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

Ecological impacts of time-variable exposure regimes to the fungicide azoxystrobin on freshwater communities in outdoor microcosms

This paper evaluates the effects of different time-varying exposure patterns of the strobilurin fungicide azoxystrobin on freshwater microsocosm communities. These exposure patterns included two treatments with a similar peak but different time-weighted average (TWA) concentrations, and two treatments with similar TWA but different peak concentrations. The experiment was carried out in outdoor microcosms under four different exposure regimes; (1) a continuous application treatment of 10 μg/L (CAT10) for 42 days (2), a continuous application treatment of 33 μg/L (CAT33) for 42 days (3), a single application treatment of 33 μg/L (SAT33) and (4) a four application treatment of 16 μg/L (FAT16), with a time interval of 10 days. Mean measured 42-d TWA concentrations in the different treatments were 9.4 μg/L (CAT10), 32.8 μg/L (CAT33), 14.9 μg/L (SAT33) and 14.7 μg/L (FAT16). Multivariate analyses demonstrated significant changes in zooplankton community structure in all but the CAT10 treated microcosms relative to that of controls. The largest adverse effects were reported for zooplankton taxa belonging to Copepoda and Cladocera. By the end of the experimental period (day 42 after treatment), community effects were of similar magnitude for the pulsed treatment regimes, although the magnitude of the initial effect was larger in the SAT33 treatment. This indicates that for long-term effects the TWA is more important for most zooplankton species in the test system than the peak concentration. Azoxystrobin only slightly affected some species of the macroinvertebrate, phytoplankton and macrophyte assemblages. The overall no observed ecologically adverse effect concentrations (NOEAEC) in this study was 10 µg/L