Urea Purification via Low-Pressure Stripping
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Solution Overview
Problem
Urea production plants face challenges in achieving high purity urea solutions suitable for NOx emission abatement systems, particularly in maintaining low concentrations of impurities and alkalinity, which is crucial for preventing catalyst poisoning and corrosion, and existing methods require complex equipment and high capital expenditure.
Innovation Solution
A process and plant design that reacts CO2 and NH3 under high pressure, expands the urea synthesis stream to reduce pressure, and includes low-pressure stripping to purify the urea solution, recycling the condensate back to the synthesis reactor, thereby avoiding high-pressure stripping and reducing impurity levels, and optionally diluting the solution to achieve target concentrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If high-pressure stripping is used to purify urea solution, then purification effectiveness is improved, but device complexity and capital expenditure increase
Solution Approach 1:
The patent changes the pressure parameter from high-pressure stripping to low-pressure stripping (vacuum conditions), achieving effective purification while simplifying equipment requirements and reducing capital expenditure
Solution Approach 2:
The patent utilizes phase transition of water from liquid to vapor through evaporation at low pressure, enabling purification without requiring complex high-pressure stripping equipment
2Device complexity
If low-pressure stripping is used to purify urea solution, then device complexity is reduced, but purification effectiveness may deteriorate
Solution Approach 1:
The patent introduces a condenser as an intermediary device that condenses water vapor back to liquid form, enabling effective water removal at low pressure and achieving purification effectiveness comparable to or better than high-pressure methods
Solution Approach 2:
The patent implements a feedback loop where condensed water is recycled back to the synthesis reactor, optimizing the purification process and maintaining high effectiveness while using simpler low-pressure equipment
3Reliability
If urea solution is produced with high purity to prevent catalyst poisoning, then reliability of NOx abatement system is improved, but production cost increases
Solution Approach 1:
The patent changes operating parameters to low-pressure conditions, achieving high purity urea solution that protects catalysts while reducing production costs through simplified equipment and lower energy consumption
Solution Approach 2:
The patent enables the system to self-regulate purity levels through the low-pressure evaporation and condensation process, ensuring catalyst-protective purity without requiring additional expensive purification stages
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 results in a purified urea solution with low alkalinity and impurity levels, suitable for use in NOx abatement systems, reducing catalyst poisoning and corrosion risks while minimizing capital expenditure and equipment complexity.
Implementation Method 1
reacting CO2 and NH3 under urea synthesis conditions in a urea synthesis reactor operating at high pressure, to give a urea synthesis stream containing urea, NH3, CO2 and an amount of carbamate
Implementation Method 2
expanding the urea synthesis stream in a recovery section thereby reducing the pressure, wherein the urea synthesis stream that is expanded comprises at least 90 wt.% of said amount of carbamate
Implementation Method 3
heating at least part of the expanded urea synthesis stream in one or more dissociation units at medium and/or low pressure, to give an aqueous urea stream and a recovery section vapour containing NH3 and CO2
Implementation Method 4
heating at least part of the expanded urea synthesis stream in one or more dissociation units at medium and/or low pressure, to give an aqueous urea stream and a recovery section vapour
Implementation Method 5
subjecting in a purification section at least part of the aqueous urea stream to purification, wherein the purification is preferably performed by stripping, more preferably by low pressure (LP) stripping, to remove (excess) ammonia
Implementation Method 6
the purification section off-gas is condensed to give purification section condensate and said purification section condensate is recycled to said urea synthesis reactor
Data Source
Figure 1
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AI summary
Processes and plants for the production of purified urea solution are described. In a described urea production process, urea is produced in a synthesis section without a high pressure stripper and the urea solution is subjected to purification after the recovery section, to give purified urea solution and off-gas. The purification comprises e.g. steam stripping.