Combined Cycle Plant Ventilator Valve Control for Startup Stability
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The control system for the reheat steam line becomes unstable during startup due to sudden changes in steam flow rate when the ventilator valve is closed, particularly when a small amount of steam is generated.
Innovation Solution
A control device that adjusts the ventilator valve based on a temperature-correlated threshold for determining the steam flow rate, reducing the flow change rate in the reheat steam line by altering the threshold according to the startup mode recognized by a thermometer, thereby stabilizing the control system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the ventilator valve is closed during startup to suppress exhaust steam temperature rise, then the windage loss is reduced and temperature control is improved, but the steam flow rate in the reheat steam line increases suddenly causing control system instability
Solution Approach 1:
The control device determines whether the steam flow rate has reached a predetermined value before closing the ventilator valve. This preliminary determination allows the system to prepare for the valve closure by ensuring the steam flow is at an appropriate level, thereby preventing sudden flow rate changes and maintaining control stability when the ventilator valve closes to suppress exhaust steam temperature rise.
Solution Approach 2:
The control device continuously monitors the steam flow rate and uses this feedback information to determine the appropriate timing for ventilator valve closure. By basing the closure decision on real-time flow rate measurements, the system can prevent sudden changes in reheat steam line flow and maintain control stability while still achieving temperature suppression.
2Device complexity
If a fixed threshold is used for determining steam flow rate during startup, then the control logic is simple, but the control system becomes unstable when small amounts of steam are generated
Solution Approach 1:
The control device dynamically adjusts the threshold for determining steam flow rate based on the actual steam generation conditions during startup. Instead of using a fixed threshold, the system adapts the threshold value to match the current operational state, thereby maintaining control stability even when small amounts of steam are generated while keeping the control logic relatively simple.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The control device effectively reduces the flow change rate in the reheat steam line during startup, preventing temporary instability in the control system, even when a small amount of steam is generated.
Implementation Method 1
an exhaust heat recovery boiler that generates steam using heat of the combustion gas exhausted from the gas turbine
Implementation Method 2
a reheat section that heats the steam exhausted from the first steam turbine
Implementation Method 3
a condenser that condenses the steam exhausted from the second steam turbine back into water
Data Source
AI summary
A first steam turbine and a second steam turbine of a combined cycle plant are connected by a reheat steam line via a reheat section of an exhaust heat recovery boiler. The reheat steam line and a condenser are connected by a second bypass line. A control device includes: a determination unit that determines whether or not the flow rate of first steam flowing into the first steam turbine has reached a stipulated flow rate; a command output unit that, upon determining that the flow rate of the first steam flowing into the first steam turbine has reached the stipulated flow rate, outputs a close command to close a ventilator valve that is provided in the second bypass line and is open; and a threshold alteration unit that alters the threshold with which the determination unit determines whether or not the stipulated flow rate has been reached, the threshold being positively correlated with a temperature of the first steam.