Ammonium Sulfate Crystallization Double Classification
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Solution Overview
Problem
Existing processes for producing ammonium sulfate crystals result in unsatisfactorily low average crystal size due to recycling of small crystals, which reduces production rate and requires complex equipment and control systems to maintain product quality.
Innovation Solution
A continuous process involving a second size classification step and redissolving the finest crystals before recycling them back to the crystallizer, allowing for increased average crystal size and improved throughput.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If small crystals are recycled to the crystallizer, then the total surface area of crystals increases, but the average crystal size decreases due to reduced supersaturation
Solution Approach 1:
The patent divides the crystal recycling process into segments by implementing a two-stage classification system. The first classifier separates crystals into coarse and fine fractions, and the second classifier further divides the fine fraction. This segmentation allows selective recycling of only the finest crystals (below 0.5mm), preventing them from reducing the average crystal size while still providing nucleation sites for growth.
Solution Approach 2:
The patent applies local quality by treating different crystal size fractions differently. Instead of uniformly recycling all fine crystals, the system selectively recycles only the finest fraction (below 0.5mm) while discarding or separately handling the coarser fine fraction (0.5mm and above). This localized approach ensures that only crystals small enough to act as effective nucleation sites are recycled, maintaining overall crystal size quality.
2Manufacturing precision
If residence time of crystals in the crystallizer is increased, then the average crystal size increases, but the throughput of the crystallization step decreases
Solution Approach 1:
The patent applies preliminary action by classifying and separating crystals before they enter the crystallizer. The two-stage classification system pre-sorts crystals into size fractions, ensuring that only appropriately sized crystals are recycled. This preliminary separation eliminates the need for extended residence times to achieve size separation, allowing faster throughput while maintaining crystal size quality.
Solution Approach 2:
The patent replaces the mechanical/time-dependent process of crystal growth and settling with a mechanical classification system. Instead of relying on prolonged residence time for crystals to naturally separate by size, the system uses classified screens or hydrocyclones to mechanically separate crystals by size before recycling, significantly reducing the required residence time.
3Manufacturing precision
If a second size classification step is added, then the average crystal size increases, but the device complexity increases
Solution Approach 1:
The patent segments the classification function into two distinct stages, each handling a specific size range. The first classifier handles the broader separation into coarse and fine fractions, while the second classifier focuses specifically on the fine fraction to identify the finest crystals for recycling. This segmentation of the classification task achieves superior crystal size control while keeping each individual classifier relatively simple.
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 effectively increases the average crystal size of ammonium sulfate crystals, enhancing production efficiency and reducing energy consumption while maintaining product quality.
Implementation Method 1
subjecting in a crystallizer a feed solution of ammonium sulfate to crystallization to form a first slurry of ammonium sulfate crystals
Implementation Method 2
subjecting the first slurry of ammonium sulfate crystals to a first size classification to yield a first coarse ammonium sulfate crystal fraction and a first fine ammonium sulfate crystal fraction
Implementation Method 3
redissolving at least some of the finest crystals produced from the double classification system before recycling that fraction back to the crystallizer
Data Source
AI summary
The invention relates to a process for preparing a crystalline ammonium sulfate product, which process comprises: a) subjecting in a crystallizer a feed solution of ammonium sulfate to crystallization to form a first slurry of ammonium sulfate crystals; b) subjecting the first slurry of ammonium sulfate crystals to a first size classification to yield a first coarse ammonium sulfate crystal fraction and a first fine ammonium sulfate crystal fraction; c) recycling at least part of the first fine ammonium sulfate crystal fraction to the feed solution of ammonium sulfate; and d) recovering a crystalline ammonium sulfate product from the first coarse ammonium sulfate crystal fraction, characterized in that: e) a second size classification is carried out on a second slurry of ammonium sulfate crystals to yield a second coarse ammonium sulfate crystal fraction and a second fine ammonium sulfate crystal fraction.