Two-Stage Urea Hydrolysis and Stripping Process
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Solution Overview
Problem
Current methods for treating aqueous urea solutions from urea production plants struggle to reduce residual urea and ammonia concentrations to 1 ppm or lower while minimizing apparatus size, as they require increased residence time and larger apparatus sizes, and inefficient gas-liquid contact in strippers hinders ammonia removal.
Innovation Solution
A method involving a two-stage process with steam stripping and catalytic hydrolysis using two catalyst beds at high temperatures and pressures, with countercurrent steam contact to enhance urea hydrolysis and separate ammonia and carbon dioxide, minimizing apparatus size by increasing liquid hourly space velocity (LHSV) and using catalysts like Ti, V, Fe, and oxides for efficient decomposition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a single hydrolyzer is used to reduce residual urea to 1 ppm or lower, then the urea concentration is reduced, but the residence time must be increased and the apparatus size becomes large
Solution Approach 1:
The invention divides the hydrolysis process into two separate stages: a first hydrolyzer that performs initial hydrolysis at lower temperature (130-180°C) and a second hydrolyzer that completes hydrolysis at higher temperature (180-230°C). This segmentation allows each unit to be compact while achieving the overall goal of reducing urea to 1 ppm or lower without requiring a single large apparatus
Solution Approach 2:
The invention changes the operating parameters between the two hydrolyzers: the first hydrolyzer operates at lower temperature (130-180°C) and the second at higher temperature (180-230°C). This parameter change enables efficient hydrolysis at different stages, allowing compact design while achieving high urea removal efficiency
2Use of energy by stationary object
If hydrolysis is carried out at low temperature and pressure (0.3 to 1.1 MPa, 130° C. to 180° C.), then energy consumption is reduced, but the reaction rate is slow and LHSV must be low requiring large apparatus size
Solution Approach 1:
The invention segments the hydrolysis process into two temperature zones: the first hydrolyzer operates at moderate temperature (130-180°C) consuming less energy, while the second hydrolyzer operates at high temperature (180-230°C) achieving fast reaction rate. This segmentation allows the system to benefit from both low energy consumption and high productivity
Solution Approach 2:
The invention ensures continuous hydrolysis action by connecting the first and second hydrolyzers in series, where the effluent from the first hydrolyzer becomes the feed for the second. This continuous action maintains high productivity throughout the process while managing energy consumption efficiently
3Device complexity
If stripping is carried out without trays or packing for gas-liquid contact, then apparatus complexity is reduced, but gas-liquid contact area is insufficient and stripping efficiency is low
Solution Approach 1:
The invention uses packing materials with high surface area to volume ratio inside the stripper to provide extensive gas-liquid contact area. These porous or structured packing materials enable efficient mass transfer of ammonia and carbon dioxide from liquid to gas phase without requiring complex tray structures, thus maintaining low device complexity while achieving high stripping efficiency
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 effectively reduces residual urea and ammonia concentrations to 1 ppm or lower, increases LHSV, and minimizes apparatus size by promoting efficient hydrolysis and stripping, overcoming the limitations of single-bed hydrolyzers and inefficient gas-liquid contact in existing technologies.
Implementation Method 1
a first stripping step of stripping an aqueous solution containing urea, ammonia and carbon dioxide with steam at a pressure of 0.2 to 0.6 MPaA in a first stripper to separate ammonia and carbon dioxide from this aqueous solution into a gas phase
Implementation Method 2
a hydrolysis step of hydrolyzing urea in the solution obtained from the first stripping step at an LHSV of 10 to 20 h−1, at a pressure of 1.1 to 3.1 MPaA and at a temperature of 180 to 230° C. in a catalytic hydrolyzer which is a hydrolyzer including a catalyst
Implementation Method 3
a hydrolysis step of hydrolyzing urea in the solution obtained from the first stripping step
Implementation Method 4
a second stripping step of stripping a liquid obtained from the hydrolysis step with steam in a second stripper to separate ammonia and carbon dioxide from this liquid into a gas phase
Data Source
AI summary
A method for treating a urea aqueous solution includes a first stripping step of steam stripping an aqueous solution containing urea, ammonia and carbon dioxide at 0.2 to 0.6 MPaA in a first stripper to separate ammonia and carbon dioxide from this aqueous solution into a gas phase; a hydrolysis step of hydrolyzing urea in the solution obtained from the first stripping step at an LHSV of 10 to 20 h−1, at 1.1 to 3.1 MPaA and 180 to 230° C. in a catalytic hydrolyzer; and a second stripping step of steam stripping a liquid obtained in the hydrolysis step in a second stripper to separate ammonia and carbon dioxide from this liquid into a gas phase. The residual urea concentration can be reduced to 1 ppm or lower; the residual ammonia concentration can be decreased; LHSV can be increased; and an increase in apparatus size is minimized.