A Gas-Steam Combined Cycle Powered by Syngas Derived from Biomass

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Numerical Investigation of a Darrieus Rotor for Low-head Hydropower Generation

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CFD analysis of the energy conversion process in a fixed oscillating water column (OWC) device with a Wells turbine

Abstract Oscillating Water Column (OWC) devices, both the fixed structures and the floating ones, are an important class of Wave Energy Converter (WEC) devices. In this work, we carried out a numerical investigation aiming to give a deep insight into the fluid dynamic interaction between waves and a U-shaped OWC breakwater, focusing on the energy conversion process. The U-OWC breakwater under consideration, represents the full-scale plant installed in the Civitavecchia (near Rome) harbour. The adopted numerical method is based on the solution of the unsteady Reynolds Averaged Navier-Stokes equations (URANS). The water-air interaction is taken into account by means of the Volume Of Fluid (VOF) model. A two-dimensional domain has been adopted to investigate the unsteady flow outside and inside the OWC device. In order to simulate the action of an air turbine of the Wells type, the air chamber has been connected to the atmosphere by means of a porous medium able to reproduce its linear relationship between pressure drop and flow rate of the air turbine. Several simulations have been carried out considering periodic waves of different amplitudes in order to analyze the performance of the plant and, in particular to analyze the resonance with incoming waves, when the U-OWC is expected to absorb more energy. In order to characterize the plant efficiency, we split the energy conversion process into three main steps, 1) the primary conversion from wave energy to hydraulic energy the water discharge flowing inside the U-duct; 2) the secondary conversion from the OWC inlet to the oscillating pneumatic power made available to the turbine and, finally, 3) the turbine mechanical power output. To this purpose, the simulations of three different cases, varying wave period and height, have been carried out to quantify the energy captured by the plant and the fluid dynamic losses both in the water and in the air

Recent Combustion Strategies in Gas Turbines for Propulsion and Power Generation toward a Zero-Emissions Future: Fuels, Burners, and Combustion Techniques

The effects of climate change and global warming are arising a new awareness on the impact of our daily life. Power generation for transportation and mobility as well as in industry is the main responsible for the greenhouse gas emissions. Indeed, currently, 80% of the energy is still produced by combustion of fossil fuels; thus, great efforts need to be spent to make combustion greener and safer than in the past. For this reason, a review of the most recent gas turbines combustion strategy with a focus on fuels, combustion techniques, and burners is presented here. A new generation of fuels for gas turbines are currently under investigation by the academic community, with a specific concern about production and storage. Among them, biofuels represent a trustworthy and valuable solution in the next decades during the transition to zero carbon fuels (e.g., hydrogen and ammonia). Promising combustion techniques explored in the past, and then abandoned due to their technological complexity, are now receiving renewed attention (e.g., MILD, PVC), thanks to their effectiveness in improving the efficiency and reducing emissions of standard gas turbine cycles. Finally, many advances are illustrated in terms of new burners, developed for both aviation and power generation. This overview points out promising solutions for the next generation combustion and opens the way to a fast transition toward zero emissions power generation

Performance optimization of a gas-steam combined power plant partially fed with syngas derived from pomace

Abstract In this paper a gas-steam combined-cycle, partially fueled by syngas (produced in an embedded downdraft gasifier fed with pomace), is considered. In addition, an auxiliary combustion system is directly fed by ligno-cellulosic biomass. The thermodynamic model of the entire system is developed by means of the Cycle-Tempo software. The gasification process is supposed to occur at ambient pressure and air is used as gasifying agent. An optimization process has been introduced by means of the Design of Experiment ( DoE ) technique. The design variables and their corresponding ranges have been chosen by using a heuristic criterion. The power plant performance is represented by the thermal efficiency, _ η I , the exergetic efficiency, η II , the cost of electricity, COE, and the net return, R net . The DoE technique provided the so-called Pareto barrier, which isolates all the non-dominated solutions

Numerical Simulations of the flow field and chemical reactions of the Storage/Oxidation process within a NSC Pt - BaO Catalyst

A NOxStorage Catalyst (NSC) has been studied by means of reactive CFD simulations. In the scenario of automotive pollutant emission reduction, due to the stringent regulation, the detailed description of the chemical and physical phenomena within catalysts represents a key point in order to improve their conversion efficiency. The active part of the catalyst has been simulated as a porous medium. In this zone, surface reactions take place, which are modelled by means of an Arrhenius chemical kinetic approach, involving the Pt and BaO sites on the active surface of the matrix. Actually, two chemical mechanisms are considered, the simplest involves only BaO site, the other one includes both BaO and Ptsites. Both models are validated against data available in the literature and then applied to a real automotive catalyst geometry. Thus, a detailed description of the spatial distribution of the species is provided for both models. Lean condition is simulated in order to check the catalyst behaviour according to experimental results

Performance prediction model of multistage centrifugal Pumps used as Turbines with Two-Phase Flow

Abstract Pump as Turbines (PaTs) can be used not only in hydraulic power generation but also in chemical processes, such as refinery, where fluids containing dissolved or undissolved gases or volatiles can be expanded from a higher to a lower pressure level for energy recovery. As the gas contained in the fluid is released from the solution during expansion, the flow rate increases and additional energy is delivered with respect to the case of incompressible flow. This higher power output is very attractive. In this work, a theoretical approach is proposed in order to predict the PaT performance with a two-phase flow whose expansion characteristics are known

Numerical prediction of the natural frequency of an Oscillating Water Column operating under resonant conditions

Among the different technologies developed in order to harness wave energy, the Oscillating Water Column devices are the most accredited for an actual diffusion. Recently, Boccotti has patented the REWEC1 (REsonant sea Wave Energy Converter solution 1), a submerged breakwater that performs an active coast protection, embedding an Oscillating Water Column device, which is capable of operating under resonant conditions with that sea state, which gives the highest yearly energy contribution. The REWEC1 dynamic behavior can be approximated by means of a mass-spring-damper system. According to this approximation, a criterion for evaluating the oscillating natural frequency of the REWEC1 has been derived. This criterion has been validated against both experimental results and computational fluid dynamics simulations, performed on a REWEC1 laboratory-scale model. The numerical simulations have shown a good agreement between measurements and predictions

Yet another UFO in the X-ray spectrum of a high-z lensed QSO

Ultra-fast outflows (UFO) appear to be common in local active galactic nuclei (AGN) and may be powerful enough ($\dot{E}_{kin}$$\geq$1\% of L$_{bol}$) to effectively quench the star formation in their host galaxies. To test feedback models based on AGN outflows, it is mandatory to investigate UFOs near the peak of AGN activity, that is, at high-z where only a few studies are available to date. UFOs produce Fe resonant absorption lines measured above $\approx$7 keV. The most critical problem in detecting such features in distant objects is the difficulty in obtaining X-ray data with sufficient signal-to-noise. We therefore selected a distant QSO that gravitational lensing made bright enough for these purposes, the z=2.64 QSO MG J0414+0534, and observed it with XMM-Newton for $\approx$78 ks.} The X-ray spectrum of MG J0414+0534 is complex and shows signatures of cold absorption (N$_{H}\approx$4$\times$10$^{22}$ cm$^{-2}$) and of the presence of an iron emission line (E$\approx$6.4 keV, EW$=$95$\pm$53 eV) consistent with it originating in the cold absorber. Our main result, however, is the robust detection (more than 5$\sigma$) of an absorption line at E$_{int}\approx$9.2 keV (E$_{obs}\approx$2.5 keV observer frame). If interpreted as due to FeXXVI, it implies gas outflowing at $v_{out}\approx$0.3c. To our knowledge, this is the first detection of an UFO in a radio-loud quasar at z$\geq$1.5. We estimated that the UFO mechanical output is $\dot{E}_{kin}$$\approx$2.5$L_{bol}$ with $\dot{p}_{out}/\dot{p}_{rad}\approx$17 indicating that it is capable of installing significant feedback between the super-massive black hole (SMBH) and the bulge of the host galaxy. We argue that this also suggests a magnetic driving origin of the UFO.Comment: Accepted for publication on A&A Lette

X-raying winds in distant quasars: the first high-redshift wind duty cycle

Theoretical models of wind-driven feedback from Active Galactic Nuclei (AGN) often identify Ultra-fast outflows (UFOs) as being the main cause for generating galaxy-size outflows, possibly the main actors in establishing the so-called AGN-galaxy co-evolution. UFOs are well characterized in local AGN but much less is known in quasars at the cosmic time when SF and AGN activity peaked ($z\simeq1-3$). It is therefore mandatory to search for evidences of UFOs in high-$z$ sources to test the wind-driven AGN feedback models. Here we present a study of Q2237+030, the Einstein Cross, a quadruply-imaged radio-quiet lensed quasar located at $z=1.695$. We performed a systematic and comprehensive temporally and spatially resolved X-ray spectral analysis of all the available Chandra and XMM-Newton data (as of September 2019). We find clear evidence for spectral variability, possibly due to absorption column density (or covering fraction) variability intrinsic to the source. We detect, for the first time in this quasar, a fast X-ray wind outflowing at $v_{\rm out}\simeq0.1c$ that would be powerful enough ($\dot{E}_{\rm kin}\simeq0.1 L_{\rm bol}$) to significantly affect the host galaxy evolution. We report also on the possible presence of an even faster component of the wind ($v_{\rm out}\sim0.5c$). Given the large sample and long time interval spanned by the analyzed X-ray data, we are able to roughly estimate, for the first time in a high-$z$ quasar, the wind duty cycle as $\approx0.46\,(0.31)$ at $90\%\,(95\%)$ confidence level. Finally, we also confirm the presence of a Fe K$\alpha$ emission line with variable energy, which we discuss in the light of microlensing effects as well as considering our findings on the source.Comment: 18 pages, 11 figures, 7 tables, Accepted for publication in A&