Method for controlling a steam generator and control circuit for a steam generator

Patent metadata

Field	Value
Publication number	US-10167743-B2
Application number	US-86906910-A
Country	US
Kind code	B2
Filing date	Aug 26, 2010
Priority date	Feb 26, 2008
Publication date	Jan 1, 2019
Grant date	Jan 1, 2019

Abstract

In a method for controlling a waste heat recovery steam generator of the once-through steam generator type in a combined cycle power plant, the flow volume of the feedwater into the steam generator is controlled based on a measured steam temperature at the outlet of a superheater and on a set-point value for the steam temperature for a steam turbine. A degree of superheating at the outlet of a high-pressure evaporator, a degree of subcooling at the inlet into the high-pressure evaporator, and the measured current flow volume of the feedwater are integrated in the control system in a plurality of control steps. For an optimum operation during rapid load changes, the method especially comprises additional controlling of the degree of subcooling of the flow medium at the inlet into the high-pressure evaporator.

First claim

What is claimed is:

1. A method for controlling a steam generator of a once-through steam generator type, which is integrated in a combined cycle power plant with a steam turbine and a gas turbine, the steam generator comprising a high pressure economizer, a high pressure evaporator, and at least one superheater,
wherein opening of a valve for regulating flow volume in a feedwater supply line into the high-pressure evaporator is controlled in dependence upon a temperature set-point value for steam for the steam turbine and also upon a measured steam temperature at the outlet of the at least one superheater and by means of a plurality of control steps in series,
wherein the measured steam temperature at the outlet of the superheater, a degree of superheating in consideration of a prevailing saturation temperature at the outlet of the high-pressure evaporator and a degree of subcooling of the feedwater in consideration of a prevailing saturation temperature at the inlet into the high-pressure evaporator are integrated in the control steps,
wherein the method comprises the steps:
measuring steam temperature at the outlet of the superheater,
in a first control step, comparing the steam temperature at the outlet of the superheater with a set-point value for turbine steam temperature at the outlet of the superheater according to an operating state of the steam turbine, and generating a set-point value for the degree of superheating at the outlet of the high-pressure evaporator based on the difference between the measured value and the set-point value of the steam temperature at the outlet of the superheater,
measuring the current degree of superheating at the outlet of the high-pressure evaporator,
in a second control step, generating a set-point value for the degree of subcooling of the feedwater at the inlet of the high-pressure evaporator based on the difference between the set-point value and current measured value of the degree of superheating at the outlet of the high-pressure evaporator,
measuring the current degree of subcooling of the feedwater at the inlet into the high-pressure evaporator,
in a third control step, generating a set-point value for the flow volume for the feedwater upstream of the high-pressure evaporator based on the difference between the set-point value and the current measured value for the degree of subcooling of the feedwater at the inlet into the high-pressure evaporator,
based on the set-point value for the flow volume of the feedwater, generating a control signal for the opening of a valve in the feedwater supply line and transmitting the control signal to the valve,
wherein the set-point value for the degree of superheating at the outlet of the high-pressure evaporator is determined between a maximum value (Max Sh) and a minimum value (Min Sh), said maximum value (Max Sh) being a value established to prevent an exceeding of the steam temperature beyond a permissible material temperature at the outlet of the high pressure evaporator and said minimum value (Min Sh) being a value established to prevent a saturation state at the outlet of the high-pressure evaporator.

2. The method as claimed in claim 1 , wherein after determining the set-point value for the flow volume of the feedwater, these steps are additionally carried out:
measuring the current flow volume of the feedwater into the high-pressure evaporator,
in a fourth control step, generating a control signal for an opening position of the valve in a feedwater supply line upstream of the high-pressure evaporator based on the difference between the set-point value for the flow volume of the feedwater and the current measured flow volume,
transmitting a control signal for the opening of the valve in the feedwater supply line.

3. The method as claimed in claim 1 , wherein the set-point value for the degree of subcooling of the feedwater at the inlet into the high-pressure evaporator is determined between specified maximum and minimum values (Max Sc, Min Sc), said maximum value (Max Sc) being a value established to avoid unstable operation of the high-pressure evaporator and said minimum value (Min Sc) being a value established to prevent steaming out of the feedwater at the inlet of the high-pressure evaporator.

4. The method as claimed in claim 3 , wherein the set-point value for the flow volume is determined between specified maximum and minimum values (Max Fl, Min Fl), said maximum value (Max Fl) being a value established to ensure a flow volume below a maximum possible feedwater flow volume and said minimum value (Min Fl) being a value established to ensure the flow volume does not exceed a predetermined minimum flow volume.

5. The method as claimed in claim 1 , wherein these steps are additionally carried out:
determining a set-point flow volume through a bypass line between the outlet of a feedwater pump of the combined cycle power plant and the inlet of the high-pressure evaporator based on the difference between the current measured value of the degree of subcooling at the inlet of the high-pressure evaporator and a minimum set-point value for the subcooling which is smaller than the set-point value for the subcooling in the third control step;
based on the set-point value for the flow volume through the bypass line, generating and transmitting a control signal for an opening position of a valve in the bypass line.

6. The method as claimed in claim 5 , wherein the method additionally comprises the steps:
determining the current flow volume in the bypass line;
generating a control signal for the opening position of a valve in the bypass line, based on the set-point value for the flow volume through the bypass line and a current flow volume through the bypass line;
transmitting the control signal for a position of the valve in the bypass line.

Assignees

• Olia Hamid
• General Electric Technology Gmbh

Inventors

• Olia Hamid

Classifications

• Y02E20/16

  Combined cycle power plant [CCPP], or combined cycle gas turbine [CCGT] · CPC title

• F22B35/102

  operating with fixed point of final state of complete evaporation, e.g. in a steam-water separator · CPC title

• F22B35/007

  Control systems for waste heat boilers · CPC title

• F01K23/10 Primary

  with exhaust fluid of one cycle heating the fluid in another cycle (F01K17/025 takes precedence) · CPC title