Syngas production by methane-rich combustion in a divergent burner of porous media

The superadiabatic combustion in porous media contributes to the efficient conversion of methane to syngas. In this paper, a divergent packed bed burner of two-layer was proposed to obtain the characteristics of methane partial oxidation. The divergent angle, interface location and pellet diameter were used to study the temperature and species distributions. Results indicate that the upper limit of velocity gradually decreased as the equivalence ratio increased and the limit of the divergent burner is obviously higher than that of the cylindrical one. The increasing of the divergent angle within a certain range enhances the methane conversion and the 15° shows the best among the selected five angles. The mole fractions of H₂ and CO gradually decrease when the interface locations move from the cylindrical region to the divergent one. As the equivalence ratio increased from 1.3 to 3.5, the yields of H₂ and CO and the energy conversion efficiency of syngas increase first and then decrease, and the maximum efficiency of 45.9% appears at the equivalence ratio of 2.0. The divergent region weakens the influence of inlet velocities and contributes to the stability of reforming reactions.     

Modeling study on the production of hydrogen/syngas via partial oxidation using a homogeneous charge compression ignition engine fueled with natural gas

The production of hydrogen and syngas from natural gas using a homogeneous charge compression ignition reforming engine is investigated numerically. The simulation tool used was CHEMKIN 3.7, using the GRI-3 natural gas combustion mechanism. This simulation was conducted on the changes in hydrogen and syngas concentration according to the variations of equivalence ratio, intake temperature, oxygen enrichment, engine speed, initial pressure, and fuel additives with partial oxidation combustion. The simulation results indicate that the hydrogen/syngas yields are strongly dependent on the equivalence ratio with maxima occurring at an optimal equivalence ratio varying with engine speed. The hydrogen/syngas yields increase with increasing intake temperature and oxygen contents in air. The hydrogen/syngas yields also increase with increasing initial pressure, especially at lower temperatures, yet high temperature can suppress the pressure effect. Furthermore, it was found that the hydrogen/syngas yields increase when using fuel additives, especially hydrogen peroxide. Through the parametric screening studies, optimum operating conditions for natural gas partial oxidation reforming are recommended at 3.0 equivalence ratio, 530 K intake temperature, 0.3 oxygen enrichment, 500 rpm engine speed, 1 atm initial pressure, and 7.5% hydrogen peroxide.     

煤气化半显热回收串联水煤气变换反应流程的优化

利用Aspen Plus软件建立粗合成气的半显热回收串联变换反应的流程模型,研究了显热回收设备的出口温度对串联流程中能量利用效率的影响,以及对变换反应转化率的影响。结果表明:随着显热回收设备出口温度的提高,显热回收热量下降,变换反应的回收热量和高温变换反应的吸热量增大;变换反应的转化率随着显热回收设备出口温度的增加而提高;半显热回收串联变换反应的流程在保证能量利用率提高的同时,可灵活调节变换反应转化率。     

Gas Switching Reforming for syngas production with iron-based oxygen carrier-the performance under pressurized conditions

A four-stage Gas Switching Reforming for syngas production with integrated CO₂ capture using an iron-based oxygen carrier was investigated in this study. The oxygen carrier was first reduced using dry methane, where high methane conversion rate was achieved producing CO₂ and steam. Following the reduction stage is a transition to syngas production in an intermediate stage that begins with partial oxidation of methane while methane cracking dominates the rest of the stage. This results in substantial carbon deposition that gasifies in a subsequent reforming stage by cofeeding steam and methane, contributing to more syngas yield. Some of the deposited carbon that could not gasify during the reforming stage slip to the oxidation stage and get combusted by oxygen in the air feed to release CO₂, thereby reducing the CO₂ capture efficiency of the process. It is in this oxidation stage that heat is being generated for the whole cycle given the high exothermicity nature of this reaction. Methane conversion was found to drop substantially in the reforming stage as the pressure increases driven by the negative effect of pressure on both carbon gasification by steam and on the steam methane reforming. The intermediate stage (after reduction) was found less sensitive to the pressure in terms of methane conversion, but the mechanism of carbon deposition tends to change from methane cracking in the POX stage to Boudouard reaction in the reforming stage. However, methane cracking shows a tendency to reduce substantially at higher pressures. This is could be a promising result indicating that high-pressure operation would remove the need for the reforming stage with steam as no carbon would have been deposited in the POX stage.     

Experimental study of syngas production from methane dry reforming with heat recovery strategy

This study employed the concept of heat recovery to design a set of reformer to facilitate the methane dry reforming (MDR), through which syngas (H₂+CO) could be generated. The MDR involves an endothermic reaction and thus additional energy is required to sustain it. According to the concept of industrial heat recovery, the energy required to facilitate the MDR was recovered from waste heat. In addition, after the reforming reaction, the waste heat inside the reformer was used for internal heat recovery to preheat the reactants (CO₂+CH₄) to reduce the amount of energy required for the reforming reaction. Regarding the parameter settings in the experiments, the CH₄ feed flow rate was set at 1–2.5 NL/min and the mole ratio for CO₂/CH₄ was set at 0.43–1.22. Subsequently, an oven was used to simulate a heat recovery environment to facilitate the dry reforming experiment. The experimental results indicated that an increase in oven temperature could increase the reforming reaction temperature and elevate the energy for the reformer. H₂ and CO production could increase when the reformer gained more energy. The high-temperature gas generated from the reforming reaction was applied to facilitate internal heat recovery of reformer and preheat the reactants; thus, the efficiency of reforming and CO₂ conversion were evidently elevated. The theoretical equilibrium analysis indicated that the thermal efficiency of reforming increased with the increase of CO₂/CH₄ molar ratio. While, the thermal efficiency of reforming by experiments decreased with the increase of the CH₄ feed rate, but increased with the increase of CO₂/CH₄. In summary, the experimental results revealed that the overall H₂ was 0.017–0.019 mol/min. In addition, the reforming efficiency was 8.76%–78.08%, the CO₂ conversion was 53.92%–96.43%, and the maximum thermal efficiency of reforming was 102.3%.     

Thermodynamic analysis of hydrogen-rich syngas production with a mixture of aqueous urea and biodiesel

An auxiliary power unit based on a solid oxidation fuel cell for heavy-duty vehicles has been receiving attention for high efficiency, low emissions, and more comfort and safety in vehicles. This study explores hydrogen-rich syngas production via reforming of a mixture of aqueous urea and biodiesel by thermodynamics analysis. The aqueous urea is available from Adblue used in a selective catalyst reduction providing efficient control of nitrogen oxides from heavy-duty vehicles to minimize particulate mass and optimize fuel consumption. The results show that at a reaction temperature of 700 °C, urea/biodiesel ratio = 3, and oxygen/biodiesel ratio = 9, the highest reforming efficiency is 83.78%, H₂ production 30.43 mol, and CO production 12.68 mol. This study verified that aqueous urea could successfully replace the steam in autothermal reforming, which provides heat and increases syngas production, and reforming aqueous urea mixed with biodiesel has ultra-low sulfur, low carbon and little modifying the fuel system.     

Efficiency assessment of solar redox reforming in comparison to conventional reforming

Solar redox reforming is a process that uses solar radiation to drive the production of syngas from natural gas. This approach caught attention in recent years, because of substantially lower reduction temperatures compared to other redox cycles. However, a detailed and profound comparison to conventional solar reforming has yet to be performed. We investigate a two-step redox cycle with iron oxide and ceria as candidates for redox materials. Process simulations were performed to study both steam and dry methane reforming. Conventional solar reforming of methane without a redox cycle, i.e. on an established catalyst was used as reference. We found the highest efficiency of a redox cycle to be that of steam methane reforming with iron oxide. Here the solar-to-fuel efficiency is 43.5% at an oxidation temperature of 873 K, a reduction temperature of 1190 K, a pressure of 3 MPa and a solar heat flux of 1000 kW/m². In terms of efficiency, this process appears to be competitive with the reference process. In addition, production of high purity H₂ or CO is a benefit, which redox reforming has over the conventional approach.     

Thermodynamic analysis of high‐temperature helium heated fuel reforming for hydrogen production

In order to take full advantage of the heat from high temperature gas cooled reactor, thermodynamic analysis of high‐temperature helium heated methane, ethanol and methanol steam reforming for hydrogen production based on the Gibbs principle of minimum free energy has been carried out using the software of Aspen Plus. Effects of the reaction temperature, pressure and water/carbon molar ratio on the process are evaluated. Results show that the effect of the pressure on methane reforming is small when the reaction temperature is over 900 °C. Methane/CO conversion and hydrogen production rate increase with the water/carbon molar ratio. However the thermal efficiency increases first to the maximum value of 61% and then decreases gradually. As to ethanol and methanol steam reforming, thermal efficiency is higher at lower reaction pressures. With an increase in water–carbon molar ratio, hydrogen production rate increases, but thermal efficiency decreases. Both of them increase with the reaction temperature first to the highest values and then decrease slowly. At optimum operation conditions, the conversion of both ethanol and methanol approaches 100%. For the ethanol and methanol reforming, their highest hydrogen production rate reaches, respectively, 88.69% and 99.39%, and their highest thermal efficiency approaches, respectively, 58.58% and 89.17%. With the gradient utilization of the high temperature helium heat, the overall heat efficiency of the system can reach 70.85% which is the highest in all existing system designs. Copyright © 2014 John Wiley & Sons, Ltd.     

Syngas production through gasification of coal water mixture and power generation on dual-fuel diesel engine

In the present study, a syngas was produced by preparing coal water mixtures of two different concentrations and gasifying the coal water mixtures. An entrained-flow gasifier of 1 ton/day scale was used and, after undergoing a purification process, the produced syngas was applied to a modified diesel engine for power generation. As the gasification temperature increased, the carbon conversion and the cold gas efficiency were found to increase. In the composition of the produced syngas, the content of H₂ remained constant, that of CO increased, and those of CO₂ and CH₄ decreased. The carbon conversion increased with equivalence ratio. A maximum cold gas efficiency of 66.1% was found at the equivalence ratio of 0.43. N₂ was additionally supplied to verify the gasification characteristics depending on the gas feed flow rate. The optimum feed flow rate was verified at different slurry concentrations and equivalence ratio. The produced syngas was supplied to a modified diesel engine and operated depending on the syngas feed flow rate and the engine operation conditions. The brake thermal efficiency of the engine was constant regardless of the syngas feed flow rate. The diesel engine showed high efficiency despite the mixing of the syngas.     

Conversion of jet fuel and butanol to syngas by filtration combustion

Replacing batteries with fuel cells is a promising approach for powering portable devices; however, hydrogen fuel generation and storage are challenges to the acceptance of this technology. A potential solution to this problem is on-site fuel reforming, in which a rich fuel/air mixture is converted to a hydrogen-rich syngas. In this paper, we present experimental results of the conversion of jet fuel (Jet-A) and butanol to syngas by non-catalytic filtration combustion in a porous media reactor operating over a wide range of equivalence ratios and inlet velocities. Since the focus of this study is the production of syngas, our primary results are the hydrogen yield, the carbon monoxide yield, and the energy conversion efficiency. In addition, the production of soot that occurred during testing is discussed for both fuels. Finally, an analysis of the potential for these fuels and others to be converted to syngas based on the present experiments and data available in the literature is presented. This study is intended to increase the understanding of filtration combustion for syngas production and to illuminate the potential of these fuels for conversion to syngas by non-catalytic methods.     

Thermodynamic analysis of fossil fuels reforming for fuel cell application

At present, the infrastructure of hydrogen production, storage and transportation is poor. Fuel reforming for hydrogen production from liquid fossil fuels such as kerosene, petrol and diesel is of great significance for wide application of on-board fuel cell and distributed energy resources. In this work, the produced and heat released of kerosene, petrol and diesel reformed by different reforming methods (autothermal reforming, partial oxidation, steam reforming) were studied by means of thermodynamic analysis. Based on the thermodynamic analysis, the effect of reforming methods on the system's ideal thermal efficiency are analysed. The results show that the hydrogen concentration of syngas obtained from steam reforming is highest regardless of the fuel types. The hydrogen yielded by per unit volume of diesel is largest under same reforming method. Autothermal reforming has the largest ideal thermal efficiency among three reforming methods.     

The assessment of reformation in a porous medium-catalyst hybrid reformer under excess enthalpy condition

A porous medium-catalyst hybrid reformer for hydrogen-rich syngas production by dry autothermal reforming (DATR) was investigated in this study. In the reforming process, the reaction under excess enthalpy was explored by visualization in packed-bed catalyst reactor. The hybrid design was arranged with a porous medium (PM) in the upstream of the catalyst packed-bed. In the arrangement, the reactants were preheated by internal heat recirculation and the selectivity of H₂-rich syngas was enhanced by the catalyst surface reaction. Controlled parameters included CO₂/CH₄ and O₂/CH₄ ratios, gas hourly space velocity (GHSV) with or without porous medium. The experimental results demonstrated that the reforming reaction with the hybrid reformer could achieve excess enthalpy under the tested parameters. The excess enthalpy ratio was between 0.15 and 0.55. The temperature measurement along the axial position and image observation of the catalyst packed-bed indicated that the flame was stably held at the interface of the PM and the catalyst bed, and this enhanced fuel conversion and reforming efficiencies, especially in the low methane conversion condition. In the dry autothermal reforming process, part of the chemical energy released from the reaction supplies the energy required for a self-sustaining reaction. Therefore, the selection of the parameters was determined to achieve high reforming efficiency and low energy loss percentage. The results showed that the energy loss percentage was between 12.7 and 24.6% and reforming efficiency was between 64.4 and 79.5% with the best reforming parameter settings (O₂/CH₄ = 0.7–0.9 and CO₂/CH₄ = 0.0–2.0).     

Study on hydrogen-rich syngas production by dry autothermal reforming from biomass derived gas

In this study, the H₂-rich syngas (H₂ + CO) production from biomass derived gas (BDG) by dry autothermal reforming (DATR) is investigated. Methane and carbon dioxide is the major composition of biomass derived gas. DATR reaction combined benefits of partial oxidation (POX) and dry reforming (DR) reaction was carried out in this study. The reforming parameters on the conversion of methane and syngas selectivity were explored. The reforming parameters included the fuel feeding rate, CO₂/CH₄ and O₂/CH₄ molar ratios. The experimental results demonstrated that it not only supplied the energy required for self-sustained reaction, but also avoided the coke formation by dry autothermal reforming. It has a wide operation region to maintain the moderate production of the syngas. During the reforming process, the reformate gas temperature was between 650 and 900 °C, and energy loss percentage in reforming process was between 15 and 30%. Further, high CO₂ concentration in the reactant had a considerable influence on the heat release of oxidation, and thereby decreased the reformate gas temperature. It caused the reduction of synthesis gas concentration and assisting/impeding combustion composition (A/I) ratio. However, it was favorable to CO selectivity because of the reverse water-gas shifting reaction. The H₂/CO molar ratio between 1 and 2 was achieved by varying CO₂/CH₄ molar ratio. However, the syngas concentrations were affected by CO₂/CH₄ and O₂/CH₄ molar ratio.     

Hydrogen-rich gas production from biomass steam gasification in an updraft fixed-bed gasifier combined with a porous ceramic reformer

This paper investigates the hydrogen-rich gas produced from biomass employing an updraft gasifier with a continuous biomass feeder. A porous ceramic reformer was combined with the gasifier for producer gas reforming. The effects of gasifier temperature, equivalence ratio (ER), steam to biomass ratio (S/B), and porous ceramic reforming on the gas characteristic parameters (composition, density, yield, low heating value, and residence time, etc.) were investigated. The results show that hydrogen-rich syngas with a high calorific value was produced, in the range of 8.10–13.40 MJ/Nm³, and the hydrogen yield was in the range of 45.05–135.40 g H₂/kg biomass. A higher temperature favors the hydrogen production. With the increasing gasifier temperature varying from 800 to 950 °C, the hydrogen yield increased from 74.84 to 135.4 g H₂/kg biomass. The low heating values first increased and then decreased with the increased ER from 0 to 0.3. A steam/biomass ratio of 2.05 was found as the optimum in the all steam gasification runs. The effect of porous ceramic reforming showed the water-soluble tar produced in the porous ceramic reforming, the conversion ratio of total organic carbon (TOC) contents is between 22.61% and 50.23%, and the hydrogen concentration obviously higher than that without porous ceramic reforming.     

A thermodynamic analysis of biogas partial oxidation to synthesis gas with emphasis on soot formation

A thermodynamic analysis of synthesis gas production via partial oxidation (POX) of biogas is performed in the present article. Chemical equilibrium calculations are conducted for partial oxidation of (CH₄+CO₂) mixtures based on Gibbs free energy minimization method emphasizing soot formation. Regarding precise evaluation of carbon dioxide effects on the reforming characteristics, the obtained results are compared with the experimental data. Furthermore, the effects of steam injection at the inlet of the reformer on the coking behavior and syngas production yield are studied. To investigate the effects of the equivalence ratio (?), temperature and pressure, a broad parametric study is performed. The results reveal that the process temperature plays a pivotal role in enhancing the syngas production and soot abatement. It is also found that the pressure has an impractical effect on the syngas production yield, leading to the soot formation and decrease in both hydrogen and carbon monoxide yields. Furthermore, increasing the inlet CO₂/CH₄ makes the thermal reforming efficiency to rise at an equivalence ratio lower than 3. Meanwhile, increasing the steam to methane (S/C) ratio reduces carbon formation and enhances hydrogen production. Nonetheless, when the S/C ratio is larger than 2 at ? = 2.5 and 1 at ? = 3, the enhancement of hydrogen generation is minimized and even tends to become impractical. Therefore, near adiabatic and atmospheric condition at ? = 2.5–3 with S/C < 1 are recommended as the optimum operating routes for partial oxidation of biogas.     

Thermodynamic analysis of syngas production from biodiesel via chemical looping reforming

In this study, thermodynamic analysis of the syngas production using biodiesel derived from waste cooking oil is studied based on the chemical looping reforming (CLR) process. The NiO is used as the oxygen carrier to carry out the thermodynamic analysis. Syngas with various H₂/CO ratios can be obtained by chemical looping dry reforming (CL-DR) or steam reforming (CL-SR). It is found that the syngas obtained from CL-DR is suitable for long-chain carbon fuel synthesis while syngas obtained from CL-SR is suitable for methanol synthesis. The carbon-free syngas production can be obtained when reforming temperature is higher than 700 °C for all processes. To convert the carbon resulted from biodiesel coking and operate the CLR with a lower oxygen carrier flow rate, a carbon reactor is introduced between the air and fuel reactors for removing the carbon using H₂O or CO₂ as the oxidizing agent. Because of the endothermic nature of both Boudouard and water-gas reactions, the carbon conversion in the carbon reactor increases with increased reaction temperature. High purity H₂ or CO yield can be obtained when the carbon reactor is operated with high reaction temperature and oxidizing agent flow.     

Thermodynamic study on the integrated supercritical water gasification with reforming process for hydrogen production: Effects of operating parameters

In this paper, a conceptual process design of the integrated supercritical water gasification (SCWG) and reforming process for enhancing H₂ production has been developed. The influence of several operating parameters including SCWG temperature, SCWG pressure, reforming temperature, reforming pressure and feed concentration on the syngas composition and process efficiency was investigated. In addition, the thermodynamic equilibrium calculations have been carried out based on Gibbs free energy minimization by using Aspen Plus. The results showed that the higher H₂ production could be obtained at higher SCWG temperature, the H₂ concentration increased from 5.40% at 400 °C to 38.95% at 600 °C. The lower feed concentration was found to be favorable for achieving hydrogen-rich gas. However, pressure of SCWG had insignificant effect on the syngas composition. The addition of reformer to the SCWG system enhanced H₂ yield by converting high methane content in the syngas into H₂. The modified SCWG enhanced the productivity of syngas to 151.12 kg/100kg_feed compared to 120.61 kg/100kg_feed of the conventional SCWG system. Furthermore, H₂ yield and system efficiency increased significantly from 1.81 kg/100kg_feed and 9.18% to 8.91 kg/100kg_feed, and 45.09%, respectively, after the modification.     

Hydrogen production from an ethanol reformer with energy saving approaches over various catalysts

The reforming of ethanol for hydrogen production was carried out in this study. The effects of ethanol supply rate, catalysts, O₂/EtOH and different energy-saving approaches on the reforming temperature, H₂ + CO (syngas) concentration and thermal efficiency were investigated. The results showed that the best H₂ + CO concentration of 43.41% could be achieved by using rhodium (Rh), while the next best concentration of about 42.08% could be obtained using ruthenium (Ru). The results also showed that the conversion efficiency of ethanol, concentrations of H₂ and CO, and the energy loss ratio could be improved by heat insulation and heat recycling; and the improvement in the reforming performance was greater by the Ru catalyst rather than by the Rh catalyst with the energy-saving approaches. The greatest improvement in hydrogen production was achieved when using the Ru catalyst with the addition of steam and heat recycling system under an O₂/EtOH ratio of 0.625 and S/C ratio of 1.0.     

Mini CHP based on the electrochemical generator and impeded fluidized bed reactor for methane steam reforming

The paper presents a configuration of mini CHP with the methane reformer and planar solid oxide fuel cell (SOFC) stacks. This mini CHP may produce electricity and superheated steam as well as preheat air and methane for the reformer along with cathode air used in the SOFC stack as an oxidant. Moreover, the mathematical model for this power plant has been created. The thermochemical reactor with impeded fluidized bed for autothermal steam reforming of methane (reformer) considered as the basis for the synthesis gas (syngas) production to fuel SOFC stacks has been studied experimentally as well. A fraction of conversion products has been oxidized by the air fed to the upper region of the impeded fluidized bed in order to carry out the endothermic methane steam reforming in a 1:3 ratio as well as to preheat products of these reactions. Studies have shown that syngas containing 55% of hydrogen could be produced by this reactor. Basic dimensions of the reactor as well as flow rates of air, water and methane for the conversion of methane have been adjusted through mathematical modelling.The paper provides heat balances for the reformer, SOFC stack and waste heat boiler (WHB) intended for generating superheated water steam along with preheating air and methane for the reformer as well as the preheated cathode air. The balances have formed the basis for calculating the following values: the useful product fraction in the reformer; fraction of hydrogen oxidized at SOFC anode; gross electric efficiency; anode temperature; exothermic effect of syngas hydrogen oxidation by air oxygen; excess entropy along with the Gibbs free energy change at standard conditions; electromotive force (EMF) of the fuel cell; specific flow rate of the equivalent fuel for producing electric and heat energy. Calculations have shown that the temperature of hydrogen oxidation products at SOFC anode is 850 °C; gross electric efficiency is 61.0%; EMF of one fuel cell is 0.985 V; fraction of hydrogen oxidized at SOFC anode is 64.6%; specific flow rate of the equivalent fuel for producing electric energy is 0.16 kg of eq.f./(kW·h) while that for heat generation amounts to 44.7 kg of eq.f./(GJ). All specific parameters are in agreement with the results of other studies.     

Numerical analysis of the biomimetic leaf-type hierarchical porous structure to improve the energy storage efficiency of solar driven steam methane reforming

Due the energy resource comes from solar energy, resulting in a high working temperature, radiation field has a significant influence on the energy storage efficiency of the high temperature solar thermochemistry. In order to promote the solar energy conversion efficiency of solar driven steam methane reforming (SMR), the idea of regulate the radiation field to be in accordance with the energy conversion on-demand is proposed and the biomimetic leaf-type hierarchical porous structure solar thermochemical reactor is introduced, which can regulate the spatial distribution of solar radiation intensity and optimize the temperature field. Combined with thermochemical kinetics and Finite Volume Method (FVM), the numerical calculation model of the SMR reaction in a biomimetic solar thermochemical reactor is established to optimize the temperature field. The effects of different reaction conditions and reactor parameters on steam methane reforming hydrogen production are analyzed. The results show that methane conversion in the biomimetic leaf-type solar thermochemical reactor is increased by 4.5%.