Deaerator pressure control system

In a steam turbine power plant including a steam turbine and a deaerator, the steam turbine having a steam extraction line connected to the deaerator for pressurizing the deaerator;

• and, a second steam line for providing steam to the deaerator during periods when there is insufficient steam in the steam extraction line for meeting the deaerator steam pressure requirements;
• a system for regulating deaerator pressure comprising:
• a valve for regulating the steam flow from the second steam line into the deaerator;
• a controller for providing a valve control signal to the valve, the controller including means for sensing steam pressure in the steam extraction line and providing a valve opening signal whenever the rate of decreasing steam pressure in the steam extraction line exceeds a predetermined rate or a predetermined floor value.

In a steam turbine power plant having a steam turbine and a deaerator connected by a steam extraction line;

• and, a second steam line connected to the deaerator including a valve for controlling steam flow through the second steam line into the deaerator;
• a controller for providing a valve position signal to the valve comprising:
• a first pressure transducer connected to the steam extraction line for providing a steam pressure signal;
• a second pressure transducer connected to the deaerator for providing a deaerator pressure signal;
• signal lag means for providing a valve opening signal in response to a falling pressure signal which exceeds a predetermined rate;
• signal bypass means for providing a valve close signal in response to a rising pressure signal;
• signal bias means for providing a deadband about critical valve opening and closing values;
• signal limit means for providing a minimum pressure value for opening the valve;
• summing means receiving the valve opening and closing signals and the deaerator pressure signal to provide an error signal;
• and,
• signal amplifying and integrating means to provide a new valve position signal.

A device for controlling the flow of steam into a deaerator from a secondary steam source in response to available steam to the deaerator from a primary steam source comprising:

• means for determining a falling steam pressure signal in the primary steam source which exceeds a predetermined rate and for providing a valve open signal in response thereto;
• means for determining a minimum steam pressure in the primary steam source and providing a valve open signal in response thereto;
• and,
• means for maintaining a rising pressure signal above the minimum steam pressure and providing a valve closing signal in response thereto.

In a steam turbine power plant including a steam turbine and a deaerator;

• the steam turbine having a high pressure section and a low pressure section;
• an extraction steam line connecting the low pressure section and the deaerator and a second steam line connecting the high pressure section and the deaerator;
• valve means for controlling the steam flow in the second steam line;
• and, control means for providing a valve position signal to the valve in response to steam pressure in the steam extraction line wherein the control means comprises means for providing a valve open signal in response to a pressure decrease exceeding a predetermined rate;
• means for providing a valve open signal in response to a pressure which falls below a preset minimum;
• and, means for providing a valve close signal for a pressure rise above the preset minimum.