Nitric Acid Absorption Water Balance Control
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Solution Overview
Problem
Current industrial processes for preparing nitric acid are limited in achieving concentrations within the azeotropic range of 50 to 77.8% by weight due to constraints in water balance and nitrogen oxide emissions, requiring complex and costly modifications to manage water input and NOx levels.
Innovation Solution
A process that continuously measures the water content of the process air and adjusts the amount of process water fed to the absorber to regulate nitric acid concentration and NOx levels in the absorber offgas, using a two-stage regime with variable pressure and tray column absorption to achieve stable nitric acid concentrations and reduced NOx emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If the amount of process water fed to the absorber is increased to maintain stable operation and minimize NOx emissions, then NOx emissions are reduced, but the nitric acid concentration decreases below the desired range
Solution Approach 1:
The patent implements a feedback control system where the water content of process air is continuously measured, and based on this measurement, the amount of process water fed to the absorber is automatically adjusted. This closed-loop control enables simultaneous optimization of nitric acid concentration and NOx emissions by dynamically balancing water input according to actual process conditions
Solution Approach 2:
The patent changes the water content parameter of process air through predrying measures, which directly affects the water balance in the system. By controlling this parameter, the system can achieve the desired nitric acid concentration while maintaining stable operation and minimizing NOx emissions without requiring excessive process water
2Quantity of substance
If process air is predried by cooling and reheating to reduce water vapor content, then nitric acid concentration can be increased, but the process complexity and costs increase
Solution Approach 1:
The patent enables the system to self-regulate nitric acid concentration by measuring water content and automatically adjusting process water feed. This self-service approach eliminates the need for complex predrying apparatus, as the system uses its own operational data to maintain optimal concentration without external intervention or additional equipment
Solution Approach 2:
Instead of physically altering the process air through cooling and reheating, the patent achieves concentration control by changing the water input parameter based on measured water content. This parameter-based control approach is simpler and more cost-effective than physical predrying while achieving the same operational goal
3Quantity of substance
If the amount of process water is reduced to increase nitric acid concentration, then concentration increases, but NOx emissions increase and stable operation becomes difficult
Solution Approach 1:
The feedback control system continuously monitors water content and adjusts process water feed to maintain optimal concentration. This prevents both excessive water input (which would lower concentration) and insufficient water input (which would increase NOx emissions), enabling simultaneous achievement of high concentration and low emissions
Solution Approach 2:
The patent controls the water content parameter of process air and uses this information to adjust the process water feed rate. By dynamically changing these parameters based on actual conditions, the system achieves high nitric acid concentration while maintaining low NOx emissions and stable 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
This approach allows for simple and efficient regulation of nitric acid concentration within the desired range and NOx levels, reducing variability and operational costs by maintaining optimal water balance and NOx concentrations, achieving stable nitric acid production with concentrations between 60 to 70% by weight and NOx levels between 150 to 400 ppm.
Implementation Method 1
gaseous ammonia is combusted with air over catalyst meshes, generally composed of platinum or platinum-rhodium alloys
Implementation Method 2
catalytic gas phase oxidation of ammonia
Implementation Method 3
The reaction mixture which comprises NO and O2 from the catalytic gas phase oxidation of ammonia is cooled, in the course of which partial condensation takes place
Implementation Method 4
The gas stream is fed to a countercurrent absorption with water, in the course of which NO2, in the form of N2O4, the reactive species thereof, reacts to form nitric acid
Implementation Method 5
The reaction mixture which comprises NO and O2 from the catalytic gas phase oxidation of ammonia is cooled
Data Source
AI summary
A process for preparing nitric acid by: catalytically oxidizing ammonia, to obtain a gas mixture containing NO and O2; cooling and condensing the gas mixture, thereby further oxidizing NO with O2, to obtain a gas stream containing NO2/N2O4 and an aqueous solution containing nitric acid; and countercurrently absorbing the NO2/N2O4 from the gas stream in an absorber with process water (H2O), to obtain nitric acid and an NOx-containing absorber offgas, wherein the water content of the nitric acid is regulated to a concentration in the range from 50 to 77.8% by weight and the NOx content of the absorber offgas to a concentration in the range from 20 to 500 ppm, by continuously measuring the water content of the process air supplied to the catalytic gas phase oxidation and, as a function of this, adjusting the amount of process water (Q-H2O) fed to the absorber.