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971.
Aeration accounts for 30% to 75% of the total energy consumption in activated sludge processes (ASPs). This percentage can be significantly reduced since most aeration systems are not optimized for unsteady influent flow rates and oxygen requirements. Reconfiguration, replacement, and the application of optimal dissolved oxygen (DO) control strategies for current aeration systems within the facility and model-based optimization of DO in wastewater treatment plants can lead to impressive increased energy efficiency and savings and improved stability of the system. These measures increase the operational lifetime of the aeration equipment and improve effluent and activated sludge quality. This article provides a review of two critical nonlinear time-varying parameters that characterize the DO concentration dynamics in an ASP: the oxygen uptake rate (OUR), related to microorganism activity, and the volumetric oxygen mass transfer function, represented by the oxygen transfer rate (OTR). Second, the physico-chemical, geometric, and dynamic factors and aerator type affecting the oxygen mass transfer coefficient (K L a) are thoroughly discussed. The article concludes with model-based optimization, explaining the usefulness of accurate DO models in wastewater treatment, and provides examples for plant-wide or water chain cycle–focused optimizations. 相似文献
972.
973.
Oxygen isotope exchange experiments, H218O/H216O (”wet” anneals) and 18O2/16O2 (”dry” anneals), were performed on single crystal samples of yttria‐stabilized zirconia (YSZ) at a temperature of T = 1073 K with subsequent determination of the oxygen isotope profiles in the solid by time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS). Such experiments yielded oxygen tracer diffusion coefficients (D*) and oxygen tracer surface exchange coefficients (k*), from both the polished (smooth) and unpolished (rough) sides of single crystal samples, as a function of water partial pressure pH2O and oxygen partial pressure pO2. Isothermal values of D* were found to depend on neither pO2 nor pH2O (nor surface roughness). Isothermal values of k*, in contrast, displayed a strong dependence on pO2 or pH2O; k*wet was, in addition, 2–3 orders of magnitude higher than k*dry. Surprisingly, surface roughness had little effect on k*wet, whereas rough surfaces exhibited much higher k*dry values than smooth surfaces. Data for k*wet obtained as a function of temperature at pH2O = 18 mbar show a change in activation enthalpy at T ≈ 973 K. The behavior of k* is discussed in terms of surface composition, surface area and surface reaction mechanisms. 相似文献
974.
Chemical looping reforming (CLR) is a new technology for syngas generation. The theoretical process design aspects of syngas generation using CLR of isooctane (gasoline) are studied in this paper to assess its ability for fuel processor development for solid oxide fuel cells. The fuel processor operating conditions for maximum syngas generation at thermoneutral conditions are determined in this study using nickel oxide as oxygen carrier for different inputs of oxygen carrier within the temperature range of 600–1,000 °C at 1 bar pressure. The thermoneutral temperatures for the dual reactor fuel processor were calculated using the hot product gas stream and exothermic CLR process enthalpy to completely balance the endothermic process requirements. The thermoneutral point of 879.5 °C (NiO input of 7 moles) delivered maximum syngas (13.92 moles) using lowest amount of air (26.13 moles) in the process was found to be the most suitable thermoneutral temperature for the fuel processor operation. The novel fuel processor design can also be used for other fuels and oxygen carriers. 相似文献
975.
Palladium was electrodeposited on an electrochemically activated carbon black substrate using potentiostatic technique, with and without the addition of polyethylene glycol (PEG‐6000) as an additive. Scanning electron micrographs showed change in morphology of Pd from spherical to flower, with increasing additive concentration. As an electrocatalyst for oxygen reduction reaction (ORR), formic acid oxidation and CO stripping, Pd nanoflowers displayed three‐ to fourfold increase in electrocatalytic activity in comparison to the spherical Pd deposits in terms of electrochemical surface area (ESA) and mass specific current density. X‐ray diffraction (XRD) patterns showed, the introduction of additive with varying concentration effect the direction of Pd growth thereby changing the morphology from spherical to flower. The result demonstrates an increase in efficiency of Pd utilization achieved with the addition of PEG during electrodeposition, which could also be applicable to other precious metal electrocatalysts. A scheme for the change in Pd morphology during electrodeposition with additive is also proposed. 相似文献
976.
Anita Skulimowska Marc Dupont Marta Zaton Svein Sunde Luca Merlo Deborah J. Jones Jacques Rozière 《International Journal of Hydrogen Energy》2014
A series of three membrane types has been screened for medium temperature solid polymer electrolyte water electrolysis in membrane electrode assemblies coated with 2 mg cm−2 of iridium oxide as a catalyst for the oxygen evolution reaction, synthesised via a hydrolysis method from the hexachloroiridic acid precursor, and deposited on the membrane either directly by spray deposition or by decal transfer. The short-side-chain perfluorosulfonic acid Aquivion® ionomer of equivalent weight 870 meq g−1, in membranes of thickness 120 μm, gives higher water electrolysis performance at 120 °C than a composite membrane of Aquivion® with zirconium phosphate, while a sulfonated ether-linked polybenzimidazole, sulfonated poly-[(1-(4,4′-diphenylether)-5-oxybenzimidazole)-benzimidazole], shows promising performance and no transport limitations up to 2 A cm−2. The lowest cell voltage was observed at 120 °C for an MEA prepared using spray-coating directly on the Aquivion® membrane, 1.57 V at 1 A cm−2. 相似文献
977.
Yanjiao Ma Hui Wang Julian Key Vladimir Linkov Shan Ji Xuefeng Mao Qizhao Wang Rongfang Wang 《International Journal of Hydrogen Energy》2014
An oxygen reduction reaction (ORR) catalyst comprising ultrafine iron oxide nanoparticles supported on N-doped Vulcan carbon (FeO1.4/N-C) was prepared via a two-step method. X-ray photoelectron spectroscopy revealed the iron oxide nanoparticles comprised Fe2O3 and FeO phases with a combined average oxidation state of 2.8. The FeO1.4/N-C catalyst produced an ORR onset potential of −0.056 V and a half-wave potential of −0.190 V in alkaline media, which was comparable to that of commercial Pt/C catalyst. Moreover, FeO1.4/N-C had higher methanol tolerance than Pt/C catalyst and thus affords a promising non-precious metal ORR catalyst for fuel cells. 相似文献
978.
A. Murashkina E. Pikalova D. Medvedev A. Demin P. Tsiakaras 《International Journal of Hydrogen Energy》2014
In the present work, composite materials of the type (1–x)SrTi0.5Fe0.5O3–δ–xCe0.8(Sm0.8Sr0.2)0.2O2–δ (with х = 0, 0.25, 0.5, 0.75 and 1) are obtained by the two step solid state technique. Their transport properties are investigated in terms of their usage as mixed ionic-electronic conducting (MIEC) membrane materials for hydrogen production. It is found that, in reducing conditions the composites are characterized by mixed conductivity, which level is controlled by the electrical properties of the prevailing phase. Moreover, at 900 °C and pO2 = 10−18 atm, total conductivity, ambipolar conductivity and oxygen permeability of composites dramatically grow (each of about 500%), when the fluorite component content x increases from 0 to 1. High-conducting and strengthened material 0.5SrTi0.5Fe0.5O3–δ–0.5Ce0.8(Sm0.8Sr0.2)0.2O2–δ is chosen for making tube shaped membranes using the tape rolling method, which are successfully applied for hydrogen production in laboratory scale. The hydrogen flux reached 0.176 ml cm−2 min−1 for x = 1, T = 900 °C and emf = 10 mV. 相似文献
979.
980.