Urea Granule Core-Shell Structure for Moisture Resistance
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Solution Overview
Problem
Urea fertilizer products mixed with ammonium salts exhibit significantly reduced critical relative humidity, leading to moisture absorption issues, caking, and handling problems, especially in humid environments, and existing coating methods are costly and inefficient.
Innovation Solution
A urea granulation process where a urea solution and a urea/ammonium salt stream are sprayed into a urea granulator as a mixture or separately, with the highest amount of the urea/ammonium salt stream introduced at the granule flow inlet side and decreasing alongside the axis, and the urea solution introduced at the granule flow outlet side, forming granules with a urea-rich outer layer that encloses ammonium salt layers, reducing moisture absorption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of repair
If ammonium salts are mixed into the urea granulator to recycle ammonia salts, then ammonia salt recycling is improved, but the critical relative humidity of the product is significantly reduced leading to moisture absorption
Solution Approach 1:
The patent applies local quality by creating a core-shell structure where the granule core contains ammonium salts and the outer shell consists of pure urea. This spatial differentiation allows the hygroscopic ammonium salts to be enclosed in the core while the outer urea shell provides moisture resistance, thus resolving the contradiction between recycling ammonium salts and maintaining low moisture absorption.
Solution Approach 2:
The patent implements the nested doll principle by placing ammonium salt-containing granule cores inside a urea outer shell. The core is nested within the shell, creating a hierarchical structure where the inner ammonium salt granules are protected by the outer urea layer, enabling both ammonia salt recycling and moisture absorption resistance.
2Loss of substance
If ammonium salts are added to urea product to recover ammonia, then ammonia recovery is improved, but the product shows caking and lumping due to low critical humidity
Solution Approach 1:
The patent creates local quality differentiation by concentrating ammonium salts in the granule core while maintaining a pure urea outer shell. This spatial separation allows the core to fulfill the ammonia recovery function while the outer shell provides structural stability and prevents caking, thus resolving the contradiction between ammonia recovery and product stability.
Solution Approach 2:
The nested structure encapsulates the ammonium salt core within the urea shell, allowing the core to be recovered and reused while the stable outer shell maintains product integrity during storage and transport, preventing caking and lumping.
3Reliability
If coating systems are applied to prevent moisture absorption, then moisture resistance is improved, but production costs and device complexity increase
Solution Approach 1:
The patent merges the product formation and moisture protection functions into a single granulation process. By creating a core-shell structure during the granulation step itself, the need for separate coating systems is eliminated, thus resolving the contradiction between moisture resistance and device complexity while reducing production costs.
Solution Approach 2:
The granulation process itself generates the protective outer shell structure, making the system self-protecting against moisture. The process automatically creates the moisture-resistant configuration without requiring additional external coating equipment or steps.
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 produces urea granules with low moisture absorption capacity, eliminating the need for additional coatings and integrating ammonium salts into the production, maintaining product quality and nitrogen content, thus enhancing storage and handling in humid conditions.
Implementation Method 1
used air exiting a urea granulator that is equipped with a fluidized bed
Implementation Method 2
urea solution and a urea / ammonium salt-stream are sprayed as a mixture or separately via a feed system unit via various nozzles into the urea granulator
Implementation Method 3
The ammonia is removed from the gas stream by chemical absorption and converted to the corresponding ammonium salt
Data Source
Figure 1a~1b
Figure 2
AI summary
A method for producing urea granules having low moisture absorption capacity, with a urea granulator, having a granule flow inlet side and oppositely a granule flow outlet side, forming an axis alongside which urea granules from a urea solution and a urea / ammonium salt-stream are formed, whereby the urea solution and the urea / ammonium salt-stream are sprayed as a mixture or separately via a feed system unit via various nozzles into the urea granulator onto a seed material. In this process the highest amount of the urea / ammonium salt-stream is sprayed into the urea granulator at the granule flow inlet side and the amount of the urea / ammonium salt-stream is decreased alongside the axis of the urea granulator from the granule flow inlet side to the granule flow outlet side, whereby the urea / ammonia salt-stream comprises a urea : ammonium salt ratio between 4 and 20, a water content of 0 - 10 % by weight and optionally up to 1 - 5 % by weight additives, and the highest amount of the urea solution is sprayed into the urea granulator at the granule flow outlet side and the amount of the urea solution is decreased alongside the axis of the urea granulator from the granule flow outlet side to the granule flow inlet side.