Riser Reactor Research Articles

Three-phase CFD-DEM study on the hydrodynamics of a riser system with liquid injection

Riser reactors are frequently applied in the process industry for highly important catalytic processes. In this work, a computational fluid dynamics- discrete element method (CFD-DEM) for a riser with liquid injection was developed. This model treats the gas as a continuous phase whereas the liquid droplets and catalyst particles are treated as discrete elements. The presence of droplets causes particles to be wet, which is taken into account via coverage models of the particles. In addition, the liquid on the particles will change the collision behavior, which is included using an energy balance approach. This CFD-DEM study is conducted simulating a lab-scale pseudo-2D riser. Based on the comparison, the assumption of fully covered particles results in a significant increase in the solids holdup and clustering behavior of the riser which, especially at the low liquid flow rate, results in an over-prediction. The partial coverage simulations show that only half of the particles are covered, which has a major effect on the collisions.

Feasibility study of a process for the reduction of sulfur oxides in flue gas of fluid catalytic cracking unit using the riser reactor

In this work, a new process for achieving the recovery of elemental sulfur by utilizing a fluidized catalytic cracking (FCC) riser reactor for SOx treatment (FCC-DeSOx) is proposed. The process leverages the high temperatures and hydrocarbon concentrations in the FCC riser reactor to convert SOx into H2S. Subsequently, H2S, along with the cracked gas, is processed downstream to produce sulfur. Thermodynamic analysis of the key reduction reactions in the FCC-DeSOx process revealed that complete conversion of SOx to H2S is feasible in the dry gas (hydrogen-rich) prelift zone, as well as the upper and lower zones of the riser, upon achieving thermodynamic equilibrium. Experimental studies were conducted to replicate the conditions of these reaction zones using a low concentration of hydrogen gas as the reducing agent. Through process optimization, investigation of the minimum reaction time, and kinetic studies, the potential of this method for the complete reduction of SOx was further confirmed.

Modeling and optimizing gas solid distribution in fluidized beds

In fluidized bed reactors, uniform distribution of gas and solids is critical to achieve the desired hydrodynamic and kinetic performance. For FCC units, Technip Energies uses a proprietary distributor design to terminate both reactor risers and spent catalyst lift lines to distribute the exiting gas-solid stream into a fluidized bed.In Technip Energies' Resid FCC unit, air and spent catalyst are distributed from an upward flowing stream into a catalyst bed for coke combustion on catalyst. Proper distribution is key to achieve a uniform coke burn and an even temperature profile throughout the bed. In PropyleneMax™ Catalytic Cracking (PMcc™) technology, the reactor riser also terminates in a fluidized bed, requiring proper distribution of the hydrocarbon vapor and solid mixture into the reactor bed, which is key to providing adequate contact for further cracking to valuable products. This paper discusses Technip Energies' gas-solid distribution technology and the recent work performed to develop an improved distributor for use as a riser termination device in both the PMcc reactor and the RFCC regenerator to achieve improved performance. The use of CFD modeling to screen and evaluate the initial concepts and optimize the final selected concept are presented here. The performance matrices used to quantify the benefits of the optimized distributor design with respect to the existing one in the reactor application are highlighted, showing the benefits of improved gas solid distribution on hydrodynamic and kinetic performance. The paper presents a systematic approach to develop a novel industrial device using physics-based computational tools.

Fluidized catalytic cracking with novel emulsified feeding for increasing light oil yield and reducing additional CO2 emission

The fluid catalytic cracking unit (FCCU) is widely used in the processing of heavy oil. Fast and sufficient vaporization of heavy oil can maximize the light oil yield and reduce the coke yield. However, the inferior quality generally makes the heavy oil difficult to be vaporized. Unvaporized oil remaining on the catalyst surface will lead to high coke yield and subsequently high carbon dioxide emissions in the regenerator. The novel emulsified feeding technique can achieve secondary atomization of oil droplet through micro-explosion, which can reduce the droplet diameter and enhance the droplet vaporization. Computational Fluid Dynamics (CFD) simulation was performed to investigate the effect of emulsified feeding on the droplet vaporization and cracking reaction in the FCC riser reactor. It was found that when the reaction temperature is constant, the emulsified feeding can promote the droplet vaporization and cracking reaction. The average vaporization ratio can be improved by 1.2%-1.7%, and the light oil yield can be improved by 0.6%-0.8% compared to the conventional atomized feeding. The volume fraction of droplet near the side wall is largely reduced. The additional carbon emissions produced by unvaporized oil can therefore be reduced in the regenerator. In addition, the emulsified feeding technique will not have great impact on solids fluidization and pressure balance in the riser. The probability of micro-explosion of emulsion droplets is further discussed with respect to its effect on the vaporization and cracking reaction. The maximum light oil yield can be obtained with micro-explosion probability of 85%.

Simulation analysis of micro-explosion during emulsification feeding of residue fluidized catalytic cracking

Residue Fluidized Catalytic Cracking (RFCC) is one of the key processes to convert heavy oil into light products in refineries. The fast and sufficient vaporization of the feedstock in the FCC riser reactor can promote the catalytic cracking reaction and is beneficial for increasing the yield of light products and decreasing the yield of coke. However, fast vaporization of residue oil is extremely challenging due to its high density and viscosity. Recently, emulsified feeding technology is seen as a potential method that can effectively enhance the vaporization of RFCC feedstock. Computational Fluid Dynamics (CFD) simulations were performed in order to reveal the micro-explosion mechanism of emulsion droplet in the riser reactor. The CFD model was validated against experimental results from literature. The model was used to study micro-explosion of emulsified droplets in the gas phase and at the catalyst particle surface separately. It was found that due to the micro-explosion of emulsion oil droplets in producing large number of tiny droplets, the secondary atomization of droplets can be realized. In the gas phase, the interfacial area of emulsion droplet can be improved by 5 to 15 times. At the catalyst surface, the percentage of liquid film coverage was reduced by 32.6 %, and the droplet diameter was reduced by 92 % for the emulsified feeding technology. These results indicate that the vaporization efficiency of the residual oil can be greatly improved by this technology.

Mixing effects of high-speed jets in gas-solid riser and downer reactors

For the high-temperature and short-contact time gas-solid reaction process, riser and downer are considered appropriate reactors. To realize an intensive and complete mixing of reactants with catalysts, the feed raw is always introduced in the form of high-speed jets. In this study, in order to investigate the mixing effects of different types of high-speed jets in riser and downer, traceable ozone is injected with the high-speed feed jets to react with catalyst particles. By detecting the decomposition of ozone, the gas-solid mixing and reaction in riser and downer under the influence of both co-current and counter-current injections are analyzed. The relative ozone concentration is used to reflect the location reaction extent and its radial nonuniformity index is proposed to compare the results in riser and downer. It is found that the jet influence zone in downer provides a relatively better environment for the mixing of feed jets with catalysts. In the riser, introduction of counter-current injections could improve the uniformity of gas-solid mixing in the initial contact region of feed with catalysts.

Riser Reactor with a Multistage Oxygen Feeding Strategy for the Oxidative Coupling of Methane

Riser Reactor with a Multistage Oxygen Feeding Strategy for the Oxidative Coupling of Methane

Effect of operating conditions on the performance of riser reactor for oxidative coupling of methane

Oxidative coupling of methane (OCM) is characterized by high temperature and strong heat released. A riser reactor is designed for the OCM process to improve gas-solid contacting and heat transfer. This work illustrates the effect of hydrodynamic conditions and feed gas composition on the performance of an OCM riser reactor. The findings suggest that oxidative reactions predominantly occur within the acceleration zone and developed flow zone. Furthermore, at the low superficial gas velocity accompanied by a high solid circulating rate, the C2 yield initially increases in the acceleration zone, followed by a decrease in the developed flow zone and deceleration zone. The optimal operating conditions are a specific region corresponding to the solids holdup ranges from 0.015 to 0.02. Moreover, the C2 yield can be elevated using an appropriate feed mixture.

Artificial Intelligence for Hybrid Modeling in Fluid Catalytic Cracking (FCC)

This study reports a novel hybrid model for the prediction of six critical process variables of importance in an industrial-scale FCC (fluid catalytic cracking) riser reactor: vacuum gas oil (VGO) conversion, outlet riser temperature, light cycle oil (LCO), gasoline, light gases, and coke yields. The proposed model is developed via the integration of a computational particle-fluid dynamics (CPFD) methodology with artificial intelligence (AI). The adopted methodology solves the first principle model (FPM) equations numerically using the CPFD Barracuda Virtual Reactor 22.0® software. Based on 216 of these CPFD simulations, the performance of an industrial-scale FCC riser reactor unit was assessed using VGO catalytic cracking kinetics developed at CREC-UWO. The dataset obtained with CPFD is employed for the training and testing of a machine learning (ML) algorithm. This algorithm is based on a multiple output feedforward neural network (FNN) selected to allow one to establish correlations between the riser reactor feeding conditions and its outcoming parameters, with a 0.83 averaged regression coefficient and an overall RMSE of 1.93 being obtained. This research underscores the value of integrating CPFD simulations with ML to optimize industrial processes and enhance their predictive accuracy, offering significant advancements in FCC riser reactor unit operations.

Simple Model of an Industrial Catalytic Cracking Riser Reactor

Simple Model of an Industrial Catalytic Cracking Riser Reactor

Computational prediction of green fuels from crude palm oil in fluid catalytic cracking riser

Fluid catalytic cracking could convert crude palm oil into valuable green fuels to substitute fossil fuels. This study aimed to predict the phenomenon and green fuels yield in the industrial fluid catalytic cracking riser using computational fluid dynamics. A three-dimensional transient simulation using the Eulerian-Lagrangian with the multiphase particle-in-cell is to investigate reactive gas-particle hydrodynamics and the four-lump kinetic network model with the rare earth-Y catalyst for crude palm oil cracking behaviors. The study results show that the fluid and catalyst velocity profile increase in the middle of the riser reactor because the cracking reaction process that produces OLP and Gas products has a lighter molecular weight. The endothermic reaction causes the temperature profile to decrease because the heat of the reaction comes from the catalyst. This analysis shows that the simulation accurately predicts green fuel products from crude palm oil. As a result, the crude palm oil conversion, organic liquid product yield, and Gas yield correspond to 70 wt%, 28.8 wt%, and 27.5 wt%, respectively. Compared to the experimental study, the computational prediction of yield products showed good agreement and determined the optimal riser dimension. The methodology and results are guidelines for optimizing the FCC riser process using CPO.

Numerical analysis on the transport properties and residence time distribution of ribbon biomass particles in a riser reactor based on CFD-DEM approach

A bended ribbon biomass particle model was developed to explore the dynamic transport properties inside a riser reactor. Residence time distribution (RTD) of the particles was analyzed by using the Eulerian-Lagrange method. The effects of sampling height, particle density, particle size and gas-to-solid mass ratio on RTD were investigated. The coupled Computational Fluid Dynamics and Discrete Element Method (CFD-DEM) model was verified firstly by experimental data on pressure drop and residence time distribution density function. The simulation results demonstrated that the ribbon biomass particles display a typical annular-core spatial distribution during transportation. The RTD of particles exhibit an approximate single-peaked normal distribution. The mean residence time (MRT) can reach up to 0.7 s when the particle density is 1200 kg/m3. Particle with higher density has longer mean residence time. The flow patterns are closer to plug flow if particle length over 12 mm. The particle flow pattern is not sensitive to changes in particle density and size, while the gas-to-material mass ratio has a significant impact on it.

Effect of catalyst-to-oil ratio and catalyst temperature on determining the yield of gasoline in the riser reactor

Increasing the yield of Gasoline has been the desire of every crude oil refining process in the oil industry. The principal unit that has significantly contributed to increasing the yield of Gasoline is the Fluid Catalytic Cracking (FCC) unit. The performance of the FCC unit is dependent on many parameters, substantively the catalyst-to-oil ratio (COR) and the temperature of the catalyst (tcat) when entering the riser reactor. To understand the effect of COR and tcat, a five-lump kinetics model was developed, and the simulated result was further plugged into MINITAB 7.0 software in order to generate a set of empirical equation models. The empirical equation models predicted the optimal yield of gasoline to be 56.83%, with corresponding optimal parameters of COR and temperature of catalyst as 3.35 and 900 K, respectively. The actual yield of gasoline at 3.35 COR and 900 K catalyst temperature was 56.78%, with a 0.09% error compared to the predicted yield of gasoline. The two parameters were varied with the values from previous studies, and the predicted result compared to the actual is 7.8648 root mean square error (RMSE). Therefore, the empirical equation model is reliable in predicting the yield of gasoline with respect to the COR and temperature of catalyst.

Hydrodynamics and OCM reaction performance in a bubbling fluidized bed reactor and a riser reactor

The reasonable reactor design is of great importance for increasing the C2 yield (C2H4 and C2H6) of the oxidative coupling of methane (OCM), and the OCM reactor should remove the heat released in reactions quickly and efficiently and minimize the consecutive reaction of ethylene to carbon oxides. The fluidized bed reactor is characterized by excellent heat transfer, superior mass transport, and large handling capacity, while fewer studies focused on large-scale fluidized bed reactors for the OCM reaction. Therefore, large cold-model experiments and computational fluid dynamics simulations were conducted to investigate hydrodynamics and the OCM reaction performance in a large-scale bubbling fluidized bed (BFB) and a large-scale riser. In the BFB reactor, consecutive reactions of ethylene are acute because of the strong gas back-mixing, high solids holdup, and non-uniform solids distribution. While the consecutive reactions of ethylene are negligible due to the plug flow structure and low solids holdup in the riser reactor. Further, both reactors can achieve isothermal operation for the OCM process. The C2 selectivity of 45.4% and C2 yield of 21.1% are obtained in the riser reactor, increasing by 20.3% and 5.8% individually than that in the BFB reactor. This study provides useful information and reference to the OCM reactor design and commercialization.

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.

A Four-Lump Kinetic Model for Atmospheric Residue Conversion in the Fluid Catalytic Cracking Unit: Effect of the Inlet Gas Oil Temperature and Catalyst-Oil Weight Ratio on the Catalytic Reaction Behavior

The effects of the inlet gas oil temperature and catalyst-to-oil weight ratio on the catalytic cracking behaviors and the distribution of the product and the yield of the riser outlet main products as unconverted gas oil, gasoline, and coke were investigated on a real industrial FCC Riser reactor with a model LRC-99 catalyst and atmospheric residue derived from Niger’s crude oil of Agadem bloc was used as the feedstock. A four-lumped kinetic mathematical model is developed to predict the feedstock conversion and the product distribution by using the deactivation function coke-on- catalyst approach. The model was validated with a good agreement against real industrial fluidized bed riser reactor plant data from Niger and industrial riser data from literature sources. The results show that the inlet gas oil temperature and catalyst-to-oil weight ratio obviously affect the cracking reactions behavior and govern the reaction rates.

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

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

Flow distribution analysis of a novel fcc system through experiment study and atomic model

As the largest palm oil producer in the world, Indonesia has a promising potential to produce green fuel through the Fluid Catalytic Cracking (FCC) process. A novel FCC configuration, FCC Proto X 3, which combines a riser reactor and downer reactor in the system, has been developed. However, several valves including in the FCC system remain a black box to the flow distribution in the system. The objective of this paper is to investigate the effect of the valve setting variation on the airflow distribution of the FCC system. The methodology uses experiment and acausal modeling. The effect of valve setting variation on pressure and average velocity of the airflow has been investigated. The experiment is conducted under cold test conditions, while the acausal model of the FCC system is built by using OpenModelica. It is obtained that valve 2 which controls the flow at the channel toward the regenerator is essential due to its role in controlling the air supply combustion process in the regenerator and driving the spent catalyst particles to the regenerator. Valve 3 is responsible for controlling the flow toward the riser reactor directly. Later, it is responsible for supplying the lifting fluid to support the catalytic cracking reaction at the riser sections. Valve 4 contributes to controlling the lifting fluid to the downer reactor. It will also be responsible for supplying thermal energy from the high-temperature particle catalyst to the reactor. When all valves toward the regenerator and reactor are 100 % open, the measured average velocity at the flue gas outlet and the product outlet are 8.04 m/s and 5.775 m/s respectively. The result shows that the airflow at the FCC system tends to flow through the regenerator. The atomic model estimation also shows a similar trend to the experiment result

A Review on Lumped-Kinetic Modelling Methodologies for an industrial FCCU - riser reactor for catalytic cracking

A comprehensive review of scientific literature on various lumped kinetic models used in modelling FluidisedCatalytic Cracking Units (FCCU) used in the petrochemical industry has been done, along with a brief introductionto the working of FCCU. The most popular four lumped kinetic model has been discussed in detail along with themathematical model and then solved using MATLAB. The modified form of the model that considers axialdispersion has also been discussed. The results of the simulation have been plotted and analysed. A brief overviewof three, five, six, seven, nine, and twelve lumped kinetic models has also been discussed.

Development and application of counter‐current feed injection technology in riser reactors

AbstractA counter‐current feed injection scheme is proposed to improve the jet‐solid mixing and reaction in the injection zone of riser reactors. By analyzing the characteristics of the coupled flow field, combined with experiments and numerical simulation, the advantages of the new injection technology are investigated. Experimental results show that the particles distribute more uniformly when the feed is injected downward, which is good for the mixing and reaction of the jet with particles. By simulating the reaction in an industrial fluid catalytic cracking (FCC) riser, it is found that the yields of gasoline and liquefied petroleum gas (LPG) are increased significantly by using the counter‐current feed injection structure. Simultaneously, the formation of coke is reduced considerably. On this basis, a riser‐fluidized bed coupled reactor was designed by adopting the proposed counter‐current feed injection technology to solve the coking problem in an industrial pyridine synthesis system. Results from the side‐stream sampling show that the carbon content of the catalyst reduces significantly, indicating a decrease in coke formation. By now, the improved industrial reactor has been in stable operation for 2 years, showing good reliability.