CFD Modelling of the Impact of Flow Conditions on Scale Formation Processes

Jakob Roar Bentzon

Research output: Book/ReportPh.D. thesis

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Abstract

Scale formation from mineral crystallization presents a widespread industrial challenge and becomes increasingly costly within modern societies. It is a common cause of process equipment fouling leading to deleterious impacts and suboptimal operation, resulting in equipment failure, higher energy consumption, and reduced output. Scale prevention and removal processes involve extensive use of reaction inhibitors, solvents, and acids that present a potential threat to aquatic life and ecosystems. Consequently, accurate modelling and prediction of scale formation play a crucial role in efficiently managing the use of such chemicals while minimizing their unfavourable side effects.

While scale formation most commonly causes deleterious effects in the industry, some studies and industries induce scale formation intentionally. A relevant and recent example is the use of carbonate scale as a permanent and stable solution for carbon storage. In such applications, process control and optimization rely on a thorough understanding of the wide range of mechanisms governing crystallization.

Universal to scale formation is the significance of the ionic transport within the fluid from which the scale is crystallized. The present PhD thesis covers work carried out over the last four years to improve the scientific modelling techniques applied in numeric modelling of flow and scale formation. This thesis presents work on computational fluid dynamics (CFD) modelling of the impact of flow conditions on scale formation processes.

The scope of the project is rooted in a specific challenge, namely the formation of barium sulphate scale in the hydrocarbon producing pipelines in the Danish part of the North Sea. Barium sulphate formation incurs significant costs to the industry. The modelling of barium sulphate crystallization processes under flow conditions similar to those faced in hydrocarbon wells require a multidisciplinary understanding of crystallization.

Barium sulphate formation occurs from the crystallization of barium and sulphate ions within the water. The governing physics of the process is commonly modelled using a thermodynamic equilibrium reaction governed by a transition state from dissolved ions to nuclei and by subsequent growth of those nuclei. This can occur in the fluid bulk as suspended particles or at the interface between the fluid and solids as scale. The rates at which these forming processes occur are controlled by a combination of stochastic processes at molecular scale and largerscale variations. The molecular scale is studied in the field of physical chemistry, whereas the larger spatio-temporal variations are the subject of three-dimensional modelling methods such as CFD. Within the present PhD thesis, different aspects of the impact of fluid dynamics on barium sulphate formation are examined, and the results have been compiled into research papers.

The first paper published focuses explicitly on the modelling of the turbulent and dispersed two-phase oil-water flow common to the aforementioned pipelines. An implementation of a statistical and adaptive droplet-size distribution model into an Eulerian two-fluid model is presented. The model is used to replicate experimental studies of oil-water dispersion quantified through phase distribution and droplet sizes. While the dropletsize distribution results show a notable uncertainty, the ability to dynamically predict droplet sizes significantly aids the ability to determine phase distribution without manual input of droplet sizes. Such modelling helps predict water-wetting, which significantly affects scale formation.

Due to the low solubility of barium sulphate, effective reaction rates are often limited by mixing and transport. Within turbulent flow, mixing is strongly aided by the folding and stretching of fluid structures. At the time of the PhD study, the availability of experimental data to support numerical analysis of these effects was limited. Consequently, the research group decided to build two different flow-reactive experimental setups; a Taylor-Couette reactor and a pipe-flow-through reactor.

Based on experiments using the TaylorCouette reactor, a research paper has been published on the analysis of turbulent mixing and the impact on barium sulphate reactivity. A validated procedure for such analysis has been presented along with a novel suggestion for a turbulent Peclét number that supports numerical studies of turbulent mixing. The outcome of the paper has given the research group insights into the significance of the hydrodynamics in the reactor for its net reactivity. This research is continued in a subsequent study on inhomogeneous reactivity, which is attached to the thesis as a draft manuscript.

Finally, a phenomenological study of surface barite formation under different surface and flow conditions has been carried out on the pipe-flow reactor. The produced paper discusses transport regimes and how they impact the processes of surface growth. The outcome of the study highlights further areas of research which have been initiated at the time of writing. In summary, a range of techniques and methods modelling the impact of flow conditions on scale formation have been studied. The process has led to improvements in the current fundamental understanding of scale formation in complex flow conditions. Moreover, a fundamental basis for future research has been laid from the output research papers and data.
Original languageEnglish
Place of PublicationKgs. Lyngby
PublisherTechnical University of Denmark
Number of pages91
Publication statusPublished - 2023

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