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The authors have investigated the potential of a plant-based natural surfactant in the modification of various bubble parameters. Bubble dynamics at the orifice were studied in natural surfactant solutions extracted from the plant Sapindus mukorossi at concentrations below and above its critical micellar concentration (CMC). The results were compared to the ones obtained with Sodium Dodecyl Sulfate solutions. The CMC values of Sapindus mukorossi and Sodium Dodecyl Sulfate are 7.5 × 10−3 g/cc and 2.39 × 10−3 g/cc, respectively. A photographic method was employed to observe bubble formation at the orifice. The results show that biosurfactants, like chemical surfactants, have a comparable effect on bubble density, size, and rise velocity. Experimentally determined bubble radius, volume, and radial velocity were used to calculate various forces contributing to the bubble dynamics. The buoyancy, pressure, and surface tension forces were significantly stronger in magnitude in comparison to the gas momentum, viscous drag, and added mass forces. Our findings suggest that the significance of various dynamic forces involved in bubble growth dynamics varies according to the bubble generation frequency regimes. We report for the first time the potential of Sapindus mukorossi in altering bubble properties and surface forces at the orifice and its usage in various bubble-related industrial applications. [ABSTRACT FROM AUTHOR]

A pressure correction method is proposed considering the influence of a dual factor. The applicability of a pressure correction method coupled with a drag model is discussed along with the accuracy of the simulation results obtained by such a pressure correction method. It is found that the present pressure correction method combined with the DBS (dual bubble size) drag model can accurately reflect the changing trend of gas holdup distribution with pressure. It is also established that results from this model applied to a bubble column match well with the experimental data. Finally, when compared with other pressure correction models, the proposed model shows better robustness in three‐dimensional simulations and can predict radial gas holdup distributions with better accuracy. [ABSTRACT FROM AUTHOR]

The conventional packed bed humidifiers encounter significant drawbacks such as scale formation, spray nozzle clogging, corrosion, and relatively poor effectiveness, which adversely affect their reliability and lifespan, thereby escalating their operational and capital costs. To tackle these issues, bubble column humidifiers have been proposed. The bubble column design ensures maximum air–water interaction, enhancing component effectiveness, while obviating the need for atomizers, thereby decreasing maintenance expenses, and enhancing heat and mass transfer efficiency. Moreover, studies related to a moving streams multi-stage bubble column HDH design are lacking. Therefore, this study aims to provide a theoretical analysis of various configurations of multi-stage moving streams bubble column humidifiers, aiming to bridge the performance knowledge gap between moving stream and nonmoving stream bubble column humidifiers. A mathematical model based on heat and mass transfer was developed and validated against published data. The effect of multistaging, water inlet temperature, air inlet temperature, and inlet relative humidity on the total effectiveness, outlet humidity ratio and outlet air temperature are studied. Results reveal that multistaging is effective in boosting the maximum effectiveness of single stage bubble column humidifier from 27% and 33% to about 94% and 94%, for the parallel and series configurations, respectively. Furthermore, both series and parallel configurations show similar performance with a slightly higher performance for the series arrangement. Additionally, this study discusses the operational and maintenance differences between the parallel and series multi-stage bubble column humidifiers, with the series configuration having a more straightforward operation compared to the parallel arrangement. However, the parallel configuration requires less complicated maintenance in comparison to the series multi-stage configuration. The outcomes of this study are pivotal to understanding the optimum operating conditions of the humidifier for its possible integration with the dehumidifier. Consequently, an improved humidification dehumidification (HDH) desalination system can be attained. [ABSTRACT FROM AUTHOR]

Liquid desiccant deep dehumidification (LDDD) is an excellent energy-saving technology for low-humidity industries. Ionic liquids (ILs) are favored as optimal working fluids for LDDD, owing to their low vapor pressure, non-crystallization, and non-corrosion. The combined application of IL desiccant with the bubble column has been proven to effectively improve deep dehumidification. The present work focuses specifically on the insights into air-liquid transfer processes in bubble column dehumidifier using ionic liquid desiccant. The effect of operating parameters on volumetric transfer coefficient is examined based on the experimental platform. Meanwhile, the bubble swarms meso-scale flow structure is predicted using computational fluid dynamics coupled with a population balance model (CFD-PBM). Besides, the structure-activity relationship between meso-scale flow structure and transfer performance is investigated. The results indicated a notable phenomenon of bubble aggregation/breakage in the moist air-IL desiccant bubbly deep dehumidification (MA-ILD BDD) system, with a specific interfacial area is basically less than 40 m−1. Meanwhile, a decrease in solution temperature, correlated with a significant increase in viscosity, leads to larger turbulent eddies and a slower breakage rate. Notably, a high transfer potential difference enhances heat and mass transfer coefficients at lower solution temperatures, with the mass transfer coefficient at 4°C being approximately three times that at 10°C. As the superficial velocity changes, the specific interfacial area and heat and mass transfer coefficients have a positive synergistic effect on volumetric transfer coefficient. However, this synergistic effect is reversed with variations in solution temperature. This study aims to clarify the air-liquid transfer mechanism in bubble column dehumidifier using IL desiccant. [ABSTRACT FROM AUTHOR]

Chemical enhanced oil recovery (EOR) methods return produced water containing polymers and surfactants which poses a water treatment challenge at offshore facilities. The present work shows that numerical simulations of gas‐water systems containing these chemicals remain challenging. Computational fluid dynamics (CFD) was used to predict gas holdup in a laboratory bubble column containing brine and EOR chemicals. The synthetic produced water was treated as non‐Newtonian in the simulations to match the experimentally‐determined physical properties. Two‐ and three‐dimensional numerical simulations were performed, and the latter were shown to be more appropriate through statistical analysis. Three classical drag models were assessed, and the results indicated that none of them could account for the high liquid viscosities and low surface tensions encountered in the system. A modification to the drag model of Tomiyama et al. (1988) was proposed to account for drag increases at low bubble Reynolds numbers when liquid apparent viscosity is high and surface tension is low. The importance of considering the interaction between apparent viscosity and surface tension was also shown through statistical analysis. CFD predictions of gas holdup showed that the proposed drag modification reduced errors from approximately 30% to less than 10% when compared to the experimental data. Radial profiles of the axial liquid velocity were also assessed and are apparently related to gas holdup prediction. [ABSTRACT FROM AUTHOR]

The pyrolysis of low alkanes (in the following short "pyrolysis") has already been investigated during the 1960s. However, none of the reactor systems used at the time are capable of continuous operation. Therefore, the Karlsruhe Institute of Technology has intensified the development of the promising liquid metal bubble column technology in recent years, which is capable of continuous operation. Various key aspects have been addressed, such as scale‐up and the pyrolysis of high‐caloric natural gas. Herein, further developments for a pilot scale system have been investigated, which concern increased throughput and long‐term operation capabilities. Careful evaluation of the impact of according measures has been done, which shows that the achieved scale‐up has only negligible effects on the pyrolysis outcome. The effects of the scale‐up on residence times are negligible. The bubble formation behavior depends on the throughput and the characteristics of the orifice. Wall effects are marginal. Fundamental minimization of weeping could not be confirmed. Reactor pre‐chambers in combination with tin collection chambers are recommended for further scale‐up. An increase in the volume flow should be examined. In terms of long‐term operation , head as well as feed pressure control is recommended. [ABSTRACT FROM AUTHOR]

Based on the flow modeling and operational experience of the previous cylindrical loop reactor, we designed a sheet reactor combined with a loop reactor. The design with a cylindrical cross-section was applied to an equivalent cross-section (sheet) of several squares arranged next to each other. In accordance with the sedimentation processes experienced in the outlet branch, we created an algae trap, thereby reducing the flow to the level necessary for sedimentation. With this, I would like to achieve the already experienced, nearly 10-fold increase in algae concentration compared to the one in the mainstream.

Conventional packed bed humidifiers (PBH) are often employed in the humidification–dehumidification desalination system. However, these humidifiers need a considerable packing volume due to low heat and mass transfer characteristics. Injecting air into the water column in a bubble column humidifier (BCH) to improve heat and mass transfer is receiving increasing attention. Hence, this paper proposes a novel design of BCH for multi-stage air heating and humidification. The proposed multi-stage BCH is theoretically and experimentally investigated. The feasibility is further assessed by comparing the performance with those of PBH. Mathematical models based on the heat and mass transfer process have been developed for BCH and PBH. The simulation results revealed that the theoretical models agreed well with the experimental data. Experimental results showed that the water height in the column has a negligible effect on BCH efficiency; however, feedwater mass flow rate, superficial velocity, and coil length have a significant effect. Furthermore, findings demonstrated that two-stage BCH efficiency is about 16–21% and three-stage BCH efficiency is about 25–30% higher than single-stage BCH. Single-stage BCH achieved a vapor content difference of 27–43% higher than PBH, while two-stage and three-stage BCH achieved vapor content differences of 81–115% and 111–162% higher than PBH, respectively. [ABSTRACT FROM AUTHOR]

This work demonstrates the use of an ultrasonic methodology to monitor bubble density in a water column. A flow regime with droplet size distribution between 0.2 and 2 mm was studied. This range is of particular interest because it frequently appears in industrial flows. Ultrasound is typically used when the size of the bubbles is much larger than the wavelength (low frequency limit). In this study, the radius of the bubbles ranges between 0.6 and 6.8 times the wavelength, where wave propagation becomes a complex phenomenon, making existing analytical methods difficult to apply. Measurements in transmission–reception mode with ultrasonic transducers operating at frequencies of 2.25 and 5.0 MHz were carried out for different superficial velocities. The results showed that a time-averaging scheme is necessary and that wave parameters such as propagation velocity and the slope of the phase spectrum are related to the number of bubbles in the column. The proposed methodology has the potential for application in industrial environments. [ABSTRACT FROM AUTHOR]

Plasma-based water treatment (PWT) is a promising technology that can degrade various emerging contaminants. However, PWT application on an industrially viable scale is hindered by the lack of an efficient reactor design that combines enhanced plasma-liquid contact with high liquid throughput. This work investigates the applicability of a bubble column gas–liquid contactor to PWT. A pulsed plasma bubble column reactor with a concentric rod-cylinder electrode configuration was used to correlate contaminant removal performance with the gas–liquid contact parameters of the bubble column. A surfactant, rhodamine B dye, and a nonsurfactant, caffeine, were used as model contaminants at µM concentration levels. The bubble column characteristics, i.e., gas holdup, bubble size distribution, and gas–liquid area, were measured as a function of superficial gas velocity using image-based methods. Degradation rates of both contaminants increased with gas flowrate. For caffeine, the increase was attributed to intensified bulk liquid mixing, while dye degradation increased due to the increased gas–liquid area. Ultimately, we show that bubble column contactors significantly improve the utilization of plasma-generated reactive species toward contaminant degradation by distributing them over a large contact area. As a result, a better match between the plasma species interfacial flux and the interfacial contaminant concentration leads to improved treatment energy efficiency. Typical degradation energy efficiencies were ~ 10 g/kWh for caffeine and ~ 60 g/kWh for rhodamine B. [ABSTRACT FROM AUTHOR]

Gas-liquid contactors like bubble columns are crucial in chemical industries, yet conventional meshing methods often overlook local fluctuations, hampering accurate simulation of viscosity's damping effect on bubble behaviour. This leads to reduced gas hold-up and constrained mass transfer rates. To address these issues, a novel Computational Fluid Dynamics approach named Hybrid Multi-Phase Modelling with a Refined Mesh and Reformed Sparger is proposed. This method integrates a Refined Exterior Prismatic Hexahedral Core Mesh, combining unstructured hexahedral and prism meshes to accurately model fluid flow and bubble interactions. Global adaptive mesh refinement enhances simulation accuracy by refining mesh interfaces based on local error estimation. Additionally, a Pento-Centric Conical Orifice Sparger is introduced to produce smaller continuous bubbles and uniformly distribute them, increasing gas holdup and reducing turbulence. Finally, a Hybrid Volume of Flow with Discrete Element Method (VOF-DEM) is employed to address complex geometries, distinguishing phase interfaces with VOF and considering viscosity effects with DEM. Comparative analysis with existing techniques reveals significant improvements: skewness reduced to 0.07, orthogonal velocity increased to 0.98, and liquid velocity reached 0.25 m/s. Overall, this approach enhances gas-liquid contactor simulations, offering improved accuracy and performance in predicting bubble behaviour and mass transfer rates. [ABSTRACT FROM AUTHOR]

This study aims to analyze two-phase flow patterns of water and air in a vertical column using experimental tests, and investigate the effect of pulsed gas flow on the characteristics of the Taylor bubble under different inlet conditions. First, three patterns of bubble, slug, and churn were observed with above hundred tests and a flow patterns map was drawn. Then, the effect of the pulsed gas flow on the length of the Taylor bubble was investigated in 150 different experiments. The ranges of superficial velocity of liquid and gas phases were 0.12–0.28 m/s and 0.05–0.25 m/s, respectively. The frequency of pulsed gas feed was 0.25–4 Hz. The results of this study showed that the length of the Taylor bubble in pulsed gas feed decreases with increasing the frequency. In addition, at a fixed gas frequency, the bubble length increases with increasing gas velocity. Present study prove that the pulsed gas flow technique can reduce the length of Taylor bubbles, which will be useful for future industrial applications in two-phase gas-liquid columns. [ABSTRACT FROM AUTHOR]

A computational fluid dynamics coupled population balance model (CFD-PBM) was used to numerically simulate the fluid dynamics of bubble swarms in a bubble column containing non-Newtonian fluids. The effects of superficial gas velocity (Ug), the consistency index (K), and the flow index (n) on bubble size distribution (BSD), gas holdup, and fluid dynamic viscosity in a bubble column were analyzed at both local and overall scales. As Ug increases, the bubble breakup occurs excessively, the gas holdup increases, and the dynamic viscosity decreases. K and n were used to characterize the rheological properties of power law fluid. As K increases, fluid viscosity increases, bubble breakup rate decreases, gas holdup in the top zone is slightly lower than in the middle zone, and dynamic viscosity increases. Within the range of n from 0.45 to 1.07, when n is smallest, the relative frequency of bubbles smaller than the initial size is relatively large, and the overall and local gas holdup are the highest. When n = 1.07, the fluid exhibits shear-thickening properties, and the dynamic viscosity variations are significant. [ABSTRACT FROM AUTHOR]

Bubble columns are widely used in numerous industrial processes because of their advantages in operation, design, and maintenance compared to other multiphase reactor types. In contrast to their simple design, the generated flow conditions inside a bubble column reactor are quite complex, especially in continuous mode with counter-current liquid flow. For the design and optimization of such reactors, precise numerical simulations and modelling are needed. These simulations and models have to be validated with experimental data. For this reason, experiments were carried out in a laboratory-scale bubble column using shadow imaging and particle image velocimetry (PIV) techniques with and without counter-current liquid flow. In the experiments, two types of gases—relatively poorly soluble air and well-soluble CO2—were used and the bubbles were generated with three different capillary diameters. With changing gas and liquid flow rates, overall, 108 different flow conditions were investigated. In addition to the liquid flow fields captured by PIV, shadow imaging data were also statistically evaluated in the measurement volume and bubble parameters such as bubble diameter, velocity, aspect ratio, bubble motion direction, and inclination. The bubble slip velocity was calculated from the measured liquid and bubble velocities. The analysis of these parameters shows that the counter-current liquid flow has a noticeable influence on the bubble parameters, especially on the bubble velocity and motion direction. In the case of CO2 bubbles, remarkable bubble shrinkage was observed with counter-current liquid flow due to the enhanced mass transfer. The results obtained for bubble aspect ratio are compared to known correlations from the literature. The comprehensive and extensive bubble data obtained in this study will now be used as a source for the development of correlations needed in the validation of numerical simulations and models. The data are available from the authors on request. [ABSTRACT FROM AUTHOR]

For technical application with continuous operation of sorption-enhanced (SE) reactions, e.g., Fischer–Tropsch, a special reactor concept is required. SE processes are promising due to the negative effects of water on conversion and catalyst. The reactor concept of two interconnected slurry bubble columns combines the reaction with in situ water removal in the first, and sorbent regeneration in the second column with continuous exchange of slurry between the two. The liquid circulation rate (LCR) between the columns is studied in a cold flow model, measured by an ultrasonic sensor. The effects of different operating and geometric parameters, e.g., superficial gas velocity, liquid level and tube diameter on gas holdup and LCR are discussed and modelled via artificial intelligence methods, i.e., extremely randomized trees and neural networks. It was found that the LCR strongly depends on the gas holdup. The maximum of 4.28 L min−1 was reached with the highest exit, widest tube and highest superficial gas velocity of 0.15 m s−1. The influence of liquid level above the exit was marginal but water quality has to be considered. Both models offer predictions of the LCR with errors < 6%. With an extension of the models, particle circulation can be studied in the future. [ABSTRACT FROM AUTHOR]

Inspired by the vast potential of microalgae in the bioeconomy and the numerous applications and benefits associated with their cultivation, a multitude of pilot- and industrial-scale microalgae production systems have been developed in recent years. Both open and closed cultivation systems have been successfully utilized, with closed photo-bioreactors (PBRs) emerging as the most versatile option for various applications and products, enabling the implementation of advanced optimization strategies. Therefore, this short review provides a comprehensive overview of the different PBR configurations and their recent applications, primarily in large-scale but also in pilot- and laboratory-scale microalgae cultivation. A detailed discussion of the advantages, limitations, specific applications and recent advancements of each type of PBR is presented to aid researchers, engineers and industry stakeholders in selecting the most suitable PBR design for their specific goals and constraints. Moreover, this review highlights the major challenges impeding the full commercialization of microalgal products and forecasts future trends in the microalgae-based industry. The diverse potential applications of microalgae in various sectors, including biofuels, nutraceuticals, pharmaceuticals, agriculture and environmental remediation, underscore the versatility and significance of the relevant cultivation technologies. By offering valuable insights into the future commercial scale and trends of microalgal biotechnology, this work sheds light on the challenges and opportunities facing this burgeoning industry. [ABSTRACT FROM AUTHOR]

Bubbly flow in bubble column reactors promotes mixing necessary for many chemical processes. We show that if superhydrophobic-coated material is introduced into a bubble column, there can be a substantial difference in gas holdup and earlier initiation of churn-turbulent flow which can alter larger-scale mixing without a need to change the superficial gas velocity. Addition of superhydrophobic surface can also cause bubbles to (directly or indirectly assisted by the surface) escape faster to the free surface resulting in a reduced void fraction (i.e., reduced gas holdup). As the flow becomes optically opaque at few percent gas phase volume fraction, we utilize two dual plane wire mesh sensors to obtain velocity profiles and bubble size distributions, in addition to the traditional pressure and level based gas holdup measurements to calculate average phase fraction. Additionally, a custom build photon-counting dual energy threshold X-ray computed tomography system is employed to get a higher resolution measurement of the time average phase fraction non-intrusively. We report satisfactory agreement between these techniques with differences arising for understood reasons, and use the insight thus yielded to discuss the effect of superhydrophobic surfaces on bubble column flow dynamics.

The work proposed a novel micro-bubble system using swirling jet flow method for improving the physical absorption of CO2 in water. The effects of operating conditions; e.g. gas flow rate (from 500 to 2000 mL/min), inlet pressure (2 and 3.5 bar) and inlet CO2 concentration (from 5 to 60 % v/v in CO2/N2 gas mixture) on the physical absorption of CO2 were studied. It was found that the CO2 absorption system reached to steady state after 30 min with the outlet CO2 concentrations of 2.9 % and 8.8 % at 40 % and 60 % of inlet CO2 concentrations, respectively. These outlet CO2 concentrations demonstrated the standard of bio-methane for replacing natural gas in vehicle use, from which

Bubble columns are omnipresent in the chemical, bio-chemical, petrochemicals, petroleum industries, but their design and scale-up is complex owing to its complex hydrodynamics. Liquid velocity and gas holdup is one of the critical hydrodynamic parameters which effects the mixing, heat and mass transfer in bubble columns. CFD is widely recognized as a powerful tool for estimating critical hydrodynamic parameters but requires significant computational resources, time and expertise. These limitations restrict its practical use in hydrodynamic simulations that need real-time processing involving large-scale simulations of bubble columns. To overcome these limitations, CFD-DNN model is developed to predict the time averaged gas holdup and axial liquid velocity at various operating conditions. The DNN model was trained using CFD data that was produced for rectangular (with dimensions L=0.2 m, W=0.05 m, H=1.2 m) and cylindrical (with a diameter of 0.19 m) bubble columns. The data covers a range of operating conditions and various flow regimes. The superficial gas velocity for the rectangle column was selected at 1.33 and 7.3 mm/s, whereas for the cylindrical bubble column, it was fixed at 0.02 and 0.12 m/s. The CFD-DNN model was validated against the experimental and the CFD data from the literature. Further, the model was tested for new data that the CFD-DNN model has not seen with existing literature and showed good agreement with their data and it reflects the excellent generalization ability of the model. The proposed CFD-DNN approach improves current CFD models by providing shorter computing time, decreasing computational expenses, and reducing the expertise in CFD simulations. The accuracy of the developed CFD-DNN model was evaluated using different metrics for gas holdup and axial liquid velocity. For rectangular bubble columns, the model achieved MSE of 0.0001 for gas holdup and 0.0007 for axial liquid velocity. Similarly, for cylindrical bubble columns, the MSE values were 0.0009 for gas holdup and 0.0006 for axial liquid velocity.

AbstractThe article reports a new approach for flow regime (FR) identification and a modified correlation for gas holdup prediction in a bubble column (BC) (0.1 m inner diameter) operated with aqueous solutions of 2-pentanol at ambient conditions. The hydrodynamic behavior of mixtures of deionized water (DW) and 2-pentanol with different volume concentrations (0.5 − 2.0 vol.%) was examined. A new algorithm for estimation of the information amount (IA) from a gauge pressure (GP) signal is proposed. It is based on simultaneous statistical and error analyses of the sub-divided GP time series. The new approach extracts detailed hidden information from every sector of the time-dependent GP signal. In case of 0.5 vol.% 2-pentanol dissolved in DW, by means of the local well-pronounced IA minima, three transition velocities Utrans (at 0.043, 0.054 and 0.073 m/s) were reliably identified. The first critical velocity was comparable with the prediction of a well-known empirical correlation. When the volume concentration of 2-pentanol in DW was doubled, then the three Utrans values were distinguished at 0.049, 0.063 and 0.074 m/s, respectively. In addition, the end of the gas maldistribution state was identified at 0.041 m/s. It was found that the increase of the alcohol concentration affects the first and second Utrans values but not the third one, i.e. the onset of the complete foaming state. The overall gas holdups were also successfully predicted in both homogeneous and transition flow regimes of BC operation. One of the parameters (taking part in a dimensionless group about the scale effect) in an existing empirical correlation was modified in order to predict the overall gas holdups recorded in different aqueous solutions of 2-pentanol. The modified parameter was fitted for every mixture investigated. The average relative error was reasonably low in every case.

CO2 capture experiments were carried out in a small-scale bubble column reactor using alkaline solutions of sodium hydroxide. The results of the experiments show that a higher NaOH content in the liquid phase and elevated CO2 concentrations in the gas mixture led to a higher CO2 removal efficiency. A mathematical model was developed to describe the CO2 absorption as a function of CO2 gas inlet and OH- concentrations at low CO2 and OH- concentrations. The CO2 uptake at high OH- concentrations (high pH) was accurately predicted by the model, whereas the CO2 uptake at lower OH- concentrations could not be predicted with the same accuracy. [ABSTRACT FROM AUTHOR]

Bubble columns are widely encountered in several industries, especially in the field of nuclear safety. The Eulerian-Eulerian and the Eulerian-Lagrangian methods are commonly used to investigate bubble columns. Eulerian approaches require additional tasks such as strict volume conservation at the interface and a predefined well-structured grid. In contrast, the Lagrangian approach can be easily implemented. Hence, we introduce a fully Lagrangian approach for the simulation of bubble columns using the discrete bubble model (DBM) and moving particle semi-implicit (MPS) methods. Additionally, we propose a rigorous method to estimate the volume fraction accurately, and verified it through experimental data and analytical results. The MPS method was compared with the experimental data of Dambreak. The DBM was verified by analyzing the terminal velocity of a single bubble for each bubble size. It agreed with the analytical results for each of the four drag correlations. Additionally, the improved method for calculating the volume fraction showed agreement with the Ergun equation for the pressure drop in a packed bed. The implemented MPS-DBM was used to simulate the bubble column, and the results were compared with the experimental results. We demonstrated that the MPS-DBM was in quantitative agreement with the experimental data.

With the increasing use of renewable energy resources for the power grid, the need for long-term storage technologies, such as power-to-gas systems, is growing. Biomethanation provides the opportunity to store energy in the form of the natural gas-equivalent biomethane. This study investigates a novel plug flow reactor that employs a helical static mixer for the biological methanation of hydrogen and carbon dioxide. In tests, the reactor achieved an average methane production rate of 2.5 L C H 4 L R ∗ d (methane production [LCH4] per liter of reactor volume [LR] per day [d]) with a maximum methane content of 94%. It demonstrated good flexibilization properties, as repeated 12 h downtimes did not negatively impact the process. The genera Methanothermobacter and Methanobacterium were predominant during the initial phase, along with volatile organic acid-producing, hydrogenotrophic, and proteolytic bacteria. The average ratio of volatile organic acid to total inorganic carbon increased to 0.52 ± 0.04, while the pH remained stable at an average of pH 8.1 ± 0.25 from day 32 to 98, spanning stable and flexible operation modes. This study contributes to the development of efficient flexible biological methanation systems for sustainable energy storage and management. [ABSTRACT FROM AUTHOR]

Hydrodynamics characterization in terms of flow regime behavior is a crucial task to enhance the design of bubble column reactors and scaling up related methodologies. This review presents recent studies on the typical flow regimes established in bubble columns. Some effort is also provided to introduce relevant definitions pertaining to this field, namely, that of "void fraction" and related (local, chordal, cross-sectional and volumetric) variants. Experimental studies involving different parameters that affect design and operating conditions are also discussed in detail. In the second part of the review, the attention is shifted to cases with internals of various types (perforated plates, baffles, vibrating helical springs, mixers, and heat exchanger tubes) immersed in the bubble columns. It is shown that the presence of these elements has a limited influence on the global column hydrodynamics. However, they can make the homogeneous flow regime more stable in terms of transition gas velocity and transition holdup value. The last section is used to highlight gaps which have not been filled yet and future directions of investigation. [ABSTRACT FROM AUTHOR]

Methane pyrolysis in molten catalyst bubble (MCB) column reactors is an emerging technology that enables the simultaneous production of hydrogen and solid carbon, together with a mechanism for separating the two coproducts. In this process, methane is dispersed as bubbles into a high temperature molten catalyst bath producing hydrogen and low-density carbon, which floats to the surface of the bath from providing a means for them to be separated. However, the removal of carbon particulates from a bubbling column reactor is technically challenging due to the corrosive nature of the molten catalysts, contamination of the product carbon with the molten catalysts, high temperatures and lack of understanding of the technology options. Four potential concepts for the removal of carbon particulate from a methane pyrolysis molten metal bubble column reactor are presented, based on the pneumatic removal of the particles or their overflow from the reactor. The concepts are evaluated using a cold prototype reactor model. To simulate the operation of a high-temperature reactor at low temperatures, the dominant dimensionless numbers are identified and matched between a reference high-temperature reactor and the developed cold prototype using water, air and hollow glass microsphere particles as the representatives of the molten catalyst, gaseous phases and solid carbon particulates, respectively. The concepts are tested in the cold prototype. High rates of particle removal are achieved, but with different tradeoffs. The applicability of each method together with their advantages and disadvantages are discussed. [ABSTRACT FROM AUTHOR]

Systematic changes in interfacial forces, turbulence models for the continuous and dispersed phases, lift force coefficient, and bubble size distribution were used to evaluate, in terms of complexity, the performance of nine computational models in the simulation of the time-averaged axial liquid velocity and holdup profiles in a bubble column. The oscillation period of the gas plume was also included in this evaluation. The mesh used for the simulations was chosen after a convergence analysis carried out with four meshes. The finest mesh displayed the highest divergence from the experimental data. Such behavior indicates that the proper mesh for a simulation of a multiphase flow must consider other factors in addition to element size and the quality indicators. The standard, RNG, and realizable κ-ε models were used for the liquid phase, while an algebraic and the standard κ-ε were the models for the dispersed phase. The isotropic RNG model for the liquid phase achieved accurate predictions in the anisotropic region near the gas distributor. The algebraic approach for the gas phase produced data similar to those calculated with the standard model. The simultaneous presence of the lift and virtual mass forces led to reliable predictions, and a lift coefficient of 0.2 displayed better performance than 0.14. This coefficient produced an excessive dampening of the lift force and caused the simulations to lose accuracy. The population balances did not improve the predictions. [Display omitted] • Systematic assessment of computational models for simulations of bubble columns. • Significant role of the lift and virtual mass forces in the quality of simulations. • The lift force is part of the mechanisms producing the oscillation of the gas plume. • Additional factors to the grid convergence for choosing the right mesh. • Algebraic model of the dispersed phase simplifies the simulations. [ABSTRACT FROM AUTHOR]

This article describes the development of a new technology based on the application of liquid metal and aims to produce hydrogen by decarbonization (pyrolysis process) of both natural and artificially synthesized hydrocarbons. When biogas with a sufficiently high carbon dioxide content is used as a feedstock, or by the targeted addition of CO2 to methane, a mixture of hydrogen and carbon monoxide (synthesis gas) can be produced. Furthermore, the paper describes another very interesting application of the technology to create negative emissions. In this scenario, the processes direct air capture, methanation, electrolysis and methane pyrolysis are combined to synthesize solid carbon from atmospheric CO2. The broad range of process options investigated indicates that, when the technology is scaled up to industrial scale, the result will be a process that is flexible in both the use of reactants and the resulting products. [ABSTRACT FROM AUTHOR]

Detailed knowledge of the flow characteristics, bubble movement, and mass transfer is a prerequisite for the proper design of multiphase bioreactors. Often, mechanistic spatiotemporal models and computational fluid dynamics, which intrinsically require computationally demanding analysis of local interfacial forces, are applied. Typically, such approaches use volumetric mass-transfer coefficient (kLa) models, which have demonstrated their predictive power in water systems. However, are the related results transferrable to multiphase fermentations with different physicochemical properties? This is crucial for the proper design of biotechnological processes. Accordingly, this study investigated a given set of mass transfer data to characterize the fermentation conditions. To prevent time-consuming simulations, computational efforts were reduced using a force balance stationary 0-dimension model. Therefore, a competing set of drag models covering different mechanistic assumptions could be evaluated. The simplified approach of disregarding fluid movement provided reliable results and outlined the need to identify the liquid diffusion coefficients in fermentation media. To predict the rising bubble velocities uB, the models considering the Morton number (Mo) showed superiority. The mass transfer coefficient kL was best described using the well-known Higbie approach. Taken together, the gas hold-up, specific surface area, and integral mass transfer could be accurately predicted. [ABSTRACT FROM AUTHOR]

To improve the design and scale-up processes of bubble column reactors (BCRs), it is necessary to characterize the hydrodynamics by means of flow regime behavior. This study examines the impact of industrial heat exchangers and superficial gas velocities on flow regimes, pressure drop, and gas holdup in BC and SBC. A simulated Fischer–Tropsch bubble column is constructed. The experimental study utilized a Perspex column with a diameter of 0.14 m. Moreover, 18 copper tubes with a 0.16 m diameter are fitted into the bubble column. The selection of tubes in SBC was carried out in accordance with TEMA recommendations to ensure optimal heat dissipation. These tubes were made to resemble the industrial Fischer–Tropsch reactor by covering 25% of the bubble column's cross-sectional area. In order to enhance the measurement and comprehension of the hydrodynamics within the reactor, this study employs a method measured the total gas hold-up and detected pressure fluctuations using three differential pressure transducers (Keller type PA 21Y/4). The column was equipped with a perforated plate air distributor, and glass beads were used as the solid phase. The gas distributor is constructed of porous polyethylene with pore sizes of 0.5 mm and plate thicknesses of 3 mm. To comprehend and assess the impact of tube configuration on the pressure drop; gas holdup; and regime transition velocities, the experimental data were recorded across a broad range of superficial gas velocities (i.e., 0.036–0.27 m/s). The findings suggest that higher superficial gas velocities result in amplified pressure fluctuations, with a recorded increase of 0.108 to 0.15 bar in pressure drop at a gas velocity of 0.27 m/s in the air-water system. Equipping the bubble/slurry bubble column with an industrial heat exchanger to the bubble/slurry bubble column resulted in a modest increase in pressure drop of around 0.042 bar, which disrupted the uniform flow and delayed regime transitions. Furthermore, the inclusion of solids leads to a 10% decrease in gas holdup, while the heat exchanger only slightly improves it by 5%. Drift flux analysis is a helpful tool for determining transition points. In the case of U-shaped heat exchanger tubes, the transition velocities can be altered by 1.7 m/s in BC. The results of this investigation will offer an exhaustive understanding of fluid dynamics as well as guidance in the design of reactors for extremely exothermic processes. [ABSTRACT FROM AUTHOR]

This work demonstrates the use of an ultrasonic methodology to monitor bubble density in a water column. A flow regime with droplet size distribution between 0.2 and 2 mm was studied. This range is of particular interest because it frequently appears in industrial flows. Ultrasound is typically used when the size of the bubbles is much larger than the wavelength (low frequency limit). In this study, the radius of the bubbles ranges between 0.6 and 6.8 times the wavelength, where wave propagation becomes a complex phenomenon, making existing analytical methods difficult to apply. Measurements in transmission–reception mode with ultrasonic transducers operating at frequencies of 2.25 and 5.0 MHz were carried out for different superficial velocities. The results showed that a time-averaging scheme is necessary and that wave parameters such as propagation velocity and the slope of the phase spectrum are related to the number of bubbles in the column. The proposed methodology has the potential for application in industrial environments.

Hydrogen can be produced via methane pyrolysis in a molten metal bubble column to create separable carbon. Tin is used as a base metal in this study, and catalytically active metals such as nickel and copper are added to it. The study uses a differential equation that takes into account both parallel catalytic surface reactions on the bubble surface and conventional noncatalytic reactions in the gas bulk. The research analyzes the effect of molten metal type, temperature, and orifice diameter on the bubble surface-to-volume ratio and their effects on the catalytic surface reaction and the gas phase reaction in the bubble. The results indicate that the 5 wt% Ni–Sn mixture performs best among the studied alloys, with a calculated surface reaction fraction of approximately 90% at 950 °C, confirming the dominant effect of catalytic activity. In addition, the study estimates the conversion under different conditions of temperature, orifice diameter, and molten metal height by solving the differential equation using kinetic parameters derived from experimental results. The results can be used for future reactor design.

A one-dimensional (1D) molten-metal-based bubble-column reactor (MMBCR) model coupled with heat transfer and axial dispersion was developed for non-oxidative CH 4 pyrolysis to produce low-carbon H 2. The MMBCR model included mass, momentum, and energy balances, accounting for catalytic and non-catalytic reaction kinetics, and hydrodynamic parameters such as the gas holdup (α G), gas velocity (u G), bubble size (d b), and specific interfacial surface area of bubbles (a s). The 1D MMBCR model was compared with other 1D reactor models and bench-scale experimental data for CH 4 conversion (X M). The MMBCR model agreed well with the experimental data. When heat transfer and axial dispersion were considered for an industrial-scale MMBCR to produce 10,000 Nm3/h, the reactor length increased to 2.4 times higher than that estimated by the model without axial dispersion to meet 80% X M. The MMBCR model has the potential to design industrial-scale MMBCRs and optimize operating conditions. [Display omitted] • One-dimensional molten metal-based bubble column reactor (MMBCR) model was developed. • MMBCR model for CH 4 pyrolysis was coupled with heat transfer and axial dispersion. • Heat transfer and axial dispersion slightly affect bench-scale MMBCRs CH 4 conversion. • Axial dispersion lowered the CH 4 conversion of an industrial-scale MMBCR by 17%. • The MMBCR model is useful to design the reactors and optimize operating conditions. [ABSTRACT FROM AUTHOR]

This study proposed a new approach for measuring bubble size distribution, bubble mean diameter, Sauter mean bubble diameter, and gas holdup using a double‐sensor conductivity probe in an air/water two‐phase system bubble column. The results for the two‐phase system were compared and calibrated using analyses from bubble images taken by a digital camera from the side of the column wall. Good agreement was observed between the two techniques. The same double‐sensor conductivity was used in an air/water/solids three‐phase system. The conductivity probe captured the change in bubble dynamic behaviour inside the pulp phase; however, the presence of the solids made it more challenging to measure. As a result, the VisioFroth commercial package, using images taken from the top of the froth layer, could be used in conjunction with the double‐sensor conductivity probe to show the dynamic evolution of mineralized bubbles from the pulp zone to the froth zone in a flotation process. [ABSTRACT FROM AUTHOR]

The process of biological methanation in bubble column reactors was established in single reactors and cascade by the joint research project BioStore (SAB, FKZ: 100310024). In order to increase the efficiency of the process, energy‐intensive components such as agitators or gas separation were not used as far as possible. Furthermore, the gas injection system was optimized as a performance‐determining component in order to maximize conversion and methane rate. As a result, methane content of over 96 vol % and a methane formation rate of 2 L/(L × d) were achieved in continuous operation. This fulfils a technical requirement for direct injection into the natural gas grid. [ABSTRACT FROM AUTHOR]

Scale-up bubble columns for wet air oxidation (WAO) represent a novel solution to the growing problem of sodium acetate-containing waste discharge. This study used an axial dispersion model to simulate a reactor at a high temperature of 320 °C. By minimizing the structure size and gas fed into the system, the estimated optimal reactor dimensions were obtained. At the optimized reactor diameter, total height, initial oxygen partial pressure, and superficial gas velocity of 1 m, 7 m, 40 bar, and 0.07 m/s, respectively, a degradation efficiency of over 90% was obtained, at which the residual concentration of sodium acetate degraded from 700 mol/m3 to 70 mol/m3. The axial distributions of the dissolved oxygen, sodium acetate, and oxygen concentrations in the gas were nearly uniform. The bubble column reactor exhibited an intermediate state between well-mixed flow and plug flow for both liquid and gas. [ABSTRACT FROM AUTHOR]

Water scarcity is a pressing global issue driving the need for efficient and sustainable water reuse and desalination technologies. In the last two decades, humidification–dehumidification (HDH) has emerged as a promising method for small-scale and decentralized systems. This paper presents a comprehensive review of recent scientific literature highlighting key advancements, challenges, and potential future directions of HDH research. Because the HDH process suffers from low heat and mass transfer, as well as thermodynamic limitations due to the mild operating conditions, this work indicates three main strategies for HDH enhancement: (1) Advanced Heat and Mass Transfer Techniques, (2) Integration with Other Technologies, and (3) Optimization of System Operative Conditions. Particularly for advanced HDH systems, the reference GOR values exceed 3, and certain studies have demonstrated the potential to achieve even higher values, approaching 10. In terms of recovery ratio, there appear to be no significant process constraints, as recycling the brine prepared in innovative schemes can surpass values of 50%. Considering electricity costs, the reference range falls between 1 and 3 kWh m–3. Notably, multi-stage processes and system couplings can lead to increased pressure drops and, consequently, higher electricity costs. Although consistent data are lacking, a baseline SEC reference value is approximately 360 kJ kg–1, corresponding to 100 kWh m–3. For comparable SEC data, it is advisable to incorporate both thermal and electric inputs, using a reference power plant efficiency of 0.4 in converting thermal duty to electrical power. When considering the utilization of low-temperature solar and waste heat, the proposed exergy-based comparison of the process is vital; this perspective reveals that a low-carbon HDH desalination domain, with II-law efficiencies surpassing 0.10, can be achieved. [ABSTRACT FROM AUTHOR]

For technical application with continuous operation of sorption-enhanced (SE) reactions, e.g., Fischer–Tropsch, a special reactor concept is required. SE processes are promising due to the negative effects of water on conversion and catalyst. The reactor concept of two interconnected slurry bubble columns combines the reaction with in situ water removal in the first, and sorbent regeneration in the second column with continuous exchange of slurry between the two. The liquid circulation rate (LCR) between the columns is studied in a cold flow model, measured by an ultrasonic sensor. The effects of different operating and geometric parameters, e.g., superficial gas velocity, liquid level and tube diameter on gas holdup and LCR are discussed and modelled via artificial intelligence methods, i.e., extremely randomized trees and neural networks. It was found that the LCR strongly depends on the gas holdup. The maximum of 4.28 L min−1 was reached with the highest exit, widest tube and highest superficial gas velocity of 0.15 m s−1. The influence of liquid level above the exit was marginal but water quality has to be considered. Both models offer predictions of the LCR with errors < 6%. With an extension of the models, particle circulation can be studied in the future.

Bubble columns are widely used in numerous industrial processes because of their advantages in operation, design, and maintenance compared to other multiphase reactor types. In contrast to their simple design, the generated flow conditions inside a bubble column reactor are quite complex, especially in continuous mode with counter-current liquid flow. For the design and optimization of such reactors, precise numerical simulations and modelling are needed. These simulations and models have to be validated with experimental data. For this reason, experiments were carried out in a laboratory-scale bubble column using shadow imaging and particle image velocimetry (PIV) techniques with and without counter-current liquid flow. In the experiments, two types of gases—relatively poorly soluble air and well-soluble CO2—were used and the bubbles were generated with three different capillary diameters. With changing gas and liquid flow rates, overall, 108 different flow conditions were investigated. In addition to the liquid flow fields captured by PIV, shadow imaging data were also statistically evaluated in the measurement volume and bubble parameters such as bubble diameter, velocity, aspect ratio, bubble motion direction, and inclination. The bubble slip velocity was calculated from the measured liquid and bubble velocities. The analysis of these parameters shows that the counter-current liquid flow has a noticeable influence on the bubble parameters, especially on the bubble velocity and motion direction. In the case of CO2 bubbles, remarkable bubble shrinkage was observed with counter-current liquid flow due to the enhanced mass transfer. The results obtained for bubble aspect ratio are compared to known correlations from the literature. The comprehensive and extensive bubble data obtained in this study will now be used as a source for the development of correlations needed in the validation of numerical simulations and models. The data are available from the authors on request.

Liquid-phase dispersion in a continuous flow bubble column was studied using computational fluid dynamics (CFD) and different combinations of turbulence and biphasic models. The results were compared with the experimental data obtained by the stimulus-response method in an air-water pilot-scale bubble column (2 m tall, 0.234 m internal diameter). Two flow combinations were examined: high flow rates of 3.2 m3 h−1 and 4.5 m3 h−1 and low flow rates of 1.98 m3 h−1 and 0.954 m3 h−1 for water and air, respectively. The objective was to evaluate commercial CFD 16.1 software to predict flow behavior beyond macroscale parameters such as hold-up or mixing time. The turbulence models that best replicated the experimental tracer dispersion were large eddy simulation-type models: scale-adaptive simulation (SAS) and shear stress transport-SAS. The simulations qualitatively predicted the tracer concentration with time but were unable to reveal the small-scale perturbations in the biphasic system. The predicted tracer residence time was double or triple the measured times for low and high flow, respectively. [ABSTRACT FROM AUTHOR]

The increasing share of renewable electricity in the grid drives the need for sufficient storage capacity. Especially for seasonal storage, power-to-gas can be a promising approach. Biologically produced methane from hydrogen produced from surplus electricity can be used to substitute natural gas in the existing infrastructure. Current reactor types are not or are poorly optimized for flexible methanation. Therefore, this work proposes a new reactor type with a plug flow reactor (PFR) design. Simulations in COMSOL Multiphysics ® showed promising properties for operation in laminar flow. An experiment was conducted to support the simulation results and to determine the gas fraction of the novel reactor, which was measured to be 29%. Based on these simulations and experimental results, the reactor was constructed as a 14 m long, 50 mm diameter tube with a meandering orientation. Data processing was established, and a step experiment was performed. In addition, a kLa of 1 h−1 was determined. The results revealed that the experimental outcomes of the type of flow and gas fractions are in line with the theoretical simulation. The new design shows promising properties for flexible methanation and will be tested. [ABSTRACT FROM AUTHOR]

We have investigated the effect of the surfactant Sodium Dodecyl Sulfate on the bubble growth and detachment processes in a bubble column system. A modified pendant drop model was employed to determine the dynamic surface tension. The dynamic surface tension approached the static surface tension value within a few seconds. A photographic technique and a laser-based electro-optical method were used to study the bubble size variation and the generation frequency, respectively. Parameters like bubble generation frequency, size, growth rate, and contact angle were found to be a strong function of surfactant concentration. Our results show that the addition of surfactant significantly reduces the bubble lifetime at the orifice. Such a decrease in the bubble lifetime has a direct impact on the bubble growth rate and departure size. Furthermore, bubble parameters vary with surfactant concentration only up to the critical micellar concentration. [ABSTRACT FROM AUTHOR]

Three ionic liquids (ILs) containing the same cation but different anions were synthesized and used to separate SO2 from its mixture with air in a semi‐batch bubble column absorber. Desulphurization efficiency was determined using a state‐of‐the‐art experimental set‐up relevant to chemical process industries concerning the important process variables. The virgin and exhausted ILs were characterized using TGA, FTIR, and 1H NMR analyses. The concentrations of SO2 at the inlet to and exit from the absorber were measured using a ZRJFAY36, Fuji, Japan infrared SO2 analyzer. A maximum of 92 percent removal efficiency (PRE) was achieved from a feed gas containing 250–1500 ppm SO2 with the use of 2‐hydroxyethyl ammonium lactate [MEA][L] or tri (2‐hydroxyethyl) ammonium lactate ([TEA][L]), as the absorbents. This could be further enhanced by the interactive effect of the simultaneous increase in the superficial velocity of the gas and the volume of IL fed into the absorber. However, PRE was about 20% less with tri (2‐hydroxyethyl) ammonium salicylate ([TEA][S]). It was observed that the ILs, [MEA][L] and [TEA][L], were fairly suitable for flue gas desulphurization in industrial situations. A design criterion for continuous operation using two semi‐batch absorbers has been proposed. [ABSTRACT FROM AUTHOR]

A dynamic one-dimensional numerical model of methane pyrolysis within a rising and pyrolysing bubble in a column of molten N i 0.27 B i 0.73 , as a molten catalyst, is presented. The model predicts both the behavior of the rising bubble in the column and the chemical reactions within it, accounting for any variations in bubble diameter and rising velocity, which have previously been assumed to be constant. The conservation equations of energy, mass and momentum are solved simultaneously using the implicit Gauss–Seidel numerical method. The model accounts for the main parameters contributing to the methane pyrolysis reaction. The reliability of the model was assessed by comparison with the available experimental data from the literature and a reasonable agreement was found. Considering the model assumptions, the results show that, for the assessed conditions, more than 97% of the overall conversion occurs at the interface of the bubble and the molten bath, while the reaction within the bubble contributes only <3% of the overall conversion. A sensitivity analysis was also undertaken to the variations in the bubble size, column height, molten bath temperature, pressure, gas composition and temperature. Calculations show that methane conversion is more sensitive to the molten bath temperature than the initial gas temperature. Furthermore, it decreases significantly with any increase in pressure. Also, at pressures of > 2 MPa, the equilibrium condition is achieved within the bottom one-third of the column for the assessed conditions. [Display omitted] • Numerical model of a single rising and pyrolysis methane bubble in molten catalyst. • Effects of various parameters on methane conversion studied. • Methane conversion increases by ∼12% as bubble size is reduced from 2.6 to 0.6 mm. • Methane conversion decreases as pressure increases from 0.1 to 8 MPa. [ABSTRACT FROM AUTHOR]

This contribution presents the results of continued investigations on the production of hydrogen by means of pyrolysis in a liquid metal bubble column reactor, as developed at the Karlsruhe Institute of Technology in recent years. Part I of this contribution described the motivation and the methodology of this study, as well as a significant scale-up, and discussed its results for pure methane pyrolysis. Here in part II, two additional experimental campaigns with methane–ethane mixtures (MEMs) and high-calorific natural gas (nGH) will be presented and discussed for the first time, using the up-scaled liquid metal bubble column reactor. It could be proven that an MEM as the feed gas led to an increase in methane conversion at low temperatures, which is consistent with the literature data. The nGH pyrolysis confirms this trend and also results in a significant rise in methane conversion compared to pure methane pyrolysis. Furthermore, the nGH pyrolysis leads to an increased methane conversion even at higher temperatures compared to MEM pyrolysis. Additionally, both MEM and nGH pyrolysis also showed a shift in the formation of by-products toward lower temperatures. [ABSTRACT FROM AUTHOR]

Hydrogen is not only an important industrial chemical but also an energy carrier with increasing demand. However, the current production techniques are based on technologies that result in massive CO2 emissions. In contrast, the pyrolysis of alkanes in a liquid metal bubble column reactor does not lead to direct CO2 emissions. In order to transfer this technology from lab-scale to industrial applications, it has to be scaled up and the influences of the most common constituent of natural gas on the pyrolysis process have to be determined. For this study, the liquid metal bubble column technology developed at the KIT was scaled up by a factor of 3.75, referred to as the reactor volume. In this article, the experimental setup containing the reactor is described in detail. In addition, new methods for the evaluation of experimental data will be presented. The reactor, as well as the experimental results from pure methane pyrolysis (PM), will be compared to the previous generation of reactors in terms of methane conversion. It could be proven that scaling up the reactor volume did not result in a decrease in methane conversion. For part II of this publication, methane-ethane (MEM) gas mixtures and high calorific natural gas (nGH) were pyrolyzed, and the results were discussed on the basis of the present part I. [ABSTRACT FROM AUTHOR]