Shorter Start-up Time Research Articles

Sol-Gel Thin-Film Electrolyte Anode-Supported SOFC – From Layer Development To Stack Testing

One of the current R&D projects on solid oxide fuel cells concerns the reduction of the operation temperature. Nowadays stacks with anode-supported cells and an LSCF-cathode operate typically at a mean temperature of 700°C. The minimum temperature for SOFC using natural gas is approx. 650°C due to reforming limitations. Reducing temperatures below 600°C leads to lower costs, shorter start-up time and thus in-time power delivery by the system (e.g. for auxiliary power units). Forschungszentrum Jülich is also working on the development of an SOFC operating at 400°C for special applications, which can be fueled either with hydrogen (produced by, for example, electrolysis using renewable energy) or with reformate gas based on, for instance, ethanol/methanol. The main challenge for using the SOFC at such low temperatures is, besides electrode activities, overcoming the resistances, especially the ohmic resistance of the electrolyte. This can be achieved in two ways: by introducing materials which show higher oxygen diffusivity or by using the classical materials and minimizing the electrolyte thickness down to values below 2µm.

Characterization and quantification of anammox start-up in UASB reactors seeded with conventional activated sludge

The start-up of anammox process inoculated with anaerobic granular sludge and nitritation sludge were carefully investigated in two upflow anaerobic sludge blanket (UASB) reactors. Three major bioprocesses related in anammox start-up i.e. anammox, denitrification and cell lysis, were quantified in both reaction and microbial growth aspects in the four consecutive phases namely cell lysis phase, lag phase, activity elevation phase and stationary phase. The results showed that anammox was negligible when cell lysis was predominant in the reactors; however, the density of anammox bacteria objectively increased in this phase due to the biomass reduction caused by hydrolysis. During lag phase, poor anammox was detected; while denitrification and cell lysis were the two leading reactions. Anammox performance of the reactors was significantly enhanced in activity elevation phase. Denitrification continuously weakened in stationary phase and anammox gradually became the dominant reaction. Nevertheless, heterotrophic denitrification still predominated throughout the start-up course due to the extremely low growth rate of anammox bacteria. Results also suggested that the inoculation strategy using nitritation sludge as the main inoculum commixing with anaerobic granular sludge could contribute to the relatively shorter start-up time and better reactor performance. Such an alternative may prove effective strategy for full-scale application of anammox process.

Using a glass fiber separator in a single-chamber air-cathode microbial fuel cell shortens start-up time and improves anode performance at ambient and mesophilic temperatures

A shorter start-up time and highly negative anode potentials are needed to improve single-chamber air-cathode microbial fuel cells (MFCs). Using a glass fiber separator reduced the start-up time from 10d to 8d at 20°C, and from 4d to 2d at 30°C, and enhanced coulombic efficiency (CE) from <60% to 89% (20°C) and 87% (30°C). Separators also reduced anode potentials by 20–190mV, charge transfer resistances by 76% (20°C) and 19% (30°C), and increased CV peak currents by 24% (20°C) and 8% (30°C) and the potential range for redox activity (−0.55 to 0.10mV vs. −0.49 to −0.24mV at 20°C). Using a glass fiber separator in an air-cathode MFC, combined with inoculation at a mesophilic temperature, are excellent strategies to shorten start-up time and to enhance anode performance and CE.

The analyses of the start-up process of a planar, anode-supported solid oxide fuel cell using three different start-up procedures

Three start-up procedures for an anode-supported planar SOFC are proposed and investigated numerically in the present study. The first is to introduce the inlet fuel at the operation temperature after the heat-up process is completed. The second is to incorporate the anode-recycling mechanism into the start-up process. The third is to fix the difference between the inlet-fuel temperature and the cell minimum temperature. The numerical results obtained from the present study show that the effective maximum absolute temperature-gradient is exhibited in the early stage of the start-up process. For the present investigated SOFC configuration, the required start-up time for the case using methane is 3.2-fold longer than that using hydrogen. The effective maximum absolute temperature-gradient for the case using hydrogen is 2.2-fold larger than that utilizing methane. The endothermic internal reforming reaction of methane has a positive effect on the accommodation of the temperature uniformity during the start-up process. The anode-recycling mechanism significantly reduces the start-up time For the fixed-temperature-difference start-up procedure, a properly selected temperature difference may lead to a smaller effective maximum absolute temperature-gradient in the early stage and a shorter start-up time by accelerating the start-up pace in the later stage.

Experimental study of the start-up of a fuel cell stack for backup power application

The transient response of proton exchange membrane fuel cells during start-up is an important issue for backup power systems which require a very short start-up time in order to limit the use of batteries during a blackout. The start-up procedure of a ten cells stack was studied: in the first stage the cathode channel initially filled with nitrogen was supplied with oxygen in open circuit then in the second stage it was connected to the load. The influences of the current time-profile (step or ramp), the cell voltage at the connection and the gas flow rates on the voltage variation were investigated. It was found that the voltage value during the filling of the cathode is not sufficient to determine which fraction of the cathode was filled with oxygen. In most cases, high oxygen flow rates allow reducing the start-up time of the stack. Furthermore, for fixed current density and stoichiometric coefficients it was found that a minimum start-up time exits. The analysis of transient response to current steps showed that around 70% of the maximum electrical power was available less than 2 s after the beginning of the start-up procedure.

Performances analysis of a compact kW-scale ATR reactor for distributed H2 production

The distributed production of hydrogen takes on a growing consensus among the different methods for feeding fuel cells. The auto-thermal reforming of hydrocarbons is a candidate as the best method for producing hydrogen on a small scale. Since auto-thermal reforming reactor is fed with hydrocarbon, water and air, their mixing may play a fundamental role on the final process performances, by influencing hydrocarbon conversion, reaction selectivity, and hydrogen production. To obtain a very compact reaction system, reactants pre-heating and products cooling were realized in a special heat exchange system, fully integrated in the reactor. To study the reaction trend along the catalytic bed, a multipoint analysis system was set-up, allowing to monitor both temperature and composition in several points of catalytic bed, and then in several space velocity conditions. The preliminary tests showed very short start-up time, and fast response to the feed variations, confirming that the proposed reaction system is an interesting solution for distributed and non-continuous hydrogen production.

Internal currents in response to a load change during fuel cell start-up

The transient response of proton exchange membrane fuel cells during start-up is an important issue for backup power systems. These require a very short start-up time which limits the use of batteries during a blackout. In this study the fuel cell was initially inerted with nitrogen at the cathode and thus the start-up procedures occurred in two stages: gas supply in open-circuit and load connection. The influence of the current time-profile, the cell voltage at the connection and the gas flow rates on the voltage variation were investigated using a segmented fuel cell permitting the measurements of the internal local currents. We found that the voltage during the filling of the cathode is not sufficient to determine which fraction of the cathode was filled with oxygen. In the case of a step change in current, the start-up time decreases as the voltage at the moment the cell is connected increases. In response to a ramp, the asymptotic power value is reached quickly.

A Microfluidic Reactor for Energy Applications

Miniature microbial fuel cells have recently drawn lots of attention as portable power generation devices due to their short startup time and environmentally-friendly process which could be used for powering small integrated biosensors. We designed and fabricated a microbial fuel cell in a microfluidic platform. The device was made in polydimethylsiloxane with a volume of 4 µL and consisted of two carbon cloth electrodes and proton exchange membrane. Shewanella Oneidensis MR-1 was chosen to be the electrogenic bacterial strain and inoculated into the anode chamber. Ferricyanide was used as the catholyte and pumped into the cathode chamber at a constant flow rate during the experiment. The miniature microbial fuel cell generated a maximum current of 2.59 µA and had a significantly short startup time.

Future Power Plant Requirements

AbstractDie Dynamik der Stromerzeugung aus Photovoltaik‐ und Windkraftanlagen und die Qualität der Prognosen insbesondere von Windstrom bestimmen die Anforderungen an die Dynamik konventioneller Kraftwerke. Moderne Kohle‐ und GuD‐Kraftwerke sind flexibel und können zumindest mittelfristig die fluktuierende Einspeisung aus erneuerbaren Energien (EE) ausgleichen. GuD‐Kraftwerke weisen deutlich kürzere Anfahrtszeiten auf. Mit der zukünftig geringeren Kraftwerksauslastung sind die niedrigeren Investitionskosten der wesentliche Vorteil von GuD‐Kraftwerken. Weiter steigende Anteile EE benötigen Speicher. Aufgrund der hohen Energiedichte eignen sich synthetische Energieträger für eine jahreszeitliche Speicherung. Vergasungskraftwerke weisen gegenüber dem heutigen Dampfkraftwerk für feste Brennstoffe Vorteile auf.

Treatability study of using low frequency ultrasonic pretreatment to augment continuous biohydrogen production

Low frequency ultrasonic treatment was investigated to enhance hydrogen production by bacteria under both batch and continuous operation. Optimal ultrasonic time and intensity as examined in batch experiments were found to be 10 s and 100 W, respectively. Hydrogen production was increased by 20% while ultrasonic treatment could effectively shorten batch test reaction times. Using these optimized conditions, continuous experiments were conducted in two parallel expanded granular sludge bed (EGSB) reactors. The ultrasonic treated EGSB reactor obtained a specific hydrogen production rate of 4.38 L/g VSS·d, which was 32% higher than that in the control reactor. Ethanol-type fermentation was achieved at a faster rate and with a 72.7% shorter startup time using ultrasonic treatment. Microbial activity under ultrasonic treatment was shown to resist lower pH and to maintain satisfactory hydrogen production.

Effects of activated sludge flocs and pellets seeds on aerobic granule properties

Aerobic granules seeded with activated sludge flocs and pellets (obtained from activated sludge flocfs) were cultivated in two sequencing batch reactors and their characteristics were compared. Compared with granules seeded with activated sludge flocs, those seeded with pellets had shorter start-up time, larger diameter, better chemical oxygen demand removal efficiency, and higher hydrophobicity, suspended solid concentration, and Mg 2+ content. The different inocula led the granule surface with different microbial morphologies, but did not result in different distribution patterns of extracellular polymeric substances and cells. The anaerobic bacterium Anoxybacillus sp. was detected in the granules seeded with pellets. These results highlighted the advantage of pellet over activated sludge floc as the seed for aerobic granulation and wastewater treatment.

Novel Approaches for the Integration of High Temperature PEM Fuel Cells Into Aircrafts

Reduced greenhouse gas emissions via improved energy efficiency represent the ultimate challenge for the energy economy of the future. In this context, fuel cells for power generation aboard aircrafts have a promising potential to effectively contribute to the greening of air transportation. They can simplify today’s aircraft comprising electric, pneumatic, and hydraulic systems toward a more electric airplane. Although they are not considered in the short term as an alternative propulsion system for commercial aviation, many efforts are being devoted to their use as auxiliary power units and even aiming to build a distributed power network that might alleviate duties of the engine driven generators. In addition they allow new functions such as zero emission during taxiing on ground and/or increase safety by replacing the emergency ram-air turbine (RAT) by a fuel cell based emergency power generator. The present paper focuses on the effort that Compañía Española de Sistemas Aeronáuticos (CESA) is putting into the development of an aeronautical fuel cell system based on a high-temperature PEMFC covering all aspects from fundamental research in materials and processes to final integration concepts as a function of different architectures. A great deal of time and effort has been invested to overcome the challenges of PEM fuel cell operation at high temperatures. Among the advantages of these systems are the enhancement of electrochemical kinetics, the simplification of water management and cooling, the recovery of wasted heat, and the possibility of utilizing reformed hydrogen thanks to higher tolerance to impurities. However, new problems arise with the high-temperature concept that must be addressed such as structural and chemical degradation of materials at elevated temperatures. One of the aeronautical applications, where a fuel cell has an important role to play in the short term is the emergency power unit. Weight and mechanical complexity of traditional ram-air turbines could be drastically reduced by the introduction of a hydrogen fueled system. In addition, the output of the fuel cell is aircraft’s speed independent. This means additional power supply in case of emergency allowing a safer landing of the aircraft. However, a RAT replacement must overcome the specific difficulties concerning the very short start-up times allowed and the heating/cooling strategies to quickly raise the temperature to elevated levels and accurately maintaining the optimum operating range once in service.

Experimental Investigation of Heat Transfer Enhancement of the Heat Pipe Using CuO-Water Nanofluid

This paper presents an experimental investigation of the heat transfer characteristics of the heat pipe with CuO-water nanofluid. For this purpose, CuO nanoparticles of 30 nm size were dispersed in distilled water to form stable suspension containing 0.1% ~ 2.0% mass concentrations of nanoparticles, and then the heat pipe was produced after CuO-water nanofluid was added in it as the working fluid. Experimental results show that the use of CuO-water nanofluid hold a lower start-up temperature and shorter start-up time for the evaporation section of the heat pipe compared to distilled water. Their heat transfer performance of the evaporation section and condenser section has been improved than that of distilled water. The heat transfer coefficient of nanofluid is higher than that of the base liquid and found to increase by 29.4% and 125.0% for the mass concentration of 0.5% compared with the heat pipe using distilled water while the input power ranging from 15W to 45W. By examining the thermal resistance, it was found that the thermal resistance has been significantly decreased compared with the heat pipe with distilled water. The thermal resistance of heat pipe using CuO-water nanofluid at a mass concentration of 0.5% is 0.36K/W when the input power is 45W, while the thermal resistance of heat pipe using distilled water is 0.80K/W. Further analysis indicates that the heat pipe using CuO-water nanofluid at 1.0% mass concentrations has the best heat transfer performance.

Bayesian statistical treatment of the fluorescence of AFLP bands leads to accurate genetic structure inference

Ever since the introduction of allozymes in the 1960s, evolutionary biologists and ecologists have continued to search for more powerful molecular markers to estimate important parameters such as effective population size and migration rates and to make inferences about the demographic history of populations, the relationships between individuals and the genetic architecture of phenotypic variation (Bensch & Akesson 2005; Bonin et al. 2007). Choosing a marker requires a thorough consideration of the trade-offs associated with the different techniques and the type of data obtained from them. Some markers can be very informative but require substantial amounts of start-up time (e.g. microsatellites), while others require very little time but are much less polymorphic. Amplified fragment length polymorphism (AFLP) is a firmly established molecular marker technique that falls in this latter category. AFLPs are widely distributed throughout the genome and can be used on organisms for which there is no a priori sequence information (Meudt & Clarke 2007). These properties together with their moderate cost and short start-up time have made them the method of choice for many molecular ecology studies of wild species (Bensch & Akesson 2005). However, they have a major disadvantage, they are dominant. This represents a very important limitation because many statistical genetics methods appropriate for molecular ecology studies require the use of codominant markers. In this issue, Foll et al. (2010) present an innovative hierarchical Bayesian method that overcomes this limitation. The proposed approach represents a comprehensive statistical treatment of the fluorescence of AFLP bands and leads to accurate inferences about the genetic structure of natural populations. Besides allowing a quasi-codominant treatment of AFLPs, this new method also solves the difficult problems posed by subjectivity in the scoring of AFLP bands.

Treatment of food processing wastewater in a full-scale jet biogas internal loop anaerobic fluidized bed reactor

A full-scale jet biogas internal loop anaerobic fluidized bed (JBILAFB) reactor, which requires low energy input and allows enhanced mass transfer, was constructed for the treatment of food processing wastewater. This reactor has an active volume of 798 m(3) and can treat 33.3 m(3) wastewater per hour. After pre-treating the raw wastewater by settling, oil separating and coagulation-air floating processes, the reactor was operated with a relatively shorter start-up time (55 days). Samples for the influent and effluent of the JBILAFB reactor were taken and analyzed daily for the whole process including both the start-up and stable running periods. When the volumetric COD loading fluctuated in the range of 1.6-5.6 kg COD m(-3) day(-1), the COD removal efficiency, the volatile fatty acid(VFA)/alkalinity ratio, the maximum biogas production and the content of CH(4) in total biogas of the reactor were found to be 80.1 ± 5%, 0.2-0.5, 348.5 m(3 )day(-1) and 94.5 ± 2.5%, respectively. Furthermore, the scanning electron microscope (SEM) results showed that anaerobic granular sludge and microorganism particles with biofilm coexisted in the reactor, and that the bacteria mainly in bacilli and cocci were observed as predominant species. All the data demonstrated that the enhanced mass transfer for gas, liquid and solid phases was achieved, and that the formation of microorganism granules and the removal of inhibitors increased the stability of the system.

Electrical enhancement of DMFC by Pt–M/C catalyst-assisted PVD

Direct methanol fuel cells (DMFC) are studied extensively owing to their simple cell configuration, high volume energy density, short start-up time and operation reliability. However, the major drawbacks include high production cost, catalyst and methanol crossover poisoning. This study presents a simple method for Pt–M/C catalyst preparation using a magnetron sputtering (MS) and metal-plasma ion implantation (MPII) technique. The Pt catalysts were sputtered onto a gas diffusion layer (GDL), followed by implanting Cr, Fe, Ni, and Mo catalysts using MPII (accelerating voltage is 20 kV and implantation fluence is 1 × 10 16 ions/cm 2). The crystallinity and microstructure of the catalyst films were analyzed using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electronic microscopy (SEM) and transmission electronic microscopy (TEM). The cell performance was tested using potential stat/galvano station. The results indicate that the membrane electrode assembly for Pt–Ni/C, Pt–Fe/C and Pt–Cr/C catalysts can enhance DMFC cell performance, compared with traditional Pt/C and Pt–Ru/C. The maximum Pt–Ni/C power density is 2.4 mW/cm 2 with an open circuit voltage (OCV) 0.334 V when tested at a methanol concentration of 1 M.

Plains End Power Station – gas reciprocating engines in a grid-stability power plant

The Plains End Power Station located in Colorado, USA, is one of the largest power plants with reciprocating engines as prime movers. In two units of this power plant there are totally 34 engine-generator sets driven by Wartsila reciprocating engines. Total installed capacity of the plant is ca. 230 MW. Plains End Power Station serves a source of peakload power and grid-stability plant, which is particularly important in an area with high wind power capacity. Features of the used engines like their high operational flexibility and very short start-up time, combined with the layout of multiple parallel gensets of relatively small outputs, greatly facilitates this type of operations, allowing to quickly and reliably supply amount of power currently needed for grid balancing. The paper presents operational experience and specific operational conditions of a peakload and grid-stability plant using gas reciprocating engines.

Base-Load Cycling on a System With Significant Wind Penetration

Certain developments in the electricity sector may result in suboptimal operation of base-load generating units in countries worldwide. Despite the fact they were not designed to operate in a flexible manner, increasing penetration of variable power sources coupled with the deregulation of the electricity sector could lead to these base-load units being shut down or operated at part-load levels more often. This cycling operation would have onerous effects on the components of these units and potentially lead to increased outages and significant costs. This paper shows the serious impact increasing levels of wind power will have on the operation of base-load units. Those base-load units which are not large contributors of primary reserve to the system and have relatively shorter start-up times were found to be the most impacted as wind penetration increases. A sensitivity analysis shows the presence of storage or interconnection on a power system actually exacerbates base-load cycling until very high levels of wind power are reached. Finally, it is shown that if the total cycling costs of the individual base-load units are taken into consideration in the scheduling model, subsequent cycling operation can be reduced.

Microbial and Physicochemical Characteristics of Compact Anaerobic Ammonium-Oxidizing Granules in an Upflow Anaerobic Sludge Blanket Reactor

Anaerobic ammonium oxidation (anammox) is a promising new process to treat high-strength nitrogenous wastewater. Due to the low growth rate of anaerobic ammonium-oxidizing bacteria, efficient biomass retention is essential for reactor operation. Therefore, we studied the settling ability and community composition of the anaerobic ammonium-oxidizing granules, which were cultivated in an upflow anaerobic sludge blanket (UASB) reactor seeded with aerobic granules. With this seed, the start-up period was less than 160 days at a NH(4)(+)-N removal efficiency of 94% and a loading rate of 0.064 kg N per kg volatile suspended solids per day. The formed granules were bright red and had a high settling velocity (41 to 79 m h(-1)). Cells and extracellular polymeric substances were evenly distributed over the anaerobic ammonium-oxidizing granules. The high percentage of anaerobic ammonium-oxidizing bacteria in the granules could be visualized by fluorescent in situ hybridization and electron microscopy. The copy numbers of 16S rRNA genes of anaerobic ammonium-oxidizing bacteria in the granules were determined to be 4.6 x 10(8) copies ml(-1). The results of this study could be used for a better design, shorter start-up time, and more stable operation of anammox systems for the treatment of nitrogen-rich wastewaters.

A direct comparison amongst different technologies (aerobic granular sludge, SBR and MBR) for the treatment of wastewater contaminated by 4-chlorophenol

Environmental concern on chlorinated phenols is rising due to their extreme toxicity even at low concentrations and their persistency in water and soils. Since the high amount of published data often lacks in terms of uniformity, direct comparisons amongst different treatment technologies are very difficult, or even impossible. In this study, granular sludge developed in an acetate-fed Granular sludge Sequencing Batch Reactor (GSBR) was used for the aerobic degradation of low chlorinated 4-chlorophenol (4CP), with readily biodegradable sodium acetate (NaAc) as growth substrate. A conventional Sequencing Batch Reactor (SBR) and a Membrane BioReactor (MBR) were operated in parallel under the same 4CP influent concentrations and/or 4CP volumetric organic loading rates as the GSBR, in order to carry out a direct comparison in terms of 4CP removal efficiencies and specific removal rates, effluent quality, waste sludge production, system simplicity, land area requirement, start-up times, NaAc dosage as growth substrate and maximum applied 4CP volumetric organic loading rate. A decision matrix was built to define the best technology to suit different scenarios: the GSBR was proved to be the most suitable technology when system simplicity, low land area requirement and short start-up times were considered as critical parameters for decision making.