2,518 research outputs found
Strong responses of Southern Ocean phytoplankton communities to volcanic ash
No full textVolcanic eruptions have been hypothesized as an iron supply mechanism for phytoplankton blooms; however, little direct evidence of stimulatory responses has been obtained in the field. Here we present the results of twenty-one 1–2?day bottle enrichment experiments from cruises in the South Atlantic and Southern Ocean which conclusively demonstrated a photophysiological and biomass stimulation of phytoplankton communities following supply of basaltic or rhyolitic volcanic ash. Furthermore, experiments in the Southern Ocean demonstrated significant phytoplankton community responses to volcanic ash supply in the absence of responses to addition of dissolved iron alone. At these sites, dissolved manganese concentrations were among the lowest ever measured in seawater, and we therefore suggest that the enhanced response to ash may have been a result of the relief of manganese (co)limitation. Our results imply that volcanic ash deposition events could trigger extensive phytoplankton blooms, potentially capable of significant impacts on regional carbon cycling
Volcanic ash fuels anomalous plankton bloom in subarctic northeast Pacific
No full textUsing multiple lines of evidence, we demonstrate that volcanic ash deposition in August 2008 initiated one of the largest phytoplankton blooms observed in the subarctic North Pacific. Unusually widespread transport from a volcanic eruption in the Aleutian Islands, Alaska deposited ash over much of the subarctic NE Pacific, followed by large increases in satellite chlorophyll. Surface ocean pCO2, pH, and fluorescence reveal that the bloom started a few days after ashfall. Ship-based measurements showed increased dominance by diatoms. This evidence points toward fertilization of this normally iron-limited region by ash, a relatively new mechanism proposed for iron supply to the ocean. The observations do not support other possible mechanisms. Extrapolation of the pCO2 data to the area of the bloom suggests a modest ∼0.01 Pg carbon export from this event, implying that even large-scale iron fertilization at an optimum time of year is not very efficient at sequestering atmospheric CO2
The density, construction and drag coefficient of electrostatic volcanic ash aggregates.
Full text linkRecent laboratory experiments have demonstrated that electrostatic charges generated during the fragmentation of volcanic pumice cause rapid aggregation of the silicate particles produced. Here, we present measurements of the mass and component particle size distribution of individual, electrostatically bound aggregates produced during these experiments. Particles produced by fracturing pumice aggregated as they fell ∼1.5 m within an enclosed fall chamber. Aggregate mass measurements indicate aggregate densities of ∼200 kg m−3 or less. The component particle size analysis demonstrates exponential-type cumulative distributions which are dominated (on a volume basis) by particles ∼10–40 μm in diameter and contain few particles >70 μm. By representing these particles as disks of 5 μm thickness the calculated aggregate densities are in agreement with those derived from the aggregate mass measurements and indicate a relatively constant aggregate density with size (in contrast with previous results from fall velocities). Combining the density measurements with fall velocity data allows the drag coefficient of aggregates to be determined. Empirical equations developed to describe the particle size distribution within aggregates are used to derive relative aggregation coefficients for the electrostatic aggregation process. Our results can be used within numerical models of volcanic plumes in order to improve their representation of electrostatic aggregation processes
From Dome to Disease: The Respiratory Toxicity of Volcanic Cristobalite
Full text linkExposure to fine-grained volcanic ash can potentially cause acute and chronic respiratory disease. The toxicity of ash is likely to vary depending on the type and style of eruption; eruptions at dome-forming volcanoes, in particular, can produce ash containing substantial quantities of respirable crystalline silica, a recognised human carcinogen and causative agent of silicosis. Volcanic domes crystallise crystalline silica as cristobalite, which is metastable at dome-forming temperatures (ca. 850 °C), through deposition from silica-saturated vapours and through devitrification of volcanic glass.
Five dome-forming volcanoes are studied to constrain the hazard posed by volcanic cristobalite, including: Colima, Mexico; Merapi, Indonesia; Mount St. Helens, USA; Santiaguito, Guatemala; and Unzen, Japan. The evolution of the cristobalite hazard is investigated from crystallisation in volcanic settings to its potential effect on biological systems, through a series of petrological, physicochemical and toxicological studies.
We rationalise the presence of metastable cristobalite below its stability field in all domes studied by way of a textural investigation, and conclude that the incorporation of aluminium and sodium into the silica structure facilitates crystallisation. Since particle toxicology is dependent on composition and structure, the observation of cation substitutions is expanded in a geochemical and thermodynamic investigation of volcanic cristobalite to constrain its mineralogy. We find that incorporation of 1-4 wt. % aluminium leads to a poorly-ordered cristobalite structure. This investigation facilitates a mineralogical comparison of the cristobalite hazard among volcanic locations and provides the framework for assessing volcanic cristobalite toxicity. We investigate the ability of volcanic ash to elicit an in vitro pro-inflammatory response, focusing on silica-mediated experiments, and relate the influence of structure and composition to the potential physiological burden. We find that volcanic cristobalite can be mineralogically considered as a single entity among locations, and that cristobalite-bearing ash is less toxic than expected. Nonetheless, we recommend that eruptions be considered on a case-by-case basis to most effectively aid the risk mitigation work of disaster managers globally
An advanced adjustable switch hybrid (Ash) concept for high power automotive converters
No full textIn this paper, we introduce an Adjustable Switch Hybrid (ASH) converter concept. The ASH targets the optimization of the electrical performance of high-powered automotive drive-trains depending on the different load conditions during drive cycles. The new concept employs in principle the previously reported Cross Switch (XS) Hybrid having a parallel arrangement of bipolar Silicon IGBTs and unipolar SiC MOSFETs for benefiting from the different electrical characteristics of each paralleled device. However, the ASH relies on a computational approach for the continuous and dynamic adjustments of the Si-IGBT to the SiC MOSFET area ratio through the gate units depending on the load conditions. In practical terms, changes in the loading conditions can be sensed and data will then be sent back to the ASH gate drive unit for the optimum device ratio selection. In other words, the ASH provides the drivetrain with an Electronic Transmission System or Gear type functionality.Accepted Author ManuscriptDC systems, Energy conversion & Storag
Nathan Gray : What they brought back
No full textPublished to accompany the exhibition held at Gertrude Contemporary Project Room, Melbourne Art Fair, 4-8 August 2010.Catalogue essay by Ash Kilmartin
Pore solution composition of alkali-activated slag/fly ash pastes
No full textThe pore solutions of a series of hardened alkali-activated slag/fly ash pastes were extracted by the steel-die method, and analyzed using ICP-OES analysis technique. According to the saturation index from thermodynamic calculations, the pore solutions of alkali-activated slag pastes kept oversaturated with respect to solid reaction products with time. In the pore solutions of alkali-activated fly ash pastes, an increase of temperature (from 40 °C to 60 °C) led to decreases of the concentrations of Si, Al, Ca, Na, OH−, K, Fe and Mg, while the soluble silicate in the alkaline activator resulted in increases of the concentrations of these elements. Compared to the alkali-activated slag paste with the same alkaline activator, 50% replacement of slag by fly ash did not result in a substantial change of the pore solution composition. Based on the experimental results, conceptual models were proposed to describe the elemental concentrations in the pore solutions.Accepted Author ManuscriptMaterials and Environmen
Creating coagulants through the combined use of ash and brine
No full textSludge incineration and seawater desalination are two approaches that can be used in the disposal of waste activated sludge (WAS) and for obtaining fresh water. As resource recovery from wastewater treatment and water purification is a topic of particular interest in these times, “water mining” has become a focus of research, with phosphate/P-recovery from WAS incineration ash, and extraction of useful elements from the brine of desalination being important steps in the pursuit of a circular/blue economy. However, P-recovery from ash involves removing metals, which need to be disposed of carefully, as does the brine collected. If cations in the ash and anions in the brine could be combined in order to produce coagulants/flocculants, a new circular model would be established. A preliminary experiment for this purpose has demonstrated that a liquid poly‑aluminum chloride (PAC) could be synthesized from the aluminum ion/Al3+ removed from the ash and the original brine. With this work, we synthesized the liquid PAC by a hydrothermal method, and the results from infrared spectrometer demonstrated that the synthesized PAC was similar to a commercial PAC. Moreover, the synthesized PAC was able to efficiently reduce the effluent turbidity of wastewater treatment plants (WWTPs), especially when compared with the commercial PAC. It is therefore important that research in this area be continued in order to improve the quality of synthesized coagulants and to produce different coagulants based on cations and anions in ash and brine.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.BT/Environmental Biotechnolog
Synergy of phosphate recovery from sludge-incinerated ash and coagulant production by desalinated brine
No full textWet-chemical approach is widely applied for phosphate recovery from incinerated ash of waste activated sludge (WAS), along with metals removed/recovered. The high contents of both aluminum (Al) and iron (Fe) in WAS-incinerated ash should be suitable for producing coagulants with some waste anions like Cl− and SO42− With acid (HCl) leaching and metals’ removing, approximately 88 wt% of phosphorus (P) in the ash could be recovered as hydroxylapatite (HAP: Ca5(PO4)3OH); Fe3+ in the acidic leachate could be selectively removed/recovered by extraction with an organic solvent of tributyl phosphate (TBP), and thus a FeCl3-based coagulant could be synthesized by stripping the raffinate with the original brine (containing abundant Cl− and SO42−). Furthermore, a liquid poly-aluminum chloride (PAC)-based coagulant could also be synthesized with Al3+ removed from the ash and the brine, which behaved almost the same in the coagulation performance as a commercial coagulant on both phosphate and turbidity removals. Both P-recovery from the ash and coagulant production associated with the brine would enlarge the markets of both ‘blue’ phosphate and ‘green’ coagulants.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.BT/Environmental Biotechnolog
Predicting Ash Deposition In A Cyclone-Fired Coal Boiler Under Variable Load Conditions
Full text linkToday, a significant number of coal-fired power plants are required to decrease the operating load as a result of intermittent power availability from wind or solar sources. Low load conditions introduce a number of challenges for these plants, such as decreased efficiency and degradation of system components due to cycling. Ash deposition on heat transfer surfaces makes these problems even worse. The overall goal of this project is to improve the understanding of fireside ash deposition behavior as the load fluctuates, thereby allowing for more efficient operations. To accomplish this goal, a computation fluid dynamic (CFD) based simulation methodology was developed and refined to match field test measurements of deposition rates at 33%, 75%, and 100% load conditions in a cyclone fired boiler burning a North Dakota lignite coal. The deposition rate measurements were taken between the secondary superheater and reheater sections of the boiler. These measurements showed a significant reduction in deposition rates during with a decrease in operational load. The primary objective in this study was to discover the mechanisms behind these observations. First, operational data from the power plant was used to carry out simulations of the full boiler. Simulations were carried out to match gas temperatures and velocities within the boiler. Decoupled simulations of the ash deposition process in the vicinity of the secondary superheater were carried out once the gas temperatures and velocities were confirmed to be adequately represented. This corresponded to the location where the deposition measurements were taken. The results of these decoupled simulations showed that in addition to the gas velocities and temperatures, the fly-ash particle size distribution (PSD) and their composition and concentration were all important variables in deposition rate predictions. Assuming an ash partitioning of 50% - 50% between the slag and fly-ash at the cyclone and a reasonable estimate of the fly-ash PSD (from literature), a critical viscosity and particle kinetic energy (PKE) based capture criterion, the trends in the measured deposition rates were predicted successfully. In addition, the mass flow rates of fly-ash in the size range of 10 to 30 microns was determined to be critical. This was the size range of particles where the most significant increase of impaction efficiencies occurred by inertial impaction. The next goal was to ascertain if the assumed ash partitioning ratio and the fly-ash PSD that resulted in match to the deposition rate measurements could be predicted using well-resolved simulations of the cyclone barrel. Plant operational data of the cyclone flow rates encompassing the load conditions 50% – 100% were employed to simulate combustion within a single cyclone barrel in the boiler. First, the sensitivity of different modeling parameters on the combustion characteristics within the cyclone were investigated in the absence of any particle capture criterion at the cyclone walls (that is no ash being captured in the slag layer). These results showed that the gas temperatures at the cyclone barrel outlet were only mildly sensitive (roughly within 150 K) to the heterogeneous char combustion modeling methodology. A decrease in load resulted in higher residence times for particles inside the cyclone barrel. This is likely attributed to more swirling of the particles caused by lower gas velocities. Variations in the parent fuel PSD did not impact the outlet gas temperature or char burnout significantly. Next, the particle kinetic energy – particle viscosity based capture criterion was modified to account for the highly swirling turbulent flow within the cyclone barrel to predict the ash portioning. The PSD at the cyclone outlet and the percent of total ash captured in the slag layer were close to initial estimates employed in the decoupled ash deposition calculations. The ash partitioning did not vary significantly across different cyclone loads when employing the shrinking sphere heterogeneous combustion model and their magnitude (~50%) was in line with previous field observations for this parent fuel ash composition
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