Combined Cycle Startup via Steam Bypass and Attemperation
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Solution Overview
Problem
Traditional combined cycle power systems face inefficiencies and high emissions during startup and loading due to low load holds and restricted gas turbine loading rates, leading to increased starting and loading times and fuel consumption, especially with more frequent power fluctuations.
Innovation Solution
The method involves loading the gas turbine at an increased rate and maintaining constant high pressure and intermediate pressure steam temperatures to the steam turbine, using attemperators and bypass paths to control steam flow and pressure, allowing for faster and more efficient steam turbine loading while minimizing emissions and fuel consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the gas turbine is held at low load to control steam temperature increase rate, then steam temperature control is improved, but starting and loading time increases and emissions increase
Solution Approach 1:
A bypass path with a bypass valve is introduced as an intermediary between the HRSG and steam turbine. This bypass path allows steam to be diverted away from the steam turbine during startup, enabling independent control of steam temperature without requiring low-load holds on the gas turbine. The bypass mechanism decouples the gas turbine loading rate from steam temperature control, resolving the contradiction.
Solution Approach 2:
The system changes the control parameter from gas turbine load (traditional method) to bypass valve position and steam flow distribution. By controlling the bypass valve to divert steam flow, the system can increase gas turbine loading rate while maintaining steam temperature within acceptable ranges, thereby reducing startup time without compromising temperature control.
2Strength
If the gas turbine is held at low load to match steam temperature with turbine metal temperature, then turbine thermal stress is reduced, but fuel consumption increases
Solution Approach 1:
The bypass path acts as an intermediary that separates gas turbine operation from steam turbine thermal constraints. By diverting excess steam through the bypass, the gas turbine can operate at higher loads for faster fuel combustion and energy generation, while the steam turbine receives controlled steam amounts to maintain safe temperature differentials and minimize thermal stress.
Solution Approach 2:
The bypass mechanism enables continuous full-load operation of the gas turbine during startup, maintaining optimal combustion efficiency and fuel utilization. Instead of interrupting useful energy generation through low-load holds, the system continuously generates maximum energy from the gas turbine while managing steam delivery to the turbine through the bypass, eliminating wasted fuel consumption.
3Strength
If the gas turbine loading rate is restricted to control HRSG warming rate, then HRSG thermal stress is reduced, but starting and loading time increases
Solution Approach 1:
The steam flow path is segmented into two independent routes: the main path through the steam turbine and the bypass path with the bypass valve. This segmentation allows the gas turbine to load at high rates while the bypass valve controls the amount of steam actually delivered to the steam turbine, decoupling HRSG warming rate from gas turbine loading rate and enabling faster startup without excessive thermal stress.
Solution Approach 2:
The bypass valve provides dynamic control of steam flow distribution, allowing the system to adapt steam delivery to the steam turbine's thermal capabilities while the gas turbine operates at optimal loading rates. This dynamic flow management enables the HRSG to warm up at controlled rates without restricting the gas turbine's loading speed, maintaining both thermal safety and operational efficiency.
4Temperature
If low load holds are implemented during startup, then steam temperature control is improved, but air emissions increase
Solution Approach 1:
The bypass path serves as an intermediary that enables steam temperature control without requiring low-load holds. By controlling the bypass valve to divert or direct steam flow, the system maintains steam temperature within acceptable ranges while the gas turbine operates at higher loads, avoiding the high emissions associated with low-efficiency low-load operation.
Solution Approach 2:
The control strategy changes from adjusting gas turbine load to adjusting bypass valve position and steam flow distribution. This parameter change allows the gas turbine to operate in its high-efficiency, low-emission operating range during startup while still achieving the required steam temperature control through bypass-mediated flow management.
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 reduces emissions, shortens starting and loading times, and decreases fuel consumption by optimizing gas and steam turbine loading, achieving faster and more efficient combined cycle power generation.
Implementation Method 1
heat recovery steam generator for supplying steam to the steam turbine
Implementation Method 2
at least one attemperator coupled to the heat recovery steam generator
Data Source
AI summary
Methods and apparatus for fast starting and loading a combined cycle power system are described. In one example embodiment, the method includes loading the gas turbine at up to it's maximum rate, and loading the steam turbine at its maximum rate with excess steam bypassed to the condenser while maintaining the temperature of steam supplied to the steam turbine at a substantially constant temperature from initial steam admission into the steam turbine until all steam generated by the heat recovery steam generator is being admitted to the steam turbine while the gas turbine operates at up to maximum load.