Step-by-step methodology of developing a solar reactor for emission-free generation of hydrogen

This study presents a methodology to develop a solar reactor based on the thermodynamics and kinetics of methane decomposition to produce hydrogen with no emissions. The kinetic parameters were obtained in the literature for two cases; methane laden with carbon particles and methane without carbon particles. Results show that there is significant difference in experimentally obtained and theoretically predicted methane conversion. The paper also presents a parametric study on the effects of temperature, pressure and the influence of inert gas composition, which is fed along with methane, on the thermodynamics of methane decomposition. Results show that there is significant effect of the inert gas presence in the feeding gas mixture on the equilibrium of methane conversion and product gas composition. Results also show that higher conversions are obtained when the carbon particles laden with methane. The step-by-step reactor design methodology for homogenous methane decomposition and the parametric study results presented in this paper can provide a very useful tool in guiding a solar reactor design and optimization of process operating conditions.status: publishe

Thermogravimetric Analysis of Carbon Based Catalysts on Methane Decomposition

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Residence time distribution and flow field study of aero-shielded solar cyclone reactor for emission-free generation of hydrogen

This paper provides a thorough analysis on the flow field and Residence Time Distribution (RTD) of our “aero-shielded cyclone solar reactor” designed to generate hydrogen from solar thermal methane cracking process. The analysis has been carried out based on the results from flow dynamics, and residence time distribution by using Computational Fluid Dynamics (CFD). Kinetics is taken from the literature and the reactor volume is estimated based on a plug flow reactor assumption. Residence time distribution characteristics are obtained by gas tracer injection method, and particle tracking method. Based on the results of our flow studies, “reactors in series model” is adopted to model the aero-shielded cyclone reactor. Path lines show that operating variables have significant effect on the flow behavior inside the reactor. Results show that thermo chemical properties of the gases have effect on the flow behavior which significantly affect the mean residence time in the reactor. Results also show that the residence time, spread of the tracer by variance, and the number of reactors in series are observed to be changed by change in the flow rate, type of screening gas, and methane mole fraction in the feed.status: publishe

Thermogravimetric analysis of activated carbons, ordered mesoporous carbide-derived carbons, and their deactivation kinetics of catalytic methane decomposition

This study presents the deactivation kinetics of methane decomposition for the activated carbons Fluka-05105 and Fluka-05120, ordered mesoporous carbon (CMK-3), and ordered mesoporous carbide-derived carbon (DUT-19). The experimental and thermodynamically predicted carbon deposition, the average and total hydrogen production, and the effect of flow rate on carbon formation rate of these catalysts were investigated. Results indicate that the experimental conditions chosen were within the reaction control regime. Catalytic activity was calculated via two different definitions present in literature: one in terms of carbon deposition rate and the other in terms of carbon mass deposited. Deactivation kinetics were obtained by fitting the experimental data by nonlinear regression analysis. Differences between the two methods in determining activity resulted in significant changes in the estimation of deactivation kinetics. The activity calculated based on the rate method results in the best fit of experimentally collected data. A deactivation order and methane concentration dependency of approximately 1.0 and 0.5 were determined for all the catalysts tested (Fluka-05105, Fluka-05120, CMK-3, and DUT-19). The activation energy of deactivation (Ed) was determined to be 192, 154, 166, and 181 kJ/mol for Fluka-05120, Fluka-05105, CMK-3, and DUT-19, respectively. DUT-19 was the best performing catalyst in terms of carbon formation rate, total carbon production, hydrogen production rate, average hydrogen production, and total hydrogen production

Thermogravimetric Analysis of Activated Carbons, Ordered Mesoporous Carbide-Derived Carbons, and Their Deactivation Kinetics of Catalytic Methane Decomposition

This study presents the deactivation kinetics of methane decomposition for the activated carbons Fluka-05105 and Fluka-05120, ordered mesoporous carbon (CMK-3), and ordered mesoporous carbide-derived carbon (DUT-19). The experimental and thermodynamically predicted carbon deposition, the average and total hydrogen production, and the effect of flow rate on carbon formation rate of these catalysts were investigated. Results indicate that the experimental conditions chosen were within the reaction control regime. Catalytic activity was calculated via two different definitions present in literature: one in terms of carbon deposition rate and the other in terms of carbon mass deposited. Deactivation kinetics were obtained by fitting the experimental data by nonlinear regression analysis. Differences between the two methods in determining activity resulted in significant changes in the estimation of deactivation kinetics. The activity calculated based on the rate method results in the best fit of experimentally collected data. A deactivation order and methane concentration dependency of approximately 1.0 and 0.5 were determined for all the catalysts tested (Fluka-05105, Fluka-05120, CMK-3, and DUT-19). The activation energy of deactivation (Ed) was determined to be 192, 154, 166, and 181 kJ/mol for Fluka-05120, Fluka-05105, CMK-3, and DUT-19, respectively. DUT-19 was the best performing catalyst in terms of carbon formation rate, total carbon production, hydrogen production rate, average hydrogen production, and total hydrogen production.status: publishe

Effect of reactor geometry on the temperature distribution of hydrogen producing solar reactors

Global effects of greenhouse gas emissions associated with the current extensive use of fossil fuels are increasingly attracting research groups and industry to find a solution. In order to reduce or avoid such emissions, solar thermal cracking of natural gas has been studied by many research groups as a clean and economically viable option for hydrogen production with zero CO2 emissions. By utilization of concentrated solar energy as the source of high temperature process heat, natural gas is decomposed into hydrogen gas and high grade carbon using a solar reactor. Our previous study shows that temperature distribution inside the solar reactor has significant effect on hydrogen production. In this paper, we expand our previous study by demonstrating that reactor geometry has a notable impact on temperature distribution inside the solar reactor and therefore it has an impact on natural gas to hydrogen conversion. Results show that there are approximately 22% and 32% losses from spherical and cylindrical reactors, respectively, while hydrogen production amount varies from 1.27 g/s to 8.95 g/s for spherical reactor, and 0.94 g/s to 8.94 g/s for cylindrical reactor geometry.status: publishe