1,721,056 research outputs found
Tecniche per l'integrazione di scambi termici all'interno di sistemi energetici complessi
No full textOptimum operation of a real renewable smart energy system including thermal electric and hydro storages
No full textSmart energy systems are meant as groups of energy conversion units that fulfill the requirements of several users’ demands exploiting the available energy sources according to “smart rules”.
This paper considers a smart energy system composed by both programmable units (hydroelectric plant, bio-oil and bio-gas internal combustion engines and woodchip boilers) and a non-programmable photovoltaic unit, which serve a group of users (houses, hotels, shops, craft workshops and industries) that requires thermal energy and electricity. The choice of the type and size of the system units was previously made according to government incentives on renewable energy production and historical data of users’ demands. Off-design models of each unit are built to properly simulate the system behavior starting from nameplate data supplied by the manufacturers and measured data from the field. A general optimization approach is then applied to search for the optimum operation of the total system, which maximizes the profit deriving from selling/using the generated electricity and thermal energy. The capacities of thermal and electric storages are also an outcome of the optimum operating strategy of the total system: results show that the optimum operation strategy can be achieved by including a thermal storage to reduce the use of boilers, while the inclusion of an electric storage is disadvantageous
Analisi e ottimizzazione della configurazione di un macrosistema di conversione di energia
Full text linkThe depletion of fossil fuel sources and the increasing difficulty in the search and development of alternative sources push to the search of more complex energy systems configurations to enhance efficiency and reduce costs. This, in turn, requires more efficient (but simple) tools to predict systems behavior with the required level of accuracy (simulation tools), and increases the number of options both in the system design and operation (optimization procedures).
A general approach for energy systems simulation and optimization is first presented in this thesis, which applies at any level of system complexity and dimensions. The attention is then focused on Macro-Systems, consisting of a set of energy systems which convert primary energy sources into different energy forms required by the users, the former being variable both in time and space, the latter depending also on market rules and users characteristics. Reliable models are built to forecast Macro-Systems behavior. Binary variables are included in these models at design level to decide the inclusion or exclusion of a single plant or to decide its on-off status at off-design conditions depending on the objective being considered. At the same time detailed models of the single plants that are expected to be included in the Macro-Systems are developed to extract reliable Fuel-Products relationships of each plant to be included in the Macro-System model. These relationships are in general well approximated by linear functions. Constraints on the variability in time of each plant load are also included to model their real behavior.
The design and off-design optimization problems of Macro-Systems described by these models belongs to the wider MILP (Mixed-Integer Linear Programming) dynamic optimization problems, which is analyzed in the first part of this thesis, describing in particular the “dynamic programming” technique that is used to simplify the search of the solution. An original approach for the decomposition of the dynamic optimization problems into two sub-problems is then proposed to simplify the search of the solution and reduce the computational effort without a significant loss in accuracy. Finally, two applications are presented: the first one refers to traditional steam and combined cycle power plants operating in the German power free market generation system. The reduction in profits generated by these plants deriving from the priority assigned to renewable power systems in the market is evaluated using real price and fuel cost data in a period of four years. The second application deals with a complex Macro-Systems for combined heat and power production feeding a district heating network with variable demand. The volume of a thermal storage system which keeps the electric power generation independent of the thermal demand is optimized according to the maximum profit of the whole Macro-System in a year of operation
Tecniche per l'Integrazione di Scambi Termici all'Interno di Sistemi Energetici Complessi
No full textUna delle vie per ottenere elevate prestazioni in sistemi di conversione di potenza è quella di creare una stretta integrazione
termica tra i componenti di tali sistemi: quando all’interno di un sistema vi è la presenza di una o più sorgente di calore
inutilizzate è conveniente sfruttare tali sorgenti con pozzi freddi già presenti nel sistema, o con nuovi pozzi opportunamente
aggiunti. Lo sfruttamento di queste sorgenti deve avvenire in modo coerente e con le minori perdite exergetiche possibili.
La forte integrazione termica che ne deriva porta all’ottenimento di strutture talvolta molto complesse nelle quali
l’individuazione di possibili miglioramenti può risultare difficoltosa senza l’ausilio di strumenti adatti alla semplificazione
di tale ricerca. In questo articolo vengono raccolte, analizzate e applicate diverse tecniche per la sintesi dei sistemi
energetici. Il primo metodo considerato è la Pinch Analysis, una serie di regole che permettono lo studio degli scambi di
calore interni ai sistemi grazie alla costruzione di curve che rappresentano lo scambio termico complessivo. Queste
procedure risolvono parte delle problematiche relative all’integrazione di processi, in particolare quando siano assegnate
portate e temperature dei flussi termici. Gli strumenti derivanti dalla Pinch Analysis vengono utilizzati per lo studio di
diversi impianti di potenza nei quali la rigenerazione interna può dar luogo a configurazioni efficienti ma di notevole
complessità. Viene successivamente presentata e applicata una nuova tecnica per la sintesi dei sistemi energetici
recentemente proposta all’interno del Dipartimento di Ingegneria Meccanica dell’Università di Padova, la cui peculiarità
consiste nel poter determinare le temperature dei flussi termici ottimali per il sistema complessivo indipendentemente dalla
configurazione della rete di scambiatori
TSO-STO: A two-step approach to the optimal operation of heat storage systemswith variable temperature tanks
No full textMixed-Integer Linear Programming (MILP) has been generally used in the recent past to evaluate the optimal operation of heat storage systems for district heating. In fact, model equations and constraints can be linearized to strongly reduce the computational time without a significant loss in accuracy, and other simplifying hypotheses can be introduced, such as the constant value of the heat storage temperature. This paper presents instead a non-linear model of a Combined Heat and Power (CHP) system with a variable temperature heat storage serving a district heating network. Optimal operation for a fixed time-dependent demand is searched by varying CHP system loads. The objective is the maximization of management profit in a deregulated electricity market, taking into account investment (CHP and heat storage systems) and operating costs. The nature of the problem is investigated and a new approach for the decomposition of the objective function is proposed to simplify the solution procedure. The impact of different fuel costs and average electricity prices on the results is also analyzed. © 2012 Elsevier Ltd
Off-design dynamic model of a real Organic Rankine Cycle system fuelled by exhaust gases from industrial processes
No full textORCs (Organic Rankine Cycles) represent an effective option to exploit low grade heat fluxes, the characteristics of which not only affect design, but also performance and stability during operation.
This paper presents a detailed design and off-design dynamic model of a superheated regenerative
ORC system using the exhaust gases of an industrial process. The point of view is that of a designer who
has to predict the system behavior both at steady-state and transient operation to get a reliable and
efficient operation. Real physical and operating characteristics of all components are considered, with
particular attention to the geometries of shell-and-tube commercial heat exchangers to properly
simulate mass and thermal inertias. A suitable control system is chosen to govern the off-design operation
taking into account all real operating constraints.
Results show a slight decrease in gross system efficiency (less than 1% point) either varying the oil
mass flow rate (in the range 80-110%) at constant temperature of the cold sink or this temperature (of
10 °C) at constant oil mass flow rate. Simulation of the transient behavior demonstrates the effectiveness
of the control system on ORC stability under variation of the hot source mass flow rate and cold sink
temperature
Optimum choice and placement of concentrating solar power technologies in integrated solar combined cycle systems
No full textConcentrating solar power plants projects have been rapidly increasing over the last few years driven by the advances in the solar technology. The operational issues associated with the variable nature of solar energy could be overcome by integrating the solar input into fossil-fuelled power plants. In this paper solar energy is added to the bottoming part of a state-of-the-art three pressure level natural gas combined cycle and parabolic trough, linear Fresnel and solar tower technologies are considered in the search for the optimum integration. Detailed models of the combined cycle and solar field are built in the Thermoflex® environment to evaluate the performance of different integrated solar combined cycle system configurations. Results show how the placement of solar heat addition affects the heat absorption in the heat recovery steam generator and, in turn, the overall system performance. Unlike solar-only power plants which call for the highest temperature concentrating solar technologies to maximize thermal efficiency, the best integration is obtained here using moderate temperature concentrating solar technologies which enable a significant reduction of the heat transfer irreversibility in the heat recovery steam generator. Accordingly, high solar radiation-to-electricity conversion efficiencies approaching 30% are achieved using well-established solar technologies
Supercritical CO2 and air Brayton-Joule versus ORC systems for heat recovery from glass furnaces: Performance and economic evaluation
No full textThis paper evaluates the thermodynamic and economic performance of four different heat recovery systems (HRSs) applied to two hollow glass furnaces providing 1.2 to 4 MWt of wasted heat at 450°C. Organic Rankine Cycle (ORC), two configurations of supercritical CO2 Brayton-Joule cycle (sCO2) and an innovative regenerative air Brayton-Joule cycle generating compressed air and/or power are modeled at both design and off-design conditions. The aim is to find the most commercially attractive HRS for the considered glass furnaces, as representative of small-to-medium size ones, taking into account all physical and technological constraints. The optimized designs of all systems are first obtained by identifying “average” heat recovery conditions from real data. Off-design simulations are then conducted to predict the behavior of the HRSs considering ambient temperature variations and furnaces ageing process. Results show that the ORC systems are the most attractive HRS available in the market for small-size furnaces while the air Brayton-Joule cycle appears to be the best choice when bigger furnaces are
considered. On the other hand, the sCO2 cycle systems show the highest power output in the whole range of furnace sizes while being still penalized by the too high costs deriving by their early-stage precommercialization
phase
Fase 2: Technical and thermodynamic analysis of the selected technologies
No full textRapporto per Enel Ingegneria e Ricerca Spa, nell’ambito del progetto “ANALISI TECNICA DELL’INTEGRAZIONE DI DIVERSE TECNOLOGIE SOLARI CON UN CICLO COMBINATO
On the optimum integration of solar energy into natural gas combined cycles
No full textConcentrating solar power plant projects have been rapidly increasing over the last few years driven by the advancements in the solar technology. While the early power plants were mainly based on parabolic trough collectors using thermal oil as heat transfer fluid, a significant number of large scale power plants either built recently or in the development phase use linear Fresnel collectors and solar tower technology. Moreover, molten salts and water/steam are often preferred as heat transfer fluid. The operational issues associated with the variable nature of solar energy could be overcome by integrating the solar input into a fossil-fuelled power plant. In this paper the integration of solar energy into the bottoming part of a three pressure levels natural gas combined cycle having a rated power output of 400 MW is analyzed. The three main concentrating solar power technologies, namely parabolic trough, linear Fresnel and solar tower are considered in the search for the optimum integration. Detailed models of the combined cycle and solar field are built in the Thermoflex® environment and the performance of different systems configurations is evaluated. Results show how the position of solar heat addition affects the heat absorption in the heat recovery steam generator (HRSG) and, in turn, the overall plant performance. A proper integration makes the solar heat available at moderate/high temperatures while simultaneously generating heat sinks at high temperatures in the HRSG. The best integration options increase the average temperature of heat absorption in the HRSG and, by improving the thermal matching with the flue gases, decrease the irreversibility of the combined cycle. Accordingly, high solar heat to power conversion efficiencies in the 40-50% range are achieved even at moderate solar heat temperatures due to the favorable synergies in the integrated plant
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