Variable Eductor for Gas Stream Temperature Control
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Solution Overview
Problem
Combined-cycle power plants face increased thermal stress on Heat Recovery Steam Generators (HRSGs) due to higher exhaust temperatures from more efficient combustion turbines and increased cycling, leading to frequent component failures.
Innovation Solution
An apparatus and method for controlling the temperature of a gas stream by adding a second gas with a lower temperature, such as ambient air, to the main gas stream, using a variable eductor design that allows for control over the amount and rate of the second gas added, thereby reducing the temperature or rate of temperature increase of the main gas stream.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If combustion turbine efficiency is increased to reduce fuel consumption, then energy efficiency improves, but exhaust temperature increases causing thermal stress on HRSG components
Solution Approach 1:
A variable eductor device is introduced as an intermediary component in the exhaust duct. This device uses the kinetic energy of the exhaust flow to draw in cooling air from the environment, which then mixes with the hot exhaust gases. The cooling air acts as a mediator that reduces the temperature of the exhaust stream before it enters the HRSG, thereby protecting components from thermal stress while maintaining the high efficiency benefits of the combustion turbine.
2Productivity
If rapid startup is performed to meet power demand, then productivity improves, but thermal stress on HRSG components increases due to rapid temperature increase
Solution Approach 1:
The variable eductor device is activated during the startup sequence to perform preliminary cooling of the exhaust stream. By introducing cooling air before the exhaust enters the HRSG, the system prevents rapid temperature excursions that would cause thermal stress. This preliminary cooling action allows for faster startup times while protecting the HRSG components from thermal shock.
3Temperature
If attemperating sprays are used to control steam temperature, then steam temperature control improves, but external tube walls remain exposed to high heat
Solution Approach 1:
The invention extracts the temperature control function from the steam side and moves it to the exhaust gas side. Instead of spraying water into the steam to control temperature, the variable eductor device introduces cooling air directly into the exhaust stream upstream of the HRSG. This removes the harmful thermal exposure from the tube walls by cooling the exhaust gases before they contact the heat transfer surfaces, while still achieving the desired steam temperature control.
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 solution effectively reduces thermal stress on HRSGs by controlling the temperature and rate of temperature change of exhaust gas streams from gas turbines during startup and transient operations, minimizing component failures and extending equipment lifespan.
Implementation Method 1
a variable eductor design that allows for control over the amount and rate of the second gas added
Implementation Method 2
adding a second gas with a lower temperature, such as ambient air, to the main gas stream
Implementation Method 3
adding a second gas with a lower temperature, such as ambient air, to the main gas stream... thereby reducing the temperature or rate of temperature increase of the main gas stream
Data Source
AI summary
The invention provides various designs of an apparatus and method for attemperating a gas stream temperature. The apparatus of the present invention provides a body through which a gas stream passes that permits, as desired, a second gas, such as gas outside of the gas duct or such as ambient air, to be added to the main gas stream to attemperate the temperature of the main gas stream. The body or device may be referred to as a variable eductor having a plurality of openings through which a second gas may pass into the main gas stream. The openings may be opened or closed, and the variable eductor provides control over which openings and the degree to which each opening is opened. In some designs the variable eductor is inserted between two portions of a gas duct. The variable eductor has widespread application, such as downstream of a gas turbine to attemperate the exhaust gas temperature during startup.