Continuous Fluid Bed Crystallizer Control for Stable Crystal Size
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Solution Overview
Problem
Existing processes for producing large crystal products, such as ammonium sulphate, in fluid bed crystallizers face challenges with unstable average crystal size and issues like crystal sticking and cumbersome dosing of fine crystals, leading to inefficient production and market specification deviations.
Innovation Solution
A continuous process is developed where the weight percentage of crystals in the external circulation circuit is controlled within a narrow range by adjusting the height of the crystal bed and using on-line measurements to maintain stable crystal size, avoiding seed crystal sticking and optimizing production yields.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If fine crystals are dosed to control crystal size distribution, then average crystal size can be adjusted, but crystal sticking occurs and dosing becomes cumbersome
Solution Approach 1:
The patent extracts the problematic dosing operation by implementing an automated dosing system that removes fine crystals from a reservoir and introduces them into the crystallizer through a dosing device. This extraction eliminates the need for manual handling and dosing of fine crystals, resolving the sticking and operational complexity issues while maintaining precise control over crystal size distribution.
Solution Approach 2:
The patent introduces a dosing device as an intermediary component between the fine crystal reservoir and the crystallizer. This intermediary mechanism automates the introduction of fine crystals, eliminating direct contact and manual dosing operations that cause sticking problems, while enabling precise control of crystal size distribution through automated dosing rates.
2Manufacturing precision
If external circulation rate is increased to improve crystal size uniformity, then crystal size distribution narrows, but productivity decreases due to longer residence time required
Solution Approach 1:
The patent changes the operational parameters by implementing automated control of the external circulation rate based on real-time monitoring of crystal size distribution. The system dynamically adjusts the circulation rate to optimize both crystal size uniformity and productivity, rather than maintaining a fixed high circulation rate that limits production speed.
Solution Approach 2:
The patent implements a feedback control system where crystal size distribution is continuously monitored and the external circulation rate is automatically adjusted in response. This feedback mechanism enables the system to maintain narrow crystal size distribution while optimizing productivity, as the circulation rate is increased only when needed to correct size variations rather than being constantly high.
3Length of moving object
If crystal bed height is increased to improve crystal growth, then larger crystals are produced, but mass transfer efficiency decreases
Solution Approach 1:
The patent segments the crystallizer into distinct zones with different crystal bed heights optimized for specific functions. The upper portion has a higher crystal bed for growth, while the lower portion maintains better mass transfer efficiency. This segmentation allows large crystals to form in the upper zone without compromising the mass transfer efficiency in the lower zone, resolving the contradiction between crystal size and mass transfer.
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 process ensures stable average crystal size and high yields of large crystal products, meeting market specifications by controlling the weight percentage of crystals in the external circulation circuit, thereby improving handling and use of the product.
Implementation Method 1
a fluid bed crystallizer, said fluid bed crystallizer comprising a crystallization vessel and means for mechanically impacting of crystals
Implementation Method 2
an external circulation circuit comprising means for determining properties of the slurry in the external circulation circuit and a heat exchanger
Data Source
AI summary
The invention relates to a continuous process for preparing large crystal products of a crystalline product in a fluid bed crystallizer, said fluid bed crystallizer comprising a crystallization vessel and means for mechanically impacting of crystals; and connected to the crystallization vessel (i) a feed line; (ii) an external circulation circuit comprising means for determining properties of the slurry in the external circulation circuit and a heat exchanger; and (iii) a product withdrawal line, wherein—for any specific crystalline product and at any flow rate chosen in the external circulation circuit—the weight percentage of crystals of the crystalline product in the slurry in the external circulation circuit, ECCWPC, is controlled by said means for determining properties of the slurry within a specified and predetermined narrow range having a maximum and minimum value not more apart than at most 25% by weight and falling within the range of from 1 to 50% by weight. Preferably, the crystalline product is ammonium sulphate, and the ECCWPC is controlled within a range of from 3 to 20% by weight, preferably of from 5 to 15% by weight, more preferably of from 8 to 12% by weight. The product obtained may be further subjected to size classification by screening.