Bio-fuel reformation for solid oxide fuel cell applications. Part 1: Fuel vaporization and reactant mixing

A new configuration of a mixing chamber integrated with a customized porous nozzle has been developed to completely vaporize heavy hydrocarbon fuels (e.g., diesel, biodiesel) and achieve homogenous mixing of fuel/air/steam. This proposed configuration suppresses hydrocarbon thermal pyrolysis and solid carbon formation in the fuel vaporization step. The porous nozzle promotes the micro-explosion of emulsified fuel and accelerates secondary atomization to reduce the droplet size. The mixing chamber with customized nozzle was integrated in a single-tube reformer system in order to analyze its effect on diesel and biodiesel auto-thermal reforming (ATR). It has been demonstrated that the customized nozzle not only improved the hydrogen production rate and the reforming efficiency, but it also stabilized the chemical reactions within the reformer and prevented the reactor inlet from high temperature sintering. For diesel ATR, this mixing chamber–reformer combination enabled operation at relatively low reformer temperature without forming solid carbon. This study is one component of a three-part investigation of bio-fuel reforming, also including biodiesel (Part 2) and biodiesel–diesel blends (Part 3).     

Bio-fuel reformation for solid oxide fuel cell applications. Part 3: Biodiesel–diesel blends

The auto-thermal reforming (ATR) performance of diesel blended with biodiesel (e.g., B5, B10, B20, B40, and B80) was investigated and compared to pure diesel and biodiesel ATR in a single-tube reformer with ceramic monolith wash-coated rhodium/ceria–zirconia catalyst. The initial operating condition of the ATR of all studied fuels was set as total moles of oxygen from air, water, and fuel per mole of carbon (O/C) = 1.47, moles of water to carbon (H₂O/C) = 0.6, and gas hourly space velocity = 33,950 h⁻¹ at 1223 K reformer temperature, to achieve the same syngas (H₂ + CO) production rate. A direct photo-acoustic micro-soot meter was applied to quantify the dynamic evolution of carbon formation and a mass spectrometer was used to measure the gas composition of reformer effluents. The blends with more biodiesel content were found to have a lower syngas production rate and reforming efficiency, and require more air and higher reformer temperature to avoid carbon formation. Strong correlations between ethylene and solid carbon concentration were observed in the reformation of all the fuels and blends, with more biodiesel content tending to have higher ethylene production. This study is one component of a three-part investigation of bio-fuel reforming, also including fuel vaporization and reactant mixing (Part 1) and biodiesel (Part 2).     

Thermodynamic study of hydrogen production from crude glycerol autothermal reforming for fuel cell applications

This study presents a thermodynamic analysis of hydrogen production from an autothermal reforming of crude glycerol derived from a biodiesel production process. As a composition of crude glycerol depends on feedstock and processes used in biodiesel production, a mixture of glycerol and methanol, major components in crude glycerol, at different ratios was used to investigate its effect on the autothermal reforming process. Equilibrium compositions of reforming gas obtained were determined as a function of temperature, steam to crude glycerol ratio, and oxygen to crude glycerol ratio. The results showed that at isothermal condition, raising operating temperature increases hydrogen yield, whereas increasing steam to crude glycerol and oxygen to crude glycerol ratios causes a reduction of hydrogen concentration. However, high temperature operation also promotes CO formation which would hinder the performance of low-temperature fuel cells. The steam to crude glycerol ratio is a key factor to reduce the extent of CO but a dilution effect of steam should be considered if reforming gas is fed to fuel cells. An increase in the ratio of glycerol to methanol in crude glycerol can increase the amount of hydrogen produced. In addition, an optimal operating condition of glycerol autothermal reforming at a thermoneutral condition that no external heat to sustain the reformer operation is required, was investigated.     

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.     

Hydrogen rich gas production by the autothermal reforming of biodiesel (FAME) for utilization in the solid-oxide fuel cells: A thermodynamic analysis

The thermodynamics of the autothermal reforming (ATR) of biodiesel (FAME) for production of hydrogen is simulated and evaluated using Gibbs free minimization method. Simulations are performed with water-biodiesel molar feed ratios (WBFR) between 3 and 12, and oxygen-biodiesel molar feed ratio (O_XBFR) from 0 to 4.8 at reaction temperature between 300 and 800 °C at 1 atm. Yields of H₂ and CO are calculated as functions of WBFR, O_XBFR and temperature at 1 atm. Hydrogen rich gas can be produced by the ATR of biodiesel for utilization in solid-oxide fuel cells (SOFCs). The best operating conditions for the ATR reformer are WBFR≥9 and O_XBFR = 4.8 at 800 °C by optimization of the operating parameters. Yields of hydrogen and carbon monoxide are 68.80% and 91.66% with 54.14% and 39.2% selectivities respectively at the above conditions. The hydrogen yield from biodiesel is higher than from unmodified oils i.e., transesterification increases hydrogen yield. Increase in saturation of the esters, results in increase in methane selectivity, while an increase in unsaturation results in a decrease in methane selectivity. Increase in degree of both saturation and unsaturation of esters, increases coke selectivity. Similarly an increase in the linoleic content of esters, increases coke selectivity.     

Measurement and analysis of carbon formation during diesel reforming for solid oxide fuel cells

Experiments and equilibrium analysis were conducted to study carbon formation during diesel reforming for a solid oxide fuel cell-based auxiliary power unit (APU) application. A photo-acoustic instrument provided direct measurements of solid carbon concentration in the reformer effluent stream, which could be correlated to reformate gas composition (as determined via mass spectrometer) and reformer temperature. These measurements were complimented by equilibrium calculations based upon minimization of total Gibbs free energy. It was determined that oxygen-to-carbon ratio (O/C), fuel utilization fraction and anode recycle fraction all influence the degree of carbon formation, and that once significant carbon concentration is measured, the reformer performance begins to show marked degradation. At a fixed operating point, lowering the reformer temperature produced by far the largest change in effluent carbon concentration. Systematic variation in O/C, fuel utilization and anode recycle revealed the interdependence among reformer temperature, effluent gas composition and carbon concentration, with a strong correlation between carbon and ethylene concentrations observed for [C₂H₄] > 0.8%. After each experiment, baseline reformer performance could be recovered by operation under methane partial oxidation (POx) conditions, indicating that reformer degradation results at least in part from carbon deposition on the reformer catalyst.     

Fuel flexibility study of an integrated 25 kW SOFC reformer system

The operation of solid oxide fuel cells on various fuels, such as natural gas, biogas and gases derived from biomass or coal gasification and distillate fuel reforming has been an active area of SOFC research in recent years. In this study, we develop a theoretical understanding and thermodynamic simulation capability for investigation of an integrated SOFC reformer system operating on various fuels. The theoretical understanding and simulation results suggest that significant thermal management challenges may result from the use of different types of fuels in the same integrated fuel cell reformer system. Syngas derived from coal is simulated according to specifications from high-temperature entrained bed coal gasifiers. Diesel syngas is approximated from data obtained in a previous NFCRC study of JP-8 and diesel operation of the integrated 25 kW SOFC reformer system. The syngas streams consist of mixtures of hydrogen, carbon monoxide, carbon dioxide, methane and nitrogen. Although the SOFC can tolerate a wide variety in fuel composition, the current analyses suggest that performance of integrated SOFC reformer systems may require significant operating condition changes and/or system design changes in order to operate well on this variety of fuels.     

Combustion characteristics of mixture of anode off gas and LNG in reformer

Fuel processing system which converts hydrocarbon fuel into hydrogen rich gas (by stream reforming, partial oxidation, auto-thermal reforming) needs high temperature environment (600-1000 °C). Generally, anode off gas or mixture of anode off gas and LNG are used as input gas for a fuel reformer. In order to constitute efficient and low emission burner system for fuel reformer, it is necessary to elucidate the combustion and emission characteristics of fuel reformer burner. In this study, lean flat flame using the ceramic porous burner was analyzed numerically and experimentally. Burning velocity of anode off gas calculated by CHEMKIN simulation was 51.8 cm, which was faster than that of LNG having 40.63 cm/s at the stoichiometric ratio because of high composition of hydrogen in anode off gas. As composition of LNG in mixture of anode off gas + LNG is increased, the burning velocity decreases and in the other hand the adiabatic temperature increases. CO, NO_x were measured below 50 ppm in operating load range of the reformer. Blue flame pattern was found as stable flame region for design of fuel reformer and anode off gas flame was maintained in blue flame pattern at equivalence ratio 0.55-0.62 under 1-5 kW power range.     

Temperature and hydrogen flow rate controls of diesel autothermal reformer for 3.6 kW PEM fuel cell system with autoignition delay time analysis

In this paper catalyst temperature and hydrogen flow rate controls are an area of interest for autothermal reforming (ATR) of diesel fuel to provide continuous and necessary hydrogen flow to the on-board fuel cell vehicle system. ATR control system design is important to ensure proper and stable performance of fuel processor and fuel cell stack. Fast system response is required for varying load changes in the on-board fuel cell system. To cope with control objectives, a combination of PI and PID controllers are proposed to keep the controlled variables on their setpoints. ATR catalyst temperature is controlled with feedback PID controller through variable OCR (oxygen to carbon ratio) manipulation and kept to the setpoint value of 900 °C. Additionally diesel auto-ignition delay time is implemented through fuel flow rate delay to avoid complete oxidation of fuel. Hydrogen flow rate to the fuel cell stack is kept to setpoint of required hydrogen flow rate according to fuel cell load current using PI controller. An integrated dynamic model of fuel processor and fuel cell stack is also developed to check the fuel cell voltage. Product gas composition of 35, 18 and 4% is achieved for hydrogen, nitrogen, and carbon dioxide, respectively. The results show fast response capabilities of fuel processor following the fuel cell load change and successfully fulfills the control objectives.     

Characterization of kilowatt-scale autothermal reformer for production of hydrogen from heavy hydrocarbons

Catalytic autothermal reforming is considered one of the most effective methods of producing hydrogen from heavy hydrocarbon fuels, such as diesel fuel, for fuel cell or emissions reduction applications. This article describes an investigation of the reactor characteristics and catalytic efficiency of a kilowatt-scale catalytic autothermal reformer currently being developed at Argonne National Laboratory. Dodecane and hexadecane were used individually as surrogates for diesel fuels to simply the reaction study and the interpretation of the test results. The reforming of these hydrocarbon fuels was examined at a variety of oxygen-to-carbon and steam-to-carbon ratios at gas hourly space velocities ranging from 10,000 to 100,000 h⁻¹. At steady state, the product composition correlated well with that calculated from thermodynamic equilibrium at a representative equivalent temperature. The oxygen-to-carbon ratio was determined to be the most significant operating parameter that influenced the reforming efficiency; the reforming efficiency (and the selectivity to CO_x) increased with increasing oxygen-to-carbon ratio up to about 0.42, at which value the maximum efficiency was attained.     

Thermodynamic analysis and heat integration for hydrogen production from bio-butanol for SOFC application: Steam reforming vs. autothermal reforming

Thermodynamic analysis of hydrogen production by steam reforming and autothermal reforming of bio-butanol was investigated for solid oxide fuel cell applications. The effects of reformer operating conditions, e.g., reformer temperature, steam to carbon molar ratio, and oxygen to carbon molar ratio, were investigated with the objective to maximize hydrogen production and to reduce utility requirements of the process and based on which favorable conditions of reformer were proposed. Process flow diagram for steam reforming and autothermal reforming integrated with solid oxide fuel cell was developed. Heat integration with pinch analysis method was carried out for both the processes at favorable reformer conditions. Power generation, electrical efficiency, useful energy for co-generation application, and utility requirements for both the processes were compared.     

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.     

The effect of reformer gas mixture on the performance and emissions of an HSDI diesel engine

Exhaust gas assisted fuel reforming is an attractive on-board hydrogen production method, which can open new frontiers in diesel engines. Apart from hydrogen, and depending on the reactions promoted, the reformate typically contains a significant amount of carbon monoxide, which is produced as a by-product. Moreover, admission of reformed gas into the engine, through the inlet pipe, leads to an increase of intake air nitrogen to oxygen ratio. It is therefore necessary to study how a mixture of syngas and nitrogen affects the performance and emissions of a diesel engine, in order to gain a better understanding of the effects of supplying fuel reformer products into the engine.     

Thermodynamic analysis of the autothermal reforming of glycerol using supercritical water

Hydrogen can be produced by autothermal reforming of glycerol using supercritical water (SCW). With the aid of AspenPlus™, a systematic thermodynamic analysis of this process has been carried out by the total Gibbs free energy minimization method, which computes the equilibrium composition of synthesis gas (syngas). The predictive Soave-Redlich-Kwong equation of state (EOS) has been used as thermodynamic method in the simulation of the supercritical region. A sensitivity analysis has been conducted both for a pure glycerol feed and pretreated crude glycerol feed coming from biodiesel production. Simulations run so as to calculate the O₂ needed to enter the Gibbs reactor (reformer) for achieving the thermoneutral condition (no external heat to sustain the reformer operation is required). Thus, the effect of the main operating parameters (reforming temperature, water to glycerol mole ratio, glycerol purity in the feed of crude glycerol, oxygen to glycerol mole ratio and the inlet feed temperature) aimed to the hydrogen production has been investigated, by obtaining the mole fraction and molar flow-rate of components in syngas, as well as the hydrogen yield. By this way, the most thermodynamic favorable operating conditions at which glycerol may be converted into hydrogen by autothermal reforming using SCW have been identified. As a second part of the study, a conceptual design and an energy and exergy analysis of the overall process will be performed later.     

GC-MS determination of low hydrocarbon species (C1–C6) from a diesel partial oxidation reformer

The partial oxidation (POx) reforming of Ultra Low Sulphur-Diesel (ULSD), rapeseed methyl ester (RME) - biodiesel and Fischer–Tropsch synthetic diesel fuels (SD) were studied by using a fixed-bed reactor. The ease of reforming the three fuels was first examined at different O/C feed ratios at constant gas hourly space velocity (GHSV) of 35 k h⁻¹ over a prototype monolith catalyst (1%Rh/CeO₂–ZrO₂). The hydrocarbon species (C₁–C₆) produced in the reformer were analyzed using direct gas injection gas chromatography mass spectrometry (GC-MS). Under the same O/C ratios for 35 k h⁻¹ the fuels conversion and process efficiency was dependent on the fuel type, and followed the general trend: SD > biodiesel > ULSD. The GC-MS analysis shows that both, biodiesel and ULSD diesel produced significantly higher amounts of alkenes compared to SD fuel. Fuel with relatively high aromatics content such diesel can be efficiently reformed to syngas over the catalyst used in this study but the reformer operating range (e.g. O/C ratio and space velocity) is limited compared to paraffinic fuels such as FT-SD. At increased GHSV of 45 k h⁻¹ and O/C = 1.75, the diesel fuel conversion efficiency to syngas (H₂ and CO) was improved significantly and the formation of intermediate species such as methane, ethylene, and propylene was reduced considerably as a result of the increased peak reaction temperatures. The reduced HC species and increased H₂ concentration in the reactor product gas from the reforming of FT-SD fuel can provide significant advantages to the IC engine applications.     

Comparative life cycle assessment of hydrogen pathways from fossil sources in China

Emissions of multiple hydrogen production pathways from fossil sources were evaluated and compared with that of fossil fuel production pathways in China by using the life cycle assessment method. The considered hydrogen pathways are gasoline reforming, diesel reforming, natural gas reforming, soybean‐derived biodiesel (s‐biodiesel) reforming, and waste cooking oil‐derived biodiesel reforming. Moreover, emissions and energy consumption of fuel cell vehicles utilizing hydrogen from different fossil sources were presented and compared with those of the electric vehicle, the internal combustion engine vehicle, and the compression ignition engine vehicle. The results indicate both fuel cell vehicles and the electric vehicle have less greenhouse gas emissions and energy consumption compared with the traditional vehicle technologies in China. Based on an overall performance comparison of five different fuel cell vehicles and the electric vehicle in China, fuel cell vehicles operating on hydrogen produced from natural gas and waste cooking oil‐derived biodiesel show the best performance, whereas the electric vehicle has the worse performance than all the fuel cell vehicles because of very high share of coal in the electricity mix of China. The emissions of electric vehicle in China will be in the same level with that of natural gas fuel cell vehicle if the share of coal decreases to around 40% and the share of renewable energy increases to around 20% in the electricity mix of China. Copyright © 2016 John Wiley & Sons, Ltd.     

Design of a methanol reformer for on-board production of hydrogen as fuel for a 3 kW High-Temperature Proton Exchange Membrane Fuel Cell power system

The method of Computational Fluid Dynamics is used to predict the process parameters and select the optimum operating regime of a methanol reformer for on-board production of hydrogen as fuel for a 3 kW High-Temperature Proton Exchange Membrane Fuel Cell power system. The analysis uses a three reactions kinetics model for methanol steam reforming, water gas shift and methanol decomposition reactions on Cu/ZnO/Al₂O₃ catalyst. Numerical simulations are performed at single channel level for a range of reformer operating temperatures and values of the molar flow rate of methanol per weight of catalyst at the reformer inlet. Two operating regimes of the fuel processor are selected which offer high methanol conversion rate and high hydrogen production while simultaneously result in a small reformer size and a reformate gas composition that can be tolerated by phosphoric acid-doped high temperature membrane electrode assemblies for proton exchange membrane fuel cells. Based on the results of the numerical simulations, the reactor is sized, and its design is optimized.     

Hydrogen production from glycerol steam reforming for low- and high-temperature PEMFCs

This paper presents a thermodynamic study of a glycerol steam reforming process, with the aim of determining the optimal hydrogen production conditions for low- and high-temperature proton exchange membrane fuel cells (LT-PEMFCs and HT-PEMFCs). The results show that for LT-PEMFCs, the optimal temperature and steam to glycerol molar ratio of the glycerol reforming process (consisting of a steam reformer and a water gas shift reactor) are 1000 K and 6, respectively; under these conditions, the maximum hydrogen yield was obtained. Increasing the steam to glycerol ratio over its optimal value insignificantly enhanced the performance of the fuel processor. For HT-PEMFCs, to keep the CO content of the reformate gas within a desired range, the steam reformer can be operated at lower temperatures; however, a high steam to glycerol ratio is required. This requirement results in an increase in the energy consumption for steam generation. To determine the optimal conditions of glycerol steam reforming for HT-PEMFC, both the hydrogen yield and energy requirements were taken into consideration. The operational boundary of the glycerol steam reformer was also explored as a basic tool to design the reforming process for HT-PEMFC.     

Performance improvement of diesel autothermal reformer by applying ultrasonic injector for effective fuel delivery

Technology for the reforming of heavy hydrocarbons, such as diesel, to supply hydrogen for fuel cell applications is very attractive and challenging due to its delicate control requirements. The slow reforming kinetics of aromatics contained in diesel, sulfur poisoning, and severe carbon deposition make it difficult to obtain long-term performance with high reforming efficiency. In addition, diesel has a critical mixing problem due to its high boiling point, which results in a fluctuation of reforming efficiency. An ultrasonic injector (UI) have been devised for effective diesel delivery. The UI can atomize diesel into droplets (∼40 μm) by using a piezoelectric transducer and consumes much less power than a heating-type vapourizer. In addition, reforming efficiencies increase by as much as 20% compared with a non-UI reformer under the same operation conditions. Therefore, it appears that effective fuel delivery is linked to the reforming kinetics on the catalyst surface. A 100-W_e, self-sustaining, diesel autothermal reformer using the UI is designed. In addition, the deactivation process of the catalyst, by carbon deposition, is investigated in detail.     

Heat exchanger design for autothermal reforming of diesel

The increasing electrification of vehicles for passenger and heavy duty transport requires the deployment of efficient, low-emission power sources. Auxiliary Power Units (APUs) based on fuels cells offer an excellent solution, especially for supplying power during idling mode. For urban transport applications, gaseous hydrogen appears to be the best fuel option, whereas long-distance applications are better served by a liquid energy carrier. The autothermal reforming of liquid fuels such as diesel presents a simple and efficient method for producing hydrogen for fuel cell APUs. Heat integration for steam generation and air pre-warming are the key elements to a compact autothermal reformer design. With the aid of intense CFD simulations, a reformer construction was achieved with the high power density of 3.3 kW_th/l. Experimental validation indicates high hydrogen concentrations of between 32 and 36%, depending on diesel quality. In combination with already existing results, the newest autothermal reformer (ATR) generation enables the set-up of a complete APU system, fulfilling the U.S. Department of Energy (DOE) targets for fuel cell-based APUs.