Fluid Catalytic Cracking Regenerator Research Articles

A CFD study on the start-up hydrodynamics of fluid catalytic cracking regenerator integrated with chemical looping combustion

ABSTRACT The integration of chemical looping combustion with fluid catalytic cracking (CLC-FCC) is an innovative concept that serves as a cost-effective method for CO2 capture in refineries. This approach has the potential to reduce refinery CO2 emissions by 25–35%, offering a promising solution. As in the conventional FCC unit, it is common for CLC-FCC regenerators to be exposed to an on-off process while they are being maintained and cleaned. The novelty of this research lies in its specific focus on a less-explored phase (start-up) of CLC-FCC regenerators, the application of advanced CFD modeling, and the comprehensive analysis of operational parameters that influence the system’s performance. To validate the CFD simulations of the different drag models for solid-gas granular, bed density profiles under steady-state conditions, collected from industrial processes, were used. For the flow period based on the start-up process of the drag models, the fluidization gas inlet geometry of the regenerator, flow regime (laminar and turbulent), and superficial gas velocity were comprehensively investigated to reveal their effects on hydrodynamic characteristics. The results show that Gidaspow and Syamlal-O’Brien drag models of the solid-gas multiphase granular flow exhibited a better fit with industrial data. The Syamlal-O’Brien and Gidaspow models closely align with industrial data under steady-state conditions, displaying similar bed densities in the dense phase region (230–310 kg/m3 for Syamlal-O’Brien and 235–300 kg/m3 for Gidaspow). During the initial stage (less than 0.2 seconds), both laminar and turbulent models yield comparable bed density profiles, approximately 510 kg/m3 in the dense phase. However, as the process progresses, the dense phase density decreases to about 250–350 kg/m3 at around 0.5 seconds, with laminar flow models showing a slightly better fit with industrial data. Notably, at 0.5 seconds of fluidization time, inlet geometries having better gas distribution achieve a highly diluted phase with bed densities of 10–20 kg/m3. Reaching a steady state, the bed density decreases from around 400 kg/m3 to 260–300 kg/m3, expanding into a higher section of the regenerator where it aligns well with industrial data. The increase in superficial gas velocity would result in the clarification of the difference and well mixing of the solid-gas multiphase flow.

Techno-economic feasibility of fluid catalytic cracking unit integrated chemical looping combustion – A novel approach for CO2 capture

Oil refineries are collectively responsible for about 4–6% of the global CO2 emissions, largely because of the regenerator part of the Fluid Catalytic Cracking (FCC) unit (25–35%). An advanced combustion technology, also called chemical looping combustion (CLC), has been recently presented as a novel CO2 capture process for FCC units; however, no study provides the economic feasibility of a CLC-FCC unit. In this study, a techno-economic feasibility of the novel CLC-FCC unit was presented for the first time based on a case study with 50,000 barrels feed per day. A rigorous mass and energy balance estimation shows that 96 vol% of coke regeneration (combustion) was achieved in the FCC regenerator by using a stoichiometrically required amount of metal oxide (CuO modified catalysts) at 750 °C for 45 min. The preliminary energy penalty calculations of the proposed CLC-FCC unit (0.21 GJ/ton CO2) is relatively lower compared to the post-combustion (3.1–4.2 GJ/t CO2) via amine solvent and oxy-fuel combustion (1.8–2.5 GJ/t CO2) units reported in the literature. The equipment purchase cost (EPC) is 1.1 times higher than a standalone FCC unit due to the increase in the number of processing equipment required. The cash flow analysis results reveal a yearly basis average CO2 capture cost of 0.0106 US$/kg of CO2 (∼10.6 US$/ton CO2) for the CLC-FCC unit, which is lower compared to the other conventional CCS technologies i.e. oxy-fuel combustion and post-combustion. Factors such as EPC, capital expenditure (CAPEX), and discount rate significantly influenced the capture cost. In contrast, the CO2 capture cost is not influenced by a change in oxygen carrier and electricity cost.

Computational Fluid Dynamics Simulation of a Fluid Catalytic Cracking Regenerator

The aim of this study is to simulate a Fluid Catalytic Cracking (FCC) Regenerator, of a local refinery, using the Fluent Ansys.13 program and subsequently to investigate the impact of the change in geometry on the unit’s performance. Three different geometrical models of FCC Regenerator were simulated. The Solid Works program was used to build up the computational domain and the commercial CFD code Ansys-Fluent 13 was used for meshing, models setup and solving. Three cases were examined: base case with a single air inlet, case one with five air inlets, and case two with five air inlets, however with the catalyst inlet axis raised by 100%. The results showed that the carbon solid mass content (used to represent the coke) decreases from 0.39 to 0.23 in the base case and to 0.12 in case one and to 0.19 in case two for the regenerated catalyst. Case one resulted in a decrease in carbon content by 100%, with a carbon monoxide emission of 10ppm (the base case at a value of 200ppm) which increased in case two to 100ppm. Furthermore the impact of air mass flow rate in case one (best case) was investigated starting with a mass flow rate of 29.5kg/s. The flow rate was further increased by 100% and 200% which resulted in a carbon mass content of 0.092 and 0.08 respectively.

Influence of coke heterogeneity and the interaction between different coke species on the emission of toxic HCN and NOx from FCC spent catalyst regeneration

Concerning the emissions of hydrogen cyanide (HCN) and other N-bearing air pollutants from the fluid catalytic cracking (FCC) regeneration units, this paper has conducted a comprehensive testing and surface characterisation of four industrial spent catalysts, aged catalysts and hard coke sample in three different schemes, Ar-TPD, O2 -TPO and rapid heating to elaborate the transformation of N upon the influence of the heterogeneity of coke and N speciation. In the Ar-TPD scheme, the surface N is responsive for the emission of gaseous NH3 from pyrrolic N-5 and HCN from both pyridinic N-6 and quaternary N-Q. The removal of soft coke is beneficial in promoting the surface exposure of hard coke, thereby increasing the HCN emission dramatically. In the O2-TPO scheme, the oxygen accessibility is the principal factor governing the emission of HCN. The external soft coke is able to access the bulk O2 firstly, the combustion of which in turn provides heat back to promote the cracking of internal hard coke from the same and neighbouring particles to release more HCN. The induction effect of bulk O2 is also superior over the spent catalyst properties in formulating a nearly identical trend of HCN emission for all the four spent catalysts tested. Finally, for the use of rapid heating scheme that is typical in a commercial FCC regenerator, it is effective in accelerating the volatilisation of soft coke quickly, thereby promoting the oxygen accessibility to hard coke and the internal N-bearing precursors so as to mitigate the emission of HCN effectively. The use of a large superficial velocity of gas is further effective in sweeping the volatiles including HCN away from the catalyst, promoting their oxidation extent accordingly.

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.

Investigation of the hydrodynamics in the regenerator of fluid catalytic cracking unit integrated by chemical looping combustion

Oil refineries are responsible for 4–6% of global CO2 emissions, and 20–35% of these emissions released from the regenerator of Fluid Catalytic Cracking (FCC) units, which are the essential units for the conversion of heavier petroleum residues (vacuum gas oil) into more valuable products. Chemical looping combustion (CLC) has been recently proposed to mitigate the CO2 emissions released from the regenerator of FCC units with a lower energy penalty. However, a detailed experimental and modelling investigation is still necessary in order to identify the hydrodynamics in the regenerator of chemical looping combustion integrated with fluidised catalytic cracking (CLC-FCC). A computational fluid dynamic (CFD) study was conducted to understand the hydrodynamic behaviours of gas-solid two-phase flow in the regenerator of the CLC-FCC unit, based on a three-dimensional multiphase model (Eulerian-Eulerian) with the kinetic theory of granular flow.The results provide a useful insight into regenerator hydrodynamics, in terms of oxygen carrier modified FCC catalysts and FCC coke distribution profiles, in the regenerator of CLC-FCC. The conventional drag models (Syamlal-O'Brien and Gidaspow) predict a bed density profiles of a dense phase (250–300 kg/m3) at the dense phase (0–0.25 of h/H), and a dilution phase from h/H = 0.25 to 0.50 of regenerator. The bed density profile is indistinguishable from the industrial data provided for conventional FCC regenerators. The fluidisation gas (CO2) passes through the centre of the regenerator where the fluidisation gas splits the catalyst particles from the centre to the walls, to create a dilute particle phase in the centre and a dense particle-phase near the wall, which is one of the characteristic flow regimes in circulating fluidised bed reactors. The particles in the centre demonstrate an upward flow trend with a particle velocity above 3.0 m/s while the dense particles near the wall tend to go down with relatively low particle velocity of <0.5 m/s, which creates vortexes and a non-uniform particle distribution in the regenerator. The distribution of the fluidising gas provides better mixing of solid particles in the entrance and the optimisation of the superficial gas velocities (1.0 m/s) to create a distributed flow regime with developed vortexes through the dense and dilute phases. Furthermore, the laminar and turbulent flow models demonstrated no significant differences in terms of axial bed density profile in the regenerator of the CLC-FCC concept. These findings demonstrated that the hydrodynamics of catalysts in the CLC-FCC regenerator successfully predicted with CFD modelling and the prediction results aligned well with the conventional FCC regenerator.

MP-PIC simulation of the effects of spent catalyst distribution and horizontal baffle in an industrial FCC regenerator. Part II: Effects on regenerator performance

Improving distribution uniformity of spent catalyst and adding horizontal baffles are two effective measures to improve the regeneration performance of a fluid catalytic cracking (FCC) unit. In this study, the effects of the spent catalyst distribution and horizontal baffle on the regeneration performance of an industrial coaxial compact FCC regenerator is simulated using an Eulerian-Lagrangian multi-phase particle in cell (MP-PIC) method with coupled hydrodynamic and coke-burning kinetics models. The coke-burning kinetics model developed by Arbel et al. (Ind Eng Chem Res, 1995, 34(4): 1228–1243) is used in the simulation. The MP-PIC simulations successfully predicted agreeable temperatures in the industrial regenerator. Serious afterburning in the freeboard was also successfully predicted. The effectiveness of the two intensification measures in enhancing the performance of an industrial FCC regenerator were proved, as indicated by the restrained afterburning in the freeboard, the increased coke burning efficiency, the lower coke content in the regenerated catalysts. Comparatively, adding a properly design horizontal baffle was proved to be more effective and should be a primary intensification measure used in industrial regenerators. A better spent catalyst distributor was suggested to be used to help the inserted horizontal baffles further improve the performance of the regenerator. By the simulation, more flow-reaction coupling mechanisms during the regeneration process are capable to be understood in more depth. The effectiveness of different intensification measures depends both on the resulted matching quality between the distributions of spent catalyst and oxygen in the main air, and the solids residence time distribution.

Development of IoT to regulate burning in FCC regenerators

Fluid catalytic cracking (FCC) is a conversion process used in petroleum refineries to convert high-fuel hydrocarbon fractions into other low FCC hydrocarbon fractions. Our research team is researching the FCC using palm oil so that it can become fuel. Regenerators are controlled and monitored by using the Internet of Things technology. The thermocouple sensor in the regenerator and stepper motor 28BY J-48 as an actuator on the ejector valve is controlled by Arduino Mega 2560 and ESP8266 for data reading and processing. The results of this study show that the design of IoT on the FCC regenerator uses Blynk applications have been running properly. The sensor and data actuator can be read by ESP8266 which is then sent to the Blynk server via the cellular network. This shows the ability of a data logger can used in the range’s internet wifi smartphone.

MP-PIC simulation of the effects of spent catalyst distribution and horizontal baffle in an industrial FCC regenerator. Part I: Effects on hydrodynamics

Improving distribution uniformity of spent catalyst and adding horizontal baffles are two effective measures to improve the regeneration performance of a fluid catalytic cracking (FCC) unit. In this study, an industrial coaxial compact FCC regenerator is simulated using a Eulerian- Lagrangian multi-phase particle in cell (MP-PIC) method. By using the energy-minimization multi-scale (EMMS) drag model based on turbulent flow regime, the MP-PIC simulation predicts the typical solids fraction profile which is in good agreement with industrial data. The Crosser grid (a typical horizontal baffle) is successfully constructed with the help of “virtual baffles” in simulation. The simulation results show that, after adding Crosser grid (a new horizontal fluidized bed baffle by our group), the bed height increases slightly, the lateral mal-distribution index of solids decreases and the descending flux of spent catalysts decreases significantly. The distribution uniformity of spent catalyst distribution along the bed cross section is more uniform when spent catalyst particles are distributed more uniformly. The presence of gas cushion beneath the Crosser grid allows it to act as a pseudo gas distributor, eliminating gas channeling and decreasing zones of low fluidization quality. The rising bubbles are absorbed by the gas cushion and new small bubbles are generated above the Crosser grid, thereby strengthening the gas–solid contact. The guiding vanes of Crosser grid accelerate the lateral movement of particles. The Crosser grid also proves its stronger suppression on the axial back-mixing of solids.

Demonstrating the applicability of chemical looping combustion for the regeneration of fluid catalytic cracking catalysts

Fluid Catalytic Cracking (FCC) units are responsible for roughly 25% of CO2 emissions from oil refineries, which themselves account for 4–6% of total global CO2 emissions. Although post- and oxy-combustion technologies have been proposed for CO2 capture in FCC, Chemical Looping Combustion (CLC) may also be a potential approach that has lower energy consumption. An equilibrium catalyst (ECat) was first modified with oxidised oxygen carriers (CuO, Co3O4, Mn2O3) using wet-impregnation, and their reduced states (Cu, CoO, Mn3O4, MnO) were generated by hydrogen reduction. To demonstrate that the impregnated reduced oxygen carriers had no significant negative effects on cracking, the prepared catalysts were used to crack n-hexadecane using the standard FCC microactivity test (ASTM D3907-13). The CLC behaviour of coke deposited on the reduced oxygen carrier impregnated ECats, was investigated with the stoichiometrically required amount of oxidised oxygen carrier impregnated ECat in lab scale fixed-bed and fluidised-bed reactors equipped with an online mass spectrometer to monitor CO2 release. Although the conversion and liquid to gas ratio were largely unaffected, coke selectivity did increase with the impregnation of reduced oxygen carriers. However, this increase is mostly attributed to solvent extractable coke. It is possible to reach about 90 vol% combustion efficiency of the coke deposited on ECat using mechanically mixed with CuO and Mn2O3, but the regeneration temperature required, 800 °C, is considerably higher than that under typical regenerator conditions of 650–750 °C for 30–60 min. However, relatively high combustion efficiencies of greater than 94 vol% of the coke deposited on reduced Cu and Mn3O4 impregnated ECat were achieved with the stoichiometrically required amount of CuO and Mn2O3 impregnated ECat at 750 °C for 45 min., close to conventional FCC regenerator conditions.

Void Properties in Dense Bed of Cold-Flow Fluid Catalytic Cracking Regenerator

Fluid catalytic cracking (FCC) processes have been used widely in petroleum refineries. FCC regenerators play important roles for maintaining catalyst activity and supply the reaction heat. The regenerator efficiency is mainly connected to the hydrodynamics of the fluidized bed, because the gas and solid behaviors are very important factors in mass and heat transfer. The void properties, such as chord length, rising velocity, frequency, and fraction, have been determined in a large cold flow model (0.48 m-ID × 6.4 m-high) of the FCC regenerator, which was geometrically scaled down from a commercial FCC unit. The local void chord length, rising velocity, frequency, and fraction exhibit their maximum value along the radial direction of the bed. The cross-sectional mean void chord length, rising velocity, and fraction increase and the cross-sectional mean void frequency decreases with height in the bed. The variation of void properties in the FCC regenerator with turbulent fluidized bed exhibit similar trends to those in a bubbling fluidized bed. The void properties in the FCC regenerator have been correlated with the experimental parameter on the basis of bubbling bed concept. The predicted void velocities based on the correlations agreed well with the experimental data from present and previous studies. A modified bubbling fluidized bed model could describe the void properties in the regenerator operated in turbulent fluidized bed regime.

INFLUENCE OF MICROSPHERIC CATALYST HEAT TREATMENT ON THE STRUCTURE AND CATALYTIC PROPERTIES

Oktifine 480P catalyst, containing catalytic additives, is used on refineries in Ufa to boost light olefin production and increase gasoline octanes in the Fluid Catalytic Cracking (FCC) process. Under the hydrothermal conditions present in the FCC regenerator (typically > 700 oC and > 8 % steam), FCC catalysts partly deactivates. Zeolite undergoes to dealumination and partial structural collapse, thereby losing activity, micropore surface area, and has changes in selectivity. Fresh catalyst are added at appropriate respective levels to the FCC unit to keep overall targeted steady state activity and selectivity. To pin down change rate of the structure and catalytic properties of the catalyst after heat treatment a number of studies were done. For research, microspheric catalyst Oktifine 480P, produced on Ishimbay Specialized Chemical Plant of Catalysts, was exposed to thermal treatment under 700 oС, 760 oС, 800 oС temperatures. ASTM D3907 standard feed was used for micro-activity cracking testing at 480 oС. Fresh catalyst Oktifine 480P was very active at vacuum gasoil cracking, micro-activity was estimated to 90,3 %. The micro-activity of heat treated samples were slowly decreasing by temperature increasing but still very high to compare with micro-activity of equilibrated sample of catalyst. So micro-activities for thermal treated samples under 700 oС, 760 oС, 800 oС were respectively 87,5 %, 85,2 %, 84 %, 85 % and micro-activity of equilibrated sample of catalyst was 42,4 %.

CFD simulation of gas–solid flow patterns in a downscaled combustor-style FCC regenerator

To investigate the gas–solid flow pattern of a combustor-style fluid catalytic cracking regenerator, a laboratory-scale regenerator was designed. In scaling down from an actual regenerator, large-diameter hydrodynamic effects were taken into consideration. These considerations are the novelties of the present study. Applying the Eulerian–Eulerian approach, a three-dimensional computational fluid dynamics (CFD) model of the regenerator was developed. Using this model, various aspects of the hydrodynamic behavior that are potentially effective in catalyst regeneration were investigated. The CFD simulation results show that at various sections the gas–solid flow patterns exhibit different behavior because of the asymmetric location of the catalyst inlets and the lift outlets. The ratio of the recirculated catalyst to spent catalyst determines the quality of the spent and recirculated catalyst mixing and distribution because the location and quality of vortices change in the lower part of the combustor. The simulation results show that recirculated catalyst considerably reduces the air bypass that disperses the catalyst particles widely over the cross section. Decreasing the velocity of superficial air produces a complex flow pattern whereas the variation in catalyst mass flux does not alter the flow pattern significantly as the flow is dilute.

Identification of overheating of an industrial fluidized catalytic cracking regenerator

Considerable overheating can be observed on the outer surface of the fluidized catalytic cracking regenerator. The maximum temperature values and the location of overheating areas change over time. Considering the long times between overhauls (of up to 5 years), it is difficult to pinpoint the factors that cause overheating. An examination of the insulation layer during renovation works does not reveal any obvious damage that could have been responsible for the phenomenon. In order to explain the observed overheating process, a thermal and strength analysis of the fluid catalytic cracking regenerator was conducted. A new algorithm is formulated for identification of the refractory lining state and the heat transfer coefficient between the FCC zeolite catalyst particles and the regenerator walls. The heat transfer coefficient on the regenerator inner surface is estimated after its repair, when no overheating areas are visible. The heat transfer coefficients due to radiation and natural and forced convection are determined based on measured values of the regenerator shell and air temperatures, wind velocity and air pressure. The regenerator outer steel surface temperature is measured using an infrared camera.The presented numerical model of the catalytic cracking regenerator wall enables identification of the wall overheating process. The numerical simulation shows how cracks can open and close in the insulation layer depending on atmospheric conditions. This paper puts forward a new method of identifying heat transfer coefficients and cracks in the refractory lining. The unknown heat transfer coefficient on the regenerator inner surface and the crack dimensions will be calculated by means of the inverse method. A least squares objective function is defined to select parameters such that the computed temperatures will agree within certain limits with the temperature values measured experimentally.The information about the crack size can be used for an on-line assessment of the refractory lining, during the lining modification, and also to estimate the remnant life of steel pressure elements. The method accuracy is presented during real measurements performed by means of an infrared camera using the Gaussian error propagation rule.

Effect of Steam Deactivation Severity of ZSM-5 Additives on LPG Olefins Production in the FCC Process.

ZSM-5-containing catalytic additives are widely used in oil refineries to boost light olefin production and improve gasoline octanes in the Fluid Catalytic Cracking (FCC) process. Under the hydrothermal conditions present in the FCC regenerator (typically >700 °C and >8% steam), FCC catalysts and additives are subject to deactivation. Zeolites (e.g., Rare Earth USY in the base catalyst and ZSM-5 in Olefins boosting additives) are prone to dealumination and partial structural collapse, thereby losing activity, micropore surface area, and undergoing changes in selectivity. Fresh catalyst and additives are added at appropriate respective levels to the FCC unit on a daily basis to maintain overall targeted steady-state (equilibrated) activity and selectivity. To mimic this process under accelerated laboratory conditions, a commercial P/ZSM-5 additive was hydrothermally equilibrated via a steaming process at two temperatures: 788 °C and 815 °C to simulate moderate and more severe equilibration industrial conditions, respectively. n-Dodecane was used as probe molecule and feed for micro-activity cracking testing at 560 °C to determine the activity and product selectivity of fresh and equilibrated P-doped ZSM-5 additives. The fresh/calcined P/ZSM-5 additive was very active in C12 cracking while steaming limited its activity, i.e., at catalyst-to-feed (C/F) ratio of 1, about 70% and 30% conversion was obtained with the fresh and steamed additives, respectively. A greater activity drop was observed upon increasing the hydrothermal deactivation severity due to gradual decrease of total acidity and microporosity of the additives. However, this change in severity did not result in any selectivity changes for the LPG (liquefied petroleum gas) olefins as the nature (Brønsted-to-Lewis ratio) of the acid/active sites was not significantly altered upon steaming. Steam deactivation of ZSM-5 had also no significant effect on aromatics formation which was enhanced at higher conversion levels. Coke remained low with both fresh and steam-deactivated P/ZSM-5 additives.

Numerical simulation of a commercial FCC regenerator using Multiphase Particle-in-Cell methodology (MP-PIC)

Catalyst regeneration process has recently been the subject of comprehensive research investigations focusing mainly on the chemistry of the regeneration while overlooking the bed hydrodynamics and its effects on the regeneration performance. For this purpose, an industrial Fluid Catalytic Cracking (FCC) regenerator is simulated using a Multi-Phase Particle-In-Cell (MP-PIC) approach. The simulation is performed using a three-dimensional regenerator design with complex internals in order to study bed hydrodynamics, thermal effects, and chemical kinetics. The numerical model is then used to study typical industrial issues linked to the operation of industrial regenerators such as erosion areas, standpipe drainage, and CO emission levels. It is noticed that total outlet gas flow exceeds total inlet flow due to the formation of coke combustion products, an undersized standpipe, and inefficient placement of the air distributor rings. Highest erosion occurs in the feed line and plate. A low-temperature column exists in the center of the unit, and the highest temperatures are outside of the diplegs in the periphery of the freeboard. Elevated CO levels are present in the outlet gas because of poorly designed air distributor rings and lower than optimal temperatures in the unit. These simulation results show the numerous modeling capabilities of the MP-PIC approach to identify possible performance and reliability issues of an industrial process. Some redesign proposals have been made to enhance the FCC regenerator operations.

CFD modeling of the coke combustion in an industrial FCC regenerator

Fluid Catalytic Cracking (FCC) is one of the most important conversion processes used in refineries all over the world. It is used for the conversion of heavy oil feed with high boiling temperature to produce gasoline, diesel, propylene and other valuable products. Coke deposits on the catalyst during the catalytic conversion and deactivates it, therefore catalyst is continuously regenerated in the FCC process. The regeneration step is essential as it directly impacts the products yields. The coke combustion also generates NOx and SOx emissions which levels are highly influenced by the bed hydrodynamics, the operation parameters and the reactor configuration, and are important to quantify. For all these reasons, the understanding of the regenerator hydrodynamic and kinetic is essential.This paper presents a study on the coupling of Barracuda™ CFD code with a coke combustion kinetic model developed at IFP Energies nouvelles to simulate an industrial FCC regenerator. Regenerator operating and performance data, including catalyst samples for coke analysis, are acquired on a selected industrial unit to evaluate the model. The results provide useful insight on the regenerator performance characteristics in terms of air distribution, coke burning rate and temperature profile in the regenerator. The steady state flue gas composition and regenerator dense and dilute phase temperatures are well predicted by the CFD simulation. The CFD prediction of the bed density is underestimated compared to the industrial data. The duration required to completely regenerate the catalyst is also estimated from the results. The CFD coupled coke combustion kinetic model presented in this paper enables us to evaluate the influence of the fluidized bed hydrodynamic on the catalyst regeneration in an industrial FCC regenerator. The developed model serves as a useful tool for the evaluation of future technology development in the FCC regenerator.

Modeling FCC spent catalyst regeneration with computational fluid dynamics

Regeneration of spent catalyst is key to the successful operation of the fluid catalytic cracking (FCC) unit. The coke laden spent catalyst from oil cracking in the FCC riser is burned off in the regenerator. The heat generated raises the circulating catalyst temperature and, in turn, helps crack the oil to valuable products in the riser. Efficient regeneration depends on good spent catalyst and combustion air distribution. Ideally, the combustion air is designed to match the spent catalyst distribution.The FCC regenerator has been modeled using various techniques. Technip Stone & Webster Process Technology (Technip) is using computational fluid dynamic (CFD) techniques to develop a tool that simultaneously models both hydrodynamics and coke combustion in the FCC regenerator. Descriptions of the coke burning kinetics are provided through proprietary combustion kinetic equations with appropriate kinetic constants. The results provide detailed qualitative mapping of the regenerator’s behavior in terms of flue gas composition, temperature distribution including afterburning, regenerator bed density in both axial and radial planes. The CFD, coupled with spent catalyst regeneration kinetic model, is used is to evaluate the regenerator performance of a commercial regenerator. The results were used as basis to recommend hardware and operational modifications. The proposed modifications were subsequently modeled using the CFD kinetic tool to quantify the benefits.

Numerical simulation and optimization of an industrial fluid catalytic cracking regenerator

Fluid catalytic cracking (FCC) is one of the most important conversion processes in petroleum refineries. FCC regenerator is a key part of an FCC unit to recover the solid catalyst reactivity by burning off the deposited coke on the catalyst. In this paper, a three-dimensional multi-phase, multi-species reacting flow computational fluid dynamics (CFD) model was established to simulate the flow and the reactions inside an FCC regenerator. The Euler-Euler approach, where the two phases (gas and solid) are considered to be continuous and fully inter-penetrating, is employed. A modified drag force model was applied on the CFD model with appropriate influential cluster diameters of particle grouping phenomenon. The developed CFD model was validated by using plant data. With the validated CFD model, the flow characteristics and the inner-phase and inter-phase reactions were studied. The results showed that the effect of oxygen enrichment on the catalysts recovery efficiency was limited when the oxygen enrichment exceeded 5%.