Nitrate Salt Heat Transfer Medium for High-Temperature Solar Thermal Stability
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Solution Overview
Problem
Current heat transfer media, such as organic thermal oils, decompose at temperatures above 400°C, limiting the efficiency of solar thermal power plants, and existing nitrate salt mixtures like sodium nitrate and potassium nitrate decompose above 565°C, releasing nitrogen oxides, which is undesirable.
Innovation Solution
A nitrate salt composition comprising 60% by weight sodium nitrate and 40% by weight potassium nitrate, with additional alkali metal nitrites and alkali metal carbonates, which can be used as both a heat transfer and heat storage medium, effectively operating above 565°C while minimizing the release of nitrogen oxides.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If organic thermal oil is used as heat transfer medium, then ease of operation is improved, but temperature limit is restricted to below 400°C due to decomposition
Solution Approach 1:
The patent changes the chemical composition parameters of the heat transfer medium from organic thermal oil to an inorganic salt mixture (sodium nitrate, potassium nitrate, and lithium nitrate). This parameter change enables the system to operate at temperatures above 400°C (up to 565°C) while maintaining operational stability, resolving the temperature limit constraint of organic oils.
2Temperature
If nitrate salt mixture (60% NaNO3 + 40% KNO3) is used as heat transfer medium, then temperature limit is improved to 565°C, but harmful gas release increases due to nitrogen oxide decomposition
Solution Approach 1:
The patent creates a composite salt mixture containing three components: sodium nitrate (60-70 wt%), potassium nitrate (20-30 wt%), and lithium nitrate (5-15 wt%). This composite formulation leverages the high temperature stability of lithium nitrate to suppress the decomposition and nitrogen oxide release of the sodium-potassium nitrate mixture, enabling operation at 565°C with reduced harmful emissions.
Solution Approach 2:
Lithium nitrate acts as a stabilizing intermediary in the salt mixture. It modifies the decomposition behavior of the sodium-potassium nitrate blend, raising the decomposition temperature and reducing nitrogen oxide release. The lithium nitrate component mediates between the temperature requirements and the harmful emission constraints.
3Productivity
If heat transfer medium temperature is increased above 400°C, then energy efficiency is improved, but medium stability deteriorates due to decomposition
Solution Approach 1:
The patent changes the chemical composition parameters from organic thermal oil to an inorganic nitrate salt mixture containing lithium nitrate. This parameter change fundamentally alters the thermal stability characteristics, enabling the medium to maintain reliability and resist decomposition at temperatures above 400°C (up to 565°C), thus supporting higher energy efficiency operation.
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 nitrate salt composition allows for continuous operation at elevated temperatures with reduced nitrogen oxide release, enhancing the efficiency of solar thermal power plants and enabling demand-driven electrical energy generation by serving as both a heat transfer and storage medium.
Implementation Method 1
Heat transfer media are media that are heated by a heat source, such as the sun in solar thermal power plants
Implementation Method 2
You can then transfer this heat to another medium, for example water or a gas, preferably via a heat exchanger
Implementation Method 3
Heat accumulators contain heat accumulator media, usually material compositions, for example the mixtures according to the invention, which can store an amount of heat over a certain period of time
Data Source
AI summary
The invention relates to a nitrate salt composition, containing as the essential constituents A) an alkali metal nitrate and optionally an alkali metal nitrite in a total amount in the range of 90 to 99.84% by weight, and B) an alkali metal compound selected from the group comprising B1) alkali metal oxide, B2) alkali metal carbonate, B3) alkali metal compound that decomposes in the temperature range of 250°C to 600°C to form alkali metal oxide or alkali metal carbonate, B4) alkali metal hydroxide MetOH, in which Met denotes lithium, sodium, potassium, rubidium, caesium, B5) alkali metal peroxide Met2O2, in which Met denotes lithium, sodium, potassium, rubidium, caesium, and B6) alkali metal superoxide MetO2, in which Met denotes sodium, potassium, rubidium, caesium in a total amount in the range of 0.16 to 10% by weight, the percentages being relative to the nitrate salt composition.