Multistage Thermochemical Heat Storage for Low-Temperature Desorption
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Solution Overview
Problem
Current thermochemical heat storage systems face challenges with low storage density at typical solar collector temperatures and undesirable processes such as melting, coagulation, and chemical side reactions, especially with materials like zeolite and hygroscopic salts.
Innovation Solution
A closed system using multiple thermochemical modules connected through a central tube allows for multistage drying and desorption at lower temperatures, utilizing different materials like zeolites, silica gel, and hygroscopic salts, which reduces heat loss and increases storage density without destabilizing the materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If typical solar collector temperatures (90°C) are used for drying thermochemical materials, then the storage density is limited, but increasing the temperature would reduce heat loss and improve storage density
Solution Approach 1:
The system divides the drying process into multiple stages using multiple thermochemical modules with different materials (zeolite, silica gel, hygroscopic salts). Each module operates at different temperature levels, progressively removing water from the sorbent. This segmentation allows achieving high storage density without requiring a single high-temperature step, thus reducing overall heat loss while maintaining material stability.
2Quantity of substance
If high storage density is achieved using hygroscopic salts, then storage capacity increases, but material stability decreases due to melting, coagulation, and chemical side reactions
Solution Approach 1:
The drying process is segmented across multiple modules, each containing different thermochemical materials with complementary properties. Zeolite and silica gel modules operate at lower temperatures to remove bulk moisture, while hygroscopic salt modules complete the drying at controlled conditions. This prevents any single material from being exposed to temperatures that would cause melting or coagulation, maintaining material stability while achieving high storage density.
Solution Approach 2:
The system uses intermediate thermochemical modules (zeolite, silica gel) as mediators between the heat source and the hygroscopic salt modules. These intermediate materials perform the initial drying at lower temperatures, protecting the hygroscopic salts from direct exposure to high temperatures that would cause instability, while still enabling the hygroscopic salts to achieve their high storage density potential in the final drying stage.
3Quantity of substance
If multiple thermochemical modules are used for multistage drying, then storage density and material stability improve, but system complexity increases
Solution Approach 1:
The system is segmented into multiple independent but interconnected thermochemical modules, each with a specific function in the drying sequence. This modular segmentation allows for standardized design and operation of each unit, making the overall complex system manageable through repetition of proven module designs rather than a single complex integrated system.
Solution Approach 2:
Each thermochemical module is designed to be multi-functional: it can operate as a drying stage, a heat storage unit, and a material stabilization zone. The modules can potentially be interchanged or reconfigured based on operational needs. This universality reduces the need for entirely different components for each function, managing system complexity while achieving multistage drying and high storage density.
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 enables higher storage density and stability of thermochemical materials during desorption, allowing for more efficient seasonal heat storage with reduced heat loss and material instability issues.
Implementation Method 1
Na2S·1/2H2O + 4 1/2 H2O ←→ Na2S·5H2O + heat
Implementation Method 2
The charging process to store the energy is an endothermic reaction wherein heat is supplied to split compound AB into compounds A and B
Implementation Method 3
the water vapour thus formed is condensed in the water condenser
Implementation Method 4
a water condenser and at least two thermochemical modules, wherein the water condenser and the thermochemical modules are connected in such a way that predetermined condensers and/or modules can be brought into contact independently of each other
Data Source
Figure 1(A)~1(B)
Figure 2
Figure 3(A)~3(B)
AI summary
The present invention discloses a closed system for thermochemical storage comprising at least one water condenser and at least two thermochemical modules, wherein a first thermochemical module comprises a first thermochemical material and a second thermochemical module comprises a second thermochemical material, and wherein the at least one water condenser and the thermochemical modules are connected so that water vapour can be exchanged individually between any two selected from the list consisting of the at least one water condenser and the at least two thermochemical modules. A method for desorption in the system according to the invention is also described. In this method, the first thermochemical module is used as a condenser to dry the second thermochemical module.