Abstract
While considering the human use of energy, “where” and “when” are often more important than “how” and “how much”. Human beings do not simply need energy: they need it wherever and whenever they decide. An energy system is therefore satisfactory when it is able to guarantee the right quantity and form of energy in the right moment (for all required time) and at the place of need.
This is a preview of subscription content, log in via an institution to check access.
Access this chapter
Tax calculation will be finalised at checkout
Purchases are for personal use only
Notes
- 1.
For solid and liquid substances (at room temperature) this aspect is little relevant: conversely, it is very much significant for low temperature liquefied and pressurised gases, since in these cases the weight of the container is often of the same order of magnitude as the gas therein contained.
- 2.
Kinetic energy and potential energy are also taken into consideration.
- 3.
Physically, then, J is dimensional.
- 4.
It is possible to assume that positive and negative height variations along the pathway are equivalent, that is to say the height of the starting point is the same as the end point.
- 5.
Considering for crude oil a dynamic viscosity of 0.215 Pa s and a density of 0.86 kg/l.
- 6.
In general, for long distances (typical of oil pipelines) the term relating to kinetic energy becomes negligible compared to load losses:
\( J \cdot g \cdot D > > \frac{1}{2} \cdot v^{2} \Rightarrow L \cong J \cdot g \cdot D \).
- 7.
Safety and damage risks vary according to the Countries and the regional areas crossed.
- 8.
Propane and butane are contained in natural gas (see Sect. 2.5.4.2).
- 9.
The density of gaseous methane at 75 bar and room temperature amounts to 55.9 kg/m3, whereas at the liquid state it amounts to 424.7 kg/m3.
- 10.
Between the exit of one stage and the access to the next, the liquid is cooled at constant temperature. In this way the needed compression work decreases.
- 11.
Considering the compression ratio as equal in the different stages.
- 12.
The k value used concerns the average temperature between the initial and the final one. The calculation can be made through the following procedure: a value of the end temperature is hypothesised and the average temperature is calculated, followed by the calculation of the value of k and the value of end temperature that is compared to the hypothesised one. If a marked difference is obtained, the value of T 2 is assumed as the one calculated, and the same procedure is followed until the value hypothesised and the value calculated of end temperature coincide (or, better, the difference is not limited to a given value considered as acceptable).
- 13.
It is evident how the variation of kinetic energy is negligible compared to the compression work.
- 14.
Referred to atmospheric pressure (p r = p ass–1 bar).
- 15.
Gas density at 200 bar amounts to 159.5 kg/m3.
- 16.
The density of liquefied methane gas at −163°C amounts to 427.4 kg/m3.
- 17.
The values shown relate to transportation only and do not consider the energy spending for compression, liquefaction and regasification.
- 18.
The energy density (kJ/m3) of natural gas at 75 bar is similar to the one that hydrogen owns (described in detail afterwards) at a pressure of 350 bar.
- 19.
Gas density at 75 bar amounts to 57.9 kg/m3.
- 20.
Often, in relation to electric power, reference is made to transportation and distribution: transportation means high or very high voltage transportation for long distances from the production plants to the AT/MT transformation plants, whereas distribution means the medium–low voltage transportation for limited distances from the MT/BT transformation plants to end users.
- 21.
Represents the phase shift between voltage and current.
- 22.
Tokyo, Kawasaki, Sapporo, Yokohoma and Sendai.
- 23.
Osaka, Kyōto, Nagoya, Hiroshima.
- 24.
Namely the ratio between the electric power available from the accumulator for use and the electric power spent to charge the accumulator.
- 25.
It is widely known, however, that positive charges are so called by convention; as a matter of fact, it is negative charges that enter, electrons, and therefore the terms should be used the other way around!
- 26.
When current has the value of C (Ah), that is to say the value of capacity, the battery is discharged after 1 h. If the value of current is 5C, the battery is discharged in 1/5 of an hour (20 min), whereas finally if current amounts to C/10 the battery will be discharged in 10 ore.
- 27.
An ideally polarisable electrode is an electrode with an infinite polarisation resistance and, at the same time, the curve in diagram i/V is a horizontal straight line. Conversely, for an electrode ideally not polarisable, the polarisation resistance is null, and the line in diagram i/V is vertical. In the former case the potential can be varied without having any current leaking in the circuit; in the latter case, the potential cannot be shifted from the balance value for the very high current values (infinite) that would be produced. In practice, polarisation resistance takes finished values that can range from fractions of Ω to several MΩ.
- 28.
The relevant dielectric constant indicates the number of times by which the electric field is reduced between the plates of the condenser compared to the case of vacuum. For instance, water is used (ε r = 80) as dielectric, between the plates there will be an electric field 80 times lower than in the case of vacuum.
- 29.
Namely the ratio between the electric power produced by the potential gravitational energy of a given quantity of water and the electric power spent for its storage.
- 30.
Hydrogen: 10,692 kJ/Nm3; Methane: 34,535 kJ/Nm3.
- 31.
Between the exit from one stage and the access to the next one, the fluid is cooled at constant temperature. In this way, the total compression work decreases.
- 32.
Considering the compression ratio as equal for the different stages.
- 33.
- 34.
Calculated through the Van der Waals equation. At high pressures, since the effects of interactions between the gas particles and the volume of particles themselves are not negligible (being both considered as null in the ideal gas law) the ideal gas law is not applicable, since it originates significant errors (hydrogen density at 200 bar and 25°C calculated with the ideal gas law is 16.16 kg/m3).
- 35.
In ideal gases, in a free expansion, temperature remains constant.
- 36.
For all gases a temperature exists, called reversal temperature, below which the Joule–Thomson coefficient is positive, whereas in case of higher temperatures it is negative.
- 37.
Other gases as helium can be used as well.
- 38.
Considered as the ratio between the minimum liquefaction work of hydrogen (ΔG between gaseous hydrogen at 300 K and liquid hydrogen at 20 K) and the energy actually spent.
- 39.
Electrons own an intrinsic angular phase, associated to a magnetic phase. This property is defined as electronic spin and can have two different stages, characterised by a magnetic quantum number of spin, m s , which can have two values only: +1/2 or −1/2.
- 40.
Theoretically speaking, the conversion process from ortho to para is spontaneous, but very slow: the time to halve the conversion is over one year at 77 K. This means that, considering the cooling times, this conversion de facto does not take place. Furthermore, from the energy viewpoint, it is convenient to carry out the conversion at high temperatures since the conversion enthalpy increases as temperature decreases.
- 41.
The formation enthalpy varies with the temperature.
- 42.
Similarly to what happens in other accumulators.
- 43.
This phenomenon depends on the temperatures and conditions of thermal exchange. The diagram in the figure refers to tests made at 50°C and with an internal heat exchanger (described in Table 3.18): this mode of thermal exchange is more efficient than the one of a temperature bath, in which the thermal power is supplied through the external wall of the tank.
- 44.
The density of hydrogen compressed at 200 bar is 14.2 kg/m3.
- 45.
The density of liquefied hydrogen at −253°C is 71 kg/m3.
- 46.
The values shown refer to transportation only and do not consider the energy necessary for compression and liquefaction.
- 47.
All over the world (USA, Japan, France, Germany, Italy, etc.) some thousands of kilometres of pipelines are nowadays used for the transportation of hydrogen.
- 48.
See Sect. 3.5.6.4.
- 49.
In this case, the fluid used for (primary) transport is not the same that reaches the radiator (secondary); the former releases heat to the latter in a heat exchanger; therefore, it is necessary to have a fluid at a temperature markedly higher than the end use on, in order to allow heat exchange.
- 50.
Since heat transmission is a “slow” phenomenon, quick transformations can be considered with a good approximation as adiabatic.
References
ENEA, Rapporto energia e ambiente (2010); also: European Environment Agency (2008), Energy and Environment Report 2008, Rep 6/2008, ISBN 978-92-9167-980-5.
Zuttel A (2004) Hydrogen storage methods. Springer, Heidelberg
Innocenti L, Il consumo energetico nella produzione, stoccaggio e distribuzione dellı idrogeno, http://didattica.dma.unifi.it/website/pub/Energetica/EMT1_05_matdid/Idrogeno.pdf
Zamfirescu C, Dincer I (2008) Using ammonia as a sustainable fuel. J Power Sources 185(1):459–465
Modak JM (2002) Haber Process for ammonia synthesis. Resonance, 7(9):69–77 DOI: 10.1007/BF02836187
Holladay JD, et al (2009) An overview of hydrogen production technologies. Catalysis Today. 139(4):244–260
Gruhn S, Sackett B (2008) Wind to NH3: Freedom fertilizer - Green fertilizer and fuel for the future, the 5th Ammonia Fuel Conference; Minneapolis
Zamfirescu C, Dincar I (2007) Ammonia as a green fuel and hydrogen sources for vehicular applications, Elsevier
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. ENEA Report, Rome
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
Copyright information
© 2012 Springer-Verlag London Limited
About this chapter
Cite this chapter
Orecchini, F., Naso, V. (2012). Energy Vectors. In: Energy Systems in the Era of Energy Vectors. Green Energy and Technology. Springer, London. https://doi.org/10.1007/978-0-85729-244-5_3
Download citation
DOI: https://doi.org/10.1007/978-0-85729-244-5_3
Published:
Publisher Name: Springer, London
Print ISBN: 978-0-85729-243-8
Online ISBN: 978-0-85729-244-5
eBook Packages: EngineeringEngineering (R0)