Nitrate Salt Composition Stabilization for High-Temperature Heat Storage
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Solution Overview
Problem
Heat transfer media based on nitrate salt mixtures and nitrite salt mixtures used in solar thermal power stations face degradation at high temperatures, leading to reduced long-term operating temperatures and increased corrosiveness, making them unsuitable for extended use.
Innovation Solution
A nitrate salt composition comprising alkali metal nitrates and alkaline earth metal nitrates, optionally with alkali metal nitrites and alkaline earth metal nitrites, is treated with an additive containing nitric acid, nitrous acid, and oxygen-comprising gases to enhance thermal stability and prevent degradation, allowing for higher long-term operating temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If nitrate salt mixtures are used as heat transfer media at high temperatures, then heat transfer efficiency is improved, but the salt mixtures degrade leading to reduced long-term operating temperature range and increased corrosiveness
Solution Approach 1:
The patent applies preliminary action by adding nitric acid and oxygen-comprising substances to the nitrate salt mixture before operation to pre-oxidize it. This pre-treatment establishes a stable oxidizing environment that prevents subsequent degradation during high-temperature operation, thereby maintaining the temperature range and property stability throughout the operational lifecycle
Solution Approach 2:
The patent changes the chemical composition parameters of the heat transfer medium by introducing nitric acid (typically 5-50% by weight) and oxygen-comprising substances. This parameter change transforms the salt mixture from a degradation-prone state to a stabilized state with extended operating temperature range and reduced corrosiveness, directly resolving the reliability issue while maintaining high temperature capability
2Productivity
If nitrate salt mixtures operate at high temperatures for extended periods, then energy transfer capability is improved, but degradation occurs reducing the operating temperature range
Solution Approach 1:
By modifying the chemical composition through addition of nitric acid and oxygen-comprising substances, the patent changes the thermal and chemical stability parameters of the salt mixture. This enables the mixture to maintain its heat transfer capability at higher temperatures for extended periods without degradation, thus extending the sustainable operating temperature range while preserving productivity
Solution Approach 2:
The patent ensures continuous useful action by preventing degradation through pre-oxidation and stabilization. The treated salt mixture maintains consistent heat transfer properties over extended operational periods, allowing continuous high-temperature operation without the temperature range reduction that would otherwise limit prolonged productivity
3Quantity of substance
If nitrate salt mixtures are used as heat storage media, then thermal energy storage is improved, but corrosiveness increases over time
Solution Approach 1:
The patent changes the chemical state parameters of the nitrate salt mixture by introducing nitric acid and oxygen-comprising substances. This transformation reduces the corrosiveness parameter while maintaining the heat storage capacity, as the stabilized oxidizing environment prevents the chemical degradation that would otherwise increase corrosiveness over time
Solution Approach 2:
The patent converts the potentially harmful effect of nitrate salt degradation into a benefit by deliberately introducing controlled oxidation through nitric acid and oxygen-comprising substances. This pre-oxidation transforms what would be harmful degradation products into a stable, less corrosive operational state, thereby maintaining heat storage capacity while reducing harmful corrosiveness
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 treatment process stabilizes the nitrate salt composition, maintaining its properties and preventing degradation, thus extending the long-term operating temperature range and reducing corrosiveness, making it suitable for higher temperature applications in solar thermal power stations.
Implementation Method 1
The nitrate salt composition is brought into contact with an additive comprising nitric acid and/or nitrous acid and oxygen-comprising gas having an oxygen partial pressure which is equal to or greater than that in air and/or oxygen-generating compounds
Data Source
AI summary
Method of maintaining or widening the long-term operating temperature range of a heat transfer medium and/or heat storage medium comprising a nitrate salt composition selected from the group consisting of alkali metal nitrate and alkaline earth metal nitrate and optionally alkali metal nitrite and alkaline earth metal nitrite, wherein the nitrate salt composition is brought into contact with an additive comprising the components nitric acid and/or nitrous acid and oxygen-comprising gas having an oxygen partial pressure which is equal to or greater than that in air and/or oxygen-generating compounds and optionally nitrogen oxides and/or compounds which generate further nitrogen oxide.