Combined cycle power plant black start method where steam turbine provides increase in demanded load

Patent metadata

Field	Value
Publication number	US-9328668-B2
Application number	US-201213600965-A
Country	US
Kind code	B2
Filing date	Aug 31, 2012
Priority date	Sep 7, 2011
Publication date	May 3, 2016
Grant date	May 3, 2016

Abstract

A reliable and flexible black start network restoration for a combined cycle power plant can be achieved by synchronizing a steam turbine and ramping that steam turbine up to an operating point where a maximum power increase is achieved. The resulting steam turbine load change can be compensated by the gas turbine. The increase in the demanded load can be provided by the steam turbine. The load of the steam turbine can also be gradually reduced to increase its load-increasing capacity.

First claim

What is claimed is:

1. A method for operating a combined cycle power plant during a black start, the combined cycle power plant comprising a gas turbine and a steam turbine that generate alternating voltage of an assigned frequency and deliver the alternating voltage to an AC network via an electric generator connected to the gas turbine and an electric generator connected to the steam turbine, wherein flue gas of the gas turbine is used for producing steam for the steam turbine for network restoration, the method comprising:
a) supplying internal consumers by the gas turbine in island mode, an operating point of the gas turbine being set for such supplying such that a minimum steam temperature is achieved for the steam turbine;
b) synchronizing and ramping up the steam turbine in island mode to an operating point at which a maximum power increase is achievable, a load change of the steam turbine created from the internal consumers being compensated for by the gas turbine such that a network-side power consumption corresponds to zero MW;
c) connecting consumer loads block by block;
d) providing power for an increase in demanded load from the connected consumer loads via the steam turbine;
e) reducing a load of the steam turbine gradually while increasing a load on the gas turbine to maintain power output from the combined cycle power plant such that load-increasing capacity of the steam turbine is increased such that a subsequent change to steam turbine operations is actuatable to accommodate an increase in load at a later time; and
f) repeating steps c) to e) until a base load of the combined cycle power plant is achieved.

2. The method as claimed in claim 1 , wherein in step a) provision is made for the minimum steam temperature which is determined or regulated on account of a rotor temperature of the steam turbine and by an optimum operating point of the gas turbine.

3. The method as claimed in claim 1 wherein in step b) total output power is used for the station service of the combined cycle power plant such that the steam turbine alone, or the steam turbine and the gas turbine together, or the gas turbine alone, provides power for the internal consumers based upon an optimum operating point for the gas turbine.

4. The method as claimed in claim 1 , wherein in step b) surplus power available via operation of the steam turbine and the generator connected to the steam turbine that cannot be used by any internal consumer as the combined power plant operates in island mode is used for operating a compressor of the gas turbine.

5. The method as claimed in claim 1 , wherein in steps a) and b), in island mode of the power plant the current generated by generators connected to an alternating current network corresponds to zero.

6. The method as claimed in claim 1 , wherein in step d) the demanded load is provided by a coordinated and simultaneous reaction of the gas turbine, the steam turbine, and one or more bypass stations that are configured to discharge steam from an evaporator to a condenser such that a portion of steam from the evaporator bypasses the steam turbine, and wherein network frequency is selectively controlled by the gas turbine or the steam turbine.

7. The method as claimed in claim 1 , wherein in step d) the demanded load is provided totally by the steam turbine.

8. The method as claimed in claim 1 , wherein as a result of a permanent provision of the demanded load by the steam turbine the load ranges of the gas turbine operation which is restricted by process or emissions limitations are avoided.

9. The method as claimed in claim 1 , wherein the steam turbine is operated so that both the possibility of a load increase and of a load decrease of the steam turbine is provided.

10. The method as claimed in claim 1 , wherein a minimum load of the steam turbine is maintained in such a way that in the case of single-shaft configurations opening of the coupling, or in the case of multishaft configurations opening of the generator circuit-breaker, is avoided.

11. The method as claimed in claim 1 , wherein the minimum steam temperature is determined based on a rotor temperature of the steam turbine.

12. The method as claimed in claim 1 , comprising:
controlling the minimum steam temperature based on a rotor temperature of the steam turbine and by an optimum operating point of the gas turbine that allows a corresponding exhaust temperature of the flue gas of the gas turbine.

13. The method as claimed in claim 1 , wherein in step d) the demanded load is provided by the steam turbine so that a gap between a demanded load and a total reaction of the gas turbine is covered by the steam turbine.

14. The method as claimed in claim 1 , wherein in step d) the demanded load is provided by a coordinated and simultaneous reaction of the gas turbine, the steam turbine, and at least one bypass station, each bypass station being configured such that steam from an evaporator of a waste heat steam generator bypasses the steam turbine and is sent directly to a condenser that condenses steam for sending the condensed steam to the evaporator of the waste heat steam generator.

15. The method as claimed in claim 14 , wherein network frequency is selectively controlled by the gas turbine or the steam turbine.

16. A method for operating a combined cycle power plant during a black start, the combined cycle power plant comprising a gas turbine and a steam turbine that generate alternating voltage of an assigned frequency and deliver the alternating voltage to an AC network via an electric generator connected to the gas turbine and an electric generator connected to the steam turbine, wherein flue gas of the gas turbine is used for producing steam for the steam turbine for network restoration, the method comprising:
a) supplying steam to the steam turbine via operation of the gas turbine in island mode during the black start, an operating point of the gas turbine being set for such supplying such that a minimum steam temperature is achieved for the steam turbine;
b) synchronizing and ramping up the steam turbine in island mode to an operating point at which a maximum power increase is achievable, a load change of the steam turbine created from internal consumers being compensated for by the gas turbine ramping down while the steam turbine is ramped up while a network-side power consumption corresponds to zero MW during the black start;
c) connecting consumer loads block by block; and
d) providing power for an increase in the demanded load created via the connecting of the consumer loads via the steam turbine.

17. The method of claim 16 , comprising:
e) after the consumer loads are connected, reducing the load of the steam turbine gradually such that load-increasing capacity of the steam turbine is increased such that a subsequent change to steam turbine operations is actuatable to accommodate an increase in load at a later time; and
f) during the gradual reduction of load of the steam turbine, increasing load of the gas turbine to maintain power output.

18. The method of claim 17 , comprising:
controlling the minimum steam temperature based on a rotor temperature of the steam turbine and by an optimum operating point of the gas turbine that allows a corresponding exhaust temperature of the flue gas of the gas turbine.

19. The method of claim 16 , comprising:
e) after a first block of the consumer loads are connected:
reducing the load of the steam turbine such that load-increasing capacity of the steam turbine is increased such that a subsequent chan

Assignees

• Schlesier Jan
• Olia Hamid
• Schoenenberger Martin
• Liebau Martin
• Alstom Technology Ltd

Inventors

• Schlesier Jan
• Olia Hamid
• Schoenenberger Martin
• Liebau Martin

Classifications

• F22B1/1815

  using the exhaust gases of gas-turbines · CPC title

• Y02E20/14

  Combined heat and power generation [CHP] · CPC title

• F01K13/02 Primary

  Controlling, e.g. stopping or starting · CPC title

• F01K23/101

  Regulating means specially adapted therefor (F01K23/105, F01K23/108 take precedence) · CPC title

• F02C6/18

  using the waste heat of gas-turbine plants outside the plants themselves, e.g. gas-turbine power heat plants (using waste heat as source of energy for refrigeration plants F25B27/02; using the waste heat of a gasturbine for steam generation or in a steam cycle see F01K23/10) · CPC title