Simulation of Hydrodynamics of the Riser Reactor for Catalytic Cracking of Crude Oil to Chemicals

Abstract

Direct catalytic cracking of crude oil to chemicals (ccCOTC) has become the development trend in the petrochemical industry. A riser is one of the key reactors in a ccCOTC process. In this work, a two-fluid model (TFM) was used to simulate a relationship between the reactor geometry and gas–solid flow in a typical riser (inside diameter of 17 mm and height of 4.5 m) established in our laboratory, with the aim of improving chemical yield and optimizing the reactor geometry in a ccCOTC process. The effects of key geometric parameters, including the angle between an oblique pipe for catalyst return and the vertical riser (α), the distance between the nozzle orifice and catalyst return oblique pipe (L), the ratio of height to diameter in the prelifting zone (H/D), and the number of catalysts returning to oblique pipes (n), on the distribution of catalyst particles and product profiles were studied. An optimized reactor geometry was proposed according to the index of gas–solid dispersion evenness. To further know the effect of the riser geometry on the product distribution, the two-fluid model (TFM) coupled with a four-lumped kinetic model was used to predict the cracking product profiles along the riser axial. It was found that the ccCOTC riser can remarkably enhance the yield of target chemicals (C2–C4 olefins, benzene, toluene, and xylene), which was approximately 3.1% higher than the result from the pilot test (using the riser before geometry optimization). This work could provide fundamental support on the design of a reactor to maximize light olefins and monocyclic aromatic hydrocarbons in the ccCOTC process.

Simulation of Crude Oil to Chemicals Based on Mesoscale Filtered Drag Subgrid Model

“… τ̿ g and τ̿ s denotes gas stress tensor and solid stress tensor. The energy conservation equations of gas and solid phases can be seen in our previous work . Meanwhile, the traditional solid stress tensor and solid pressure in this work are given by eqs and , respectively. τ̿ normals = λ normals ∇ normalu normals normalI̿ + μ normals [ false( ∇ normalu normals + ∇ normalu normals normalT false) − 2 3 ∇ · u s I̿ ] p s = ε s ρ s θ s [ 1 + 2 g 0 ε s false( 1 + normale s false) ] …”

“…This work also considers the catalyst cracking reaction including the 4-lump kinetic equation and species transport equations reported in our previous work . Additionally, the relevant species transport equations are as follows: Crude oil: .25em ∂ ∂ t ( ρ g ε g y 0 ) + ∇ · ( ρ g ε g y 0 v⃗ g ) = prefix− ∇ · ( ε g j⃗ g 0 ) − ( k 1 + k 2 + k 3 ) y 0 ε g · α int · ρ g Heavy oil: .25em ∂ ∂ t ( ρ g ε g y 1 ) + ∇ · ( ρ g ε g y 1 …”

“… and denotes gas stress tensor and solid stress tensor. The energy conservation equations of gas and solid phases can be seen in our previous work . Meanwhile, the traditional solid stress tensor and solid pressure in this work are given by eqs and , respectively. …”

“…This work also considers the catalyst cracking reaction including the 4-lump kinetic equation and species transport equations reported in our previous work . Additionally, the relevant species transport equations are as follows: Here, k i (1/s) denotes the reaction rate constant of component i ; y 0 is the mass fraction of crude oil; y 1 represents the mass fraction of heavy oil; y 2 describes the mass fraction of light oil; y 3 denotes the mass fraction of olefins and aromatics products; α int (m 2 ) is the gas–solid contact area and can be written as eq . …”

Particle-Scale Simulation Study of Size-Induced Segregation Characteristics of Binary Particles in a Liquid–Solid Fluidized Bed

“…The Eulerian–Eulerian and Eulerian–Lagrangian methods are proposed to simulate dense multiphase flow. In the Eulerian–Eulerian method, particles are treated as continuum and solved in the Eulerian manner, just like fluid. , Via this method, Cai et al studied the hydrodynamics of a binary mixture in a supercritical carbon dioxide fluidized bed. Xie et al studied the mixing/segregation property with various gas velocity and size ratio of binary mixtures in a pilot-scale fluidized bed.…”