Exhaust Cooling Airflow Control for Combined Cycle Turbines
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Solution Overview
Problem
Combined cycle power generation systems face challenges in operational flexibility and emission control during start-up, with higher emissions and reduced power output due to lower gas turbine loads, and under-frequency grid events lead to decreased power generation and potential component damage from over-firing.
Innovation Solution
An airflow control system that includes a fan to draw in excess air, a mixing area to cool exhaust gases, and an airflow regulation system to divert air into the compressor component, allowing for temperature reduction and increased air flow during under-frequency events, enhancing power output and reducing emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the gas turbine is held at a lower load to control HRSG inlet temperature during start-up, then thermal stresses in the steam turbine are reduced, but emissions increase significantly and power output decreases
Solution Approach 1:
The patent introduces a cooling air system as an intermediary between the gas turbine exhaust and the HRSG. This system includes cooling air intake means, cooling air flow control means, and mixing means that inject cooling air into the exhaust gas stream. The cooling air acts as a mediator to reduce exhaust gas temperature to protect the HRSG from thermal stresses while allowing the gas turbine to operate at higher loads, thereby reducing emissions and increasing power output during start-up
2Temperature
If the gas turbine is held at a lower load to control HRSG inlet temperature during start-up, then thermal stresses in the steam turbine are reduced, but power output decreases
Solution Approach 1:
The cooling air system serves as an intermediary that enables the gas turbine to operate at higher loads during start-up by actively cooling the exhaust gas stream before it enters the HRSG. This allows the HRSG to be protected from thermal stresses while the gas turbine generates maximum power, resolving the contradiction between temperature control and power output
3Productivity
If the firing temperature of the gas turbine is increased to produce more power during under-frequency grid events, then power output is maintained, but operational life expectancy of hot gas path components is reduced
Solution Approach 1:
The cooling air system acts as an intermediary that allows the gas turbine to operate at higher loads during under-frequency events without increasing firing temperature. By cooling the exhaust gas stream, the system enables higher power output while protecting hot gas path components from excessive thermal exposure, thus maintaining both productivity and reliability
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 solution improves power generation efficiency and reduces emissions during start-up and under-frequency events, extending gas turbine component life while maintaining HRSG inlet temperature, and allows for quick frequency adjustments to meet variable grid demands.
Implementation Method 1
a fan coupled to the shaft upstream of the gas turbine system, the fan drawing in an excess flow of air through an air intake section
Implementation Method 2
a mixing area for receiving an exhaust gas stream produced by the gas turbine system; an air extraction system for extracting a first portion of the excess flow of air to provide bypass air, and for diverting the bypass air into the mixing area to reduce a temperature of the exhaust gas stream
Implementation Method 3
a heat recovery steam generator for receiving the reduced temperature exhaust gas stream and for generating steam
Data Source
AI summary
An airflow control system for a combined cycle turbomachine system in accordance with an embodiment includes: an airflow generation system for attachment to a rotatable shaft of a gas turbine system, the airflow generation system drawing in an excess flow of air through an air intake section; a mixing area for receiving an exhaust gas stream produced by the gas turbine system; an air extraction system for extracting a first portion of the excess flow of air to provide bypass air, and for diverting the bypass air into the mixing area to reduce a temperature of the exhaust gas stream; and an airflow regulation system for diverting a second portion of the excess flow of air into the compressor component and, in response to an under-frequency grid event, for increasing the second portion of the excess flow of air diverted into the compressor component.