Use of a nitrate salt composition as a heat transfer or heat storage medium for first operation of an apparatus containing these media
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Solution Overview
Problem
Conventional nitrate salt compositions used in solar-thermal power stations decompose upon heating, leading to the formation of decomposition gases, which cause overheating, reduce heat removal efficiency, and increase nitrogen oxide emissions, making the start-up process slow and uneconomical.
Innovation Solution
A nitrate salt composition comprising alkali metal nitrates and alkali metal nitrites, with a controlled nitrite content and oxygen partial pressure, is used as a heat transfer and storage medium, allowing for faster heating to high temperatures without significant gas evolution, thereby reducing the risk of overheating and nitrogen oxide emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If conventional nitrate salt compositions are used as heat transfer medium, then heat transfer function is provided, but decomposition gases are formed causing overheating and reducing heat removal efficiency
Solution Approach 1:
The patent modifies the chemical composition parameters of the nitrate salt by adding alkali metal nitrites (1-15 mol%) to the existing nitrate salt composition. This parameter change alters the thermal decomposition behavior of the salt mixture, suppressing gas evolution while maintaining heat transfer capabilities at high temperatures up to 620°C.
Solution Approach 2:
The invention creates a composite heat transfer medium by combining multiple components: alkali metal nitrates (sodium nitrate, potassium nitrate), alkaline earth metal nitrates (calcium nitrate, strontium nitrate), and alkali metal nitrites (sodium nitrite, potassium nitrite). This composite composition synergistically reduces decomposition gas formation while maintaining effective heat transfer properties.
2Quantity of substance
If conventional nitrate salt compositions are heated to high temperatures, then heat storage capacity increases, but nitrogen oxide emissions increase
Solution Approach 1:
By adjusting the chemical composition parameters—specifically incorporating 1-15 mol% alkali metal nitrites and optimizing the ratio of different nitrate salts—the patent modifies the thermal decomposition pathway. This reduces nitrogen oxide emissions while preserving the heat storage capacity necessary for solar-thermal power station operation at temperatures up to 620°C.
3Productivity
If conventional nitrate salt compositions are used, then heat transfer function is provided, but start-up process is slow and uneconomical
Solution Approach 1:
The modified nitrate salt composition with added nitrites exhibits improved thermal stability and reduced gas evolution during heating. This allows faster heating rates during the start-up phase without risking overheating or excessive gas formation, thereby reducing start-up time and improving the economic viability of solar-thermal power stations.
4Productivity
If nitrate salt composition is heated quickly to high temperatures, then operational efficiency improves, but risk of overheating increases
Solution Approach 1:
The patent optimizes the chemical composition parameters of the nitrate salt mixture by incorporating specific amounts of alkali metal nitrites (1-15 mol%). This composition modification suppresses decomposition gas formation and improves thermal stability, enabling rapid heating to high temperatures (up to 620°C) during operation while maintaining reliability and preventing overheating during the start-up phase.
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 enables quicker and more efficient heating to high temperatures, reducing the risk of overheating and nitrogen oxide emissions, and allows for a smaller amount of salt to be used, thus improving the start-up process and operational efficiency of solar-thermal power stations.
Implementation Method 1
Heat stores comprise heat storage media, usually compositions, for example the mixtures according to the invention, which can store a quantity of heat for a particular time
Implementation Method 2
Heat transfer media are media which are heated by a heat source, for example the sun in solar-thermal power stations, and transport the heat comprised therein over a particular distance
Data Source
AI summary
A heat transfer or storage medium containing a nitrate salt composition including at least one alkali metal nitrate and optionally alkaline earth metal nitrate; and, at least one alkali metal nitrite and optionally alkaline earth metal nitrite in an amount of 1.1 to 15.0 mol %. The molar amount of the alkali metal nitrite and optionally alkaline earth metal nitrite for a desired temperature is calculated byxnitrite=K6(T)K6(T)+PO2Xnitrite is the mole fraction of nitrite,K6(T) is the temperature-dependent equilibrium constant of the reaction nitrate ⇄nitrite+½ oxygen (NO3−⇄ NO2−+½ O2),pO2 is the oxygen partial pressure and T is the temperature of the nitrate salt composition.