1,721,015 research outputs found
Techno-economic analysis of closed OTEC cycles for power generation
No full textThis study aims at offering a techno-economic evaluation of closed OTEC cycles for on-shore installations. A flexible Matlab®suite has been developed to identify plant design parameters (temperature difference of cold and warm seawater, pinch-point temperature difference of evaporator and condenser etc.) that guarantee the maximum value of γ (ratio between electricity output and heat exchangers area). The optimization model is able to handle different working fluids through the addition of specific correlations that consider fluid influence on heat transfer coefficients and turbine performance. Each plant component is technically analyzed and, in particular, plate heat exchangers were considered for evaporator and condenser and sized accurately with Aspen EDR®, while expander was analyzed with the in-house code Axtur. For warm seawater temperature of 28 °C and cold seawater temperature of 4 °C (8500 kg/s taken from 1000 m depth), ammonia cycle is the best solution characterized by efficiency equal to 2.2% and net power output equal to 2.35 MWe. The obtained LCOE (269 €/MWhe) confirms how OTEC technology is not ready to compete in energy market. Nevertheless, remote zones (i.e. small islands archipelagos), which are often characterized by high electricity price, represent interesting scenarios where OTEC technology could be a promising alternative to conventional power production technologies
Off-design performance of closed OTEC cycles for power generation
Full text linkThe present study illustrates the development of a detailed model to estimate the part-load performance of an ammonia closed OTEC system for on-shore installations. A previously published Matlab® suite is extended by accounting for off-design conditions in terms of variable seawater temperature and mass flow on the cycle performance. The off-design behavior of each component is thoroughly discussed, with particular attention devoted to the single-stage axial-flow turbine, whose performance maps are obtained by means of three-dimensional CFD simulations. Assuming a representative plant sized for warm seawater temperature of 28 °C and cold seawater temperature of 4 °C (8500 kg/s taken from 1000 m depth), the model predicts an annual electricity yield of 15.963 GWhe and LCOE of 316 €/MWhe when including seawater measured data of a simile-Hawaiian site. Moreover, a sensitivity analysis is assessed in order to identify the best design parameters (i.e. warm seawater temperature and cold seawater mass flow rate) that minimize the LCOE for the given location. The new design guarantees a reduction of approximately 11% of the LCOE (284 €/MWhe). The simulation capabilities of the developed model prove it as valuable tool to estimate the OTEC competitiveness in different scenarios
Studio dell’associazione tra inquinamento atmosferico e ricoveri ospedalieri per patologie respiratorie nella città di Novara
No full textSmall scale solar tower coupled with micro gas turbine
No full textThis paper studies a small-scale CSP system composed of a solar tower and a recuperative air micro gas turbine (i.e. net power in the 100–200 kWe range). A code is developed to determine the optical performance of the heliostat field coupled with a secondary concentrator, while another code computes the thermal engine performance. The 832 m2 heliostat field layout is taken from a real plant, while the secondary optics is studied to maximize the optical-thermal efficiency. The selected secondary concentrator (CPC), with an aperture diameter of 0.5 m and an acceptance angle of 35° tilted of 52.5°, guarantees an overall optical efficiency of 77.9% in design conditions (Spring equinox, solar noon) and of 66.9% on yearly basis. For every Effective DNI (EDNI) and ambient temperature the turbine operation is optimized allowing to achieve a yearly solar-to-electricity efficiency of 16.3%. Summing up the cost of each component, an overall plant cost of about 2300 €/kW (peak) and a LCOE of 175 €/MWh are obtained. A sensitivity analysis on design EDNI, impacting on turbine size, is performed showing that its reduction from 700 W/m2 to 550 W/m2 allows reducing the LCOE down to 158 €/MWh, a value competitive with large-scale solar towers. The possibility of hybridization of plant (i.e. improving the gas turbine power output in selected hours, by means of biomethane or natural gas combustion) was considered to further reduce the LCOE
Studio della distribuzione del biossido di azoto aerodisperso in una piccola realtà urbana piemontese
No full textPART LOAD ANALYSIS OF A CONSTANT INVENTORY SUPERCRITICAL CO2 POWER PLANT FOR WASTE HEAT RECOVERY IN CEMENT INDUSTRY
Full text linkPART-LOAD OF STEAM RANKINE CYCLES FOR SOLAR SALTS-BASED CONCENTRATING SOLAR POWER PLANTS
No full textThis work proposes two ad hoc part-load control strategies for steam cycles adopted in concentrated solar power plants. The control strategies are designed to keep the molten salt temperature above the minimum allowed value set by solidification issues in the 30-100 % load range. Particularly critical is the temperature of molten salts in contact with the heat exchanger tubes, the so called skin temperature. The first control strategy adopts a turbine with controlled extraction and readmission valve while the second strategy employs a throttling valve and a feedwater preheating loop. Off-design simulations show that both strategies are capable of avoiding the molten salts solidification issue but at the cost of a non negligible penalty (up to -1.9 percentage points) in power block efficiency at low loads (30- 50%). The off-design analysis considers also the effect of ambient temperature variations and the optimization of the cooling fan rotational speed. The results are used to derive best-fit polymonials relating the power block efficiency to the ambient temperature and load
Monitoring nitrogen dioxide and its effects on asthmatic patients: two different strategies compared
No full textA two-step procedure for the selection of innovative high temperature heat transfer fluids in solar tower power plants
No full textThis work compares with a two-step procedure the performance of different Heat Transfer Fluids (HTF) for high temperature receiver applications (up to 715 °C) in advanced Solar Tower (ST) plants. The most promising molten salts and liquid metals are initially selected and ranked according to their performance, estimated with different Figures of Merit (FoM) available in literature or newly defined. For the best performing fluids, different hydraulic configurations and tube diameters at fixed receiver size are tested. The optimized external tubular receiver configuration for each HTF is then implemented in a ST plant and its performance is assessed through a detailed techno-economic analysis, considering the use of a direct thermal energy storage system and of a sCO2 based power cycle. As a second step, the yearly electricity yield and the LCOE are evaluated for two different sites. Results show NaCl–MgCl2 as the best option for the considered type of plant with a LCOE of 151 $/MWh, which is anyhow 10% higher than the reference Solar Salts case
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