Vapour-Only Cycling to Bypass Pinch Points in Solar Thermal Storage
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Solution Overview
Problem
Solar power stations using molten salt as both heat transfer fluid and sensible heat storage medium face limitations due to the 'pinch point' problem, which restricts the maximum temperature that can be attained, and issues with high-temperature stability and solid phases at ambient temperature, particularly in distributed solar dish technologies.
Innovation Solution
Cycling water in a superheated vapour state for heat transfer to a single sensible heat storage medium, using separate heat exchange subsystems and a pumping subsystem with a steam separator and compressor to manage temperature and pressure thresholds, allowing the heat transfer fluid to bypass the heat exchanger when necessary, and using a mixture of salt compounds for efficient heat storage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If water is used as heat transfer fluid and cooled from superheated steam to liquid water, then heat transfer capability is improved, but a pinch point problem occurs that limits the maximum temperature of the storage medium
Solution Approach 1:
The patent extracts the harmful condensation phase change from the heat transfer process. By using superheated steam that remains in the vapour state throughout heat exchange, the system eliminates the temperature plateau that causes the pinch point problem, allowing continuous temperature differential and unlimited storage medium heating.
Solution Approach 2:
The patent changes the thermal state parameter of the heat transfer fluid from condensing steam to superheated vapour. This parameter change ensures the fluid remains above the saturation curve, maintaining a continuous temperature gradient with the storage medium and eliminating the pinch point constraint on maximum temperature.
2Device complexity
If molten salt is used as both heat transfer fluid and sensible heat storage medium, then system simplicity is improved, but the pinch point problem restricts maximum temperature attainment
Solution Approach 1:
The patent separates the heat transfer fluid function from the storage medium function. By using superheated steam exclusively for heat transfer and molten salt only for storage, the system avoids the pinch point problem while maintaining operational simplicity, as the steam never condenses within the heat exchanger.
Solution Approach 2:
The patent changes the operating parameters of the heat transfer fluid to maintain it in a superheated vapour state throughout the heat exchanger. This parameter change eliminates the temperature plateau during phase change, allowing the storage medium to reach higher temperatures without the pinch point constraint.
3Stability of the object's composition
If synthetic oil is used as heat transfer fluid, then high temperature stability is improved up to about 400°C, but the maximum temperature of the sensible heat storage medium is limited
Solution Approach 1:
The patent uses water/steam as a heat transfer fluid that can be continuously regenerated. The steam transfers heat and is then condensed externally (not in the heat exchanger), allowing continuous circulation without degradation. This replaces the limited-stability synthetic oil with an infinitely recyclable fluid system.
Solution Approach 2:
The patent changes the heat transfer fluid from synthetic oil to water in superheated vapour state. This parameter change allows operation at temperatures exceeding 400°C while maintaining fluid stability, as the water remains in vapour form and does not undergo thermal decomposition that limits oil-based systems.
4Temperature
If solar dish technologies directly heat molten salt at the focal point, then high temperature capability is improved, but reticulation complexity increases and freezing risk occurs during night or cloudy periods
Solution Approach 1:
The patent extracts the heat transfer function from the storage medium. By using superheated steam as a dedicated heat transfer fluid that never freezes, the system eliminates the freezing risk in pipe networks while maintaining high temperature capability. The molten salt remains exclusively in storage tanks where it is continuously heated.
Solution Approach 2:
The patent introduces superheated steam as an intermediary heat transfer fluid between the solar collector and the molten salt storage medium. This intermediary remains in vapour state throughout circulation, eliminating freezing risks in pipes while efficiently transferring high temperatures to the storage medium.
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 avoids the pinch point problem, maintains high temperature capabilities, and simplifies the energy storage system by using a single sensible heat storage medium, enhancing power generation efficiency and operational reliability in solar power stations.
Implementation Method 1
solar collector to heat water to a temperature and pressure above a second set of thresholds
Implementation Method 2
water to cause the water to change phase from liquid to vapour
Implementation Method 3
a compressor is operable to compress the vapour
Implementation Method 4
a heat exchanger system is in communication with the solar collector, the steam separator and the compressor, the heat exchanger system being arranged to cool the vapour below the saturation temperature corresponding to the pressure of the vapour
Implementation Method 5
cool the vapour below the saturation temperature corresponding to the pressure of the vapour so that the vapour condenses to liquid water
Implementation Method 6
a pump is operable to pump the liquid water from the heat exchanger system to the solar collector
Data Source
Figure 1~2
Figure 3~4
AI summary
Heat transfer fluid in vapour only state is cycled through solar collector(s) (12) and a sensible heat storage medium (14) to transfer heat from the solar collector(s) (12) to the sensible heat storage medium (14). The heat transfer fluid is a liquid at ambient temperature, but substantially in the vapour state throughout the entire cycle when in operation.