Carbon dioxide (CO2) concentrations in the atmosphere have increased significantly over the past century. Many methods have been devised to reduce CO2 industrial emissions, e.g., CO2 postcombustion absorption by amine-based solvents. Solvent degradation losses are very critical in this process, due to economic and environmental issues. The two main degradation pathways of amine-based aqueous solutions in the presence of CO2 are oxidative and thermal degradation. In this work, a lab-scale pilot plant has been set up to carry out degradation experiments during continuous and dynamic cycles of absorption and stripping with three different amine solvents: MEA (monoethanolamine) used as benchmark solvent for CO2 capture, a blend of 1MPZ (1-methylpiperazine) and PZ (piperazine), and a blend of MDEA (methyldiethanolamine) and MEA. The experimental data have been used to assess the performance of CO2 absorption over time and experimental conditions. The variation of CO2 fraction at the gas outlet of the reactor has been used as an indicator of solvent degradation. To simulate the behavior of the plant at different experimental conditions and with each solvent, a dynamic model has been developed, on the basis of the validation of a fast reaction regime. It reproduces accurately the pilot plant’s behavior during the absorption and stripping phases. Among the solvents’ physical properties, the effect of viscosity appears to be the most critical for the CO2 absorption efficiency. Kinetics of solvent degradation has finally been optimized to match experimental observations. Of the three solvents studied, 1MPZ/PZ is the most stable, whereas MEA and MDEA/MEA have quite similar degradation rates.

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The Next-CSP project aims at improving the performances of central receiver Solar Thermal Electric (STE) plants through the development and integration of a new technology based on high temperature (800°C) particles used as both heat transfer fluid and storage medium. The objective of the present paper is to define the best combined cycle configuration by exploring various design options where Turbine Exhaust Temperature (TET) and compressor outlet temperature vary. Regarding the Dense Particle Suspension Heat eXchanger (DPS-HX) train that provides the heat input to the gas turbine's working air, a particular attention is paid to the particle-side layout. A decent net cycle efficiency can be achieved by a two-reheat topping cycle with a TET of 600°C, with equal expansion ratios and a 3 pressure-reheat Rankine cycle at 160-20-3 bars / 585 / 575°C. Further increasing the low pressure (LP) turbine expansion ratio would result in a less bulky and cheaper LP DPS-HX, at the expense of cycle efficiency. Adjusting the HP and IP pressure ratios can simplify the particle-side layout of the DPS-HX train, again at the expense of efficiency (at least 0.5% pt). With a two-reheat topping cycle, the particles cannot be expected to enter the receiver at a temperature far below 600°C. The impact of that high receiver inlet temperature and of the resulting moderate storage density on the plant's efficiency and economics should be discussed further. Similarly, a detailed techno-economic optimization of the DPS-HX train should be performed in order to define the optimal pressure drops and temperature differences.

This work presents a techno-economic parametric study of an innovative central receiver solar thermal power plant layout that applies the combined cycle (CC) as thermodynamic power cycle and a multi-tower solar field configuration together with open volumetric air receivers (OVARs). The topping gas turbine (GT) is powered by an air-air heat exchanger (two heat exchanger trains in the case of reheat). In order to provide dispatchability, a high-temperature thermocline TES system is placed upstream the gas turbine. The aim is threefold, (i) investigating whether the multi-tower concept has a techno-economic advantage with respect to conventional single-tower central receiver plants, (ii) indicating the technoeconomic optimum power plant configuration, and (iii) benchmarking the technoeconomic optimum of the CC plant against that of a conventional single-cycle Rankine steam plant with the same receiver and TES technology. It is concluded that the multi-tower configuration has a techno-economic advantage with respect to the conventional single-tower arrangement above a total nominal solar power level of about 150 MW. However, the benchmarking of the CC against a Rankine single-cycle power plant layout shows that the CC configuration has despite its higher solar-to-electric conversion efficiency a higher LCOE. The gain in electricity yield is not enough to outweigh the higher investment costs of the more complex CC plant layout.