Multi-tubular Fixed Bed Reactor Research Articles

One-stage ethanol to butadiene process: Analysis and design of a multi-tubular fixed bed reactor

The paper develops a design feasibility study of a multi-tubular polytropic fixed bed reactor for the one-stage ethanol to 1,3-butadiene (ETB) process employing a modified MgO-SiO2 catalyst. The analysis quantifies the effect of the internal diffusion on scaling up the catalyst activity and selectivity by considering a complex chemistry of seven parallel/series reactions described by detailed kinetic modelling. The efficient numerical solution takes advantage from the MATLAB™ function bvp5c. The simulation model allows scanning the catalytic process by profiles of species’ concentrations, reaction rates and effectiveness factors, inside the catalyst particle and over the reactor. The butadiene yield is controlled by the accumulation in particle of ethanol and key intermediates, as acetaldehyde and crotonaldehyde, related to internal chemical reaction with diffusion and external mass and heat transport rates. The catalyst performance depends significantly on the pellet size that becomes optimization variable for catalyst selection and reactor design. Catalyst particles in the range 2 to 3 mm with tubes of to 25 to 40 mm diameters are the most efficient for achieving 80% butadiene carbon selectivity suitable for an industrial process. The modelling approach is generic for calculating the catalyst effectiveness and designing catalytic chemical reactors involving complex reactions.

Carbon dioxide conversion via reverse water-gas shift reaction: Reactor design

The reverse water gas shift (RWGS) reaction converts carbon dioxide (CO2) and hydrogen (H2) to syngas, which is used to produce various high-added-value chemicals. This process has attracted great interest from researchers as a way of mitigating the potential environmental impacts of this greenhouse gas, with emphasis on global warming. This work aims to model and simulate an industrial catalytic reactor using kinetic data for the RWGS reaction. The simulation was carried out in Aspen Plus® v10. The thermodynamic analysis showed that the appropriate conditions for the reaction are feed molar ratio (H2/CO2) of 0.8:1, 750 °C, and 20 bar. The RWGS process proceeds in a multi-tubular fixed bed reactor with 36.26% CO2 conversion and 96.41% CO selectivity, at residence times in the order of 2.7 s. These results are at near-equilibrium CO2 conversion with higher CO selectivity.

Effect of multilayered catalytic bed on temperature profiles and catalytic performance for Fischer–Tropsch synthesis over Co/Al2O3 catalyst in a multitubular fixed-bed reactor

Fischer-Tropsch synthesis (FTS) is a widely recognized process that catalytically converts syngas into higher hydrocarbons and oxygenates, which are ultimately upgraded into transportation fuels and chemicals. Effective temperature control and heat dissipation are crucial considerations due to the exothermic nature of the FT reaction. Underutilization of the catalytic bed is another challenge in fixed-bed reactors. The implementation of a multilayered catalytic bed, with the catalytic activity in an ascending order, has shown positive effects in addressing these issues. It mitigates adiabatic temperature rise, reduces the maximum reactor temperature, and minimizes catalyst deactivation at high temperatures. Moreover, this multilayered bed effectively addresses the underutilization issue by ensuring optimal utilization of the entire bed as the catalytic activity transitions from one layer to another during the reaction. Layers with a higher cobalt loading remain active until the completion of the reaction, resulting in minimal fluctuations in CO conversion. To achieve uniform temperature profiles, catalytic activities, and product distributions in all reactor tubes in a multitubular reactor, it is imperative to maintain consistent reaction conditions, utilize the same catalyst loading in all tubes, employ an appropriate heating system, and implement an efficient cooling system to dissipate the heat generated by the exothermic reaction. Furthermore, investigations into the properties of the used catalysts after the reaction indicate that catalyst deactivation primarily occurs due to the deposition of FT products on the catalyst surface and pores and blockage of active cobalt sites, and sintering of cobalt particles.

Flexible operations of a multi-tubular reactor for methanol synthesis from biogas exploiting green hydrogen

The present modelling work studies the steady state and transient performances of a multi–tubular fixed bed reactor for methanol production from biogas. The modelled system comprises a methanol synthesis reactor, a flash unit, and accounts for the unconverted gas recycle. The novel concept herein proposed and assessed is the possibility to run a multi–tubular methanol synthesis reactor flexibly, i.e., using the carbon dioxide present in biogas, together with renewable H2, to increase methanol productivity, only when this is economically convenient. Accordingly, the methanol synthesis multi–tubular reactor under study is run in two operating conditions: when the cost of green hydrogen is high, the excess of CO2 present in biogas is vented and the reactor is fed with CO2-lean syngas only; conversely, in the presence of affordable renewable H2, CO2 and green H2 are cofed to the reactor. This study focuses in particular on the impacts of the two working conditions on the methanol productivity, as well as on temperature profiles and transient behaviour of the reactor. The effects of tube length and number are also simulated. The study shows that the multi–tubular reactor design well manages both operating conditions and that the steady-state conditions can be reached in a few hours after the switch from one condition to the other. In view of a small scale process, simulations show that it is better to reduce the tube number rather than their length, as the latter choice would lead to unacceptable temperature hotspots, due to a worsening of convective heat transfer.

Design and fabrication of a multi-tubular fixed bed reactor for acetone production as a pilot plant model for chemical engineering training in developing nations

In this work, the design and fabrication of a pilot-scale multi-tubular fixed bed reactor have been carried out with the aid of computational software (MATLAB R2010b), aiming to process 6.5 L/h of isopropanol to acetone using non-adiabatic thermal conditions. The reactor fabricated would serve as a demonstration rig to enhance research practice, teaching, and learning processes in Advanced Reactor Analysis. The acetone production studied involves four stages, which are simultaneous vaporization and dehydrogenation, condensation, and storage. In the simultaneous vaporization and dehydrogenation, isopropanol is heated to 473 K indirectly to change the phase of raw material from liquid to vapor. In comparison, isopropanol is dehydrogenated to be acetone and hydrogen with 50 % conversion using Cu/SiO2 composite as a catalyst in the multi-tubular fixed bed reactor at 473 K and 1 bar. Condensation occurs when an ice bath cools down the vapor product to liquid. Hence, the condensed product is tested for acetone, and the overall cost analysis for the whole process iscalculated. The design can be a model for other chemical engineering schools to fabricate a locally made reactorfor the training and re-training of chemical engineers, especially in developing nations.

Model Analysis of the Effects of Active Phase Distribution at the Pellet Scale in Catalytic Reactors for the Direct Dimethyl Ether Synthesis

The direct synthesis of dimethyl ether (DME) from syngas is an exothermic process, which requires two different catalyst functions in the same reactor: methanol (MeOH) synthesis and dehydration to DME. The two functions can be intimately mixed in hybrid pellets, located on separated pellets or coupled in core@shell-engineered pellets. In this work, a multitubular fixed-bed reactor, loaded with the catalyst configurations mentioned above, has been investigated by mathematical modeling. It is shown that the different spatial distribution of the active phases has a drastic impact on reactor performance. Using the mechanical mixture of separated pellets, the DME yield is hindered by intraparticle diffusion limitations. The hybrid catalyst, minimizing the diffusion length between methanol synthesis and dehydration catalyst functions, provides better DME yield performances but higher hotspot temperatures and can suffer from deactivation issues due to the detrimental interaction between the two catalytic functions. The MeOH@DME configuration, which allows for a limited contact between the catalyst active phases, guarantees DME yields comparable to those of hybrid pellets while moderating the hotspot temperature.

Trimetallic Au-Cu-La/AC for Acetylene Hydrochlorination in a Multi-Tubular Fixed Bed Reactor

The metal chloride of LaCl3 was chosen to modify the Au-Cu/AC to decrease the noble metal of gold and enhance the catalytic performances. Then a mercury-free catalyst of Au-Cu-La/AC was prepared by the impregnation method, and the fresh Au-Cu-La/AC and Au-Cu/AC catalysts were also characterized in comparison. The catalytic performances of mercury-free catalysts for acetylene hydrochlorination were carried out for 3500 hours in a multi-tubular fixed bed reactor. The additives of La can make the active species dispersed well and retard the aggregation of particles. And the acetylene conversion rate remained stable over 98.5% with the fluctuations, less than 1%, and the selectivity of vinyl chloride maintained the stability of 99% or higher, which indicated that the mercury-free catalyst has excellent catalytic performances for acetylene hydrochlorination.

Use of a micro-porous membrane multi-tubular fixed-bed reactor for tri-reforming of methane to syngas: CO2, H2O or O2 side-feeding

A one-dimensional heterogeneous model for four configurations of a reactor, three micro-porous membrane reactors with O2 (O-MMTR), CO2 (C-MMTR) or H2O (H-MMTR) side-feeding strategy and one traditional reactor (i.e., multi-tubular fixed-bed reactor (MTR)), was developed to explain tri-reforming of methane to produce syngas. Effect of various side-feeding strategies on reactor performance containing CH4 and CO2 conversion, H2/CO ratio, and H2 yield was investigated under the same condition and then described by chemical species and temperature profiles. It was found that use of side-feeding strategies could be feasible, beneficial, and flexible in terms of change in membrane thickness and shell-side pressure for syngas production with H2/CO = 2 which is proper for methanol and Fischer-Tropsch process, and = 1.2 which is suitable for DME direct synthesis. However, the syngas produced by the MTR is only appropriate for the methanol and Fischer-Tropsch synthesis under the base case conditions. Also, the results show that the micro-porous membrane reactors have higher CO2 conversion, based on the H2/CO = 1.2; so these strategies are more environmentally friendly compared to the traditional reactor.

Detailed geometrical analysis of statistical activity variations in diluted catalyst beds

In multitubular fixed bed reactors for heterogeneously catalyzed, highly exothermic gas phase reactions the catalyst bed is usually diluted with inert particles for improving the heat management. To help balancing the heat generation and heat removal out of the reactor by catalyst bed dilution, the active and inert particles have to be mixed as well as possible. Otherwise, the thermal stability of the reactor cannot be guaranteed and, e.g., catalyst deactivation or thermal runaway may take place because of the formation of local hotspots. Since loading a mixture of active and inert particles into a reactor tube inherently is a statistical process, fluctuations in local activity cannot be avoided. We have analyzed this phenomenon in detail based on numerically generated 3-dimensional randomly packed beds of spheres. The statistical process of loading a mixture of particles into a reactor tube was mimicked by a random number based approach. The simulations show that activity variations are evenly distributed along the axial direction, whereas in radial direction the fluctuations become larger towards the tube center. The synthetic packed beds provide detailed information about the packed bed structure, which has been used to identify accumulations of active particles in local clusters. This evaluation reveals significant non-idealities compared to the assumption of a uniform activity profile, e.g., clusters of up to 20 active particles could be observed. Especially for highly diluted beds and/or low D/d ratios typical for highly exothermic reactions this aspect should be kept in mind during process development and design.

P2G movable modular plant operation on synthetic methane production from CO2 and hydrogen from renewables sources

Renewables are steadily growing becoming a significant part of the global energy mix, in particular in the power sector. An attractive solution could be represented by Power to Gas (PtG), an energy storage strategy. In the PtG process renewable or excess electric energy is used for water electrolysis to produce hydrogen that is then combined with CO2 and converted into methane (synthetic or substitute natural gas, SNG) through the Sabatier reaction. SNG is particularly interesting because leads to an easily transportable (in the existing infrastructures) fuel with a wide proven market for power, thermal and mobility final use applications. The key issue consist on putting together green hydrogen produced by electrolysis fed by renewables with high content CO2 gases supplied from different sources (e.g. syngas from gasification, biogas, geothermic fields, soil gas and gas wells). In this work the CO2 hydrogenation process, coupled with renewables, has been study in a modular, moveable, skidable plant, in the scale of 0.2–1 Nm3/h of produced SNG. The pilot plant is equipped with a methanation unit constituted by a multi-tubular fixed bed reactor able to work in cooled or adiabatic conditions; water produced is separated by a plate&shell condenser. Several sensors, an online gas analysis system and a data acquisition system allow monitoring continuous experimental tests. The methanation facility is able to work in the range of 1–5 bars. The paper reports the results of first experimental activities related to SNG production with Ru based supported catalyst. The experimental activity was carried out in order to check the operability of all components and to improve the knowledge on methanation process in different conditions relevant to Power-to-Gas applications. Different weighted hourly space velocity (WHSV), gas inlet composition, reagent mixture, H2/CO2 ratio, temperature and pressure conditions have been investigated. Increasing pressure drives CH4 production as CO2 conversion is kinetically boosted by raising pressure. Results show that a decreasing trend of XCO2 is observed by increasing WHSV. Results indicate high CO2 per pass conversion with CO2/H2 concentrate feed using Ru based catalyst. Finally the effect of CH4 in the feed was studied emulating two reactors in series. Biogas representative CO2/H2/CH4 mixtures were tested in order to study direct methanation as a biogas upgrading technology.

Theoretical investigation of ethane oxidative dehydrogenation over MoVTeNbO catalyst in fixed-bed reactors with intermediate water removal

Oxidative dehydrogenation of ethane (ODHE) is a promising method for ethylene production. In comparison with the conventional methods which need high quantities of heat and also release considerable amount of COx, ODHE is more favorable in terms of energy and environment. This article presents an investigation on water removal effects on the performance of a multi-tubular fixed bed reactor over MoVTeNbO catalyst. Its performance is analyzed in terms of ethylene and COx selectivities and productions. Results show that ethylene and COx selectivities can reach from 87% and 19% to 91% and 12% respectively, which leads to 20% increase in ethylene and 28% reduction in COx productions. Also, it was shown that reactor temperature is reduced with water removal and its hotspot decreased from 500 °C to 460 °C that provides more controllable condition. Furthermore, a 20-bed mode membrane-like reactor is investigated for more water removal which results more than 94% ethylene selectivity. According to the results membrane reactor can be a proper choice for ODHE process with water removal.

On the influence of particle shape and process conditions in the pressure drop and hydrodynamics in a wall-effect fixed bed

ABSTRACTA low tube-to-particle diameter ratio (dt/de,p) fixed bed, packed with spherical and nonspherical catalyst supports, was used to investigate pressure drop at varying temperature (298–673 K) and inlet pressure (245–294 kPa). The dt/de,p ranged from 3 to 6, namely, a large wall-effect fixed bed, with an average void fraction between 0.38 and 0.61. These conditions pertain to multitubular fixed-bed reactors used for exothermic reactions. The pressure drop was notably influenced by the particle size and morphology as well as temperature. The use of particles with dt/de,p < 5 and relatively large bed void fractions (>0.55) appeared suitable for pressure drop control. The fluid velocity profiles were calculated by applying the Navier–Stokes–Darcy–Forchheimer equation computing the respective permeability parameters with refitted state-of-the-art pressure drop correlations. The fluid flow exhibited different velocity zones across the fixed bed, the highest velocity zone being located near the reactor wall. The axial velocity component was influenced by the catalyst morphology, as well as temperature and inlet pressure.

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.

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

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

Integrated reactor staging and plant optimization of a Biomass-To-Liquid technology

In this work an industrial Biomass-To-Liquid (BTL) plant simulation and optimization are presented. Biomass is first gasified with oxygen and steam, and the produced syngas is fed to a multi-tubular fixed bed reactor for Fischer-Tropsch (FT) synthesis, obtaining a distribution of hydrocarbons with different molecular weight. A simplified model for the biomass gasification section is implemented in HYSYS® V8.4, while the Fischer-Tropsch reactor is simulated using MATLAB® R2013a. The kinetic parameters of the FT reaction have been determined by using a non-liner regression performed with the experimenta data obtained with a bench-scale FT-rig. The model developed for the Fischer-Tropsch reactor takes into account the catalytic pellet's effectiveness factor and the eventual formation of a liquid phase in each point along reactor’s axial coordinate. The whole BTL plant is simulated connecting MATLAB and HYSYS. Moreover, the staging of the Fischer-Tropsch reactor is studied performing a techno-economic analysis of three different plant configurations and evaluating the corresponding pay-back time.

Modeling of the maleic anhydride circulating fluidized bed reactor

Abstract Maleic Anhydride (MA) production by selective oxidation of n-butane in a Multi-Tubular Fixed Bed reactor is constrained by the flammability limits. The use of Fluidized Bed circumvents this constraint but suffers from high back mixing. The Circulating Fluidized Bed (CFB) reduces the back mixing of the catalyst and enhances the catalyst activity by reactivating the catalyst. A simple reactor model with suitable hydrodynamic and kinetic models at the operating conditions of both the pilot and commercial MA CFB reactors is proposed. A dispersion model with variable gas density is used for modeling the hydrodynamics of these reactors. The reactors' configurational complexities are also accounted for in the model. The data fitting exercise of the proposed reactor model is performed. The proposed method simultaneously minimizes the total bias based on the individual biases for each component of the multi component reactor system and the total error in a multi-objective framework.

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.

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.