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2012 | OriginalPaper | Buchkapitel

4. Energy Conversion and Transformation Plants

verfasst von : Fabio Orecchini, Vincenzo Naso

Erschienen in: Energy Systems in the Era of Energy Vectors

Verlag: Springer London

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Abstract

The energy necessary for end-use has different forms (mechanic, luminous, electric, thermal); it can be of different origin, and there are different processes that make it available. The primary sources directly available in nature are not always conveniently and efficiently usable in the processes from which the most suitable form of energy for end-use can be obtained. For this reason, in almost all cases, primary sources undergo conversion or transformation processes, whose outcome is indicated by the so-called secondary sources.

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Vorheriges Kapitel Energy Vectors

Nächstes Kapitel Distributed Generation and Cogeneration

This introduces a thermodynamic limit to the conversion process efficiency, the so called Carnot efficiency.

These plants can also be powered with solar, nuclear, or other types of energy.

It can also be expressed according to mass flow rate Q, instead of power N, that is to say:

$$ N_{\text{sq}} = {\frac{n\sqrt Q }{{H_{m}^{3/4} }}} $$

The values shown are obtained by expressing n in revolutions/min., Q in m³ and H_m in m.

In general, action (or impulse) turbines are those in which there is no pressure difference in the operating period between inlet and outlet from the impeller, whereas in reaction turbine the outlet pressure is lower than the one at the inlet of the impeller.

For small heads (i.e. 10 m), head variations, although limited in absolute terms, entail variations that from a percentage viewpoint are relevant for the head itself.

50 or 60 Hz (see Sect. 3.5.4.1).

Other materials (for instance organic materials) are being studied.

Device converting the inlet direct current into alternating one.

As a matter of fact, the definition of BOS efficiency often includes other factors of loss that are not linked to other parts of the system, but still to the module and in particular to some of its peculiar operating conditions. These are the losses due to the effect of temperature, losses due to reflection on the frames of modules, etc. In the case of isolated systems, the battery charge and discharge process entails an additional loss, which can be estimated as amounting to nearly 10% of energy.

Solar radiation in Rome with a tilt of 30°, azimuth equal to 0 and without shading.

Standard conditions provide for an incident radiation of 1 kW/m².

Considering air, a perfect gas is H = c _p·T and being c _p constant H and T only differ for a scale factor, therefore the cycle has the same form on planes H–S and T–S.

In the ideal cycle, the reversible isentropic compression and expansion transformations are considered.

At the usual values of the compression ratio, nearly β = 12, the air is in a combustion chamber at the pressure of nearly 12 bar. In those cases in which high compression ratio values are adopted, β = 30, obviously a higher pressure for natural gas, nearly 35 bar, is necessary.

From (4.21) it is readily evident that by decreasing the fuel flow rate, T ₃ decreases.

For instance, to halve the electric power supplied, it is necessary to bring the power supplied by the turbine at nearly 83% of the nominal value.

The exact value (National Institute of Standards and Technology—2008) is F = 96,485.3399 C/mol.

$ G = H - TS.$

$ H = U + pv.$

The reaction ΔG of water formation in standard conditions (T = 25°C and p = 1 bar) amounts to 228,888 J/mo, the number of moles (n) involved in the reaction is 2, and the number of electrons transported by each (hydrogen) ion is 1.

The reaction ΔH to water formation in standard conditions amounts to 242,000 J/mol.

The passage of current generates irreversibility; therefore it is possible to consider V as the driving force in case of irreversible transformations.

$ \Updelta V = E - E \cdot \varepsilon = {\frac{\Updelta G}{n \cdot F}}\left( {1 - \varepsilon } \right).$

The platinum content for this type of cells presently amounts to nearly 0.6 mg/cm². The electric power supplied by a cell per unit of anodic surface is nearly 0.4 W/cm², therefore the Platinum content amounts to 1.5 g/kW. The cost of Platinum is about 40 €/g, which means that the cost of the Platinum alone contained in the anode amounts to about 60 €/kW.

Phosphoric acid solidifies at 42 ± 5°C.

The quantities of CO₂ requested are by far higher than those normally contained in the air: two moles of CO₂ every mole of O₂. Air contains nearly 20% (in moles) of oxygen and 388 ppm (parts per million) of CO₂, which accounts for 0.039%. Therefore, on average, in the air the ratio CO₂/O₂ amounts to 0.00195, that is to say over 1,000 lower than the one demanded.

The efficiency of the real cycle (differently from the ideal one) varies according to the number of revolutions of the engine and presents a maximum of nearly 2/3 of the maximum number of revolutions.

For this reason, heat pumps are more suitable for mild climate.

At absolute zero the Fermi level or Fermy energy is, at absolute zero, the highest energy level occupied by the “free” electrons of the conduction band. It is typical of the material considered and weakly depends on temperature. At higher temperatures, some free electrons can be at higher levels, according to the statistical distribution function provided by the Fermi–Dirac theory.

This admission does not introduce a significant error.

Excitation consists in the removal of electrons from the stable orbit, made by other electrons accelerated by an electric field.

Due to the fact that these sources emit a light whose spectrum is discontinuous.

See Sect. 1.2.10.2.1.

The necessary heat is produced by the combustion of a given quantity of methane.

Also at high temperatures and pressures, the reaction is never complete.

Carbonaceous solid product mainly made up of carbon, containing residues at a high molecular weight, as furan-derivatives and phenol compounds.

“Liquid oily” fraction containing water and compounds with a low molecular weight as aldehydes, acids, ketones, alcohols, heavy hydrocarbons condensed at temperatures lower than 20−100°C.

In the presence of the two phases of liquid and steam, the pressures of the steam phase (p _α and p _β) only depend on the temperatures exciting in containers (T _A and T _E).

That is in line with the hypothesis according to which α is far more volatile than β.

Being α more volatile than β, the steam will be richer than α compared to the liquid phase.

Normally the pressure at the condenser is nearly 10 times as much as higher than the one at the evaporator.

Also in this type of pumps, therefore, there is a compression: however, compared to the case of compression heat pumps where a gas is compressed through a compressor, in the absorption ones a liquid is compressed through a pump, and therefore the compression work is much smaller.

Caputo C (1979) Le turbomacchine vol III. Editoriale ESA. ISBN:88.405.3216.1. Also: Logan E (1983) Turbomachinery: basic theory and applications, CRC press, ISBN 9780824791384, and Baskharome EA (2006) Principles oh turbomachinery in air breathing engines, Cambridge University Press, ISBN 9780521858106

Pello’ PM (1990) Impianti di accumulo mediante pompaggio per la generazione elettrica: il caso italiano in L’energia elettrica no° 9 p 369

Maccari A, Vignolini M (2001) Progetto di massima di un impianto pilota per la produzione di 2000 m³/giorno di idrogeno solare basato sul processo ut-3

Nucara A, Pietrafesa M (2001) Elementi di illuminotecnica, Universita’ degli Studi “Mediterranea” di Reggio Calabria; Facolta’ di Ingegneria; Dipartimento di Informatica Matematica Elettronica e Trasporti. Also: Dilouie C, Advanced lighting controls: energy saving, productivity technology and applications, The Fairmont Press, ISBN 0-88173-510-8

Titel: Energy Conversion and Transformation Plants
verfasst von: Fabio Orecchini
Vincenzo Naso
Verlag: Springer London
Buch: Energy Systems in the Era of Energy Vectors
Print ISBN: 978-0-85729-243-8

Electronic ISBN: 978-0-85729-244-5

Copyright-Jahr: 2012
DOI: https://doi.org/10.1007/978-0-85729-244-5_4

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