Operation of gas turbine power plant with carbon dioxide separation

Abstract

The invention relates to a method for operating a gas turbine power plant, including a gas turbine, a HRSG following the gas turbine, an exhaust gas blower, and a carbon dioxide separation plant which separates the carbon dioxide contained in the exhaust gases and discharges it to a carbon dioxide outlet, the gas turbine, HRSG, exhaust gas blower, and carbon dioxide separation plant being connected by means of exhaust gas lines. According to the method a trip of the gas turbine power plant includes the steps of: stopping the fuel supply, switching off the exhaust gas blower, and controlling the opening angle of a VIGV at a position bigger or equal to a position required to keep a pressure in the exhaust gas lines between the HRSG and the exhaust gas blower above a minimum required pressure. The invention relates, further relates to a gas turbine power plant configured to carry out such a method.

Claims

1. A method for operating a gas turbine power plant in the event of an emergency shutdown, the gas turbine power plant including a gas turbine, a HRSG downstream of the gas turbine, an exhaust gas blower, and a carbon dioxide separation plant which separates carbon dioxide contained in exhaust gases and discharges separated carbon dioxide to a carbon dioxide outlet, the gas turbine, HRSG, exhaust gas blower, and carbon dioxide separation plant being connected by exhaust gas lines, the method comprising: stopping a fuel supply, switching off the exhaust gas blower, and controlling an opening angle of a VIGV at a position larger than or equal to a position configured to keep a pressure in the exhaust gas lines between the HRSG and the exhaust gas blower above a minimum required pressure to prevent hazardous pressure differences between the exhaust gas side of the HRSG and ambient air.

2. The method for operating a gas turbine power plant according to claim 1, wherein the opening angle of the VIGV is controlled as a function of the pressure in the exhaust gas lines between the HRSG and the exhaust gas blower.

3. The method for operating a gas turbine power plant according to claim 1, wherein the opening angle of the VIGV is controlled as a function of the pressure in the exhaust gas lines between an exhaust gas re-cooler and the exhaust gas blower.

4. The method for operating a gas turbine power plant according to claim 1, wherein the opening angle of the VIGV is kept unchanged at the position when an emergency shutdown signal was received at an emergency shutdown initiation time until a first delay time is reached.

5. The method for operating a gas turbine power plant according to claim 4, wherein the VIGV is closed to a VIGV closed position until a VIGV closed time is reached.

6. The method for operating a gas turbine power plant according to claim 5, wherein a power supply to the VIGV is deactivated when a third delay time is reached.

7. The method for operating a gas turbine power plant according to claim 5, wherein a power supply to the VIGV is deactivated once the VIGV reaches the VIGV closed position.

8. The method for operating a gas turbine power plant according to claim 1, wherein the opening angle of the VIGV is increased to an VIGV open position when an emergency shutdown signal was received at an emergency shutdown initiation time.

9. The method for operating a gas turbine power plant according to claim 1, wherein the opening angle of the VIGV is kept at an opening angle larger than or equal to the opening angle of the VIGV at the time when an emergency shutdown signal was received until a speed of the gas turbine is reduced to a speed limit for closing the VIGV.

10. The method for operating a gas turbine power plant according to claim 1, wherein a cooling air re-cooler is switched off when the emergency shutdown is initiated.

11. A gas turbine power plant, comprising: a gas turbine; a HRSG following the gas turbine; an exhaust gas blower; a carbon dioxide separation plant configured to separate the carbon dioxide contained in exhaust gases from the gas turbine, HRSG and exhaust gas blower and discharge separated carbon dioxide to a carbon dioxide outlet, the gas turbine, HRSG, exhaust gas blower, carbon dioxide separation plant being connected by exhaust gas lines; and a controller configured to control the opening angle of a VIGV at a position larger than or equal to a position configured to keep a pressure in the exhaust gas lines between the HRSG and the exhaust gas blower above a minimum required pressure during a trip of the gas turbine power plant to prevent hazardous pressure differences between the exhaust gas side of the HRSG and ambient air.

12. A gas turbine power plant according to claim 11 comprising: at least one of a HRSG exit pressure sensor and an exhaust gas blower inlet pressure sensor.

13. A gas turbine power plant according to claim 12 wherein the controller is configured to open the VIGV as a function of at least one of a pressure measured by the HRSG exit pressure sensor and a pressure measured by the exhaust gas blower inlet pressure sensor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

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

(2) FIG. 1 shows a schematic illustration of a gas turbine power plant with an exhaust gas blower;

(3) FIG. 2 shows a schematic illustration of a gas turbine power plant with an exhaust gas blower and the pressure profile in the exhaust gas lines;

(4) FIG. 3 shows a schematic illustration of an exemplary change of the VIGV and pressure of power oil over time during a trip;

(5) FIG. 4 shows a schematic illustration of another exemplary change of the VIGV and pressure of power oil over time during a trip.

DETAILED DESCRIPTION

(6) FIG. 1 shows a schematic illustration of the main elements of a gas turbine power plant according to an exemplary embodiment. The gas turbine 6 comprises a compressor 2; the combustion air compressed therein being delivered to a combustion chamber 3 and being burnt there with fuel 5. The hot combustion gases are subsequently expanded in a turbine 4. The useful energy generated in the gas turbine 6 is then converted into electrical energy, for example, by means of a generator (not illustrated) arranged on the same shaft.

(7) The hot exhaust gases emerging from the turbine 4 are conducted through an exhaust gas line 7 for the optimal utilization of the energy still contained in them to a HRSG 8 (Heat Recovery Steam Generator, or in a waste heat boiler) and are used for evaporating feed water 16 and for generating live steam 15 for a steam turbine (not illustrated) or for other plants. The steam circuit is indicated merely schematically by the HRSG 8. The steam turbine, condenser, various pressure stages, feed water pumps, etc. are not shown since these are not the subject of the invention.

(8) The exhaust gases from the HRSG 8 are conducted further on, downstream of the HRSG 8, through the exhaust gas line 7 in an exhaust gas re-cooler 9. In this exhaust gas re-cooler 9, which may be equipped with a condenser, the exhaust gases are cooled to somewhat (typically 5° C. to 20° C.) above ambient temperature. Downstream of this exhaust gas re-cooler 9, in the exhaust gas line 7, an exhaust gas blower 10 is arranged which is followed by a carbon dioxide separation plant 11. In this carbon dioxide separation plant 11, carbon dioxide is separated out of the exhaust gases and discharged via a carbon dioxide outlet (14). The separated carbon dioxide can then, for example, be compressed for further transport and storage.

(9) The carbon dioxide lean exhaust gas 18, low in CO2, from the carbon dioxide separation plant 11 is discharged into the surroundings via a chimney 13. The pressure loss of the carbon dioxide separation plant 11 can be overcome by means of the exhaust gas blower 10. Depending on the design and back pressure of the gas turbine 6 or HRSG 8, moreover, the pressure loss of the re-cooler 9, of the exhaust gas lines 7, of the chimney 13 and/or of the HRSG are also at least partly overcome by means of the exhaust gas blower 10.

(10) Upstream of the exhaust gas re-cooler 9 is arranged a bypass chimney 12 which makes it possible to operate the gas turbine and HRSG when the carbon dioxide separation plant 11 is not operative, for example for maintenance work. In normal operation, the inlet to the bypass chimney 12 is closed, so that all the exhaust gases are discharged into the surroundings through the re-cooler 9, the exhaust gas blower 10, the carbon dioxide separation plant 11 and the chimney 13. In bypass operation, the inlet into the bypass chimney 12 is opened, so that the exhaust gases can be discharged into the surroundings directly via the bypass chimney 12. To regulate the exhaust gas streams, flaps or valves may be arranged in the exhaust gas lines 7 and the bypass chimney 12. For example, a flap (not shown) may be arranged in the exhaust gas line 7 between the bypass chimney and exhaust gas re-cooler 9, in order to suppress flow into the re-cooler in the event of a shutdown of the carbon dioxide separation plant 11.

(11) The gas turbine power plant 1 comprises a controller 22 for controlling the operation of the gas turbine, the HRSG (typically also including a water steam cycle—not shown) and the this carbon dioxide separation plant 11 including the re-cooler 9 and the exhaust gas blower 10. Typically a plant controller 22 has a hierarchical architecture with sub-controllers for the main components, e.g. one sub-controller for the gas turbine 6, one sub-controller for the water steam cycle and one controller for the carbon dioxide separation plant 11

(12) The gas turbine 6 comprises a VIGV 19 (variable inlet guide vane) for controlling the inlet mass flow of the compressor 2. The fuel flow can be controlled by a fuel control valve 23. The exhaust gas blower 10 can be controlled to match the mass flow of the exhaust gas mass flow entering the carbon dioxide separation plant 11 with the exhaust gas mass flow leaving the gas turbine 6. Matching of the exhaust gas mass flow entering the carbon dioxide separation plant 11 with the exhaust gas mass flow leaving the gas turbine 6 leads to the correct pressure in the exhaust gas line 7. For measurement of the pressure in the exhaust gas system a HRSG exit pressure measurement 20 and an exhaust gas blower inlet pressure measurement 21 are installed along the exhaust gas flow path.

(13) The VIGV 19 and the fuel control valve 23, respectively an actuator and/or position transmitter, are connected to the controller 22 by a control line 24. Further, the exhaust gas blower 10 is connected to the controller 22 by a control line 24, and the HRSG exit pressure measurement 20 as well as the exhaust gas blower inlet pressure measurement 21 are connected to the controller 22 by control lines 24.

(14) FIG. 2 shows the plant from FIG. 1 in even more simplified form. In addition, the pressure profile in the exhaust gas line 7, the HRSG 8, the exhaust gas re-cooler 9, the exhaust gas blower 10 and the carbon dioxide separation plant 11 is indicated for standard operation S and for the critical operating state during conventional a trip T (emergency shutdown). The pressure profile in the exhaust gas line 7 is further shown for operation with the proposed controlled VIGV position V.

(15) The pressure profile for standard operation S is selected in the example shown such that, between the gas turbine and the bypass chimney 12, it corresponds to the pressure profile in a conventional gas turbine combined-cycle power plant without carbon dioxide separation, that is to say the pressure at the outlet of the turbine is so high that the pressure loss of the HRSG 8 is overcome. Downstream of the HRSG 8, the pressure b is virtually identical to the ambient pressure. Downstream of the exhaust gas re-cooler 9, the pressure c falls below the ambient pressure before it is raised by the exhaust gas blower 10 to a pressure d which is sufficiently high to overcome the pressure loss of the carbon dioxide separation plant 11 and discharge the exhaust gases into the surroundings via the chimney 13. The exhaust gas blower 10 is regulated such that the pressure at the inlet of the bypass chimney 12 is virtually identical to the ambient pressure.

(16) Starting from the pressure profile for standard operation S, the pressure in the exhaust gas tract, in the event of a trip T, falls within a few seconds, since the exhaust gas blower conveys a higher exhaust gas stream than emerges from the turbine. The pressure is below ambient pressure as early as at the outlet of the turbine. The pressure falls further due to the pressure loss of the exhaust gas lines 7, HRSG 8 and exhaust gas re-cooler 9. The under-pressure in the HRSG 8 and re-cooler 9 and also in the exhaust gas lines 7 may in this case become dangerously high. The pressure is raised again only by the exhaust gas blower 10 to an extent such that the pressure loss, reduced in proportion to the volume flow, of the carbon dioxide separation plant 11 can be overcome.

(17) In order both to avoid a high under-pressure, a new method of controlling the VIGV 19 in case of a trip is proposed leading to a moderate pressure distribution at all times.

(18) The change of the VIGV and pressure of power oil over time during a shut-down shown according to an exemplary embodiment is shown in FIG. 3.

(19) According to the state of the art the VIGV is closed from a VIGV.sub.open position to a VIGV.sub.closed position as fast as possible (not shown in FIG. 3) once the controller receives a trip signal or determines to trip the machine based on other measurements.

(20) According to the proposed method and in contrast to the conventional method the VIGV is kept in the open position VIGV.sub.open for a first delay time t.sub.1 and then closed to a VIGV closed position VIGV.sub.closed. In this example it is closed with a constant closing speed to reach the VIGV closed position VIGV.sub.closed at prescribed time called VIGV closed time t.sub.2. Shortly after the VIGV reaches the VIGV closed position VIGV.sub.closed the power oil for driving the actuators of the VIGVs is shut off at a third delay time t.sub.3.

(21) If the plant was operating at part load the VIGV does not have to be in a fully open position before the shutdown. According to this embodiment the VIGV will be kept at an unchanged position till the first delay time t.sub.1 is reached.

(22) FIG. 4 shows a schematic illustration of another exemplary change of the VIGV and pressure of power oil over time during a trip. FIG. 4 is based on FIG. 3. Here the gas turbine was operating at part load before the trip occurs. Correspondingly the VIGV is closed to a part load position VIGV.sub.part. The method shown in FIG. 4 differs from the method of FIG. 3 in that the VIGV is opened to VIGV open position VIGV.sub.open between the time of the trip t.sub.0 and a VIGV open time t.sub.4. The VIGV open time t.sub.4 can be predetermined or a function of the part load position of the VIGV before the trip and the (maximum) opening speed of the VIGV.