G. Manfrida

University of Florence, Florens, Tuscany, Italy

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Publications (29)29.26 Total impact

  • Giampaolo Manfrida, Riccardo Secchi
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    ABSTRACT: The stochastic nature of several renewable energy sources has raised the problem of designing and building storage facilities, which can help the electricity grid to sustain larger and larger contribution of renewable energy. Seawater pumped electricity storage is proposed as a good option for PV (Photovoltaic) or solar thermal power plants, located in suitable places close to the coast line. Solar radiation has a natural daily cycle, and storage reservoirs of limited capacity can substantially reduce the load to the electricity grid. Different modes of pump operation (fixed or variable speed) are considered, the preliminary sizing of the PV field and seawater reservoir is performed, and the results are comparatively assessed over a year-long simulated operation. The results show that PV pumped storage, even if not profitable in the present situation of the renewable energy Italian electricity market, is effective in decreasing the load on the transmission grid, and would possibly be attractive in the future, also in the light of developing off-grid applications.
    Energy 05/2014; 69:470-484. · 4.16 Impact Factor
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    ABSTRACT: Offshore applications allow to exploit different renewable energy sources (wave, wind, solar) that are complementary each other, due to their statistical yearly distributions.In this paper, we discuss an offshore platform for energy production from renewable energy sources coupled with three energy storage systems. The proposed offshore platforms uses a Compressed Air Energy Storage (CAES) to timely shift the electricity production from the demand.The performance of the system related to a north Tyrrhenian Sea location was evaluated by a simulation model developed integrating three different software packages (Matlab, EES, TRNSYS).The system was designed to produce 564 kWh on the 2 h a day where peak electricity demand takes place. The results showed that the system is able to produce 177,000 kWh per year.This offshore power plant is conceived for local users (tourist resorts, villages), especially if placed in small or medium islands, wishing to qualify for extensive use of renewable energy.
    Energy 12/2012; 48(1):566–576. · 4.16 Impact Factor
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    ABSTRACT: Selecting the best design options for turbo-expanders to be used in Organic Rankine Power Cycle applications is a difficult task, with special reference to the low-temperature applications (T < 150 °C) which are relevant for specific fields in rapid development (geothermal binary plants, solar thermal energy conversion systems). A wide literature exists on the optimal selection of the working fluid from the thermodynamic point of view; while the fluid dynamics design is often based on the direct application of CFD techniques, without a preliminary screening on the issues of application of a specific working fluid. In practice, however, the selection of the working fluid has relevant effects both on the cycle thermodynamics and on the fluid dynamic losses and turbo-expander efficiency. Referring to a radial-type turbo-expander, a comparison of different working fluids is presented and discussed.
    Applied Energy 09/2012; 97:601–608. · 5.26 Impact Factor
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    ABSTRACT: The flow in the second stage stator of a gas turbine with contoured end-wall is measured in a low speed wind tunnel. The investigation is focused on the flow in proximity to the blade trailing edge and in the wake. The measurements include mean velocity, total and static pressure at the cascade exit together with the analysis of intensity and spectral characteristic of turbulence. Measurements have been carried out using a miniaturized five-hole pneumatic probe developed in-house and a single hot wire anemometer on a measurement grid covering different distances from the blade trailing edge. The very fine measurement grids allow a detailed description of secondary flows and the possibility to trace the development of the vortex structures in the trailing edge region. The combined use of the pneumatic probe and of the hot-wire measurements allow to get a wide set of information on mean and turbulent characteristics of the three-dimensional flow at the exit of the cascade and identify the changes in the flow at different blade spans.
    Flow Turbulence and Combustion 04/2012; 64(4):253-278. · 1.27 Impact Factor
  • R. Strube, G. Manfrida
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    ABSTRACT: In order to reduce CO2 emissions from a power plant, CO2 can either be captured from the flue gases or from the syngas stream in a gasification plant. In this paper, the authors compare the effect of CO2 capture on power plant performance for a pulverised coal power plant with post-combustion CO2 capture, an Integrated Gasification Combined Cycle (IGCC) with either separate or co-capture of CO2 and H2S, as well as an oxy-fuel power plant with cryogenic CO2 purification. The highest impact on power plant performance is observed for post-combustion capture, while CO2 purification in oxy-fuel combustion has the lowest specific energy penalty for CO2 capture of all investigated options. All processes were simulated with Aspen Plus.
    International Journal of Greenhouse Gas Control - INT J GREENH GAS CONTROL. 01/2011; 5(4):710-726.
  • R. Strube, G. Pellegrini, G. Manfrida
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    ABSTRACT: In this paper the authors compare monoethanolamine (MEA) to aqueous ammonia (AA) and a solvent mixture of aqueous ammonia and ethanol (EAA) with respect to their post-combustion CO2 capture performance and their environmental impact. Simulation of all processes was carried out with Aspen Plus® and compared to experimental results for CO2 scrubbing with ammonia. Of special interest was the formation of stable salts, which could be observed in the experimental CO2 capture with both ammonia solvents. If CO2 can be captured in the form of ammonium salts, energy requirements are greatly reduced, since no energy is required for solvent regeneration and CO2 compression. The environmental impact of CO2 capture was investigated for a 500 MW pulverised coal power plant employing Life Cycle Assessment (LCA) using the software SimaPro®. For a comprehensive evaluation of this impact, influencing factors such as solvent production and solvent emissions were included. With kinetics taken into account, no salt formation could be observed in CO2 removal with aqueous ammonia. The necessary reduction of ammonia emissions leads to further energy requirements, and solvent production as well as the remaining ammonia losses to the environment have a more significant environmental impact than CO2 removal with MEA.
    Fuel and Energy Abstracts 01/2011; 36(6):3763-3770.
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    G Pellegrini, R Strube, G Manfrida
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    ABSTRACT: a b s t r a c t In order to reduce CO 2 emissions from a power plant, CO 2 can be captured either from the syngas that is to be burned or from the flue gases exiting the energy conversion process. Postcombustion capture has the advantage that it can be applied to retrofit existing power plants. In this paper the authors compare two primary amines (MEA and DGA) to ammonia with respect to their capability to capture CO 2 from a flue gas stream. The ammonia process captures CO 2 by formation of stable salts, which are separated from the solvent stream by filtration or sedimentation. These salts can be used commercially as fertil-izers. Energy requirements are greatly reduced, since no heat is required for solvent regeneration, and no compression of the separated CO 2 is necessary. Energy, however, is required for the reduction of ammonia emissions. In order to obtain the solid ammonia salts, their solubility has to be reduced by modification of the solvent and by lowering absorption temperature. With and without separation of the salt products, ammonia proved to be an alternative solvent with high CO 2 removal efficiency. Simulation of all processes was carried out with Aspen Plus Ò and compared to experimental results for CO 2 scrubbing with ammonia.
    Energy. 01/2010; 35(2).
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    ABSTRACT: The guiding idea behind oxy-fuel combustion power cycles is guaranteeing a high level of performance as can be obtained by today's advanced power plants, together with CO2 separation in conditions ready for transport and final disposal. In order to achieve all these goals, oxy-combustion – allowing CO2 separation by simple cooling of the combustion products – is combined with large heat recovery and staged expansions/compressions, making use of new components, technology and materials upgraded from modern gas turbine engines. In order to provide realistic results, the power plant performance should include the effects of blade cooling. In the present work an advanced cooled expansion model has been included in the model of the MATIANT cycle in order to assess the effects of blade cooling on the cycle efficiency. The results show that the penalty in efficiency due to blade cooling using steam from the heat recovery boiler is about 1.4 percentage points, mainly due to the reheat of the steam, which, on the other hand, leads to an improvement in specific work of about 6%.
    Energy 01/2009; 34(12):2240-2247. · 4.16 Impact Factor
  • Daniele Fiaschi, Roberto Graniglia, Giampaolo Manfrida
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    ABSTRACT: The possibility of improving the performance of deep well solar pumping systems by using centrifugal pumps with variable rotational speed and modular number of working stages (i.e. Divided Shaft Pump, DSP) was investigated and compared with traditional systems equipped with pumps having a fixed number of stages (i.e Standard Centrifugal Pump, SCP). Starting from commercially available pumps with a given head–mass flow characteristic, a visual simulation tool for the evaluation of the modified DSP pump performance and costs was developed. In principle, it would be possible to use the desired number of modular stages, thus achieving the highest efficiency of the system for all conditions of radiation. In practice, in order to reduce the DSP pump costs to an affordable level, only one shaft breakpoint is suggested (and then two modular blocks of stages), whose optimised position is determined by the simulation program on the basis of insolation curve during the daylight and required head and shaft speed.Referring to a 30 m2 PV system (about 3000 W peak power) and to a well depth of 100 m and considering a commercial 46-stage submersible pump, it was found that a breakpoint at the 31st impeller produced an increase close to 9% of the yearly pumped water yield with respect to a conventional, non-modular pump.For the above system, assuming that the cost of a modified modular pump is 1.5 times higher than that of a standard pump, the payback time varies from 0.5 to 2.5 years when the water sale price ranges between 1.1 and 0.6 €/m3.
    Solar Energy. 01/2005;
  • M. Liszka, G. Manfrida, A. Ziebik
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    ABSTRACT: The case study here presented deals with modernization of an industrial combined heat and power (CHP) plant located in a medium capacity steelworks industrial site. It is proposed to couple the existing power plant with a new gas turbine unit fired with Corex export gas. This fuel is a cold, low Btu by-product of the Corex process for pig iron production.The idea is to select the right distribution of heating surfaces in the heat recovery steam generator (HRSG) connected to a previously selected gas turbine and to the existing bottoming cycle in order to maximize the efficiency and economical profits of the whole plant.The study was performed using several simulation tools: a complete simulation of the system by means of engineering equation solver and a dedicated Fortran language code capable of performing all energy balances. For the correct design of the HRSG, a pinch analysis was applied. The whole set of simulation tools allowed comparing different solutions, of which the most promising ones are presented and discussed.
    Energy Conversion and Management. 01/2003;
  • G. Manfrida, A. Corti, D. Contini
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    ABSTRACT: In this paper, the results from a plume diffusion experiment on a small-scale model of a two-stack waste incinerator, carried out in a developed boundary-layer wind-tunnel, will be presented. A brief description of the tunnel, the measurement system, and the artificially developed neutral boundary layer is given. The experiments investigate ground-level concentration measurements and vertical and horizontal concentration profiles taken at different distances from the stacks. The results are compared with widely used Gaussian models like ISC3 and ADMS2.
    Int. J. of Environment and Pollution. 01/2001; 16(1/2/3/4/5/6):216-226.
  • A. Corti, D. Contini, G. Manfrida, L. Procino
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    ABSTRACT: In this paper results concerning a diffusion experiment on a small scale model of a waste incinerator, carried out in a boundary layer wind tunnel, will be presented. At the beginning a description of the measurement system that has recently been placed in the wind tunnel will be given together with a study of repeatability of the measurements results. A comprehensive study of the flow mean characteristics at different position in the tunnel working section will be reported and at the end some vertical and horizontal concentration profiles results will be described and discussed.
    Environmental Monitoring and Assessment 01/2000; 65(1):191-199. · 1.59 Impact Factor
  • Bruno Facchini, Daniele Fiaschi, Giampaolo Manfrida
    Journal of Engineering for Gas Turbines and Power-transactions of The Asme - J ENG GAS TURB POWER-T ASME. 01/2000; 122(2).
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    ABSTRACT: The environmental impact of electric power production through an Integrated Gasification Combined Cycle (IGCC) fired by dedicated energy crops (poplar Short Rotation Forestry (SRF)) is analysed by a Life Cycle Assessment approach. The results are compared with the alternative option of producing power by conventional fossil fueled power plants. The energy and raw materials consumption and polluting emissions data both come from experimental cases. Thermodynamic models are applied for simulation of the energy conversion system. The results establish relative proportions for both consumption and emissions of the two energy systems, in detail. Considerable differences emerge about the environmental impact caused by the different gasification conditions. The evaluation of the environmental effects of residues of the pesticides in ground/surface water and in the soil required a particular care, as well as the characterisation of all chemicals (herbicides, fungicides and insecticides) used for the crops.
    Energy Conversion and Management. 01/1999;
  • M. Ruggiero, G. Manfrida
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    ABSTRACT: Energy conversion systems based on biomass utilisation are particularly interesting because of their contribution to the limitation of global CO2 emissions; within the possible methods for energy-based biomass utilisation, thermal gasification appears as the most mature technology. In the first design stage, the designer of these systems, or the user looking for performance predictions under different operating conditions, has advantages of running thermochemical simulations allowing a prediction of the syngas composition and calorific value. The equilibrium model described in this paper is very simple, but it considers chemical species typically encountered by biomass gasifiers, and was tested against published experimental data.
    Renewable Energy 01/1999; · 3.36 Impact Factor
  • D Fiaschi, G Manfrida
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    ABSTRACT: In this work, a new Semi-Closed Gas Turbine Cycle (SCGT) configuration is presented, named Semi-Closed Gas Turbine/Regenerative Combined Cycle (SCGT/RCC). The SCGT/RCC is an hybrid combination of the SCGT/CC and SCGT/RE cycle concepts, including both partial regeneration of the gas turbine and coupling to a bottoming steam cycle by a small-size Heat Recovery Steam Generator (HRSG). An energy and exergy analysis is carried out for several configurations and operating conditions. A preliminary analysis of the RHE size, CO2 absorption potential and related effects on the cycle performance is presented, at several operating conditions and investigating three possible plant operation modes. The performance of the SCGT/RCC is very interesting at optimized operating conditions (specific power exceeding 550 kJ/kg of compressor inlet flow rate, efficiencies close to 50% including a 80% CO2 removal). This plant is a promising solution that combines the positive features of semi-closed gas turbines, allowing a drastic reduction of size and capital costs for both HRSG and RHE and maintaining high values of performance.
    Energy Conversion and Management. 01/1999;
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    Andrea Corti, Daniele Fiaschi, Giampaolo Manfrida
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    ABSTRACT: The analysis of the SCGT (Semi-Closed Gas Turbine cycle) is extended to the treatment of acid condensation (sulphur compounds) at the exit of the separator (SEP), with reference to different possible configurations already studied from the thermodynamic and environmental points of view. This detailed analysis was considered necessary because the natural gas fuel can contain a small amount of H2S which, reacting with air, can form SO2 and finally sulphuric acid. This can represent a problem (mainly from the economic point of view) because of the possibility of sulphuric acid condensation at the exit of the separator, where the temperature can reach values below the acid dew point of the mixture.The data obtained from ENI publications were used for the natural gas composition, and a 0.005% H2S molar fraction was additionally hypothesized. With these assumptions, about 0.1% SO2 can be found in the exhaust gases at the separator inlet.Aspen Plus was used in order to evaluate the chemical effects of the acidity of the condensate produced in the separator. An evaluation about costs of the devices to be used for condensation of the recirculated flue gas humidity has been performed, considering use of the special materials necessary for reducing the aggressive effects of acid water condensation.A final evaluation of the overall conversion system plant is also produced, showing the economic balance in terms of resulting cost of the unit of electrical energy produced and of inlet power in terms of fuel.The results are also evaluated in terms of CO2 emissions, considering the ratio between the global cost of the power generation plant and the global carbon dioxide emissions, compared to other types of energy conversion open cycle solutions.
    Energy Conversion and Management. 01/1999;
  • D Fiaschi, G Manfrida
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    ABSTRACT: An advanced cycle for the thermodynamic conversion of energy, which is particularly relevant in applications involving the use of cryogenic fuels and oxidants, is analysed by an exergy balance approach. This allows a check on which components are responsible for the largest irreversibilities and opens the way to further plant optimisation.
    International Journal of Hydrogen Energy 01/1999; 24(8):731-739. · 3.55 Impact Factor
  • Daniele Contini, Marco Ruggiero, Giampaolo Manfrida
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    ABSTRACT: The results of the investigation of the reactive flow in a scaled-down (≅1:3) model of a gas turbine combustion chamber are presented. The lean-premix combustion chamber model was tested at atmospheric pressure; measurements in the reactive flow were taken by using a two-channel fibre-optic laser Doppler anemometer with Al2O3 seeding on the air flow. Measurements cover a wide region of the axial-symmetric combustion chamber at points characterised by different seeding conditions and data rates, including the flame development and recirculating zones. This work presents a detailed analysis of the fluctuating components of flow velocity; mean flow properties are presented as a prerequisite. Frequency and time domain characteristics of turbulence including power density spectra, autocorrelation coefficients and time integral scales are reported and discussed, and a physical description of the reacting turbulent flow field is attempted.
    Revue Générale de Thermique 01/1998; 37(10):843-852.
  • Daniele Fiaschi, Giampaolo Manfrida
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    ABSTRACT: In the present paper, an exergy analysis of the SCGT/CC cycle is presented. Exergy destruction has been analysed at the component level in order to identify the critical plant devices, considering several operating conditions. The power-plant configuration is similar to that presented in previous works, with the possibility of total or partial water injection in the combustion chamber at peakload conditions.Combustion, heat recovery steam generator (HRSG), water injection/mixing and water recovery system are the main sources of losses, representing globally more than 80% of the overall exergy destruction. The second-law efficiency ranges between 49% and 53%, moving from the fully injected to the not injected condition. These values are close to those of standard open cycles, which means a good potential for the SCGT/CC cycle, which has several advantages from the point of view of containment of emissions and capability of peakload shaving.Peakload operation (with partial or total water re-injection) involves additional waste of exergy, but is attractive as it can be very extended for this plant configuration. Some critical components, such as condensing heat exchanger, show some sensitivity to the operating parameters, which however only marginally affects the cycle performance.
    Energy Conversion and Management - ENERG CONV MANAGE. 01/1998; 39(16):1643-1652.