J. Koralewska

Kinetics of Reaction-Crystallization of Struvite in the Continuous Draft Tube Magma Type Crystallizers—Influence of Different Internal Hydrodynamics

Abstract A laboratory-scale reaction-crystallization process of struvite synthesis from diluted water solution of Mg 2+ , NH 4 + and PO 4 3− ions was studied. The research covered the tests of two original constructions of continuous jet-pump Draft Tube Magma (DTM)-type crystallizers with internal circulation of suspension (upward/downward). Interactions between constructional, hydrodynamic and kinetic factors were established and discussed. Nucleation and linear growth rates of struvite crystals were calculated on the basis of population density distribution. Kinetic model of idealized Mixed Suspension Mixed Product Removal (MSMPR) crystallizer considering the size-dependent growth mechanism was applied (Rojkowski hyperbolic equation). For comparison purposes the kinetic data corresponded to a simpler, continuous draft tube-type crystallizer equipped with propeller agitator were analyzed. It was concluded that crystal product of larger size was withdrawn from the jet-pump DTM crystallizer of the descending flow of suspension in a mixing chamber.

THE INFLUENCE OF PROCESS PARAMETERS ON STRUVITE CONTINUOUS CRYSTALLIZATION KINETICS

ABSTRACT Experimental data concerning the kinetics of mass crystallization of struvite during the process of magnesium ion removal from water with the use of ammonium dihydrogenphosphate, NH4H2PO4, addition under alkaline conditions are presented. The tests were carried out in a continuous laboratory DTM MSMPR crystallizer with internal circulation of suspension (T = 298 K). The influence of concentration of Mg2 + ions in the raw material, pH of the process environment, and residence time of suspension on the nucleation and growth rates of struvite crystals was established. Kinetic parameters were evaluated from the crystal size distributions using selected size-dependent growth (SDG) models.

Size-dependent growth kinetics of vitamin C crystals in water solutions of L(+)-ascorbic acid with the addition of methanol and ethanol

Size-dependent growth kinetics of vitamin C crystals in water solutions of L(+)-ascorbic acid with the addition of methanol and ethanol Growth kinetics of vitamin C crystals during the batch mass crystallization process in L(+)-ascorbic acid - methanol - ethanol - water system was determined. The linear growth rate values were estimated on the basis of the product crystal size distributions. The kinetic model of the continuous process in a MSMPR crystallizer was adopted for the batch mode description according to Nyvlts conception, taking the sizedependent growth (SDG) rate effects into consideration. The kinetic parameter values were determined with a Rojkowski hyperbolic SDG model. A good compatibility between the experimental product crystal population density distributions and the SDG model predictions was observed. The interpretation of the kinetic data was presented and discussed.

Multilayer perceptron as the tool for modeling of reaction crystallization of barium sulphate in MSMPR crystallizer

One of the most ecologically harmful industrial wastes are the post-processed, used quenching salts, especially rich in BaCl2. Original method of their neutralization is based on their dissolution in water followed by a complex reaction crystallization process (after solid (NH4)2SO4 addition) effecting in production of barium sulphate. The process regime, which determines the crystalline product quality, depends on many technological parameters which individually influence various partial processes in micro- and macroscale. Facing this intrinsic complexity of the process its reliable analytical model has not been elaborated up till now. Application of artificial neural networks (e.g. multilayer perceptrons) for thorough description of such complex systems is substantiated since these need only the scattered information incorporated within the raw experimental data. An alternative model of the system behavior - numerical but free of any simplifying assumptions - is thus possible. Neural network simulation effects concerning reaction crystallization of barium sulphate in a DT MSMPR crystallizer are presented and discussed.

Kinetics of the continuous reaction crystallization of barium sulphate in BaCl2 - (NH4)2 SO4 - NaCl - H2O system - neural network model

Kinetics of the continuous reaction crystallization of barium sulphate in BaCl2 - (NH4)2 SO4 - NaCl - H2O system - neural network model One of the main toxic components of post quenching salts formed in large quantities during steel hardening processes is BaCl2. This dangerous ingredient can be chemically neutralized after dissolution in water by means of reaction crystallization with solid ammonium sulphate (NH4)2 SO4. The resulting size distribution of the ecologically harmless crystalline product - BaSO4 - is an important criteria deciding about its further applicability. Presence of a second component of binary quenching salt mixture (BaCl2-NaCl) in water solution, NaCl, influences the reaction-crystallization process kinetics affecting the resulting product properties. The experimental 39 input-output data vectors containing the information about the continuous reaction crystallization in BaCl2 - (NH4)2 SO4 - NaCl - H2 O system ([BaCl2]RM = 10-24 mass %, [NaCl]RM = 0-12 mass %, T = 305-348 K and τ = 900-9000 s) created the database for the neural network training and validation. The applicability of diversified network configurations, neuron types and training strategies were verified. An optimal network structure was used for the process modeling.