Urea Synthesis Stripping via Heated CO2 Passivation
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Solution Overview
Problem
Current urea synthesis processes face challenges with low CO2 conversion rates and equipment corrosion due to aggressive conditions, requiring costly materials and maintenance for passivation, and inefficient thermal control leading to suboptimal conversion.
Innovation Solution
The process involves feeding a heated CO2 stream containing a passivating agent to the stripper, optimizing the reactor and stripper temperatures, and eliminating the need for separate compressors by integrating the passivation agent into the CO2 stream, allowing for self-stripping and improved corrosion resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high pressure and temperature are used to enhance CO2 conversion, then urea synthesis efficiency improves, but equipment corrosion increases
Solution Approach 1:
The patent introduces a passivating agent that converts the harmful corrosive environment into a beneficial protective state by forming a passive film on metal surfaces. The passivating agent, added in controlled amounts (10^-6 to 10^-2 mol/L), transforms the aggressive high-temperature high-pressure conditions from harmful to harmless by preventing corrosion while maintaining the necessary reaction conditions for high CO2 conversion.
Solution Approach 2:
The patent changes the chemical composition parameter of the reaction medium by introducing a passivating agent with specific properties (oxidizing capability, solubility in reaction medium). This parameter change enables the system to withstand higher temperatures and pressures without corrosion, thus improving CO2 conversion while protecting equipment.
2Reliability
If separate compressors are used for passivation agent delivery, then corrosion protection is improved, but device complexity increases
Solution Approach 1:
The patent merges the passivation agent delivery system with the existing CO2 compression system. Instead of using a separate compressor, the passivating agent is introduced through the CO2 compression and delivery infrastructure that already exists in the urea synthesis plant. This integration eliminates additional equipment while maintaining reliable corrosion protection.
Solution Approach 2:
The CO2 compression system performs dual functions: it compresses CO2 for the urea synthesis reaction and simultaneously delivers the passivating agent to protect equipment. This multi-functionality reduces device complexity by eliminating dedicated passivation agent compression equipment while maintaining effective corrosion protection.
3Productivity
If high NH3/CO2 ratio is used to enhance conversion, then CO2 conversion improves, but thermal control difficulty increases
Solution Approach 1:
The passivating agent acts as an intermediary that stabilizes the thermal environment in the reactor. By forming a protective film on heat exchange surfaces and metal components, it improves heat transfer efficiency and stabilizes temperature distribution, making thermal control easier even at high NH3/CO2 ratios required for enhanced CO2 conversion.
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 CO2 conversion rates, optimizes reactor and stripper processability, reduces maintenance costs, and prevents corrosion, while maintaining optimal thermal conditions for efficient urea synthesis.
Implementation Method 1
feeding a heated CO2 stream containing a passivating agent to the stripper, optimizing the reactor and stripper temperatures, and eliminating the need for separate compressors by integrating the passivation agent into the CO2 stream, allowing for self-stripping and improved corrosion resistance
Implementation Method 2
feeding a heated CO2 stream containing a passivating agent to the stripper, optimizing the reactor and stripper temperatures
Implementation Method 3
The decomposition of ammonium carbamate is effected in the decomposers by supplying heat from the outside by means of indirect thermal exchange with a warmer fluid
Implementation Method 4
The synthesis of urea is effected by the reaction of ammonia and carbon dioxide at a high pressure and temperature, the subsequent separation of urea from the mixture containing the non-reacted products and recycling of the same to the reactor
Data Source
Figure 1
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AI summary
An enhanced process is described for the synthesis of urea from ammonia and carbon dioxide, at a high pressure and temperature, with the formation of ammonium carbamate as intermediate, which includes a high pressure synthesis section, comprising at least one separation step by decomposition-stripping with ammonia of the non-converted ammonium carbamate, carried out in a vertical apparatus, commonly called stripper, characterized in that said step also comprises a feeding, in the lower part of said stripper, of a stream of CO2, heated to a temperature ranging from 130 to 230°C, in a quantity of 1 to 15% by weight with respect to the total weight of the fresh CO2 fed to the process, containing a passivating agent in such a quantity that its equivalent content of O2 in moles varies from 0.05% to 0.80% with respect to the moles of CO2 of said stream.