Urea Synthesis Oxygen Feed Optimization
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Solution Overview
Problem
Current urea synthesis methods face challenges in achieving a balance between corrosion resistance and productivity, particularly in terms of oxygen concentration, material cost, and production process efficiency, leading to high construction and operating costs.
Innovation Solution
A urea synthesis method using general-purpose austenitic-ferritic duplex stainless steel with specific composition ranges in the urea synthesis apparatus, optimizing oxygen feed concentration to minimize corrosion prevention oxygen usage, thereby reducing equipment size and costs, and enhancing reaction yield.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If oxygen is fed as an oxidant to form a passivation film on the metal surface, then corrosion resistance is increased, but inert gases increase and reaction yield decreases
Solution Approach 1:
The patent optimizes the oxygen concentration parameter to a specific range (100-2000 ppm with respect to CO2) to achieve the minimum required for passivation film formation while minimizing inert gas accumulation. This parameter optimization resolves the contradiction by finding the precise threshold where corrosion protection is achieved without excessive oxygen interfering with the urea synthesis reaction yield.
2Reliability
If the amount of oxygen fed is increased to enhance corrosion resistance, then passivation film formation is improved, but running cost is adversely affected
Solution Approach 1:
The patent applies partial action by feeding oxygen at a controlled, minimal concentration (100-2000 ppm) rather than excessive amounts. This partial oxygen feed is sufficient to maintain passivation film integrity for corrosion protection while avoiding the need for large-scale oxygen removal equipment, thereby reducing running costs associated with energy-consuming scrubbers and hydrogen combustion removal apparatuses.
3Ease of manufacture
If general-purpose austenitic-ferritic duplex stainless steel is used, then material and construction costs are reduced, but corrosion resistance may be insufficient without adequate oxygen feed
Solution Approach 1:
The patent specifies precise compositional parameters for general-purpose austenitic-ferritic duplex stainless steel (Cr: 21-26 wt%, Ni: 4.5-7.5 wt%, Mo: 2.5-3.5 wt%, N: 0.08-0.30 wt%) to achieve adequate corrosion resistance. Combined with optimized oxygen feed concentration (100-2000 ppm), these material parameter specifications enable the use of cost-effective general-purpose stainless steel while maintaining reliable corrosion protection.
4Productivity
If oxygen feed concentration is optimized, then reaction yield increases and equipment size decreases, but corrosion prevention oxygen usage must be minimized
Solution Approach 1:
The patent establishes a specific oxygen feed concentration range (100-2000 ppm with respect to CO2) that represents an optimal parameter window. Within this range, the oxygen concentration is sufficient to maintain passivation film integrity for corrosion prevention while being low enough to minimize inert gas accumulation, thereby maximizing reaction yield and allowing for reduced equipment size.
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 method significantly reduces material and construction costs, decreases inert gas usage, and increases reaction yield by optimizing oxygen feed concentrations, eliminating the need for energy-consuming scrubbers and hydrogen combustion removal apparatuses, while maintaining excellent corrosion resistance.
Implementation Method 1
a method of mixing oxygen with carbon dioxide and ammonia, starting raw materials, to form about 1 to 3 nm of a passivation film comprising hydroxides of Fe and Cr and an oxide of Cr at high temperature and high pressure
Implementation Method 2
Urea is an important raw material for a nitrogen-based fertilizer... synthesized by reacting ammonia with carbon dioxide
Data Source
AI summary
There is provided a urea synthesis method having excellent reliability and productivity with the amount of oxygen used as a corrosion-resistant agent minimized without using special duplex stainless steel. In a urea synthesis apparatus having a synthesis tower, a stripper, and a condenser, general-purpose austenitic-ferritic duplex stainless steel with Cr content: 21 to 26 wt %, Ni content: 4.5 to 7.5 wt %, Mo content: 2.5 to 3.5 wt %, N content: 0.08 to 0.30 wt %, C content: 0.03 wt % or less, Si content: 1.0 wt % or less, Mn content: 2.0 wt % or less, P content: 0.04 wt % or less, and S content: 0.03 wt % is used as a urea synthesis apparatus material in at least some of parts where the urea synthesis apparatus comes into contact with a fluid having corrosiveness, and oxygen feed concentration with respect to carbon dioxide is 100 to 2,000 ppm.