H2 Fraction Research Articles

Valorization of sewage sludge through catalytic sub- and supercritical water gasification

Sub- and supercritical water gasification is applied to recover energy from sewage sludge in a batch reactor. The effects of reaction temperature and water-soluble additives as catalysts on gasification were examined. The resultant products, including syngas, hydrochar and liquid residues were characterized. The rise of temperature without the presence of catalysts increased the yield of H2 (0.06 (350 °C) to 1.91 mol/kg (450 °C) and enhanced the gasification efficiency (1.29–19.61%), and decreased total organic carbon (TOC) by 68.50% in liquid residue. The changes in product distribution and characteristics of hydrochar and liquid residue implied that the organic matters in sewage sludge were dissolved and hydrolyzed in sub- and supercritical water, resulting in the production of syngas. The catalytic effect of different catalysts in relation to the H2 gas yield was in the following order: KOH > NaOH > Na2CO3 ≈ K2CO3. In the case of catalytic supercritical water gasification at 400 °C, the highest molar fraction (37.28%) and yield of H2 (1.60 mol/kg) were obtained in the presence of KOH. Furthermore, the scanning electron microscopy (SEM) analysis indicated that a conversion and dissolution of the organic matters in sewage sludge to liquid and gas, produced a porous, fragmented structure and disintegrated surface of hydrochar.

CFD simulation of the steam gasification of millimeter-sized char particle using thermally thick treatment

A detailed char gasification model is developed using a multiphase Eulerian–Lagrangian algorithm and thermally thick treatment. The model is first validated by both gasification and combustion experiments of a millimeter-sized char particle. Temperature and mass loss histories as well as the particle morphology evolution correspond well with the existing results. Then the steam gasification of a 5 mm char particle is simulated and detailed physical and chemical conversion processes inside the particle are explored. During gasification, three distinct layers, i.e., the outer ash layer, the intermediate layer and the core layer, are identified based on the intraparticle porosity distribution. Simulation results show that the highest H2O and CO2 mass fractions locate in the ash layer, while the intermediate and core layers contain the highest H2 and CO mass fractions, respectively. Moreover, effects of several parameters are also explored. It is found that the Stefan flow caused by the mass transfer plays a key role in determining the diffusion and convection behavior during gasification. The strength of the Stefan flow in the intermediate layer appears to be two orders of magnitude smaller than that of the inflow and has an influence on the shifting from a kinetically-controlled mode to a diffusion-controlled mode. In addition, the char consumption rate in the intermediate layer increases with an increase in steam mass fraction, gasification temperature and inflow velocity while it decreases with increasing particle diameter. Meanwhile, the char consumption rate caused by CO2 is much smaller than that due to steam.

Gasification of coking wastewater in supercritical water adding alkali catalyst

In this study, the influence of alkali precipitation on the gasification of coking wastewater with KOH as catalyst at 540 °C, 25 MPa was investigated. Adding the KOH increased H2 fraction and the gas yield. The alkali is accumulated in the reactor, and the catalytic effect was further improved with reaction time prolonging. The precipitated alkali in the reactor still showed high catalytic effect on the subsequent gasification of coking wastewater without further adding the alkali. The catalytic activity was slightly reduced owning to the transformation of KOH to K2CO3 and KHCO3. A novel 4-lump kinetic model for coking wastewater in SCWG including feedstock, CH4, CO, and CO2 lumps is proposed. The kinetic parameters are estimated for each involved reaction.

Assessment of low‐rank coal and biomass co‐pyrolysis system coupled with gasification

To utilize low-rank coal and biomass in a highly efficient and environmental-friendly manner, a co-pyrolysis system coupled with char gasification is investigated. This system has five main units, namely, the drying and mixing, pyrolysis, cooling and separation, combustion, and gasification units, which are simulated by ASPEN plus based on experimental data. Results show that 37% of the pyrolysis char is burned to supply heat for pyrolysis and drying processes based on cascade utilization of heat energy, whereas the rest is sent to a gasifier. The sensitivity analysis is performed to investigate the impacts of steam and O2 injection on gas composition, gasification temperature, carbon conversion efficiency, heating value of gas during gasification, and gas production efficiency. The fractions of H2, CH4, CO, and CO2 demonstrate diverse variation tendencies with an increasing equivalence ratio and steam-to-char (S/C) ratio. However, carbon conversion efficiency reaches its peak of 99.91% when the equivalence ratio is approximately 4 regardless of S/C ratio. An equivalence ratio of 4 and S/C ratio of 0.15 are used as decent examples to calculate the mass balance and to simulate the overall system. Results show that 1000 kg/h coal and 500 kg/h biomass can produce 285.83 m3/h pyrolysis gas and 2580.78 m3/h gasification gas with low heating values of 8.20 and 9.746 MJ/m3, respectively.

Optimal Operation of an Integrated Energy System Incorporated With HCNG Distribution Networks

Most industrial practices for turning power into hydrogen face a similar challenge, i.e., hydrogen consumption. One solution is injecting hydrogen into the existing natural gas (NG) infrastructure, so as to enter the market without expensive investments. However, a major concern regarding HCNG (Hydrogen enriched compressed natural gas) is the amount of hydrogen that can be added to the natural gas infrastructure without any modification. The current studies have focused on the modeling of HCNG components under various H2 fractions, but there is a lack of research on the system operation of HCNG, especially when incorporated with dispersed renewables and CHP plants. To fill in the gaps from the component to the system level, this paper proposes a comprehensive HCNG operation model coupled with the operations of an electrical and heating network. Via this model, the system performance incorporated with HCNG distribution networks could be studied under various H2 fractions and HCNG load portfolios (HLP). The numerical studies demonstrate the benefits of integrating the HCNG distribution network, especially in terms of local balancing of distributed generators and minimizing the operational costs.

Prediction of gaseous products from refuse derived fuel pyrolysis using chemical modelling software - Ansys Chemkin-Pro

There can be observed global interest in waste pyrolysis technology due to low costs and availability of raw materials. At the same time, there is a literature gap in forecasting environmental effects of thermal waste treatment installations. In the article was modelled the chemical composition of pyrolysis gas with main focus on the problem in terms of environmental hazards. Not only RDF fuel was analysed, but also selected waste fractions included in its composition. This approach provided comprehensive knowledge about the chemical composition of gaseous pyrolysis products, which is important from the point of view of the heterogeneity of RDF fuel. The main goal of this article was to focus on the utilitarian aspect of the obtained calculation results. Final results can be the basis for estimating ecological effects, both for existing and newly designed installations.Pyrolysis process was modelled using Ansys Chemkin-Pro software. The investigation of the process were carried out for five different temperatures (700, 750, 800, 850 and 900 °C). As an output the mole fraction of H2, H2O, CH4, C2H2,C2H4, C3H6, C3H8, CO, CO2, HCl and H2S were presented. Additionally the reaction pathways for selected material were presented.Based on obtained results, it was established that the residence time did not influenced on the concentration of products, contrary to temperature. The chemical composition of pyrolytic gas is closely related to wastes origin. The application of Chemkin-Pro allowed the calculation of formation for each products at different temperatures and formulation of hypotheses on the reaction pathways involved during pyrolysis process. Further, based on the obtained results confirmed the possibilities of using pyrolysis gas from RDF as a substitute for natural gas in energy consumption sectors. Optimization of the process can be conducted with low financial outlays and reliable results by using calculation tools. Moreover it can be predicted negative impact of obtained products on the future installation.

Plasma Gasification With Municipal Solid Waste As A Method Of Energy Self Sustained For Better Urban Built Environment: Modeling and Simulation

The plasma gasification method is known as a new technology to produce hydrogen from MSW as a fuel for power generation. Recently, it has become a crucial issue due to the rapid increasing amount of waste, along with the increasingly national population in Indonesia. The goal of waste management is as a material recovery (MR), as an energy recovery (ER) and minimizing the environment impact. The plasma gasification modeling was developed based on plasma torch technology to estimate the syngas composition and energy potential. The process simulation is optimized for mixed steam and air as a gasifying agent. This study is to obtain the essential parameter to have the better content of H2 in the syngas, better plant efficiency and lowest CO2 emission for developing urban built environment with lesser greenhouse gases (GHG). Result shows that, the ratio of Steam to Waste: 0.08 %, the air mass flow rate: 1.11*10−3 kg/s and the steam mass flow rate: 01.11*10−4 kg/s gain the highest molar fraction of H2 : 32.09%, Syngas Yield : 1.28 Nm3/kg, Carbon Conversion Efficiency : 5.83%, Cold Gasification Efficiency : 77.96% and the CO2 emission : 2.23*10−4 kg/s.

Numerical analysis of flow, mixture formation and combustion in a direct injection natural gas engine

Numerical simulation of flow, mixture formation and combustion in a direct injection natural gas engine was conducted using the large-eddy simulation method. The dynamic thickened flame model coupling with a skeletal methane reaction mechanism was implemented and applied for the combustion simulation. In Situ Adaptive Tabulation (ISAT) method was used for the efficient chemistry solving. It was found that in-cylinder large-scale vortices are principally formed as the fuel jet impinges on the cylinder wall, and they enter the combustion chamber due to the effect of the squish flow at the end of the compression stoke. Most of in-cylinder combustible mixtures begin to be produced after the jet-wall impingement. Under the stoichiometric condition, with the delay of the fuel injection timing, the distribution of in-cylinder equivalence ratio is wider at the ignition timing, and the inhomogeneity of mixtures increases. The fuel injection timing determines the in-cylinder dominant combustion mode and the flame displacement speed at the initial stage of flame propagation by affecting the distribution of mixture equivalence ratio at the ignition timing, thereby affecting the increase of the flame area. Mass fractions of CO, H2, H-atom and N2O in the rich-burn region are higher than those in the lean-burn region. Mass fractions of O-atom, OH, NCN, HCN and NNH in the lean-burn region are higher than those in the rich-burn region. In the region with temperature below 1800 K, NO is principally produced by NO2 conversion, while in the region with temperature above 1800 K, NO is mainly produced by the thermal pathway.

The coupling performance during reactive sorption enhanced reforming (ReSER) process: Simulation and experimental studies

The coupling performance of nano-CaO carbonation with the steam methane reforming (SMR) during reactive sorption enhanced reforming process (ReSER) for hydrogen production was studied by simulation and experimental evaluation. A two-dimensional axial symmetric pseudo-homogeneous mathematic model was established based on nano-CaO carbonation kinetics with the Boltzmann equation style and SMR reaction kinetics. The coupling performance was studied by varying carbonation rate constant (kcarb) and the maximum carbonation conversion (Xmax) in the model. The mathematic model was numerically solved by the COMSOL Multiphysics software and experimentally evaluated using commercial nano-CaO as the CO2 adsorbent. An average relative deviation of 3.86% of CH4 conversion was obtained between the simulated and experimental results. The simulation results indicated the conversion of the CH4 was improved from 88% to 95.3% by increasing kcarb from 1.6 s−1 to 5.74 s−1 and the period of pre-breakthrough time could be extended from 2 min to 20 min by increasing Xmax from 0.3 to 0.9. CH4 conversion of maximum 94.1% when reaction was under 650 °C and 1 bar, the highest molar fraction of H2 of 99.7% when reaction at 600 °C and 1 bar, and the maximum enhancement factor of 45.4% was obtained at 576.3 °C, 2.8 bar.

An Energy and Exergy Analysis of Biomass Gasification Integrated with a Char-Catalytic Tar Reforming System

Adequate tar removal is a recurrent challenge for biomass gasification. Materials such as char and activated char are promising catalysts for tar reforming because of their activity, inexpensiveness, and constant production during gasification. Although the behavior of char and activated char as catalysts has been previously studied, an evaluation of the thermodynamic efficiencies of the tar reforming process using char as a catalyst still lacking. This work analyzes the performance of a two-stage system, where gasification is followed by tar reforming using char catalysts. For the study, a model based in a combination of equilibrium thermodynamics and chemical kinetics was developed. The first stage, where gasification occurs, was simulated with a thermodynamic equilibrium model. Gasification equilibrium models available in the literature only predict the fractions of H2, CO, CO2, and CH4; the model developed for this work also predicts the formation of a three-model tar with different characteristics (b...

Development of a high‐temperature two‐stage entrained flow gasifier model for the process of biomass gasification and syngas formation

This paper presents development of the Mitsubishi Heavy Industries (MHI) gasifier utilizing an analogy between a model with coal feedstock and the model with torrefied woody biomass. A computational fluid dynamics (CFD) model was primarily developed for coal gasification, and the simulation results were validated with similar published work and experimental measurements. The model was extended for the woody biomass to predict the gasifier performance under the gasification process. The results were used to compare the effect of fuel type on the gasifier performance and gaseous product compositions. The second-level injection nozzles were modified tangentially, and the flow characteristics, species yields, and temperature were evaluated. The possibility of reducing the gasifier length from 13 to 8 m is also evaluated for different total length. The results revealed that using woody biomass leads to a decrease in the mole fraction of CO and H2 at the gasifier outlet compared with coal. An opposite trend was observed for CO2 and CH4 compositions. The contributions of modified second-level nozzles to the total gas composition and exit temperature only account for less than 3%. Reducing the gasifier length from 13 to 8 m increased the exit temperature from 1289 to 1340 K, but the changes in the exit gas composition were less than 2%. The new design of the MHI gasifier can reduce the investment costs by reducing the gasifier length as well as using biomass instead of coal.

Effect of Hydrogen Addition on the Sooting Tendency of 1,3-Butadiene Premixed Flames

Mole fractions and formation-depletion pathways of the first aromatic ring and its precursors, acetylene and propargyl radical as well as those of naphthalene are numerically investigated during the co-combustion of 1,3-butadiene/H2 mixtures in low pressure premixed laminar flames conditions. The molar fraction of H2 in the mixture is varied from 0 to 60% by adding 10% of hydrogen to the neat butadiene flame and by keeping the inert mole fraction (argon) and the equivalence ratio constants. The effect of hydrogen is investigated by using a modified Chemkin II version and by differentiating its chemical effect from its thermal and dilution effects. The obtained results indicate that the butadiene/H2 oxidation process is controlled by the synergism between hydrogen dilution and chemical effects. Regardless of the hydrogen amount added to the fuel mixture, two routes are evolved in the benzene formation process, the direct C4 + C2 route and the indirect C3 route, evolving fulvene as an intermediate species. Besides, the collected data reveal that hydrogen doping induces a noticeable decrease in the concentrations of all the studied species inferring that the hydrogen blended fuels are less prolific in soot formation than the neat 1,3-butadiene fuel. The observed decrease is dependent on the hydrogen initial concentration in the fuel mixture as well as on the nature of its effect.

Solubility and mass transfer of H2, CH4, and their mixtures in vacuum gas oil: An experimental and modeling study

Abstract In this work, the solubility data and liquid-phase mass transfer coefficients of hydrogen (H2), methane (CH4) and their mixtures in vacuum gas oil (VGO) at temperatures (353.15–453.15 K) and pressures (1–7 MPa) were measured, which are necessary for catalytic cracking process simulation and design. The solubility of H2 and CH4 in VGO increases with the increase of pressure, but decreases with the increase of temperature. Henry's constants of H2 and CH4 follow the relation of ln H = − 413.05/T + 5.27 and ln H = − 990.67/T + 5.87, respectively. The molar fractions of H2 and system pressures at different equilibrium time were measured to estimate the liquid-phase mass transfer coefficients. The results showed that with the increase of pressure, the liquid-phase mass transfer coefficients increase. Furthermore, the solubility of H2 and CH4 in VGO was predicted by the predictive COSMO-RS model, and the predicted values agree well with experimental data. In addition, the gas–liquid equilibrium (GLE) for H2 + CH4 + VGO system at different feeding gas ratios in volume fraction (i.e., H2 85% + CH4 15% and H2 90% + CH4 10%) was measured. The selectivity of H2 to CH4 predicted by the COSMO-RS model agrees well with experimental data. This work provides the basic thermodynamic and dynamic data for fuel oil catalytic cracking processes.

Numerical study of syngas production via CH4–H2S mixture partial oxidation

The detailed kinetic mechanism of pyrolysis and oxidation of the H2S–CH4 mixture was developed. The mechanism was validated on experimental data on the ignition delay, laminar flame velocity, conversion degree of H2S and CH4, as well as on the yield of main conversion products – H2 and CO. The developed mechanism was used for a numerical study of the conversion degree of H2S and CH4, the syngas yield and syngas composition during partial oxidation of the H2S–CH4 mixture with H2S/CH4 = 1/9, 1/4 and 3/1 in a plug flow reactor of 1 m in length in the wide range of initial temperature (T0 = 600–1400 K) and fuel-to-air equivalence ratio (ϕ = 1–30). It is shown that the maximum relative yield of syngas can be obtained at ϕ = 3–5 depending on T0 and the H2S/CH4 ratio in the fuel. The mole fraction of H2 in syngas is higher than that of CO. For the mixture with H2S/CH4 = 3/1, the mole fraction of H2 can be greater than the equilibrium value in a certain range of ϕ∼6–10. The reasons for this effect are analyzed. The mole fraction of CO in conversion products rapidly decreases with increasing ϕ. As a result, the ratio γH2/γCO increases fast with the growth of ϕ. Besides H2 and CO, the conversion products can contain S2 and NO (at ϕ∼2), CS (at ϕ∼3), CS2 (at 3 < ϕ < 10), unburned hydrocarbons (at ϕ > 3) and other species. The least amount of conversion byproducts is observed at ϕ = 3–3.5 when there is the maximum syngas yield. Syngas selectivity turned out maximal at ϕ = 2.5–3. Therefore, ϕ∼3 seems to be the most optimal value for carrying out the conversion of H2S–CH4 mixtures.

Optimal neighbourhood to nurture giants: a fundamental link between star-forming galaxies and direct collapse black holes

ABSTRACT Massive 104–5 M⊙ black hole seeds resulting from the direct collapse of pristine gas require a metal-free atomic cooling halo with extremely low H2 fraction, allowing the gas to cool isothermally in the presence of atomic hydrogen. In order to achieve this chemo-thermodynamical state, the gas needs to be irradiated by both Lyman–Werner (LW) photons in the energy range of 11.2–13.6 eV capable of photodissociating H2 and 0.76 eV photons capable of photodetaching H−. Employing cosmological simulations capable of creating the first galaxies in high resolution, we explore if there exists a subset of galaxies that favour direct collapse black hole (DCBH) formation in their vicinity. We find a fundamental relation between the maximum distance at which a galaxy can cause DCBH formation and its star formation rate (SFR), which automatically folds in the chemo-thermodynamical effects of both H2 photodissociation and H− photodetachment. This is in contrast to the approximately three order of magnitude scatter seen in the LW flux parameter computed at the maximum distance, which is synonymous with a scatter in ‘Jcrit’. Thus, computing the rates and/or the LW flux from a galaxy is no longer necessary to identify neighbouring sites of DCBH formation, as our relation allows one to distinguish regions where DCBH formation could be triggered in the vicinity of a galaxy of a given SFR.

Parametric gasification process of sugarcane bagasse for syngas production

This research focuses on parametric influence on product distribution and syngas production from conventional gasification. Three experimental parameters at three different levels of temperature (700, 800 and 900 °C), sugarcane bagasse loading (2, 3 and 4 g) and residence time (10, 20 and 30 min) were studied using horizontal axis tubular furnace. Response Surface Methodology supported by central composite design was adopted in order to investigate parameters impact on product distribution (i.e., gas, tar and char) and gaseous products (i.e., H2, CO, CO2 and CH4). The highest H2 fraction obtained was 42.88 mol% (36.91 g-H2 kg-biomass−1) at 3 g of sugarcane bagasse loading, 900 °C and 30 min reaction time. The temperature was identified as the most influential parameter followed by reaction time for H2 production and diminishing the bio-tar and char yields. An increase in sugarcane bagasse loading, on other hand, favored the production of bio-tar, CO2 and CH4 production. The statistical analysis verified temperature as most significant (p-value 0.0008) amongst the parameters investigated for sugarcane bagasse biomass gasification.

Investigation of CaO Influences on Fast Gasification Characteristics of Biomass in a Fixed-bed Reactor

The CaO was added into the sawdust with different mass ratios of 1%, 5% and 10% respectively for biomass gasification in a fixed-bed reactor at a temperature from 600 to 900 °C, and combining the micro-characterizations with SEM and XRD, the mechanisms of CaO as tar pyrolysis catalyst and carbon absorbent during gasification process were also investigated. It was found that at 700 °C the volume fraction of H2 could reach 44% with 10% CaO added, meanwhile, the condition with 5% CaO added at 700 °C was found to be the best one due to its higher tar removal rate, lower CO2 release and higher released combustible gas amounts. Moreover, the tar yield decreased due to intense pyrolysis reaction with the increasing reaction temperature, but above 800 °C the CaCO3 produced by absorbing CO2 would undergo severe decomposition reaction, which will reduce the activity of calcium oxide, and the excess CaO could also play a role during the combustion process, and as a result lead to the decreased quality of combustible gaseous products.

The relation between 5780 and 5797 diffuse interstellar bands, CH/CH+ molecules, and atomic or molecular hydrogen

Correlations between column densities of neutral and molecular hydrogen and strengths of major 5780 and 5797 Å diffuse interstellar bands (DIBs) based on spectra of 66 OB stars were analyzed. We confirm that the 5797 Å DIB is more tightly correlated with column density of molecular hydrogen while the 5780 DIB – with that of atomic hydrogen. This leads to a reasonably tight relation between the molecular fraction of H2 and equivalent width ratio of the 5797 and 5780 major diffuse bands with correlation coefficient equal to 0.77 ± 0.05. Column densities of CH and CH+ molecules were used to analyze correlations between abundances of CH/CH+ molecules and strengths of the major 5780 and 5797 DIBs. The 5780 DIB is better correlated with the column density of methydyline cation than the 5797 DIB. A relation with correlation coefficient equal to 0.95 ± 0.02 based on precise column densities, between column densities of CH and H2 molecules, is also presented; in other words, the column densitiy ratio in the case of H2 and CH molecules in the ISM is equal to (2.01 ± 0.09) × 107.

Carbon formation on the surface during the reduction of iron oxide particles by CO and CO/H2 mixtures

Carbon deposition on the iron surface is of great interest due to a good performance to prevent sticking during the direct reduction (DR) in the fluidized bed. The promising routes of carbon formation were investigated by the density function theory (DFT). An innovative kinetic model, which considers adsorption and decomposition of CO, is applied to control the carbon content of direct reduction iron in the two-stages reduction process. The results show that the CO bond of CO is stretched due to the attractive force of surface iron atoms on the C and O atoms. The added H2 can significantly improve this CO bond stretch to decrease the barrier energy of CO decomposition. The formation of carbon is sensitive to the temperature and the added H2 can extend the temperature range for carbon formation and reduce the temperature of the maximum rate of carbon formation. Besides, the proper concentration of H2 added in the CO/H2 mixtures can improve the formation of carbon shell. However, the carbon shell will not be formed under a condition of extremely high mole fraction of H2 because H2 increases the adsorption energy of CO on the iron surface.

Comparison of the gasification performance in the downdraft fixed-bed gasifier fed by different feedstocks: Rice husk, sawdust, and their mixture

In order to figure out the compatibility of downdraft gasifiers on different feedstocks, performance of a fixed-bed downdraft gasifier fed by rice husk, sawdust, and their mixture (1:1 by mass) are compared in the present work. Gasification is performed with varying equivalence ratio, i.e. 0.15, 0.20, and 0.25. Gasification air is injected into the reactor via three tuyers located at 330 mm above the grate. Gasification characteristics (temperature profile of the reactor, fuel consumption rate, volume fraction of CO, H2, and CH4 in the producer gas) and performance of the gasifier (lower heating value of the producer gas and cold gas efficiency of the gasifier) are observed and analyzed. The results indicate that the gasifier is compatible for rice husk, sawdust, or their mixture. Optimum equivalence ratio for gasification of the rice husk, sawdust, and the mixture are 0.20, 0.20, and 0.15, respectively. At the optimum equivalence ratios, lower heating values of the producer gas are 3.13, 2.69, and 0.35 MJ/Nm3 for rice husk, sawdust, and the mixture. Meanwhile, cold gas efficiencies are 72.73%, 69.27%, and 82.08%, correspondingly.