Multi-tubular Reactor Research Articles

The technological prospects of repurposing methane steam reformers into ammonia crackers for decarbonized H2 production

The decarbonization of hydrogen production can be accelerated by repurposing existing methane steam reformers into ammonia crackers. Through kinetic modeling, reactor optimization, and process integration, we demonstrated the viability of repurposing industrial reformers into NH3 crackers using a Co-Ba-Ce extrudate catalyst. First, we combined an improved kinetic rate expression, validated through experiments, with a high-fidelity 2-D model to optimize the operation of a multi-tubular reactor with a fixed capacity of 7000 Nm3 h−1. Subsequently, we used heat integration techniques to integrate the reactor with supplementary and separation units. We proved the process energy efficiency to be 65.7% before heat integration and 75.3% for the integrated plant. The integrated, optimized plant results demonstrated the necessity of implementing an adiabatic pre-cracker, an element typically omitted in catalytic NH3 decomposition techno-economic models. Our findings underscore the importance of real-world constraints and operational aspects in designing and optimizing NH3 conversion processes.

Validation of a mathematical model for the simulation of a multitubular and multitask solar reactor

Solar reactors represent an opportunity to obtain chemical reactions at high temperatures, saving costs in energy supply through the concentration of solar energy. Multitubular and Multitask (M&M) solar reactors are one of the options that allow the production of hydrogen and the production of synthesis gas through the gasification of hydrocarbon materials. The complexity of the phenomena involved in this type of reactor requires a robust mathematical model capable of integrating all heat transfer mechanisms. Some previous efforts made for the simulation of reactors use overly complex models that neglect some heat transfer mechanisms such as convection, and despite this have high computational cost, thus reducing the possibility of intensive debugging and the capacity of a sensitivity and uncertainty analysis. In this work, a mathematical model of distributed and transient parameters is presented that considers all the mechanisms of heat transfer by convection, radiation, and conduction in the components of a solar reactor of Multitubular and Multitask type, under a finite difference solution scheme and using the matrix method to calculate the radiation emitted from the components in 2D, offering a code with fast simulation and low computational cost. The model is validated with experimental data from the Multitubular and Multitask solar reactor, satisfactorily reproducing the prediction of the tube and wall temperatures under the conditions to which the reactor was subjected, reaching temperatures close to 1430 K in the tubes. The maximum relative error was equal to −7.4 % in the tube temperatures during a part of the experiment, acceptable given the complexity of the phenomena. The experiment lasted 180 min, and the simulation time spent around 38 s using a commercial computing processor. The model has the ability to quickly and satisfactorily reproduce the behavior of a Multitubular and Multitask type solar reactor, taking into account all the heat transfer mechanisms that had been omitted in previous works.

Enhancing the methanol yield of industrial-scale fixed bed reactors using computational fluid dynamics models

Achieving our decarbonisation goals for the maritime transport sector requires the bulk production of liquid hydrocarbon fuels, suitable for the existing infrastructure, such as methanol (MeOH). For this, optimisation of fixed bed chemical reactors is vital. Unlike demonstration-scale setups, optimising the design of such reactors using Computational Fluid Dynamics (CFD) models is both cheaper and faster. In this study, using a 2D pseudo-homogeneous CFD model, a single tube from a multi-tubular industrial-scale MeOH reactor is simulated. Using available experimental data, the CFD model was validated yielding excellent accuracy, with an average error of 2.6 %. The model identified a temperature hot-spot near the bed entrance, while the predicted pressure drop was 11 % of the operating pressure. Both effects could considerably reduce the efficiency of the reactor, either by catalyst deactivation or by increasing the compressor requirements, respectively. Through a parametric study where the tube’s length and diameter were varied within the ±50 % range, 53 total cases are produced and solved, creating an extensive pareto set of data for the key output parameters, such as methanol production, pressure, and temperature. A response surface was also generated, revealing the interconnection between the tube’s design and the operating parameters. This enabled a performance optimisation of the reactor design for two industrially relevant scenarios, with the optimised reactor achieving a 6.9 % higher MeOH yield and a 75 % reduced pressure drop. Through industrial involvement, the reactor can be further optimised, and would act as a critical foundation for more extensive techno-economic and socio-economic evaluations for sustainable carbon–neutral methanol production.

Comprehensive economic analysis of a multi-tubular reactor

ABSTRACT Multi-tubular reactors allow for highly selective and mostly highly exothermic catalytic or non-catalytic reactions to occur making them essential in various industrial processes. Our Present work was to develop a generalised rigorous costing method applicable to industrially designed multi-tubular reactors. In this report, a Fischer–Tropsch (F-T) industrial multi-tubular reactor was rigorously costed. Capital costs totalled to R,52,491,606 with material costs attributing the highest cost contribution (48%). The operating cost amounted to R,18,258,067 with cleaning and maintenance attributing the highest cost contribution(67%). The reactor purchase price was evaluated to R,36,201,107. This differed by 41.5% from the purchase price found using a shell and tube heat exchanger costing method. The total annual cost (TAC) assuming a 3-year payback was found to be R,35,755,269.

Magnetic resonance imaging of trickle flow

AbstractTrickle bed reactors (TBR) are widely used in the chemical industries. These reactors involve gas and liquid flow through a catalyst‐packed bed. For optimal TBR performance, it is crucial to achieve a uniform distribution of gas and liquid among the catalyst particles. However, in multitubular reactors with slender tubes, flow maldistribution near the tube walls is a common issue. Therefore, a comprehensive understanding of local phase and flow distribution is essential for designing and operating reactors with slender tubes. This article employs Magnetic Resonance Imaging (MRI) to characterize the three‐dimensional distribution of the two‐phase trickle flow within a slender tube. Three quantities are characterized: gas‐liquid‐solid distribution, particle wetting efficiency, and the flow field. Structure and flow MRI images are processed to calculate these quantities. Additionally, a novel postprocessing technique is introduced to determine the liquid distribution over individual particle surfaces. This distribution is determined at several axial and radial positions.

An Analysis of Fixed-Bed Catalytic Reactors Performances for One-Stage Butadiene Synthesis from Ethanol

The present study assesses, using a theoretical approach, the performances of two widely used fixed-bed reactors for the ethanol-to-butadiene (ETB) one-stage (Lebedev) process: multibed adiabatic reactors (MBAR) with inter-bed heating and a multitubular reactor (MTR). The mathematical model consists of mass and heat conservation equations at catalyst particle and particle bed scales, coupled with a published kinetic model specific for a modified MgO–SiO2 catalyst. The process simulations at the level of catalyst particle have shown that the inter-phase concentration and temperature gradients are negligible, the only physical step with a limiting influence on process kinetics being the internal diffusion. A simplified version of the reactor model was also formulated, including empirical expressions developed in the study for the calculation of internal effectiveness factors. The reactor simulations highlighted that the MBAR with inter-bed heating by injection of hot reactants provides worse butadiene (BD) yields as a consequence of reduced reaction times (due to reactant by-pass of catalyst beds). The MBAR with inter-bed heating using heat exchangers provides better performances but inferior to those of MTR if the number of catalyst beds is less than six. A preliminary optimization study for the MBAR and MTR is also presented. The results showed that the maximization of BD yield has the drawback of a low BD production rate, whereas the maximization of BD production rate corresponds to a relatively low BD yield and high ethanol and inert recycles. A trade-off between the two extreme cases can be attained by maximizing the income generated by reactor operation.

A Priori Knowledge-Based Dual Hierarchical RNN for Spatial–Temporal Process Modeling: Using a Multitubular Reactor as a Case Study

Deep learning methods have been rapidly developed in recent decades. In this work, they are extended to model spatial-temporal industrial processes. Instead of pure black-box data-driven modeling approaches, the proposed model encodes the domain knowledge and physical rules governing the spatiotemporal system, called a dual-hierarchical recurrent neural network (DH-RNN). Both spatial and temporal relationships are modeled by multiple RNNs with diverse structures, which need correct specifications of all the interactions between spatial and temporal variables with a priori knowledge of the real process. A more accurate prediction can be obtained with fewer parameters employed in the network. And the effectiveness of the proposed DH-RNN is verified via a real ethylene oxychlorination process.

Heat transfer intensification in compact tubular reactors with cellular internals: A pilot-scale assessment of highly conductive packed-POCS with skin applied to the Fischer-Tropsch synthesis

Heat management poses severe constraints when designing non-adiabatic multi-tubular packed-bed reactors for strongly exothermic or endothermic catalytic processes. The exploitation of conduction in the solid matrix of engineered continuous internals (e.g., honeycomb monoliths, open-cell foams, periodic open-cell structures) as a heat transfer mechanism alternative, or possibly additional, to fluid-phase convection, is a promising strategy to relax some of these constraints, offering new opportunities for the intensification of catalytic reactors. Preliminary experimental data and modelling studies show that this is particularly true for compact-scale applications, when conductive internals are packed with catalyst micro-pellets. In this work, through pilot-scale testing, we show that overall heat transfer coefficients as high as 1300 W/m2/K can be achieved in periodic open-cell structures (POCS) made of a highly conductive aluminium alloy, 3D printed with an external continuous skin and packed with 300–400 μm catalyst micro-pellets. To this aim, a Fischer-Tropsch experimental campaign has been carried out in a pilot-scale rig, using an established 20 wt% Co/Al2O3 catalyst formulation and a tubular reactor (28.80 mm I.D., 20 cm catalyst bed length) externally cooled with an isothermal diathermic oil. Thanks to the outstanding heat transfer properties of the packed-POCS reactor, by progressively increasing the oil temperature from 180 °C to 225 °C, once-through CO conversions as high as 70 % have been measured at gas hourly space velocities exceeding 4000 cm3(STP)/h/gcat, resulting in C5+ yields in excess of 0.35 g/h/gcat, with a CH4 selectivity always below 15 %. Such performances, made possible by the intensified heat management granted by the adopted reactor internals, are among the best ever reported for a compact-scale Fischer-Tropsch tubular reactor.

Implementing gain scheduling approach to control large-scale production of diethyl oxalate in a catalytic fixed bed multi-tubular reactor

In the large-scale production of Diethyl Oxalate (DEO), numerous control and optimization challenges are faced. These issues are targeted in this study by implementing a gain scheduling approach to control a catalytic fixed bed multi-tubular reactor designed for DEO production. A novel inferential modeling method, developed using Python and response surface methodology, was applied to simulate the dynamics of the reactor, and the inlet coolant temperature was identified as the most influential parameter. An inferential control system was implemented that utilized gain scheduling for Proportional Integral Derivative (PID) controllers. The results showed that the proposed PID controller gains offered fast and stable responses, even at high conversion setpoints. However, minimization of response overshoot at high amplitudes of step changes proved challenging, leading to a decrease in conversion estimator accuracy. The use of a quadratic model from response surface methodology for the regression of the inferential estimator was proposed, showing improved prediction accuracy over the linear model. These findings provide valuable insights and guide future optimization in the design and operation of reactors for large-scale DEO production.

Downsizing Sustainable Aviation Fuel Production with Additive Manufacturing—An Experimental Study on a 3D printed Reactor for Fischer-Tropsch Synthesis

Sustainable aviation fuels (SAF) are needed in large quantities to reduce the negative impact of flying on the climate. So-called power-to-liquid (PtL) plants can produce SAF from renewable electricity, water, and carbon dioxide. Reactors for these processes that are suitable for flexible operation are difficult to manufacture. Metal 3D printing, also known as additive manufacturing (AM), enables the fabrication of process equipment, such as chemical reactors, with highly optimized functions. In this publication, we present an AM reactor design and conduct experiments for Fischer-Tropsch synthesis (FTS) under challenging conditions. The design includes heating, cooling, and sensing, among others, and can be easily fabricated without welding. We confirm that our reactor has excellent temperature control and high productivity of FTS products up to 800 kgC5+ mcat−3 h−1 (mass flow rate of hydrocarbons, liquid or solid at ambient conditions, per catalyst volume). The typical space-time yield for conventional multi-tubular Fischer-Tropsch reactors is ~100 kgC5+ mcat−3 h−1. The increased productivity is achieved by designing reactor structures in which the channels for catalyst and cooling/heating fluid are in the millimeter range. With the effective control of heat release, we observe neither the formation of hot spots nor catalyst deactivation.

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.

Experimental studies on novel multi tubular reactor with shell having integrated buffer storage

This study concentrates on experimental analysis of a large scale metal hydride based hydrogen storage reactor having 50 kg LaNi5. In order to cater the heat transfer limitations of hydrogen storage in large scale systems, the present design have been developed as multi tubular reactor with shell having integrated buffer storage configuration with 7 tubes supported by means of 4 baffles having total 50 kg LaNi5 distributed equally among them and water as heat transfer fluid flows across the shell for heat transfer. The experimental study was performed for studying the absorption and desorption performance of the present hydrogen reactor wherein in case of absorption the parameters varied were HTF flow rate at 30 °C and supply pressure of hydrogen and in case of desorption which was carried out at atmospheric pressure, HTF flow rate and HTF temperature were varied. The metal hydride reactor reversibly stores 680 g of hydrogen amounting to 1.34 wt% of gravimetric capacity of metal hydride and equivalent energy storage of 10.4 MJ. In case of absorption, when the flow rate selected was 20 LPM the absorption time for 90 % reaction completion was observed to be 1286 s (21.4 min) at 30 bar H2 supply pressure. In case of desorption studies, it was observed that the varying flow rate from 15 to 25 LPM has negligible effect on hydrogen desorption hence 15 LPM was selected as flow rate for further desorption experiments. Further increasing HTF temperature from 60 °C to 80 °C improves the performance significantly.

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.

Effect of C3-Alcohol Impurities on Alumina-Catalyzed Bioethanol Dehydration to Ethylene: Experimental Study and Reactor Modeling

The impact of feedstock impurities on catalytic process is among the crucial issues for processing real raw materials. A real and model 92%-bioethanol contaminated with 0.03–0.3% mol 1-propanol or 2-propanol were used to make ethylene on a proprietary alumina catalyst in isothermal flow reactor. We proposed a formal kinetic model to describe the impure bioethanol conversion to ethylene and byproducts and used it to evaluate the multi-tubular reactor (MTR) for 60 KTPA ethylene production. The simulated data agree well with experimental results. Under reaction-controlled conditions, C3-alcohols strongly suppress the formation of by-products and ethylene-from-ethanol, and slightly inhibit the formation of ethylene-via-ether. It is the suppression of the ethylene-via-ether route that causes a decrease in ethanol conversion. The predominant formation of ethylene-via-ether results in an increased ethylene yield but doubling the catalyst load is required to achieve conversion as for pure feedstock. 2-Propanol has a stronger effect on dehydration than 1-propanol. Diffusion inside the grain’s levels out the effect of C3-alcohols on the process in MTR, giving an ethylene yield as high as ~98% while dehydrating a contaminated 92% ethanol. However, impurities dilute ethanol and generate propylene (which contaminates target product), and these worsen feedstock consumption and ethylene productivity in MTR.

Development of improved correlations for shell side heat transfer co-efficient in multi-tubular reactors network heat exchanger

The multi-tubular reactor takes the form of a shell and tube heat exchanger. The baffles that became of interest were the disk and doughnut baffles as they provided a 15 % greater effectiveness than the commonly used segmental baffle. The shell side heat transfer coefficient is usually predicted by correlations developed by Donohue (1949) and Goyal & Gupta (1984) for disk and doughnut baffles. However, these correlations result in inaccuracies due to the complexity of the configuration. Therefore, Slipcevic (1978), had developed a new method to calculate the shell side heat transfer coefficient. The Slipcevic method takes into consideration the annular flow, the crossflow and the doughnut flow. However, certain portions were gone unconsidered by this method. Therefore, the aim of this study was to modify the Slipcevic method to generate a more accurate shell side heat transfer coefficient. The heat transfer coefficient calculated using the original Slipcevic method was determined to be 58.6 W/m^2. K. The modified method resulted in a coefficient of 49.9 W/m^2. K. The modification resulted in a coefficient 14.8 % less than the original method. Since the simulated value for the propylene process was 15.8 % lower than the Slipcevic procedure, this revealed that the modification was slightly more accurate. The difference of 6.5 % between the two percent differences may be due to inaccuracies resulting from the assumptions of triangular gaps and that the wall viscosities were equivalent to the bulk viscosities.

Continuous multi-column sorption-enhanced dimethyl ether synthesis (SEDMES): Dynamic operation

In this work the continuous production of dimethyl ether (DME) by sorption-enhanced DME synthesis (SEDMES) technology has been demonstrated for the first time with a multi-column test-rig. A continuous single-pass carbon yield up to 95%, higher than ever reported before, has been achieved. The multi-column experiments have also shown that SEDMES can be operated at lower temperatures (220°C) than previously reported. This allows a higher temperature rise, making higher conversions possible while allowing even larger reactor tube diameters. Whereas the anticipated multi-tubular reactor concept is complex and costly, larger reactors could facilitate the economic valorisation. The SEDMES reactor model cannot only describe the transient behaviour of the process during the cyclic steady-state well, but also the dynamic approach towards the cyclic steady-state is adequately captured. Capturing the dynamic operation is of large interest with respect to process flexibility, especially for Power-to-X systems.

Numerical modelling and heat transfer optimization of large-scale multi-tubular metal hydride reactors

Heat management during the absorption/desorption process is a key aspect in improving the performance of large-scale hydrogen storage systems. In this article, the absorption and desorption performance of a multi-tubular hydride reactor is numerically investigated and optimized for 60 kg mass of LaNi5 alloy. The 90% absorption with 7, 14, and 19 tubes is achieved in 985, 404, and 317 s with an overall reactor weight of 78.46, 88, and 88.2 kg, respectively. The 14-tube reactor performance is investigated by introducing the longitudinal fins inside the tubes. The reactor performance is enhanced by allocating fins into different pairs of half and full fins constrained by overall fin volume. A thermal resistance network model is presented to investigate the effect of fin distribution and coolant velocity on equivalent resistance of the metal hydride reactor. Storage performance obtained from numerical model validates the thermal resistance analysis from heat transfer viewpoint. With six full fins, 90% hydrogen absorption is achieved in 76 s. However, tubes with 6, 8, and 12 pairs of half and full fins require 74, 58, and 54 s, respectively. The 14-tube reactor with 8 pairs of half and full fins is used for quantifying the augmentation in the absorption performance in response to operating conditions (supply pressure and heat transfer fluid temperature). A design methodology is outlined for the development of a large-scale multi-tubular hydride reactor based on a heat transfer optimization strategy.

How Temperature Measurement Impacts Pressure Drop and Heat Transport in Slender Fixed Beds of Raschig Rings

The axial temperature profile of a packed bed is often measured by thermocouples placed either directly in the bed or inside a thermowell centered in the reactor tube. Quantifying the impact of the thermocouple well on fluid flow, heat transport, and consequently on the measured temperatures is still an unresolved challenge for lab-scale reactors but especially, and even more so for multitubular reactors in industry. Particle-resolved computational fluid dynamics (PRCFD) simulations are a suitable approach to investigate the changes in transport phenomena exerted by inserting thermocouple wells into packed beds because they take into account the local packed bed structures. In this study, PRCFD simulations are performed based on design of simulation experiments (DoSE). The effect of the thermowell diameter and its thermal conductivity on the deviations between packed beds with and without thermowells is statistically quantified for characteristic integral quantities like pressure drop and tube wall-bed Nusselt number. The axial temperature profiles inside the thermowells can be computed efficiently with reasonably accuracy applying the Nusselt number correction as derived in this study from the DoSE in a one-dimensional pseudo-homogeneous energy balance.

Design of a Multi-Tubular Catalytic Reactor Assisted by CFD Based on Free-Convection Heat-Management for Decentralised Synthetic Methane Production

A simple reactor design for the conversion of CO2 methanation into synthetic methane based on free convection is an interesting option for small-scale, decentralised locations. In this work, we present a heat-management design of a multi-tubular reactor assisted by CFD (Ansys Fluent®) as an interesting tool for scaling-up laboratory reactor designs. The simulation results pointed out that the scale-up of an individual reactive channel (d = 1/4′, H = 300 mm) through a hexagonal-shaped distribution of 23 reactive channels separated by 40 mm allows to obtain a suitable decreasing temperature profile (T = 487–230 °C) for the reaction using natural convection cooling. The resulting heat-management configuration was composed of three zones: (i) preheating of the reactants up to 230 °C, followed by (ii) a free-convection zone (1 m/s air flow) in the first reactor section (0–25 mm) to limit overheating and, thus, catalyst deactivation, followed by (iii) an isolation zone in the main reactor section (25–300 mm) to guarantee a proper reactor temperature and favourable kinetics. The evaluation of the geometry, reactive channel separation, and a simple heat-management strategy by CFD indicated that the implementation of an intensive reactor cooling system could be omitted with natural air circulation.

Comparison between 1D and 2D numerical models of a multi-tubular packed-bed reactor for methanol steam reforming

The hydrogen-rich gas produced in-situ by methanol steam reforming (MSR) reactions significantly affects the performance and endurance of the high-temperature polymer electrolyte membrane (HT-PEM) fuel cell stack. A numerical study of MSR reactions over a commercial CuO/ZnO/Al2O3 catalyst coupling with the heat and mass transfer phenomena in a co-current packed-bed reactor is conducted. The simulation results of a 1D and a 2D pseudo-homogeneous reactor model are compared, which indicates the importance of radial gradients in the catalyst bed. The effects of geometry and operating parameters on the steady-state performance of the reactor are investigated. The simulation results show that the increases in the inlet temperature of burner gas and the tube diameter significantly increase the non-uniformity of radial temperature distributions in reformer tubes. Hot spots are formed near the tube wall in the entrance region. The hot-spot temperature in the catalyst bed rises with the increase in the inlet temperature of burner gas. Moreover, the difference in simulation results between the 1D and 2D models is shown to be primarily influenced by the tube diameter. With a methanol conversion approaching 100% or a relatively small tube diameter, the simplified 1D model can be used instead of the 2D model to estimate the reactor performance.