Multi-tubular Reactor Research Articles

Optimal design and operation of Fischer-Tropsch microchannel reactor for pilot-scale compact Gas-to-Liquid process

Design and operation of pilot-scale (1.0 BDP) compact GTL process comprising of reforming section, CO2 separating section, and Fischer-Tropsch (FT) synthesis section is presented. Detailed systematic computer-aided design procedure adopted to design a modular 0.5 BPD pilot-scale microchannel reactor used in the pilot plant operation is also presented. The modular microchannel FT reactor block design consists of 528 process channels and numerous coolant channels arranged in cross-cocurrent-cross configuration for adequate heat removal. On average 98.27% CH4 conversion to syngas in reforming section comprising of a pre-reformer unit and a tri-reformer unit, and CO2 separation rate of 36.75% along with CO/H2 reduction from 2.67 to 2.08 in CO2 membrane separation section were achieved from the entire pilot plant operation duration of 450 h. Parallel operation of FT microchannel reactor and multitubular fixed-bed type FT reactor for comparison showed that multitubular fixed-bed type reactor undergoes reaction runaway for the applied process conditions, while microchannel reactor showed adequate temperature control. Overall CO conversion of 83% and adequate temperature control at three different applied operating temperatures of 220 °C, 230 °C, and 240 °C subsequently during the 139 h FT reactor operation demonstrated the appreciable performance of the present microchannel FT reactor designed.

Direct synthesis of dimethyl ether in multi-tubular fixed-bed reactors: 2D multi-scale modelling and optimum design

The scope of this work is to explore the viability of the direct synthesis of dimethyl ether (DME) over bifunctional catalysts, such as mixtures of CuO/ZnO/Al2O3 and γ-Al2O3 at industrial scale. To accomplish this purpose, the process is simulated using a phenomenological mathematical model considering momentum, mass and energy balances, applied to both the catalyst particles and reactor bed, which is solved in 2D axisymmetric coordinates. This constitutes a step beyond most of the available studies for the modelling of the DME synthesis reaction, based on simple 1D isothermal models.The use of this detailed model revealed the importance of intraparticle mass and heat transfer, with effectiveness factors within the range 0.5–1.1. At the reactor scale, radial phenomena were found to be relevant. A design-sensitivity analysis of mass flux, catalyst fraction, pressure, feed temperature, cooling potential and tube diameter on the reactor performance was carried out. An optimized reactor design that provides 80% CO conversion operating at inlet temperature and pressure 245 °C and 40 bar, corresponds to 0.02 m diameter, 8.50 m length and 3600 h−1 gas-hourly space velocity with a yield of dimethyl ether of 0.53.

Material selection for multi-tubular fixed bed reactor Fischer-Tropsch reactor

Multi-tubular, fixed bed, Fischer-Tropsch reactor (MFBR) appears as an essential technology for the energy future; moreover it is required to improve and to reduce operation costs. This research used multi-criteria decision making methods (MCDM) for the material selection of a MFBR. It focused on fulfilling the technological requirements for constructing the vessel and piping of a MFBR, while costs reduction is considered as part of the analysis. The MCMD methods are complex proportional assessments of alternatives which apply methods such as grey relations (COPRAS-G), operational competitiveness rating analysis (OCRA), a new additive ratio assessment (ARAS) and technique for order of preference by similarity to ideal solution (TOPSIS). The criteria weighting was performed by compromised weighting method composed of analytic hierarchy process (AHP) and entropy methods. The ranking results showed that ASME SA-106 and ASME SA-106 29 would be the best materials for the vessel and piping of a MFBR.

Methyl-Tert-Butyl-Ether Synthesis Reactor Modelling and Optimization Using an Aspen Custom Modeler

Abstract A pseudo-homogeneous model of methyl-tert-butyl-ether (MTBE) synthesis in a multi-tubular packed-bed reactor has been developed using an Aspen Custom Modeler (ACM) for selecting optimum operating strategies, for the maximization and enhancement of MTBE production, and isobutylene consumption, respectively. The model accounts for mass, energy and momentum balances; and the effectiveness factor is evaluated in a onedimensional pseudo-homogeneous model. The kinetic investigation contains kinetic rate expressions as given by the effectiveness factor for accounting the resistance of pellets in terms of mass and heat transfer. An activity coefficient can be used in order to systematically obtain a new steady-state solution. The model used literature-based correlations for the estimation of heat transfer coefficients. The value of the coefficient for gascoolant heat transfer can be adjusted by using a tuning coefficient in order to enrich the process data. Reasonable agreement was found between model predictions and data under similar conditions. The studies concerning model sensitivity compute the optimum temperature, pressure, feed flow rate, methanol/isobutylene ratio, heat removal rate, etc. of the reactor and suggest optimum operating conditions of the reactor.

Simplified Kinetic Modeling of Propane Aromatization over Ga-ZSM-5 Zeolites: Comparison with Experimental Data

This paper presents new results about experimental tests and kinetic modeling of propane aromatization on a Ga-ZSM-5 zeolite. The presence of gallium as a doping metal promotes dehydrogenation reactions, limiting the formation of side products (cracking fuel gas) and increasing the yield to aromatics. In this study, kinetic tests of propane aromatization at different values of reaction temperature (500, 525, and 550 °C) and contact time (0.07, 0.14, and 0.28 h) are performed in a multi-tubular reactor, aiming at investigating the complex reaction scheme of propane aromatization at a constant pressure (3 bar). Based on the obtained experimental data, a kinetic analysis is performed considering cracking products (methane and ethane/ethylene) and main aromatic compounds (benzene, toluene, xylenes, and ethylbenzene). This simplified approach is found to be a robust tool to predict products distribution when experimental data points are not enough to perform a reliable model parameters estimation. In the speci...

Process Intensification of n‐Butane Oxidation to Maleic Anhydride in a Millistructured Reactor

AbstractThe oxidation of n‐butane to maleic anhydride over an industrial vanadyl pyrophosphate oxide catalyst was investigated experimentally in millistructured reactors with varying slit widths to investigate the process intensification potential of this reaction. Although the smaller reactor behaved isothermally, even in the presence of high n‐butane concentrations, moderate hot spots never exceeding more than 15 K above the salt bath temperature occurred in the larger catalyst channel. After exposure to high n‐butane concentrations, a certain amount of catalyst deactivation was observed, which could be partly restored through reoxidation with pure oxygen. The reactor‐specific maleic anhydride productivities obtained are much larger than those in conventional multitubular reactors.

Supercritical hydrothermal degradation of hazardous organic wastes with a view to utilizing the potential energy of gaseous products

The method of supercritical hydrothermal degradation was applied to neutralize hazardous organic-containing substances and persistent organic pollutants (polychlorinated biphenyls, organochlorine pesticides, wastewater, and agro-industrial waste) in the autothermal and allothermic modes. It has been established that the realizable modes of supercritical hydrothermal oxidation and pyrolysis provide a degree of decomposition of the investigated organic-containing waste not less than 99.5%, accompanied by the formation of a high-enthalpy steam−gas mixture or combustible gases. The possibility of utilization of the potential energy of gaseous reaction products on a specially designed experimental setup with a multi-tubular spiral-type reactor, which is a part of an autonomous energy complex for generating heat and electric power, is examined.

Transient behavior of a multi-tubular cavity solar thermochemical reactor

A three-dimensional transient heat transfer model is presented to predict the start-up operation of a multi-tubular cavity reactor under concentrated irradiation in a solar furnace. The reactor consists of a cavity containing nine absorber tubes, through which a suspension of CeO2 in Argon flows. An iterative splitting scheme coupling a Continuous Random Walk, a Finite Volume, and a Ray-Tracing Monte Carlo methods, is implemented to estimate the temperature gradients in the tubes and gas-particle media. The radiation heat transfer among the tubes and cavity walls is considered, as well as conduction and convection in the tubes and the particle suspension. During the initial heating stage, gradients are mainly angular, while in steady-state they are primarily axial. The former may cause tube bending or cracking, and strategies to reduce them are examined. In particular, different heating ramps were simulated, which was found to reduce these initial thermal gradients.

Techno-economic assessment of an energy self-sufficient process to produce biodiesel under supercritical conditions

This paper presents a conceptual design, simulation and techno-economic assessment of an energy self-sufficient process to produce 10,000t per year of biodiesel using supercritical methanol and propane as cosolvent. A suitable heat-integrated design of the process was performed using a part of the produced biodiesel (7.4wt.%) to achieve the energy self-sufficiency for the plant. The simulations were performed by Aspen Plus considering a continuous multitubular reactor operating at 280°C, 128bar, methanol-to-oil molar ratio of 24, propane-to-methanol molar ratio of 0.05, and a residence time of 9.7min. The use of flash separators instead of distillation columns for methanol and propane separation contribute significantly to reduce the energy requirement, with respect to other studies. Final products are high purity of methyl esters (99.8%) and glycerol (96.4%). The economic analysis of the biodiesel plant resulted in a break-even point for the biodiesel selling price of 0.479€/kg (at 10% rate of return), so the process can compete with the existing alkali and acid catalyzed processes.

Olefina arinen ekoizpena hondakin plastikoetatik

Lan honetan, poliolefinetatik abiatuta, olefinak ekoizteko bi estrategia ezberdin alderatzen dira. Bi kasuetan, lehen etapan, iturri-ohantze konikoko erreaktorean plastikoaren pirolisia egin da. Bigarren etapari dagokionez, bi aukera daude pirolisian sorturiko hegazkorren crackinga egiteko; alde batetik, ohantze finkoan, cracking katalitikoa HZSM-5 zeolita katalizatzaile modura erabiltzea, eta, bestetik, tutu anitzeko erreaktorean tenperatura altuko cracking termikoa erabiltzea.

CFD study on the radial distribution of coolants in the inlet section of rod-baffle-multi-tubular reactor

CFD method was employed to investigate the radial distribution of coolants in the inlet section of rod baffle multi-tubular reactor. It was found that the reactor had poor distribution of coolants. In view of this problem, the detailed structures of incident channel, shape of baffle ring and distance between tube plate and the first rod baffle were discussed to study their effect on the radial distribution. The simulation results showed that incident channels 0#, 1#, 3#, 5# and 6# could improve radial distribution of coolants significantly, and the effect of incident channels 2# and 4# was relatively limited. The zigzag baffle ring was proved to prevent short pass near the shell wall. In addition, the radial distribution of coolants was also improved with distance between tube plate and the first rod baffle increasing from 85 mm to 242mm. The simulation results can provide guidance for designing multi-tubular reactor with rod baffles.

Modeling of a tubular solar reactor for continuous reduction of CeO2: The effect of particle size and loading on radiative heat transfer and conversion

A solar multi-tubular reactor for non-stoichiometric reduction of CeO2 is modeled under continuous operation. An aerosol, consisting on CeO2 particles and Argon, flows upwards through the reactor vertical tubes. Heat, mass and radiation transfer phenomena are efficiently implemented in an axisymmetric domain by using multi-mesh, multi-step, Finite-Volume and Monte Carlo methods. Reaction, particle diffusion, conduction, forced convection as well as radiation absorption, emission and anisotropic scattering are considered. The kinetic model for the non-stoichiometric reduction of CeO2 is taken from Ishida et al. (2014). Model results at steady-state focus on the effect of changing particle loading and diameter at different average residence times. For particle diameters of 1–20μm, increasing particle size favors uniform radiation absorption, minimizing temperature gradients. Finally, for an outer tube surface temperature of 2500K, a particle loading of 0.1kg/m3 and average residence time of 30–60s are recommended.

Derivation of Pareto Optimal Operating Policies Based on Safety Indices for a Catalytic Multi-tubular Reactor Used for Nitrobenzene Hydrogenation

When highly exothermic/hazardous reactions are conducted in the presence of parametric uncertainty, derivation of optimal operating policies for a chemical reactor has to simultaneously consider several objectives of sustainability. The paper uses an original methodology to generate the Pareto optimal solutions when reactor productivity and safety objectives (expressed in probabilistic terms) are simultaneously considered using the process and reactor model in a simple way, in the presence of technological constraints, uncertainty in safety boundaries, and random fluctuations in control variables. An example is provided for the industrial fixed-bed tubular reactor used for the catalytic hydrogenation of nitrobenzene to aniline in vapour-phase.

Novel multi-tubular fixed-bed reactors’ shell structural analysis based on numerical simulation method

In the present contribution, a numerical study of fluid flow and heat transfer performance in a pilot-scale multi-tubular fixed-bed reactor with a novel configuration for propylene-to-acrolein oxidation reaction is presented using a three-dimensional computational fluid dynamics method (CFD) to ensure the uniformity condition using molten salt as a heat carrier medium on shell side. The effects of multiscale structural parameters including the number of baffles, baffles cut, central nontube region and the number of flow channels on pressure drop and heat transfer are considered. The simulations suggest that heat transfer coefficient per pressure drop is reduced with increasing number of baffles. By the single factor sensitivity analysis it was shown that the central region is the key factor in the structural design of a multi-tubular fixed-bed reactor.

Oxidation of methanol to formaldehyde in microchannel reactors: prospects and limitations

Some features of the behavior of highly exothermic selective oxidation processes in a monolith microchannel reactor (MCR) are studied experimentally using the oxidation of methanol to formaldehyde on a Fe–Mo catalyst as an example. The process can be intensified considerably by intensively withdrawing heat from the reaction zone, operating at increased methanol concentrations of up to 12–12.5%, and using catalyst particles smaller than 0.25 mm to increase the useful product yield per unit of catalyst volume by 7–12 times, compared to multitubular reactors. The thermal operating mode of MCRs is close to the optimum theoretical regime for this class of processes, thereby making it easier to achieve high selectivity to formaldehyde. Due to the abovementioned reduction in the activity of Fe–Mo catalyst in MCRs, the prospects for using MCRs in this process must be estimated along with solving the problem of catalyst stability. The use of MCRs appears to be very promising and technologically sound when dealing with catalytic processes whose intensification is not accompanied by an appreciable reduction in activity.

Ceramic counterflow reactor for autothermal dry reforming at high temperatures

Dry reforming (DRM) is a very promising route for producing carbon rich syngas from key future feed stocks of chemical industry: CO2 and methane. Partial combustion of methane with pure oxygen, preferably produced via water electrolysis, can be used to compensate for the required heat of reaction in autothermal operation of DRM. Therefore, a novel reactor concept is presented. The multitubular reactor consists of an inert section to perform efficient heat integration and a catalytically coated reaction section where temperatures far above 1000°C are realized by means of ceramic materials, a suitable catalyst, and simultaneous combustion. A prototype laboratory scale reactor, equilibrium models, and a detailed kinetic model are used to measure the reactor performance in laboratory and in industrial scale. A stable operation is predicted in large scale reactors since constantly high reaction temperatures around 1000°C can prevent harmful coke formation. Besides, the high temperatures enable CO2 conversions above 60% along the catalyst zone in a reactor which is characterized by a very simple and scalable design.

A Heterogeneous Multiscale Dynamic Model for Simulation of Catalytic Reforming Reactors

The present work aims to establish a generic reforming reaction scheme to evaluate the performance of catalytic reforming systems with the aid of a one-dimensional heterogeneous dynamic model. The novelty of the numerical model stems from the direct inclusion of interphase (fluid-to-particle surface), intraparticle (within particle), and intrareactor heat and mass transport resistances under transient conditions. The developed model accounts for the multicomponent gas mixture physicochemical properties and correlations for calculating mass and heat transfer coefficients. Effective macroscopic properties within the particle are calculated by incorporating diffusivities and conductivities of the porous network characteristics accounting for Knudsen and molecular transport as well as tortuosity and porosity of the overall porous path. The industrial case of a steam-methane reforming multitubular reactor was studied as the most representative case of the generic reaction scheme, with all mass/energy resistances present under severe pressure and temperature conditions. It was shown that there are notable diffusional limitations within the particle, whereas there are also temperature and partial pressure gradients due to the heat and mass transport resistances in the particle film layer. It is further demonstrated that the proposed model can be utilized as a versatile design tool for catalytic reactor development and optimization.

Geometric optimization of a solar cubic-cavity multi-tubular thermochemical reactor using a Monte Carlo-finite element radiative transfer model

In the present study, the optimization of a multi-tubular solar thermochemical cavity reactor is carried out. The reactor consists of a cubic cavity made of woven graphite, housing nine 2.54 cm diameter tungsten tubes. A heat transfer model is developed and implemented considering high-temperature radiative transfer at steady state. The temperature distribution on the receiver tubes is determined by using a hybrid Monte Carlo-finite volume approach. The optimization aims at maximizing average tube temperature by varying tube locations. Optimal tube distributions are explored by using a custom-made stochastic, multi-parameter, global optimization algorithm. A considerable increase in average temperature as well as improvement on temperature uniformity is found in the optimized tube arrays. Patterns among the different optimal distributions are found, and general features are discussed.

Modeling-based optimization of a fixed-bed industrial reactor for oxidative dehydrogenation of propane

An industrial scale propylene production via oxidative dehydrogenation of propane (ODHP) in multi-tubular reactors was modeled. Multi-tubular fixed-bed reactor used for ODHP process, employing 10000 of small diameter tubes immersed in a shell through a proper coolant flows. Herein, a theory-based pseudo-homogeneous model to describe the operation of a fixed bed reactor for the ODHP to correspondence olefin over V2O5/γ-Al2O3 catalyst was presented. Steady state one dimensional model has been developed to identify the operation parameters and to describe the propane and oxygen conversions, gas process and coolant temperatures, as well as other parameters affecting the reactor performance such as pressure. Furthermore, the applied model showed that a double-bed multitubular reactor with intermediate air injection scheme was superior to a single-bed design due to the increasing of propylene selectivity while operating under lower oxygen partial pressures resulting in propane conversion of about 37.3%. The optimized length of the reactor needed to reach 100% conversion of the oxygen was theoretically determined. For the single-bed reactor the optimized length of 11.96m including 0.5m of inert section at the entrance region and for the double-bed reactor design the optimized lengths of 5.72m for the first and 7.32m for the second reactor were calculated. Ultimately, the use of a distributed oxygen feed with limited number of injection points indicated a significant improvement on the reactor performance in terms of propane conversion and propylene selectivity. Besides, this concept could overcome the reactor runaway temperature problem and enabled operations at the wider range of conditions to obtain enhanced propylene production in an industrial scale reactor.

Performance Study of a Thermally Double Coupled Multi-Tubular Reactor by Considering the Effect of Flow Type Patterns

Abstract In this study, a steady-state heterogeneous one-dimensional model predicts the performance of a thermally double coupled auto-thermal multi-tubular reactor for simultaneous production of hydrogen, benzene, methanol and dimethyether (DME) in an economical approach for both co- and counter- current modes of operation. Reversed flow of cyclohexane has been considered for the counter-current flow regime. The simulation results for co- and counter-current modes have been investigated and compared with corresponding predictions for conventional methanol reactor and traditional coupled methanol reactor. In addition, various operating parameters along the reactor have been studied. The simulation results present that methanol yield in co- and counter- current modes are reached to 0.3735 and 0.3363 in a thermally double coupled reactor, respectively. Also, results for counter-current mode show a superior performance in hydrogen and benzene production. Finally, the results of simulation illustrate that the coupling of these reactions could be beneficial.