Ammonia Oxidation Temperature Control for Higher NO Selectivity
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Solution Overview
Problem
Existing nitric acid production processes face inefficiencies in catalytic ammonia oxidation, leading to suboptimal yield and increased plant costs, as they rely on adjusting the ammonia-to-air ratio to control reaction temperature, which is not thermodynamically optimal for each operating condition.
Innovation Solution
The method involves independent temperature control of the process gas mixture before entering the oxidation reactor by indirect heating or cooling, using steam, secondary air, electric current, or fuel gases like hydrogen, and adjusting the process air compressor settings to maintain an optimal reaction temperature for nitrogen monoxide selectivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the ammonia-to-air ratio is adjusted to control reaction temperature, then the reaction temperature can be regulated, but the nitrogen monoxide selectivity is not optimized for each operating condition
Solution Approach 1:
The control of reaction temperature is separated from the ammonia-to-air ratio adjustment. The patent introduces independent temperature control mechanisms (such as preheating devices, cooling devices, or heat exchangers) that can regulate temperature without changing the stoichiometric composition of the reactants. This segmentation allows simultaneous optimization of both temperature regulation and nitrogen monoxide selectivity.
Solution Approach 2:
The patent changes the control parameter for temperature from ammonia-to-air ratio to independent temperature control parameters (such as preheating temperature, cooling rate, or heat exchange efficiency). This parameter change enables precise temperature control while maintaining optimal ammonia-to-oxygen ratio for maximum nitrogen monoxide selectivity.
2Productivity
If additional oxygen (secondary air) is added to accelerate NO oxidation to NO2, then the formation of HNO3 is accelerated, but the overall process efficiency is reduced due to heat generation
Solution Approach 1:
The patent applies preliminary cooling measures before the oxidation step. By pre-cooling the gas mixture or the reactor environment before introducing secondary air for NO oxidation, the exothermic reaction heat is dissipated more effectively, preventing excessive temperature rise and improving overall process efficiency while maintaining high HNO3 formation rate.
3Productivity
If the reaction temperature is increased to improve ammonia oxidation efficiency, then the conversion rate increases, but the selectivity to nitrogen monoxide decreases
Solution Approach 1:
The patent segments the oxidation process into distinct stages with different temperature optima. The first stage (ammonia to NO) operates at lower temperatures (800-900°C) to maximize selectivity, while subsequent oxidation stages (NO to NO2 and further to HNO3) occur at different temperature conditions. This temporal and spatial segmentation allows each reaction to operate at its optimal temperature.
Solution Approach 2:
The patent implements dynamic temperature control where the temperature profile changes over time and space within the reactor. By using multiple heating/cooling zones or staged temperature adjustment, the system dynamically adapts temperature to match the optimal requirements of each reaction stage, maintaining high ammonia conversion while preserving nitrogen monoxide selectivity.
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 enhances the efficiency of ammonia oxidation to nitrogen monoxide, optimizing yield and reducing plant costs by maintaining a targeted reaction temperature, independent of the ammonia-to-air ratio, thereby improving the overall nitric acid production process.
Implementation Method 1
the catalytic oxidation of ammonia gas to nitrogen monoxide by means of an oxygen-containing gas in the presence of a catalyst
Implementation Method 2
indirect heating or cooling, using steam, secondary air, electric current, or fuel gases like hydrogen
Implementation Method 3
indirect heating or cooling, using steam, secondary air, electric current, or fuel gases like hydrogen
Implementation Method 4
fuel gases like hydrogen
Data Source
Figure 1
AI summary
The invention relates to a method for the catalytic oxidation of ammonia gas by means of an oxygen-containing gas, particularly by means of air, in the presence of a catalyst containing a noble metal, to form nitrogen monoxide, in which, according to the invention, the temperature of an ammonia-air mixed gas is adjusted before contact with the catalyst to a value that is optimum in terms of the nitrogen monoxide selectivity of the reaction. A more detailed observation of the process of the catalytic NH3 oxidation according to the above-mentioned reaction equation (I) 4 NH3 + 5 O2 → 4 NO + 6 H2O (I) would lead to the realisation that the optimum operating mode of a NH3-burner in a HNO3-installation is not achieved by maintaining a constant gauze temperature of the catalyst gauze by automatic adjustment of the NH3 : air ratio. Rather, there is an optimum temperature for each operating condition, which should not be adjusted by modifying the NH3 : air ratio, but by modifying the temperature of the NH3-air mixed gas before contact with the catalyst gauzes.