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Abstract

Thermal cracking is an industrial process sensitive to both temperature and pressure operating conditions. The use of internally ribbed reactors is a passive method to enhance the chemical selectivity of the process, thanks to a significant increase of heat transfer. However, this method also induces an increase in pressure loss, which is damageable to the chemical yield and must be quantified. Because of the complexity of turbulence and chemical kinetics, and as experimental measurements remain very expensive, the real advantage of such geometries in terms of selectivity is however poorly known and hard to assess.

This work aims at evaluating the real benefits of internally ribbed reactors in terms of chemical yields, and at proposing innovative reactor designs. This is made possible via Large Eddy Simulations (LES), which are used to study the reactive flow inside several reactor geometries. The AVBP code, which solves the Navier-Stokes compressible equations for turbulent flows, is used in order to simulate thermal cracking thanks to a specific numerical methodology. In particular, the effect of pressure loss and heat transfer on chemical conversion are compared for both a smooth and a ribbed reactor in order to conclude about the impact of wall roughness in industrial operating conditions. An optimization methodology, based on series of LES, is finally developed and an innovative reactor design for thermal cracking applications, which maximizes the chemical yield, is proposed.

Jury

Kevin VAN GEEM              Ghent University                             Referee

Laurent JOLY                       ISAE SUPAERO Toulouse           Referee

Tom ALDERWEIRELDT    TOTAL Ghent                                  Member

Angelo IOLLO                      Université de Bordeaux                 Member

Franck NICOUD                  Université de Montpellier              Member

Marouan NEMRI                 TOTAL Gonfreville                         Invited member

Bénédicte CUENOT           CERFACS Toulouse                      Advisor

Eléonore RIBER                  CERFACS Toulouse                      Co advisor