Fluidized Bed Reactor Model Research Articles

Three-dimensional computational fluid-dynamic simulation of polypropylene steam gasification

Among the recycling techniques, gasification allows to obtain a hydrogen-rich gas from polypropylene (PP), a widely used thermoplastic material. In this work, devolatilization and steam gasification tests of PP were conducted in fluidized bed reactors. The results show a gas yield of 1.3 and 3.0 Nm3/kgPP, and a tar content of 117.3 and 20.9 g/Nm3 from devolatilization and gasification, respectively. Experimental results provide an overall overview of this process, able to produce a syngas with an H2-content of 50 vol%dry.Experimental data coupled with kinetic analysis were used to develop a computational fluid dynamic model (CFD) capable of describing both thermal degradation and subsequent gasification reactions. Although some discrepancies on water conversion and H2/CO ratio probably related to the influence of steam in radical chain-scission the model allows to describe gas production and hydrocarbons evolution providing important support for modeling and sizing of fluidized bed reactors on an industrial scale.

Modeling of a catalytic fluidized bed reactor via coupled CFD-DEM with MGM: From intra-particle scale to reactor scale

The Computational Fluid Dynamics - Discrete Element Method (CFD-DEM) method is extended by coupling with the multi-grain model (MGM) to include particle growth due to a gas-solid reaction, as well as intra- and inter-particle phenomena such as heat and mass transfer, and reaction, next to the inter-particle and fluid-particle interactions in the reactor. This comprehensive model treats each particle individually and accounts for changes in particle properties due to both the particle growth and temporal and spatial variations of the process conditions. It also captures the impact of the change in the particles' properties on the fluidized bed reactor characteristics, such as the hydrodynamic regime. The results of the model revealed that the fluidization characteristics and solids mixing can be altered by particle growth. Particle growth also led to the formation of a particle size gradient along the height of the reactor. The coupling allows for monitoring of both external and internal mass transfer limitations. For the adopted reaction kinetics, growth rate and properties the external mass transfer limitations remained negligible, however the internal mass transfer limitation plays a significant role in the process performance.

Fluidized Bed Reactor Modeling and Simulation with Aspen Plus

Fluidized bed reactor is useful for heterogeneous (multiphase) reactions, separations, size enlargement, coating, and blending in chemical and pharmaceuticals industries. To develop a model and simulation of this reactor with advanced systems process engineering software (Aspen Plus). Aspen plus has the capability to simulate real factory performance, design improved plants, and intensify profitability in present plants. This modeling and simulation are applied Geldart B particle classification, GGC is used for particle size distribution function, Newton parameters for mass convergence, and Ergun equation is used for minimum fluidization velocity calculation and pressure drop through the fluidized bed reactor. Generally, most of the predictions model from Aspen plus is a reasonable agreement through the experimental results. Advantage of this investigation is used small quantity of bed particles and identified their melting point temperature is above 340°C. This fluidized bed reactor model and simulation is functional for aluminum hydroxide decomposition reaction. The feed 275 kg/hr of Al(OH)3is converted into 169.6 kg/hr of aluminum oxide (Al2O3) and 89.9 kg/hr of water. A total mass conversion percent is 94.4% of aluminum hydroxide.

A comprehensive assessment of endogenous bubbles properties in fluidized bed reactors via X-ray imaging

Properties of endogenous bubbles released during the devolatilization of a single biomass particle under inert conditions have been investigated by means of advanced X-ray imaging techniques. Distribution of void fraction showed that endogenous bubbles structure resembles that of classic bubbles observed in fluidized bed reactors, constituted by a cloud, wake and a central void region. A value of about 0.25 for the wake fraction has been obtained from experiments, which is in agreement with literature data for Geldart B particles. Volume of cloud region as a function of relative bubble velocity was generally well-described by the theoretical models of Davidson and Murray, showing effective recirculation of volatile matter around the bubble. Moreover, lack of mixing between bubbles and emulsion phase, as predicted by the Davidson's theory for classic bubbles, confirmed the bypass phenomenon observed for endogenous bubbles in previous studies. Owing to the non-invasive nature of the X-ray technique employed, it was possible to estimate the main features of endogenous bubbles with high accuracy. Knowledge provided in this work can be easily implemented to improve modelling of fluidized bed reactors applied to advanced thermochemical conversions, such as gasification and pyrolysis, of biomass and waste materials. • Devolatilization of biomass in fluidized beds generates endogenous bubbles • Advanced X-ray imaging provided comprehensive assessment of endogenous bubbles • Bubbles void fraction distribution is obtained by means of the Beer-Lambert law • Endogenous bubbles consist of a wake, cloud, and central gas-rich region • Endogenous bubbles strongly resemble traditional bubbles in bubbling regime

Numerical simulation and multi-process coupling analysis for biomass pyrolysis fluidized bed reactor based on synergistic effects between biomass and nitrogen inlet modes

Biomass fast pyrolysis fluidized bed reactor is regarded as one of the most promising technologies for high value utilization of biomass. In this work, one two-dimensional fluidized bed reactor model was established, coupling with multiphase CFD simulation method and pyrolysis reaction kinetics, and further verified by the experimental data. This work mainly investigated the effects of biomass inlet and nitrogen inlet modes on multi-process characteristics, such as flow behavior, heat transfer and pyrolysis reaction. The synergistic effects between the two inlet modes were further explored and thus would affect the three-phase pyrolysis product distribution. The results showed that the spatial particle distribution and temperature distribution in the dense phase zone were becoming more uniform and the tar yield increased when the biomass inlet mode changed from single nozzle to double nozzles jetting opposite. Besides, when the nitrogen nozzle number was set as one and the auxiliary gas velocity was set as 0.15 m/s, much larger local circulation formed in the dense phase zone, meanwhile the particle volume fraction and temperature became more evenly distributed, which was conducive to the biomass pyrolysis process. The nitrogen inlet mode was found to show a greater impact on the tar yield compared to the biomass inlet mode. For single gas inlet mode, one biomass nozzle should be preferred for lower auxiliary gas velocity and the opposite double nozzle would be better for higher auxiliary gas velocity. The synergistic effects between biomass and nitrogen inlet modes were further summarized, which were found to have a positive impact on the biomass pyrolysis reaction characteristics. Based on the above conclusions, this work could provide a feasible theoretical guidance for designing fluidized bed pyrolysis reactor and optimizing the biomass pyrolysis process.

Overview of Fluidized Bed Reactor Modeling for Chemical Looping Combustion: Status and Research Needs

Overview of Fluidized Bed Reactor Modeling for Chemical Looping Combustion: Status and Research Needs

Application of Aspen Plus fluidized bed reactor model for chemical Looping of synthesis gas

Chemical Looping Combustion technologies are a recent innovation with a natural ability to capture carbon dioxide. In these processes, two interconnected fluidized bed reactors are employed to achieve oxidation and reduction reactions separately. In the current study, an Aspen Plus simulation uses the specialized Fluidized Bed Reactor block to model a Fuel Reactor in which carbon monoxide and hydrogen react with hematite. This reactor block includes a hydrodynamic model that describes the solid volume fraction, particle size distribution and solids entrainment effects, and a reactor model that employs reaction kinetics for the gas–solid reactions. A comparison is performed with an established Stoichiometric Reactor approach for validation purposes, and results agree closely. Several sensitivity studies are carried out to explore the impacts of process variables on carbon dioxide generation and selected hydrodynamic parameters. For the range of conditions simulated, these studies revealed that solid volume fraction decreases with the height of the bed and with increasing superficial velocity. It is also observed that the height to diameter ratio of the fluidized bed is a key variable in sizing the reactor. Based on an analysis performed on two distributor configurations, a bubble cap is the best option to provide a smaller pressure drop. The results presented in the current work also suggest that the application of the Fluidized Bed Reactor model in Aspen Plus provides additional design insights and is a valuable alternative to the commonly used Stoichiometric Reactor approach.

Application of Aspen Plus Fluidized Bed Reactor Model for Chemical Looping of Synthesis Gas

Application of Aspen Plus Fluidized Bed Reactor Model for Chemical Looping of Synthesis Gas

Design and development of pyrolyser for processing agricultural waste

The design paper focuses on developing a circular quick pyrolysing reactor that normally converts the agricultural biomass into biochar. The uniqueness incorporated in the design criteria is easy to attain high heating potential in the combustion chamber. All the supporting components in the reactor enhance control on temperature that supports even distribution of heat transfer and withholding the volatile organic compound with reasonable residence time. The design specifications are adopted with proper kinetic studies and making of the real time model that can operate 100 kg of biomass in 1 h duration. The fluidized bed reactor models normally have the ability to transfer heat even in low voids and can circulate high solid content within their limits which normally combust the biomass within less vapor residence time. In addition to pyrolyser design the importance of processing the agricultural waste for pollution free environment has been highlighted in this research outcome.

Perovskite oxygen carrier with chemical memory under reversible chemical looping conditions with and without SO2 during reduction

Oxygen carrier materials (OCM) are usually exposed to sulfur-contained gases in the fuel reactor for chemical looping combustion. This work provides both experimental and model work to understand the SO2 effect on the heterogeneous redox kinetics of a CaMn0.375Ti0.5Fe0.125O3-δ-based perovskite oxygen carrier. The cycle reactivity and redox kinetics under reducing conditions were conducted with and without SO2 in a micro-fluidized bed thermogravimetric analysis technology (MFB-TGA). The redox kinetic behaviors were simulated by a bubbling fluidized bed reactor model coupled with a two-stage kinetic model. The SO2 can react with the perovskite to increase the oxygen transfer capacity from 4 wt% to 5 wt%. When the temperature is higher than 1173 K, SO2 has almost no effect on the H2 reduction reactivity, while the oxidation reactivity decreases by 50%, but the oxidation is still fast enough to achieve 4 wt% capacity within 8 s. When the temperature is lower than 1173 K, there is a significant sulfur-poisoning effect during oxidation and reduction. The analyses of XRD, SEM-EDS, and in-situ DRIFTS indicated that most of the absorbed sulfur mainly existed in the sulfate/sulfide shell on the particle surface. The chemical kinetics and physical structure of CaMn0.375Ti0.5Fe0.125O3-δ perovskite can be completely recovered in the absence of SO2, and this perovskite oxygen carrier is chemically memorable and reversible in its solid structure. The fundamental understanding of the sulfur effect on the redox kinetics and solid structure of the perovskite oxygen carrier provides a new insight to the material development and corresponding reaction mechanisms.

Simulation of a sorbent enhanced gasification pilot reactor and validation of reactor model

Sorption enhanced gasification (SEG) is a promising technology for production of a renewable feedstock gas for biofuel synthesis processes. The technology has been previously demonstrated at pilot scale. Scaling of the technology to an industrial size requires knowledge from governing phenomena. One-dimensional bubbling fluidized bed (BFB) reactor model was developed and validated against experimental data from 200kWth dual fluidized bed facility. Sub-models for biomass gasification, reactive bed material and fluidized bed hydrodynamics were incorporated into the model frame. The model gave satisfactory predictions for bed material conversion, temperature profiles and gas composition of the producer gas. The conducted validation improved understanding of bed material conversion, water–gas shift reaction and hydrodynamics and their role in SEG reactors. Further refinement and comprehensive validation of the model with additional data from the pilot is required. The knowledge from the comprehensive validation can be utilized in simulation of an industrial size reactor.

Studies on Solids Flow in a Cold Model of a Dual Fluidized Bed Reactor for Chemical Looping Combustion of Solid Fuels

Abstract The results of investigations on solids flow in a cold model of the dual fluidized bed reactor designed for chemical looping combustion of solid fuels (DFB-CLC-SF) are presented in this paper. The constructed unit consists of two interconnected reactors. The first one, so-called fuel reactor (FR), is operated under bubbling fluidized bed (BFB) conditions, whereas the second one, so-called air reactor (AR), is structurally divided into two sections. The bottom part of AR works under BFB while the upper part, i.e., the riser, is operated in the fast fluidized bed (FFB) regime. In these studies, the air was used for fluidization process in all parts of the DFB-CLC-SF reactor. The glass beads with similar parameters to oxygen carriers (OCs) used in the CLC process were utilized as an inventory. The fluidization conditions are controlled by using the sets of pressure sensors installed around the circulation loop. The experimental data acquired in the tests are further employed to the analysis of solids behavior in a cold model of the DFB-CLC-SF reactor. The main goal of these studies was to establish the conditions for smooth fluidization, which concurrently provide the required residence time of solids in both reactors that is one of the most crucial factors in the CLC process. It was found that the fluidizing gas velocity in reactors has a significant impact on solids behavior and the investigated parameters. However, what is the most important, it was confirmed that the operation condition of the DFB-CLC-SF reactor can be adjusted to meet the requirements resulting from the properties of OCs.

A fluidized-bed model for NiMgW-catalyzed CO2 methanation

The reduction of carbon dioxide to methane by hydrogen (“CO2 methanation”) using renewable energy is a promising process for recycling CO2. Better catalysts and better reactors are both required for the practical application of CO2 methanation. This study examines how the operating parameters affect CO2 methanation in a highly efficient fluidized-bed reactor. We first measured the kinetics of the CO2 methanation reaction using an NiMgW catalyst, which has been reported to exhibit superior catalytic performance. We then developed a fluidized-bed reactor model based on an earlier model for CO2 methanation. The fluidized bed model indicated that the NiMgW was indeed superior to two other previously studied catalysts in terms of faster conversion of reactants and higher concentrations of product CH4 throughout the reactor. The overall rate of production of CH4 increased with temperature and H2/CO2 ratio and decreased as the inlet reactant flow rate, catalyst particle diameter, and catalyst particle sphericity increased.

Hydrodynamic characteristics and model of fluidized bed reactor with immobilised cells on activated carbon for biohydrogen production

A mathematical model of minimum fluidization velocity (Umf) was developed based on the hydrodynamic characteristics of the fluidized bed reactors (FBR) with immobilised cells attached to activated carbon at thermophilic biohydrogen fermentation. The maximum hydrogen productivity rate of 7.8 mmolH2/L.h and hydrogen yield of 2.2 molH2/mol of sugar consumed was obtained when the HRT was shortened from 48 h to 6 h. The presence of the immobilised cells enriched the biomass composition in the FBR from 4.9 to 7.1 g VSS/L and maximum energy generated was 58.7 KJ H2/L.d. The FBR had to be operated at a high Umf of 0.05–0.44 cm/s and a low terminal velocity of 2.11 cm/s to prevent the immobilised cells from washed out from the FBR, hence achieved an adequate fluidization system. A screening of the microbial population by DGGE revealed that the T. thermosaccharolyticum sp. was dominant for all the HRTs, thereby indicating that this bacterium is resilient towards environmental disturbances.

Downer fluidized bed reactor modeling for catalytic propane oxidative dehydrogenation with high propylene selectivity

This study reports a simulation of the catalytic propane oxidative dehydrogenation (PODH) in a circulating fluidized bed downer reactor. A relevant kinetics based on experimental work by the authors (Rostom and de Lasa, 2018), developed in a fluidized CREC Riser Simulator is considered. As well, Computational Particle Fluid Dynamics (CPFD) models featuring either “Particle Clusters” or “Single Particles” flows are implemented. The CPFD results obtained in a 20-m length unit show a 28% propane total conversion and 93% propylene selectivity using the “Single Particle” flow model. However, and once the more rigorous particle cluster flow is accounted for, the propane conversion is reduced significantly to 20%, while the propylene selectivity remains at 94% level. Thus, the obtained results show that, a PODH simulation using CPFD, requires one to account for “Particle Clusters”. This type of comprehensive model is required to establish unambiguously the downer reactor performance and is of critical value for the development of downflow reactors for other catalytic processes.

On the Structure of the Space of States for a Thermal Model of Fluidized-Bed Reactor–Regenerator Units and Control Visualization Principles

A system of differential equations for the dynamics of thermal states in reactor–regenerator units with finely dispersed catalysts is proposed. Special attention is paid to the existence of positive feedback between thermal and chemical processes by two mutually connected channels, such as the temperature and the degree of residual cocking on a catalyst after regeneration. It has been shown that this system of model equations for the thermal dynamics of a reactor–regenerator unit is characterized by the multiplicity of steady states in the space of the mentioned variables. The three-dimensional phase patterns of the system are analyzed, and the bifurcations of steady-state solutions in the parametric region are studied. The problem of operative control based on state space structure visualization algorithms is considered.

Two-stage modeling strategy for industrial fluidized bed reactors in gas-phase ethylene polymerization processes

Fluidized bed reactor is one of the main units in gas-phase ethylene polymerization processes. Due to the complexity in the polymerization kinetics, hydrodynamic behavior and heat transfer, the modeling and simulation have played an important role in the real operations of industrial polymerization reactors. In this paper, a two-stage modeling strategy for industrial fluidized bed reactors in gas-phase ethylene polymerization processes is proposed. The kinetics of polymerization reactions is computed in the first stage based on a comprehensive kinetics model while the hydrodynamic behavior and heat transfer in the industrial fluidized bed reactors are computed in the second stage based on a set of partial differential equations (PDEs). The polymerization kinetics, hydrodynamic behavior and heat transfer are integrated into the modeling and simulation of industrial fluidized bed reactors in gas-phase ethylene polymerization processes.

On concentration polarisation in a fluidized bed membrane reactor for biogas steam reforming: Modelling and experimental validation

The production of pure hydrogen through the steam reforming of biogas in a fluidized bed membrane reactor has been studied. A phenomenological one-dimensional two-phase fluidized bed reactor model accounting for concentration polarisation with a stagnant film model has been developed and used to investigate the system performance. The validation of the model was performed with steam reforming experiments at temperatures ranging from 435 °C up to 535 °C, pressures between 2 and 5 bar and CO2/CH4 ratios up to 0.9. The permeation performance of the ceramic-supported PdAg thin-film membrane was first characterized separately for both pure gas and gas mixtures. Subsequently, the membrane was immersed into a fluidized bed containing Rh supported on alumina particles and the reactor performance, viz. the methane conversion, hydrogen recovery and hydrogen purity, was evaluated under biogas steam reforming conditions. The resulting hydrogen purity under biogas steam reforming conditions was up to 99.8%. The model results were in very good agreement with the experimental results, when assuming a thickness of the stagnant mass transfer boundary layer around the membrane equal to 0.54 cm. It is shown that the effects of concentration polarisation in a fluidized bed membrane reactor can be well described with the implementation of a film layer description in the two-phase model.

Sorption enhanced steam methane reforming on catalyst-sorbent bifunctional particles: A CFD fluidized bed reactor model

Sorption Enhanced Steam Methane Reforming (SE-SMR) has been proposed as an efficient novel technology to increase hydrogen yield and reduce the environmental footprint in comparison to state of art H2 production processes. Sorbent/catalyst materials characterized by stable behaviour over multiple reforming/calcination cycles may ensure to achieve almost stationary operating conditions utilizing a dual fluidized bed system (the reformer and the sorbent regenerator) with a solid circulation loop. Bifunctional, Combined Sorbent-Catalyst Materials (CSCM) are under development to integrate endothermic catalytic reforming and heterogeneous CO2 sorption in one particle, decrease mass and heat transfer resistances and reduce the solid hold-up in the reactors.This paper deals with the numerical simulation of a pilot scale bubbling fluidized bed SE-SMR reactor by means of a Two-Dimensional Computational Fluid-Dynamic (2D CFD) approach. The hydrodynamic picture is supplemented with a comprehensive Particle Grain Model (PGM) previously developed to describe the kinetics of catalytic and sorption functions, and successfully validated with micro-reactor reactivity tests and multi-cycle thermo-gravimetric sorption tests. The effect of repeated carbonation-calcination steps (the “history” of the granular material) is included in the computation of the reactor performance by utilizing the appropriate size of the sorbent grains in the carbonation rate expression.The numerical results show quantitatively the positive influence of carbon dioxide sorption on the reforming process, at different operating conditions, specifically the enhancement of hydrogen yield and reduction of methane residual concentration in the reactor outlet stream. A preliminary validation of CFD simulations is also carried out utilizing experimental data obtained from a pilot scale bubbling fluidized bed SE-SMR reactor (total bed mass≈14kg).An estimate is provided for the inward heat flow that would be required to operate the reactor in stationary temperature conditions: it is substantially reduced by the exothermic sorption process and could be satisfied by means of the solid circulation loop connecting the SE-SMR reactor to the high temperature calciner in the whole dual fluidized bed system.

On the development of a polyolefin gasification modelling approach

Gasification is a promising alternative for polymeric waste valorization when mechanical recycling is unfeasible on account of its heterogeneity or partial contamination, or simply when it yields a product of lower quality than what the market requires. Apart from its application for electricity generation, the waste-derived syngas shows a great potential for chemical waste recycling for the synthesis of hydrogen, methane, natural gas or methanol. In spite of the effort devoted so far to the experimental demonstration of these processes to enable this technology to access commercial stage, it is still necessary to develop detailed models of the process that allow a precise prediction of the resulting syngas composition, as well as tar formation and global efficiency of the process. This research work presents the development of a polyolefin gasification model for fluidized bed reactors. The model details the behaviour of primary pyrolysis and homogeneous reactions of oxidation, steam reforming, aromatization and thermal cracking. To accomplish this, it adopts new modelling strategies for the definition of primary tar species in order to reflect their twofold nature (aliphatic and aromatic), as well as to describe kinetics and stoichiometry involved in thermal cracking processes of tar species. The model is able to successfully predict the generation, volume composition and heating value of the syngas, final tar generation and global efficiency of the process.