Fines Control in Crystallization Reactors via pH Cycling
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Solution Overview
Problem
Existing methods for removing and recovering phosphorus from aqueous solutions, such as fluidized bed reactors, often produce undesirable small crystals ('fines') instead of larger crystals, which hampers the efficient recovery of materials like struvite and calcium phosphate.
Innovation Solution
The method involves altering the pH of the solution to increase the solubility of fines, allowing them to dissolve while maintaining conditions for the growth of larger crystals, by periodically or continuously adjusting the reaction conditions in a reactor or fines destruct zone to control the supersaturation ratio and acid dosing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high growth conditions with high supersaturation ratio are maintained to enhance crystal growth rate, then the growth rate of larger crystals is improved, but the concentration of fines increases due to high nucleation rate
Solution Approach 1:
The patent applies periodic action by cycling between high supersaturation conditions (to promote crystal growth) and low supersaturation conditions (to reduce fines nucleation). The system periodically adjusts the supersaturation ratio, allowing crystals to grow during high supersaturation phases while minimizing fine particle formation during low supersaturation phases, thus resolving the contradiction between growth rate and fines concentration.
Solution Approach 2:
The patent implements dynamics by making the supersaturation ratio variable rather than static. The system dynamically adjusts operating parameters (such as pH, temperature, or component concentrations) to modulate the supersaturation level over time, enabling transition between growth-promoting and fines-reducing conditions, thereby achieving both high crystal growth rates and low fines concentration.
2Quantity of substance
If low supersaturation ratio is maintained to reduce nucleation of fines, then the concentration of fines is reduced, but the growth rate of larger crystals decreases
Solution Approach 1:
The system uses periodic action to alternate between low supersaturation conditions (which reduce fines nucleation) and high supersaturation conditions (which enhance crystal growth). During low supersaturation phases, fine particle formation is minimized, and during subsequent high supersaturation phases, crystal growth is accelerated, achieving both objectives over the complete cycle.
Solution Approach 2:
The patent applies dynamics by dynamically adjusting the supersaturation ratio to match process needs. Rather than maintaining a constantly low supersaturation, the system dynamically increases supersaturation at appropriate times to boost crystal growth after fines have been suppressed, thereby achieving both low fines concentration and high growth rates through time-dependent control.
3Quantity of substance
If pH is altered to increase solubility of fines for destruction, then the concentration of fines is reduced, but the reaction conditions must be frequently adjusted which increases operational complexity
Solution Approach 1:
The patent implements feedback control by monitoring the concentration of fines and automatically adjusting pH or other reaction conditions in response. When fines concentration exceeds a threshold, the system adjusts pH to increase solubility and destroy fines, then returns to normal conditions when fines are reduced, thereby automating the complex operational adjustments and reducing manual intervention requirements.
Solution Approach 2:
The system applies self-service by using the properties of the crystallization process itself to control fines. By leveraging pH-dependent solubility changes and the natural response of the system to supersaturation adjustments, the process self-regulates fines concentration through inherent chemical equilibria, reducing the need for complex external control mechanisms.
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 effectively reduces the concentration of fines, enhancing the growth rate of larger crystals and improving the efficiency of crystal recovery by maintaining a balance between the rates of crystal formation and dissolution.
Implementation Method 1
altering a pH of a solution or liquor from which the crystals are being grown. The pH may be altered in a direction such that the fines are rendered more soluble and therefore dissolve
Implementation Method 2
the fines, which have large ratios of surface area to volume as compared to larger particles may dissolve at a high rate
Implementation Method 3
the high growth conditions may correspond to supersaturated conditions for a substance being produced. In some embodiments a supersaturation ratio (ratio of the product of concentrations of constituents of the substance to the product of concentrations corresponding to equilibrium) is above a threshold to achieve a high growth rate of crystals
Implementation Method 4
causing the dissolved materials in the solution to precipitate into crystals under first reaction conditions
Data Source
AI summary
Methods and apparatus for precipitating dissolved materials from a solution involve reduction of fines. In an embodiment, the method comprises: introducing a solution into a reactor, causing the dissolved materials in the solution to precipitate into crystals under a first reaction condition, adjusting the reaction condition from the first reaction condition to a second reaction condition, maintaining the reaction condition in the second reaction condition to cause a sub-population of the crystals to dissolve, and adjusting the reaction condition from the second reaction condition to the first reaction condition. In an embodiment, the apparatus comprises a reaction tank, a recycling path and at least an acid injector which is configured for dosing an acid into solution flow in the recycling path.