Multi-tubular Reactor Research Articles

A 3D Transient CFD Simulation of a Multi-Tubular Reactor for Power to Gas Applications

A 3D stationary CFD study was conducted in our previous work, resulting in a novel reactor design methodology oriented to upgrading biogas through CO2 methanation. To enhance our design methodology incorporating relevant power to gas operational conditions, a novel transient 3D CFD modelling methodology is employed to simulate the effect of relevant dynamic disruptions on the behaviour of a tubular fixed bed reactor for biogas upgrading. Unlike 1D/2D models, this contribution implements a full 3D shell cooled methanation reactor considering real-world operational conditions. The reactor’s behaviour was analysed considering the hot-spot temperature and the outlet CH4 mole fraction as the main performance parameters. The reactor start-up and shutdown times were estimated at 330 s and 130 s, respectively. As expected, inlet feed and temperature disruptions prompted “wrong-way” behaviours. A 30 s H2 feed interruption gave rise to a transient low-temperature hot spot, which dissipated after 60 s H2 feed was resumed. A 20 K rise in the inlet temperature (523–543 K) triggered a transient low-temperature hot spot (879 to 850 K). On the contrary, a 20 K inlet temperature drop resulted in a transient high-temperature hot spot (879 to 923 K), which exposed the catalyst to its maximum operational temperature. The maximum idle time, which allowed for a warm start of the reactor, was estimated at three hours in the absence of heat sources. No significant impacts were found on the product gas quality (% CH4) under the considered disruptions. Unlike typical 1D/2D simulation works, a 3D model allowed to identify the relevant design issues like the impact of hot-spot displacement on the reactor cooling efficiency.

Model-Based Analysis for Ethylene Carbonate Hydrogenation Operation in Industrial-Type Tubular Reactors

Hydrogenation of ethylene carbonate (EC) to co-produce methanol (MeOH) and ethylene glycol (EG) offers an atomically economic route for CO2 utilization. Herein, aided with bench and pilot plant data, we established engineering a kinetics model and multiscale reactor models for heterogeneous EC hydrogenation using representative industrial-type reactors. Model-based analysis indicates that single-stage adiabatic reactors, despite a moderate temperature rise of 12 K, suffer from a narrow operational window delimited by EC condensation at lower temperatures and intense secondary EG hydrogenation at higher temperatures. Boiling water cooled multi-tubular reactors feature near-isothermal operation and exhibit better operability, especially under high pressure and low space velocity. Conduction oil-cooled reactors show U-type axial temperature profiles, rendering even wider operational windows regarding coolant temperatures than the water-cooled reactor. The revelation of operational characteristics of EC hydrogenation under industrial conditions will guide further improvement in reactor design and process optimization.

Oxygen feeding strategies for methane ATR

The performance of different reactor designs for methane autothermal reforming (ATR) with diverse options of O 2 feeding is comparatively explored. The designs under consideration include a single bed reactor with O 2 feed at the inlet, multibed reactors in series with inter-bed oxygen injection, and a multitubular membrane reactor with O 2 feeding through the porous wall. The distribution of O 2 leads to low O 2 concentrations in the reaction mixture and less severe thermal conditions. The evolution of methane reforming and combustion reactions proceeds in parallel due to a suitable degree of reduction of the Ni catalyst. Particularly, the membrane reactor can produce H 2 in a more distributed way along the reactor. The leakage of O 2 at the membrane reactor outlet can be prevented with a final section of a non-porous wall. The modified membrane reactor demonstrates flexibility to carry out the methane ATR with lower temperatures without deterioration of H 2 yield. • The distribution of O 2 feeding leads to less severe thermal conditions. • Low O 2 concentrations allow a suitable degree of reduction of the catalyst. • The leakage of O 2 at the outlet of the membrane reactor is a drawback. • A final section of non-porous wall in the membrane reactor prevents the O 2 leakage. • Membrane reactor can perform methane ATR at lower temperatures with high yields of H 2 .

The role of effectiveness factor on the modeling of methanol steam reforming over CuO/ZnO/Al2O3 catalyst in a multi-tubular reactor

A pseudo-homogeneous model for the methanol steam reforming process was developed based on reaction kinetics over a CuO/ZnO/Al 2 O 3 catalyst and non-adiabatic heat and mass transfer performances in a co-current packed-bed reactor. A Thiele modulus method and an intraparticle distribution method were applied for predicting the effectiveness factors for main reactions and providing insights into the diffusion-reaction process in a cylindrical catalyst pellet. The results of both methods are validated and show good agreements with the experimental data, but the intraparticle distribution method provides better predictions. Results indicate that increases in catalyst size and bulk fluid temperature amplify the impact of intraparticle diffusion limitations, showing a decrease in effectiveness factors. To satisfy the requirements of a high temperature polymer electrolyte membrane fuel cell stack, the optimized operating conditions, which bring the methanol and CO concentrations to less than 1 % vol in the reformate stream, are determined based on the simulation results. • One-dimensional pseudo-homogeneous model of a packed-bed methanol steam reformer. • Two methods to obtain approximate solutions of the catalytic effectiveness factor. • Validation of reaction kinetics and effectiveness factors with experimental data. • Effects of main operating parameters on the intraparticle heat and mass transfer. • Optimized conditions to obtain less than 1% of CH 3 OH and CO in reformate gas.

Modelling the hydrodynamics and kinetics of methane decomposition in catalytic liquid metal bubble reactors for hydrogen production

Bubble reactors using molten metal alloys (e.g, nickel-bismuth and copper-bismuth) with strong catalytic activity for methane decomposition are an emerging technology to lower the carbon intensity of hydrogen production. Methane decomposition occurs non-catalytically inside the bubbles and catalytically at the gas-liquid interface. The reactor performance is therefore affected by the hydrodynamics of bubble flow in molten metal, which determines the evolution of the bubble size distribution and of the gas holdup along the reactor height. A reactor model is first developed to rigorously account for the coupling of hydrodynamics with catalytic and non-catalytic reaction kinetics. The model is then validated with previously reported experimental data on methane decomposition at several temperatures in bubble columns containing a molten nickel-bismuth alloy. Next, the model is applied to optimize the design of multitubular catalytic bubble reactors at industrial scales. This involves minimizing the total liquid metal volume for various tube diameters, melt temperatures, and percent methane conversions at a specified hydrogen production rate. For example, an optimized reactor consisting of 891 tubes, each measuring 0.10 m in diameter and 2.11 m in height, filled with molten Ni0·27Bi0.73 at 1050 °C and fed with pure methane at 17.8 bar, may produce 10,000 Nm3.h−1 of hydrogen with a methane conversion of 80% and a pressure drop of 1.6 bar. The tubes could be heated in a fired heater by burning either a fraction of the produced hydrogen, which would prevent CO2 generation, or other less expensive fuels.

Improved Correlations for Shell Side Heat Transfer in Multi Tubular Reactors

Improved Correlations for Shell Side Heat Transfer in Multi Tubular Reactors

Mixed Reality-based chemical reactor visualization

A multi-tubular reactor for butadiene synthesis was developed, visualized using Microsoft HoloLens2, and built to allow immersive human interaction. Fluid analysis is particularly important in reactor design, including heat generation, temperature distribution, and mole fraction of reactants and products. Flow analysis is mostly executed with CFD tools like Open FOAM and ANSYS Fluent. Post processing software visualizes the CFD findings. However, the post-processing software is focused on the engineer, which lacks user-friendliness for the user who actually builds the reactor [Matthias Berger and Verina Cristie, 2015]. Contemporary technologies like virtual reality and mixed reality were applied to improve this. Virtual reality is a technique that creates a virtual world in a three-dimensional digital environment that blocks out the actual world. Furthermore, mixed reality technology interacts with virtual things made in the real world, minimizing heterogeneity and creating a smart environment where reality and virtuality are united by maximizing immersion. So, using Unity 3D, a gaming engine, a multi-tube reactor was created in virtual reality. Menus, selection windows, and buttons are also implemented in C# to facilitate interaction. This VR was then deployed to Microsoft HoloLens2 via Visual Studio. The HoloLens2 is an un tethered wearable holographic computer that offers bidirectional video, speech, and MR composite communication [Guy Martin et al., 2019]. An integrated mixed reality system was finally created that instantly reflected mutual conversation. This approach can also be employed in distillation towers, heat exchangers, separators, pumps and other process equipment performance monitoring. Smart manufacturing and a digital twin termed future plant can be accomplished by observing the actual process and implementing an autonomous data interaction system.

Use of biomass-derived glycerol as an alternative to fossil fuels for aniline production: Energy saving and environmental aspects

Catalytic reduction of nitrobenzene is the leading technological step in aniline production. The hydrogen required for this stage, is dominantly produced from fossil fuels through reforming processes, which take much energy and emit large amounts of CO2. Biomass-derived glycerol steam reforming is an attractive alternative to traditional reforming to reduce the dependence on hydrocarbon resources and mitigate climate change. This research aims to analyze a mass- and heat-integrated multi-tubular membrane reactor, containing nitrobenzene hydrogenation (exothermic-side) and glycerol steam reforming (endothermic-side) for co-production of aniline and syngas. In this process, hydrogenation reaction acts as a heat source for glycerol reforming, while hydrogen produced in the endothermic-side simultaneously permeates through the membrane, reacts with nitrobenzene to produce aniline and enhances the equilibrium glycerol conversion. Besides, the steam produced in the exothermic-side is continuously recycled to the entrance of the endothermic-side. The role of different parameters on reactor performance is realized using a heterogeneous model. Numerical results show that by adjusting the adequate operating conditions, glycerol and nitrobenzene conversion above 80% and syngas with H2/CO ratio in the range of 2.0–2.5, suitable for Fischer-Tropsch and methanol synthesis processes, can be achieved. In addition, this integrated process is promising in terms of energy saving, environmental pollution mitigation, feasibility and effectiveness for industrial-scale application; however, experimental proof-of-concept is required to ensure the safe operability of this process.

Multi-scale model of a top-fired steam methane reforming reactor and validation with industrial experimental data

A multi-scale model is presented for a steam methane reforming reactor. The reactor is a typical top-fired, packed-bed multi-tubular reactor. The model embeds, at the microscopic scale, a 1-dimensional simulation of mass transport and reaction inside the catalyst particles. At the intermediate (mesoscopic) scale, the tubular reactor model is based on local mass, energy, and momentum balances, coupled to appropriate steam methane reforming reaction kinetics; the equations are written and solved in 2-dimensional cylindrical symmetry. At the macroscopic level, the tube simulation is then coupled to the furnace simulation. For the latter, a 1-dimensional model is proposed, based on local mass and energy balances, coupled to linear combustion kinetics. Overall, the model contains only one adjustable parameter i.e., Lf, the length of the flame in the furnace. The model equations are integrated through a finite element method. The predictive capability of the model is assessed through validation against previous literature results, as well as three sets of experimental data obtained from a full-scale industrial SMR reactor, operating from middle to high capacity. The model makes it possible to account for the effects of the catalyst features, on the one hand, and the operating conditions of the furnace, on the other. The model provides a detailed study of the phenomena occurring inside the steam methane reforming reactor, with an acceptable computational burden and time. This lays the foundations for in-depth fault detection and identification studies and online deployment of the model for control purposes.

CO2 methanation in a shell and tube reactor CFD simulations: high temperatures mitigation analysis

CO2 methanation is gaining increasing interest in the last years as a way of storage of the energy surplus produced by renewable energy sources. Shell and tube reactors are among the most widespread type of methanation reactors. One-dimensional pseudo-homogenous/heterogeneous models and CFD (Computational Fluid Dynamics) models using some simplifications, as imposed heat exchange coefficients and constant coolant temperatures, have been applied up to now to study the problem. In this article those simplifications have been removed and the CO2 methanation in a cooled multi-tubular catalyst reactor has been investigated through 3D CFD simulations, using a commercial software and a porous model. Nitrogen and oil cooling have been studied and the results have been compared. The goal is to identify suitable solutions that allow the use of gas cooling, while maintaining low temperature levels and high conversions. The oil cooling case has been also analyzed for comparison and in the perspective of a future system upgrade. After a validation of the model using the available experimental data, a sensitivity analysis has been conducted for what concerns coolant and reactants temperatures and flow rates, catalyst load and operating pressure in the tubes. Strategies for the high temperatures mitigation in the reactive zones have been evaluated and discussed. In particular the proposed technique of catalyst uneven distribution has revealed to be very effective. The model has proved to be very useful for a detailed analysis of the phenomenon and for obtaining essential data that resulted difficult to measure by experimentation.

Bridging the Gaps: from Particle-resolved to Multi-tubular Reactor Simulation

Packed bed reactors have been widely used in the chemical and process industry for several decades. They can be difficult to design and operate due to their size and complexity. Therefore, there is still room for improvement of the performance of these reactors and rigorous simulations can help here to achieve desired goals with lower upfront investment. Recent advances in modeling particle-resolved packed beds allows a detailed inside in the flow, species and temperature distribution in the beds and therefore also into the conversion of the surface reactions. Based on these simulations, model parameters for 1D-models can be estimated. These 1-D models can then be used to calculate performance of multi-tubular reactors, either by running a computationally expensive simulation with resolved tubes or by coupling the CFD simulation to an advanced process modeling tool like gPROMS. In the latter case, the flow non-uniformity as well as certain flow properties like coolant velocity and temperature is taken from the CFD simulations, while on the process modeling side heat transfer and reactions in the packed bed are calculated based on the simplified 1D models. This modeling approach is fully 2-way coupled and highly efficient in terms of accuracy and especially runtime and it can be embedded into a flow sheet simulation.In this contribution, we will present the whole simulation process and how the different steps intertwine with each other starting from the detailed particle resolved simulation all the way down to the flow sheet simulation. The benefit of this approach will be demonstrated based on several examples.

Nicotinic acid synthesis at elevated β-picoline load: Exploring the possibility to intensify the process

The paper investigates the basics for increasing the productivity of gas-phase catalytic oxidation processes effected in multi-tubular reactors due to their operation at more concentrated feedstock. Obviously, an increase in initial concentration of the oxidizable reagent seems very attractive, but it is associated with the need to modify the process parameters and/or technological chart in order to achieve the required performance figures. This often entails excessive formation of by-products and therefore overheating of the catalyst bed due to increased heat generation. The cumulative effect of many factors can prevent attaining an acceptably high conversion of feedstock and the yield of target products within a reasonable size of a multi-tubular reactor. The problems we studied are quite typical for highly exothermic catalytic oxidation processes, but are not widely discussed in the literature. On the example of nicotinic acid (NA) synthesis in multi-tubular reactor, we investigated the advantages of the process with elevated feed load (β-picoline), in comparison with the conventional conditions. On the basis of comprehensive process simulation supported by the experimental evidence, for the first time we have shown how the process should be operated to achieve a significant progress in the reactor performance and the target product yield. Our theoretical study showed that the rise in the initial β-picoline concentration from ∼0.8 to ∼3% accompanied by a relevant adjusting of the process parameters leads to a dramatic 1.5–2-fold gain in the specific productivity of catalyst; this could greatly improve the reactor capacity. Optionally, a given production capacity of multi-tubular reactor may be ensured by ∼2 times less number of tubes. Thus, the synthesis of NA at elevated initial feed of β-picoline shall be significantly enhanced in comparison with the conventional process.

Model Analysis of the Role of Kinetics, Adsorption Capacity, and Heat and Mass Transfer Effects in Sorption Enhanced Dimethyl Ether Synthesis.

The role of kinetics, adsorption capacity, and heat and mass transfer effects in the sorption enhanced dimethyl ether synthesis (SEDMES) is investigated by means of a 2D+1D model of a single tube of an industrial-scale, externally cooled, multitubular reactor that simulates the reaction/adsorption step of the SEDMES cycle. The effect of the adsorbent/catalyst weight ratio is analyzed, showing that a trade-off between DME productivity and yield originates from the balance of kinetics and adsorption capacity in the reactor tube. The effects of internal diffusion in catalyst particles are shown to have a strong impact on effective reaction rates: significant yield/productivity improvements are obtained when using a mechanical mixture of catalysts with small particle diameters or by rearranging the distribution of the two active phases in hybrid or core@shell pellets. The thermal effects in the reactor, which are increasingly critical upon intensifying the SEDMES process conditions, are also addressed.

Scaling Relations for Autothermal Operation of Catalytic Reactors

Autothermal operation (AO) has several advantages for carrying out highly exothermic catalytic partial oxidation (CPO) and/or oxidative dehydrogenation (ODH) reactions compared to traditional cooled multitubular reactors. In steady-state autothermal operation (AO), there is no heat addition to the reactor or intentional heat removal by cooling through reactor walls; the heat of reaction is removed mainly by convective flow of the cold feed. The existence of an ignited high temperature (and conversion) state at the lowest possible feed temperature and/or space time is essential. This work examines the impact of various design and operating variables on the feasibility and economic scale-up of shallow packed-bed catalytic reactors for autothermal operation. Specifically, we present scaling relations that can be used to examine the impact of effective bed thermal conductivity, bed length, particle size, catalyst activity, reaction kinetics, and operating pressure on the extinction (blow-out) flow rate or feed temperature for large scale autothermal CPO and ODH reactors operated close to the adiabatic limit. The scale-up relations derived for a single-step CPO/ODH reaction are verified by numerical simulations. They are also validated using the highly complex oxidative coupling of methane (OCM) as an example.

Effects of Reactor Type on the Economy of the Ethanol Dehydration Process: Multitubular vs. Adiabatic Reactors

Effects of Reactor Type on the Economy of the Ethanol Dehydration Process: Multitubular vs. Adiabatic Reactors

A unified framework for the mathematical modelling, predictive analysis, and optimization of reaction systems using computational fluid dynamics, deep neural network and genetic algorithm: A case of butadiene synthesis

The fight against climate change and environmental pollution have set the agenda for efficient reaction systems design. It has necessitated now more than ever, the careful design and optimization of chemical processes that result in carbon production. In this study, a unified framework for the mathematical modelling and simulation, prediction, and optimization of reaction systems is proposed. A computational fluid dynamics (CFD) simulation of butadiene synthesis over a ferrite catalyst in a 3D shell and multi-tubular reactor was executed. A rigorous mathematical formulation of the process kinetics and multiscale heat transfer was incorporated into an OpenFOAM CFD model using a porous media. The CFD model was validated against experimental data using gas concentrations, temperature, and CO2 partial pressure with a maximum error of 3.2% (97% accuracy). The developed model was then used to generate data sets for both prediction and optimization of the reaction conditions in terms of temperature, flow rate, and feed compositions using Deep Neural Network (DNN) and Genetic Algorithm (GA). Another surrogate model was developed for temperature control (cooling side) optimization by utilizing the coolant flow rate, flow directions (co-current and countercurrent), coolant types (water and solar salt), and velocity. Dynamic evolution and steady-state contours of the species concentration distributions were predicted with our DNN model with only an error of 1.26% (98.74% accuracy). Our results clearly indicated that higher reactor performance indices that exceed those of the conventional optimization approach in terms of conversion (99.98%), yield (93.28%), and selectivity (92.3%) are obtainable with the proposed framework. The mathematical models, DNN surrogate models, and the genetic algorithms that were integrated as a unified framework can be adopted for designing other reactor systems.

Simulation and Design of a Water-Gas Shift Catalytic Multitubular Reactor with Integrated Heat Exchange

A 2D steady-state phenomenological model used for sizing a multitubular catalytic reactor for water-gas shift reaction is presented. The model contemplates momentum, mass, and energy balances. In a...

Dynamic Simulation of Hydrogen Iodide Decomposition in Catalytic Multi-Tubular Reactor

Sulfur-Iodine thermochemical cycle process has been considered a promising method to generate hydrogen from water. One of the main limitations of this process lies in the hydrogen iodide decomposer section, which requires substantial amount of heat at high temperature. The present study analyses the heat transfer limitation effect on the performance of hydrogen iodide decomposition in a multi-tubular catalytic reactor by means of dynamic simulation. The extensive numerical simulation shows that the inlet temperature heating medium (Helium gas) should be at least 700°C so to enable at least 90% conversion when the inlet molar fraction of hydrogen iodide is 0.6. Lowering the inlet heating medium will require the reduction in the inlet molar fraction of hydrogen iodide in order to keep the conversion at 90% and above.

Reactor modelling and design for sorption enhanced dimethyl ether synthesis

Sorption Enhanced DiMethyl Ether Synthesis (SEDMES) is a promising option to overcome thermodynamic limitations of conventional DME production processes. In this work a 2D + 1D heterogeneous dynamic model of the reaction/adsorption step in a tube of an externally cooled multitubular fixed bed SEDMES reactor is developed in order to investigate the effect of design and operating parameters on thermal behavior and DME yield performances of the reactor. The model is validated by comparison with experimental results from a bench scale unit, including the dynamics of the outlet composition and the temperature trajectories in different points along the axial coordinate. Simulations with the validated model address the effect of the CO/CO2 ratio in the feed. The results confirm that, thanks to the effective in-situ H2O removal, the DME yield performances (65–70% in this work) of SEDMES are poorly sensitive on the CO/CO2 ratio. Accordingly, on increasing the CO2 content in the feed, SEDMES provides larger advantages with respect to conventional DME direct synthesis. Calculations of maximum temperatures achieved along the axial coordinate show that catalyst thermal stress in the hottest inlet zone of the SEDMES reactor slightly increases with the CO content in the feed due to faster kinetics of the DME production reactions. However, thanks to the dilution effect provided by the adsorption material, maximum bed temperature keeps ∼ 20–30 K below the catalyst stability limit reported in the literature (573 K). Accordingly, larger tube diameters (up to 46.6 mm) than in conventional reactors for the direct synthesis of DME can be adopted with less than 2% loss in DME yield.

3-D Multi-Tubular Reactor Model Development for the Oxidative Dehydrogenation of Butene to 1,3-Butadiene

The oxidative dehydrogenation (ODH) of butene has been recently developed as a viable alternative for the synthesis of 1,3-butadiene due to its advantages over other conventional methods. Various catalytic reactors for this process have been previously studied, albeit with a focus on lab-scale design. In this study, a multi-tubular reactor model for the butadiene synthesis via ODH of butene was developed using computational fluid dynamics (CFD). For this, the 3D multi-tubular model, which combines complex reaction kinetics with a shell-side coolant fluid over a series of individual reactor tubes, was generated using OpenFOAM®. Then, the developed model was validated and analyzed with the experimental results, which gave a maximum error of 7.5%. Finally, parametric studies were conducted to evaluate the effect of thermodynamic conditions (isothermal, non-isothermal and adiabatic), feed temperature, and gas velocity on reactor performance. The results showed the formation of a hotspot at the reactor exit, which necessitates an efficient temperature control at that section of the reactor. It was also found that as the temperature increased, the conversion and yield increased whilst the selectivity decreased. The converse was found for increasing velocities.