1,721,006 research outputs found
Double-Gaussian Distributed Activation Energy Model for Coal Devolatilization
No full textUnderstanding and modeling of coal pyrolysis assume particular importance, since it is the first step of combustion and gasification processes. The complex reactions occurring during pyrolysis lead to difficulties in the process modeling. The aim of this work is to find a global kinetic model that well represents the pyrolysis of two different coals with opposite rank, a sub-bituminous and an anthracite coal, in order to carry out the kinetic parameters of the process. The Distributed Activation Energy Model (DAEM) was used to fit experimental data obtained with a thermogravimetric analysis. The model assumes that a series of first order parallel reactions occurs sharing the same pre-exponental factor, k(0), and having a continuous distribution of the activation energy. One of the limits of the standard Gaussian DAEM is that with this model is not possible to distinguish the primary from the secondary pyrolysis. A two Gaussians DAEM was developed considering that two classes of reactions take place having the same k(0) and different distribution of activation energy. Since in the model k0 is highly correlated with the mean activation energies, it was fixed at characteristic values taken from literature
Methane pyrolysis in molten media: The interplay of physical properties and catalytic activity on carbon and hydrogen production
No full textMethane pyrolysis is now considered a promising process for producing clean hydrogen and high-value carbon materials. However, it requires very high temperatures (above 1000 degrees C) due to the kinetic barriers posed by the stable C-H bond, and the production of carbon presents a significant challenge. While solid catalysts can lower the operational temperatures to some extent, they are hindered by carbon accumulation, which deactivates the catalysts and clogs reactors, thus limiting process scalability. Recently, molten media have emerged as potential catalysts for methane pyrolysis. These media offer numerous advantages, including high thermal conductivity and resistance to deactivation via sintering or coking. Despite these advantages, a comprehensive understanding of how the physical properties and intrinsic catalytic activities of molten media influence methane pyrolysis is lacking. This review addresses this gap by examining the roles of physical properties, mainly surface tension, and catalytic activity in methane conversion and carbon morphology. The analysis of apparent activation energies across various molten media indicates that their physical properties significantly impact methane reactivity, challenging the conventional notion of catalytic activity. In summary, this review explores the synergistic effects of molten media's physical and catalytic properties on methane pyrolysis, highlighting the potential for these systems to revolutionize the process by enhancing efficiency and reducing operational challenges. Understanding these interactions is key to advancing the scalability and applicability of methane pyrolysis technologies for sustainable hydrogen production
Olive oil residue gasification and syngas integrated clean up system
No full textGasification is one of the most promising technologies to convert low quality fuels into more valuable ones. The main problem in the use of biomass in gasification processes is the high amount of tar released in the pyrolysis step. It is thus necessary to recover the tar and to transform it in lighter combustible gas species such as CH4, CO and H2 by means of catalytic processes. In this work the gasification of olive husk is performed in order to produce a high quality syngas, composed mainly of carbon monoxide and hydrogen, using an innovative laboratory scale plant composed of a unique reactor divided into three sections. The first section is dedicated to the pyrolysis, the second to the gasification of char produced during pyrolysis and the third to the catalytic reforming of tar. In the reformer two catalysts were tested: a CeO2 promoted bimetallic Ni-Co catalyst and a Ni catalyst, both supported on γ-Al2O3. This plant design allows one to minimize the heat dispersion enhancing the energy efficiency of the unit
Activated biochars used as adsorbents for dyes removal
Get PDFAdsorption represents one of the most interesting technique for the removal of pollutants from wastewaters. Activated carbons show the best performances on this kind of processes but their high production costs limit their applications. In this context a big challenge is to find new materials having characteristic similar to those of commercial activated carbons but being environmental friendly and cheaper. In this work the adsorption efficiency of activated biochars produced from pine wood was investigated on the removal of dyes from water. An innovative method for the activation of the biochar using deep eutectic solvents (DES) was tuned and the characteristics of the obtained adsorbent material were compared with those of biochar activated with traditional method and non-activated biochar. The best adsorption capacities were obtained with the DES activated biochar, reaching a value of 480 mg/g for the methylene blue adsorption. Adsorption isotherm and kinetic models were applied to experimental data in order to understand the adsorption mechanism of the process
Methane dry reforming over nickel perovsikite catalysts
Get PDFIn recent years dry reforming of methane (DRM) has received considerable attention as a promising alternative to steam reforming for synthesis gas (H2 and CO) production. This process could be industrially advantageous, yielding a syngas with a H2/CO ratio close to 1, suitable for Fischer-Tropsch synthesis to liquid hydrocarbons and for production of valuable oxygenated chemicals. The major drawback of the process is the endothermicity of the reaction that implies the use of a suitable catalyst to work at relatively low temperatures (923-1,023 K). Higher temperatures would make the process unaffordable for an industrial development and would increase the risk of undesirable side reactions, such as coke formation, that are the main causes of catalyst deactivation. In this work the activity of nickel perovskite catalysts were studied and the results were compared with rhodium perovskite. It is well known that rhodium is very active and stable for dry reforming but its high cost makes its utilization limited. The Ni, due to its low cost, is a promising substitute even if it is more susceptible to coking. The perovskite structure allows a high dispersion of the metal into the catalyst increasing the catalytic activity. In this work the Ni perovskite was obtained with two methods (auto-combustion and modified citrate methods). The results pointed out that the Ni perovskite obtained with the auto-combustion method is a promising route for the use of Ni in this process. The experimental tests show that with Ni catalyst very good activity can be achieved from temperature of 973 K
CFD model of a spinning disk reactor for nanoparticle production
Get PDFThe use of a spinning disk reactor (SDR) was investigated for the continuous production of nanoparticles of hydroxyapatite. SDR is an effective apparatus for the production of nanoparticles by wet chemical synthesis. Rotation of the disc surface at high speed creates high centrifugal fields, which promote thin film flow with a thickness in the range 50-500 ?m. Films are highly sheared and have numerous unstable surface ripples, giving rise to intense mixing. SDR performances are strongly affected by the adopted operating conditions such as the influence of rotation speed that determines the attainment of micro-mixing and the feeding point location that has a great influence on the particle size distribution of the product. The experimental device consists of a cylindrical vessel with an inner disk, 8.5 cm in diameter, made by PVC coated by an acrylic layer. The rotational velocity of the disc is controlled and ranges from 0 to 147 rad/s. The reagent solutions are fed over the disk at a distance of 5 mm from the disc surface through tubes, 1 mm in diameter. A computational fluid dynamic model, validated in a previous work, was used to optimize the operative conditions of SDR. Through the CFD model it is possible to analyse the hydrodynamic of the thin liquid film formed on the disk at different speed rotations and to individuate the best mixing conditions between the reagents varying the feeding point positions. The production of hydroxyapatite was also investigated adding the reaction kinetic to model the product formation in the liquid phase and the population balance equation to predict particle size distribution. The simulation results were compared with available experimental data showing that the CFD model is fully capable to describe the process and qualifies as a suitable engineering tool to perform the SDR process design. Copyright © 2015, AIDIC Servizi S.r.l
Double distribution activation energy model as suitable tool in explaining biomass and coal pyrolysis behavior
Get PDFUnderstanding and modeling of coal and biomass pyrolysis assume particular importance being the first step occurring in both gasification and combustion processes. The complex chemical reaction network occurring in this step leads to a necessary effort in developing a suitable model framework capable of grasping the physics of the phenomenon and allowing a deeper comprehension of the sequence of events. The aim of this work is to show how the intrinsic flexibility of a model based on a double distribution of the activation energy is able to properly describe the two separate steps of primary and secondary pyrolysis, which characterize the thermochemical processing of most of the energetic materials. The model performance was tested by fitting the kinetic parameters from experimental data obtained by thermogravimetric analysis of two materials, which represent very different classes of energy source: a microalgae biomass and a sub-bituminous coal. The model reproduces with high accuracy the pyrolysis behavior of both the materials and adds important information about the relative occurring of the two pyrolysis steps
Biomass gasification plant and syngas clean-up system
Get PDFGasification is recognized as one of the most promising technologies to convert low quality fuels into more valuable ones. The principal problem related with the use of biomass in gasification processes is the high amount of tar released during the pyrolysis step. It is thus necessary to recover tar and to transform it in lighter combustible gas species such as CH4, CO and H-2. In this work the experimental results of a medium industrial scale plant fed with olive husk and having a capacity of 250 kWt are presented. The gasifier is composed by a up-draft reactor which is followed by a secondary fixed bed reactor filled with alluminium oxide spheres having high porosity dedicated to the tar conversion reactions. The syngas is then used to feed an internal combustion engine with a production of 60 kWe
The hydrothermal decomposition of biomass and waste to produce bio-oil
No full textThe hydrothermal decomposition of biomass is an alternative to the traditional pyrolysis processes to obtain liquid fuels with an increased energy density. Hydrothermal liquefaction is claimed to produce bio-oils with improved characteristics such as a reduced content of oxygen, avoiding at the same time the energy consuming biomass drying step necessary in the traditional thermochemical processes. However, at present the use of this technology is limited by the severe conditions needed and by the difficulties connected with the realization of a continuous process. In this work an innovative process, operating at atmospheric pressure and at moderate temperatures, is proposed, where water subcritical conditions are achieved locally by means of the energy released during cavitation. The process was tested on lab-scale on two biomass feeds obtaining a crude bio-oil with a composition very similar to that of fossil oil and greatly improved respect to those obtained in traditional pyrolysis processes. © 2014 WIT Press
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