Combined Gas Steam Turbine Evaporator Feed Water Control
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Solution Overview
Problem
Modern combined gas and steam turbine systems face challenges in rapidly releasing power reserves without compromising operational efficiency, especially during frequency disruptions in the electric grid, as conventional methods often result in inefficient throttling of turbine valves and limited flexibility in power adjustments.
Innovation Solution
The method involves temporarily increasing the feed water flow through the evaporator by switching from 'BENSON control mode' to 'level control mode', allowing for an immediate reduction in overheating and increased feed water flow, which discharges thermal energy as additional power in the steam turbine, enabling rapid power reserve release with minimal invasive modifications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the feed water flow rate is increased rapidly to release power reserves, then the power output increases immediately, but the specific enthalpy of the moving fluid deviates from desired values causing high material stresses
Solution Approach 1:
The control system performs preliminary action by predicting future operating states and pre-adjusting the feed water flow rate accordingly. The predictive controller calculates future desired values based on current system state and anticipated load changes, allowing the system to prepare for power reserve release while maintaining safe operating parameters and avoiding sudden material stresses.
Solution Approach 2:
The system implements dynamic control by continuously adapting the feed water flow rate based on real-time operating conditions. The controller dynamically adjusts parameters to maintain optimal specific enthalpy values while enabling rapid power output changes, transforming the static control approach into a flexible dynamic system that can respond to grid frequency disruptions without compromising material integrity.
2Strength
If the feed water flow rate is controlled to maintain desired specific enthalpy, then material stress is reduced, but the response time for power reserve release is delayed
Solution Approach 1:
The predictive controller performs preliminary calculations to determine future desired feed water flow rates based on anticipated operating changes. By predicting the need for power reserve release before it occurs, the system can pre-position control parameters to enable rapid response while maintaining safe specific enthalpy values, thus achieving both fast response and material protection.
Solution Approach 2:
The control system continuously monitors actual operating parameters including specific enthalpy, feed water flow rate, and power output. This feedback mechanism allows the controller to verify that rapid power reserve release is achieving desired results while maintaining safe operating limits, enabling real-time adjustments to optimize both response speed and material stress management.
3Power
If conventional throttling methods are used to release power reserves, then power output increases, but operational efficiency decreases due to inefficient valve throttling
Solution Approach 1:
The system changes operating parameters by adjusting feed water flow rate and evaporator heat input in coordinated fashion rather than relying on turbine valve throttling. This parameter change approach maintains more efficient operating conditions by avoiding the energy losses inherent in conventional throttling methods, enabling power reserve release with minimal efficiency penalty.
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
This approach allows for a rapid and efficient power increase without significant efficiency loss, providing an immediate power leap that can be maintained or exceeded by the gas turbine, enhancing system flexibility and reducing material stress on the steam generator.
Implementation Method 1
an evaporator adjoins the economizer and can preferably be constructed as a forced flow evaporator and in particular as what is known as a BENSON evaporator. The moving fluid is then in the form of steam or a water-steam mixture at the evaporator outlet
Implementation Method 2
A waste heat steam generator is a heat exchanger which recovers heat from a hot flow of gas
Implementation Method 3
The steam is then fed to the steam turbine... the overheated steam then flows into the high pressure part of the steam turbine, expands there
Data Source
AI summary
A method of operating a combined gas and steam turbine system is provided. The system includes a gas turbine, a waste heat steam generator with an evaporator heating area, and a steam turbine. Fluid is fed to the waste heat steam generator as feed water. A primary control loop controls a feed water flow rate. Taking into account heat stored in the evaporator heating area, a primary desired value for the feed water flow rate is determined based upon a desired overheating value characteristic of a temperature by which the fluid exceeds a boiling point as the fluid exits the evaporator heating area and based upon a heat flow parameter characteristic of a heat flow transfer from fuel gas to the fluid via the evaporator heating area. The desired overheating value is lowered from a first value to a second value in order to activate an instantaneous power reserve.