Thermal Storage Unit for Combined-Cycle Power Plants
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Solution Overview
Problem
Combined-cycle power plants face reduced thermal efficiency during peak-demand periods due to the use of less efficient duct firing to increase power output, which is not ideal for meeting fluctuating energy demands.
Innovation Solution
Incorporating a thermal energy storage unit with a cold and hot tank containing a thermal storage working medium, such as molten salt, that facilitates direct heat transfer through a heat exchanger to supplement steam production and power output, thereby reducing the need for duct firing during peak demand hours.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If duct firing is used to generate additional power output during peak-demand periods, then power output is increased to meet increased energy demand, but thermal efficiency is reduced
Solution Approach 1:
The system stores thermal energy in advance during periods of low power demand by heating a thermal storage medium (such as molten salt) in hot tanks. This preliminary accumulation of thermal energy allows the plant to rapidly generate additional power during peak-demand periods without resorting to inefficient duct firing, thus maintaining high thermal efficiency while meeting increased energy demand.
Solution Approach 2:
The thermal storage medium acts as an intermediary between the steam cycle and the power demand. By storing thermal energy in the hot tanks and releasing it through heat exchangers to generate additional steam, the system decouples the direct relationship between fuel combustion and power generation, enabling efficient power output adjustment during peak demand without the energy losses associated with duct firing.
2Productivity
If combined-cycle power plant operates at minimum load during early morning hours, then power output is reduced to match lower energy demand, but thermal efficiency is maintained
Solution Approach 1:
During early morning hours when power demand is low, the system operates the combined-cycle plant at minimum load to maintain thermal efficiency. The excess thermal energy that would otherwise be wasted is captured and stored in the thermal storage system by heating the molten salt in the hot tanks. This allows the plant to discard minimal power output while recovering and storing the thermal energy for later use during peak demand periods.
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 enhances power plant efficiency during peak demand periods by using stored thermal energy to boost steam production and power output, maintaining higher efficiency compared to conventional methods, and provides an energy boost to the electricity supply grid.
Implementation Method 1
The thermal storage unit includes a cold tank containing the thermal storage working medium in a cold state and a hot tank containing the thermal storage working medium in a heated state
Implementation Method 2
The heat exchanger facilitates a direct heat transfer of thermal energy between the thermal storage working medium in the thermal storage unit and the working fluid supplied from the steam generating source to the steam turbine
Data Source
AI summary
Thermal energy storage is leveraged to store thermal energy extracted from a bottom cycle heat engine. The thermal energy stored in the thermal energy storage is used to supplement power generation by the bottom cycle heat engine. In one embodiment, a thermal storage unit storing a thermal storage working medium is configured to discharge thermal energy into the working fluid of the bottom cycle heat engine to supplement power generation. In one embodiment, the thermal storage unit includes a cold tank containing the thermal storage working medium in a cold state and a hot tank containing the working medium in a heated state. At least one heat exchanger in flow communication with the bottom cycle heat engine and the thermal storage unit facilitates a direct heat transfer of thermal energy between the thermal storage working medium and the working fluid used in the bottom cycle heat engine.