A grid of hydrogen refuelling stations comparable to gasoline is essential for improving the individual transport based on fuel cell technology. To avoid transport and storage problems with hydrogen, ...small-scale hydrogen production plants are required. During the project BioRobur a pilot-plant with a hydrogen output of 50 Nm³/h was constructed and investigated. The plant is based on the autothermal reforming of biogas with a noble metal catalyst. All required reactants are stored or produced at the plant side. The purification of the synthetic gas is not considered.
Within the article the plant efficiency and the cold gas efficiency were measured at different temperatures, oxygen to carbon ratios and gas hourly space velocities. Additionally the workload of the pilot-plant was varied, showing a highly reliable operation for a workload of at least 20%. Furthermore, the hydrogen production costs of the pilot-plant were compared with other common technologies, like electrolysis and steam reforming.
•Autothermal reforming of biogas at pilot-plant.•Highest plant efficiency of 75% at an O/C-ratio of 0.8–0.9.•Partial load operation down to 20%.•Production costs are 0.16 €/kWh (5.32 €/kg).
Experiments have been carried out in a specially designed 36 m2 compartment. The experimental results show the main phenomena during the fire and smoke propagation in the compartment before sprinkler ...activation and additionally the interaction between the hot flue gases in the smoke layer and the water spray. The axial temperature profiles at three characteristic positions inside the compartment were measured. A comparison of a standard sprinkler and a High-Pressure Water Mist system (HPWM) revealed two different phenomena, which are flue gas scrubbing and recirculation motion, respectively – both eventually leading to an increased smoke obscuration inside the compartment.
•Formation of the stable smoke layer due to the combustion process could be observed.•Flue gas scrubbing due to the high specific drop loading after sprinkler activation.•Diluted flue gas recirculation after High-Pressure Water Mist (HPWM) activation.•Gradual dilution of smoke and finally complete dissolution of stratified smoke layer.
•The laminar burning velocity has been measured with the Heat Flux method.•Liquid fuels, namely iso-octane, ethanol and their blends, with air were investigated.•With rising ethanol fraction, the ...laminar burning velocity increases.•Measurements are compared to numerical simulations.•Simulations cannot predict the exact value but the trend of the burning velocity.
The substitution of gasoline with bio-ethanol is an intended way to reduce the climate impact of the traffic sector. To extend the knowledge of fundamental flame properties of ethanol/iso-octane flames and improve the numerical predictions for the effect of ethanol blending in internal combustion engines, measurements of the laminar burning velocity of established blend ratios of ethanol and iso-octane were carried out and compared to existing numerical mechanisms. The measurements were carried out with the Heat Flux burner, with thermocouples of type E at the burner plate, which was adapted with an evaporation unit based on direct vaporization to investigate the liquid fuels. The preheating temperature ranges from 298K to 373K and the pressure is atmospheric. First measurements of the laminar burning velocity of ethanol/air and iso-octane/air flames were carried out for validating the system. A good agreement with available literature data could be achieved for the investigated equivalence ratios from 0.7 to 1.4. Furthermore laminar burning velocities of different iso-octane/ethanol/air blends, namely E10, E24, E40 and E85, are presented. Through variation of the preheating temperatures (298K, 323K, 348K and 373K) the temperature dependency could be analyzed. The uncertainty analysis of the measurements has been revealed. Numerical simulations were carried out using different chemical mechanisms for ethanol/air flames, iso-octane/air flames as well as various fuel blends and preheating temperatures and are compared to the experimental data. The agreement is evaluated through a classification of the discrepancy between both.
•Measured concentration profiles of fuel-rich CH4/O2-flames using a GC/MS.•Profile-shift (up to 1.4 mm) caused by the probe determined from detailed CFD.•Syngas production (H2/CO2 and CO/H2O ratio) ...depends essentially on mechanism used.•Detailed analysis of two mechanisms to identify differences in major products.•C2H2 decomposition is better reproduced by CalTech2.3 due to detailed Cx chemistry.
Combustion processes with pure oxygen (oxy-fuel) instead of air as an oxidant are attractive for e.g. high temperature thermal or thermochemical and gasification processes. The absence of nitrogen as an inert gas leads in such combustion processes to an increase in temperature and species concentrations. The scope of this study is the determination of axial profiles of major educts (CH4, O2) and major combustion products such as H2, H2O, CO and CO2 in flat fuel-rich premixed methane-oxygen flames (2.5 ≤ ϕ <3.0). A Heat-Flux-burner was used to stabilize a quasi-adiabatic one-dimensional flame at a preheating temperature of TP = 300 K and atmospheric pressure. Gas samples were taken at different HAB using a quartz probe and analyzed by a GC/MSD. The influence of the probe on determined species concentrations was investigated using CFD simulations. Additionally, one-dimensional calculations with detailed chemistry were performed using the GRI3.0 and CalTec2.3 mechanism. Their differences in regards to H2, H2O and CO concentrations were thoroughly investigated and could be explained by the detailed C2-chemistry of the CalTech2.3. The results of the analyzed gas samples show a rapid reduction and increase in the flame zone, of the educts, major products and higher hydrocarbons (C2H2, C2H4 and C6H6), respectively. Both mechanisms show a sharper gradient of the synthesis gas production in comparison to the experimental results, nevertheless a tendency towards the CalTech2.3 scheme is observed. In the post flame zone the determined species concentrations of H2 and CO2 correspond to the results of the GRI3.0, whereas in the case of H2O and CO the CalTech2.3 showed better performance. The calculations of higher hydrocarbons are in better agreement with higher equivalence ratio.
The paper presents a study on the combustion of S2 over a wide range of air/fuel ratios, employing numerical flame calculations, including a sulfur/oxygen reaction mechanism; reaction zone structures ...as well as the corresponding laminar burning velocities are reported. The numerical simulations are based on a detailed reaction mechanism derived from a H/O/S combustion mechanism from the literature after removing all reactions of hydrogen-containing species. Using reaction rate coefficients from the literature in the calculations brings about burning velocities in the order of magnitude of 300 cm s–1 at T 0 = 373 K and under stoichiometric conditions. Sensitivity analysis of the computed results identified which reaction rate has crucial influence on the burning velocity and flame structure. It turned out that the sensitivity coefficients of burning velocity with respect to the rate coefficient of reaction S + O2 → SO + O are by far the largest sensitivity coefficients. Further investigations have been performed on the basis of different values of the rate constant of reaction S + O2 → SO + O taken from the literature and from our own calculations. The obtained significant changes in burning velocities as well as in species profiles elucidate the sensitivity of the burning velocity and flame structure on the magnitude of the reaction rate coefficient of this reaction and stress the importance of this reaction. This work constitutes a necessary and to be continued footstep toward a validated reaction mechanism for the combustion of sulfur.
Thermochemistry and kinetic pathways on the 2‐butanone‐4‐yl (CH3C(=O)CH2CH2•) + O2 reaction system are determined. Standard enthalpies, entropies, and heat capacities are evaluated using the G3MP2B3, ...G3, G3MP3, CBS‐QB3 ab initio methods, and the B3LYP/6‐311g(d,p) density functional calculation method. The CH3C(=O)CH2CH2• radical + O2 association reaction forms a chemically activated peroxy radical with 35 kcal mol−1 excess of energy. The chemically activated adduct can undergo RO−O bond dissociation, rearrangement via intramolecular hydrogen transfer reactions to form hydroperoxide‐alkyl radicals, or eliminate HO2 and OH. The hydroperoxide‐alkyl radical intermediates can undergo further reactions forming ketones, cyclic ethers, OH radicals, ketene, formaldehyde, or oxiranes. A relatively new path showing a low barrier and resulting in reactive product sets involves peroxy radical attack on a carbonyl carbon atom in a cyclic transition state structure. It is shown to be important in ketones when the cyclic transition state has five or more central atoms.
In this paper the results of the operation of a pilot-plant with a hydrogen output of 50 Nm³/h are discussed. This plant shows the possibility of distributed production of hydrogen for the ...powertrains based on hydrogen. The focus of the investigations is the long-term behavior of the novel Nickel-based catalyst. This includes experimental studies of the impact of the start-up sequence on the reforming performance after the necessary activation of the catalyst. Additionally the prospective demand of hydrogen requires an analysis of the start-up time of the plant. The focus was a short start-up time without harming the catalyst.
The increasing need for more efficient and less emissive technologies has shifted the focus of combustion research towards technologies involving combustion in porous inert media. Although burners of ...this type have started to be examined and characterized over the past years, nonintrusive experimental methods are needed to describe the actual processes taking place inside the porous structure. In the present work, the technique of laser induced fluorescence (LIF) is employed to visualize the flame stabilization process inside porous media combustion, utilizing the excitation and subsequent detection of the hydroxyl radical (OH). In order to perform planar measurements inside the porous combustion zone, optical access along the porous structure had to be accomplished. Optical access along the porous structure allowed the laser beam to reach the probe volume and to detect sufficient fluorescence amount. This was realized by creating a thin gap of similar width as the porous cavities. The optical gap size and positioning were chosen so as to yield the most suitable configuration for a sufficient signal to noise ratio without significant disturbance of the combustion process in the porous reaction zone. The experiments were conducted for various thermal loads and excess air ratios for methane/air combustion. The main scope of this work is to demonstrate how the flame structure is influenced by the thermal load and the equivalence ratio over a wide operational range. The flame stabilization in the porous inert medium at fixed position, which is almost independent of the flow rate in some cases, is also observed. Moreover, an experimental characterization of the wide, stable operating conditions of the porous burner is given, along with the description of the flame zone inside the porous matrix.
•High speed images and LES of breakup of a high-viscous liquid jet by coaxial air.•Combination of a compressible LES with the VOF method.•CFD code was validated for a broad range of gas ...velocities.•Primary breakup is controlled by a Kelvin–Helmholtz instability.
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The conversion of low-grade fossil and biogenic energy resources (petcoke, biomass) to a synthesis gas in a high pressure entrained flow gasification process opens a wide spectrum for high efficient energy conversion processes. The synthesis gas can be used for production of methane (SNG), liquid fuels (BtL, CtL) or as fuel for operation of a gas turbine in a combined cycle power plant (IGCC). The production of a tar free high quality syngas is a challenging objective especially due to the fact that typical liquid or suspension fuels for entrained flow gasifiers feature viscosities up to 1000 mPas. Fuel droplet conversion at typical entrained flow gasification conditions is characterized by heat up, evaporation and subsequent degradation of the vapour phase. To guarantee a high fuel conversion rate in the gasifier an efficient atomization of the fuel is required. Mainly twin-fluid burner nozzles are used for atomization of those typically high viscous fuels. The present study is focused on the assessment of the accuracy of CFD computations for the primary breakup of high-viscosity liquids using an external mixing twin fluid nozzle. In a first step experiments were performed with a Newtonian glycerol-water-mixture featuring a liquid viscosity of 400 mPas. Jet breakup was investigated using a high speed camera as well as PIV and LDA-System for a detailed investigation of the flow field. In a second step the experimental results serve as reference data to assess the accuracy of CFD computations. Compressible large eddy simulations (LES) were performed to capture the morphology of the primary breakup as well as the important flow field characteristics. A Volume of Fluid (VOF) approach was used to track the unsteady evolution and breakup of the liquid jet. Comparison of experimental and numerical results showed good agreement with respect to breakup frequency, velocity fields and morphology.
BioRobur is a project aimed to produce hydrogen from biogas through an auto-thermal reforming (ATR) process, in which innovative catalytic systems are used to promote the ATR reactions involved in ...the process for the conversion of biogas into syngas. A detailed LCA study of hydrogen production from biogas ATR using the BioRobur technology has been performed. LCA analysis has been also conducted for other two conventional processes for the production of hydrogen from biogas: the steam reforming and water hydrolysis (a biogas-fueled Internal Combustion engine (ICE) followed by an Electrolyser). A comparison between these technologies has been made from both the environmental and the energetic viewpoints. The LCA has demonstrated that BioRobur is the most environmentally friendly of considered processes. Moreover, the ICE plus Electrolyser has resulted to be the because of the very large amount of biogas needed for the least efficient process, due to the low conversion yield of biogas into energy of the ICE.
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•Detailed LCA of different technologies for conversion of biogas into H2.•The ATR-based BioRobur process is the most sustainable and energy efficient.•The ATR process has ∼4% GWP and 5% GER less than a biogas-fed SR process.•IC engines with alkaline electrolyser is the least efficient and sustainable process.
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