1,721,033 research outputs found
Design of an onboard auxiliary power and desalination unit powered by a stirling engine
No full textA partire dalla crescente richiesta di maggiori prestazioni e comfort a bordo delle imbarcazioni da diporto, è stato studiato e realizzato un innovativo sistema integrato per la produzione di energia elettrica ed acqua dolce. Il prototipo, che si inserisce nel filone della micro cogenerazione distribuita, prevede l'utilizzo di un motore Stirling da 1 kWe, il cui calore di risulta è utilizzato per la produzione di circa 150 l/giorno di acqua dolce per mezzo di un impianto di dissalazione termica a singolo effetto.
Di tale impianto sono state inizialmente valutati la fattibilità tecnica, le caratteristiche e le prestazioni conseguibili. In seguito, studi teorici e codici di calcolo hanno portato alla definizione della configurazione finale del prototipo funzionante. A questo punto, è stata avviata la fase di caratterizzazione e di valutazione delle prestazioni effettive in comparazione con sistemi di dissalazione a membrana già in commercio.
In generale, l'analisi sperimentale ha dimostrato una ottima corrispondenza delle prestazioni reali con quelle preventivate dagli studi teorici. In particolare, ai carichi nominali (@50°C) l'impianto termico ha presentato una producibilità di acqua dolce di circa 7 l/h ed una potenza termica di scambio all’evaporatore superiore a quella di progetto (5 kWt).
L’analisi sperimentale, inoltre, ha contribuito alla comprensione di numerose interconnessioni tra i diversi parametri di processo. In accordo con quanto preventivato, la produzione di acqua dolce è risultata fortemente dipendente dal contenuto salino dell’acqua
trattata e dalla differenza di temperatura tra il fluido termovettore caldo e l’acqua salata nel serbatoio evaporatore. Tuttavia, anche alle condizioni operative più severe l’impianto ha raggiunto prestazioni molto interessanti. In aggiunta, l’apparato ha dimostrato una risposta eccellente a potenze termiche d’ingresso variabili nel tempo, confermando l’opportunità di funzionare alimentato anche da forme differenti di calore di scarto
Environmental and energy assessment of a small-scale solar Organic Rankine Cycle trigeneration system based on Compound Parabolic Collectors
No full textDuring the last years, combined cooling, heating, and power (CCHP) systems have drawn a lot of attention thanks to their low greenhouse gas (GHG) emissions, high efficiency and cost benefits. Considering the increasing interest on sustainability assessment of novel energy generation technologies, in this paper a life cycle assessment of an innovative small-scale solar Organic Rankine Cycle (ORC) trigeneration plant is performed. The plant under investigation is composed of a 50 m2 Compound Parabolic Collectors (CPC) solar field, a 3 m3 diathermic oil storage tank, a 3.5 kWe ORC plant and a 17 kWc absorption chiller. After the set-up of the inventory data of the different subsystems, a sensitivity analysis of the environmental and energy performance of the plant has been conducted by varying: (i) the system adjustment parameters; (ii) the size of the solar field and the consequent solar multiple index of the plant; and (iii) the organic working fluid of the ORC unit. Results of the analysis confirmed that the Life cycle assessment (LCA) is of paramount importance for the appropriate selections of component specifications and operating conditions of the integrated system. In particular, the investigation has revealed that the variation of the adjustment parameters brings to slight modifications of the energy performance and has a limited impact on the environmental output whilst the proper selection of the working fluid and the size of the solar field can result in an appreciable environmental optimization of the whole plant
Novel characterisation of biofuel-integrated phytoremediation of liquid wastes with Scenedesmus obliquus
No full textThis study investigates the feasibility of in situ phytoremediation of leachate and wastewater in municipal solid waste facilities using microalgae and their valorisation for biofuel production. Laboratory-scale experiments were conducted by cultivating the Scenedesmus obliquus microalga in a diluted growth medium inside a 4 L indoor photobioreactor, operating in batch mode. Volumetric productivity data were employed to evaluate the economic viability of the system. Then, a numerical model developed in Aspen Plus was used to estimate the utility requirements for upgrading crude microalgae oil into biodiesel meeting commercial specifications. The results indicate that, although the resulting biodiesel satisfies UNI EN 14214 quality standards, the limited biomass productivity remains a critical constraint for economic feasibility. Remuneration, in terms of net present value is achievable only under scenarios that combine high biomass yield and microalgae oil sale prices exceeding 2–2.5 € kg−1. The system generates 57–722 k€ after 20 years
Simulation analysis of an innovative micro-solar 2kWe Organic Rankine Cycle plant for residential applications
No full textIn this paper a 2kWe small scale Organic Rankine Cycle system coupled with a concentrated solar linear Fresnel lens collector is investigated using a simulation analysis. Coupling small scale solar technologies with ORC system is a well-known solution in low temperature ranges. Efforts exist to achieve higher temperatures and overall efficiencies but at present such systems represent a challenge at small scale. This work is part of the EU funded Innova MicroSolar project about development and optimization of a solar linear Fresnel lens concentrator coupled with 2kWe Organic Rankine Cycle plant and with a PCM thermal storage system for residential applications. In this paper a preliminary assessment of the performance of two of the main components of such system (i.e. solar linear Fresnel lens collector and ORC) is presented. A dynamic analysis of the system is performed by varying the operating conditions. In particular the influence of the system configuration and working temperatures on the ORC overall efficiency is evaluated. The final aim of the work indeed is to assess the best working conditions for such micro-CHP to be integrated in residential buildings
Comparative sensitivity analysis of micro-scale gas turbine and supercritical CO2 systems with bottoming organic Rankine cycles fed by the biomass gasification for decentralized trigeneration
No full textIn this article, the performance of a micro gas turbine (mGT) and a supercritical CO2 (sCO2) system fuelled by a biomass gasifier and with similar nominal net power output is compared. Both plants include a bottoming organic Rankine cycle system to maximise the electrical power output. Using a component-oriented, off-design modelling approach a sensitivity analysis is performed by varying the main operating parameters. In addition, the integrated systems are also evaluated in combination with a network of residential apartments to assess their adaptability to variable users' thermal and electrical demands.
Results have shown that at full load and ambient temperature of 15 °C, the average net electric power of the whole integrated sCO2 system is around 126 kWe which is approximately 25% higher than the one of the mGT system, but with a lower net electric efficiency resulting in 75% higher biomass consumption. Nonetheless, the net thermal power production of the integrated sCO2 system is almost 355 kWt which is 4.35 times higher than the mGT system resulting in higher overall efficiency. When combined with residential apartments, the sCO2 system proves to be suitable for 140 apartments operating with higher overall efficiency compared to the mGT system coupled with 30 apartments
Hybrid system with micro gas turbine and PV (photovoltaic) plant: Guidelines for sizing and management strategies
No full textThis paper presents a hybrid system consisting of a 100 kWe micro gas turbine (MGT) that juxtaposes the energy production of a photovoltaic (PV) plant whose yearly yield is available by on field measurements. The aim of the work is to model and investigate the behavior and the performance of a hybrid MGT-PV system under the topical constraint of firming renewable power and hence of guaranteeing a reliable power production to the grid. We propose a solution for the sizing of the PV plant and two strategies for the management of the hybrid system in order to guarantee a reliable day-ahead hourly forecast of the electric power that can be actually produced by the plant under whatever ambient condition. The results ascertain the advantages of the upgraded system in terms of natural gas consumption (−16%) and and NOX (∼ −33%) with a higher local emission of CO. In particular, the proposed hybrid system: i) solves the problem due to the unpredictability of PV energy production; ii) grants a significant reduction of the primary fuel usage and specific energy cost; but iii) increases the level of local pollutants, since it internalizes the emissions previously generated in a centralized power plant to produce the amount of electricity of the hybrid system
Municipal scale scenario: Analysis of an Italian seaside town with MarkAL-TIMES
Full text linkThis work presents three 25-year energy scenarios developed with the TIMES model generator for Pesaro, a seaside municipality in central Italy. It evaluates the effectiveness of local-scale energy policies in three sectors: households, transport, and the public sector (PS). Since the local energy demand is affected by summer tourism, seasonal consumption by holiday homes was also studied. Three scenarios were hypothesized: Business as Usual (BAU), Exemplary Public Sector (EPS), and Exemplary Municipality (EM). The EPS scenario models the exemplary role that recent European directives attribute to the PS in setting energy efficiency and technology penetration targets for itself; the EM scenario extends these targets to the household sector. In particular, the study underscores the potential of micro-cogeneration technologies in achieving local environmental targets, even though their diffusion would involve an increase in local energy consumption due to internalization of the primary energy used to produce electricity, which would no longer be wholly imported from outside municipal boundaries. The study provides information to local decision-makers by estimating the cost of implementing a number of energy policies. Finally, the study discusses the adequacy of TIMES as a tool to analyse municipal-scale scenarios
Modelling the Italian household sector at the municipal scale: Micro-CHP, renewables and energy efficiency
Full text linkThis study investigates the potential of energy efficiency, renewables, and micro-cogeneration to reduce household consumption in a medium Italian town and analyses the scope for municipal local policies. The study also investigates the effects of tourist flows on town's energy consumption by modelling energy scenarios for permanent and summer homes. Two long-term energy scenarios (to 2030) were modelled using the MarkAL-TIMES generator model: BAU (business as usual), which is the reference scenario, and EHS (exemplary household sector), which involves targets of penetration for renewables and micro-cogeneration. The analysis demonstrated the critical role of end-use energy efficiency in curbing residential consumption. Cogeneration and renewables (PV (photovoltaic) and solar thermal panels) were proven to be valuable solutions to reduce the energetic and environmental burden of the household sector (−20% in 2030). Because most of household energy demand is ascribable to space-heating or hot water production, this study finds that micro-CHP technologies with lower power-to-heat ratios (mainly, Stirling engines and microturbines) show a higher diffusion, as do solar thermal devices. The spread of micro-cogeneration implies a global reduction of primary energy but involves the internalisation of the primary energy, and consequently CO2 emissions, previously consumed in a centralised power plant within the municipality boundaries
Investigation on the use of a novel regenerative flow turbine in a micro-scale Organic Rankine Cycle unit
No full textReliable and low-cost expanders are fundamental for the competitiveness of small-scale Organic Rankine Cycle (ORC) plants using low-temperature heat sources. Regenerative flow turbines (RFTs) can be considered a low-cost and viable alternative expander, yet their performance needs to be fully investigated. Therefore, the use of an RFT in a micro-scale ORC test bench is investigated in this work through a modelling study. Specifically, three-dimensional CFD simulations are carried out to assess the performance of the considered expander with varying operating conditions and a numerical model of a non-regenerative, small-scale ORC system is developed to investigate its potential in waste heat recovery (WHR) applications.
Using R245fa as the working fluid, the CFD analysis shows that the expander achieves a maximum total-to-static isentropic efficiency of about 44% in the investigated operating range. The small-scale ORC system has a net output power in the range 100–600 W and a net cycle efficiency of 1–2.3%. Moreover, a comparison with two scroll expanders having different built-in volume ratios shows that the RFT operates with higher isentropic efficiencies in low mass flow rates and pressure ratios thus highlighting its suitability for low-temperature WHR applications, especially when considerable fluctuations of the heat source are expected
Comparative study of steam, organic Rankine cycle and supercritical CO2 power plants integrated with residual municipal solid waste gasification for district heating and cooling
No full textAmong the different waste-to-energy solutions, gasification is considered a promising option and an alternative to landfilling of residual municipal solid waste (RMSW). Therefore, the potential of RMSW air gasification in combination with three different power cycles for district cooling and heating applications is investigated. The model of a fluidized bed air gasifier developed in Aspen Plus is integrated with the models of steam turbine (ST), organic Rankine cycle (ORC), and supercritical CO2 (sCO2) Brayton cycle power plants for the combined cooling, heating, and power production in district networks.
The results of the numerical study show that the ST power plant provides higher electrical power compared to the other systems, while sCO2 exhibits better thermal power and the maxima combined energy conversion efficiency. In between, ORCs prove to be a reliable and flexible solution for varying RMSW compositions and temperature levels of the district network. The size of the district network strongly varies with scenarios and in the best case, more than 1,400 residential buildings can be connected to the trigeneration plant considering 20 ktons/year of RMSW input to the gasifier
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