Continuous Mixed Suspension Mixed Product Removal Crystallizer Research Articles

Optimal start-up strategies of a combined cooling and antisolvent multistage continuous crystallization process

A model-based optimization methodology was developed to systematically address all possible optimal start-up scenarios of a multistage combined cooling and antisolvent continuous MSMPR (mixed-suspension, mixed-product removal) crystallizer. The crystallization of aspirin (acetylsalicylic acid, ASA) in ethanol (solvent) and water (antisolvent) was used as a case study. A steady state optimization was firstly conducted to optimize the crystallizer design and operating conditions and set-up the reference trajectories. The discretised profiles of the jacket temperatures, antisolvent flowrates and seeding policies, which includes the seed flowrates, loading and mean size, were used as decision vectors for the dynamic optimization problem. Scenarios with single and combined decision vectors were addressed and analysed in start-up situations involving prefilled or empty vessels. The impact of simplified optimization and operating procedures or refined discretization schemes were also addressed. It was shown that several options may provide comparable performance and the start-up time can be improved by nearly 80% in the case of combined decision vectors involving all possible decision vectors.

Struvite nucleation and crystal growth kinetics from cattle liquid manure

Cattle liquid manure (CLM) in future may become excellent raw material for the solid mineral fertilizers production. Phosphates(V) recovery from CLM can be done, e.g. through reaction crystallization of sparingly soluble salts: magnesium and ammonium phosphate(V) hexahydrate MgNH4PO4·6H2O (MAP, struvite) or/and calcium phosphates(V). The original kinetic calculations based on experimental test results concerning continuous reaction crystallization of sparingly soluble phosphates(V) from cattle liquid manure in a continuous laboratory DT MSMPR (Draft Tube, Mixed Suspension Mixed Product Removal) crystallizer with internal circulation of suspension driven by propeller stirrer are presented. Two kinetic models of continuous mass crystallization in MSMPR crystallizer: SIG (Size Independent Growth) and RE SDG (Rojkowski Exponential Size Dependent Growth) were adopted. Advantageous effects of: low pH (8.5), elongated mean residence time of suspension in a crystallizer (3600 s) and magnesium ions excess in relation to phosphate(V) ions concentration (1.2:1) on the process results were observed. Under the considered process conditions linear crystal growth rates of struvite were: G from 4.11 × 10−3 to 1.01 × 10−2 µm s−1 and G∞ from 5.30 × 10−3 to 1.02 × 10−2 µm s−1.

Design and optimization of production parameters for boric acid crystals with the crystallization process in an MSMPR crystallizer using FBRM® and PVM® technologies

In crystallization studies, newly developed technologies, such as Focused Beam Reflectance Measurement (FBRM) and Particle Vision and Measurement (PVM) are applied for determining on-line monitoring of a representation of the Chord Length Distribution (CLD) and observe the photographs of crystals respectively; moreover recently they are widely used. Properly installed, the FBRM ensures on-line determination of the CLD, which is statistically associated to the Crystal Size Distribution (CSD). In industrial crystallization, CSD and mean crystal size as well as external habit and internal structure are important characteristics for further use of the crystals. In this paper, the effect of residence time, stirring speed, feeding rate, supersaturation level and the polyelectrolytes such as anionic polyacrylamide (APAM) and non-ionic polyacrylamide (NPAM) on the CLD as well as the shape of boric acid crystals were investigated by using the FBRM G600 and the PVM V819 probes respectively in an MSMPR (Mixed Suspension Mixed Product Removal) crystallizer. The CSD and kinetic data were determined experimentally using continuous MSMPR crystallizer running at steady state. The population density of nuclei, the nucleation rate and the growth rate were determined from the experimental population balance distribution when the steady state was reached.

Obtaining Monodisperse Melamine Phosphate Grains by a Continuous Reaction Crystallization Process

A continuous MSMPR (mixed-suspension mixed-product removal) crystallizer was used in the process of obtaining melamine phosphate in a precipitation reaction. The effects of the mean residence time of the suspension in the crystallizer and of the concentration of the melamine suspension in water on the efficiency of the process and the quality of the product obtained were studied. Kinetic parameters of the reaction crystallization process under study were estimated. The grain size distribution of the crystals and the specific surface area of the grains were determined. Morphology was defined by means of a shape factor and coefficients of inhomogeneity and variation. Well-formed, homogeneous crystals of similar specific surface areas and practically identical small pore volumes were obtained. This work shows that, within the studied range of solid-phase concentrations and mean residence times, it is possible to obtain a product of monodisperse grains and predicted grain size by controlling the concentration...

Phosphates (V) recovery from phosphorus mineral fertilizers industry wastewater by continuous struvite reaction crystallization process

Continuous DT MSMPR (Draft Tube Mixed Suspension Mixed Product Removal) crystallizer was provided with typical wastewater from phosphorus mineral fertilizers industry (pH < 4, 0.445 mass % of PO43−, inorganic impurities presence), dissolved substrates (magnesium and ammonium chlorides) and solution alkalising the environment of struvite MgNH4PO4·6H2O reaction crystallization process. Research ran in constant temperature 298 K assuming stoichiometric proportions of substrates or 20% excess of magnesium ions. Influence of pH (8.5–10) and mean residence time (900–3600 s) on product size distribution, its chemical composition, crystals shape, size–homogeneity and process kinetics was identified. Crystals of mean size ca. 25–37 μm and homogeneity CV 70–83% were produced. The largest crystals, of acceptable homogeneity, were produced using 20% excess of magnesium ions, pH 9 and mean residence time 3600 s. Under these conditions nucleation rate did not exceed 9 × 107 1/(s m3) according to SIG (Size Independent Growth) MSMPR kinetic model. Linear crystal growth rate was 4.27 × 10−9 m/s. Excess of magnesium ions influenced struvite reaction crystallization process yield advantageously. Concentration of phosphate(V) ions decreased from 0.445 to 9.2 × 10−4 mass %. This can be regarded as a very good process result. In product crystals, besides main component – struvite, all impurities from wastewater were detected analytically.

Evolution of crystal size distributions in a CMSMPR—the effect of temperature, flow rate, and mixing speed with time

A continuous mixed-suspension, mixed-product removal (CMSMPR) crystallizer with automatic computer control and data acquisition was constructed. Operating this CMSMPR at rpm’s greater than 100 rpm assures well-mixed conditions. The crystallization of NaCl, an impurity in a concentrated CaCl2 solution, was performed by cooling under well-mixed conditions. Atomic absorption spectrometry (AAS) and inductively coupled plasma-atomic emission spectrometry (ICP-AES) have been used to measure solution concentrations. Scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), light microscopy and particle size analyzer with advanced laser light scattering have been used to characterize the crystals produced by the CMSMPR crystallizer. Octahedral NaCl crystals are observed. Steady state crystal size distribution (CSD) is observed at nine to ten times the mean residence time for the crystallizer. The CSD has been analyzed to look at the details of nucleation, growth, and aggregation rate as a function of crystallization temperature, rpm, and feed flow rate with the application of a Hounslow’s constant aggregation rate equation.

Distribution of dye into KDP crystals in a continuous MSMPR crystallizer

Colored potassium dihydrogen phosphate (KDP) crystals from a dye (sky blue) solution were produced in a mixed suspension mixed product removal (MSMPR) crystallizer. The crystal size distribution (CSD) of the KDP crystals was correlated by a size-dependent growth rate model. The growth rate increased with crystal size, but it decreased as the residence time increased. Two different concentrations of dye in the solution were examined for MSMPR crystallization of KDP crystals. The colored crystals from the solution with low dye-concentration generated regular-shaped KDP crystals. The dye distribution coefficient into the regular-shaped KDP crystals was less than unity. However, the colored crystals from the solution with high dye-concentration formed the special-shaped KDP crystals having no (1 0 0) sector. The dye distribution coefficient into the special-shaped KDP crystals from the dye solution was larger than unity. The dye distribution coefficient as a function of crystal size was presented, and then the relationship between the aspect ratio of the morphology of KDP crystals and dye distribution coefficient was discussed. As a result, a distribution model of dye impurity in KDP crystals for an MSMPR crystallizer could be first proposed in this work.

Inclusion of mother liquor inside KDP crystals in a continuous MSMPR crystallizer

The crystal size distribution (CSD) of potassium dihydrogen phosphate (KDP) and inclusion ratio of mother liquor have been measured in a mixed suspension mixed product removal (MSMPR) crystallizer. A small amount of sodium dihydrogen phosphate (SDP) was added as an impurity tracer in order to measure the inclusion ratio of mother liquor inside the KDP crystals. The effects of residence time on the CSD and inclusion of mother liquor were investigated. The crystal growth rate and nucleation rate were determined from the population density balance theory by assuming a size-dependent function of the growth rate, because the size-dependent growth rate of KDP crystals was observed under a microscope. MSMPR operation with a shorter residence time produced larger KDP crystals, and showed more size-dependency of the growth rate. The inclusion ratio was depicted as a function of crystal size, growth rate, and agglomeration. The degree of agglomeration was effectively correlated with the inclusion ratio of the KDP crystals that had a large hardness property.

Neuro‐Fuzzy Control of a Continuous Cooled MSMPR Crystallizer

AbstractThis work deals with the design and application of a neuro‐fuzzy controller of the magma density of the fine crystals for the stabilisation of the crystal size distribution (CSD) of the product from an MSMPR (Mixed Suspension, Mixed Product Removal) continuous crystallizer. The cooling crystallization of potassium sulphate from aqueous solutions in a pilot‐scale stirred vessel was investigated. A control strategy, based on the elimination of fines by using a combined sedimentation‐dissolution device, is presented. The control scheme was successfully applied to a pilot‐scale draft‐tube (DT) crystallizer and yielded promising results. The proposed process control system allowed the reduction of the fines fraction by more than 30 %, while maintaining operation stability and short transient responses.

Design of seed crystal specifications for start-up operation of a continuous MSMPR crystallizer

In the industrial crystallization, seeding technology is often used for start-up operation. The applications vary from batch to continuous crystallization. It is known that the required time for the start-up operation changes by seed crystal specifications experientially. In this study, designing seed crystal specifications for a continuous mixed-suspension mixed-product removal (MSMPR) crystallizer was investigated to shorten the required time for start-up operations. The changes of crystal size distribution (CSD) during start-up operation were simulated by using conventional MSMPR crystallizer model.It was shown that the addition of seed crystals in start-up operations had a remarkable influence on the changes in CSD. As a result of experiments and simulation with various specifications of seed crystals, a strategy to design adequate seed crystals was proposed.

Mixing, reaction and precipitation: an interplay in continuous crystallizers

The two-environment micromixing model of Ng and Rippin (1965, Third Europ. Symp. Chem. React. Engng, pp. 161–165. Pergamon Press, Oxford) and the IEM (Interaction by Exchange with the Mean) model are extended to a process involving the elementary chemical reaction between two reactant species and subsequent crystallization of product in a continuous crystallizer with premixed feeds at the entry. The sensitivity of these models to Damko¨hler number and dimensionless micromixing parameter is explored. The computationally efficient two-environment model appears to characterize satisfactorily the micromixing effects in a continuous reactive precipitator while the IEM model description in a continuous MSMPR (mixed suspension mixed product removal) crystallizer is better suited to a nearly segregated system.

Temperature effects on the crystallization kinetics of size-dependent systems in a continuous mixed-suspension mixed-product removal crystallizer

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTTemperature effects on the crystallization kinetics of size-dependent systems in a continuous mixed-suspension mixed-product removal crystallizerJenn Fang Wu, Clifford Y. Tai, Wei Koun Yang, and Lii Ping LeuCite this: Ind. Eng. Chem. Res. 1991, 30, 9, 2226–2233Publication Date (Print):September 1, 1991Publication History Published online1 May 2002Published inissue 1 September 1991https://doi.org/10.1021/ie00057a027RIGHTS & PERMISSIONSArticle Views705Altmetric-Citations12LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (899 KB) Get e-Alerts Get e-Alerts

Determination of crystallization kinetics from batch experiments

Three types of batch crystallization model experiments are considered: a) crystallization in which a constant supersaturation is maintained throughout the experiment (e.g. by programmed cooling); b) crystallization during which supersaturation is produced at a constant rate; c) crystallization (e.g. by precipitation) in which an initial supersaturation produced at the beginning gradually decreases during the run. The kinetic data obtained in the first case are of the same kind as those obtained in a continuous MSMPR (mixed suspension - mixed product removal) crystallizer. The two remaining types of experiment, on the other hand, can only provide relative kinetic data with respect to a reference run.