Steam reforming of propane in a fluidized bed membrane reactor for hydrogen production

Steam reforming of propane was carried out in a fluidized bed membrane reactor to investigate a feedstock other than natural gas for production of pure hydrogen. Close to equilibrium conditions were achieved inside the reactor with fluidized catalyst due to the very fast steam reforming reactions. Use of hydrogen permselective Pd₇₇Ag₂₃ membrane panels to extract pure hydrogen shifted the reaction towards complete conversion of the hydrocarbons, including methane, the key intermediate product. Irreversible propane steam reforming is limited by the reversibility of the steam reforming of this methane. To assess the performance improvement due to pure hydrogen withdrawal, experiments were conducted with one and six membrane panels installed along the height of the reactor. The results indicate that a compact reformer can be achieved for pure hydrogen production for a light hydrocarbon feedstock like propane, at moderate operating temperatures of 475–550 °C, with increased hydrogen yield.     

A comparative assessment of homogeneous propane reforming at intermediate temperatures

The study compares the performance of different pathways for gas-phase (non-catalytic) fuel reforming between 600 and 1000 °C. Specifically, the conversion of propane to hydrogen-rich syngas was investigated numerically and experimentally for pyrolysis (Py), steam reforming (SR), partial oxidation (POx), and autothermal reforming (ATR). Experiments were conducted in a tubular quartz reactor, where temperatures were imposed externally; reactants were diluted with nitrogen to reduce the impact of endothermic/exothermic reactions on the variation of gas-phase temperatures. In experiments, product concentrations of hydrogen, carbon monoxide, carbon dioxide, methane, and a range of hydrocarbon species were measured at predetermined operating conditions. The performance of each homogeneous reforming process was evaluated and compared by assessing propane conversion and production efficiencies for hydrogen and other species of interest. At 600 °C, propane conversion was low, but increased substantially with temperature; complete conversion was achieved at 1000 °C. Furthermore, findings show improved hydrogen production efficiencies of POx/ATR when compared to Py/SR. Experimental results are substantiated by numerical simulations with detailed chemical kinetics; numerical results are in good agreement with experiments at identical operating conditions. Experimental and numerical results for non-catalytic propane reforming at all tested temperatures (600–1000 °C) imply a negligible impact of steam addition to the process, as results for SR resemble Py results, and ATR closely follows POx characteristics. As such, results clearly show that steam does not play an active role in gas-phase reforming of propane at intermediate temperatures.     

Exergy analysis of biomass staged-gasification for hydrogen-rich syngas

Using Aspen Plus simulations, exergy analyses of hydrogen-rich syngas production via biomass staged-gasification are carried out for three configurations, namely, staged-gasification with pyrolysis gas combustion and char gasification (C-1), staged-gasification with pyrolysis gas reforming and char gasification (C-2), and staged-gasification with pyrolysis gas reforming and char combustion (C-3). The results show that, for the gasification and reforming processes, the exergy loss of pyrolysis gas with tar reforming is less than that of char gasification. As for the system, it is conducive to generating hydrogen by making full use of the hydrogen element (H) in biomass instead of the H in water. The benefits of C-1 are that it removes tar and produces higher yield and concentration of hydrogen. However, C-2 is capable of obtaining higher exergy efficiency and lower exergy loss per mole of H₂ production. C-3 theoretically has greater process performances, but it has disadvantages in tar conversion in practical applications. The appropriate gasification temperature (T_G) are in the range of 700–750 °C and the appropriate mass ratio of steam to biomass (S/B) are in the range of 0.6–0.8 for C-1 and C-3; the corresponding parameters for C-2 are in the ranges of 650–700 °C and 0.7–0.8, respectively.     

Photochemical hydrocarbon fuel regeneration: Hydrogen-rich fuel from CO2

This paper presents the concept of photochemical hydrocarbon fuel regeneration by CO₂ transformation to hydrogen-rich fuel. The first stage of this system is CO₂ capture and algae (Chlorella vulgaris) growing. The second stage is the gasification of algae biomass to produce hydrogen-rich gas and its combustion. To compile the heat and mass balance, the thermodynamic analysis was performed under various operating parameters: temperature 400–800 °C, pressure 1–10 bar 1 kg of biomass was gasified with 1.2 kg of water. The heat of combustion of hydrogen-rich gas after gasification is up to 43% higher than the heat of combustion of initial biomass. The fuel regeneration degree is up to 0.9 when 30% of CO₂ is captured by water and proceded by algae. Moreover, the analyzed photochemical fuel regeneration system allows heat recuperation. The heat regeneration degree is calculated and the maximum value is about 0.9 is reached at 600 °C.     

Autothermal reforming of n-dodecane and desulfurized Jet-A fuel for producing hydrogen-rich syngas

Catalytic reforming is a technology to produce hydrogen and syngas from heavy hydrocarbon fuels in order to supply hydrogen to fuel cells. A lab-scale 2.5 kW_t autothermal reforming (ATR) system with a specially designed reformer and combined analysis of balance-of-plant was studied and tested in the present study. NiO–Rh based bimetallic catalysts with promoters of Ce, K, and La were used in the reformer. The performance of the reformer was studied by checking the hydrogen selectivity, CO_x selectivity, and energy conversion efficiency at various operating temperatures, steam to carbon ratios, oxygen to carbon ratios, and reactants' inlet temperatures. The experimental work firstly tested n-dodecane as the surrogate of Jet-A fuel to optimize operating conditions. After that, desulfurized commercial Jet-A fuel was tested at the optimized operating conditions. The design of the reformer and the catalyst are recommended for high performance Jet-A fuel reforming and hydrogen-rich syngas production.     

Ultra-rich combustion in parallel channels to produce hydrogen-rich syngas from propane

Although hydrogen is abundant in nature, it is primarily bound into other molecules such as hydrocarbons. The conversion, or reforming, of a hydrocarbon into a hydrogen-rich syngas may be accomplished through either catalytic or non-catalytic processes. In this paper, we examine a non-catalytic reactor for syngas production that consists of multiple parallel channels with alternating flow directions. Heat recirculation between channels with opposing flow directions promotes reactions of rich mixtures beyond the conventional flammability limit. Experimental results with propane/air mixtures show that stable reaction fronts are obtained at a wide range of equivalence ratios and inlet velocities. The performance of the reactor with propane/air is compared to previously published results with methane/air mixtures, where significant differences are attributed to the more complex reaction chemistry of rich propane combustion.     

Application of exhaust gas fuel reforming in diesel and homogeneous charge compression ignition (HCCI) engines fuelled with biofuels

This paper documents the application of exhaust gas fuel reforming of two alternative fuels, biodiesel and bioethanol, in internal combustion engines. The exhaust gas fuel reforming process is a method of on-board production of hydrogen-rich gas by catalytic reaction of fuel and engine exhaust gas. The benefits of exhaust gas fuel reforming have been demonstrated by adding simulated reformed gas to a diesel engine fuelled by a mixture of 50% ultra low sulphur diesel (ULSD) and 50% rapeseed methyl ester (RME) as well as to a homogeneous charge compression ignition (HCCI) engine fuelled by bioethanol. In the case of the biodiesel fuelled engine, a reduction of NO_x emissions was achieved without considerable smoke increase. In the case of the bioethanol fuelled HCCI engine, the engine tolerance to exhaust gas recirculation (EGR) was extended and hence the typically high pressure rise rates of HCCI engines, associated with intense combustion noise, were reduced.     

Greenhouse effect reduction and energy recovery from waste landfill

Waste management systems are a non-negligible source of greenhouse gases. In particular, methane and carbon dioxide emissions occur in landfills due to the breakdown of biodegradable carbon compounds operated on by anaerobic bacteria. The conventional possibilities of reducing the greenhouse effect (GHE) from waste landfilling consists in landfill gas (LFG) flaring or combustion with energy recovery in reciprocating engines. These conventional treatments are compared with three innovative possibilities: the direct LFG feeding to a fuel cell (FC); the production of a hydrogen-rich gas, by means of steam reforming and CO₂ capture, to feed a stationary FC; the production of a hydrogen-rich gas, by means of steam reforming and CO₂ capture, to feed a vehicle FC. The comparison is carried out from an environmental point of view, calculating the specific production of GHE per unit mass of waste disposed in landfill equipped with the different considered technologies.     

Simulation of exhaust gas reforming of propane in a heat exchange integrated microchannel reactor

Exhaust gas reforming of propane to a hydrogen-rich mixture in a single, heat-exchange integrated, adiabatic, catalytic microchannel is modeled and simulated at different exhaust gas compositions from conventional gasoline and diesel fueled engines. Propane is considered as the model hydrocarbon for the complex fuels such as gasoline and diesel. The single microchannel is considered to be the characteristic unit of the catalytic exhaust gas reformer involving identical channels located parallel to each other. Steady-state simulations, carried out by the finite volume method, involve parametric variations of the total feed flow rate, and the amounts of propane and steam injected externally into the exhaust gas (reformer feed) stream. The results show that effective heat transfer and uniform temperature distribution, which are critical for the successful operation of the exhaust gas reformer, can be obtained in the microchannel configuration even at low gas hourly space velocities (GHSVs) at which the conventional packed-bed reformers usually lead to remarkable hot-spot formation. Production of H₂ and CO is favored by the addition of higher amounts of propane and steam into the reformer feed. Increasing the total feed flow rate, hence the GHSV is found to improve heat distribution along the microchannel at the expense of reduced product yields due to insufficient contact time.     

Thermodynamic analysis of hydrogen production via sorption-enhanced steam methane reforming in a new class of variable volume batch-membrane reactor

Combined reaction–separation processes are a widely explored method to produce hydrogen from endothermic steam reforming of hydrocarbon feedstock at a reduced reaction temperature and with fewer unit operation steps, both of which are key requirements for energy efficient, distributed hydrogen production. This work introduces a new class of variable volume batch reactors for production of hydrogen from catalytic steam reforming of methane that operates in a cycle similar to that of an internal combustion engine. It incorporates a CO₂ adsorbent and a selectively permeable hydrogen membrane for in situ removal of the two major products of the reversible steam methane reforming reaction. Thermodynamic analysis is employed to define an envelope of ideal reactor performance and to explore the tradeoff between thermal efficiency and hydrogen yield density with respect to critical operating parameters, including sorbent mass, steam to methane ratio and fraction of product gas recycled. Particular attention is paid to contrasting the variable volume batch-membrane reactor approach to a conventional fixed bed reaction–separation approach. The results indicates that the proposed reactor is a viable option for low temperature distributed production of hydrogen from methane, the primary component of natural gas feedstock, motivating a detailed study of reaction/adsorption kinetics and heat/mass transfer effects.     

Emissions reductions using hydrogen from plasmatron fuel converters

Improvements in internal combustion engine and aftertreatment technologies are needed to meet future environmental quality goals. Systems using recently developed compact plasmatron fuel converters in conjunction with state-of-the-art engines and aftertreatment catalysts could provide new opportunities for obtaining substantial emissions reductions. Plasmatron fuel converters provide a rapid response, compact means to transform a wide range of hydrocarbon fuels (including gasoline, natural gas and diesel fuel) into hydrogen-rich gas. Hydrogen-rich gas can be used as an additive to provide NO_x reductions of more than 80% in spark ignition gasoline engine vehicles by enabling very lean operation or heavy exhaust engine recirculation. It may also be employed for cold start hydrocarbon reduction. If certain requirements are met, it may also be possible to achieve higher spark ignition engine efficiencies (e.g., up to 95% of those of diesel engines). These requirements include the attainment of ultra lean, high compression ratio, open throttle operation using only a modest amount of hydrogen addition. For diesel engines, use of compact plasmatron reformers to produce hydrogen-rich gas for the regeneration of NO_x absorber/adsorbers and particulate traps for diesel engine exhaust aftertreatment could provide significant advantages. Recent tests of conversion of diesel fuel to hydrogen-rich gas using a low current plasmatron fuel converter with non-equilibrium plasma features are described.     

Autothermal reforming of aliphatic and aromatic hydrocarbon liquids

The process of catalytic partial oxidation of hydrocarbon liquids in the presence of steam to generate a hydrogen-rich gas is called autothermal reforming (ATR), wherein no external heat source other than reactants preheat is required. As an alternative to conventional steam reforming, the ATR process, considered for use with fuel cell power plants, may expand the range of fuels that can be converted to hydrogen to include middle distillate fuels derived from petroleum or coal.Carbon formation constitutes the main problem in autothermal reforming of heavy fuels under conditions of high thermal and conversion efficiency. A better understanding of the parametric effects on carbon formation in ATR can be obtained by studying the basic types of components that occur in heavy fuels (paraffins, aromatics, olefins and sulfur compounds). Experimental results are presented here for the ATR of paraffins (n-hexane, n-tetradecane) and aromatics (benzene, naphthalene) over supported nickel catalysts. Under similar operating conditions, reaction temperatures and intermediates, and the propensity for carbon formation in the autothermal reformer have been found to be characteristic of the hydrocarbon type used. The effects of various operating parameters on carbon formation are illustrated for the different fuels used in ATR. In tests with aliphatic/aromatic mixtures, synergistic effects have been determined.     

Performance and emissions characteristics of a lean-burn marine natural gas engine with the addition of hydrogen-rich reformate

The exhaust gas-fuel reforming technique known as reformed exhaust gas recirculation (REGR) can generate on-board hydrogen-rich gas mixture (i.e., reformate) by catalytic reforming of the exhaust gas and fuel added into the reformer and then recirculate the reformate into the engine cylinder, which can realize the combination of hydrogen-rich lean combustion and exhaust gas recirculation. The REGR technique can be employed to achieve efficient and stable lean-burn combustion for the marine engine fueled with natural gas (i.e., marine NG engine) and it is considered as an effective way to meet the stringent ship emissions regulations. In the present study, an experimental investigation into the effects of reformate addition ratio (R_re) and excess air ratio (λ) on the combustion and emissions characteristics of a marine NG engine under various loads was conducted, and the potential of applying the REGR technique in a marine NG engine to achieve low emissions (i.e., International Maritime Organization Tier Ⅲ emissions legislations for international ships) was discussed. The results indicate that the addition of the hydrogen-rich reformate gases can extend lean-burn limit. For a given λ, the flame development duration and rapid combustion duration decrease with the increase of R_re, and the combustion efficiency is improved. The brake specific NO_x emissions first increase and then decrease with the increase of R_re due to the competition between the combustion phase and total heat release value. The brake specific THC emissions decline with the increase of R_re, while the reverse holds for the brake specific CO emissions, and the behavior tends to be obvious under large λ. It is demonstrated that the combination of REGR and the lean-burn combustion strategy can improve the trade-off relationship between the NO_x emissions and brake specific fuel consumption of the marine NG engine to meet the IMO Tier Ⅲ NO_x emissions legislations and maintain relatively low brake specific fuel consumption.     

Biomass gasification coupled with producer gas cleaning,bottling and HTS catalyst treatment for H2-rich gas production

The aim of the present study is to demonstrate the production of hydrogen-rich fuel gas from J. curcas residue cake. A comprehensive experimental study for the production of hydrogen rich fuel gas from J. curcas residue cake via downdraft gasification followed by high temperature water gas shift catalytic treatment has been carried out. The gasification experiments are performed at different equivalence ratios and performance of the process is reported in terms of producer gas composition & its calorific value, gas production rate and cold gas efficiency. The producer gas is cleaned of tar and particulate matters by passing it through venturi scrubber followed by sand bed filter. The clean producer gas is then compressed at 0.6 MPa and bottled into a gas cylinder. The bottled producer gas and a simulated mixture of producer gas are then subjected to high temperature shift (HTS) catalytic treatment for hydrogen enriched gas production. The effect of three different operating parameters GHSV, steam to CO ratio and reactor temperature on the product gas composition and CO conversion is reported. From the experimental study it is found that, the presence of oxygen in the bottled producer gas has affected the catalyst activity. Moreover, higher concentration of oxygen concentration in the bottled producer gas leads to the instantaneous deactivation of the HTS catalyst.     

Gasification of diesel oil in supercritical water for fuel cells

Experiments have demonstrated the reforming of hydrocarbons in supercritical water. The hydrocarbons were reformed in a continuously operated tubular V4A reactor. The influences of four different commercial steam reforming catalysts were analysed. The experimental results showed that n-decane can be converted to a hydrogen-rich gas. Furthermore, experiments with diesel oil showed the possibility of fuel conversion at low temperature with commercial steam reforming catalysts. Low temperatures and the use of catalysts lead to inhibition of coke formation during the process. The supercritical reforming offers the possibility of a new low temperature hydrocarbon conversion process to hydrogen for fuel cell applications.     

Development of a porous burner unit for glycerine utilization from biodiesel production by Supercritical Water Reforming

In the production of biodiesel from vegetable oils, glycerine is produced as a by-product, yielding an amount of about 10 percent of the quantity of biodiesel produced. The glycerine-market is saturated by the growing biodiesel production, so that an alternative use of glycerine is sought. An alternative is the conversion of glycerine into a hydrogen-rich synthesis gas through the procedure of Supercritical Water Reforming (SCWR), from which other energy conversion processes can be made. In the present project, inter alia a porous burner is meant to be used as a heat source for the reforming. This burner technology allows an effective and low-emission combustion of different fuels in a high performance modulation. By individual adjustment, the burner is meant to burn the generated hydrogen-rich synthesis gas and glycerine.     

Synthesis gas generation on-board a vehicle: Development and results of testing

The present work is focused on the development of energy-efficient internal combustion engines with minimized CO, CO₂, CH and NO_x emissions. In frame of this concept, a method for hydrogen-rich gas generation onboard a vehicle and, in particular, its application as an additive to the engine fuel was suggested and tested experimentally. For practical realization of the method, the catalysts for hydrocarbon fuel reforming to synthesis gas were created, compact under-hood mounted synthesis gas generator was designed, and integrated ICE-synthesis gas generator control system was developed. The tests proved fuel economy in city cycle and considerable decrease of CO, CO₂, CH and NO_x emissions. The prospects of the technology for the development of energy-efficient environmentally benign engines are analyzed.     

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.     

Comparison between direct and indirect (prechamber) spark ignition in the case of a cogeneration natural gas engine,part I: engine geometrical parameters

The operation of a cogeneration internal combustion engine with unscavenged prechamber ignition was investigated. The objective was to evaluate the potential to reduce the exhaust gas emissions, particularly the CO emissions without exhaust gas after treatment. The investigation was carried out on a small size gas engine (150 kW) and required the development of cooled prechambers and the modification of the engine cylinder heads. The limit of the conventional lean burn operating mode with direct ignition is discussed and the prechamber geometrical configuration is presented. Through the generation of gas jets in the main chamber, the use of a prechamber strongly intensifies and accelerates the combustion process. The prechamber operation reduces significantly the emissions of CO and total hydrocarbon (THC) for same NO_x emissions. The use of a piston generating significantly more turbulence leads to a somewhat higher fuel conversion efficiency without affecting significantly the CO and THC emissions at low NO_x emissions. Further improvement associated with the adjustment of the engine operating parameters and the turbocharger characteristics, as well as a comparison between direct and prechamber ignition operation are presented in the second part (II) of this publication.     

Reduction of greenhouse gas emission on a medium-pressure boiler using hydrogen-rich fuel control

The increasing emission of greenhouse gases from the combustion of fossil fuel is believed to be responsible for global warming. A study was carried out to probe the influence of replacing fuel gas with hydrogen-rich refinery gas (R.G.) on the reduction of gas emission (CO₂ and NO_x) and energy saving. Test results show that the emission of CO₂ can be reduced by 16.4% annually (or 21,500 tons per year). The NO_x emission can be 8.2% lower, or 75 tons less per year. Furthermore, the use of refinery gas leads to a saving of NT$57 million (approximately US$1.73 million) on fuel costs each year. There are no CO₂, CO, SO_x, unburned hydrocarbon, or particles generated from the combustion of added hydrogen. The hydrogen content in R.G. employed in this study was between 50 and 80 mol%, so the C/H ratio of the feeding fuel was reduced. Therefore, the use of hydrogen-rich fuel has practical benefits for both energy saving and the reduction of greenhouse gas emission.