Variable Eductor Gas Stream Temperature Control
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Solution Overview
Problem
High-temperature gas streams from gas turbines cause thermal stress to infrastructure, particularly during startup, leading to significant challenges for heat recovery steam generators (HRSGs) due to rapid temperature increases, which existing technologies have not adequately addressed.
Innovation Solution
A variable eductor apparatus that allows ambient air or a second gas to be introduced into the gas stream to control temperature and rate of temperature change by creating a pressure differential, using movable shutters or a rotating sleeve to regulate the flow of the second gas into the gas stream, thereby reducing thermal stress on downstream equipment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high-temperature gas streams are transported through infrastructure, then energy transmission efficiency is improved, but thermal stress on infrastructure increases
Solution Approach 1:
A variable eductor device is introduced as an intermediary component in the gas stream path. The eductor uses a high-velocity fluid jet to create a low-pressure region that draws in secondary gas, which then mixes with the primary hot gas stream. This intermediary mixing process reduces the temperature of the gas stream before it reaches downstream infrastructure, thereby reducing thermal stress while maintaining energy transmission capability
Solution Approach 2:
The invention changes the temperature parameter of the gas stream by introducing a secondary gas through the variable eductor. By controlling the amount of secondary gas mixed in, the temperature of the gas stream can be dynamically adjusted to an optimal range that reduces thermal stress on infrastructure while maintaining acceptable energy transmission efficiency
2Speed
If rapid temperature increase occurs during gas turbine startup, then startup speed is improved, but thermal stress on HRSG increases
Solution Approach 1:
The variable eductor is positioned upstream in the gas stream path to perform preliminary cooling before the gas reaches the HRSG. During startup, the eductor introduces secondary gas that pre-cools the hot exhaust gas, preventing the rapid temperature increase that would otherwise cause thermal stress on the HRSG while allowing the turbine to maintain its startup speed
Solution Approach 2:
The eductor acts as an intermediary cooling system that mediates between the hot turbine exhaust and the HRSG. By controlling the injection of secondary gas through the eductor, the system can manage the rate of temperature change to protect the HRSG during rapid startup conditions
3Adaptability or versatility
If multiple startup cycles are performed to meet flexible operation demand, then operational flexibility is improved, but cumulative thermal stress on HRSG increases
Solution Approach 1:
The variable eductor system incorporates feedback control that monitors gas stream temperature and adjusts the amount of secondary gas injection accordingly. During multiple startup cycles, the feedback control ensures that temperature is managed within safe limits for the HRSG, preventing cumulative thermal stress while allowing the system to respond flexibly to operational demands
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
Effectively reduces the temperature and rate of temperature increase of the gas stream, minimizing thermal stress on HRSGs and related components during startup and transient operations without requiring complex cooling systems or significant auxiliary power, and can be easily installed as a retrofit in existing infrastructure.
Implementation Method 1
A variable eductor apparatus that allows ambient air or a second gas to be introduced into the gas stream to control temperature and rate of temperature change by creating a pressure differential
Implementation Method 2
pulling a second gas, such as a gas from outside of a gas duct, through the corresponding opening and into the gas duct and the gas stream passing through the gas duct
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.