3D Steam Cracking Reactor Technology: The Good, the Bad and the Ugly

Over the last decades, the simulation of steam cracking units has received a lot of research interest at the Laboratory for Chemical Technology (LCT). This ongoing research has amongst others, resulted in the development of an extensive and accurate kinetic network for pyrolysis of hydrocarbons ranging from ethane to hydrotreated vacuum gas oil, i.e. CRACKSIM [1, 2]. This network has been implemented in a 1-dimensional reactor simulation program, i.e. COILSIM1D. This program has been validated extensively using industrial data and experimental results obtained from the LCT pilot plant set-up [3].

However, the use of a simple plug flow model shows several important shortcomings. The common assumption of radial temperature and concentration uniformity due to high Reynolds numbers has proven to be not always valid [4]. As there is a current trend towards using new reactor geometries such as Kubota’s patended ‘Mixing Element Radiant Tube’ (MERT), Technip’s Swirl Coil design and others, even two-dimensional models do not suffice to take into account the complex flow patterns prevalent inside these tubes [5]. Recent advances in commercial Computational Fluid Dynamic packages and ever increasing computational power have now made it possible to study the effects of these 3D geometries and even incorporate relatively complex kinetics in these simulations and even coking models. By simulating the influence of the reactor geometry on product yields and coking rates, existing designs can be evaluated and new reactor designs can be developed. In the present contribution we will illustrate this with a few case studies of 3D reactor geometries and distinguish between the good, the bad and the ugly.

1.         Hillewaert, L. P., J. L. Dierickx, and G. F. Froment, Computer-generation of reaction schemes and rate-equations for thermal-cracking. AIChE Journal, 1988. 34(1): p. 17-24.

2.         Van Geem, K. M., M. F. Reyniers, and G. B. Marin, Challenges of modeling steam cracking of heavy feedstocks. Oil & Gas Science and Technology-Revue De L Institut Francais Du Petrole, 2008. 63(1): p. 79-94.

3.         Van Geem, Kevin M., Steven P. Pyl, Marie-Françoise Reyniers, Joeri Vercammen, Jan Beens, and Guy B. Marin, On-line analysis of complex hydrocarbon mixtures using comprehensive two-dimensional gas chromatography. Journal of Chromatography A, 2010. 1217(43): p. 6623-6633.

4.         Van Geem, K. M., G. J. Heynderickx, and G. B. Marin, Effect of radial temperature profiles on yields in steam cracking. AIChE Journal, 2004. 50(1): p. 173-183.

5.         Györffy,  Michael,  MERT  Technology  Update:  X-MERT. AlCHE:  Ethylene  Producers Meeting 2009: Tampa Bay.