1,721,082 research outputs found
Solar electricity generation in hybrid thermal power plants
No full textThe EU Directive on renewable sources, Directive 2009/28/EU, requires European countries to increase renewable energy uses until they reach 20% of gross final energy consumption. This target has been distributed among the member states which have put incentives on renewable energy uses and renewable electricity generation.
Among renewable sources, solar energy is one of the most interesting but it presents a key issue: it is a non-dispatchable renewable energy source. For this reason, when solar energy is used to produce electricity, concentrated solar thermal power plants are often integrated in conventional fossil power plants (hybrid power plants); in this case it is very important to distinguish the amount of electricity produced by this renewable source from the one produced by fossil source, since the two heat inputs can contribute to electricity production in different measure. It is possible to elaborate numerical models able to quantify performance of hybrid power plants and to allocate the total electricity for each energy source: for example, assuming a constant fuel consumption and adding solar heat, these numerical simulations allow evaluating the extra electricity generated, that is really the electricity from solar energy. However, such an evaluation is impossible during power plant operation.
This paper presents a simple, but effective, methodology able to distinguish electricity generation of each energy source during hybrid power plants operation: it is necessary to know (by measures) only heat input from fuel and solar energy, initial and final temperatures of working fluid during heat addition and rejection, and the factor of internal losses. This last parameter is very important and this paper not only demonstrates that it doesn't depend on solar energy share but it also proposes its evaluation. Finally the paper compares results of this methodology with those of numerical models here elaborated showing their perfect correspondence in solar electricity evaluation
Hybrid thermal power plants: Solar-electricity and fuel-electricity productions
No full textIn response to global climate target, over the last decade renewable electricity generation from solar energy has grown rapidly and hence measures to deal with its non-dispatchable nature. Integrating concentrating solar plants in conventional fossil power plants is a widely researched solution to tackle solar energy intermittency. This results in hybrid power plants whose total electricity production consists of two different contributions (solar and fuel-electricity) that can be evaluated separately by implementing numerical methods based on the so-called "with and without solar energy" approach. Nonetheless, such evaluation cannot be carried out in actual power plants operation where fossil and renewable contributions are not discernible from each other within the overall production.To overcome this limitation, and consequently allow the total electricity generated to be properly partitioned among energy sources, this study proposes and validates an alternative "on-line and real-time" method to quantitatively assess solar and fuel-electricity by subdividing the overall cycle efficiency into subsequent ones related to the different energy conversion processes during real plant operation. Required input can be derived from available operating data except for factor of internal losses that, however, showing negligible dependence on solar energy and power plant load, can be reasonably assumed constant and estimated in dedicated calculations
Energy and environmental analysis of glass container production and recycling
No full textThis work aims at examining, from an energy and environmental standpoint, one production cycle which is extremely energy-consuming, namely the glass production for drink containers. More specifically, the industrial process is first analysed as is, so as to evaluate and assess its energy needs and its associated environmental impact. As a second step the influence of glass container recycle and reuse on energy consumption and pollutant emission is investigated. To this end the recycling chain operation is illustrated and appropriate working hypotheses for the modified process are formulated, so that its energy and environmental performance can be evaluated. Finally, the two production scenarios are compared by means of LCA (Life Cycle Assessment) methodology, to the purpose of determining the best recycling percentage for glass containers from the standpoint of energy consumption and pollutant emission minimization, taking also into account the waste legislation currently in forc
Cogenerazione ad alto rendimento Parte A: inquadramento normativo e procedure generali di calcolo
No full textDal 1 gennaio 2011, con l’introduzione in ambito nazionale della Cogenerazione ad Alto Rendimento (CAR), il contesto legislativo di incentivazione della cogenerazione
è mutato e, conseguentemente, sono cambiate le condizioni sia per valutare la fattibilità tecnico-economica di nuovi impianti di cogenerazione sia per
esercire in condizioni ottimali gli impianti esistenti. Nel presente lavoro, suddiviso in due parti, si intendono analizzare i seguenti aspetti:
- Parte A: inquadramento normativo della CAR, classificazione degli impianti e procedure generali di calcolo per le tipologie impiantistiche più rappresentative;
- Parte B: valutazioni numeriche finalizzate a caratterizzare le prestazioni CAR delle diverse soluzioni impiantistiche e ad analizzare l’impatto della nuova legislazione
sul potenziale applicativo di ciascuna soluzione
Cogenerazione ad alto rendimento - CAR Parte B: le prestazioni di impianti di cogenerazione industriale
No full textNella Parte A del presente lavoro è stato fornito l’inquadramento normativo della CAR e sono state illustrate le procedure generali di calcolo per le tipologie impiantistiche
più rappresentative della cogenerazione industriale. Sulla base dei parametri emersi da tale illustrazione, in questa Parte B vengono condotte valutazioni
numeriche finalizzate a caratterizzare le prestazioni CAR delle diverse soluzioni impiantistiche e ad analizzare l’impatto della nuova legislazione sul potenziale
applicativo di ciascuna soluzione impiantistica
Advanced power plants with very low CO2 emissions
No full textIntegrated Gasification Combined Cycle (IGCC) power plants represent one of the most appealing options to produce electricity from coal with interesting plant efficiency and low environmental impact. Usually, these power plants are equipped with oxygen-blown gasifiers which have two main advantages with respect to air-blown reactors: high values of cold gas efficiency and an N2 deprived syngas. The aim of this paper is to compare three different oxygen production technologies for oxidant supply to the gasification island. An IGCC power plant with pre-combustion CO2 capture has been modelled considering: (i) a cryogenic distillation Air Separation Unit (ASU) based on a pumped liquid oxygen cycle; (ii) an innovative Oxygen Transport Membrane (OTM) based oxygen production technology integrated in the power island; (iii) an innovative oxygen separation system based on open gradient magnetic field (magn-AS, magnetic air separation). An overall heat and material balance has been estimated to evaluate plant performances and compare the three options; our thermodynamic analysis shows a promising improvement of the overall plant performance for the IGCC power plants equipped with these innovative technologies nonetheless several key issues deserve a more in depth analysis to assess the real potentialities of these technologies
Natural gas decarbonization technologies for advanced power plants
No full textIn this paper two options for H-2 production, by means of natural gas, are presented and their performances are evaluated when they are integrated with advanced H-2/air cycles. In this investigation two different schemes have been analyzed: an advanced combined cycle power plant (CC) and a new advanced mixed cycle power plant (AMC). The two methods for producing H-2 are as follows: (1) steam methane reforming: it is the simplest and potentially the most economic method for producing hydrogen in the foreseeable future; and (2) partial oxidation of methane: it could offer an energy advantage because this method reduces the energy requirement of the reforming process. These hydrogen production plants require material and energetic integrations with power section and the best interconnections must be investigated in order to obtain good overall performance. With reference to thermodynamic and economic performance, significant. comparisons have been made between the above introduced reference plants. An efficiency decrease and an increase in the cost of electricity has been obtained when power plants are equipped with a natural gas decarbonization section. The main results of the performed investigation are quite variable among the different H2 production technologies here considered: the efficiency decreases in a range of 5.5 percentage points to nearly 10 for the partial oxidation of the natural gas and in a range of about 9 percentage points to over 12 for the steam methane reforming. The electricity production cost increases in a range of about 41-42% for the first option and in a range of about 34-38% for the second one. The AMC, coupled with partial oxidation, stands out among the other power plant solutions here analyzed because it exhibits the highest net efficiency and the lowest final specific CO2 emission. In addition to this, economic impact is favorable when AMC is equipped with systems for H-2 production based on partial oxidation of natural gas
Advanced mixed cyles based on steam- methane reforming and air blown combustion
No full textIn this paper the overall performance of a new advanced mixed cycle (AMC), fed by hydrogen-rich fuel gas, has been evaluated. Obviously, hydrogen must be produced and here we have chosen the steam-methane reforming for its production, quantifying all the thermal and electric requirements. At first, the thermodynamic performance of this cycle has been investigated in comparison with that attainable by combined cycle power plants (CC). Then, the power plants have been integrated with the fuel production system. Including all the material and energetic flows, the overall performance has been evaluated. The main result of the performed investigation is that, while the two power plants attain the same efficiency level without H2 production requirements (about 56% for AMC and 55.8% for CC), the AMC power plant achieves a net electric efficiency of about 48% when integrated with H2 production plant: it is about 3 points higher than the efficiency evaluated for the CC equipped with the same H2 production plant (about 45%). The final carbon dioxide emissions are about 0.0742 and 0.079 kg/kWh for AMC and CC respectively
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