Gas turbine power plant with exhaust gas recirculation

Abstract

A method for operating a gas turbine power plant, and a gas turbine power plant in which fresh air is delivered to a compressor inlet and is accelerated in the compressor inlet and a recirculated first exhaust gas substream is delivered into a region of the compressor inlet in which the fresh air is accelerated to an extent such that the difference between total pressure and static pressure in the fresh air is greater than or equal to a pressure difference which is required in order to suck a target mass flow of the recirculated first exhaust gas substream into the compressor inlet.

Claims

1. A method for operating a gas turbine power plant with exhaust gas recirculation, the gas turbine power plant including a gas turbine with a compressor having an inlet, a waste heat recovery steam generator, an exhaust gas divider, a recirculation line, and an exhaust gas recooler, said method comprising: delivering fresh air into the compressor inlet, the fresh air being accelerated in the compressor inlet; controlling the exhaust gas divider to divide exhaust gases from the gas turbine into (1) a first exhaust gas substream for recirculation into an intake stream of the gas turbine and (2) into a second exhaust gas substream for discharge from the gas turbine power plant; recirculating the first exhaust gas substream for delivery, separately from the fresh air, into the compressor inlet; delivering the recirculated first exhaust gas substream, separately from the fresh air, as far as a region of the compressor inlet in which the fresh air is accelerated to an extent such that a difference between total pressure and static pressure in the accelerated fresh air is greater than or equal to a pressure difference for sucking a target mass flow of the recirculated first exhaust gas substream into the compressor inlet; introducing the recirculated first exhaust gas substream to the accelerated fresh air via a plurality of delivery ducts arranged so as to be distributed circumferentially, upstream of the compressor, on a diameter of an intake duct and concentrically to a shaft of the gas turbine; and controlling a quantity of the recirculated first exhaust gas substream by changing an axial position of outlet orifices of the plurality of delivery ducts relative to the compressor inlet.

2. The method as claimed in claim 1, comprising: conducting fresh air into a flow duct of the recirculated first exhaust gas substream via a control or regulating element when the gas turbine is under part load and/or is being started.

3. A gas turbine power plant, comprising: a gas turbine; a waste heat recovery steam generator; a compressor having a compressor inlet; an exhaust gas divider configured to, during operation, divide exhaust gases (1) into a first exhaust gas substream for recirculation into an intake stream of the gas turbine and (2) into a second exhaust gas substream for discharge from the gas turbine power plant; a plurality of ducts for introducing the recirculated first exhaust gas substream to fresh air delivered to the compressor inlet in the intake stream, the plurality of ducts being arranged so as to be distributed circumferentially, upstream of the compressor, on a diameter of an intake duct and concentrically to a shaft of the gas turbine, an axial distance from outlet orifices of the plurality of ducts to the compressor inlet being adjustable in order to regulate or control a quantity of the recirculated first exhaust gas substream, the outlet orifices being sufficiently close to the compressor that, when the gas turbine is in operation, a static pressure at the outlet orifices is sufficiently low that a difference between total pressure and static pressure of the intake stream is greater than or equal to a pressure difference which is required in order to suck a target mass flow of the recirculated first exhaust gas substream into the compressor intel; and a recirculation line for recirculating the first exhaust gas substream from the exhaust gas divider and connected to the plurality of ducts.

4. The gas turbine power plant as claimed in 3, wherein the recirculation line is connected to an inlet for fresh air via a control or regulating element.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

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

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

(3) FIG. 2 shows a gas turbine power plant with recirculation of the exhaust gases and introduction of exhaust gases into a region of the compressor inlet with reduced static pressure;

(4) FIG. 3 shows a perspective view of a divided compressor inlet for introducing recirculated exhaust gases into a region of the compressor inlet with reduced static pressure;

(5) FIG. 4 shows an illustration of the pressure profile in a detail from a compressor inlet upstream of the compressor entry;

(6) FIG. 5 shows a detail of a compressor inlet with a separation element;

(7) FIG. 6 shows a detail of a compressor inlet with a radially variable separation element;

(8) FIG. 7 shows a detail of a compressor inlet with an axially variable separation element;

(9) FIG. 8 shows a compressor inlet with recirculation of the exhaust gases through a multiplicity of delivery ducts arranged in the form of a circle around the gas turbine axis in the compressor inlet.

DETAILED DESCRIPTION

(10) FIG. 1 shows a diagrammatic illustration of the essential elements of a gas turbine power plant with exhaust gas recirculation. The gas turbine 6 comprises a compressor 1, the combustion air compressed therein being delivered to a combustion chamber 4 and being burnt there with 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.

(11) The hot exhaust gases 8 emerging from the turbine 7 are used, for optimal utilization of the energy still contained in them, in a waste heat recovery steam generator (HRSG) 9 in order 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. The steam circuit is illustrated in simplified form and merely diagrammatically in the example. Various pressure stages, feed water pumps, etc. are not shown since these are not the subject of the invention.

(12) The exhaust gases from the waste heat recovery steam generator 9 are divided, downstream of the waste heat recovery steam generator 9 in such a plant, into a first exhaust gas substream 21 and a second exhaust gas substream 20 in an exhaust gas divider 29 which can be open loop or close loop controlled. The first exhaust gas substream 21 is returned to the intake line of the gas turbine 6 and is mixed with fresh air 2 there. The unreturned second exhaust gas substream 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 this 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.

(13) The second exhaust gas substream may also be led to the chimney 32 directly via an exhaust gas bypass 24 having a bypass flap 12.

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

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

(16) FIG. 2 shows diagrammatically an exemplary embodiment of a gas turbine power plant with a compressor inlet which is divided into two sectors, a feeder for fresh air issuing in a first sector 3 of the compressor inlet 3 and a feeder for the recirculated exhaust gas substream 21 issuing into a second sector 3 of the compressor inlet 3. The two inlet sectors 3, 3 adjoin the flow duct of the compressor 1 on that side of the compressor inlet 3 which faces the compressor. The second sector 3 reaches into a region of the compressor inlet 3 in which, when the gas turbine is in operation, the flow is accelerated so sharply that the static pressure has fallen to an extent such that the first exhaust gas substream 21 overcomes the pressure losses in the recirculation line and the pressure loss of the exhaust gas recooler 27.

(17) Low-pressure and medium-pressure cooling gas 33, 34 is branched off from the compressor 1 and delivered for cooling to the hot gas parts of the gas turbine. Further, high-pressure cooling gas 28 is branched off at the end of the compressor or of the following diffuser and is delivered for cooling to the hot gas parts of the gas turbine. FIG. 2 illustrates, for the sake of simplification, only a delivery of cooling gas to the high-pressure turbine 16 and in each case a low-pressure and a medium-pressure cooling gas 33, 34 to the low-pressure turbine 17. For the sake of simplification, a delivery of cooling gas to the combustion chambers 14, 15 is not illustrated, the high-pressure combustion chamber 14 typically being cooled by means of high-pressure cooling air 28 and the low-pressure combustion chamber 15 typically being cooled by means of medium-pressure cooling air 34.

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

(19) FIG. 3 shows in perspective a diagrammatic illustration of a divided compressor inlet for the introduction of exhaust gases into a region of the compressor inlet with reduced static pressure. The fresh air 2 is delivered from one side to the first sector 3 of the compressor inlet 3, is deflected horizontally in this and, after further deflection, is delivered in the direction of the gas turbine axis to the compressor via an annular outlet area.

(20) The recirculated first exhaust gas substream 21 is conducted axially opposite to the main flow direction of the gas turbine to a plane upstream of the compressor inlet 3, is deflected in the second sector 3 of the compressor inlet and is conducted from the side, above the gas turbine axis, upstream of the entry into the gas turbine. As a result of a second deflection, the recirculated first exhaust gas substream 21 is conducted in the direction of the height of the gas turbine axis and is delivered to the compressor, after a further deflection, via an annular outlet area. The two sectors 3, 3 are separated by a partition 45 which reaches into a region having low static pressure, by which the recirculated first exhaust gas substream 21 is sucked into the compressor 1.

(21) The pressure profile in a compressor inlet 3 is shown diagrammatically in FIG. 4. This shows a detail of the compressor inlet 3 upstream of the compressor entry, in which, because of flow acceleration, the pressure falls sharply from an entry pressure p.sub.1 until it reaches the compressor entry pressure p.sub.3. A 90% isobar 47 is depicted in the example. The static pressure has fallen at this 90% isobar 47 to 90% of total pressure as a result of flow acceleration. When the recirculated first exhaust gas substream is introduced into that region of the compressor inlet 3 which lies downstream of these isobars, 10% of the ambient total pressure is available for conveying the recirculated first exhaust gas substream. Typically, a lowering of the static pressure by 5% is sufficient to bring about a return of the exhaust gas into the compressor inlet. In the case of large recirculation lines with low pressure losses, and taking into account possible overpressure in the exhaust system when the recirculated first exhaust gas substream is branched off, a lesser lowering of the static pressure may be sufficient. Thus, introduction may be possible into a region in which the static pressure is lowered by only 1% or 2% of the total pressure. Depending on the desired outflow velocity of the recirculated first exhaust gas substream at the outlet from the second sector of the compressor inlet, a greater lowering of the static pressure may be required and may amount to up to 20% or 30% of the total pressure.

(22) FIG. 5 shows a diagrammatic illustration of a detail of a compressor inlet 3 directly upstream of the compressor. The detail is delimited toward the shaft of the gas turbine by the shaft cover 38 and outwardly by the compressor housing 40. A separation element 45 separates the first sector 3 for the introduction of fresh air 2 from the second sector 3 for introducing the recirculated first exhaust gas substream 3. The pressure of the fresh air p.sub.2 at the entrance of the illustrated detail in the first sector 3 is higher than the pressure of the recirculated first exhaust gas substream p.sub.21 at the entrance of the illustrated detail in the second sector 3. Both pressures p.sub.2, p.sub.21 are markedly higher than the static pressure at the compressor entry p.sub.3. On account of the higher initial pressure, the fresh air is accelerated more sharply in the first sector 3, so that the velocity of the fresh air v.sub.2 at the end of the separation element 45 is higher than the velocity of the recirculated exhaust gas substream v.sub.21. A shear flow separated by a shear layer 50 is thereby formed.

(23) FIGS. 6 and 7 show examples of variable separation elements 49 which make it possible to regulate or control the recirculated first mass exhaust gas stream 21. Typically, in versions with a variable separation element 49, the compressor inlet 3 is divided into two sectors 3, 3 by a fixed partition 45 and a portion of the fixed partition is replaced or supplemented by a variable separation element 49 solely in the outlet region of the sectors 3, 3.

(24) FIG. 6 shows a diagrammatic illustration of a detail of a compressor inlet 3 with a radially variable separation element 49 which adjoins a fixed partition 45. The outlet end may be widened or narrowed in the radial direction.

(25) In order to increase the recirculated first mass exhaust gas stream 21, the variable separation element 49 may be widened in the radial direction away from the axis of the gas turbine in the flow direction, so that the outlet area from the second sector 3 is increased. This makes it possible, for the same flow velocity, to have the inflow of a higher mass flow of recirculated first exhaust gas substream 21.

(26) In order to reduce the recirculated first mass exhaust gas stream 21, the variable separation element 49 may be pushed together in the radial direction toward the axis of the gas turbine, so that the outlet area from the second sector 3 is reduced. Consequently, for the same flow velocity, the inflow of recirculated first exhaust gas substream 21 is reduced.

(27) As an alternative exemplary embodiment, FIG. 7 shows a diagrammatic illustration of a detail of a compressor inlet 3 with an axially variable separation element 49.

(28) In order to increase the recirculated first mass exhaust gas stream 21, the variable separation element 49 may be displaced in the axial direction (to the right) in the flow direction, so that the outlet from the second sector 3 lies in a region having a higher flow velocity and correspondingly lower static pressure.

(29) In order to reduce the recirculated first mass exhaust gas stream 21, the variable separation element 49 may be displaced in the axial direction (to the left) opposite to the flow direction, so that the outlet from the second sector 3 lies in a region having a lower flow velocity and correspondingly higher static pressure.

(30) FIG. 8 shows an alternative delivery of the recirculated exhaust gases 21. Instead of a separate delivery of the recirculated exhaust gases 21 via a second sector 3, divided off by a metal sheet, 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 delivery ducts 39 arranged in the form of a ring axially on the inner wall of the compressor inlet 3. Suitable delivery 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 entry. In the example shown, the pipe connection pieces reach into the inlet nozzle (bellmouth) of the compressor 1. In the example shown, the axial position of the outlet orifices of the pipes can be regulated. This may take place, for example, by means of a telescopic lengthening or shortening of the pipe or displacement of the entire pipe by means of a flexible pipe connection.

(31) The version with a multiplicity of delivery ducts 39 has the advantage that a partition 45 is not needed for separating the compressor inlet 3. This has the advantage during operation that the ratio of fresh air 2 to recirculated exhaust gas 21 can be changed independently of the area ratio of the inlet sectors. Moreover, the displacement of individual pipes can be implemented mechanically in a simpler way than that of a variable partition.