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.     

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%.     

Rapid start-up strategy of 1 kWe diesel reformer by solid oxide fuel cell integration

A rapid start-up strategy of a diesel reformer for on-board fuel cell applications was developed by fuel cell integration. With the integration with metal-supported solid oxide fuel cell which has high thermal shock resistance, a simpler and faster start-up protocol of the diesel reformer was obtained compared to that of the independent reformer setup without considering fuel cell integration. A reformer without fuel cell integration showed unstable reactor temperatures during the start-up process, which affects the reforming catalyst durability. By utilizing waste heat from the fuel cell stack, steam required at the diesel autothermal reforming could be stably provided during the start-up process. The developed diesel reformer was thermally sustainable after the initial heat-up process. As a result, the overall start-up time of the reformer after the diesel supply was reduced to 9 min from the diesel supply compared to 22 min without fuel cell integration.     

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.     

Fast start-up of a diesel fuel processor for PEM fuel cells

Fuel cell systems based on liquid fuels are particularly suitable for auxiliary power generation due to the high energy density of the fuel and its easy storage. Together with industrial partners, Oel-Waerme-Institut is developing a 3 kW_el PEM fuel cell system based on diesel steam reforming to be applied as an APU for caravans and yachts. The start-up time of a fuel cell APU is of crucial importance since a buffer battery has to supply electric power until the system is ready to take over. Therefore, the start-up time directly affects the battery capacity and consequently the system size, weight, and cost.     

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.     

Effects of fuel cell anode recycle on catalytic fuel reforming

The presence of steam in the reactant gas of a catalytic fuel reformer decreases the formation of carbon, minimizing catalyst deactivation. However, the operation of the reformer without supplemental water reduces the size, weight, cost, and overall complexity of the system. The work presented here examines experimentally two options for adding steam to the reformer inlet: (I) recycle of a simulated fuel cell anode exit gas (comprised of mainly CO₂, H₂O, and N₂ and some H₂ and CO) and (II) recycle of the reformate from the reformer exit back to the reformer inlet (mainly comprised of H₂, CO, and N₂ and some H₂O and CO₂). As expected, anode gas recycle reduced the carbon formation and increased the hydrogen concentration in the reformate. However, reformer recycle was not as effective due principally to the lower water content in the reformate compared to the anode gas. In fact, reformate recycle showed slightly increased carbon formation compared to no recycle. In an attempt to understand the effects of individual gases in these recycle streams (H₂, CO, CO₂, N₂, and H₂O), individual gas species were independently introduced to the reformer feed.     

Quantitative analysis of sub-ppm traces of hydrocarbons in the product gas from diesel reforming

The autothermal reforming of middle distillates is a favored reforming technique for fuel cell-based auxiliary power units (APUs) in the transport sector. The efforts made in recent years to produce a high quality reformate have been reflected in a variety of improvements to the reactors and mode of operation of the fuel processing systems. By these means, the concentrations of contaminants, especially traces of hydrocarbons in the gas phase, frequently drops below the previous detection limit. In this paper, a new GC/MS method is developed to reduce the detection limit of the analytics into the sub-ppm range. This work is intended to serve as a valuable step to showing which traces of hydrocarbons can still be qualitatively and quantitatively expected in a high quality reformate. This contribution may help determine the multitude of hydrocarbonous substances that can have a detrimental long-term effect on catalysts and adsorbents in a fuel cell-based APU system operated with middle distillates.     

Catalytic burner with internal steam generation for a fuel-cell-based auxiliary power unit for middle distillates

A catalytic burner (CAB) was developed, which utilizes the anode off-gas of a high temperature polymer electrolyte fuel cell (HT-PEFC). This CAB has two functions within the HT-PEFC-system: It has to convert completely all combustible components including methane and carbon monoxide, even in the low ppm range and it has to provide steam to the autothermal reformer (ATR). Thereby it increases the system's overall efficiency.     

Analysis of potential fuel consumption and emissions reductions from fuel cell auxiliary power units (APUs) in long-haul trucks

The idling of heavy-duty trucks results in additional emissions, fuel consumption, and cost. Small fuel cell auxiliary power units (APUs) (now in development) are promising alternatives to idling the main engine. A solid oxide fuel cell (SOFC) APU is particularly attractive, because in conjunction with a reformer, it could operate on widely available diesel fuel. Because fuel cell APUs may not only reduce environmental impacts, but also reduce operating costs, this application has been cited as an attractive early market niche for fuel cells. Our objective is to determine whether SOFC APUs are likely to soon be economically feasible for those trucks that idle most and what energy and environmental benefits are probable. We estimate the APU market size as a function of APU costs by applying Monte Carlo sampling and net present value (NPV) economic analysis to our ADVISOR-based vehicle fuel consumption model. Emissions and fuel economy benefits estimates are then presented as a function of varying market penetration levels, assuming installation on only new vehicles and removal at the end of the 4-year SOFC lifecycle. With modest economic incentives from government and continuing fuel cell technology improvements, we find that SOFC APUs might be economically feasible for up to 15% of the long-haul truck population (60,000 trucks) in the United States in the 2015 time frame, resulting in a 30% reduction of heavy-duty truck fuel use during overnight idling and a 40% reduction in oxides of nitrogen (NO_x) produced during idling.     

Micro methanol reformer combined with a catalytic combustor for a PEM fuel cell

This paper presents the development of a micro methanol reformer for portable fuel cell applications. The micro reformer consists of a methanol steam reforming reactor, catalytic combustor, and heat exchanger in-between. Cu/ZnO was selected as a catalyst for a methanol steam reforming and Pt for a catalytic combustion of hydrogen with air. Porous ceramic material was used as a catalyst support due to the large surface area and thermal stability. Photosensitive glass wafer was selected as a structural material because of its thermal and chemical stabilities. Performance of the reformer was measured at various test conditions and the results showed a good agreement with the three-dimensional analysis of the reacting flow. Considering the energy balance of the reformer/combustor model, the off-gas of fuel cell can be recycled as a feed of the combustor. The catalytic combustor generated the sufficient amount of heat to sustain the steam reforming of methanol. The conversion of methanol was 95.7% and the hydrogen flow of 53.7 ml/min was produced including 1.24% carbon monoxide. The generated hydrogen was the sufficient amount to operate 4.5 W polymer electrolyte membrane fuel cells.     

Static and dynamic modeling of a diesel fuel processing unit for polymer electrolyte fuel cell supply

This article introduces the energetic macroscopic representation (EMR) as approach for the dynamic modeling of a diesel fuel processing unit. The EMR is the first step toward model-based control structure development. The autothermal fuel processing system containing: heat exchanger, reformer, desulfurization, water gas shift, preferential oxidation and condensation is divided into a multitude simple subblocks. Each subblock describes an elementary step of the fuel conversion, several of these blocks may occur in a single module. Calculations are carried out using two basic principles: mass and energy balances. For model-based control development, it is imperative that the model represents dynamic behavior, therefore temperature and pressure dynamics are taken into account in the model. It is shown that the model is capable to predict the stationary behavior of the entire fuel processing unit correctly by comparison with given data. Predictions regarding reformer heat up, temperature and pressure dynamics are also provided.     

Analysis of the market for diesel PEM fuel cell auxiliary power units onboard long-haul trucks and of its implications for the large-scale adoption of PEM FCs

Proton exchange membrane fuel cells (PEM FCs) offer a promising alternative to internal combustion engines in road transport. During the last decade PEM FC research, development and demonstration (RD&D) activities have been steadily increasing worldwide, and targets have been set to begin their commercialisation in road transport by 2015–2020. However, there still is considerable uncertainty on whether these targets will actually be met. The picture is complex and market and technology issues are closely interlinked; investment in RD&D projects is essential but not sufficient; the development of suitable early markets is also necessary and policy is set to play an important role. Auxiliary power units (APUs) are generally regarded as one important early market for FCs in transport. This paper analyses the possible future market for diesel PEM FC APUs onboard long-haul trucks and its implications for the development of PEM FCs in general. The analysis, part of the project HyTRAN (EC Contract no. 502577), is aided by the use of a dynamic simulation model of technology and markets developed by the author. Results suggest that an interesting window of opportunity for diesel PEM FC APUs exists but this is subject to additional research particularly targeted at the rapid development of fuel processors.     

A compact integrated fuel-processing system for proton exchange membrane fuel cells

A compact integrated fuel-processing system consisting of a plate-fin reformer (PFR) and a multi-stage preferential oxidation reactor is designed in this paper. The PFR, which was based on a plate-fin heat exchanger, is very compact, and reactant vaporization, methanol steam reforming and combustion are all integrated in it. Both internal plate-fins and external catalytic combustion were used to enhance heat transfer of the reformer, which offers both high methanol conversion ratio and low CO concentration, so that the water–gas shift reactor, which provides primary CO cleanup, is not necessary in this fuel-processing system. This will result in simplification of the fuel-processing system design and capital cost reduction. The performance of the main components in the fuel-processing system has been investigated. The axial temperatures of the different chambers in PFR were uniform, and the temperatures at the inlet and outlet of the PROX reactors were controlled strictly by plate-fin exchangers so that it could minimize parasitic hydrogen oxidation. In addition, the results indicated that this fuel-processing system can provide a high concentration of hydrogen and the system efficiency is always maintained above 75%. It is further demonstrated that the fuel-processing system could be operated autothermally and exhibited good test stability.     

Integrated standalone hybrid solar PV,fuel cell and diesel generator power system for battery or supercapacitor storage systems in Khorfakkan,United Arab Emirates

Renewable energy resources play a very important rule these days to assist the conventional energy systems for doing its function in the UAE due to high greenhouse gas (GHG) emissions and energy demand. In this paper, the analysis and performance of integrated standalone hybrid solar PV, fuel cell and diesel generator power system with battery energy storage system (BESS) or supercapacitor energy storage system (SCESS) in Khorfakkan city, Sharjah were presented. HOMER Pro software was used to model and simulate the hybrid energy system (HES) based on the daily energy consumption for Khorfakkan city. The simulation results show that using SCESS as an energy storage system will help the performance of HES based on the Levelized cost of energy (LCOE) and greenhouse gas (GHG) emissions. The HES with SCESS has renewable fraction (68.1%) and 0.346 $/kWh LCOE. The HES meets the annual AC primary load of the city (13.6 GWh) with negligible electricity excess and with an unmet electrical load of 1.38%. The reduction in GHG emissions for HES with SCESS was 83.2%, equivalent to saving 814,428 gallons of diesel.     

Design of compact methanol reformer for hydrogen with low CO for the fuel cell power generation

The effect of the heat transfer area and the thermal conductivity of the reactor materials are evaluated with three identical structured reactors having multiple columned-catalyst bed and using three different reactor materials, aluminum alloy, brass and stainless steel. A series of compact methanol reformers are then designed and fabricated with the use of large reactor surface area in catalyst beds and high heat transfer constant to produce hydrogen fuel with 2–4 ppm of CO for the fuel cell (FC) power generation. The same design principle is successfully used for easy scale up of the reactor capacity from 250 L/h to 10,000 L/h. This low CO hydrogen (68–70%) used as the fuel for the fuel cell power generation provides a very competitive cost of hydrogen and electric power, $0.20–0.23/m³ of H₂ and $0.196/KWh, respectively.     

A survey of nickel‐based catalysts and monolithic reformers of the onboard fuel reforming system for fuel cell APU applications

This paper presented a detailed survey of the catalysts for fuel reforming, including nickel‐based catalysts with alkalis, alkaline earths, rare earths, noble metals, and hydrotalcite‐type precursors. All these additions can enhance the Ni catalysts in regarding with activity, coke resistivity, and sintering resistivity. Smaller Ni particle size, more even particle dispersion, and less free NiO and NiAl₂O₄ can be obtained with these additions. Physicochemical characterization, activity, stability, coke resistance, and the effects of different precursors were summarized and compared. Development of the most commonly used monolithic reformer was also summarized, and different reformer configurations were presented chronologically. Homogeneous mixing of the completely evaporated fuel with air and steam, as well as uniform distribution of the mixture flow are the two main concerns in reformer design. Reforming energy conversion efficiency around 80%, power density above 3 kW/L, and specific power above 3 kW/kg are also reported in the most recent monolithic reformer. Copyright © 2016 John Wiley & Sons, Ltd.     

An optimal method of the energy consumption for fuel cell hybrid tram

Energy conservation running for vehicle has been a promising research hotspot in the many universities and research institutions. In order to improve the energy utilization rate in the vehicle running process, an optimization method of the energy consumption and recycle based on fuel cell (FC)/supercapacitor (SC) hybrid tram is proposed in this paper. In the method, a tram operation energy management strategy based on Pontriagin's minimum principle (PMP) can effectively was proposed what adjusts the output power of FC and SC and decreases hydrogen consumption. In addition, a tram breaking velocity curve with maximum energy recovery and the allocation strategy between regenerative force and mechanical braking force be also studied in this paper. According to the simulation results, it could be obtained that the Energy conservation rate is about 5% higher than the un-optimized, it will effectively decrease hydrogen consumption.     

Research on ADHDP energy management strategy for fuel cell hybrid power system

Fuel cell hybrid power system is a prospective power source for electrical vehicles. To reduce hydrogen consumption and enhance dynamic performance of the system, Action Dependent Heuristic Dynamic Programming (ADHDP) energy management strategy for the fuel cell hybrid power system was proposed. Firstly, topology of the system was analyzed and mathematical model was established through mechanism analysis. Secondly, framework of the ADHDP algorithm was presented, and it was followed by training algorithm for evaluating network and executing network of ADHDP based on Back Propagation (BP) algorithm. Finally, hardware-in-the-loop (HIL) simulation of the fuel cell hybrid power system was carried out to demonstrate the proposed ADHDP algorithm under real operating conditions. The results show that evaluating network and executing network of ADHDP have good convergence performance under different operating conditions. Compared with the other algorithms, the proposed ADHDP energy management strategy has better fuel economy and dynamic performance.     

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.