Flash Crystallization for Low-Biuret Urea Powder
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Solution Overview
Problem
Current methods for producing urea powder for NOx abatement, such as diesel exhaust fluid (DEF), face challenges with high biuret levels and additive presence, leading to costly and energy-intensive processes, and difficulties in transporting concentrated urea solutions due to caking and precipitation issues.
Innovation Solution
A process involving flash crystallization of an aqueous urea stream at subatmospheric pressure to produce a solid crystallized urea powder with low water content, which is free-flowing and can be easily transported and dissolved to form a high-quality DEF solution, while also reducing biuret content and avoiding the need for additives.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If urea is produced as a concentrated solution for DEF, then the product quality meets specifications, but transportation costs increase due to transporting large volumes of water
Solution Approach 1:
The invention changes the physical state parameter of urea from solution to solid powder form through flash crystallization. This parameter change allows the product to be transported in concentrated form without excessive water, reducing transportation volume by a factor of 3-5 times compared to solution transport, while maintaining the ability to produce high-quality DEF solution at the point of use
Solution Approach 2:
The invention separates the production and application locations. Urea is produced as solid powder at the production site, transported to the application site, and then dissolved to form DEF solution. This segmentation allows optimized transportation of the solid powder form while maintaining the required solution quality at the point of use
2Productivity
If urea is produced as a powder for transportation, then transportation efficiency improves, but the powder must be free-flowing without caking which requires additives
Solution Approach 1:
The invention utilizes flash crystallization, a rapid phase transition from liquid to solid, to produce urea powder with a specific crystalline structure. This rapid phase transition creates free-flowing granular particles that do not cake or stick together, eliminating the need for anti-caking additives while maintaining excellent flow properties for efficient transportation
Solution Approach 2:
The flash crystallization process changes multiple parameters simultaneously: temperature, pressure, and cooling rate. These parameter changes produce a specific particle morphology and surface characteristics that prevent caking and ensure free-flowing properties, enabling additive-free powder production
3Ease of manufacture
If conventional urea finishing methods are used, then solid urea is produced, but biuret levels are high requiring costly removal processes
Solution Approach 1:
The flash crystallization process involves rapid cooling and phase transition that kinetically favors the formation of pure urea crystals while excluding biuret and other impurities. This rapid phase change prevents the formation of biuret during crystallization and allows easy separation of high-purity urea powder from the mother liquor containing impurities
Solution Approach 2:
The process extracts pure urea crystals from the reaction mixture through flash crystallization, leaving biuret and other impurities in the remaining liquid phase. This extraction occurs naturally during the rapid crystallization process, eliminating the need for costly subsequent removal processes
4Strength
If additives are used to prevent caking, then particle strength improves, but the presence of additives like formaldehyde makes the product unsuitable for DEF
Solution Approach 1:
The rapid flash crystallization produces particles with inherent mechanical strength due to the crystalline structure formed during rapid phase transition. The quick cooling rate creates a dense, strong crystal lattice that provides sufficient particle strength without requiring any binding additives, thus avoiding contamination with formaldehyde or other harmful substances
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 process results in a low-biuret, free-flowing urea powder that can be easily transported and dissolved to produce DEF, extending catalyst life and reducing transportation costs by minimizing water usage and energy requirements.
Implementation Method 1
subjecting said solution to flash crystallization at a subatmospheric pressure, so as to obtain a solid crystallized urea containing product
Implementation Method 2
subjecting said solution to flash crystallization at a subatmospheric pressure, so as to obtain a solid crystallized urea containing product and an ammonia and water containing vapor
Implementation Method 3
subjecting said solution to flash crystallization at a subatmospheric pressure, so as to obtain a solid crystallized urea containing product and an ammonia and water containing vapor
Implementation Method 4
subjecting said solution to flash crystallization at a subatmospheric pressure
Data Source
AI summary
Disclosed is a process for the preparation of a urea product suitable for being diluted with water so as to form an aqueous urea comprising solution for use in a unit for the reduction of NOx in combustion engine exhaust gases, also known as Diesel Exhaust Fluid (DEF) or to be used in De NOx systems of exhaust vapor from industrial furnaces. The process comprises obtaining an aqueous urea solution from or after a recovery section in a urea production process. This solution, which has a low content of impurities, is subjected to flash crystallization at a low pressure, so as to obtain a solid crystallized urea containing product, which is a free-flowing powder containing less than 0.2 wt. % water. This product is packaged under conditions such that the water content in the packaged product is maintained below 0.2 wt. %. The invention can also be used in a method of increasing the capacity of an existing urea plant.