Computational fluid dynamics‐based design of finned steam cracking reactors

Abstract

The use of one-dimensional reactor models to simulate industrial steam cracking reactors has been one of the main limiting factors for the development of new reactor designs and the evaluation of existing three-dimensional (3-D) reactor configurations. Therefore, a 3-D computational fluid dynamics approach is proposed in which the detailed free-radical chemistry is for the first time accounted for. As a demonstration case, the application of longitudinally and helicoidally finned tubes as steam cracking reactors was investigated under industrially relevant conditions. After experimental validation of the modeling approach, a comprehensive parametric study allowed to identify optimal values of the fin parameters, that is, fin height, number of fins, and helix angle to maximize heat transfer. Reactive simulations of an industrial Millisecond propane cracker were performed for four distinct finned reactors using a reaction network of 26 species and 203 elementary reactions. The start-of-run tube metal skin temperatures could be reduced by up to 50 K compared to conventionally applied tubular reactors when applying optimal fin parameters. Implementation of a validated coking model for light feedstocks shows that coking rates are reduced up to 50%. However, the increased friction and inner surface area lead to pressure drops higher by a factor from 1.22 to 1.66 causing minor but significant shifts in light olefin selectivity. For the optimized helicoidally finned reactor the ethene selectivity dropped, whereas propene and 1,3-butadiene selectivity increased with a similar amount. The presented methodology can be applied in a straightforward way to other 3-D reactor designs and can be extended to more complex feedstocks such as naphtha.

Periodic reactive flow simulation: Proof of concept for steam cracking coils

“…The use of these enhanced tubular reactors has recently received increased attention in the field of steam cracking as a way of limiting the unwanted side reactions that lead to coke deposition on the reactor surface. Application of alternative, 3D reactor designs allowing operation at reduced inner wall temperatures is believed to result in increased run lengths and hence significant economic gains …”

“…The simulated reactor was previously described by Schietekat et al and is in principle a simple straight tube, that is, the feedstock enters at the bottom of the furnace, close to the gas‐fired floor burners, and exits at the top of the radiant section without turns or bends. This industrially applied reactor type is known to achieve a high selectivity toward light olefins due to the short residence times in the order of milliseconds.…”

“…is performed under the assumption of negligible Soret diffusion, radiation heat transfer and buoyancy forces. It has previously been shown that these assumptions are valid in the present application domain of steam cracking …”

Multi‐scale systems engineering for energy and the environment: Challenges and opportunities

“…125 On a larger scale, researchers have simulated systems with mass, energy, and momentum transport while also developing elementary reaction kinetics. Schietekat et al 126 developed a 3-D CFD model to investigate a steam cracking reactor that provided accurate yields of cracking products. Sundaram and Froment 127,128 presented one of the earliest examples of a parameter estimation model on paraffin cracking.…”

Impact of Radiation Models in Coupled Simulations of Steam Cracking Furnaces and Reactors

“…As the reaction families dictating the chemistry in steam cracking reactors have been well-known for many years, fundamental process simulation tools for the simulation of steam cracking reactors have been used extensively since the pioneering work of Dente et al31 in the late seventies. Although several authors have used the twodimensional 32, 33 and three-dimensional15,24,[34][35][36][37] reactor models for the simulation of steam…”