxygen content of the oxygen-reduced gas compressed by the compressor and introduced into the combustion chamber is at least 3% below an average oxygen content of cooling gases branched off from the compressor.

8. The method as claimed in claim 1, comprising: when the gas turbine is under part load and/or is being started, guiding the fresh air into the inner sector of the compressor inlet via a regulating element.

9. A gas turbine power plant, comprising: a compressor having a compressor inlet; a combustion chamber following the compressor; a turbine following the combustion chamber, wherein an inlet cross section of the compressor, which a flow duct of the compressor follows, is divided into an inner sector in relation to an axis of rotation of the compressor and an outer sector in relation to the axis of rotation of the compressor, wherein the inner sector and the outer sector of the inlet cross section are separated by an inlet guide plate, and wherein an entry point of fresh air and an oxygen-reduced gas into the compressor inlet is normal to an axis of rotation of the compressor; a shroud segments attached to each guide vane and moving blade of the compressor is aligned with the inlet guide plate; a feed for the oxygen-reduced gas, having an oxygen concentration lower than an average oxygen concentration of a compressor intake flow during operation of the gas turbine, wherein the feed is connected to the inner sector of the compressor inlet; and a fresh air feed connected to the outer sector of the compressor inlet.

10. The gas turbine power plant as claimed in ciaim 9, wherein the gas turbine power plant comprises: an exhaust gas divider which is connected by a recirculation line to the inner sector for recirculation of a first exhaust gas flow as the oxygen-reduced gas and which is connected to an exhaust gas line for discharge of a second exhaust gas flow into surroundings.

11. The gas turbine power plant as claimed in claim 9, wherein the inner sector and the outer sector of the compressor inlet are configured as concentric circular rings at a connection to the flow duct of the compressor.

12. The gas turbine power plant as claimed in claim 9, wherein an area ratio of an area of connection of the outer sector to the flow duct of the compressor to an area of connection of the inner sector to the flow duct of the compressor is selected so as to be equal to a ratio of volume flows of the fresh air to a first exhaust gas flow as the oxygen-reduced gas under design conditions of the gas turbine.

13. The gas turbine power plant as claimed in claim 9, comprising: a regulating element by which an area ratio of an area of connection of the outer sector to the flow duct of the compressor to an area of connection of the inner sector to the flow duct of the compressor is variable to match the area ratio to changes in a ratio between the fresh air and a first exhaust gas flow as the oxygen-reduced the gas.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Preferred embodiments of the disclosure are described below by means of the drawings which serve merely for explanatory purposes and are not to be interpreted restrictively. In the drawings:

(2) FIG. 1 shows a diagrammatic illustration of a gas turbine power plant with recirculation of the exhaust gases according to the prior art;

(3) FIG. 2 shows a diagrammatic illustration of a gas turbine power plant with recirculation of the exhaust gases and with the coaxial introduction of exhaust gases and fresh air into the compressor;

(4) FIG. 3 shows a diagrammatic illustration of a divided compressor inlet and compressor of a gas turbine power plant with recirculation of the exhaust gases;

(5) FIG. 4 shows a diagrammatic illustration of a detail of a compressor inlet and compressor of a gas turbine with recirculation of exhaust gases and with separating shroud segments on compressor guide vanes and compressor moving blades;

(6) FIG. 5 shows a diagrammatic illustration of a compressor inlet and compressor of a gas turbine power plant with recirculation of the exhaust gases via a multiplicity of feed ducts arranged in the compressor inlet in the form of a circle about the gas turbine axis.

DETAILED DESCRIPTION

(7) FIG. 1 shows a diagrammatic illustration of the essential elements of a gas turbine power plant. The gas turbine 6 comprises a compressor 1, and the combustion air compressed therein is delivered to a combustion chamber 4 and burnt there by means of fuel 5. The hot combustion gases are subsequently expanded in a turbine 7. The useful energy generated in the turbine 7 is then converted into electrical energy, for example, by means of a first generator 25 arranged on the same shaft 37.

(8) The hot exhaust gases 8 emerging from the turbine 7, and so as to optimally utilize the energy still contained in them in a waste heat recovery steam generator 9 (HRSG), are employed to generate fresh steam 30 for a steam turbine 13 or for other plants. The useful energy generated in the steam turbine 13 is then converted into electrical energy, for example, by means of a second generator 26 arranged on the same shaft 37. The steam circuit is illustrated in the example in simplified form and merely diagrammatically. Various pressure stages, feed water pumps, etc. are not shown since these are not the subject of the invention.

(9) In such a plant, the exhaust gases from the waste heat recovery steam generator 19 are divided into a first exhaust gas subflow 21 and a second exhaust gas subflow 20 downstream of the waste heat recovery steam generator 9 in an exhaust gas divider 29 which can be regulated. The first exhaust gas subflow 21 is returned to the intake line of the gas turbine 6 and intermixed there with fresh air 2. The non-returned second exhaust gas subflow 20 is discharged into the surroundings or, as in this example, is cooled further via an exhaust gas recooler 23 and delivered to a CO.sub.2 separation system 18. Low-CO.sub.2 exhaust gases 22 are discharged from the latter into the surroundings via a chimney 32. In order to overcome the pressure losses of the CO.sub.2 separation system 18 and the exhaust gas line, an exhaust gas blower 10 may be provided. The CO.sub.2 31 separated in the CO.sub.2 separation system 18 is typically compressed and diverted for storage or further treatment. The CO.sub.2 separation system 18 is supplied via steam extraction with steam branched off from the steam turbine 13.

(10) The second exhaust gas subflow may also be routed directly to the chimney 32 via an exhaust gas bypass 24 having a bypass flap 12.

(11) The returned first exhaust gas flow 21 is cooled to somewhat above ambient temperature in an exhaust gas recooler 27 which may be equipped with a condenser. Downstream of this exhaust gas recooler 27, a booster or exhaust gas blower 11 for the recirculation flow 21 may be arranged. This returned exhaust gas flow 21 is intermixed with the fresh air 2 before the mixture is delivered as an intake flow via the compressor inlet 3 of the gas turbine 6.

(12) In contrast to FIG. 1, a gas turbine with sequential combustion is illustrated in FIG. 2. The method can be applied to gas turbines with a combustion chamber and to gas turbines with sequential combustion. Versions for gas turbines with a combustion chamber and for gas turbines with sequential combustion are also possible correspondingly.

(13) FIG. 2 shows diagrammatically an exemplary embodiment of a gas turbine power plant with a compressor inlet which is divided into two sectors, a feed for fresh air 2 issuing in an outer sector 3 of the compressor inlet 3 and a feed for an exhaust gas flow 21 issuing into an inner sector 3 of the compressor inlet 3.

(14) The two inlet sectors 3, 3 directly follow the flow duct of the compressor 1 on that side of the compressor inlet 3 which faces the compressor. The outer sector 3 for fresh air in this case issues onto an outer annular area of the flow duct, and the inner sector 3 for exhaust gas recirculation issues onto an inner annular area of the flow duct.

(15) Low-pressure and medium-pressure cooling gas 33, 34 is branched off from the radial outer wall of the compressor 1 and is delivered to the hot gas parts of the gas turbine for cooling purposes. Further, at the end of the compressor, high-pressure cooling gas 28 is branched off from the radial outer wall of the compressor or of the adjoining diffuser and is delivered to the hot gas parts of the gas turbine for cooling purposes. For the sake of simplification, FIG. 2 illustrates only a cooling gas feed to the high-pressure turbine 16 and to the low-pressure turbine 17. For the sake of simplification, a cooling gas feed to the combustion chambers 14, 15 is not illustrated, although the high-pressure combustion chamber 14 is typically cooled by high-pressure cooling air 28 and the low-pressure combustion chamber 15 typically cooled by medium-pressure cooling air 34. Since the oxygen-rich fresh air is guided into the region outside the compressor, a large part of said fresh air is routed as cooling gas 33, 34, 28 around the combustion chambers 14, 15, while the low-oxygen recirculated exhaust gases are compressed in the core region of the compressor 1 as far as the compressor end and enter the high-pressure combustion chamber 14. As a result of the separation of the gas feed in the compressor inlet 3, a large fraction of low-oxygen recirculated exhaust gases is guided into the high-pressure combustion chamber 14. The oxygen fraction in the inlet gases of the low-pressure combustion chamber 15 is thus also markedly reduced, as compared with a plant in which the recirculated exhaust gases 21 are intermixed with fresh air 2.

(16) In order to implement a homogeneous velocity profile in the flow toward the compressor in various operating states of the gas turbine and the associated changes in the fraction of recirculated exhaust gas 21 and the compressor intake quantity, in the exemplary embodiment shown in FIG. 2 a regulating element 42 is provided, via which fresh air 2 is admixed to the first exhaust gas flow 21 before said fresh air is introduced into the compressor 1 via the inner sector 3 of the compressor inlet 3.

(17) FIG. 3 shows diagrammatically an exemplary embodiment of a divided compressor inlet and compressor of a gas turbine power plant with recirculation of the exhaust gases. In the example shown, the compressor inlet 3 is divided by an inlet guide plate 45 into an outer sector 3 for fresh air 2 and an inner sector 3 for recirculated exhaust gases 21. This division of the compressor inlet 3 leads to an essentially coaxial inflow of recirculated exhaust gas 21 and fresh air into the compressor 1. In the example shown, the recirculated exhaust gases 21 are compressed in the compressor 1 by means of an annular space adjacent to the shaft 37 on the inside. The fresh air 2 is compressed in the compressor 1 in an annular space adjacent to the compressor casing 40 on the outside. In the example shown, gas for the secondary gas system of the gas turbine 6 is branched off via compressor extraction points 41 at two points in the compressor 1. The secondary gas is typically used for the cooling of hot gas parts and moreover, depending on the design, is used, for example, in the bearing region as scavenging or sealing gas. Low-pressure cooling gas 33 is branched off from the first extraction point 41 and medium-pressure cooling gas 34 is branched off from the second extraction point 41. High-pressure cooling gas 28 is branched off from the compressor plenum 36. High-pressure cooling gas 35 also flows from the end of the compressor 1 into a channel between the shaft cover 46 and the shaft 37 in order to cool the shaft 37.

(18) Even in the case of a coaxial feed of fresh air 2 and recirculated exhaust gas 21, intermixing of fresh air 2 and of recirculated exhaust gas 21 occurs on account of secondary flows in the compressor 1. This can reduce the positive effect of the separate feeding of fresh air 2 and recirculated exhaust gas 21 in the compressor inlet. In order to minimize this intermixing in the compressor 1, a compressor with blades having separating shroud segments is proposed.

(19) FIG. 4 shows an exemplary embodiment in which all the compressor guide vanes 43 and all the compressor moving blades 44 are designed with separating shroud segments 38 which, in the assembled state, join together at each stage to form a coherent separating shroud.

(20) One version of a separating shroud is shown in section B-B by the example of the first compressor stage. In the example, at each moving blade, a separating shroud segment 38 is arranged at about 50% of the height of the airfoil and extends essentially perpendicularly with respect to the airfoil in the radial direction.

(21) FIG. 5 shows an alternative feeding of the recirculated exhaust gases 21. Instead of separate feed of the recirculated exhaust gases 21 via an inner sector 3, partitioned off by a plate, of the compressor inlet for recirculated exhaust gases 21, an undivided compressor inlet 3 is used, into which the recirculated exhaust gases 21 are introduced via a multiplicity of feed ducts 39 arranged in the form of a ring axially on the inner wall of the compressor inlet 3. Suitable feed ducts 39 are, for example, pipes or pipe connection pieces, the outlet ends of which are oriented parallel to the main flow in the direction of the compressor inlet. In the example shown, the pipe connection pieces reach into the entry nozzle (bellmouth) of the compressor 1 in order to minimize intermixing with fresh air 2.

(22) The pipe connection pieces may also end in the actual compressor inlet 3 or end even at the wall of the compressor inlet 3. The ends should preferably be arranged in the form of a ring about the axis of the gas turbine.

(23) The version with a multiplicity of feed ducts 39 has the advantage that there is no need for an inlet guide plate 45 in order to separate the compressor inlet 3. The advantage of this, during operation, is that the ratio of fresh air to recirculated exhaust gas can be changed independently of the area ratio of the inlet sectors.