Design and development of a diesel and JP-8 logistic fuel processor

The paper describes the design and performance of a breadboard prototype for a 5 kW fuel-processor for powering a solid oxide fuel cell (SOFC) stack. The system was based on a small, modular catalytic Microlith auto-thermal (ATR) reactor with the versatility of operating on diesel, Jet-A or JP-8 fuels. The reforming reactor utilized Microlith substrates and catalyst technology (patented and trademarked). These reactors have demonstrated the capability of efficiently reforming liquid and gaseous hydrocarbon fuels at exceptionally high power densities. The performance characteristics of the auto-thermal reactor (ATR) have been presented along with durability data. The fuel processor integrates fuel preparation, steam generation, sulfur removal, pumps, blowers and controls. The system design was developed via ASPEN^® Engineering Suite process simulation software and was analyzed with reference to system balance requirements. Since the fuel processor has not been integrated with a fuel cell, aspects of thermal integration with the stack have not been specifically addressed.     

An experimental study of methanol autothermal reformation as a method of producing hydrogen for transportation applications

This study investigates autothermal reforming (ATR) of methanol as a method of producing fuel cell-grade hydrogen for transportation applications. From the previous works in autothermal reformation, it is known that while the steam-to-carbon ratio (S/C) may somewhat affect the efficiency of ATR, the oxygen-to-methanol ratio (O₂/CH₃OH) is a more significant parameter in ATR of higher hydrocarbons. Methanol differs from higher hydrocarbons in that it is reformed at relatively low temperatures and, therefore, may respond to O₂/CH₃OH differently from higher hydrocarbons. According to the past studies, the optimum O₂/CH₃OH for ATR of methanol is equal to 0.23. However, this conclusion is based on models which utilize assumptions that are not necessarily accurate, such as complete fuel conversion and ideal reaction products. This study presents experimental data that shows how the ATR reactor efficiency varies with O₂/CH₃OH. The results from this study may serve as a baseline for future research of autothermal reforming of hydrocarbon fuels as a method of producing hydrogen in transportation applications.     

Self-sustained operation of a kWe-class kerosene-reforming processor for solid oxide fuel cells

In this paper, fuel-processing technologies are developed for application in residential power generation (RPG) in solid oxide fuel cells (SOFCs). Kerosene is selected as the fuel because of its high hydrogen density and because of the established infrastructure that already exists in South Korea. A kerosene fuel processor with two different reaction stages, autothermal reforming (ATR) and adsorptive desulfurization reactions, is developed for SOFC operations. ATR is suited to the reforming of liquid hydrocarbon fuels because oxygen-aided reactions can break the aromatics in the fuel and steam can suppress carbon deposition during the reforming reaction. ATR can also be implemented as a self-sustaining reactor due to the exothermicity of the reaction. The kW_e self-sustained kerosene fuel processor, including the desulfurizer, operates for about 250 h in this study. This fuel processor does not require a heat exchanger between the ATR reactor and the desulfurizer or electric equipment for heat supply and fuel or water vaporization because a suitable temperature of the ATR reformate is reached for H₂S adsorption on the ZnO catalyst beds in desulfurizer. Although the CH₄ concentration in the reformate gas of the fuel processor is higher due to the lower temperature of ATR tail gas, SOFCs can directly use CH₄ as a fuel with the addition of sufficient steam feeds (H₂O/CH₄ ≥ 1.5), in contrast to low-temperature fuel cells. The reforming efficiency of the fuel processor is about 60%, and the desulfurizer removed H₂S to a sufficient level to allow for the operation of SOFCs.     

Autothermal reforming of JP8 on a Pt/Rh catalyst: Catalyst durability studies and effects of sulfur

Autothermal reforming (ATR) of commercial grade JP8 was performed on a Pt/Rh catalyst deposited on a monolith. This study investigated catalyst performance under three test conditions: (i) 120 startup and shutdown cycles, (ii) 80 h of continuous operation with sulfur-free fuel, and (iii) 370 h of testing with JP8 containing 125 ppm of sulfur. Axial reactor temperature profiles and gas composition data showed that startup and shutdown cycling had no impact on catalyst performance. When durability testing was done with fuel containing 125 ppm of sulfur, the catalyst deactivated initially, which was reflected by a decrease in H₂ concentration and decrease in fuel conversion. However, after 250 h of operation the activity stabilized at 66% fuel conversion and product concentrations were constant for the remaining 120 h of testing. The presence of sulfur resulted in higher CO selectivity, lower H₂ concentrations, and lower fuel conversions compared to data with sulfur-free fuel. The data suggests that the presence of sulfur primarily affects steam reforming reactions, and CO oxidation. Regeneration was attempted with air and with fuel-lean combustion but initial H₂ yields and carbon selectivity were not achieved.     

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).     

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.     

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.     

Comparative study of gasoline,diesel and biodiesel autothermal reforming over Rh-based FeCrAl-supported composite catalyst

Catalytic autothermal reforming (ATR) of a number of hydrocarbon fuels was studied over composite RhCZ-S catalyst (0.24 wt% Rh supported on structured Ce_0.75Zr_0.25O_2-δ-ƞ-Al₂O₃/FeCrAl carrier). Iso-octane and n-hexadecane as model compounds of gasoline and diesel fuel, respectively, showed similar properties in ATR process, indicating weak influence of molecular weight and branching degree of liquid alkanes on catalyst performance. Biodiesel ATR characteristics were similar to those of n-hexadecane ATR, as the utilized biodiesel predominantly contained alkanes, being products of fatty acid tail fragments hydrogenation. Even in the case of gasoline ATR, sufficient amount of monoaromatics did not influence a lot on the catalyst performance. Diesel ATR showed rather different situation: the catalyst tended to lose activity due to coking, and incomplete fuel conversion was observed. Analysis of unreacted fuel revealed bi- and polyaromatic compounds (mainly naphtalenes and antracenes) were difficult to convert.     

On-board reforming of biodiesel and bioethanol for high temperature PEM fuel cells: Comparison of autothermal reforming and steam reforming

In the 21st century biofuels will play an important role as alternative fuels in the transportation sector. In this paper different reforming options (steam reforming (SR) and autothermal reforming (ATR)) for the on-board conversion of bioethanol and biodiesel into a hydrogen-rich gas suitable for high temperature PEM (HTPEM) fuel cells are investigated using the simulation tool Aspen Plus. Special emphasis is placed on thermal heat integration. Methyl-oleate (C₁₉H₃₆O₂) is chosen as reference substance for biodiesel. Bioethanol is represented by ethanol (C₂H₅OH). For the steam reforming concept with heat integration a maximum fuel processing efficiency of 75.6% (76.3%) is obtained for biodiesel (bioethanol) at S/C = 3. For the autothermal reforming concept with heat integration a maximum fuel processing efficiency of 74.1% (75.1%) is obtained for biodiesel (bioethanol) at S/C = 2 and λ = 0.36 (0.35). Taking into account the better dynamic behaviour and lower system complexity of the reforming concept based on ATR, autothermal reforming in combination with a water gas shift reactor is considered as the preferred option for on-board reforming of biodiesel and bioethanol. Based on the simulation results optimum operating conditions for a novel 5 kW biofuel processor are derived.     

JP-8 catalytic cracking for compact fuel processors

In processing heavier hydrocarbons such as military logistic fuels (JP-4, JP-5, JP-8, and JP-100), kerosene, gasoline, and diesel to produce hydrogen for fuel cell use, several issues arise. First, these fuels have high sulfur content, which can poison and deactivate components of the reforming process and the fuel cell stack; second, these fuels may contain non-volatile residue (NVR), up to 1.5 vol.%, which could potentially accumulate in a fuel processor; and third is the high coking potential of heavy hydrocarbons. Catalytic cracking of a distillate fuel prior to reforming can resolve these issues. Cracking using an appropriate catalyst can convert the various heavy organosulfur species in the fuel to lighter sulfur species such as hydrogen sulfide (H₂S), facilitating subsequent sulfur adsorption on zinc oxide (ZnO). Cracking followed by separation of light cracked gas from heavies effectively eliminates non-volatile aromatic species. Catalytic cracking can also convert heavier hydrocarbons to lights (C₁–C₃) at high conversion, which reduces the potential for coke formation in the reforming process. In this study, two types of catalysts were compared for JP-8 cracking performance: commercially-available zeolite materials similar to catalysts formulated for fluidized catalytic cracking (FCC) processes, and a novel manganese/alumina catalyst, which was previously reported to provide high selectivity to lights and low coke yield. Experiments were designed to test each catalyst’s effectiveness under the high space velocity conditions necessary for use in compact, lightweight fuel processor systems. Cracking conversion results, as well as sulfur and hydrocarbon distributions in the light cracked gas, are presented for the two catalysts to provide a performance comparison.     

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.     

Long-term stability at fuel processing of diesel and kerosene

The long-term stability at autothermal reforming of diesel fuel and kerosene was studied using Juelich's autothermal reformer ATR 9.2, which is equipped with a commercial proprietary RhPt/Al₂O₃–CeO₂ catalyst. The experiment was run for 10,000 h of time on stream at constant reaction conditions with an O₂/C molar ratio of 0.47, a H₂O/C molar ratio of 1.9, and a gas hourly space velocity of 30,000 h⁻¹. Kerosene produced via the gas-to-liquid process and diesel fuel synthesized via the bio-to-liquid route were used. Both fuels were almost free of mass fractions of sulfur and aromatics. The trends for the desired main products of autothermal reforming H₂, CO, CO₂, and CH₄ were almost stable when kerosene was used. When the fuel mass flow was switched to diesel fuel however, different modes of catalyst deactivation occurred (active sites blocked by carbonaceous deposits, sintering processes), leading to a decrease in the concentrations of H₂ and CO₂ with a simultaneous increase in the CO content. This paper defines carbon conversion as the decisive criterion for evaluating the long-term stability during autothermal reforming of kerosene and diesel fuel. Carbon conversion was diminished via three different pathways during the long-term experiment. Undesired byproducts found in the gas phase leaving the reactor had the strongest impact on carbon conversion. These byproducts included ethene, propene, and benzene. Furthermore, a liquid oily residue was detected floating on the condensed unconverted mass flow of water. This happened once during the whole experiment. Finally, undesired organic byproducts were dissolved in the mass flow of unconverted water. These were found to be straight-chain and branched paraffins, esters, alcohols, acids, aldehydes, ketones, etc. Nevertheless, at the end of the long-term experiment, carbon conversion still amounted to more than 98.2%.     

Recent advances in diesel autothermal reformer design

The autothermal reforming of diesel fuel is a catalytic process that runs at temperatures of 700 °C–900 °C. Long-chain hydrocarbon molecules react with steam and O₂, yielding a product gas that mainly consists of CO, CO₂, CH₄ and H₂. H₂ is essential for the operation of fuel cell systems. The Forschungszentrum Jülich has been engaged in the cooperative development of technical apparatus for this reaction to be applied in fuel cell systems over the past 15 years, together with many other research groups worldwide, and this paper deals with reactor ATR 14, which is considered the preliminary end-product of Jülich's research and development in this field. This paper briefly summarizes Jülich's earlier reactor generations and then describes the most recent improvements embodied in the ATR 14. Additionally, the experimental evaluation of the ATR 14 is presented, which demonstrates that it can be operated over a broad load range and with almost complete carbon conversion.     

Purification of metallurgical grade silicon by a solar process

The purification of upgraded metallurgical silicon by extraction of boron and phosphorus was experimentally demonstrated using concentrated solar radiation in the temperature range 1550–1700 °C. The process operated with a flow of Ar at reduced pressure (0.05 atm) for elimination of P, and with a flow of H₂O for elimination of B. Impurity content decreased by a factor of 3 after a 50-min solar treatment, yielding Si samples with final average content of 2.1 ppm_w B and 3.2 ppm_w P.     

Equilibrium model validation through the experiments of methanol autothermal reformation

This study investigates autothermal reforming (ATR) of fuel cell-grade methanol as a method for producing hydrogen for transportation applications. From previous work in autothermal reformation, it is clear that while the steam-to-carbon ratio (S/C) may somewhat affect the efficiency of ATR, the oxygen-to-carbon ratio (O₂/CH₃OH) is a more significant parameter in ATR of higher hydrocarbons. According to past studies, the optimum O₂/CH₃OH for ATR of methanol is equal to 0.23. However, this conclusion is based on models which utilize assumptions that are not necessarily accurate. This study presents experimental data that shows how ATR reactor efficiency varies with O₂/CH₃OH. Reactor efficiency data is compared to equilibrium model outputs in order to quantify the effect of O₂/CH₃OH as well as validate the equilibrium model. The results from this study serve as a baseline for future research of autothermal reforming of hydrocarbon fuels as a method for producing hydrogen in real applications.     

Performance of a PEMFC system integrated with a biogas chemical looping reforming processor: A theoretical analysis and comparison with other fuel processors (steam reforming,partial oxidation and auto-thermal reforming)

In this work, the performance of a PEMFC (proton exchange membrane fuel cell) system integrated with a biogas chemical looping reforming processor is analyzed. The global efficiency is investigated by means of a thermodynamic study and the application of a generalized steady-state electrochemical model. The theoretical analysis is carried out for the commercial fuel cell BCS 500W stack. From literature, chemical looping reforming (CLR) is described as an attractive process only if the system operates at high pressure. However, the present research shows that advantages of the CLR process can be obtained at atmospheric pressure if this technology is integrated with a PEMFC system. The performance of a complete fuel cell system employing a fuel processor based on CLR technology is compared with those achieved when conventional fuel processors (steam reforming (SR), partial oxidation (PO) and auto-thermal reforming (ATR)) are used. In the first part of this paper, the Gibbs energy minimization method is applied to the unit comprising the fuel- and air-reactors in CLR or to the reformer (SR, PO, ATR). The goal is to investigate the characteristics of these different types of reforming process to generate hydrogen from clean model biogas and identify the optimized operating conditions for each process. Then, in the second part of this research, material and energy balances are solved for the complete fuel cell system processing biogas, taking into account the optimized conditions found in the first part. The overall efficiency of the PEMFC stack integrated with the fuel processor is found to be dependent on the required power demand. At low loads, efficiency is around 45%, whereas, at higher power demands, efficiencies around 25% are calculated for all the fuel processors. Simulation results show that, to generate the same molar flow-rate of H₂ to operate the PEMFC stack at a given current, the global process involving SR reactor is by far much more energy demanding than the other technologies. In this case, biogas is burnt in a catalytic combustor to supply the energy required, and there is a concern with respect to CO₂ emissions. The use of fuel processors based on CLR, PO or ATR results in an auto-thermal global process. If CLR based fuel processor is employed, CO₂ can be easily recovered, since air is not mixed with the reformate. In addition, the highest values of voltage and power are achieved when the PEMFC stack is fed on the stream coming from SR and CLR fuel processors. When a H₂ mixture is produced by reforming biogas through PO and ATR technologies, the relative anode overpotential of a single cell is about 55 mV, whereas, with the use of CLR and SR processes, this value is reduced to ∼37 and 24 mV, respectively. In this way, CLR can be seen as an advantageous reforming technology, since it allows that the global process can be operated under auto-thermal conditions and, at the same time, it allows the PEMFC stack to achieve values of voltage and power closer to those obtained when SR fuel processors are used. Thus, efforts on the development of fuel processors based on CLR technology operating at atmospheric pressure can be considered by future researchers. In the case of biogas, the CO₂ captured can produce additional economical benefits in a ‘carbon market’.     

Suppression of ethylene-induced carbon deposition in diesel autothermal reforming

Diesel has high-hydrogen density and well-developed infrastructure, which are beneficial properties for fuel cell commercialization. However, diesel reforming poses several technical difficulties, including carbon deposition, sulfur poisoning, and fuel delivery. Specifically, carbon deposition can cause catastrophic failures in diesel reformers. In diesel reformate gas, the concentration of ethylene, a carbon precursor, is higher than other shorter hydrocarbons (C₂–C₄). In this study, we examine the cause of ethylene formation in diesel reforming. Ethylene formation can be closely related to paraffins' decomposition from homogeneous reaction. A portion of the catalyst active sites can become occupied with aromatic compounds, degrading the activity of the catalyst. Thus, a portion of the paraffins is decomposed via non-catalytic, homogeneous reactions, accounting for much of the observed ethylene formation. In this study, reforming conditions and fuel delivery method are investigated with respect to ethylene formation. By using a diesel ultrasonic injector, reactant mixing was enhanced, resulting in suppression of ethylene formation. This subsequently inhibited the ethylene-induced carbon deposition and improved the long-term performance of diesel ATR (autothermal reforming).     

Comparative study of fuel gas production for SOFC from steam and supercritical-water reforming of bioethanol

Theoretical study of fuel gas (H₂ + CO) production for SOFC from bioethanol was carried out to compare performances between two reforming technologies, including steam reforming (SR) and supercritical-water reforming (SCWR). It demonstrates that the fuel gas productions are comparable among the two reforming systems; however, SCWR requires the operation at much higher temperature and pressure than SR. The maximum hydrogen yield can be obtained at 850 K, atmospheric pressure, ethanol to water molar feed ratio of 1:20 for SR system and at 1300 K, 22.1 MPa, and ethanol to water feed ratio of 1:20 for SCWR. The use of a distillation column to purify the bioethanol feed was proven to improve the fuel conversion efficiency of both systems. The analysis reveals that SCWR is a promising system for fuel production for SOFC when a gas turbine is incorporated to the system for energy recovery. Further, it is not necessary to distil bioethanol to obtain too high ethanol recovery (i.e. >90%) as higher energy consumption at the distillation column could lead to lower overall thermal efficiency.     

Autothermal reforming of ethanol on noble metal catalysts

Autothermal reforming of ethanol on zirconia-supported Rh and Pt mono- and bimetallic catalysts (0.5 wt-% total metal loading) was studied as a source of H₂-rich gas for fuel cells. The results were compared with those obtained on a commercial steam reforming catalyst (15 wt-% NiO/Al₂O₃). The Rh-containing catalysts exhibited the highest selectivity for H₂ production and were stable in 24 h experiments. The formation of carbonaceous deposits was lower on the noble metal catalysts than on the commercial NiO/Al₂O₃ catalyst. Thus, the Rh-containing catalysts are more suitable than the commercial NiO/Al₂O₃ catalysts for the ATR of ethanol.     

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.