Optimal process design for direct olivine carbonation

  • Optimaler Prozessentwurf zur direkten Karbonisierung von Olivin

Bremen, Andreas Michael; Mitsos, Alexander (Thesis advisor); Bardow, André (Thesis advisor)

Aachen : RWTH Aachen University (2022, 2023)
Book, Dissertation / PhD Thesis

In: Aachener Verfahrenstechnik Series AVT.SVT - Process Systems Engineering 28 (2022)
Page(s)/Article-Nr.: 1 Online-Ressource : Illustrationen, Diagramme

Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2022


Employing mineral carbonation products as a cementitious substitute could reduce the cement industry's greenhouse gas emissions. Yet, a transition towards low-emission cement requires financially competitive cement production at standardized product specifications. This is the first work that addresses this challenge by modeling and optimizing a direct mineral carbonation process, subject to product specifications for the blended cement product based on the European cement standard. The novelty of this work lies in the bottom-up mineral carbonation modeling approach ranging from the reaction system to the scenario level for calculating of objectives in the optimization formulation. The first step towards the process model is the development of a mechanistic tubular reactor model that comprises three tasks: (1) Modeling dynamic aqueous electrolyte systems under consideration of chemical equilibrium, (2) developing a dynamic model of the mineral carbonation reaction system that accounts for the significant mechanistic effects, and (3) the reformulation of the dynamic model of the reaction system to a stationary tubular reactor model under consideration of flow properties. For the modeling of transient aqueous electrolyte systems, we follow the equation-oriented approach of writing balance equations in reaction invariants and replacing the embedded Gibbs free energy minimization problem with a reformulation of the Karush-Kuhn-Tucker conditions to yield a system of differential-algebraic equations. We provide the open-source Modelica package ElectrolyteMedia for the modeling of transient aqueous electrolyte systems under consideration of chemical equilibrium in combination with detailed thermodynamic model equations for gas, liquid, and solid phases. The mechanistic model of the reaction system considers both (fast) equilibrium reactions and kinetically-limited reactions. Hence, we use the equation-oriented approach to describe the chemical equilibrium of the gas and liquid phase and formulate surface-controlled reactions between solid and liquid phases based on nonideal thermodynamics. We account for the particle size distribution of raw material and product phases by writing population balances considering nucleation and growth of particles. We then transform the dynamic reaction system to a stationary tubular reactor model to account for the effects along the axial direction of the reactor, e.g., the reaction progress. Subsequently, we develop an industrial-scale process model comprising pretreatment, reaction, and separation steps. We incorporate the tubular reactor model into the reaction step and design the pretreatment to meet the required reactor feed specifications. The design of the separation step accounts for product specifications in a business case of a CEM II blended cement consisting of ordinary Portland cement and the carbonation product. We employ mathematical optimization to further refine the proposed process design in the next step. We compute the blended cement's production cost and carbon footprint by using Bayesian optimization. We find Pareto optimal operating conditions of the mineral carbonation process for today's and future scenarios. Our results show that the cost of mineral carbonation in the cement industry can be competitive in the future while cutting greenhouse gas emissions up to 54%.


  • Chair of Process Systems Engineering [416710]