Fluidized-bed Catalytic Cracking Unit Research Articles

CREC Optical-Fibre Sensors for Hydrodynamic Studies in Gas−Solid Fluidized Beds

Optical probes can be employed in dense and dilute fluidized beds. Their application is useful to determine particle volume fraction, bubble velocity, bubble size, and solid segregation in dense-phase fluidized-bed reactors, as well as particle-cluster velocity, size, and shape, in downer/riser units. The CREC-UWO team has developed a unique and miniaturized CREC Optiprobes System (CREC-GS-OPS) equipped with a GRIN (graded refraction index) lens. The GRIN lens creates a small volume of high light irradiation by focusing a laser a few millimetres away from the front of the probe tip. This design minimizes sensor intrusiveness and, as a result, provides trustworthy measurements of hydrodynamic parameters. Through the application of the CREC-GS-OPS, advances have been achieved, leading to (a) the development of a “Y-back” unit with graphite ferrules that protects the optiprobes from fibre-optic stresses and prevents the loss of sensor calibration and (b) the establishment of statistically-based data analysis. It is envisioned that through the introduction of a few design changes, the CREC Optiprobes will be made suitable for high-temperature applications. This will allow the measurement of catalyst flow recirculation (among other measurements), in industrial-scale fluidized-bed catalytic cracking units involving fluidized riser crackers and catalyst regenerators.

Investigation and Control of Fluidized Bed Catalytic Cracking Unit

The fluidized catalytic cracking (FCC) unit is one the main unit of the oil refinery, its objective is upgraded heavy low value petroleum streams into higher value products, mainly gasoline and olefin. In this process the catalyst is circulated into the regenerator, the coke is burned, and the catalyst is regenerated. Many parameters are used to control FCC, the most importantare temperature, which should be kept at (505? C ) and the catalyst temperature (655? C). Other parameters are the level and flow rate of the catalyst. In this work, control strategy was build and the transfer functions were detected, so, the characteristic equations were calculated as well as the open- loop transfer functions. Tuning, stability analysis and simulation response of the system were achieved by using Routh, direct substitution, RootLocus and bode methods

Investigation and Control of Fluidized Bed Catalytic Cracking Unit

The fluidized catalytic cracking (FCC) unit is one of the main units of the oil refinery, its objective is to upgrade heavy low-value petroleum streams into higher-value products, mainly gasoline and olefin. In this process the catalyst is circulated into the regenerator, the coke is burned, and the catalyst is regenerated. Many parameters are used to control FCC, the most important is temperature, which should be kept at (505C ) and the catalyst temperature (655 C). Other parameters are the level and flow rate of the catalyst. In this work, a control strategy was built and the transfer functions were detected, so, the characteristic equations were calculated as well as the open-loop transfer functions. Tuning, stability analysis and simulation response of the system were achieved by using Routh, direct substitution, RootLocus and bode methods

Natural and Activated Allophane Catalytic Activity Based on the Microactivity Test in Astm Norm 3907/D3907M-2019

The optimal conditions of the catalytic activation of allophane were evaluated for possible use as a catalyst within a fluidized bed catalytic cracking unit (FCC). The physicochemical properties of natural allophane and activated allophane were studied by using an alkaline activating agent, followed by a hydrothermal treatment. For the characterization, analytical techniques were used: Fourier transform infrared spectroscopy, particle size, (BET) surface area, thermogravimetry (TGA), X-ray diffraction (XRD), chemisorption, X-ray fluorescence (XRF), atomic force microscopy (AFM), and chromatography. The catalytic evaluation was determined by the (MAT) micro activity test equipment constructed according to ASTM D-3907/D3907M-2019. In addition, the Navier–Stokes 3D equations (nonlinear partial derivatives) were studied, which allow studying molecular dynamics contributing substantively to chemical kinetics describing the process of decomposition of crude oil in thermal cracking, determining the maximum temperature at which it retains its properties through the action of heat.

A twin-fluid injector for FCC feed injection

In Fluidized Bed Catalytic Cracking (FCC) process, hydrocarbon feed undergoes vapour phase cracking in presence of hot regenerated catalyst to produce valuable products like LPG, Gasoline and Diesel. FCC feed injection system is most critical hardware component of FCC unit in order to get desired product yield by minimizing the undesirable dry gas and coke yield. Typically, twin-fluid nozzles (hydrocarbon and stream) are used to atomize the feed. In the present study, a twin-fluid injector, with an internal impactor to minimize the droplet size and velocity, is designed, developed and characterized. The performance of the feeding injector was evaluated using water and air as operating fluids and the droplet size and velocity were measured 150 mm downstream of the injector tip using a PDPA system for different water and air flow rates. The average droplet size (D32) showed an increase while the droplet velocity remained almost constant with the increase in the liquid flow rate for a given flow rate of air, consistent with the increase in droplet size with decreasing air-liquid ratio for twin–fluid atomizers. But, for a given liquid flow rate, the droplet SMD decreased and the droplet velocity increased with increasing airflow rate, which can be attributed to the increase in overall kinetic energy due to the increase in air flow rate. The flow rate of liquid was seen to be independent of air flow rate unlike conventional twin-fluid atomizers. The droplet size was found to be a function of ALR and the local volume flux of the droplets was found to be a function of the liquid flow rate.

Mixed stochastic-deterministic tube MPC for offset-free tracking in the presence of plant-model mismatch

This paper presents a stochastic-tube model predictive control (MPC) strategy that systematically handles plant-model mismatch, guarantees stability in the presence of changing operating conditions, and ensures offset-free tracking for all reachable operating conditions. The key notion of this work is to separate the system uncertainty into two distinct sources of additive bounded state error. The first source is a non-random uncertainty that represents mismatch between the linear model of the controller and the true plant (as well as other types of persistent disturbances). The second source represents random fluctuations due to either the intrinsic stochastic variability of the system, or exogenous disturbances. Recursive feasibility and stability of the stochastic-tube MPC strategy is guaranteed by defining the terminal invariant set to include the effect of changes in the steady-state operating conditions. Offset-free tracking is achieved with a disturbance estimator that can be tuned independently of the controller. To reduce the conservatism inherent to robust control performance, a new filter model for deterministic disturbances is proposed that predicts uncertainty in the future evolution of the disturbances based on a bound on how quickly the plant-model mismatch can vary. The stochastic-tube MPC strategy is demonstrated on two simulation case studies—a benchmark DC-DC converter and an industrially-motivated fluidized-bed catalytic cracking unit.

Indoor/Outdoor Relationships and Anthropogenic Elemental Signatures in Airborne PM2.5 at a High School: Impacts of Petroleum Refining Emissions on Lanthanoid Enrichment.

Outdoor emissions of primary fine particles and their contributions to indoor air quality deterioration were examined by collecting PM2.5 inside and outside a mechanically ventilated high school in the ultraindustrialized ship channel region of Houston, TX over a 2-month period. By characterizing 47 elements including lanthanoids (rare earth elements), using inductively coupled plasma-mass spectrometry, we captured indoor signatures of outdoor episodic emissions arising from nonroutine operations of petroleum refinery fluidized-bed catalytic cracking units. Average indoor-to-outdoor (I/O) abundance ratios for the majority of elements were close to unity providing evidence that indoor metal-bearing PM2.5 had predominantly outdoor origins. Only Co had an I/O abundance ratio >1 but its indoor sources could not be explicitly identified. La and 17 other elements (Na, K, V, Ni, Co, Cu, Zn, Ga, As, Se, Mo, Cd, Sn, Sb, Ba, W, and Pb), including air toxics were enriched relative to the local soil both in indoor and outdoor PM2.5 demonstrating their noncrustal origins. Several lines of evidence including receptor modeling, lanthanoid ratios, and La-Ce-Sm ternary diagrams pointed to petroleum refineries as being largely responsible for enhanced La and total lanthanoid concentrations in the majority of paired indoor and outdoor PM2.5.

Structural and morphological evolutions of spent FCC catalyst pellets toward NaA zeolite

Spherically shaped pellets, usually discarded after use in fluidized-bed catalytic cracking units (FCCs), were converted to zeolite A-surface-enriched pellets. The final pellets were obtained through a two-step treatment consisting of: (1) alkaline thermal activation followed by (2) a hydrothermal crystallization in selected reaction conditions. The alkaline thermal activation provided pellets mainly constituted by silico-aluminate compounds. When the pellets are heated at 800 °C in contact with sodium carbonate, a structural rearrangement occurs which includes nepheline, crystalline aluminosilicate, and an amorphous fraction expected to be silicon-enriched, preserving the pellet original geometry. Afterward, reaction mixtures were prepared by adding sodium hydroxide solution to the heat-treated product. Then, commercial sodium aluminate was added. During the hydrothermal synthesis at 85 ± 3 °C, zeolite A was formed from the calcined product and NaAlSiO4 turned out to be an intermediary crystalline compound. The LTA crystals were already observed for a reaction time of 0.5 h, but the highest conversion to pure zeolite A was reached after 6 h. Those final round solid pellets showed an external surface fully covered by well anchored zeolite A cubic crystals about 1–2 μm in size. Such materials may be very useful in ion exchange, molecular sieving, and adsorption processes. The crystalline ordering was followed by XRD, SEM, NMR, and water adsorption.

Removal and cementitious immobilization of heavy metals: chromium capture by zeolite-hybridized materials obtained from spent fluid cracking catalysts

An alternative for the reutilization of spent catalyst industrial residue for removal and immobilization of heavy metals is presented. A solid containing about 80% (w/w) of NaA zeolite was hydrothermally synthesized by reconversion of a spent catalyst discarded from a fluidized-bed catalytic cracking unit (FCC). The obtained material (ZFCC) was afterwards used for Cr(III) removal from aqueous solutions. Chromium cation was incorporated in the zeolitized structure by ionic exchange in liquid media, and the exchange level was determined by atomic absorption spectrometry. To analyze the viability of final disposal for the chromium sludge obtained using this methodology (Cr-ZFCC), cement mortars containing Cr-ZFCC in variable percentages were prepared and their mechanical and metal retention properties were evaluated. Mechanical strengths and drying shrinkage shown by mortars containing not more than Cr-ZFCC 5% (w/w) were similar to those corresponding to control mortars without zeolitic additions. Leaching tests indicated that mortars with Cr-ZFCC 5% (w/w) produce an effective immobilization of Cr(III) and should be considered as a viable alternative for safe chromium disposal.

The fluidized-bed catalytic cracking unit building its future environment

Fluidized-bed catalytic cracking (FCC) has been considered as one of the largest catalytic process in the world. FCC is the name for a complex process unit that cracks long molecules from gas oils and residua into added value shorter fuel compounds; additionally, this process can be used to produce important petrochemical precursors, such as propylenes. Although historically FCC has been used to optimise production of light cycle oils, gasoline and olefins, nowadays is convenient to revisit its mission. In order to integrate FCC process inside current development and environment respect, it is necessary to see it as a very flexible process. This flexibility will require deeper knowledge about environmental impact of process operation and production objectives, transport phenomena and catalytic reactions taking place inside the riser, the main reactor of the FCC converter, and energy balance integrating energy recovered/generated in the regenerator. This work is devoted to briefly review some propositions about the use of FCC converters and how these aspects demand knowledge of riser reactors, change in the methodology to estimate effective reaction rates (consequence of variation of kinetic and transport phenomena, at catalyst scale and along the riser) and catalyst activity, as well as control actions and its effect on the energy balance of the converter; operation and environmental concerns surrounding this process are addressed. Finally, it tries to draw attention on some facts that need to be analysed in order to ensure the sustainable development of this important process in the short future.

Design of Controllers for a Fluidized Catalytic Cracking Process

Fluidized-bed catalytic cracking (FCC) units, are one of the most complex and interactive processes in the refining industry, hence they are difficult to operate and to control; on the other hand they are one of the main producers of gasoline, which is an incentive to improve operation policies. Control of the FCC has been and continues to be a challenging and important problem. A control system is composed of several interacting control loops. The number of feasible alternative configurations of control loops is very large. Multiloop control systems are often used for industrial multivariable processes because of their simplicity. Relative gain array is used to minimize the interaction and to select the variable pairings. This work is concerned with the design of multivariable feedback control configurations for FCC units. Sufficient conditions to achieve regulation in terms of the steady-state gain matrix are provided, allowing to obtain a systematic procedure for analyzing multiloop control configurations of complex and interacting processes. Numerical simulations on a dynamical model based on a FCC unit operating in the partial-combustion mode are used to show the effectiveness of several control configurations under disturbances.

Robust Gold-Decorated Silica−Titania Pebbles for Low-Temperature CO Catalytic Oxidation

A deposition-precipitation (DP) process was used to prepare silica-titania core-shell pebbles decorated with nanocrystalline gold suitable for low-temperature catalytic oxidation of carbon monoxide (CO). The microstructure, phase content, crystallography, and catalytic activity were correlated with the pH (3-8), aging time (15, 30, 60 min), and heat treatment employed for gold crystallization (200-400 degrees C). A homogeneous metal distribution, high gold loading (3.7-4.4 wt %), and superior interfacial adhesion between gold and titania were obtained when the support pebbles were prepared at 600 degrees C, a temperature lower than that required for the anatase-to-rutile transformation. Nucleation and growth of {111} faceted gold was favored at mid-pH (6.4-8), while smaller crystals (<7.5 nm) were obtained at short aging times (<or=60 min) and low growth temperatures (<or=300 degrees C). Catalytic activity was optimized by homogeneously dispersing gold nanocrystals (3 nm) using pH 6.4 and an aging time of 30 min. These robust materials may offer superior activity and lifetimes when deployed in fluidized bed catalytic cracking units.

Multi-objective optimization of an industrial fluidized-bed catalytic cracking unit (FCCU) using two jumping gene adaptations of simulated annealing

Multi-objective optimization of industrial chemical engineering operations using simulated annealing (SA), genetic algorithm (GA) and their adaptations often requires large amounts of computational (CPU) time. Any adaptation to speed up the solution procedure is, thus, desirable. The performance of the evolutionary technique, multi-objective simulated annealing (MOSA), is found to improve by the use of two adaptations, MOSA-JG and MOSA-aJG, inspired by the concept of jumping genes (JG) in biology. This is because of the increase in diversity. These adaptations are similar to those used with NSGA-II [Kasat, R. B., & Gupta, S. K. (2003). Multiobjective optimization of an industrial fluidized-bed catalytic cracking unit (FCCU) using genetic algorithm with the jumping genes operator. Computers & Chemical Engineering, 27, 1785]. Optimization of three benchmark problems and two computationally intensive, real-life, two- and three-objective problems [Kasat, R. B., Kunzru, D., Saraf, D. N., & Gupta, S. K. (2002). Multiobjective optimization of industrial FCC units using elitist nondominated sorting genetic algorithm. Industrial & Engineering Chemistry Research, 41, 4765] for an industrial FCCU, are studied. The aJG adaptation of MOSA leads to non-dominated optimal solutions having a good spacing and reasonable maximum spread of the non-dominated solutions. These adaptations can prove to be of considerable value for solving other computationally intensive problems in chemical engineering.

Multi-objective optimization of an industrial fluidized-bed catalytic cracking unit (FCCU) using genetic algorithm (GA) with the jumping genes operator

The multi-objective optimization of industrial operations using genetic algorithm and its variants, often requires inordinately large amounts of computational (CPU) time. Any adaptation to speed up the solution procedure is, thus, desirable. An adaptation is developed in this study that is inspired from natural genetics. It is based on the concept of jumping genes (JG; transposons). The binary-coded elitist non-dominated sorting genetic algorithm (NSGA-II) is adapted, and the new code, NSGA-II-JG, is used to obtain solutions for the multi-objective optimization of an industrial fluidized-bed catalytic cracking unit (FCCU). This unit is associated with a complex model that is highly compute-intense. The CPU time required for this problem is found to reduce fivefold when NSGA-II-JG is used, as compared to when NSGA-II is used. Solutions of similar two-objective optimization problems for the FCCU are compared. NSGA-II-JG also gives improved convergence characteristics and spread of the optimal Pareto points for two simpler multi-objective optimization problems studied here. Indeed, in one problem, where several optimal Pareto fronts exist, the new code gives the correct, global optimal Pareto set, while the original code (binary-coded NSGA-II) converges to local Paretos. The JG operator is associated with some kind of macro–macro-mutation and introduces higher exploratory capabilities, counteracting the effect of elitism in NSGA-II. We, thus, have a better algorithm incorporating the advantages of elitism. This adaptation can prove to be of considerable value for solving other compute-intense problems in chemical engineering.

Multiobjective Optimization of Industrial FCC Units Using Elitist Nondominated Sorting Genetic Algorithm

This study provides insights into the optimal operation of the fluidized-bed catalytic cracking unit (FCCU). A five-lump model is used to characterize the feed and the products. The model is tuned using industrial data. The elitist nondominated sorting genetic algorithm (NSGA-II) is used to solve a three-objective function optimization problem. The objective functions used are maximization of the gasoline yield, minimization of the air flow rate, and minimization of the percent CO in the flue gas using a fixed feed (gas oil) flow rate. The decision variables and several important state variables corresponding to the optimal conditions of operation are obtained. The optimal solutions correspond to the unstable, saddle-kind, middle steady states. The procedure used is quite general and can be applied to other industrial FCCUs. The optimal results obtained here provide physical insights that can help one in obtaining and interpreting such solutions.

A novel non-intrusive probe of particle motion and gas generation in the feed injection zone of the feed riser of a fluidized bed catalytic cracking unit

The random impact of particles with diameters less than 500 μm at the wall of a gas fluidized bed or transfer line is a frequency independent “white noise” excitation source, for frequencies below 50 kHz, of the wall vibrational energy. In previous papers it has been demonstrated that the average acceleration power spectrum over the wall of a laboratory fluidized bed generated by such an “Acoustic Shot Noise” (ASN) source can supply the first quantitative data on the average mean squared particle fluctuation velocity, or granular temperature, T*, at the wall as a function of superficial gas velocity and particle diameter. In this paper we present and analyze the first experimental data on ASN excitation of the wall of 14 transfer lines with inner diameters ranging from 2–9 ft, carrying 10–80 tons of catalyst and coke particles per minute. Our focus is the first data on the particle normal velocity and density, derived from this data, along the wall of a Fluid Bed Catalytic Cracking Unit (FCCU) where gas generated by thermal and catalytic cracking of injected heavy oil at one location is the dominant source of particle motion along the entire transfer line. Simultaneous RMS acceleration measurements of the wall vibrational energy produced by acoustic shot noise are presented along the length of such “feed risers”, with inner diameters ranging from 12 to 68 in., before and after feed injection on four FCCUs converting 15 to 110 kbbl of heavy oil per day into lighter fractions that are appropriate for gasoline production. The data includes measurements of significant changes in the RMS acceleration along the feed riser on the same unit that result from changes in significant process variables. The field data demonstrates the power of the acoustic shot noise probe to detect changes in the chemistry and physics of gas generation and particle motion in the feed injection zone of a fluidized bed catalytic cracking unit, The direct acoustic shot noise data is a unique measure of the particle normal velocity and density at the wall. Estimates of the axial velocity and mean density of the particles are readily derived from this data using heuristic models. Both sets of data can serve as unique and critical boundary condition for validating computer flow codes, numerical simulations, and fundamental two phase theories of particle motion and density at the wall of such transfer lines which are major components of such significant processes as the catalytic cracking of oil into gasoline or fluidized bed coal combustion.

Dynamic modeling of catalyst consumption in catalytic cracking

This article proposes a mathematical model of catalyst consumption in fluidized-bed catalytic cracking units which have dust collection equipment that continuously return the catalysts to the process. The equilibrium characteristics of the fluidized system and the dust collection system is influenced by the following factors: the rate of increase of the amount of fine fractions as a result of abrasion of the large particles, the rate of entrainment of solid particles from the bed to the cyclone zone, and the efficiency of collection of the fine fractions. The most important parameters of the equilibrium are the particle size distribution of the catalyst in the system and the rate of loss of mass from the system. It is concluded that the described mathematical model gives a sufficiently correct description of the interrelation among the basic parameters of the solid phase that influence the catalyst consumption in fluidized-bed systems, and that the model can be used in practical calculations.