Urea Granulation Plume Opacity Reduction via Aerosol Stage Inversion
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Solution Overview
Problem
Existing urea granulation processes face challenges in reducing visible downwind plume opacity caused by aerosol emissions and in efficiently recycling ammonium salts, which are diluted due to high temperature equipment and hygroscopic nature, leading to suboptimal ammonium salt concentration for reintegration into the process.
Innovation Solution
A method and device that alter the sequence of process steps in urea granulation, including a granulator, dust scrubber, acidic scrubber, and aerosol stage with specialized spray and collection devices, allowing for efficient separation and recovery of ammonium cyanate, ammonia, and water, and subsequent hydrolysis to generate ammonium salts for recycling, avoiding dilution and reducing aerosol emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If the sequence of process steps is altered to place the aerosol stage after the acidic scrubber, then aerosol emissions are reduced and ammonium cyanate is recovered, but the process complexity increases
Solution Approach 1:
The process is divided into distinct stages: dust scrubbing stage, acidic scrubbing stage, and aerosol stage. Each stage targets specific components (dust, ammonia, aerosols) separately, allowing for optimized treatment at each step and reducing overall emissions while maintaining manageable process complexity through modular design.
Solution Approach 2:
The aerosol stage is positioned after the acidic scrubber to perform preliminary removal of aerosols containing ammonium cyanate before final discharge. This preliminary action prevents aerosol emissions from reaching the atmosphere while allowing the recovered ammonium cyanate to be reintegrated into the urea production process.
2Quantity of substance
If high temperature equipment is used to concentrate ammonium salt solution, then ammonium salt concentration increases, but energy consumption and equipment cost increase
Solution Approach 1:
The process utilizes the existing heat from the granulation process itself to evaporate water from the ammonium salt solution. The granulator's thermal energy is redirected to concentrate the scrubber bleeds, eliminating the need for separate high-temperature concentration equipment and reducing additional energy consumption.
Solution Approach 2:
The water evaporation step is merged with the existing granulation process by utilizing the granulator's thermal field. The scrubber bleeds are introduced into the granulator where they are concentrated through evaporation of water using the granulator's heat, combining two functions (granulation and concentration) into one operational unit.
3Object-generated harmful factors
If the aerosol stage is placed before the acidic scrubber, then aerosol removal is efficient, but ammonium cyanate cannot be effectively recovered
Solution Approach 1:
Instead of removing aerosols first and then treating the gas stream, the process inverts the sequence by first performing acidic scrubbing to convert aerosols into ammonium cyanate in solution, then recovering the ammonium cyanate from the liquid phase. This inversion enables effective recovery while still achieving aerosol removal.
4Object-affected harmful factors
If ammonium salt solution is diluted, then hygroscopic absorption is reduced, but recycling efficiency decreases
Solution Approach 1:
The process performs preliminary concentration of the ammonium salt solution through water evaporation in the granulator before recycling. By removing excess water in advance, the solution achieves optimal concentration for recycling, preventing hygroscopic absorption issues while maintaining high recycling efficiency and process productivity.
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 reduces aerosol emissions, enhances the recovery of ammonium salts, and allows for higher ammonium salt concentrations, improving the economic efficiency and effectiveness of the recycling process without the need for expensive high-temperature equipment, resulting in reduced visible plume opacity and enhanced process upgrading.
Implementation Method 1
The melt is introduced into a granulator which carries out a granulation at elevated temperature and evaporates the water in the melt
Implementation Method 2
Due to the high temperature, a portion of the urea is converted into ammonium cyanate according to a reversible reaction
Implementation Method 3
When spraying this solution in a granulator a great part of ammonium cyanate vaporizes into gaseous ammonia and cyanic acid
Implementation Method 4
By a condensing reaction aerosols creating the downwind detached plume opacity are created
Implementation Method 5
In acid solution (less than pH 5) there is a rapid hydrolysis of cyanate
Implementation Method 6
a following aerosol stage with spray and collection devices, releasing a first stream of an exhaust of air, and a second stream of ammonium cyanate and water
Implementation Method 7
The ammonium cyanate further decomposes with water to ammonium carbonate
Data Source
AI summary
The invention relates to a method for reducing aerosol emissions from a urea granulation plant with a recovery of the resulting scrubber bleeds, with • a granulator producing urea from a concentrated urea solution and an evaporation of the included water, giving urea granulates and an exhaust of dust, ammonia and ammonium cyanate, and • a following scrubbing or removing stage for the dust, and • a following scrubbing acid stage, resulting in a first stream comprising mainly aerosols and a second stream comprising ammonium salts, and • a following aerosol stage with spray and collection devices, releasing a first stream of an exhaust of air, and a second stream of ammonium cyanate and water, and • the second stream of the aerosol stage of ammonium cyanate and water is recovered into the urea granulation plant or into a urea fertilizer plant.