Thermal Decomposition Of Methane Research Articles

Investigation of the Minimum Ignition Energy Required for Combustion of Coal Dust Blended with Fugitive Methane

Ventilation Air Methane (VAM) significantly contributes to global warming. Capturing and mitigating these emissions can help combat climate change. One effective method is the thermal decomposition of methane, but it requires careful control to prevent explosions from the high temperatures involved. This research investigates the influence of methane concentration and coal dust particle properties on the minimum ignition energy (MIE) required for fugitive methane thermal decomposition and flame propagation properties. This knowledge is crucial for the mining industry to effectively prevent and mitigate accidental fires and explosions in VAM abatement plants. Coal dust samples from three different sources were selected for this study. Experiments were conducted using a modified Hartmann glass tube and a Thermal Gravimetric Analyser (TGA). The chemical properties of coal dust were determined through ultimate and proximate analysis. The particle size distribution was determined using a Mastersizer 3000 apparatus (manufactured by Malvern Panalytical, Malvern, UK). The results showed that the MIE is significantly affected by coal dust particle size, with smaller particles (<74 µm) requiring less energy to ignite compared to coarser particles. Additionally, blending methane with coal dust further reduces the MIE. Introducing methane concentrations of 1% and 2.5% into the combustion space reduced the MIE by 25% and 74%, respectively, for the <74 µm coal dust size fraction. It was observed that coal dust concentration can either raise or lower the MIE. Larger coal dust concentrations, acting as a heat sink, reduce the likelihood of ignition and increase the MIE. This effect was noted at a methane concentration of 2.5% and coal dust levels above 3000 g/m3. In contrast, small amounts of coal dust had little impact on MIE variation. Moreover, the presence of methane during combustion increased the upward flame travel distance and propagation velocity. The flame’s vertical travel distance increased from 124 mm to 300 mm for a coal dust concentration of 300 g·m−3 blended with 1% and 2.5% methane, respectively.

Literature Review on Thermodynamic and Kinetic Limitations of Thermal Decomposition of Methane

The state of the art in methane pyrolysis does not yet provide a definitive answer as to whether the concept of an elementary reaction is universally applicable to the apparently simple process of methane dissociation. Similarly, the literature currently lacks a comprehensive and unambiguous description of the methane pyrolysis process and, in particular, a single model that would well represent its course at both the micro and macro scales. Given the wide range of conditions under which this reaction can occur—whether thermal or thermo-catalytic, in solid or fluidized bed reactors—it is crucial to evaluate the usefulness of different kinetic models and their compatibility with basic thermodynamic principles and design assumptions. To address these research gaps, the authors analysed the thermodynamic and kinetic dependencies involved in the thermal decomposition of methane, using the synthesis of methane from its elemental components and its reversibility as a basis for exploring suitable kinetic models. Using experimental data available in the literature, a wide range of kinetic models have been analysed to determine how they all relate to the reaction rate constant. It was found that regardless of whether the process is catalytic or purely thermal, for temperatures above 900 °C the reversibility of the reaction has a negligible effect on the hydrogen yield. This work shows how the determined kinetic parameters are consistent with the Kinetic Compensation Effect (KCE) and, by incorporating elements of Transition State Theory (TST), the possibility of the existence of Entropy–Enthalpy Compensation (EEC). The indicated correspondence between KCE and EEC is strengthened by the calculated average activation entropy at isokinetic temperature (∆SB=−275.0 J·(mol·K)−1). Based on these results, the authors also show that changes in the activation energy (E=20–421 kJ·mol−1) can only serve as an estimate of the optimal process conditions, since the isoconversion temperature (Tiso=1200−1450 K>Teq) is shown to depend not only on thermodynamic principles but also on the way the reaction is carried out, with temperature (T) and pressure (P) locally compensating each other.

Reducing carbon dioxide emissions when using methane-hydrogen fuel

AIM. To determine optimal modes for methane decarbonization, as well as to assess CO2 emissions during subsequent combustion of the pyrolysis gas, including together with the natural gas in various ratios.METHODS. The processes of thermochemical conversion of methane into hydrogen and condensed carbon in a reactor with external heating of the walls were considered. The thermal energy required for gas pyrolysis is obtained by burning a mixture of air and part of the pyrolysis gas, which is free from solid carbon particles. When performing numerical studies of pyrolysis processes, a kinetic model of one-dimensional flow of the reacting mixture was used with an external supply of thermal energy through the walls of an axisymmetric channel (tubular reactor).RESULTS. The mechanism of chemical interaction during the thermal decomposition of methane was developed, taking into account the formation of condensed carbon in the temperature range from 1000 to 1200 °C. The main energy indicators and the composition of pyrolysis gas were determined at various values of the pyrolysis temperature and the degree of carbon conversion.CONCLUSION. Carbon dioxide emissions from the combustion of pyrolysis gas, including together with the natural gas, were assessed. When developing pyrolysis technologies and applying them on an industrial scale, it is advisable to use part of the resulting pyrolysis gas with a high hydrogen content to provide thermal energy for the processes of thermal decomposition of the feedstock. According to the calculations, the share of this part reaches ≈ 35% of the total amount of pyrolysis gas. This approach, as opposed to burning the natural gas for this purpose, significantly reduces CO2 emissions. The combustion of the resulting pyrolysis gas, even without removing residual hydrocarbons, is characterized by currently quite acceptable CO2 emission factors of ≈ 7-25 t CO2/TJ.

Design and modeling of a co-flow reactor for turquoise hydrogen production

This work focuses on the design of a reactor for producing clean hydrogen from methane pyrolysis in the form of the so-called “turquoise hydrogen”. In addition to its simple geometry, the fundamental concept and the main novelty of the proposed method rely on using part of the methane to produce the required heat needed for the thermal decomposition of methane (TDM). The reactor configuration for hydrogen production is shown to produce significant advantages in terms of greenhouse gas (GHG) emissions. A reactive flow CFD model incorporating also soot formation mechanism has been first developed and validated with experimental results available in the literature and then used to design and characterize the performances of proposed reactor configuration. 3D CFD simulations have been carried out to predict the behavior of the reactor configuration; a sensitivity analysis is used for clearing the aspect related to key environmental parameters, e.g., the global warming impact (GWI). The real potential of the proposed design resides in the low emissions and high efficiency with which hydrogen is produced at the various operating conditions (very flexible reactor), albeit subject to the presence of carbon by-product. This suggests that this type of methane conversion system could be a good substitute for the most common hydrogen production technologies.

Study on the mechanism of constructing structure defects on surface of activated carbon with carbon black to promote hydrogen production by thermal-decomposition of methane

Hydrogen production from catalytic decomposition of methane is a promising method of hydrogen production that caters to low-carbon energy sources. The low cost and easy regeneration of carbon-based catalysts is more compatible with the concept of sustainability than metal catalysts. The key problem with catalytic decomposition using activated carbon is the rapid deactivation of the activated carbon due to structural changes caused by the production and accumulation of deposited carbon. Carbon black, on the other hand, exhibits slowly increasing catalytic performance in the catalytic decomposition of methane. Therefore, combining the properties of the two, it is proposed to disperse and load the nano conductive carbon black onto the surface of urea-modified activated carbon, so that the activated carbon can also have self-repairing ability at a later stage. It is shown that the combined application of carbon black loading and urea modification enhances the structural properties of the activated carbon by enriching the microporous structure of the activated carbon surface, increasing the disorder of its crystal structure, and altering the content and concentration of oxygen-containing functional groups on the surface. These microstructural changes combined to enhance the overall catalytic activity of the activated carbon, including its late deactivation time and catalytic performance after deactivation.

Simulation of the Thermal Decomposition of Methane at Constant Volume and Temperature Using Methods of Molecular Dynamics and Thermodynamics

Simulation of the Thermal Decomposition of Methane at Constant Volume and Temperature Using Methods of Molecular Dynamics and Thermodynamics

Analysis of methane pyrolysis experiments at high pressure using available reactor models

Most batch reactor methane thermal decomposition (MTD) studies have focused on sub-atmospheric pressures. In this study, MTD experiments were performed between 892 K and 1292 K and 4 atm inside a quasi-isothermal quartz batch reactor at residence times ranging from 0 to 300 s. At a given temperature, elevated pressure resulted in higher methane conversion compared with the sub-atmospheric conditions. A zero-dimensional, closed, isochoric, homogeneous gas-phase model was used to compare numerical predictions from available reaction mechanisms in literature to experimental data. It was found that most models accurately predict conversion at low pressure and high temperature and at high pressure and high temperature, but did not accurately predict methane, hydrogen, and intermediate species mole fractions at 4 atm and either 892 K or 1093 K. A reaction path analysis showed the reactions responsible for the delay in hydrogen formation at elevated pressure are 2CH3(+M)⟺ C2H6, C2H6 ＋ CH3⟺ C2H5 ＋ CH4, C2H6 ＋ H ⟺ C2H5 ＋ H2 and C2H5(+M)⟺ C2H4 ＋ H, where M is the collision partner. A gas-phase model accounting for the solid carbon shows that the observed discrepancy is not due to the unavailability of the carbon formation model but to slower reaction kinetics, especially at lower temperatures. The experimental data presented can be used to obtain a methane pyrolysis reaction mechanism suitable for high pressure conditions.

Deep multi-field network for physical and concentration field prediction of TDM reactor under different carbon particle distributions

In thermal decomposition of methane (TDM) reactors, the injection of carbon particles and their distribution have significant influence on field distributions, thereby impacting the yield and wall deposition rate. It is computationally intensive to analyze such influences numerically by repetitively solving the mechanism model. Therefore, we developed a multi-field network (DMN) to predict the physical and concentration fields of a TDM reactor under different inlet distributions of injected carbon particles. A set of operator networks was trained using small amounts of data generated from the mechanism model, and then, it was integrated with a multi-hidden layer neural network (NN) to form an improved physics-informed NN, which is regarded as a DMN. By comparison, the proposed DMN can predict multiple fields under any different particle distribution with higher accuracy than the traditional NN and higher efficiency than solving the mechanism model. The proposed DMN can also be used for field reconstruction using observational data.

Comparative techno-economic and life cycle greenhouse gas assessment of ammonia production from thermal decomposition of methane and steam methane reforming technologies

This study assesses the life cycle greenhouse gas (GHG) and economic feasibility of applying thermal decomposition of methane (TDM) technology for ammonia production compared to the conventional steam methane reforming (SMR) technology. A detailed process model for each ammonia-based technology was developed to get data to perform energy, life cycle GHG emissions, and economic analyses. The results showed that the SMR plant consumes 30.3% more fuel than the TDM. The life cycle GHG emissions of TDM and SMR are 1.42 and 2.51 t CO2e/t NH3, respectively. The combustion and process emissions released to the environment and electricity emissions take a large share in the life cycle emissions of SMR and TDM, respectively. The production cost of ammonia from SMR is lower than TDM by $69/t NH3. TDM requires a higher investment because of high capital costs and the huge amount of natural gas needed as feedstock. For TDM, the sale of the oxygen product does not provide sufficient revenue to outperform SMR. However, integrating a carbon capture unit into TDM makes it economic performance better than SMR (with a carbon capture unit) when the sale of oxygen is considered. The results also showed that SMR (without carbon capture unit) is more economically attractive when the carbon price benchmark is below $99/t CO2. Above this carbon price, integrating a carbon capture unit into TDM is economically preferable.

The Synthesis of Carbon Nanoparticles in a Compression Reactor in the Atmosphere of Buffer Gases

We investigated the physicochemical aspects of the gas-phase nanopowder synthesis using a cyclic compression reactor. Compression of precursors (methane, ethylene, acetylene) under conditions close to the adiabatic ones in the atmosphere of buffer monatomic gases (argon, helium, neon) was used. The influence of pressure in the reactor and volumetric ratio of precursor/buffer gas mixture on the composition, morphology, and structure of carbon-containing particles representing the pyrolysis product was studied. Complete pyrolysis was observed for all studied precursors, but under different conditions. Thermal decomposition of methane, having the minimum enthalpy of formation, was observed in an atmosphere with argon content 97.5 % at a peak pressure more than 10 MPa. Helium showed limited possibilities for thermal relaxation under the conditions of fast reactions (< 50 ms). Only acetylene with the maximum enthalpy of formation was decomposed in the atmosphere of helium. The solid reaction products represented black colored powders with a bulk density of 20–30 mg/cm3. The powders were examined by transmission electron microscopy and scanning electron microscopy, Raman scattering and X-ray diffraction analysis. The particles represent globular bulbous structures up to 100 nm in size, either hollow or filled inside. X-ray diffraction analysis showed the presence of a graphite-like structure with crystallite sizes less than 10 nm in all samples. Raman analysis showed mainly sp2 hybridization of carbon. The cyclic compression method demonstrates wide range of opportunities for the pyrolysis of hydrocarbons aiming at the production of a variety of carbon structures, which enables for the fine tuning in terms of the yield of products of the required morphology for practical use.

Methane pyrolysis characteristics for the practical application of hydrogen production system using permalloy plate catalyst

Methane pyrolysis is a hydrogen-producing method that does not emit carbon dioxide. Additionally, one of the products formed is solid carbon, which can be stored or used as a valuable byproduct to improve the economics of the process. In this study, the characteristics of the hydrogen and carbon produced by methane pyrolysis were investigated to develop a hydrogen mass-production system. Methane pyrolysis was performed in a medium-sized reactor with a capacity of approximately 40 L at a high inlet-methane flow rate using permalloy plate catalysts, which are inexpensive and more practical than supported catalysts. Notably, a maximum methane conversion of 90 % was observed with the permalloy plate catalyst. Although methane conversion increased with reactor temperature, the conversion rate decreased with an increase in flow rate. Morphological analysis results showed that when recovered at a furnace temperature of 760 °C an inlet-methane flow rate of 0.2 Nm3/h, the carbon was agglomerated, with a mixture of spherical and fibrous carbon. The compositional analysis results demonstrated that the generated carbon retained the metallic components of the catalyst, which were considered to have been removed from the catalyst surface. In addition, the amount of hydrogen generated and the efficiency of methane pyrolysis increased significantly with the furnace temperature. Furthermore, this study confirmed the optimal temperature and flow conditions for efficient methane pyrolysis. We deduced that the thermal decomposition of methane, including the gas-phase reaction, was more efficient at relatively high temperatures (above 800 °C), while designing inlet-methane flow rates specifically for each system could generate hydrogen at high efficiencies. Thus, the results of this study can also be used as an indicator to determine the optimal conditions of methane pyrolysis.

Experimental research of the process of methane pyrolysis in a layer of liquid tin aiming to get hydrogen

One of the perspective methods to get the hydrogen with zero CO/CO2 emissions is the thermal decomposition of methane. In the present work, the research was focused on the pyrolysis of methane in a layer of liquid tin. During the experiments, a 30% conversion of methane was obtained for a reactor with a height of 0.1 m. During the thermal decomposition of methane, solid carbon particles appear in the form of soot. These particles must be removed mechanically to avoid clogging the reactor.

Numerical Study on Optics and Heat Transfer of Solar Reactor for Methane Thermal Decomposition

This study aims to reduce greenhouse gas emissions to the atmosphere and effectively utilize wasted resources by converting methane, the main component of biogas, into hydrogen. Therefore, a reactor was developed to decompose methane into carbon and hydrogen using solar thermal sources instead of traditional energy sources, such as coal and petroleum. The optical distributions were analyzed using TracePro, a Monte Carlo ray-tracing-based program. In addition, Fluent, a computational fluid dynamics program, was used for the heat and mass transfer, and chemical reaction. The cylindrical indirect heating reactor rotates at a constant speed to prevent damage by the heat source concentrated at the solar furnace. The inside of the reactor was filled with a porous catalyst for methane decomposition, and the outside was surrounded by insulation to reduce heat loss. The performance of the reactor, according to the cavity model, was calculated when solar heat was concentrated on the reactor surface and methane was supplied into the reactor in an environment with a solar irradiance of 700 W/m2, wind speed of 1 m/s, and outdoor temperature of 25 °C. As a result, temperature, methane mass fraction distribution, and heat loss amounts for the two cavities were obtained, and it was found that the effect on the conversion rate was largely dependent on a temperature over 1000 °C in the reactor. Moreover, the heat loss of the full-cavity model decreased by 12.5% and the methane conversion rate increased by 33.5%, compared to the semi-cavity model. In conclusion, the high-temperature environment of the reactor has a significant effect on the increase in conversion rate, with an additional effect of reducing heat loss.

Methane Pyrolysis for Zero-Emission Hydrogen Production: A Potential Bridge Technology from Fossil Fuels to a Renewable and Sustainable Hydrogen Economy

Hydrogen plays a key role in many industrial applications and is currently seen as one of the most promising energy vectors. Many efforts are being made to produce hydrogen with zero CO2 footprint via water electrolysis powered by renewable energies. Nevertheless, the use of fossil fuels is essential in the short term. The conventional coal gasification and steam methane reforming processes for hydrogen production are undesirable due to the huge CO2 emissions. A cleaner technology based on natural gas that has received special attention in recent years is methane pyrolysis. The thermal decomposition of methane gives rise to hydrogen and solid carbon, and thus, the release of greenhouse gases is prevented. Therefore, methane pyrolysis is a CO2-free technology that can serve as a bridge from fossil fuels to renewable energies.

Carbons Formed in Methane Thermal and Thermocatalytic Decomposition Processes: Properties and Applications

The hydrogen economy will play a key role in future energy systems. Several thermal and catalytic methods for hydrogen production have been presented. In this review, methane thermocatalytic and thermal decomposition into hydrogen gas and solid carbon are considered. These processes, known as the thermal decomposition of methane (TDM) and thermocatalytic decomposition (TCD) of methane, respectively, appear to have the greatest potential for hydrogen production. In particular, the focus is on the different types and properties of carbons formed during the decomposition processes. The applications for carbons are also investigated.

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In this study, the optical properties, heat transfer capabilities and chemical reaction performance of a methane thermal decomposition reactor using solar heat as a heat source were numerically analyzed on the basis of the cavity shape. The optical properties were analyzed using TracePro, a Monte Carlo ray tracing-based program, and the heat transfer analysis was performed using Fluent, a CFD program. An indirect heating tubular reactor was rotated at a constant speed to prevent damage by the heat source in the solar furnace. The inside of the reactor was filled with a porous catalyst for methane decomposition, and the outside was insulated to reduce heat loss. The performance of the reactor, based on cavity shape, was calculated when solar heat was concentrated on the reactor surface and methane was supplied into the reactor in an environment with a solar irradiance of 700 W/㎡, a wind speed of 1 m/s, and an outdoor temperature of 25°C. Thus, it was confirmed that the heat loss of the full-cavity model decreased to 13% and the methane conversion rate increased by 33.5% when compared to the semi-cavity model.

Impact of Carbon Dioxide on the Non-Catalytic Thermal Decomposition of Methane

Economically and ecologically, the thermal decomposition of methane is a promising process for large scale hydrogen production. In this experimental study, the non-catalytic decomposition of methane in the presence of small amounts of carbon dioxide was analyzed. At large scales, natural gas or biomethane are possible feedstocks for the thermal decomposition and can obtain up to 5% carbon dioxide. Gas recycling can increase the amount of secondary components even further. Experiments were conducted in a packed flow reactor at temperatures from 1250 to 1350 K. The residence time and the amounts of carbon dioxide and hydrogen in the feed were varied. A methane conversion of up to 55.4% and a carbon dioxide conversion of up to 44.1% were observed. At 1300 K the hydrogen yield was 95% for a feed of methane diluted in nitrogen. If carbon dioxide was added to the feed at up to a tenth with regard to the amount of supplied methane, the hydrogen yield was reduced to 85%. Hydrogen in the feed decreases the reaction rate of the methane decomposition and increases the carbon dioxide conversion.

Carbon-dioxide activation by methane with iron-doped barium zirconate in chemical looping cracking system

• Fe-doped BaZr 0.9 Y 0.1 O 3−δ (BZFY) was developed as highly active catalyst. • BZFY40 exhibited the highest methane cracking activity with tubular carbon growth. • Deposited carbon removal reaction with CO 2 was completed quickly. • Cracks generated in BZFY during reduction reaction was self-repaired with BaCO 3 . • The three-reactors system was proposed as an efficient CLMC system with BZFY40. Highly efficient carriers are developed for hydrogen production by methane cracking with carbon-dioxide activation in a chemical looping system. The carrier materials comprise BaZr 0.9 Y 0.1 O 3−δ (BZY) with a high proton conductivity and Fe as a base metal, and they are prepared by doping Fe into BZY. Thermal gravimetric analysis (TGA) showed that Fe-doped BZY (BaZr 0.9− x Fe x Y 0.1 O 3−δ , BZFY) with x = 0.4 (BZFY40) exhibited a high activity for carbon deposition with methane thermal decomposition. Surface observation and kinetic analysis suggested that the high activity for carbon deposition results from the promotion of tubular carbon growth with growth-mode transition from horizontal to vertical direction for the tubular carbon on reduced BZFY40. The rapid growth of carbon tubes proceeded with the base-growth mechanism, which can provide an advantage in the stable cycle reactions. The carbon removal reaction with carbon dioxide was also investigated. In BZFY, the removal reaction was completed in ~10 min. BZFY reacted with carbon dioxide under carbon dioxide flow to generate barium carbonate. From the BZFY surface observation before and after the reactions, the BZFY plate that was mechanically broken during the carbon deposition and removal cycles could be repaired by filling cracks with carbonate in the BZFY that was generated via the reduction reaction with methane. Therefore, carbon removal from the BZFY surface with carbon dioxide contributes to maintaining the BZFY particle shape during cycles with the self-healing scheme. The BZFY40 carrier has a high activity and durability for the carbon deposition and removal cycle and provides an effective system design for carbon dioxide-free hydrogen generation.

Molecular dynamics simulation of polymerization of the carbon under thermal decomposition of methane at constant volume

Thermal decomposition of methane was simulated at high temperature and pressure using the molecular dynamics method. The calculation was carried out employing ReaxFFlg potential. We show the dependence of the decomposition products on time and the results of methane polymerization at constant temperature. We also show the influence of gradual temperature decrease at the size of the polymers.

Исследование процесса рекуперации теплоты внутри футеровки высокотемпературной установки за счет термического разложения метана

The paper has suggested the mathematical model of the heat recovery process inside the high-temperature plant`s lining using thermal decomposition of methane in conditions of high-temperature plants cooling. The examined model allows evaluation of regenerative heat use possibility to reduce heat losses through the enclosure of high-temperature plant by utilizing the heat of a liquid heat carrier which can increase high-temperature process productiveness. All high-temperature plants have a primary objective – ensure process continuity with minimal fuel flow rate using the energy of primary as well as secondary energy resources (SER). In pyrolysis conditions, methane is the most thermally stable because methane thermal decomposition happens at a temperature higher than 560°C. However, when methane reaches a significant speed of movement it decomposes at a temperature of about 900°C, and temperature 1400°C breaks up to carbon and oxygen. Natural gas, as an energy carrier, has many advantages and in comparison, with the other fuel types, it can be used to the full extent because it is easy to organize its complete combustion with minimal heat losses. It should be noted that natural gas has no ballast or harmful substances, it possesses high heat value and its combustion creates high temperatures.