Numerical Simulation of Reactive Crystallization in Stirred Tank Reactors

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School of Chemical Engineering | Doctoral thesis (article-based) | Defence date: 2018-04-20
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Date

2018

Department

Kemian tekniikan ja metallurgian laitos
Department of Chemical and Metallurgical Engineering

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Mcode

Degree programme

Language

en

Pages

94 + app. 50

Series

Aalto University publication series DOCTORAL DISSERTATIONS, 56/2018

Abstract

Model development is essential for design and scale up of multiphase chemical reactors to provide a better understanding of physical and chemical phenomena between phases at different scales. Mathematical descriptions of the reactive crystallization include mass transfer, chemical reaction, crystallization kinetics, population balance and hydrodynamics, which consist of a set of partial differential equations with high nonlinearity. A full simulation with a commercial computational fluid dynamics (CFD) software is possible with existing computational resources but not desirable during the initial stage of reactor design. The purpose of this thesis is to explore the mechanism of multiphase reactive crystallization and develop a compartmental model to combine hydrodynamics and detailed reaction efficiently. The chemical system of CO2(G)-H2O(L)-Mg(OH)2(S) is chosen as the practical application to reveal mechanisms of multiphase reactive crystallization, which couple the reactive dissolution, chemical absorption and crystallization. As modeling of such complex system is challenging, the reactive dissolution of Mg(OH)2(S) in HCl(aq) and reactive crystallization of CaCO3(S) from CO2(G) and Ca(OH)2(aq) system are studied separately. The first part of the thesis introduces the gas-liquid and solid-liquid mass transfer models based on two-film theory and Nernst-Planck electroneutrality. In addition, enhancement factor is adopted to modify mass transfer fluxes when chemical reaction occurs in liquid film. Then, population balance model is presented along with several solution techniques to calculate particle size distributions of gas bubbles and final crystal products. The closure models include nucleation and growth of crystals, breakage, coalescence and agglomeration of gas bubbles and crystals. Finally, a compartmental model combining the flow field obtained by CFD simulation and reaction mechanisms is constructed to estimate the influence of flow field on multiphase crystallization. The compartmental modelling results show that heterogeneous mixing has a strong influence on local mass transfer rates and size distribution of final crystal products. By appropriate division of the fluid domain, compartmental model can offer a more efficient simulation for reactive crystallization without the limitation of chemical components and geometries of different reactors. This characteristic highlights the potential extensibility and portability of compartmental model in reactor design and scale up.

Description

Supervising professor

Alopaeus, Ville, Prof., Aalto University, Department of Chemical and Metallurgical Engineering, Finland

Thesis advisor

Buffo, Antonio, Prof., Politecnico di Torino, Italy

Keywords

crystallization, CFD, population balance, compartmental modeling

Other note

Parts

  • [Publication 1]: Zhao Wenli, Han Bing, Jakobsson Kaj, Louhi-Kultanen Marjatta, Alopaeus Ville. Mathematical model of crystallization of magnesium carbonate with carbon dioxide from the magnesium hydroxide slurry. Computers & Chemical Engineering, 2016, 87, 180-189.
    DOI: 10.1016/j.compchemeng.2016.01.013 View at publisher
  • [Publication 2]: Zhao Wenli, Jama Ali Mohamed, Buffo Antonio, Alopaeus Ville. Population balance model and experimental validation for reactive dissolution of particle agglomerates. Computers & Chemical Engineering, 2018, 108, 240-249.
    DOI: 10.1016/j.compchemeng.2017.09.019 View at publisher
  • [Publication 3]: Zhao Wenli, Buffo Antonio, Alopaeus Ville, Bing Han, Marjatta Louhi-Kultanen. Application of the Compartmental Model to the Gas–Liquid Crystallization of CO2-Ca(OH)2 Aqueous System in a Stirred Tank. AIChE Journal 2017, 63, 378-386.
    DOI: 10.1002/aic.15567 View at publisher
  • [Publication 4]: Guo Zhichao, Han Wenxiang, Zhao Wenli, Li Liye, Wang Baodong, Xiao Yongfeng, Alopaeus Ville. The effect of microwave on the crystallization process of magnesium carbonate from aqueous solutions. Powder Technology, 2018, 328, 358-366.
    DOI: 10.1016/j.powtec.2018.01.038 View at publisher

Citation

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https://urn.fi/URN:ISBN:978-952-60-7916-5

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[diss] Kemian tekniikan korkeakoulu / CHEM