Method for operating a forced-flow steam generator operating at a steam temperature above 650°C and forced-flow steam generator

Patent metadata

Field	Value
Publication number	US-8959917-B2
Application number	US-201013387033-A
Country	US
Kind code	B2
Filing date	Jul 30, 2010
Priority date	Aug 4, 2009
Publication date	Feb 24, 2015
Grant date	Feb 24, 2015

Abstract

A method for operating a forced-flow steam generator operating at variable pressure and at a steam temperature above 650° C. and reducing the minimum forced-flow load of the forced-flow steam generator, wherein the economizer of the forced-flow steam generator includes at least one high pressure pre-heater and/or a heat transfer system for preheating the working medium, the at least one high-pressure pre-heater and/or the heat transfer system arranged upstream as viewed in the working medium circuit direction, wherein if a predetermined partial load point is exceeded, the heat absorption of the working medium within at least one high-pressure pre-heater and/or the heat transfer system is reduced so that the temperature of the water/steam working medium at the outlet of the economizer is below the boiling point relative to the corresponding economizer outlet by a predetermined temperature difference, and a forced-flow steam generator for performing the method.

First claim

The invention claimed is:

1. A method for operating a once-through steam generator operating with sliding pressure and at a steam temperature above 650° C. and for lowering its forced-flow minimum load, the once-through steam generator being incorporated into a water/steam-carrying working medium circuit of a power station, and an economizer of the once-through steam generator having upstream, as seen in the working medium circulation direction, at least one HP preheater and one heat transfer system for preheating the working medium, the working medium absorbing heat from a supplied turbine bleed steam stream within the HP preheater or preheaters and absorbing heat from a supplied auxiliary heat stream in the heat transfer system, the method comprising:
reducing, if a predetermined part load point is undershot, the heat absorption of the working medium within at least one HP preheater and the heat transfer system so that the temperature of the water/steam as a working medium at the outlet of the economizer lies at a distance of a predetermined temperature difference below the boiling temperature related to the corresponding economizer outlet pressure,
wherein the reduction in heat absorption is performed by a controlling device, the supply of the auxiliary heat stream to the heat transfer system being prevented completely by the controlling device, and at least part of the water/steam working medium stream being routed past a component located in the water/steam circuit of the heat transfer system by a bypass line.

2. The method as claimed in claim 1 , wherein the reduction in heat absorption is performed by a controlling valve which regulates the quantity of the turbine bleed steam stream supplied to the HP preheater.

3. The method as claimed in claim 1 , wherein the reduction in heat absorption is performed by a controlling valve, the supply of the turbine bleed steam stream to the HP preheater being prevented completely by the controlling valve, and at least part of the water/steam working medium stream being routed past the HP preheater by means of a bypass line.

4. The method as claimed in claim 1 , wherein the reduction in heat absorption is carried out by dividing the working medium stream into two substreams a first substream being routed through the HP preheater and a second substream being routed via a bypass line of the HP preheater, and the two substreams being regulated by at least one controlling valve.

5. The method as claimed in claim 1 , wherein the reduction in heat absorption is performed by a controlling device which regulates a quantity of the auxiliary heat stream supplied to the heat transfer system.

6. A method for operating a once-through steam generator operating with sliding pressure and at a steam temperature above 650° C. and for lowering its forced-flow minimum load, the once-through steam generator being incorporated into a water/steam-carrying working medium circuit of a power station, and an economizer of the once-through steam generator having upstream, as seen in the working medium circulation direction, at least one HP preheater and one heat transfer system for preheating the working medium, the working medium absorbing heat from a supplied turbine bleed steam stream within the HP preheater or preheaters and absorbing heat from a supplied auxiliary heat stream in the heat transfer system, the method comprising:
reducing, if a predetermined part load point is undershot, the heat absorption of the working medium within at least one HP preheater and the heat transfer system so that the temperature of the water/steam as a working medium at the outlet of the economizer lies at a distance of a predetermined temperature difference below the boiling temperature related to the corresponding economizer outlet pressure,
wherein the reduction in heat absorption is carried out by dividing the working medium stream into two substreams, a first substream being routed through the water/steam circuit-side component of the heat transfer system and a second substream being routed via a bypass line of the heat transfer system, and the two substreams being regulated by at least one controlling valve.

7. The method as claimed in claim 1 , wherein the predetermined temperature difference is 20 Kelvin.

8. The method as claimed in claim 1 , 50% of full load is taken as the predetermined part load point.

9. A once-through steam generator operable with sliding pressure and at a steam temperature above 650° C. and suitable for lowering the once-through minimum load, the once-through steam generator being incorporated into a water/steam-carrying working medium circuit of a power station, the once-through steam generator comprising:
an economizer having upstream, as seen in the working medium circulation direction, at least one HP preheater and one heat transfer system for preheating the working medium, heat being capable of being absorbed by the working medium within the HP preheater or preheaters from a turbine bleed steam stream supplied by at least one bleed steam line and heat being capable of being absorbed by the working medium in the heat transfer system from an auxiliary heat stream supplied by a supply line,
wherein, if a predetermined part load point is undershot, the heat absorption of the working medium within at least one HP preheater and the heat transfer system can be reduced so that the temperature of the water/steam as a working medium at the outlet of the economizer can be set at the distance of a predetermined temperature difference below the boiling temperature related to the corresponding economizer outlet pressure, and
wherein the heat transfer system has a bypass line.

10. The once-through steam generator as claimed in claim 9 , wherein the at least one bleed steam line is designed for controlling the turbine bleed steam stream by a controlling valve and/or the supply line for auxiliary heat is designed for controlling the auxiliary heat stream by a controlling device.

11. The once-through steam generator as claimed in claim 9 , wherein the heat transfer system is arranged upstream of the HP preheater, as seen in the direction of circulation of the working medium circuit.

12. The once-through steam generator as claimed in claim 9 , wherein, if a plurality of HP preheaters are present, the heat transfer system is arranged between the HP preheaters, as seen in the direction of circulation of the working medium circuit.

13. The once-through steam generator as claimed in claim 9 , wherein the heat transfer system is arranged parallel to the HP preheater in a parallel circuit, as seen in the direction of circulation of the working medium circuit.

14. The once-through steam generator as claimed in claim 9 , wherein the HP preheater has a bypass line.

15. The once-through steam generator as claimed in claim 9 , wherein the HP preheater has a controlling valve upstream or downstream of the HP preheater, as seen in the direction of circulation of the working medium circuit.

16. The once-through steam generator as claimed in claim 9 , wherein the heat transfer system has a controlling valve upstream or downstream of the heat transfer system, as seen in the direction of circulation of the working medium circuit.

17. The once-through steam generator as claimed in claim 14 , wherein the bypass line has a controlling valve.

Assignees

• Berndt Thoralf
• Chen Qiurong
• Alstom Technology Ltd

Inventors

• Berndt Thoralf
• Chen Qiurong

Classifications

• F01K13/02

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

• F22D1/325

  Schematic arrangements or control devices therefor · CPC title

• F01K7/34

  the engines being of extraction or non-condensing type; Use of steam for feed-water heating (feed-water heaters in general F22D) · CPC title

• F22B29/00

  Steam boilers of forced-flow type · CPC title

• F01K7/22 Primary

  the turbines having inter-stage steam heating · CPC title