Thermal energy storage system comprising a packed-bed heat storage unit and a packed-bed cold storage unit, and method for operating a thermal energy storage system
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Solution Overview
Problem
Current thermal energy storage systems using liquid salt and cooling agents are complex, inefficient, and costly due to high operating pressures, multiple heat exchangers, and high material requirements, with low current-to-current efficiency and high maintenance needs.
Innovation Solution
A thermal energy storage system utilizing packed-bed storage units with gaseous heat carriers like nitrogen, carbon dioxide, or argon, which operates at lower pressures and eliminates the need for heat exchangers, allowing for a simpler and more efficient cycle with improved temperature management and reduced material needs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If liquid salt and liquid cooling agents are used as storage media, then thermal energy storage can be achieved, but the system becomes complex with multiple heat exchangers and high operating pressures
Solution Approach 1:
The patent removes heat exchangers from the thermal energy storage system by using packed-bed storage units where the gaseous heat carrier flows directly through the storage medium. This extraction of the heat exchanger component simplifies the system architecture while maintaining thermal energy storage capability through direct contact between the heat carrier gas and the packed-bed material.
Solution Approach 2:
The patent employs gaseous heat carriers (nitrogen, carbon dioxide, or argon) that flow through the packed-bed storage units, using gas-phase heat transfer instead of liquid-phase systems. This pneumatic approach eliminates the need for liquid pumps and complex heat exchanger assemblies, reducing system complexity while achieving effective thermal energy storage and retrieval.
2Use of energy by moving object
If multiple heat exchangers are used in the system, then heat transfer can be achieved, but material requirements and costs increase
Solution Approach 1:
The patent combines the heat transfer function and the thermal energy storage function into a single integrated packed-bed unit. The gaseous heat carrier flows directly through the packed-bed material, performing both heat transfer and energy storage simultaneously, thereby eliminating the need for separate heat exchangers and reducing overall material requirements.
Solution Approach 2:
The patent extracts and eliminates heat exchangers from the system by implementing direct heat transfer between the gaseous heat carrier and the packed-bed storage medium. This removal of unnecessary components reduces material consumption and system costs while maintaining effective heat transfer through the simplified direct-contact approach.
3Power
If high operating pressures are used, then system performance can be maintained, but current-to-current efficiency decreases
Solution Approach 1:
The patent changes the operating pressure parameter from high to low pressure operation. By using gaseous heat carriers at low pressures flowing through packed-bed units, the system maintains adequate heat transfer performance through increased surface area contact and extended residence time, thereby improving current-to-current efficiency while preserving system performance.
Solution Approach 2:
The patent enhances local heat transfer quality within the packed-bed units by creating extensive contact surfaces between the gaseous heat carrier and the storage medium. This localized improvement in heat transfer efficiency compensates for the lower operating pressure, maintaining system performance while reducing energy losses and improving overall current-to-current efficiency.
4Reliability
If liquid storage media are used, then thermal energy can be stored, but the operating temperature range is limited by freezing and evaporation points
Solution Approach 1:
The patent changes the phase parameter of the heat carrier from liquid to gas, and uses packed-bed materials that can operate across a wide temperature range. This allows the system to store thermal energy at temperatures far below freezing points of liquids without solidification issues, and at high temperatures without evaporation concerns, thereby expanding the operational temperature range while maintaining reliable thermal energy storage.
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 system achieves higher current-to-current efficiency and lower operational costs with reduced material requirements and simplified operation, enabling efficient energy storage and retrieval with minimal maintenance.
Implementation Method 1
a gaseous heat carrier, such as nitrogen, carbon dioxide, or argon
Implementation Method 2
The work medium is cooled with the cold storage unit before returning to the compressor
Implementation Method 3
the work medium is adiabatically compressed in the compressor (and thus also heated)
Implementation Method 4
one adiabatic compression and one adiabatic expansion, one isobaric heat transfer at high temperatures, and one isobaric heat transfer at low temperatures
Data Source
AI summary
The invention relates to a system and a method for storing electrical energy which are based on a closed thermodynamic cycle. They make it possible to store electrical energy in a very efficient, cost-effective, and safe manner. No environmentally hazardous or expensive materials are required. The system comprises a compressor, a turbine, and two packed-bed storage units which are operated at different temperature levels.In order to load the packed-bed storage units, the cycle is operated as a counterclockwise heat pump process. In this process, the heat generated at the outlet of the compressor is expanded at a high temperature level into a first packed-bed storage unit and stored therein. The “cold” produced during the subsequent expansion of the gaseous working medium in a turbine is stored in a second packed-bed storage unit. This requires mechanical energy which is provided by an electrical machine. In order to discharge the energy storage system, the cycle is operated in reverse (i.e., as a clockwise cycle). Before entering the compressor, the working medium is cooled with the cold stored in the second packed-bed storage unit and, after compression, absorbs the heat from the high-temperature packed-bed storage system. The hot working medium at high pressure is expanded by means of the turbine and thus energy is generated.