Numerical investigation of heavy fuel droplet-particle collisions in the injection zone of a Fluid Catalytic Cracking reactor, Part I: Numerical model and 2D simulations

Abstract

This is the accepted version of the paper.This version of the publication may differ from the final published version. Permanent repository link AbstractThe present paper investigates the collisions between heavy gasoil droplets and solid catalytic particles taking place at conditions realized in Fluid Catalytic Cracking reactors (FCC). The computational model utilizes the Navier-Stokes equations along with the energy conservation and transport of species equations. The VOF methodology is used in order to track the liquid-gas interface, while a dynamic local grid refinement technique is adopted, so that high accuracy is achieved with a relative low computational cost. Phase-change phenomena (evaporation of the heavy gasoil droplet), as well as catalytic cracking surface reactions are taken into account. Physical properties of heavy and light molecular weight hydrocarbons are modeled by representative single component species, while a 2-lump scheme is proposed for the catalytic cracking reactions. The numerical model is firstly validated for the case of a single liquid droplet evaporation inside a hot gaseous medium and impingement onto a flat wall for droplet heating and film boiling conditions. Afterwards, it is utilized for the prediction of single droplet-catalyst collisions inside the FCC injection zone. The numerical results indicate that droplets of similar size to the catalytic particles tend to be levitated more easily by hot catalysts, thus resulting in higher cracking reaction rates/cracking product yield, and limited possibility for liquid pore blocking. For larger sized droplets, the corresponding results indicate that the production of cracking products is not favored, while solid-liquid contact increases. Hotter catalysts promote catalytic cracking reactions and droplet levitation over the catalytic particle, owed to the formation of a thin vapour layer between the liquid and the solid particle.

Numerical investigation of the aerodynamic breakup of a parallel moving droplet cluster

“…Two-dimensional (2-D) axisymmetric and three-dimensional (3-D) simulations are performed with the commercial CFD tool ANSYS FLUENT v16 [22] along with the use of various User Defined Functions (UDFs); these account for the following: i) adaptive local grid refinement technique around the liquid-gas interface [23], ii) adaptive time-step scheme for the implicit VOF solver based on the velocity at the droplet interface [24], and iii) moving mesh technique based on the average velocity of the droplets. The CFD model has been developed and validated in previous works of the authors for a number of applications; among them are the free fall of a droplet [23], the droplet impingement on a flat wall [25] or a spherical particle [26][27][28], the aerodynamic droplet breakup [4,24,[29][30][31][32][33][34][35] and the droplet evaporation [24,31,36]. It should be noted that he extension of the model validation for the case of droplet clusters is not possible since, to the author's best of knowledge, there are no experimental studies in the literature with droplet clusters, only a few featuring two droplets [5,15,16].…”

Numerical investigation of the aerodynamic breakup of Diesel and heavy fuel oil droplets

“…The CFD simulations are carried out using the commercial CFD tool ANSYS FLUENT v16[29] with the inclusion of various user defined functions (UDFs), used for the integration of the adaptive local grid refinement technique[30] and the adaptive time-step scheme for the implicit VOF solver. The CFD model has been developed and validated in previous works for numerous applications including the free fall of a droplet in Malgarinos et al (2015)[30], the droplet impingement on a flat wall inMalgarinos et al (2014) [31], the collision of droplet with particle in Malgarinos et al[32][33][34], the aerodynamic droplet breakup in conditions of high density ratios inStrotos et al (2015 [35][36][37][38] and the static droplet evaporation in [37][38][39]. In the present study the model validation is extended to the cases of Diesel fuel droplets and the model results are compared against the experimental data of Arcoumanis et al[3], Liu and Reitz[4] and Lee…”

Improved droplet breakup models for spray applications

“…Various User Defined Functions (UDFs) are employed for i) the adaptive local grid refinement technique around the liquid-gas interface [49], ii) the adaptive time-step scheme for the implicit VOF solver based on the velocity at the droplet interface [13], and iii) the moving mesh technique based on the average velocity of the droplet. The CFD model has been developed and validated in previous works for the case of aerodynamic droplet breakup [13,16,17,[50][51][52][53], as well as for other applications such as the free fall of droplet [49], the droplet impingement on a flat wall [54] or a spherical particle [55][56][57], and the droplet evaporation [13,52,58]. The 2-dimensional axisymmetric computational domain and boundary conditions are presented in Figure 1.…”