Scarabeus: Supercritical carbon dioxide/alternative fluid blends for efficiency upgrade of solar power plants

The future of Concentrated Solar Power technology relies on significant cost reduction to be competitive against both fossil fuel power stations and renewable technologies as photovoltaics and wind. Most of the research activity on concentrated solar power focuses on supercritical CO2 cycles to increase the solar plant efficiency together with a cost reduction. Recently, several research groups have started investigating the blending of CO2 with small amounts of additives to boost the thermodynamic cycle performance. The SCARABEUS project aims at developing and demonstrating CO2 blends in concentrating solar power plant with maximum temperatures of 700°C, power cycle efficiency above 50% and cost of electricity below 96 €/MWh. The innovative fluid and newly developed components will be validated at a relevant scale (300 kWth) for 300 h in a CSP-like operating environment

Carbon dioxide mixtures as working fluid for high-temperature heat recovery: A thermodynamic comparison with transcritical organic rankine cycles

This study aims to provide a thermodynamic comparison between supercritical CO2 cycles and ORC cycles utilizing flue gases as waste heat source. Moreover, the possibility of using CO2 mixtures as working fluids in transcritical cycles to enhance the performance of the thermodynamic cycle is explored. ORCs operating with pure working fluids show higher cyclic thermal and total efficiencies compared to supercritical CO2 cycles; thus, they represent a better option for high-temperature waste heat recovery provided that the thermal stability at a higher temperature has been assessed. Based on the improved global thermodynamic performance and good thermal stability of R134a, CO2-R134a is investigated as an illustrative, promising working fluid mixture for transcritical power cycles. The results show that a total efficiency of 0.1476 is obtained for the CO2-R134a mixture (0.3 mole fraction of R134a) at a maximum cycle pressure of 200 bars, which is 15.86% higher than the supercritical carbon dioxide cycle efficiency of 0.1274, obtained at the comparatively high maximum pressure of 300 bars. Steam cycles, owing to their larger number of required turbine stages and lower power output, did not prove to be a suitable option in this application

Energy performance and well-to-wheel analysis of different powertrain solutions for freight transportation

In this paper we compare energy performance and environmental impact of four nominal weight classes of commercial vehicles with different powertrain solutions: conventional diesel internal combustion engine (ICE), Plug-In Electric Vehicle (PHEV), Battery Electric Vehicle (BEV) and Plug-In Fuel Cell Vehicle (PFCV). First, the sizing of the various powertrain components is performed adopting a simplified calculation based on a rule-based model. Then, the energy performances are evaluated through simulation over different driving cycles carried out with a self-developed Matlab/Simulink® simulator tool based on a forward-looking approach, that implements a control strategy that targets the instant velocity specified by the driving cycle. We show that when the optimal control strategy based on the Pontryagin's Minimum Principle is adopted, the fuel consumption significantly reduces with respect to the simplified rule-based control strategy approach. Finally, the overall specific energy consumption and the corresponding greenhouse gases (GHG) emissions are evaluated by means of a well-to-wheel analysis, considering various possible scenarios, covering the main traditional and low emission solutions for production, transportation and distribution of diesel, electricity and hydrogen. As expected, the highest GHG emissions are obtained in case of fossil origin of the energy carrier, with maximum value of 270 gCO2/km/kg in case of 3.5 ton truck with traditional diesel ICE, due to the low powertrain efficiency compared to the other considered solutions. Moreover, both the specific primary energy consumption and GHG emissions proportionally reduce with tonnage, as a consequence of the progressive reduction of the fraction of the powertrain weight with respect to the total vehicle mass

Experimental and analytical procedure for the characterization of innovative working fluids for power plants applications

In the last years, several fluids have been proposed to replace steam as working fluid in power cycle for converting thermal power into electricity. This paper describes the procedure to be adopted for the selection of any innovative fluid which can be even mixtures of fluids. The first step consists of the working fluid characterization in terms of thermodynamic properties through equations of state. The equations of state have to be calibrated on experimental Vapour-Liquid Equilibrium measurements while, in the second step, the maximum operating temperature is identified through thermal stability tests. Finally, the impact of the fluid thermodynamic properties on the performance of the power cycle in which it is implemented must be assessed through modelling tools. In this work, the procedure is discussed for the mixture of CO2 and C6F14 as a potential working fluid for gas thermodynamic cycles with liquid phase compression. Results of the application of this mixture in a closed cycle show the benefit of using a CO2/C6F14 mixture which provides 3% points efficiency increase at 400 °C with respect to the pure CO2 together with a preliminary design of the expander

Water mixtures as working fluids in organic Rankine cycles

This work explores the possibility to adopt in organic Rankine cycle (ORC) plants mixtures of water (acting as solvent) plus an organic compound (acting as solute) as the working fluid. Initially an evaluation of the thermodynamic properties of the mixtures is performed, in order to assess their properties, and to point out the molar fractions which entail a near-azeotropic behaviour. Four species from three different classes of chemical compounds are investigated: 2,2,2-trifluoroethanol and n-butanol for alcohols, where the first is fluorinated, acetonitrile for nitrile class and 2-methylpyrazine as a heterocyclic aromatic compound. Simultaneously, the thermal stability of the pure substances considered as the possible solute for the mixtures is experimentally investigated in order to estimate the temperature applicability range. The ORC plant performance, from a low-enthalpy geothermal heat source (hot water stream from 100 to 200 ◦C), adopting the selected mixtures as the working fluid is finally evaluated, and the analysis includes a preliminary discussion on the turbine design; results are compared with respect to the reference case of a hypothetical plant adopting water as the working fluid