Computational fluid dynamic modelling of FCC riser: A review

CFD-DEM Evaluation of the Clustering Behavior in a Riser-the Effect of the Drag Force Model

Riser reactors are frequently applied in catalytic processes involving rapid catalyst deactivation. Typically heterogeneous flow structures prevail because of the clustering of particles, which impacts the quality of the gas-solid contact. This phenomenon results as a competition between fluid-particle interaction (i.e., drag) and particle-particle interaction (i.e., collisions). In this study, five drag force correlations were used in a combined computational fluid dynamics-discrete element method Immersed Boundary Model to predict the clustering. The simulation results were compared with experimental data obtained from a pseudo-2D riser in the fast fluidization regime. The clusters were detected on the basis of a core-wake approach using constant thresholds. Although good predictions for the global (solids volume fraction and mass flux) variables and cluster (spatial distribution, size, and number of clusters) variables were obtained with two of the approaches in most of the simulations, all the correlations show significant deviations in the onset of a pneumatic transport regime. However, the correlations of Felice (Int. J. Multiphase Flow1994, 20, 153-159) and Tang et al. [AIChE J.2015, 61 ( (2), ), 688-698] show the closest correspondence for the time-averaged quantities and the clustering behavior in the fast fluidization regime.

The mathematical catalyst deactivation models: a mini review

Catalyst deactivation is a complex phenomenon and identifying an appropriate deactivation model is a key effort in the catalytic industry and plays a significant role in catalyst design. Accurate determination of the catalyst deactivation model is essential for optimizing the catalytic process. Different mechanisms of catalyst deactivation by coke and metal deposition lead to different deactivation models for catalyst activity decay. In the rigorous mathematical models of the reactors, the reaction kinetics were coupled with the deactivation kinetic equation to evaluate the product distribution with respect to conversion time. Finally, selective and nonselective deactivation kinetic models were designed to identify catalyst deactivation through the propagation of heterogeneous chemical reactions. Therefore, the present review discusses the catalyst deactivation models designed for CO₂ hydrogenation, Fischer-Tropsch, biofuels and fossil fuels, which can facilitate the efforts to better represent the catalyst activities in various catalytic systems.

3D virtual full-loop CFD simulation of industrial two-stage FCC reaction–regeneration system

The 3D virtual full-loop CFD simulation method with two-fluid model (TFM) was developed to model an industrial two-stage FCC reaction–regeneration system. The virtual connections (mass, species, and energy) between riser reactors, disengager, stripper, and regenerator were realized by defining user-defined functions (UDFs) for boundary conditions according to the reality. Five correction factors were used to correct the reaction rates in the 14-lump FCC reaction kinetics, and two correction factors were used to correct the FCC reaction heat in the first and second riser reactors. As a result, the whole FCC reaction–regeneration system was successfully modeled in one single CFD case. A thorough and comprehensive view of the performance of reaction–regeneration system was obtained by the 3D virtual full-loop CFD simulation, which is helpful for the operating and optimization of FCC unit. The major predicted results were in a good agreement with the industrial data. The effects of operating conditions were also investigated by changing regenerated temperature, catalyst to oil (CTO) ratio, and process capacity.

A Review of Modelling of the FCC Unit—Part II: The Regenerator

Heavy petroleum industries, including the Fluid Catalytic Cracking (FCC) unit, are among some of the biggest contributors to global greenhouse gas (GHG) emissions. The FCC unit’s regenerator is where these emissions originate mostly, meaning the operation of FCC regenerators has come under scrutiny in recent years due to the global mitigation efforts against climate change, affecting both current operations and the future of the FCC unit. As a result, it is more important than ever to develop models that are accurate and reliable at predicting emissions of various greenhouse gases to keep up with new reporting guidelines that will help optimise the unit for increased coke conversion and lower operating costs. Part 1 of this paper was dedicated to reviewing the riser section of the FCC unit. Part 2 reviews traditional modelling methodologies used in modelling and simulating the FCC regenerator. Hydrodynamics and kinetics of the regenerator are discussed in terms of experimental data and modelling. Modelling of constitutive parts that are important to the FCC unit, such as gas–solid cyclones and catalyst transport lines, are also considered. This review then identifies areas where the current generation of models of the regenerator can be improved for the future. Parts 1 and 2 are such that a comprehensive review of the literature on modelling the FCC unit is presented, showing the guidance and framework followed in building models for the unit.

A Review of Modelling of the FCC Unit–Part I: The Riser

Heavy petroleum industries, including the fluid catalytic cracking (FCC) unit, are useful for producing fuels but they are among some of the biggest contributors to global greenhouse gas (GHG) emissions. The recent global push for mitigation efforts against climate change has resulted in increased legislation that affects the operations and future of these industries. In terms of the FCC unit, on the riser side, more legislation is pushing towards them switching from petroleum-driven energy sources to more renewable sources such as solar and wind, which threatens the profitability of the unit. On the regenerator side, there is more legislation aimed at reducing emissions of GHGs from such units. As a result, it is more important than ever to develop models that are accurate and reliable, that will help optimise the unit for maximisation of profits under new regulations and changing trends, and that predict emissions of various GHGs to keep up with new reporting guidelines. This article, split over two parts, reviews traditional modelling methodologies used in modelling and simulation of the FCC unit. In Part I, hydrodynamics and kinetics of the riser are discussed in terms of experimental data and modelling approaches. A brief review of the FCC feed is undertaken in terms of characterisations and cracking reaction chemistry, and how these factors have affected modelling approaches. A brief overview of how vaporisation and catalyst deactivation are addressed in the FCC modelling literature is also undertaken. Modelling of constitutive parts that are important to the FCC riser unit such as gas-solid cyclones, disengaging and stripping vessels, is also considered. This review then identifies areas where current models for the riser can be improved for the future. In Part II, a similar review is presented for the FCC regenerator system.

A Model of Catalytic Cracking: Product Distribution and Catalyst Deactivation Depending on Saturates, Aromatics and Resins Content in Feed

The problems of catalyst deactivation and optimization of the mixed feedstock become more relevant when the residues are involved as a catalytic cracking feedstock. Through numerical and experimental studies of catalytic cracking, we optimized the composition of the mixed feedstock in order to minimize the catalyst deactivation by coke. A pure vacuum gasoil increases the yields of the wet gas and the gasoline (56.1 and 24.9 wt%). An increase in the ratio of residues up to 50% reduces the gasoline yield due to the catalyst deactivation by 19.9%. However, this provides a rise in the RON of gasoline and the light gasoil yield by 1.9 units and 1.7 wt% Moreover, the ratio of residue may be less than 50%, since the conversion is limited by the regenerator coke burning ability.