Modelling dust explosions in the process industries

The overall goal of the PhD project is to implement and validate fundamental improvements to the models for particle-laden flows and combustion in the computational fluid dynamics (CFD) tool FLACS-DustEx. The main focus for the work in 2019 has been on reviewing the available combustion models that account for the effect of particles, as well as working with the integration of the Algebraic Slip Mixture Model (ASMM) into the FLACS-DustEx code. In the course of the review of combustion models, it was also considered how these could be integrated with FLACS-DustEx. From this work, a review paper was published in a special issue of Journal of Loss Prevention in the Process Industries: "A brief review on the effect of particle size on the laminar burning velocity of flammable dust: Application in a CFD tool for industrial applications". The merging of ASMM into FLACS DustEx took significantly more time and effort than anticipated, therefore, the originally planned submission of a paper on this topic in 2019 has been delayed to 2020. Two posters were presented at conferences in 2019. The first poster was presented at ISFEH2019, 21-26th of April 2019 in Saint-Petersburg, Russia, with the title of "Effect of particle size on burning velocity calculation in FLACS-DustEx". For this poster, a new approach to combustion modelling in dust explosions was presented, and FLACS-DustEx was used for simulation of a medium scale experiment with a new dispersion system performed in Gexcon. The second poster was presented in ICDERS2019, 28 July-2 August 2019, in Beijing, China, with the title of "A review of the effect of particle size and particle concentration on burning velocity calculation in FLACS-DustEx: a simplified approach". The candidate participated into two workshops in 2019. The first was a SINTEF winter school with the subject "learning from data" at Geilo, 20-25 January 2019. The second workshop was a course on turbulent combustion from the Von Karman institute for Fluid Dynamics, 20-24 May 2019 in Sint-Genesius-Rode (near Brussels), Belgium. The candidate started running experiments using size classified particles of maize starch in a 20-liter explosion vessel in the dust laboratory at Gexcon AS. For classification of different particle sizes, the candidate used several sieves that are available at Gexcon. The candidate is in process of analyzing and writing the results of this experiment in an upcoming paper. The paper will be on combustion modelling improvements in FLACS-DustEx, and the plan is to submit this paper to a relevant journal by the end of March 2020. A paper using the modified flow solver together with FLACS-DustEx, an Algebraic Slip Mixture Model (ASMM), will be submitted to a relevant journal by the end of September 2020. ASMM provides mechanical suspensions of fine particles dispersed in air. The drag force and convective acceleration in ASMM are derived for the dynamics of single particles. The performance of the model will be tested by comparing simulation results with datasets from large scale experiments performed in a 236 m3 silo. Since June 2019, the candidate trained and cooperated with a colleague on the validation of FLACS-DustEx. The candidate has also cooperated with other colleagues on preparing FLACS-DustEx and the ASMM code for integration. The focus for 2020 will be on finalizing the implementation of the multiphase flow solver and the corresponding multiphase combustion model in FLACS-DustEx, submitting two scientific papers to relevant journals, as well as finalizing and submitting the PhD thesis.

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Accidental dust explosions cause severe damage to property and loss of life in industry. Dust explosions are inherently complex phenomena, and several parameters influence the ignition sensitivity and explosion violence of dust clouds. Significant efforts have been invested in experimental investigations aimed at developing empirical correlations that can be used to estimate the consequences of dust explosions. To this end, the use of computational fluid dynamics (CFD) represents an interesting alternative. The numerical solver in FLACS is a three-dimensional (3D) CFD code that solves Favre-averaged transport equations. The modelling of particle-laden flow and heterogeneous combustion in the current version of FLACS-DustEx involves several simplifying assumptions. In spite of the simplicity of the model system, the results from previous validation work show that FLACS-DustEx can describe the course of dust explosions in relatively complex geometries with reasonable accuracy relative to the inherent spread in the experimental results. Although the results from the validation work indicate that CFD simulations can become a valuable tool for consequence modelling and design of industrial facilities, the modelling in FLACS-DustEx requires further improvements. As part of this PhD project, the candidate will populate a validation framework with relevant and prioritized dust explosion cases (experiments, accidents, etc.). Access to experimental data and research installations in the field of dust explosions has been established. The possibility of generating empirical input to the model system from laboratory-scale experiments will be critically evaluated. It may be possible to improve the currently used test apparatus and/or test procedures. The foreseen results from the project include fundamental improvements to the modelling of particle-laden flows and flame propagation in dust clouds in the CFD tool FLACS-DustEx.