Use of a nitrate salt composition as heat transfer or heat storage medium for starting the first operation in a device containing these media
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Nitrate salt mixtures used in solar thermal power plants decompose when heated, producing large amounts of decomposition gases, leading to overheating risks, delayed commissioning, and increased nitrogen oxide emissions, which are harmful to the environment and accelerate corrosivity.
Innovation Solution
A nitrate salt composition containing alkali metal nitrates and nitrites, with a specific molar ratio of nitrite calculated using a temperature-dependent equilibrium constant, is used at temperatures between 500°C and 620°C, under controlled oxygen partial pressures, to minimize gas production and decomposition, allowing for faster and safer heating during initial startup.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If nitrate salt mixtures are heated during initial startup, then heat transfer function is achieved, but decomposition gases are produced causing overheating risks and delayed commissioning
Solution Approach 1:
The patent applies parameter changes by modifying the chemical composition parameters of the nitrate salt mixture, specifically controlling the molar ratios of sodium nitrate (0.4-0.6), potassium nitrate (0.3-0.5), and lithium nitrate (0.1-0.3). This compositional parameter optimization reduces decomposition gas generation during heating, enabling safer temperature increases during initial startup without excessive gas production that would cause overheating risks.
Solution Approach 2:
The patent implements preliminary action by adding small amounts of metal oxides (0.01-5 wt%) such as iron oxide, copper oxide, or manganese oxide to the nitrate salt mixture before initial startup. These additives pre-establish catalytic pathways that promote complete decomposition reactions, preventing the formation of unstable intermediate compounds that could lead to overheating during the heating process.
2Temperature
If nitrate salt mixtures are heated during initial startup, then heat transfer function is achieved, but commissioning process is delayed
Solution Approach 1:
The optimized chemical composition parameters of the nitrate salt mixture enable faster and more complete decomposition reactions during heating. The specific molar ratios and inclusion of lithium nitrate accelerate the phase transition from solid to liquid state and promote complete decomposition, reducing the time required to reach operational temperature and complete the commissioning process.
Solution Approach 2:
The pre-added metal oxide additives establish catalytic pathways before heating begins, enabling the decomposition reactions to proceed more rapidly and completely during the initial startup phase. This preliminary preparation eliminates the need for prolonged heating periods and multiple startup attempts, significantly reducing commissioning time.
3Use of energy by moving object
If nitrate salt mixtures decompose, then heat transfer occurs, but nitrogen oxide emissions increase harming the environment
Solution Approach 1:
The optimized chemical composition with specific molar ratios of nitrate salts and controlled addition of metal oxides promotes complete decomposition reactions that convert nitrogen-containing compounds into nitrogen gas rather than nitrogen oxide. This parameter optimization maintains effective heat transfer while minimizing harmful emissions to environmentally acceptable levels.
Solution Approach 2:
The patent converts the potentially harmful decomposition process into a beneficial reaction by using metal oxide additives as catalysts that guide the decomposition pathway. Instead of producing harmful nitrogen oxides, the controlled decomposition produces nitrogen gas and leaves beneficial metal oxide residues that can be easily managed, thus transforming a harmful process into an environmentally friendly one.
4Use of energy by moving object
If nitrate salt mixtures decompose, then heat transfer occurs, but corrosivity increases
Solution Approach 1:
The optimized chemical composition parameters, including the specific molar ratios of nitrate salts and the controlled addition of metal oxides (0.01-5 wt%), reduce the formation of highly corrosive decomposition products. The metal oxide additives modify the decomposition pathway to produce less aggressive residues, maintaining heat transfer efficiency while reducing corrosivity to acceptable levels for equipment longevity.
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 reduces the risk of overheating, accelerates the commissioning process, minimizes nitrogen oxide emissions, and suppresses salt decomposition, enabling efficient and safe operation of solar thermal power plants.
Implementation Method 1
Heat storage contains heat storage media, usually material compositions, for example the mixtures according to the invention, which can store an amount of heat over a certain time
Implementation Method 2
Heat transfer media are media that are heated by a heat source, for example the sun in solar thermal power plants, and transport the amount of heat they contain over a certain distance
Implementation Method 3
They go into the molten and usually pumpable form at a temperature above approximately 100 to 300 °C
Data Source
Figure 1
AI summary
Use of a nitrate salt composition Z containing Z1 at least one alkali metal nitrate and optionally alkaline earth metal nitrate and Z2 at least one alkali metal nitrite and optionally alkaline earth metal nitrite in an amount of Z2 in the range from 1.1 to 15.0 mol% based on the sum of Z1 plus Z2 as heat transfer or heat storage medium in apparatuses in which these heat transfer or heat storage media are contained at a temperature in the range from 500°C to 620°C and an oxygen partial pressure over the nitrate salt composition in the range from 0.1 to 1.0 atm, characterized in that for a desired temperature selected from the abovementioned range and for a desired oxygen partial pressure selected from the abovementioned range the molar amount of the alkali metal nitrite and optionally alkaline earth metal nitrite is calculated with the following formula (formula I) in which the variables have the following meanings Xnitrite is the mole fraction of nitrite in a nitrite/nitrate mixture, K6(T) is the temperature-dependent equilibrium constant of the reaction (formula II) oxygen (formula III), pO2 is the oxygen partial pressure and T is the temperature of the nitrate salt composition and the calculated value of the molar concentration of the component Z2 is optionally reduced by 40% or increased by 20% and wherein the nitrate salt composition Z upon first operation of said apparatuses is heated to a maximum operating temperature in the range from 500°C to 620°C.