Enhancing efficiency of hydrocarbons to synthesis gas conversion in a counterflow moving bed filtration combustion reactor

An improvement is considered for the partial oxidation conversion of hydrocarbon gases to synthesis gas in a continuous non-premixed filtration combustion reactor with inert solid granular material flowing countercurrently to the gas flow. The reactor is supplemented with an additional heat exchanger, wherein the second reactant gas is preheated prior to supply to the middle part of the reactor. The composition of the gaseous products self-consistent with the temperature of combustion are assessed using approximation of established thermodynamic equilibrium in the products. The parametric domain for major control parameters, namely oxygen-to-fuel supply ratio, granular solid flowrate, and steam supply rate providing highly efficient conversion is determined. Calculations for the POX conversion of methane and a model biogas composition (50% methane, 40% carbon dioxide, 10% nitrogen) with air and steam are provided as examples. The calculations show that the process gives a possibility to substantially improve energy efficiency and provides a flexibility to control hydrogen yield through steam supply. The process provides a high chemical efficiency of conversion even with air used as an oxidant for conversion of low-caloric gases.     

High-pressure hydrogen production with inherent sequestration of a pure carbon dioxide stream via fixed bed chemical looping

The proof of concept for the production of pure pressurized hydrogen from hydrocarbons in combination with the sequestration of a pure stream of carbon dioxide with the reformer steam iron cycle is presented. The iron oxide based oxygen carrier (95% Fe₂O₃, 5% Al₂O₃) is reduced with syngas and oxidized with steam at 1023 K. The carbon dioxide separation is achieved via partial reduction of the oxygen carrier from Fe₂O₃ to Fe₃O₄ yielding thermodynamically to a product gas only containing CO₂ and H₂O. By the subsequent condensation of steam, pure CO₂ is sequestrated. After each steam oxidation phase, an air oxidation was applied to restore the oxygen carrier to hematite level. Product gas pressures of up to 30.1 bar and hydrogen purities exceeding 99% were achieved via steam oxidations. The main impurities in the product gas are carbon monoxide and carbon dioxide, which originate from solid carbon depositions or from stored carbonaceous molecules inside the pores of the contact mass. The oxygen carrier samples were characterized using elemental analysis, BET surface area measurement, XRD powder diffraction, SEM and light microscopy. The maximum pressure of 95 bar was demonstrated for hydrogen production in the steam oxidation phase after the full oxygen carrier reduction, significantly reducing the energy demand for compressors in mobility applications.     

Hydrogen-rich gas production for solid oxide fuel cell (SOFC) via partial oxidation of butanol: Thermodynamic analysis

Butanol partial oxidation for hydrogen-rich gas production has been studied by Gibbs free energy minimization method. The optimum conditions for hydrogen-rich gas production are identified: reaction temperatures between 1115 and 1200 K and oxygen-to-butanol molar ratios between 1.6 and 1.7 at 1 atm. Under the optimal conditions, complete conversion of butanol, 93.07%–96.56% yield of hydrogen and 94.02%–97.55% yield of carbon monoxide could be achieved in the absence of coke formation. The butanol partial oxidation with O₂ is suitable for providing hydrogen-rich fuels for Solid Oxide Fuel Cell (SOFC). Higher pressures have a negative effect, but inert gases have a positive effect, on the hydrogen yield. Coke tends to form at lower temperatures and lower oxygen-to-butanol molar ratios.     

Thermodynamic analysis of ethanol processors for fuel cell applications

A thermodynamic analysis of hydrogen production from ethanol has been carried out with respect to solid polymer fuel cell applications. Ethanol processors incorporating either a steam reformer or a partial oxidation reactor connected to water gas shift and CO oxidation reactors were considered and the effect of operating parameters on hydrogen yield has been examined. Employment of feeds with high H₂O/EtOH ratio results in reduced energy efficiency of the system. When hydrogen, non-converted in the fuel cell, is used to supply heat in the steam reformer, the effective hydrogen yield is essentially independent of the temperature of the reformer and the water gas shift reactor. Optimal operating conditions of partial oxidation processors have been determined assuming an upper limit for the preheat temperature of the feed. Results are discussed along with other practical considerations in view of actual applications.     

Noncatalytic gasification of isooctane in supercritical water: A Strategy for high-yield hydrogen production

Continuous supercritical water gasification of isooctane, a model gasoline compound, is investigated using an updraft gasification system. A new reactor material, Haynes^® 230^® alloy, is employed to run gasification reactions at high temperature and pressure (763 ± 2 °C; 25 MPa). A large-volume reactor is used (170 mL) to enable the gasification to be run at a long residence time, up to 120 s. Various gasification experiments are performed by changing the residence time (60-120 s), the isooctane concentration (6.3-14.7 wt%), and the oxidant concentration (equivalent oxidant ratio 0-0.3). The total gas yield and the hydrogen gas yield increase with increasing residence time. At 106 s and an isooctane concentration of 6.3 wt%, a very high hydrogen gas yield of 12.4 mol/mol isooctane, which is 50% of the theoretical maximum hydrogen gas yield and 92% of the equilibrium hydrogen gas yield under the given conditions, is achieved. Under these conditions, supercritical water partial oxidation does not increase the hydrogen gas yield significantly. The produced gases are hydrogen (68 mol%), carbon dioxide (20 mol%), methane (9.8 mol%), carbon monoxide (1.3 mol%), and ethane (0.9 mol%). The carbon gasification efficiency is in the range 75-91%, depending on the oxidant concentration. A comparison of supercritical water gasification with other conventional methods, including steam reforming, autothermal reforming, and partial oxidation, is also presented.     

Investigations on the behaviour of 2 kW natural gas fuel processor

In this paper, the first experimental investigations on a pre-commercial natural gas steam reformer have been presented. The fuel processor unit contains the elements as follows: desulfurizer, steam reformer reactor, CO shift converter, CO preferential oxidation (PROX) reactor, steam generator, burner and heat exchangers.The fuel processor produces 45 Nl/min of syngas in which the hydrogen concentration is about 75 vol.% and the other chemical species are nitrogen, carbon dioxide and methane. The CO concentration is below 1 ppmv, so that this reforming system is suitable for the integration with a PEM fuel cell stack.The experimental activity has been conducted in a test station, properly designed to measure the behaviour of the fuel processor. The laboratory test facility is equipped by a National Instruments Compact DAQ real-time data acquisition and control system running Labview™ software. Several measurement instruments and controlling devices have been installed. Furthermore, a gas chromatograph is used to measure the product gas composition during the tests.The aim of this work has been to analyze the behaviour of this pre-commercial steam reforming unit during its operation cycle in different operating conditions (full and partial loads) in order to study its integration with a PEM fuel cell for developing a high efficiency microcogeneration system for residential applications.     

乙醇重整制氢催化剂的国内研究进展

制氢技术是发展燃料电池的关键技术之一,而目前研究较多且具有良好应用前景的制氢技术是乙醇水蒸气重整制氢法制氢。综述了国内水蒸气重整法、部分氧化法、氧化重整法等乙醇重整制氢法的研究进展,同时综述了乙醇水蒸气重整制氢催化剂助剂、载体的研究进展。指出了在较低温度下以高转化率、低C0选择性、高氢气选择性制氢是乙醇制氢技术研究的方向。     

Process integration for hydrogen production,purification and storage using iron oxides

Hydrogen production from natural gas using a Ni-based catalyst and its later hydrogen storage with some synthetic and natural iron oxides are presented. The Ni-based catalyst showed high methane conversion, close to the equilibrium one, when producing hydrogen from methane through catalytic partial oxidation (CPO) and wet-CPO with a low steam to carbon ratio (0.5). The solid solution formation observed in the Ni-based catalyst could have enhanced its stability. The iron oxides capacity for hydrogen storage was analysed with reduction–oxidation cycles at 973 K and atmospheric pressure. The natural oxides presented structural modifications, mainly due to sinterization, which negatively affected their storage capacity and stability.     

Thermodynamic evaluation of hydrogen production from methane

Exergetic and energetic analysis has been utilized to estimate the effect of process design and conditions on the hydrogen purity and yield, exergetic efficiencies and CO₂ avoided. Methane was chosen as a model compound for evaluating single stage separation. Simple steam reforming was considered as the base – case system. The other chemical processes that were considered were steam reforming with CO₂ capture with and without chemical looping of a reactive carbon dioxide removal agent, and steam gasification with both the Boudouard reaction catalyst and the reactive carbon dioxide removal agent with and without the solids regeneration. The information presented clearly demonstrates the differences in efficiencies between the various chemical looping processes for hydrogen generation. The incremental changes in efficiencies as a function of process parameters such as temperature, steam amount, chemical type and amount were estimated. Energy and exergy losses associated with generation of syngas, separation of hydrogen from CO_x as well as exergetic loss associated with emissions are presented. The optimal conditions for each process by minimizing these losses are presented. The majority of the exergy destruction occurs due to the high irreversibility of chemical reactions. The results of this investigation demonstrate the utility of exergy analysis. The paper provides a procedure for the comparison of various technologies for the production of hydrogen from carbon based materials based on First and Second Law Analysis. In addition, two figures of merit, namely the comparative advantage factor and the sustainable advantage factor have been proposed to compare the various hydrogen production methods using carbonaceous fuels.     

Life cycle assessment of hydrogen production by methane decomposition using carbonaceous catalysts

Methane decomposition to yield hydrogen and carbon (CH₄ ? 2H₂ + C) is one of the cleanest alternatives, free of CO₂ emissions, for producing hydrogen from fossil fuels. This reaction can be catalyzed by metals, although they suffer a fast deactivation process, or by carbonaceous materials, which present the advantage of producing the catalyst from the carbon obtained in the reaction. In this work, the environmental performance of methane decomposition catalyzed by carbonaceous catalysts has been evaluated through Life Cycle Assessment tools, comparing it to other decomposition processes and steam methane reforming coupled to carbon capture systems. The results obtained showed that the decomposition using the autogenerated carbonaceous as catalyst is the best option when reaction conversions higher than 65% are attained. These were confirmed by 2015 and 2030 forecastings. Moreover, its environmental performance is highly increased when the produced carbon is used in other commercial applications. Thus, for a methane conversion of 70%, the application of 50% of the produced carbon would lead to a virtually zero-emissions process.     

Effect of in-situ and ex-situ injection of steam on staged-gasification for hydrogen production

K modified Ni-based catalysts are used to investigate the effect of in-situ and ex-situ injection of steam (ISI and ESI) on biomass pyrolysis and in-line catalytic steam reforming in a two-stage fixed bed reactor. The results show that 0.5 wt% K is appropriate to modify the Ni-based catalysts for steam reforming of biomass pyrolysis vapor. Compared to the catalytic cracking without steam addition, both ISI and ESI increase the gas yield and the carbon conversion efficiency (X_c) of the pyrolysis vapors. And the ESI is more beneficial to the conversion of pyrolysis vapors to small molecular gases. The maximum hydrogen concentration, hydrogen yield and carbon conversion efficiency (X_c) of staged-gasification can reach 53.8%, 31 mmol/g-bio, and 94.6%, respectively, when both stages are at 700 °C with ex-situ steam injection (S/C = 1.2) and 3 g catalyst loaded in the second stage. Also, the steam is beneficial to removing the depositions of graphitized coke and small molecular polycyclic aromatic hydrocarbon on the catalysts. However, it is yet difficult for steam to react with the highly ordered carbonaceous.     

Effects on CHP plant efficiency of H2 production through partial oxydation of natural gas over two group VIII metal catalysts

Blending H₂ with natural gas in spark ignition engines can increase for electric efficiency. In-situ H₂ production for spark ignition engines fuelled by natural gas has therefore been investigated recently, and reformed exhaust gas recirculation (RGR) has been identified a potentially advantageous approach: RGR uses the steam and O₂ contained in exhaust gases under lean combustion, for reforming natural gas and producing H₂, CO, and CO₂. In this paper, an alternative approach is introduced: air gas reforming circulation (AGRC). AGRC uses directly the O₂ contained in air, rendering the chemical pathway comparable to partial oxidation. Formulations based on palladium and platinum have been selected as potential catalysts. With AGRC, the concentrations of the constituents of the reformed gas are approximately 25% hydrogen, 10% carbon monoxide, 8% unconverted hydrocarbons and 55% nitrogen. Experimental results are presented for the electric efficiency and exhaust gas (CO and HC) composition of the overall system (SI engine equipped with AGRC). It is demonstrated that the electric efficiency can increase for specific ratios of air to natural gas over the catalyst. Although the electric efficiency gain with AGRC is modest at around 0.2%, AGRC can be cost effective because of its straightforward and inexpensive implementation. Misfiring and knock were both not observed in the tests reported here. Nevertheless, technical means of avoiding knock are described by adjusting the main flow of natural gas and the additional flow of AGRC.     

Numerical simulation on non-catalytic thermal process of methane reformation for hydrogen productions

The reformer that produces hydrogen from hydrocarbon is very important part of fuel cell system. One of the promising solutions has been recently considered as direct partial oxidation of hydrocarbon by excess enthalpy flame under rich and ultra-rich condition without a platinum catalyst. In this paper, excess enthalpy flame reforming process in the perforated silicon carbide tube reformer using a two dimensional approached with GRI mechanism 1.2 was investigated. The result shows that the stable excess enthalpy flame with temperature spike was observed in a perforated silicon carbide tube reformer under condition of higher equivalence ratio than rich flammability limit of methane. It is found that hydrogen rich gases could be produced through partial oxidation at very rich equivalence ratio by formation of excess enthalpy flame. The peak flame temperature of excess enthalpy flame was higher than the adiabatic flame temperature for a free laminar flame at identical conditions and excess enthalpy flame at ultra-rich equivalence ratio could become effective way to produce hydrogen rich gases from hydrocarbon. The conversion efficiency of hydrogen and carbon monoxide by partial oxidation of excess enthalpy flame was calculated as 37.64% and 60.62%, respectively at equivalence ratio of 2.0 and inlet velocity of 80 cm/s.     

“Preliminary results of hydrogen production from water vapor decomposition using DBD plasma in a PMCR reactor”

The water decomposition is considered one of the most attractive chemical processes for the production of hydrogen. The present work describes the preliminary results obtained in the experimental study of the water vapor dissociation into hydrogen and oxygen species using Dielectric-Barrier Discharge (DBD) plasma in a plate micro-channel reactor (PMCR). The water vapor molecules are injected without using carrier gas into the PMCR reactor at pressure of 100 kPa and temperature of 573 K. The applied high voltage of the plasma was within range of 14–18 kV and different steam flow rates have been analyzed within range of 100–200 ml/h. The product gases have been separated in ice trap which it was connected directly to the PMCR reactor to prevent the recombination of hydrogen and oxygen species. The concentration of the outlet species has been measured in a gas phase chromatography (GC) instrument. The PMCR reactor heating temperature effect on the water vapor decomposition has been analyzed. It was found that the water vapor is dissociated into their constituent molecular elements of hydrogen and oxygen gas using plasma. The maximum obtained mole fraction, hydrogen flow rate and conversion rate were 2.3%, 9.42 g/h, 42.51% respectively, at steam temperature of 573 K, pressure 100 kPa, PMCR heating temperature 403 K, steam flow rate of 200 ml/h and the plasma discharge high voltage of 18 kV. It was observed that the amount of evolved hydrogen concentration increased with the increase of the PMCR reactor heating temperature. Also, the thermal efficiencies versus the heat supplied have been calculated and the maximum obtained efficiency was 49.32%. Consequently, the evolved hydrogen flow rate appears to depend mainly on the plasma voltage, PMCR reactor heating temperature and the separating temperature of outlet hydrogen and oxygen species. The steam dissociation experiment will be extended to separate hydrogen and oxygen species elements at high temperature conditions.     

Simultaneous production of hydrogen and carbon nanotubes from cracking of a waste cooking oil model compound over Ni-Co/SBA-15 catalysts

Hydrogen is considered an ideal energy carrier. However, the use of fossil fuels to produce hydrogen depletes natural resources and causes environmental problems. Therefore, there is an urgent need to find alternative raw materials and technologies for the production of hydrogen. Waste cooking oil (WCO) is a renewable energy source that has emerged as a potential raw material for hydrogen production. This study describes the production of hydrogen and carbon nanotubes (CNTs) by catalytic cracking of a WCO model compound (WCOMC) performed in a lab-scale fixed bed using Ni-Co/SBA-15 catalysts. The phase, structure and reduction properties of the catalyst were analysed by using different characterisation methods. The effects of the nickel-cobalt metal content and the reaction temperature on both the hydrogen production and the quality of the CNTs were investigated. The deposited carbonaceous products were characterised to analyse their external appearance, internal structure, oxidation stability and graphitisation degree. The results indicated that the catalyst containing 20% Ni and 30% Co showed the highest activity. When reaction temperature was 800°C, the instantaneous volume fraction of hydrogen was close to 43.5 vol% and the content of hydrogen in the gas product was close to 66.5 vol%. A few multi-walled CNTs having a small diameter and some CNTs with an open-topped structure were deposited on 10%Ni-40%Co/SBA-15 and 30%Ni-20%Co/SBA-15, respectively. Thermogravimetric analysis and Raman spectroscopic analysis indicated that all CNTs showed high oxidation stability and a high degree of graphitisation.     

Conversion of fossil and biomass fuels to electric power and transportation fuels by high efficiency integrated plasma fuel cell (IPFC) energy cycle

The IPFC is a high efficiency energy cycle, which converts fossil and biomass fuel to electricity and co-product hydrogen and liquid transportation fuels (gasoline and diesel). The cycle consists of two basic units, a hydrogen plasma black reactor (HPBR) which converts the carbonaceous fuel feedstock to elemental carbon and hydrogen and CO gas. The carbon is used as fuel in a direct carbon fuel cell (DCFC), which generates electricity, a small part of which is used to power the plasma reactor. The gases are cleaned and water gas shifted for either hydrogen or syngas formation. The hydrogen is separated for production or the syngas is catalytically converted in a Fischer–Tropsch (F–T) reactor to gasoline and/or diesel fuel. Based on the demonstrated efficiencies of each of the component reactors, the overall IPFC thermal efficiency for electricity and hydrogen or transportation fuel is estimated to vary from 70 to 90% depending on the feedstock and the co-product gas or liquid fuel produced. The CO₂ emissions are proportionately reduced and are in concentrated streams directly ready for sequestration. Preliminary cost estimates indicate that IPFC is highly competitive with respect to conventional integrated combined cycle plants (NGCC and IGCC) for production of electricity and hydrogen and transportation fuels.     

Thermodynamic possibilities and constraints for pure hydrogen production by iron based chemical looping process at lower temperatures

Iron offers the possibility of transformation of a syngas or gaseous hydrocarbons into hydrogen by a cycling process of iron oxide reduction (e.g. by hydrocarbons) and release of hydrogen by steam oxidation. From the thermodynamic and chemical equilibrium point of view, the reduction of magnetite by hydrogen, CO, CH₄ and a model syngas (mixtures CO + H₂ or H₂ + CO + CO₂) and oxidation of iron by steam has been studied. Attention was concentrated not only on convenient conditions for reduction of Fe₃O₄ to iron at temperatures 400–800 K but also on the possible formation of undesired soot, Fe₃C and iron carbonate as precursors for carbon monoxide and carbon dioxide formation in the steam oxidation step. Reduction of magnetite at low temperatures requires a relatively high H₂/H₂O ratio, increasing with decreasing temperature. Reduction of iron oxide by CO is complicated by soot and Fe₃C formation. At lower temperatures and higher CO₂ concentrations in the reducing gas, the possibility of FeCO₃ formation must be taken into account. The purity of the hydrogen produced depends on the amount of soot, Fe₃C and FeCO₃ in the iron after the reduction step. Magnetite reduction is the more difficult stage in the looping process. Pressurized conditions during the reduction step will enhance formation of soot and carbon containing iron compounds.     

Exploring the opportunities for carbon capture in modular,small-scale steam methane reforming: An energetic perspective

Small-scale steam methane reforming units produce more than 12% of all the CO₂-equivalent emissions from hydrogen production and, unlike large-scale units, are usually not integrated with other processes. In this article, the authors examine the hitherto under-explored potential to utilise the excess heat available in the small-scale steam methane reforming process for partial carbon dioxide capture. Reforming temperature has been identified as a critical operating parameter to affect the amount of excess heat available in the steam methane reforming process. Calculations suggest that reforming the natural gas at 850 °C, rather than 750 °C, increases the amount of excess heat available by about 28.4% (at 180 °C) while, sacrificing about 1.62% and 1.09% in the thermal and exergetic efficiency of the process, respectively. Preliminary calculations suggest that this heat could potentially be utilised for partial carbon capture from reformer flue gas, via structured adsorbents, in a compact capture unit. The reforming temperature can be adjusted in order to regulate the amount of excess heat, and thus the carbon capture rate.     

Reforming options for hydrogen production from fossil fuels for PEM fuel cells

PEM fuel cell systems are considered as a sustainable option for the future transport sector in the future. There is great interest in converting current hydrocarbon based transportation fuels into hydrogen rich gases acceptable by PEM fuel cells on-board of vehicles. In this paper, we compare the results of our simulation studies for 100 kW PEM fuel cell systems utilizing three different major reforming technologies, namely steam reforming (SREF), partial oxidation (POX) and autothermal reforming (ATR). Natural gas, gasoline and diesel are the selected hydrocarbon fuels. It is desired to investigate the effect of the selected fuel reforming options on the overall fuel cell system efficiency, which depends on the fuel processing, PEM fuel cell and auxiliary system efficiencies. The Aspen-HYSYS 3.1 code has been used for simulation purposes. Process parameters of fuel preparation steps have been determined considering the limitations set by the catalysts and hydrocarbons involved. Results indicate that fuel properties, fuel processing system and its operation parameters, and PEM fuel cell characteristics all affect the overall system efficiencies. Steam reforming appears as the most efficient fuel preparation option for all investigated fuels. Natural gas with steam reforming shows the highest fuel cell system efficiency. Good heat integration within the fuel cell system is absolutely necessary to achieve acceptable overall system efficiencies.     

A review on current status of hydrogen production from bio-oil

Increase in energy demand and growing environmental awareness has increased interest for alternative renewable energy sources over the last few years. Hydrogen produces only water during combustion, and therefore, it is seen as an alternative fuel for locomotive application. Nonetheless, hydrogen is not an energy source; rather it is an energy carrier. Different techniques are being explored to find an economical way of generating hydrogen from renewable resources. Hydrogen production from water using sunlight is still expensive. Biomass is another alternative to produce hydrogen. Bio-oil derived from biomass using a fast pyrolysis is a potential source for hydrogen production. Although different techniques have been employed to produce hydrogen from bio-oil, significant effort has been put into steam reforming process. This paper reviews major hydrogen production techniques with a great deal of importance given to steam reforming. The important factors that are known to affect hydrogen yield are temperature, steam to carbon ratio, and catalyst type. Literature review of bio-oil steam reforming technique has been done, and a comparison of experimental conditions has been carried out. However, as a major shortcoming, this technique is accompanied by the formation of carbonaceous deposits over the catalyst surface rendering it inactive and requiring frequent regeneration. Coke formation has been cited as the major disadvantage of bio-oil reforming, and it is more pronounced when Ni based catalysts are used.