H2 Mole Fraction Research Articles

Design and experimental study of solar-driven biomass gasification based on direct irradiation solar thermochemical reactor

Solar-driven biomass steam gasification is a promising technology to produce H2-rich syngas, meanwhile achieve flexible storage of renewable energy. However, the solar gasification application also faces numerous challenges, due to its involved complex chemical reaction characteristics and the inherent the multi-physics energy conversion processes. This work designs a novel direct irradiation solar gasification reactor, with the improved optical acceptance structure and reasonable test module, and the wheat straw particle is selected as experimental sample. Employing a 9 kWe high flux solar simulator, the maximum temperature of reaction bed in this prototype reactor reaches to 1260 °C, with the average solar flux of 1171.3 kW/m2. With adjustable radiation flux as experiment factor, under the highest total radiation of 3.35 kW, the molar fraction of H2 in the produced syngas is 47.1 % with the energy upgrade factor of 1.15, and the cellulose component completes decomposition. Increasing the mass flow rate of steam reduces the syngas output while raising the H2/CO ratio of the syngas. In addition, smaller biomass particle size facilitates the reaction, thereby improving the conversion efficiency of direct irradiation gasification. The investigation results provide a meaningful reference for the efficient utilization of abundant solar and biomass energy.

Anode humidity trade-offs between proton conductivity and concentration overpotentials in protonic ceramic fuel cell: Experiments and numerical simulations

In protonic ceramic fuel cells (PCFCs), the H2 and H2O partial pressures in the anode side vary along the gas flow direction, particularly during high-fuel-utilization operation. This results in different species conductivities and overpotentials, which renders the quantitative evaluation of local performance based on H2 and H2O mole fractions important. A numerical model is developed that can reflect changes in species conductivities and overpotentials resulting from varying gas mole fractions. The numerical current density–voltage characteristic results obtained numerically agree well with those obtained via measurement in a wide range of H2–H2O gas conditions. Numerical modeling confirms a tradeoff, i.e., higher supply humidity levels result in lower electrolyte resistances but higher concentration overpotentials. The maximum output is achieved at a modest humidification level of 20%. The developed numerical model is particularly useful for optimizing the operating conditions of PCFCs with high fuel utilization.

Experiment and simulation assessment of supercritical underground coal gasification in deep coal seam

To explain the impact of geological and process factors on underground coal gasification in deep coal seam (>2200 m) and promote the efficient and clean extraction and conversion of coal, this study employs the orthogonal experimental design method to investigate the impact of CO2 coefficient (0–1), moisture content (30–80 wt%), calcite content (0–10 wt%), albite content (0–10 wt%), kaolinite content (0–20 wt%), reaction temperature (550–650 °C), and reaction pressure (23–27 MPa) on the characteristics of coal underground gasification under supercritical H2O/CO2 conditions. Furthermore, range analysis and variance analysis are utilized to determine the degree of influence of each factor and the interaction between factors. Finally, the Gibbs free energy minimization method is used to conduct a thermodynamic equilibrium analysis of coal supercritical H2O/CO2 gasification at high temperatures (750–1000 °C). The results indicate that the three most significant factors affecting the process of coal supercritical H2O/CO2 gasification are the CO2 coefficient, moisture content, and reaction temperature. The maximum carbon gasification efficiency at 650 °C in experimental cases and 1000 °C in simulation cases is 22.2% and 88.1%, respectively. Although the addition of CO2 at lower temperatures reduces the carbon gasification efficiency, at high temperatures (>900 °C), a higher initial CO2 concentration increases the carbon gasification efficiency. The addition of CO2 under conditions of low moisture content increases the mole fraction of H2, but reduces it under conditions of high moisture content (≥70 wt%). Among the three minerals, calcite has the most significant influence on the gasification process.

Blending low-carbon hydrogen with natural gas: Impact on energy and life cycle emissions in natural gas pipelines

Hydrogen (H2) is considered an alternative energy carrier to reduce greenhouse gas (GHG) emissions related to power and heat generation. A quantitative analysis was conducted to estimate the energy intensity and GHG emissions associated with the transportation of NG/H2 mixture in high-pressure transmission pipeline, considering blending ratios up to 100% of low-carbon H2. The life cycle emissions were obtained by including upstream supply chain emissions, compression and transportation emissions, and end use combustion emissions of the NG/H2 blend. This study accounts for global warming potential of fugitive methane and H2 emissions associated with pipeline transportation of the blend in the life cycle analysis. A significant reduction in the overall life cycle GHG emissions can be achieved when delivering the same volume throughput but at a reduced energy flow to end users. However, to maintain the nominal energy throughput of the pipeline regardless of the H2 mole fraction, a maximum reduction of about 6% is obtained as the H2 mole fraction in the blend will be practically limited to approximately 30% H2 when the pipeline operates at capacity.

Combustion characteristics of premixed ammonia-hydrogen/air swirl flames at elevated pressure

Ammonia (NH3)-hydrogen (H2) blends which are obtainable by NH3 cracking can be an eminent carbon-free fuel. To provide a valuable database for the practical application of cracking-based NH3-H2 fuel, the effects of pressure on the combustion characteristics of premixed NH3-H2(-nitrogen (N2))/air swirl flames are investigated in terms of H2 mole fraction in the NH3-H2 blend and fuel-equivalence ratio. Extinction mechanisms at fuel-lean and rich flames are the same for both normal and elevated pressures, though only the blowoff is observed for elevated pressure. With increasing pressure, fuel-rich limits are generally extended but fuel-lean limits are reduced, NOx emissions decrease and the condition of the maximum NOx emissions moves towards fuel-richer condition. Flame visualization exhibits the shifted main reaction zone upstream, the increased flame wrinkling and the reduced OH and NO intensities with increasing pressure. Dilution effects of N2 at elevated pressure become remarkable compared with those at normal pressure.

Reactive particle-laden flow in industrial-scale supercritical water gasification reactor: Modeling and study on flow patterns

Coal gasification in supercritical water (SCW) is a highly complicated reactive particle-laden flow process, which couples multiphase flow hydrodynamics, conjugate heat transfers, and complex chemical reactions. A quantitative understanding is the key issue for reactor design and optimization. In this study, the Eulerian-Eulerian model is used to describe the particles-SCW flow in a novel industrial-scale thermally integrated supercritical water gasification (TISCWG) reactor with conjugate heat transfer boundary conditions and porous media model. The sophisticated chemical reactions are using a species transport model with a seven-step lumped kinetics. Four zones of the TISCWG reactor and four typical flow patterns in the gasification chamber are firstly revealed as 1) the bottom accumulation region with the nonhomogeneous solids distribution and back-mixing of particles, 2) the upper developed fluidization region with the SCW and coal particles moving in a plug-flow regime in the center and a downward annular gravity-driven flow near the wall, 3) the jet-affected region strongly affected by the vortexes near the nozzle and presented as a trans-critical jet regime and 4) the dilute region where dilute solids slow down and fall back into the gasification zone. Flow in the gasification chamber is strongly affected by the heat transfer with the preheat zone, as reflected by an annular gravity-driven flow film flowing downwards near the gasification wall. A funnel-shaped structure promotes a more uniform distribution of solids in the accumulation region rather than a cylindrical structure. The effect of flow patterns on coal gasification processes is also studied. Volatile pyrohydrolysis reactions depend on the time-varying solids distribution and the gaseous products at the system outlet with a typical H2 mole fraction of 61.42% and CO2 of 34.98%.

Lean-rich combustion characteristics of methane and ammonia in the combined porous structures for carbon reduction and alternative fuel development

Ammonia as a carbon-free alternative fuel has received much attention with the consumption of fossil fuels. In order to explore the mixed combustion of methane and ammonia, a combined porous media burner was designed with pellets embedded in annular ceramic foam. And the effects of operating parameters on combustion characteristics were investigated. The results showed that the ammonia addition increased the combustion temperature and reduced carbon dioxide emissions at the equivalence ratio of <1. And the ammonia promoted the conversion of CO2 to CO for an equivalence ratio of >1. With the increasing of the ammonia ratio, the CO selectivity increased but the CO2 selectivity decreased. In addition, the mixed combustion of ammonia and methane improved the hydrogen production. The fuel ratio of methane to ammonia (0.80: 0.20) resulted in higher syngas production and lower CO2 mole fraction. The flame propagated faster in ceramic foam with lower pore densities (20 PPI) so the preheating time was greatly reduced. Moreover, the 40 PPI ceramic foam was conducive to the stability of the flame position in the upstream zone, and the H2 mole fraction achieved 10.60 % at the inlet velocity of 14 cm/s.

Influence of the H2 proportion on NH3/H2/air combustion in hot and low-oxygen coflows

This study investigated the effect of the H2 fraction on reaction dynamics and NOx formation in a premixed NH3/H2/air jet flame within a hot coflow (JHC) through numerical simulations. We found that even a small mole fraction of H2 (e.g., XH2, F = 5%) significantly enhances the ignition of the premixed NH3/air flame. However, the presence of H2 markedly intensifies the main combustion reactions only when XH2, F ≥ 30%, resulting in a sharp increase in temperature and heat release rate. Moreover, as XH2, F increases, the NOx emission first increases until XH2, F = 75% and then decreases. Without any H2 addition, a high emission of unburned NH3 occurs in the pure NH3 JHC flame. On the other hand, when XH2, F ≥ 50%, the emissions of unburned H2 and OH increase rapidly due to extremely high temperatures. Notably, maintaining XH2, F between 5% and 20% minimizes the emissions of NOx, NH3, H2, and OH. Furthermore, the preferential diffusion of H2 plays a key role in enhancing the production of active radicals (OH, O, and H), thereby significantly boosting the initiation and combustion reactions of NH3/H2 blended fuel.

A novel coal-based Allam cycle coupled to CO2 gasification with improved thermodynamic and economic performance

Coal-based Allam cycle is an advanced low-carbon and efficient power cycle that uses syngas produced by coal gasification to drive the semi-closed supercritical CO2 cycle for electric power generation. To improve the thermodynamic and economic performance, a novel coal-based Allam cycle coupled to CO2 gasification is proposed. Compared to the reference system, the steam for gasification is eliminated and the mole fraction of H2 within the raw syngas is reduced, which could effectively decrease the moisture fraction of the combustion flue gas and give enough margin to intensify heat integration. Thereby, more process heat has been saved to drive the efficient supercritical CO2 cycle and the raw syngas cooling heat is further recovered by the main recuperator. Results show that the net efficiency of the novel system soars to 43.99%, which is enhanced by 0.67% points. Moreover, the exergy efficiency increases by 0.65% points with the total exergy destruction and loss reduced by 1.23%. In addition, the total plant investment (TPI) and the cost of electricity (COE) are reduced by 1.42% and 1.39%, respectively, which proves that the novel system is also superior for commercial application.

High-speed 1-D and 2-D Raman scattering measurement for quantitative characterization of transient hydrogen jets

This paper reports the first quantitative characterization of transient hydrogen (H2) jets issued from a single-hole injector into nitrogen (N2), using high-speed 1-D and 2-D Raman scattering techniques. By employing the pulse-burst laser as the light source together with the low-noise EMCCD cameras running in subframe burst gating mode for signal collection, single-shot 1-D mole fraction of H2 (xH2) deduced from the ratio of H2 and N2 Raman scattering intensities, is obtained at repetition rate of 50 kHz. By changing the injection conditions, transient jet behaviors of both subsonic and highly under-expanded jets are well captured in single shots of 1-D, and the dynamic of the oblique shocks is visualized by local peaks in relative H2 number density. Statistical information regarding the jet behaviors is also obtained by repeating the measurement at same injection conditions, and the mixing between H2 and N2 can be directly evaluated by the average xH2. A coefficient of variance (COV) of 1.6 to 6 % is measured for all the conditions near the core region of the jets at late injection time, which demonstrates a good repeatability of the 1-D line measurements during the quasi-steady injection period. Using high-speed CMOS cameras, 2-D Raman imaging of transient H2 jets is performed at repetition rate of 10 kHz. Results in single shots demonstrate the vortices formation at the start of injection leading to turbulent mixing layers at later stages. Due to the low SNR, the accuracy and precision of the 2-D measurements is limited, and a one-to-one comparison of statistical results shows a maximum deviation of approximately 15 % from the more accurate 1-D measurements.

Evaluation of a green methanol production system using the integration of water electrolysis and biomass gasification

For a long time, the development of green shipping has been highly valued by countries and organizations. Biomass gasification-based green methanol is seen as a long-term alternative to conventional shipping fuel to reduce greenhouse gas emissions in the maritime sector. While the operational benefits of renewable methanol as a marine fuel are well-known, its cost and environmental performance depend largely on the production method. In this study, a green methanol production system based on the integration of biomass gasification and water electrolysis is proposed and evaluated via the parametric and thermodynamic analysis methods. The water electrolysis is used to increase the hydrogen content in syngas, thereby increasing the production of methanol. The results show that as the S/C ratio increases, the mass flow rate and the calorific value of product gas, the mole flow rate of methanol decreases. The enhancement of the H2/CO ratio can increase the mole fraction of H2, thereby increasing the methanol yield. The mole flow rate of methanol dramatically increases from 925.0 kmol/h to 3725.2 kmol/h. Additionally, the mole flow rate of methanol in the proposed system is 10776.0 kmol/h, larger than the traditional system of 3603.4 kmol/h. The carbon element conversion rate of the proposed system is 94.6%, higher than the 31.5% of the traditional system. This system can significantly provide an efficient green methanol production method for the shipping sector, while also helping to find a feasible solution for the consumption of renewable energy.

Comparisons of global quench limitations between downwardly-propagating and centrally-ignited premixed ammonia/air flames by intense near-isotropic turbulence

Global quench (GQ), a complete extinction, of downwardly-propagating and centrally-ignited premixed ammonia/air flames by intensive near-isotropic turbulence generated in a central region of fan-stirred cruciform burner is explored at wide ranges of the equivalence ratio (ϕ = 0.7–1.25), the r.m.s. turbulence fluctuation velocity (u′ = 0–8.4 m/s), and the ignition energy (Eig = 50–500 mJ) using pin-to-pin stainless-steel electrodes at 2-mm spark gap. Both central ignition flame kernels and downward propagation flames from the top vessel of the cruciform burner interacting with the central uniform intense turbulence are recorded to determine the required critical u′c and/or Kac for GQ, where Ka is a turbulent Karlovitz number. We find that the low-reactivity ammonia/air laminar flames cannot propagate downwardly from the top vessel at too lean (ϕ = 0.7) and too rich (ϕ = 1.25) conditions. Results show that the large downward propagation flames are much harder to be globally quenched by turbulence than the small central ignition kernels for spherical flames. The downward flame GQ criterion is independent of Eig, while the central ignition GQ criterion is influenced by Eig (the higher Eig, the larger u′c). Contrary to the common notion that the maximum critical u′c for flame GQ occurs near ϕ ≈ 1, we discover that the richer the downward propagation ammonia/air flame is, the larger u′c is. Such a surprising survival capability of rich downward propagation ammonia/air flames to GQ by intense turbulence is due to the nearly linear increase of H2 mole fraction percentage in the upstream products of the top tube of the cruciform burner from less than 1 % at ϕ = 0.9 to about 6 % at ϕ = 1.2. These turbulent downward propagation flame fronts with filiform structures prior to GQ reveal the morphology of distributed-like turbulent flames.

Sustainable co-valorization of medical waste and biomass waste: Innovative process design, optimization and assessment

A novel co-valorization process integrating plasma gasification and Fischer-Tropsch synthesis is designed for converting medical waste (MW) and biomass waste (BMW) into mixed e-fuels where the additional required hydrogen is supplied by solar-based electrolysis. Optimization and comprehensive assessments have been conducted for three scenarios with different ratios of BMW. Operations optimization based on genetic algorithm (GA) has led to a remarkable enhancement in the quality of syngas, with a more than 10% increase in H2 mole fraction. Techno-economic analysis reveals the net present values (NPVs) of three scenarios are −2.56 MM$, 3.38 MM$ and 40.1 MM$ with internal rates of return of 3.4 %, 9.5 % and 14.0 %. By improving the subside of MW treatment, the economic viabilities of all scenarios have been enhanced significantly with higher positive NPVs. Environmental assessment shows ∼2.5 kg eqCO2/kg waste and ∼0.1 g eqCO2 per MJ fuel have been generated across the system boundary and the operation of the designed process has been identified to be the largest source of emissions. These findings underscore the potential of our integrated approach to efficiently convert MW and BMW into valuable e-fuels while maintaining a focus on environmental sustainability.

Air-Blown Biomass Gasification Process Intensification for Green Hydrogen Production: Modeling and Simulation in Aspen Plus

Hydrogen produced sustainably has the potential to be an important energy source in the short term. Biomass gasification is one of the fastest-growing technologies to produce green hydrogen. In this work, an air-blown gasification model was developed in Aspen Plus®, integrating a water–gas shift (WGS) reactor to study green hydrogen production. A sensitivity analysis was performed based on two approaches with the objective of optimizing the WGS reaction. The gasifier is optimized for carbon monoxide production (Case A) or hydrogen production (Case B). A CO2 recycling stream is approached as another intensification process. Results suggested that the Case B approach is more favorable for green hydrogen production, allowing for a 52.5% molar fraction. The introduction of CO2 as an additional gasifying agent showed a negative effect on the H2 molar fraction. A general conclusion can be drawn that the combination of a WGS reactor with an air-blown biomass gasification process allows for attaining 52.5% hydrogen content in syngas with lower steam flow rates than a pure steam gasification process. These results are relevant for the hydrogen economy because they represent reference data for further studies towards the implementation of biomass gasification projects for green hydrogen production.

Optimizing fuel transport and distribution in gradient channel anode of solid oxide fuel cell

Precise geometrical adjustment of an anode is crucial for optimizing the performance of solid oxide fuel cell (SOFC). Fuel gas components of SOFC, including H2, CH4, CO, CO2 and H2O, are complex in composition but play a significant role in determining the efficiency of SOFC. This study examines the fuel transport and distribution and the resultant SOFC performance by constructing various gradient channel anode (GCA) structures. The findings show that compared to the traditional un-gradient channel anode (un-GCA) cell, the GCA cell results in more uniform gas distribution and better diffusion of fuel gases, particularly H2, CH4 and H2O. Because of the improved gas diffusion in the anode electrode, the GCA (12 μm) cell exhibits a 2.34 % improvement in power density compared to the un-GCA cell at 800 °C and 0.6 V. Additionally, after increasing the mole fractions of H2 and CH4 in the fuel gas, the power density of the GCA (12 μm) cell is improved by 2.42 % compared with that of the un-GCA cell under the same condition. This study provides clear evidence that incorporating the gradient channel structure in the anode can effectively enhance gas transport, minimize localized gas aggregation and eventually improve the performance of SOFC.

Effect of microporous layer structural parameters on heat and mass transfer in proton exchange membrane fuel cells

Proton exchange membrane fuel cells offer promising clean energy solutions for various applications. However, their performance relies heavily on the properties of the microporous layer, which plays a crucial role in transporting and distributing the components in the fuel cell. To date, the potential for optimising the microporous layer material structural parameters to enhance the fuel cell performance remains largely unexplored. This study aims to fill this research gap by conducting a comprehensive investigation of the effects of different microporous layer material structural parameters on the heat and mass transfer in the membrane electrode assembly. MATLAB was used for optimising the performance of the fuel cell components. The results show that increasing the microporous layer thickness from 5 to 50 μm significantly affects the species transport, leading to a substantial reduction in the molar fraction of H2 and O2 at the electrochemical reaction sites. Furthermore, the distribution of the liquid water saturation inside the fuel cell is influenced by the porosity and permeability of the microporous layer. By increasing the porosity from 0.3 to 0.6, the liquid water saturation at the interface of the catalyst layer and microporous layer decreases by 0.52 % and 1.12 % at output voltages of 0.5 V and 0.7 V, respectively. This reduction enhances the efficiency of internal water transport. Moreover, reducing the permeability of the microporous layer from 2 × 10-12 to 1 × 10-13 at 0.5 V and 0.7 V leads to an increase in liquid water saturation at the interface of the proton exchange membrane and the catalyst layer by 1.49 % and 0.74 %, respectively, causing hindrance to the transport of internal liquid water. This study provides valuable insights into the interplay between the properties of the microporous layer material properties and heat and mass transfer characteristics in proton exchange membrane fuel cell.

Low-temperature upcycling of polypropylene waste into H2 fuel via a novel hydrothermal tandem process.

Plastic waste is a promising and abundant resource for H2production. However, upcycling plastic waste into H2fuel via conventional thermochemical routes requires relatively considerable energy input and severe reaction conditions, particularly for polyolefin waste. Here, we report a tandem strategy for the selective upcycling of polypropylene (PP) waste into H2fuel in a mild and clean manner. PP waste was first oxidizedinto small-molecule organic acids usingpure O2as oxidantat 190 °C, followed by the catalytic reforming of oxidation aqueous products over ZnO-modified Ru/NiAl2O4catalysts to produce H2at 300 °C. A high H2yield of 44.5 mol/kgPPand a H2mole fraction of 60.5% were obtained from this tandem process. The entire process operated with almost no solid residue remaining and equipment contamination, ensuring relative stability and clean of the reaction system. This strategy provides a new route for low-temperature transforming PP and improving the sustainability of plastic waste disposal processes.

Thermodynamic analysis of using CO2 as a co-gasification agent in supercritical water gasification of glycerol

Using CO2 as a co-gasification agent in supercritical water gasification (SCWG) of glycerol is one of the promising approaches for syngas production. In this study, a non-stoichiometric two-phase model (i.e., supercritical and solid phase) is used for thermodynamic analysis of supercritical H2O-CO2 co-gasification (SCWCG) of glycerol. The Gibbs free energy of the entire system is minimized to calculate the equilibrium compositions of gaseous and solid products. The chemical potentials of gaseous products are accurately predicted by using the PR-BM equation of state. The validity of the established model is initially confirmed through its fitting with experimental data. Subsequently, the model is used to investigate the effects of various single and combined operating conditions on product compositions. The findings indicate that temperature, CO2 addition and glycerol concentration have significant influence on the process performance, whereas the pressure has a negligible effect. In addition, the theoretical maximum H2 molar fraction of 68.15% are obtained. Furthermore, the reaction heat duty and high heating value of gaseous products are analyzed. When the glycerol concentration is low, the SCWCG process turns out to be endothermic and can be energetically self-sufficient by adding a small amount of O2 at the expense of reducing the heating value of gaseous products. The study provides valuable insights on designing an optimal SCWCG process for syngas production from glycerol.

Utilization of mill rejects with biomass pellets in the existing coal power plants- a novel approach towards sustainability & fuel security

ABSTRACT The present work is focused on the possible utilization of mill rejects blended with the biomass non-torrefied pellets (made of paddy straw, dry grasses and fallen sal leaves) in the existing tangential coal-fired boiler through the gasification process. The physio-chemical analysis and combustion behavior study of the materials is done based on thermo-gravimetric analysis (TGA) and differential thermal analysis (DTA). The result shows that the gross calorific value (GCV) of the developed bio-mass pellet is about 3900–4300 kCal/kg with the mass percentage of fixed carbon (FC) and volatile matter (VM) of about 15% and 70%, respectively. From the TGA and DTG study, it is observed that about 7% weight loss was found in all pellets at a temperature range of about 85–110°C but for the mill rejects, it is about 5–6%. At the peak temperature, the maximum weight loss of pellets and mill rejects is about 0.90 gm/min and 0.16 gm/min, respectively. The combined use of mill rejects and pellets (1:1) in the updraft gasifier generates combustible syngas with mole fractions of CO and H2 of about 0.29 and 0.30, respectively with a lower heating value of about 159 kJ/mole. The direct use of generated combustible syngas into the coal-fired boiler of a 500 MW power plant increases the net energetic and exergetic performance by about 0.09 and 0.07% points, respectively and resulting in a reduction of annual CO2 emissions by about 9452 tons. Cost-benefit analysis is used to determine the feasibility of the system.

An energy-efficient and cleaner production of hydrogen by steam reforming of glycerol using Aspen Plus

Hydrogen (H2) is produced in an efficient and sustainable manner using steam reforming of glycerol in this work. Two models are used to provide anticipation about how efficiently H2 can be produced: Model 1, a stoichiometric model, and Model 2, a thermodynamic model. Model 1 helps determine the water/glycerol molar input ratio and reaction pathway. The thermodynamic feasibility of Model 1 is examined using Model 2, which then determines the optimum conditions for maximal H2 generation. Model 2 produced 1275 kmol/h of H2 with an H2 mole fraction of 0.49 at 658 °C and 1 atm of pressure. The reactor's net heat load is greatly reduced through heat integration in this study. The energy required is reduced by 29.5% as compared to when no heat integration is used. The process of separating and eliminating CO2 is accomplished by employing the principles of mass and energy balance in the Aspen Plus.