4 research outputs found
Dual Loop Line-Focusing Solar Power Plants with Supercritical Brayton Power cycles
Most of the deployed commercial line-focusing solar power plants with Parabolic Troughs (PTC) or Linear Fresnel (LF) solar collectors and Rankine power cycles use a Single Loop Solar Field (SF), Configuration 1 illustrated in Fig. 2, with synthetic oil as Heat Transfer Fluid (HTF) [1, 2]. However, thermal oils maximum operating temperature should be below ~400ºC for assuring no oil degradation, hence limiting the power cycle gross efficiency up to ~38%. For overcoming this limitation Molten Salts (MS) as HTF in linear solar collectors (PTC and LF) were recently experimented in pilot facilities [3, 4]. Direct MS main drawbacks are the equipments and components material corrosion and the salts freezing temperature, requiring heat tracing to avoid any sald solidification, hence increasing the Solar Field (SF) capital investment cost and parasitic energy looses. Concentrated Solar Power plants (CSP) with Dual Loop SF are being studied since 2012 [5] for gaining the synergies between thermal oils and MS properties. In the Dual Loop SF the HTF in the primary loop is thermal oil (Dowtherm A) [6] for heating the Balance Of Plant (BOP) working fluid from ~300ºC up to ~400ºC, and a secondary loop with Solar Salt (60% NaNO3, 40% KNO3) as HTF, for boosting the working fluid temperature from ~400ºC up to 550ºC [7, 8, 9]. The CSP Dual Loop state of the art technology includes Rankine power cycles, the main innovation of this paper is the integration between Dual Loop SF and the supercritical Carbon Dioxide (s-CO2) Brayton power cycles [10], see Configurations 2 and 3 illustrated in Fig. 3a, Fig 3b. A secondary innovation studied in this paper is the integration between thermal oil HTF (Dowtherm A) in linear solar collectors, a widely validated and mature technology, with the s-CO2 Brayton power cycles. This technical solution is very cost competitive with carbon steel receiver pipes, low SF operating pressure, and no requiring any heat tracing. Two main conclusions are deducted from this researching study. Firstly we demonstrated the higher gross plant efficiency ~44.4%, with 550ºC Turbine Inlet Temperature (TIT), provided by the Dual Loop with the Simple recuperated s-CO2 Brayton cycle with reheating, in comparison with 41.8% obtained from the Dual Loop SF and subcritical water Rankine power cycle. And finally the second conclusion obtained is the selection of the most cost competitive plant configuration with a Single loop SF with Dowtherma A and a s-CO2 Brayton power cycle due to the receiver material low cost and no heat tracing for the thermal oil
Pesticide risk assessment and management in a globally changing world—report from a European interdisciplinary workshop
[Departement_IRSTEA]Eaux [TR1_IRSTEA]BELCA [Axe_IRSTEA]DTAM-QT2-ADAPTATION [TR2_IRSTEA]ARCEAU [TR2_IRSTEA]DTAMGlobal climate change will affect worldwide agriculture in many ways. The anticipated or already occurring changes raise concerns about the sustainability of production and the ability of agriculture to feed human populations. This appeals to sustainable agriculture providing ecosystem services more efficiently than today, and accordingly to substantial evolutions of pesticide risk assessment (RA) and risk management (RM). The RA/RM issues were discussed by two European research networks in a 2011 workshop. The RA-RM-monitoring conceptual cycle tends to be virtual, with poor connections between certain steps. The design of more comprehensive emissions scenarios could improve the accuracy of predicted runoff transport, while the microcosm/mesocosm approach could help establish causal relationships between fate / exposure and populations / communities. Combined with ecological modelling, effects can be extrapolated to higher spatial and temporal scales. Risk management of diffuse sources should be designed simultaneously at the watershed and individual plot scales. Monitoring is key to assessing the effectiveness of risk reduction measures reduce and evaluate the overall quality of the aquatic compartment. More flexible monitoring strategies clearly linked to RM decisions are therefore needed. Although some technical questions remain, it is time to apply passive samplers more routinely. A set of research and development needs covering the whole RA/RM cycle is listed in conclusion
Uptake, Translocation, and Elimination in Sediment-Rooted Macrophytes: A Model-Supported Analysis of Whole Sediment Test Data
Understanding bioaccumulation in
sediment-rooted macrophytes is
crucial for the development of sediment toxicity tests using macrophytes.
Here, we explore bioaccumulation in sediment-rooted macrophytes by
tracking and modeling chemical flows of chlorpyrifos, linuron, and
six PCBs in water–sediment–macrophyte systems. Chemical
fluxes across the interfaces between pore water, overlying water,
shoots, and roots were modeled using a novel multicompartment model.
The modeling yielded the first mass-transfer parameter set reported
for bioaccumulation by sediment-rooted macrophytes, with satisfactory
narrow confidence limits for more than half of the estimated parameters.
Exposure via the water column led to rapid uptake by <i>Elodea
canadensis</i> and <i>Myriophyllum spicatum</i> shoots,
followed by transport to the roots within 1–3 days, after which
tissue concentrations gradually declined. Translocation played an
important role in the exchange between shoots and roots. Exposure
via spiked sediment led to gradual uptake by the roots, but subsequent
transport to the shoots and overlying water remained limited for the
chemicals studied. These contrasting patterns show that exposure is
sensitive to test set up, chemical properties, and species traits.
Although field-concentrations in water and sediment will differ from
those in the tests, the model parameters can be assumed applicable
for modeling exposure to macrophytes in the field