arts, T

Dedeyne, Jens

Marin, Guy

Van Geem, Kevin

Virgilio, Marco

English

Ghent University Academic Bibliography

Process Intensification through Large Eddy Simulations of Tubular Reactors  Jens N. Dedeyne1, M. Virgillio2, T. Arts2, K. M. Van Geem1, G. B. Marin1 1Laboratory for Chemical Technology, Ghent University, JensN.Dedeyne@UGent.be 2von Karman Institute for Fluid Dynamics  Light olefins are predominantly produced by steam cracking of hydrocarbons in long tubular reactors, suspended in gas fired furnaces. A limiting factor in the process is the deposition of cokes on the inner reactor tube surface, as this increases thermal resistance and pressure drop, which ultimately leads to production loss because the furnace has to be taken off-line for decoking.  Intensification of this process can be achieved by the introduction of 3D turbulators on the inside of the reactor, which is already applied industrially, e.g. MERT by Kubota[2], IHT by Lummus and Sinopec[3]. These turbulators aim at improving the radial mixing of the fluid and hence enhance the heat transfer, which implies a lower tube metal temperature (TMT) and consequently lowers the coking rate. The enhanced radial mixing also implies less radial gradients, resulting in a more uniform temperature and species distribution of the process gas as can be seen in Figure 1 (left).  On the downside, introduction of 3D elements is accompanied by an increased pressure drop over the reactor, leading to a loss of selectivity towards the desired products. Hence, implementation of these turbulators can be seen as a delicate interplay between an increased heat transfer and additional pressure losses. Hence, the design of these turbulators is not a straightforward task. To gain deeper understanding on the influence of these 3D turbulators on the flow field, Computational Fluid Dynamics (CFD) is applied. Until today, completely solving the Navier-Stokes equationswith Direct Numerical Simulation (DNS) implies resolving turbulence on every time- and length scale, and is not feasible for industrially relevant conditions (Re > 50 000). To reduce the computational cost, Large Eddy Simulation (LES) offers a valuable alternative: the range of time- and length scales that are to be resolved Figure 1: Improved temperature distribution in MERT[1] (left)  velocity flow field in MERT obtained with Large Eddy Simulations (right) is decreased by modelling the turbulence at the smallest scales and only resolving the larger eddies. This approximation is much more accurate than RANS, which models all the turbulent scales, making LES a better tool for the design and optimization of reactor geometries.[4]  Even although LES has proven to be extremely valuable, it still requires modelling and the simulation accuracy is closely linked to the accuracy of the employed models. To assess the validity of these models, highly detailed experimental data was obtained thanks to a cooperation between the Laboratory for Chemical Technology (LCT) and the Von Karman Institute (VKI). Particle image velocimetry (PIV) and liquid crystal thermography (LCT) experiments were employed to determine velocity and temperature fields for industrially applied helically finned tubular reactors.   Thanks to this effort, a validated turbulence model is proposed and used to investigate the flow field in a range of tubular reactor geometries. Special attention was given to local flow patterns, local heat transfer and overall pressure drop as these parameters have a major influence on global and local coking rate and product selectivity.  References [1] K. M. C. Corporation. (30/11/2015). MERT - Technology to improve Cracking Furnace Performance. Available: http://www.kubotamaterials.com/products/mert.html [2] M. Györffy, M. Hineno, K. Hashimoto, S.-H. Park, and M.-S. You, "Mert performance and technology update," in AIChE Spring Meeting: Ethylene Producers Conference, Tampa Bay, USA, 2009. [3] A. Carrillo, F. Bertola, G. Wang, and L. Zhang, "Intensified heat transfer technology–CFD analysis to explain how and why IHT increases runlength in commercial furnaces," in AIChE and EPC 2010 Spring National Meeting, San Antonio, TX, 2010. [4] D. J. Van Cauwenberge, C. M. Schietekat, J. Flore, K. M. Van Geem, and G. B. Marin, "CFD-based design of 3D pyrolysis reactors: RANS vs. LES," Chemical Engineering Journal, vol. 282, pp. 66-76, Dec 2015.   Acknowledgements JND acknowledges financial support from the Fund for Scientific Research Flanders (FWO), in association with the Pi-Flow project. The computational work was carried out using the STEVIN Supercomputer Infrastructure at Ghent University, funded by Ghent University, the Flemish Supercomputer Center (VSC), the Hercules Foundation and the Flemish Government – department EWI. 

3D reactor technology for steam cracking: simulation and experimental validation

https://biblio.ugent.be/publication/8523970/file/8525235.pdf

3D reactor technology for steam cracking: simulation and experimental validation

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