Challenges in hydrogen fuel sampling due to contaminant behaviour in different gas cylinders

Increasing deployment of fuel cell electric vehicles (FCEVs) has led to implementation of hydrogen quality regulations (ISO 14687:2019) to prevent FCEV loss of performance. Hydrogen refuelling stations operators must be able to send representative samples of hydrogen fuel for analysis. Stability of contaminants in sampling vessels needs to be known at ISO 14687:2019 thresholds. A 4-month stability study was carried out on mixtures of ISO 14687 contaminants at amount fractions close to the thresholds in two types of sampling cylinders (SPECTRA-SEAL® and SGS? aluminium cylinders). SPECTRA-SEAL® cylinder allowed representative sampling of CO, CO₂, CH₄, C₂H₆, N₂, Ar, He, Cl₂CH₂, H₂O, O₂, CH₂O₂ in hydrogen fuel for 2 months. SGS? cylinder allowed representative sampling of CO, CO₂, CH4, C₂H₆, N₂, Ar, He, Cl₂CH₂, H₂O, O₂, H₂S for 4 months. Further work is needed to allow representative sampling of ammonia and formaldehyde.     

Numerical simulation of hydrogen production by gasification of large biomass particles in high temperature fluidized bed reactor

Biomass as a renewable fuel compared to fossil fuels usually contains high moisture content and volatile release. Hydrogen production by large particle biomass gasification is a promising technology for utilizing high moisture content biomass particle in the high temperature fluidized bed reactor. In the present work, simulation of large particles biomass gasification investigated at high temperature by using the discrete phase model (DPM). Combustible gases with homogeneous gas phase reactions, drying process with a heterogeneous reaction, primary and secondary pyrolysis with independent parallel-reaction by using two-competing-rate model to control a high and low temperature were used. During the thermochemical process of biomass, gaseous products containing of H₂, H₂O, CH₄, CO and CO₂ was obtained. The effects of concentration, mole and mass fraction and hydrodynamics effects on gaseous production during gasification were studied. The results showed that hydrodynamic effect of hot bed is different from cold bed. Concentration and molar fraction of CO and H₂ production by continually and stably state and small amount of CO₂, H₂O, and CH₄ was obtained. The hydrodynamic of bed plays the significant role on the rate of gaseous products.     

Premium quality fuels and chemicals from the fluidised bed pyrolysis of biomass with zeolite catalyst upgrading

Biomass in the form of pine wood was pyrolysed in an externally heated fluidised bed pyrolysis reactor with nitrogen as the fluidising gas. A section of the freeboard of the reactor was packed with zeolite ZSM-5 catalyst. The pyrolysis oils before and after catalysis were collected in a series of condensers and cold traps. In addition, gases were analysed off-line by packed column gas chromatography. The composition of the oils and gases were determined before and after catalysis in relation to process conditions. The oils were analysed by liquid chromatography followed by gas chromatography/mass spectrometry. The results showed that the oils before catalysis were highly oxygenated, after catalysis the oils were markedly reduced in oxygenated species with an increase in aromatic species, producing a premium grade gasoline type fuel. The gases were CO₂, CO, H₂, CH₄, C₂H₄ and C₃H₆ and minor concentrations of other hydrocarbon gases. After catalysis the concentration of CO₂ and CO were increased. Detailed analysis of the upgraded oils showed that there were high concentrations of economically valuable chemicals. However, biologically active polycyclic aromatic species were also present in the catalysed oil, which increased with increasing catalyst temperature.     

Gasification of landfill leachate in supercritical water: Effects on hydrogen yield and tar formation

Landfill leachate was gasified in supercritical water (SCW) in a batch reactor made of 316 SS. The effects of temperature, pressure, reaction time and oxidation coefficient (OC) on the pollutant removal efficiencies and gasification characteristics were investigated. To observe the formation of tar and char visually, a capillary quartz reactor was also used. Results indicated that CO₂, H₂ and CH₄ were the most abundant gaseous products. Temperature has an appreciable effect on the gasification process. Increasing temperature enhanced the H₂ yield (GY_H2) and TOC removal efficiency (TRE) significantly. Although the influence of reaction time on the fractions of gaseous products was negligible at time above 300 s, the yields of H₂, CH₄, and CO₂ increased with reaction time whereas the CO, C₂H₄ and C₂H₆ yields decreased. Tar and char formation was evident on the interior surface of capillary quartz reactor. Adding a little oxidant could increase H₂ and CH₄ yields and decrease tar and char formation. GY_H2 reached up to the maximum of 231.3 mmol L^?1 leachate at 500 °C, 25 MPa, 600 s and 0.2 OC, which was 2.4 times of that without oxidant.     

Preparation of gas standards for quality assurance of hydrogen fuel

This study has developed traceable standards for evaluating impurities in hydrogen fuel according to ISO 14687. Impurities in raw H₂, including sub μmol/mol levels of CO, CO₂, and CH₄, were analyzed using multiple detectors while avoiding contamination. The gravimetric standards prepared included mixtures of the following nominal concentrations: 1, 2, 3–5, 8–11, 17–23, and 47–65 μmol/mol for CO₂, CH₄ and CO, O₂, N₂, Ar, and He, respectively. The expanded uncertainty ranges were 0.8% for Ar, N₂, and He, 1% for CH₄ and CO, and 2% for CO₂ and O₂. These standards were stable, while that for CO varied by only 0.5% during a time span of three years. The prepared standards are useful for evaluating the compliance of H₂ fuel in service stations with ISO 14687 quality requirements.     

ReaxFF molecular dynamics simulations of n-eicosane reaction mechanisms during pyrolysis and combustion

The pyrolysis and combustion mechanism of the hydrocarbon fuel has important scientific and practical significance. However, it is difficult to detect the whole intermediates and products using traditional methods, which brings trouble to the analysis of the reaction process. In this paper, the microscopic reaction mechanism and the main products of n-eicosane (C₂₀H₄₂) were simulated based on the reactive force field molecular dynamics (ReaxFF-MD). The effects of temperature (2000–3500 K) and oxygen on the initial decomposition, the distribution of main products, and the reactive pathways of C₂₀H₄₂ fuel were studied to determine its reaction mechanism. The initial decomposition of C₂₀H₄₂ was mainly initiated by small alkyl radicals in pyrolysis, and by the oxygen-containing radicals in combustion. The participation of oxygen had a greater effect on accelerating the decomposition reaction. The reactions involving oxygen of C₂₀H₄₂ initial decomposition accounted for 87.5% of the total reactions at 2000 K. Moreover, the detailed distribution and formation pathways of the main products of H₂, C₂H₄, CH₄, H₂O, CO, and CO₂ were depicted to construct the overall reaction mechanism of C₂₀H₄₂. •H radical formed from the composition of C₂H₄ was exactly consistent with the •H radical consumed by the generation of CH₄ and H₂ in the pyrolysis stage. The feasibility of the simulation method was verified by the result of thermal analysis. The results are helpful for further research on the reaction mechanism of hydrocarbon fuels.     

Soot surface oxidation in hydrocarbon/air diffusion flames at atmospheric pressure

Soot surface oxidation was studied experimentally in laminar hydrocarbon/air diffusion flames at atmospheric pressure. Measurements were carried out along the axes of round fuel jets burning in co-flowing dry air considering acetylene-nitrogen, ethylene, propylene-nitrogen, propane and acetylene-benzene-nitrogen in the fuel stream. Measurements were limited to the initial stages of soot oxidation (carbon consumption less than 70%) where soot oxidation occurs at the surface of primary soot particles. The following properties were measured as a function of distance above the burner exit: soot concentrations by deconvoluted laser extinction, soot temperatures by deconvoluted multiline emission, soot structure by thermophoretic sampling and analysis using Transmission Electron Microscopy (TEM), concentrations of major stable gas species (N₂, H₂O, H₂, O₂, CO, CO₂, CH₄, C₂H₂, C₂H₄, C₂H₆, C₃H₆, C₃H₈, and C₆H₆) by sampling and gas chromatography, concentrations of some radical species (H, OH, O) by deconvoluted Li/LiOH atomic absorption and flow velocities by laser velocimetry. For present test conditions, it was found that soot surface oxidation rates were not affected by fuel type, that direct rates of soot surface oxidation by O₂ estimated from Nagle and Strickland-Constable (1962) were small compared to observed soot surface oxidation rates because soot surface oxidation was completed near the flame sheet where O₂ concentrations were less than 3% by volume, and that soot surface oxidation rates were described by the OH soot surface oxidation mechanism with a collision efficiency of 0.14 and an uncertainty (95% confidence) of ±0.04 when allowing for direct soot surface oxidation by O₂, which is in reasonably good agreement with earlier observations of soot surface oxidation rates in both premixed and diffusion flames at atmospheric pressure.     

Characteristic and utilization of pyrolysis productions from Dianchi Lake’s sediment in Yunan province in China

In the process of pyrolysis of Dianchi Lake’s sediment, a large number of productions (including gas state, liquid state, and solid state) were obtained. This research analyzed the characteristics and utilization of the representative pyrolysis products by gas chromatography, gas chromatograph-mass spectrometer, Brunauer–Emmett–Teller measurements, and X-ray fluorescence methods. The main gas components were H₂, CO, CH₄, CO₂, C₂H₄, and C₂H₆ in pyrolysis productions of the Dianchi Lake’s sediment. The flammable gases, H₂, CO, and CH₄, were vastly generated at the high-temperature section (>800°C). The main liquid components of pyrolysis products were phenol and hydroxy derivatives, which have no fuel use value, but abundance of phenol and its derivatives can be used as chemical raw materials. Solid products were in the enrichment of Si, Al, Fe, and other mineral elements, which have a good application prospect as building materials.     

Chemical effects on molecular species concentrations in turbulent fires

The measurement and modeling of molecular species concentrations in turbulent pool and buoyant jet flames is described. The experimental parameters included burner diameter (2.8 mm jet nozzle, 190, 381, and 762 mm pools), theoretical combustion heat release rate (10–283 kW), lip size (0–25 mm), and fuel (CH₄, C₃H₈). Time-averaged species concentrations were obtained through axial and radial sampling probe traverses. A novel sampling probe was developed which provides a constant mass flow of flame gases that is not biased toward either hot or cold gas eddies.Local concentrations of major gas species (fuel, O₂, CO, CO₂, H₂O, N₂) in the fire are correlated by the mixture fraction, which is the fraction of atomic species present which originated in the supplied fuel. The correlation appears to be independent of pool diameter, lip size, and heat release rate. These turbulent correlations differ from the corresponding curves for laminar flames primarily due to composition broadening resulting from time average measurements of widely fluctuating components. We obtained higher than expected concentrations of CO and CO₂ in centerline measurements near the fuel source. An attempt is made ot explain these findings based on non-equal species diffusivity and local radiative extinction.The correlations obtained in this work form the basis for two closely related models: (1) for predicting mean species concentrations in turbulent flames by weighting laminar data with an assumed pdf of the mixture fraction, and (2) the chemical scaling of turbulent pool fires using Froude modeling principles. These applications are briefly discussed.     

An experimental investigation of incomplete combustion of gaseous fuels of a heavy-duty diesel engine supplemented with hydrogen and natural gas

This paper investigates the emissions of the unburned gaseous fuels of a heavy-duty diesel engine converted to operate under natural gas (NG)-diesel and hydrogen (H₂)-diesel dual fuel combustion mode. The detailed effects of the addition of H₂, NG, engine load, and engine speed on the exhaust emissions of the unburned H₂, methane (CH₄), and carbon monoxide (CO) were experimentally investigated. The combustion efficiencies of CH₄ and H₂ supplemented were also examined and compared.     

Dry and steam reforming of biomass pyrolysis gas for rich hydrogen gas

Biomass pyrolysis gas (including H₂, CO, CH₄, CO₂, C₂H₄, C₂H₆ and etc.) reforming for hydrogen production over Ni/Fe/Ce/Al₂O₃ catalysts was presented in this study. This study investigated how the operating conditions, such as the calcinations temperature of catalysts, the reaction temperature, the gas hourly space velocity (GHSV) and the ratio of H₂O/C, affect the conversion of CH₄ and CO₂ and the selectivity of hydrogen from dry and steam reforming of pyrolysis gas. The experimental results indicated that, under the conditions: the reaction temperature of 600 °C, the GHSV of 900 h⁻¹ and H₂O/C of 0.92, the reaction efficiency is the optimal. Especially, the concentration of H₂, CO, CH₄, CO₂, and C₂H_n (C₂H₄ and C₂H₆) were 36.80%, 10.48%, 9.61%, 42.62%, 0.49% respectively. The conversion of CH₄ and CO₂ reached 45.9% and 51.09%, respectively. There were all kinds of reactions during the processing of reforming of pyrolysis gas. And the main reactions changed with the operation condition. It was due to the promoting or inhibiting interaction among different constituents in the pyrolysis gas and the different activity of catalysts in the different operation condition.     

Evaluation of chemical effects of added CO2 according flame location

A numerical study has been conducted to clearly grasp the impact of chemical effects caused by added CO₂ and of flame location on flame structure and NO emission behaviour. Flame location affects the major source reaction of CO formation, CO₂+H→CO+OH and the H‐removal reaction, CH₄+H→CH₃+H₂. It is, as a result, seen that the reduction of maximum flame temperature due to chemical effects for fuel‐side dilution is mainly caused by the competition of the principal chain branching reaction with the reaction, CH₄+H→CH₃+H₂, while that for fuel‐side dilution is attributed to the competition of the principal chain branching reaction with the reaction, CO₂+H→CO+OH. The importance of the NNH mechanism for NO production, where the reaction pathway is NNH→NH→HNO, is recognized. In C‐related reactions most of NO is the direct outcome of (R171) and the contribution of (R171) becomes more and more important with increasing amount of added CO₂ as much as the reaction step (R171) competes with the key reaction of thermal mechanism, (R237), for N atom. This indicates a possibility that NO emission in hydrogen flames diluted with CO₂ shows less dependent behaviour upon flame temperature. Copyright © 2004 John Wiley & Sons, Ltd.     

Some considerations of the lean flammability limits of mixtures involving hydrogen

Consistent data regarding the flammability limits of homogeneous mixtures of hydrogen gas in air at atmospheric pressure are presented for various temperatures extending down to ?130 °C. The retardation of the combustion of lean homogeneous mixtures of hydrogen and air due to the homogeneous mixing of inerts such as CO₂, N₂ and He is also considered. Moreover, the enhancement of the flammability limits of fuel mixtures involving CO, CH₄, C₃H₈ and C₂H₄ in air due to the presence of some hydrogen is also presented. Guidelines are then suggested for predicting the role of the presence of hydrogen in the fuel-air mixtures over a wide range of concentrations and temperatures.     

Flowerlike microspheres catalyst NiO/La2O3 for ethanol-H2 production

Catalysts of nano-sized nickel oxide particles based on flowerlike lanthanum oxide microspheres with high disperse were prepared to achieve simultaneous dehydrogenation of ethanol and water molecules on multi-active sites. XRD, SEM, 77K N₂ adsorption were used to analyze and observe the catalysts’ structure, morphology and porosity. Catalytic parameters with respect to yield of H₂, activity, selectivity towards gaseous products and stability with time-on-stream and time-on-off-stream were all determined. This special morphology NiO/La₂O₃ catalyst represented more than 1000 h time-on-stream stability test and 500 h time-on-off-stream stability test for hydrogen fuel production from ethanol steam reforming at 300 °C without any deactivation. During the 1000 h time-on-stream stability test, ethanol–water mixtures could be converted into H₂, CO, and CH₄ with average selectivity values of 57.0, 20.1, 19.6 and little CO₂ of 3.2 mol%, respectively, and average ethanol conversion values of 96.7 mol%, with H₂ yield of 1.61 mol H₂/mol C₂H₅OH. During the 500 h time-on-off-stream stability test, ethanol–water mixtures could be converted into H₂, CO, CH₄ and CO₂ with average selectivity values of 65.1, 17.3, 15.1 and 2.5 mol%, respectively, and average ethanol conversion values of 80.0 mol%. For the ethanol-H₂ and petrolic hybrid vehicle (EH–HV), the combustion value is the most important factor. So, it was very suitable for the EH–HV application that the low temperature ethanol steam reforming products’ distribution was with high H₂, CO, CH₄ and very low CO₂ selectivity over the special NiO/La₂O₃ flowerlike microspheres.     

Effects of CO2 and N2 dilution on the characteristics and NOX emission of H2/CH4/CO/air partially premixed flame

For the combustion of the mixture of blast furnace gas, natural gas, and coke oven gas in industrial burners, how to improve combustion efficiency and reduce pollutant emission are of significance. To accomplish this, an industrial partially premixed burner with a combustion diagnostic system is used to experimentally reveal the characteristics and NO_X emission of H₂/CH₄/CO/air flame under CO₂, N₂, and CO₂/N₂ (replacing half of N₂ with CO₂) dilution. NO_X emission and flame length, temperature profile, along with CO, CH₄, and CO₂ concentration profiles are analyzed with the three diluents in the fuel stream under different dilution rates (0–32% by volume). Experimental results show that for lean H₂/CH₄/CO combustion, greater proportions of CO₂ in the diluent affect flame characteristics in various ways. These effects include longer flame length, lower highest flame temperature, the highest flame temperature being located farther away from the nozzle, and the highest CO₂ concentration being located nearer the nozzle. Furthermore, results of CO, CH₄, and CO₂ concentrations indicate that chemical reactions in the flame are significantly affected by CO₂ owing to the series reaction CH₄?CH₃→CO?CO₂. Finally, increasing diluents or the ratio of CO₂ in diluents has the benefit of reducing NO_X emission.     

Experimental study on pyrolysis characteristic of coking coal from Ningdong coalfield

The thermal decomposition of coal was the essential step of many reactions, thus it was widespread concerned. In order to investigate the behaviors and kinetics of coal pyrolysis, coal samples which obtained from Ningdong coalfield of China were pyrolyzed with a tubular furnace in argon atmosphere at the heating rate of 5 K min^?1. The primary gaseous products including CH₄, H₂, N₂, CO, CO₂, C₂H₄ and C₂H₆ were quantified using a gas chromatogram. It can be seen that with the temperature increasing, the yields of H₂ and CO increased, while the others decreased. In order to produce possibly much tar, the optimal temperature was 923 K. The characteristic of pyrolysis kinetics was determined by thermo gravimetric analysis measurement. The Coats–Redfern and Flynn–Wall–Ozawa methods was used to obtain kinetic parameters. The activation energy range of 50–200 kJ mol^?1 was determined.     

An experimental and modeling study of methyl propanoate pyrolysis at low pressure

Methyl propanoate (MP) pyrolysis in a laminar flow reactor was studied at low pressure (30 Torr) within the temperature range from 1000 to 1500 K. About 30 products were detected and identified in the pyrolysis process using the photoionization mass spectrometry, including H₂, CO, CO₂, CH₃OH, CH₂O, CH₂CO, C1 to C4 hydrocarbons and radicals (such as CH₃, C₂H₅ and C₃H₃). Their mole fraction profiles versus temperature were also measured. For the unimolecular dissociation reactions, the rate constants were calculated by high precision theoretical calculations. Based on the theoretical calculations and measured mole fraction profiles of pyrolysis species, a kinetic model of MP pyrolysis containing 98 species and 493 reactions was developed. The model simulates the primary decomposition process well with the calculated rate constants. According to the rate of production analysis, the decomposition pathways of MP and the formation channels of both oxygenated and hydrocarbon products were discussed. It is concluded that the main decomposition pathway is MP → CH₂COOCH₃ → CH₃CO + CH₂O → CO.     

Flame structure and NO emissions in gas combustion of low calorific heating value

Numerical study on addition effects of CO and CO₂ in fuel side (H₂/Ar) on flame structure and NO emission behaviour in counterflow diffusion flame has been conducted with detailed chemistry to fundamentally understand gas combustion of low calorific heating value. A modified Miller–Bowman reaction scheme including a complementary C₂-reaction subset is adopted. The radiative heat loss term, which is based on an optically thin model and it especially important at low strain rates, is included to cover the importance of the temperature dependence on NO emission. Special interest is taken to estimate the roles of added CO and CO₂ in fuel side on flame structure and NO emission characteristics. Increasing CO concentration in fuel side contributes to the enhancement of combustion due to the increase effect of the concentration of reactive species. The increase of added CO₂ concentration in fuel side suppresses overall reaction rate due to the high heat capacity. It is seen that chemical effects due to the breakdown of added CO₂ in fuel side make C₂-branch chemical species be remarkably formed and the prevailing contribution of prompt NO is a direct outcome of these effects. It is found that in the combined forms of H₂/CO/CO₂/Ar fuels the effects of added CO and CO₂ concentrations in fuel side compete contrarily to each other in NO emission behaviour. Particularly the role of added CO is stressed in the side of restraining prompt NO. Copyright © 2003 John Wiley & Sons, Ltd.     

Multi-species measurements in 1-butanol pyrolysis behind reflected shock waves

The kinetics of 1-butanol pyrolysis were investigated by measuring multi-species time histories using shock tube/laser absorption methods. Species time histories of OH, H₂O, C₂H₄, CO, and CH₄ were measured behind reflected shock waves using UV and IR laser absorption during the high-temperature decomposition of 1% 1-butanol/argon mixtures. Initial reflected shock temperatures and pressures for these experiments covered 1250–1650 K and 1.3–1.9 atm. Measured OH and H₂O time histories are in good agreement with previous experimental studies; measured C₂H₄, CO, and CH₄ time histories are the first reported for this fuel in shock tube experiments.Production pathways and sensitivities for the measured species are analyzed using the recent Sarathy et al. (2012) [37] detailed mechanism. Simulations using this mechanism underpredict H₂O, OH, and C₂H₄ mole fractions, overpredict CH₄ mole fractions, and significantly underpredict CO mole fractions at early times. As discussed in past papers and confirmed in this study, the branching ratios of H abstraction rates from 1-butanol, which are not precisely known, can significantly affect H₂O time history simulations. These simulations show that H₂O is produced primarily through H-atom abstraction from 1-butanol by OH, and therefore H₂O time histories are extremely sensitive to 1-butanol decomposition channels that contribute to the OH radical pool. Simulations also show that more C₂H₄ would be produced by faster decomposition of 1-butanol through several channels that also affect H₂O production. Finally, simulations show that CO time histories are strongly sensitive to 1-butanol decomposition into nC₃H₇ and CH₂OH, especially at early times. Evidence is presented that indicates this decomposition pathway is too slow in the simulations by a factor of three to five at conditions of the current study.     

Experimental investigation on influences of methanol reformate impurities in performances of high temperature proton exchange membrane fuel cells

Even though the methanol reformate can be fed into the high temperature proton exchange membrane fuel cell, the influences of different reformate components on the fuel cell are still unclear. This work investigates the effects of CO, CO₂, H₂O, and CH₃OH in the fuel gas on the fuel cell performances. The distribution of relaxation times and equivalent circuit model are employed for analysis. The results show the increase of anodic charge and mass transfer resistances are main factors of CO poisoning which results in 77 mV overpotential. The maximum overpotential difference between CO₂ and Ar is only 4 mV, which means the dilution effect of CO₂ is similar to Ar. H₂O decreases the Ohmic and anodic charge transfer resistances and reducing the overpotential by 10 mV. CH₃OH below 3% has slight positive effect on the fuel cell performance. However, 5% CH₃OH results in high overpotential of 36 mV.