Fuel Gas Heater Flow Control for Combined Cycle Stability
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Solution Overview
Problem
Gas turbine combined cycle plants face challenges in managing fuel gas temperature fluctuations due to sudden load changes, which can lead to inefficient heat transfer and pressure issues when using heated water from an exhaust heat recovery boiler as a heat source.
Innovation Solution
A control unit manages the operation of return and dump valves to regulate the flow rate of heated water in the fuel gas heater, closing the return valve and maintaining a specified opening degree of the dump valve during reduced load conditions to prevent sharp temperature rises, and stepwise increasing the dump valve opening as needed to adjust fuel gas temperature accurately.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the flow rate of heated water is reduced to control sharp temperature rise in fuel gas, then fuel gas temperature stability is improved, but heated water supply pressure increases
Solution Approach 1:
The patent introduces a flow control valve as an intermediary device on the heated water supply line to regulate the flow rate of heated water to the fuel gas heater. This mediator allows independent control of heated water flow rate separate from the return line valves, enabling temperature stability without excessive pressure buildup by dissolving the coupling between temperature control and pressure management.
Solution Approach 2:
The patent segments the heated water flow control into independent components: a supply line with a flow control valve, a return line with return valve, and a bypass with dump valve. This segmentation allows the supply pressure and flow rate to be controlled independently, resolving the contradiction between maintaining temperature stability (requiring low flow rate) and managing supply pressure (requiring adequate flow rate).
2Temperature
If the return valve is closed and dump valve is opened to reduce heated water flow rate during load reduction, then fuel gas temperature rise is controlled, but system complexity increases due to valve coordination requirements
Solution Approach 1:
The patent implements feedback control by monitoring the outlet temperature of the fuel gas heater and using this information to automatically adjust the flow control valve opening degree. The control unit continuously compares the actual temperature with the target temperature and modifies the heated water flow rate accordingly, eliminating the need for complex manual valve coordination while maintaining precise temperature control during load changes.
Solution Approach 2:
The system performs self-service through automatic control where the control unit independently manages the flow control valve based on temperature feedback without requiring operator intervention to coordinate multiple valves. The system self-regulates the heated water flow rate to maintain temperature stability, reducing operational complexity while achieving the desired temperature control during gas turbine load changes.
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 configuration effectively controls fuel gas temperature fluctuations during load changes, ensuring efficient heat transfer and reducing pressure issues by managing the flow rate of heated water, thus enhancing the operational stability of the gas turbine combined cycle plant.
Implementation Method 1
an exhaust heat recovery boiler configured to recover exhausted heat of the gas turbine to generate steam
Implementation Method 2
a fuel gas heater configured to heat fuel gas to be supplied to a combustor of the gas turbine using heated water that has been heated by the exhaust heat recovery boiler to serve as a heat source
Data Source
AI summary
A gas turbine combined cycle plant includes a fuel gas heater configured to heat fuel gas to be supplied to a combustor of a gas turbine using heated water heated by an exhaust heat recovery boiler; a return valve disposed on a heated water returning line to return heated water passing through the heater to the boiler; a dump valve disposed on a condensate line bifurcated from the heated water returning line between the return valve and the heater to return the heated water to a condenser; and a control unit configured to control operation of the return and dump valves. When load of the turbine falls below a lower limit, the control unit closes the return valve and keeps the opening degree of the dump valve at a specified degree to reduce a flow rate of the heated water flowing in the heater for a predetermined time.