4
ENERGY CARRIERS
4.1
From sources to market:
energy carriers
4.1.1 Introduction
Modern economic systems depend to an
ever-increasing extent on the availability of energy,
both for their operation and, in particular, for their
development. The various forms of energy, however,
are not the same, as they differ in their availability,
profitability, usability and efficiency compared to their
end-use.
None of the different forms of energy
available (fossil fuels such as oil, natural gas,
coal, fissile materials, and renewable sources
such as solar or wind power, hydropower, etc.) is
capable of satisfying the energy needs of society
that are linked to the main markets: heating (or
cooling) supply, mobility and transport, and
ancillary services (mechanical, electronic, etc.). It
is therefore necessary to introduce forms of
energy that can guarantee a better link between
the availability of energy sources and the
particular use required: it is precisely in this
sector that the energy carriers play their special
role (Peet, 2004).
The energy carrier is a secondary form of
energy which lends itself to being transported
(often by means of special networks) to the place
of use (Fig. 1). It consists of either a transportable
substance that can easily release the energy
Fig. 1. From primary
sources to energy services.
contained in it (as in the case of solid, liquid or
gaseous fuels, steam, hot water, etc.), or of
electricity (electric energy). At present, the latter
best enables its energy content, produced from
the most varied primary sources, to be exploited
for the needs of the end-user.
In some cases, it is not necessary to introduce an
energy carrier, as the primary source is sufficiently
versatile: for example, natural gas is capable of
heating houses, fuelling motor vehicles, etc., but it is
not always the most suitable form of energy for every
use (it is not used as aircraft fuel or in maritime
transport, whereas it is used for road transport, but
only a limited amount).
4.1.2 Life cycle
of the energy carrier
The various phases involved from generation to
the end-use of an energy carrier constitute its ‘life
cycle’. The basic operations involved in the life
cycle are (Fig. 2): a) generation from the primary
source; b) transport; c) storage (when required);
d ) distribution; e) end-use (with consequent
impact on the environment, both in local terms in
the form of emissions, and in global terms of
efficiency in conserving the energy contained in
means
primary
energy
end
end-use
technologies
supply
technologies
secondary
energy
supply efficiency
VOLUME III / NEW DEVELOPMENTS: ENERGY, TRANSPORT, SUSTAINABILITY
lifestyle
satisfaction
of needs
energy
services
end-use efficiency
lifestyle efficiency
301
ENERGY CARRIERS
energy
source
carrier production
process
transportation
carrier
storage
final use
distribution
performance
and impact on
environment
Fig. 2. Life cycle of the energy carrier.
the primary fuel throughout its transformation
cycle).
Operations are not necessarily carried out in
the aforementioned order; for example, storage
could even precede transport or could be carried
out at the same time as the final use (as in the case
of road transport). Linking energy sources with
the market, therefore, entails technological and
strategic choices as far as the processes for
obtaining the carriers, the logistics of the sources
and the end-uses are concerned.
Before making a thorough study of the impact of
the various phases on the different carriers, it is
useful to review which forms of energy are most
used for a number of end-uses. Table 1 shows the
fuels used for the different uses, also highlighting
the possible alternative fuels currently proposed as
energy carriers (of synthetic origin) for the near
future (described in greater detail below). In Table 2,
there is a comparison of the various fuels (both
carriers and primary sources) with the different
end-uses, differentiating them on the basis of their
frequency of use at world scale (obviously,
depending on the geographical area concerned and,
above all, on the relative degree of development,
there can be very different situations). In spite of
this, for some of these fuels, niche uses can be
foreseen (not shown in the table).
There are a number of considerations to be made:
• A few carriers are dedicated to well-defined uses;
for example, the use of gasoline and of diesel gas
oil is specific for road transport.
•
A few sources can be used directly without the
intermediate phase of generating the energy
carrier. The most important of these is definitely
methane; actually, it should be noted that also for
methane there is a natural gas treatment stage to
remove not just the carbon dioxide, the nitrogen
and the hydrogen sulphide, but also the higher
hydrocarbons. It would thus be more correct to
consider natural gas as an energy source, whereas
methane used commercially, should be regarded as
an energy carrier.
• Among fossil fuels, crude oil has practically no
direct use, but is converted in the refinery into the
various liquid carriers that feed a significant part
of the end-uses.
• Carriers are distinguished also by their
different physical form: gaseous for methane
and hydrogen; liquefied gas for LPG
(Liquefied Petroleum Gas) and DME
(dimethyl ether); liquid for all petroleum
derivatives, alcohols and biodiesel; solid for
some other fuels; less easily definable in the
case of electric energy, for which the real
carrier is an electric current, i.e. a flow of
electrons.
These brief considerations, regarding the chain of
production, transport and use of the energy carrier,
make us realize that the success that oil has had as an
energy source cannot be attributed only to its great
availability but also, and perhaps above all, to the ease
with which liquid hydrocarbon derivatives can be
transported, stored and distributed for their final use.
Table 1. Fuels used for end-uses
(in bold, fuels likely to be used in future as energy carriers)
Heating
(air-conditioning)
Methane, LPG,
electric energy,
firewood, naphtha,
coal, gas-oil,
heavy oils,
solar heat,
biodiesel
302
Cooking
Methane, LPG,
electric energy,
firewood, coal,
DME
Industrial/civil
uses
Road
transport
Methane, LPG,
electric energy,
naphtha, coal,
gas-oil, heavy oils
Gasoline,
diesel oil, LPG,
methane,
electric energy,
hydrogen,
methanol,
ethanol,
biodiesel, DME
Air
transport
Sea
transport
Rail
transport
Jet fuel,
aviation fuel
Marine diesel,
bunker oil,
Electric
gasoline,
energy,
hydrogen,
diesel, coal
biodiesel
ENCYCLOPAEDIA OF HYDROCARBONS
FROM SOURCES TO MARKET: ENERGY CARRIERS
Table 2. Frequency of use of fuels for different end-uses
(in bold, alternative fuels likely to be used in future as energy carriers)
Heating/airCooking
conditioning
Methane
Civil/industrial
uses
Road
transport
+++
+++
++
+
LPG
+
+++
++
+
Naphtha
(gasoline)
+
+
+++
Kerosene/jet
fuel
+
++
Gas-oil
(diesel)
++
++
Heavy
oils
++
+
Coal
+
(+)
Firewood
+
+
Electric
energy
++
++
++
(+)
Solar
(heating)
+
(+)
+
+
Hydrogen
(+)
DME
Sea
transport
+
+
+
Rail
transport
+++
+++
+++
+
++
+
Methanol
(ethanol)
Biodiesel
Air
transport
+
++
(+)
(+)
+
+
+
+
(+)
+++, of very general use; ++, of frequent use; +, seldom used; (+), could be used in future
In fact, their liquid state enables their energy density
per unit of volume to be optimized (Table 3 shows
various characteristics for some of the carriers
considered), and this has great advantages for the
storage and the distribution of the carrier. Actually,
this aspect is reflected in the higher price attributed to
the ‘liquid’ thermal unit compared with the ‘gaseous’
or ‘solid’ one.
An ideal energy carrier (Bossel et al., 2003)
could be represented by a liquid with a relatively
high boiling point (above 80°C) and a low melting
point (below ⫺40°C); such a carrier would remain
liquid under any climatic condition and at various
altitudes. In fact, gasoline and diesel gas oil are
excellent examples; their physical properties are
almost ideal for applications in the transport field as
they optimize all the phases downstream of
production of the energy carrier, from transport to
storage and to the final use. But this observation
VOLUME III / NEW DEVELOPMENTS: ENERGY, TRANSPORT, SUSTAINABILITY
should not be considered as conclusive, otherwise
there would be no explanation for the great current
success of natural gas; for this, environmental and
economic aspects play an important role.
No particular attention will be given below to the
liquid derivatives of petroleum, since they represent
the term of reference: they are produced in the
refinery, transported by ship, pipeline or tank truck,
can easily be stored in tanks, and can be readily
distributed to the end-users. Nor will solid carriers be
dealt with because they are used as carriers only in
developing countries and, eventually, this area of the
world will tend to do without this use. Attention will
be focused solely on a number of conventional carriers
(electric energy, methane and LPG), and the
opportunities and problems for certain alternative
synthetic carriers, such as hydrogen and alcohols
(methanol and ethanol) will be discussed with a glance
at bio-fuels and dimethyl ether. The various carriers
303
ENERGY CARRIERS
Table 3. Physical-chemical and motor properties of various energy carriers
Gasoline Diesel
Chemical
structure
Density
in liquid state
(kg/m3)
Propane Butane Methane Hydrogen
RCOOCH3
C2H5OH
CH3OH
(CH3)2O
C3H8
C4H10
CH4
H2
750
831
870
790
790
667
500
579
410 (LNG)
29
(200 bar)
40-55
49
125
91
130
140
90-100
Boiling point
(°C)
40-200
180-350
Lower
heating
value (mass)
(MJ/kg)
45
33.7
76
110
119
260-370
78.5
65
⫺25
⫺42
⫺0.5
⫺162
⫺253
43.5
36
27
20
28.8
46.4
45.7
49
120
36.1
31
21
16
19.4
23
26
8.1
3.4
464
350
457
430
540
316
will be examined synthetically throughout the sector,
from production to end-use, paying attention also to
the effects on the environment; the production of the
energy carrier, however, will be examined in general
terms, as it is dealt with in the following chapters.
4.1.3 Conventional energy carriers
Electric energy
The demand for electric energy (e.e.) will go on
increasing in the years to come, both in the
industrialized countries and in the developing
countries, at average rates of above 3% per annum. As
already observed, e.e. is the typical energy carrier and
its cycle is examined below.
Production
E.e. can be obtained, both on a large and on a small
scale, from fossil fuels (especially coal, natural gas and
oil), from fissile fuels (nuclear energy) and from
renewable sources (hydroelectric, wind power,
photovoltaic); it therefore has the great advantage of
being able to be produced from a wide variety of sources.
304
DME
CnH1,87n
Octane
number
Self ignition
temperature
(°C)
Ethanol Methanol
CnH2,1n
Cetane
number
Lower
heating
value (volume)
(MJ/l)
Biodiesel
Transport
The development of the electricity market also
depends on the development of advanced technologies
of electric transmission, already now vital for meeting
the growth in demand of the deregulated markets. E.e.
is transmitted from the generating stations to users by
means of electric currents along cables or lines
classified as follows: a) HV (High Voltage) or VHV
(Very High Voltage) lines over very long distances;
b) MV (Medium Voltage) lines with buried cables in
urban areas or crossing basins; c) MV suspended lines
in cities and in suburban areas for industrial and
commercial users; and d ) LV (Low Voltage)
distribution lines for small-scale users.
Worldwide, the majority of the present e.e.
transmission and distribution systems operate on
alternating current, even though direct current
systems, in given circumstances, can compete
economically with traditional alternating current
systems. In the transport field, high-temperature
superconductors could provide radical advantages, but
at the moment, the technology is still in its infancy.
It should be emphasized that the recent blackouts
in various countries has focused attention on the
ENCYCLOPAEDIA OF HYDROCARBONS
FROM SOURCES TO MARKET: ENERGY CARRIERS
electricity network and its fragility. Following the
spread of deregulation processes, the demand for
carrying e.e. has gone up, thus increasing the
likelihood of congesting (overloading) the
transmission networks, which is becoming an ever
more pressing problem in all advanced areas.
Storage
Unlike transport, which is consolidated and
efficient, e.e. storage is the weak point of this energy
carrier. Once e.e. has reached the end-user, it has to be
consumed immediately. This does not mean that no
e.e. storage systems exist (Mazza and Hammerschlag,
2004): there are various technologies covering a broad
range of applications, from those able to deal within
fractions of a second with variations/interruptions of
electricity (power quality) to those that enable
electricity supplies to be managed according to market
demand (energy management). These technologies are
called upon to ensure continuity of service; for
instance, whenever passing from one e.e. generator to
another one (bridging power).
The applications connected with power quality
include supercapacitors, flywheels, superconducting
magnetes and various types of buffer batteries. Energy
management technologies are those that enable e.e. to
be supplied for prolonged periods (for some hours)
and which produce load levelling or peak shaving,
such as pumping water back into hydroelectric basins,
pumping compressed air, and fluid electrolyte
batteries. An overview of these options is given in Fig. 3.
discharge time at
rated power
system power
ratings
The accumulation/storage systems are potentially
useful as they can be combined with renewable
sources (such as photovoltaic and wind energy) so as
to mitigate their characteristics of intermittence and to
ensure the recovery of the e.e. produced during periods
of slack demand. Storage systems based on batteries
(Linden and Reddy, 2002) come up against their main
barrier in the high investment costs which limit their
application to niche markets. The only renewable
energy that has solved this problem commercially is
hydropower, as the system of pumping water back into
hydroelectric basins is widespread (about 100 GW
installed in the world) and is used also for generating
very high power (Donalek, 2003).
Uses and impact on the environment
E.e. can be put to many different uses and at very
varied scales (see again Tables 1 and 2). Its
environmental impact is locally very positive because,
as opposed to other carriers, there is no polluting
emission in the place where the e.e. is used.
Natural gas
As already observed, natural gas is the only energy
source whose use is equivalent to that of the energy
carriers – in this case, there is no point in strictly
speaking of ‘production’ of the carrier – although to
transform the fuel into a carrier, various treatments are
necessary, and they may be more or less radical,
depending on the end-use. While acid gases and inerts
are generally always removed, hydrocarbons higher
second fractions
seconds
power quality
minutes
bridging power
high power
hours
peak shaving
load leveling
high energy
superconducting magnets
supercapacitors
flywheels
range of usage of
technologies for the storage
of electric energy
sealed batteries
fluid-electrolyte batteries
Na-S batteries
pumped hydro
compressed air
Fig. 3. Electric energy storage systems.
VOLUME III / NEW DEVELOPMENTS: ENERGY, TRANSPORT, SUSTAINABILITY
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ENERGY CARRIERS
than methane, which are known as ‘natural gas
liquids’, can be separated upstream or sent directly to
the final application.
The present high, constant growth in the demand
for natural gas is sustained, above all, by its success in
electric generation in various parts of the world; as a
consequence, this growth acts as a definite stimulus to
the development of new transport and distribution
facilities, also for uses other than the generation of
electricity (see again Table 2).
The problems connected with transport and storage
are especially examined below.
Transport
A crucial aspect for the success of gas is the
transport cost which is high compared to that of oil,
and in the past, has limited both exploration and the
development of a global energy economy based on
natural gas. Indeed, the lack of economically
acceptable alternatives for the evacuation of associated
gas, now no longer possible to be flared, at times
conditions the production of oil itself.
Various technologies compete in enabling gas to be
transported over long distances: high-pressure and
high-capacity pipelines (overland or submarine),
liquefied natural gas (LNG), compressed natural gas
(CNG), the conversion of natural gas into liquid
hydrocarbons (GTL, Gas To Liquids) and Gas To Wire
(GTW).
In the first three cases, the end market is always
natural gas, whereas in the case of GTL, it is liquid
hydrocarbons, especially for road transport. The
process involves the chemical conversion of natural
gas into fuels, especially diesel oil (or intermediates
for petrochemicals) and, above all, enables stranded
gas to be exploited; this gas is present in proven
reserves, but is not marketed because the reserves are
situated too far away for transport to be economically
viable (Harries-Rees, 2004).
GTL, in its most typical version, foresees the
transformation of natural gas into synthesis gas
(syngas), which is converted into waxy
hydrocarbons by means of the Fischer-Tropsch
reaction (see also Chapter 2.6); the waxes are then
transformed into high quality fuels by
hydrocracking; at present, various industrial
projects are underway or have been announced, and
by 2010, they should enable about 250,000 bbl/d of
products to be placed on the market. In this
chapter, attention will mostly focus on the GTL
approach which involves the synthesis of
oxygenated products such as methanol or DME.
As far as GTW is concerned, if e.e. generation
systems were convenient and feasible at the well
mouth, the optimal solution would be to transform the
306
gas into e.e. and transport the latter, applying
technologies already available such as the high-voltage
direct-current transmission of e.e. to reach great
distances (Subero et al., 2004).
However, the most common way of supplying
gas to the markets is making pipelines that connect
the reserves to the end-users. This system requires
a relatively simple technology and an energy waste
of no more than 3%. However, this is not always
feasible due to the excessive distance or
geopolitical restrictions. In such cases, when there
is easy access to the sea, the main alternative can
be LNG, even if costly liquefaction, transport and
regasification systems are required and there is
about 15% energy waste.
The two options are discussed in brief below,
focusing attention on the energy carrier’s most typical
transport and storage aspects. The option of
compressed natural gas is also examined briefly, as it
could be attractive over the short period in particular
situations.
High-pressure pipelines. In overland transport, the
constraint of distance (the limit is generally around
2,000 km) can be mitigated by using high-grade steels
(X80, X100 or X120) which enable the gas to be
transported in high-pressure pipes (up to 150 bar), a
technology that is vital for exploiting gas fields in
remote and inland areas (such as Alaska, Canada,
Siberia, etc).
In order to be economically viable, these systems
operating at high pressure have to transport large
volumes of gas using pipes of such dimensions so as
not to require any substantial modification to the
construction processes: nominal diameters from 48 to
56 inches (122-142 cm) and thicknesses of 20 to 32 mm.
This requires the use of higher transport pressures
(100-150 bar against 70-80 bar in traditional ones),
thereby permitting, at least in principle, the transport
of approximately double the mass for the same
diameter (Bruschi, 2004).
At equal cost of the thermal unit transported,
high-pressure transport involves greater distances than
covered by traditional pipelines, and is definitely of
interest to the market. Fig. 4 shows the field of
application of the various technologies currently used
in gas transport in relation to volumes and distance.
So, gas transport under high pressure in overland
pipelines (like underwater pipelines that have been
used for decades) can be a competitive solution even
for distances of over 3,000-4,000 km.
Liquefied natural gas. LNG is a liquid mixture of
hydrocarbons consisting mainly of methane, but it can
contain small quantities of ethane, propane and
nitrogen. At atmospheric pressure, it boils at a
temperature of ⫺160°C (Johnson, 2005).
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FROM SOURCES TO MARKET: ENERGY CARRIERS
30
pipelines
gas volume (109 Sm3/y)
25
high pressure
pipelines
20
LNG
15
10
gas to liquids
syndiesel, dimethyl ether, methanol
5
CNG
GTW
0
0
1,000
2,000
3,000
4,000
distance (km)
5,000
6,000
Fig. 4. Options for the transport of natural gas to the market.
Investments in the LNG chain are very great; in
the 1990s, a series of technological innovations and
process optimization measures led to a
considerable reduction in costs. Although the
technology is considered mature, the strategic lines
of technological development are focused on
reducing costs in the whole LNG sector, so as to
make it more and more competitive compared to
transport with pipelines. The LNG technological
chain (Fig. 5) includes, first and foremost, the
pretreatment of the natural gas to remove the
components that can jeopardize the subsequent
liquefaction process (water vapour, CO2, H2S and
heavy hydrocarbons) or damage the plants
(mercury). Liquefaction is accomplished by means
of refrigeration under atmospheric pressure, with
heat transfer to a cooling fluid through heat
exchange surfaces. The LNG is then stored in
insulated tanks at temperatures of ⫺162°C and at
slightly higher than atmospheric pressure. There
are three categories of storage systems: in the
single container, only the internal wall of the tanks
needs the requisites established for the low
temperatures, whereas the function of the external
wall is to support the insulating material and not to
prevent losses of liquid; in the double container,
the external wall has to prevent losses of liquid, not
vapour; and in the full container, the external wall
has to stop losses of both liquid and vapour.
Maritime transport of LNG requires special vessels
with capacities now reaching 150,000 m3 but
which, in the near future, will be as much as
215,000 m3 (Chabrelie, 2004). Qatar, which
possesses some of the largest gas reserves, has
programmed investments equal to 15 billion
dollars over the next five years to add 70 vessels to
its fleet, so as to increase LNG exports. At the end
of the procedure, the LNG is discharged from the
ships, stored again in tanks, and then pumped to
the regasification units. These are normally
operated using ‘primary’ low-head pumps, situated
directly inside the tanks and immersed in the LNG,
followed by ‘secondary’ pumps for compressing
the liquid until it reaches the final pressure
required by the user.
In the LNG chain, the production plant, the
liquefaction system, the fleet for transport and the
regasification terminal are calibrated so as to best
satisfy the specific requisites of the project.
Compressed natural gas. In the case of gas
reserves being available near markets with limited
volumes of potential demand, a technological
innovation claiming to transport CNG at competitive
costs compared to LNG or underwater pipelines could
be applied (Economides et al., 2005). The system in
question is a series of containers of composite
material, inside which are small-diameter pipe coils
made of high-strength steel, acting as a tank; the
materials used make it possible to increase the
gas/container mass ratio.
At the moment, no large-scale projects based on
CNG have yet been carried out, but this solution could
bea viable alternative to the reinjection of gas,
particularly in the case of associated gas produced
offshore (CNG gains […], 2005). Currently, CNG
finds one of its most important applications as a clean
fuel for the road transport market (in the world, there
is a circulation of about 3.3 million motor vehicles
using CNG).
Storage
Leaving aside the LNG and CNG sectors,
natural gas can be stored differently according to
the quantities concerned: from the big wells which
act also as strategic reserves for the use of this
resource, to the small reservoirs of motor vehicles
running on gas. In spite of the physical-chemical
natural
gas
natural
gas
gas
pretreatment
liquefaction
storage
shipping
storage
regasification
Fig. 5. LNG technological chain.
VOLUME III / NEW DEVELOPMENTS: ENERGY, TRANSPORT, SUSTAINABILITY
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ENERGY CARRIERS
characteristics of this carrier, storage is not a
problem and further improvements are likely,
especially for small reservoirs, using porous
adsorbent materials that are often coal based
(Lozano Castellò et al., 2002).
Liquefied petroleum gas
LPG, a mixture with a variable content of propane
and butanes, is a product of the refining industry and,
to an increasing extent, processing the wet fraction of
natural gas; although very promising, from both the
economic standpoint and for environmental properties,
its limited production volumes direct use mostly
towards specialized sectors.
At world scale, LPG deriving from natural gas
accounts for about 60% of the market. A growing
source of LPG stems from LNG projects, whose
market success leads to the production of ever larger
quantities of LPG stemming from the treatment of
associated gas.
LPG is used mainly as a fuel for household, civil
and industrial purposes: the majority of this demand
regards areas (China, India, etc.) where more than
3.5 billion people live, i.e. about 56% of the world
population (economic growth in these areas will have
a definite impact on the LPG market); a smaller but
very significant part is used as a raw material for
petrochemical derivatives (ethylene, propylene, etc.) or
for fuel components such as methyl tert-butyl ether
(MTBE) and isooctane; an even smaller part is used in
road transport. In the various end-uses, LPG always
has low emissions.
The LPG markets are in constant expansion,
especially east of Suez Canal. Japan is the chief
importing country, followed closely by China, whereas
the Middle East is the main exporter (Chandra et al.,
2005).
Production
As in the case of natural gas, LPG production also
consists essentially in separation processes from the
streams from which it originates. It should, however,
be stressed that a significant part of the LPG produced
in refineries is a by-product of various refining
processes (FCC, Fluid Catalytic Cracking, coking,
hydrocracking, etc.).
Transport
Over long distances, LPG is generally
transported by ships which have an increasingly
large capacity nowadays up to around 85,000 m3
(Hatta, 2004). There are also some examples of
long-distance transport by pipeline, for instance in
the territories of the former Soviet Union (although
rail transport is at present preferred). Recently, a
308
pipeline of almost 300 km was constructed in
Amazonia (Wertheim, 2005).
The handling of LPG in cylinders makes this
product particularly interesting for use in countries
where an adequate distribution network, e.g. of
gas, does not exist; i.e. when there are long
distances or geographical constraints or, more
generally, in developing countries. Precisely for
this reason, LPG is regarded as a ‘transition fuel’,
suitable for countries that are approaching higher
levels of development.
Storage
Considering the liquid nature (under slight
pressure) of LPG, storage is not considered a problem,
except with regard to safety, for which the maximum
attention is always necessary, even though the control
techniques are by now consolidated.
4.1.4 Innovative energy carriers
Hydrogen
In the last few years, hydrogen has been the centre
of attention of public opinion as a possible ‘pole star’
of a new energy future (Coonitz et al., 2004; Kennedy,
2004). The reasons for these great expectations can
certainly be ascribed to the use of fossil fuels which is
perceived as one of the main causes of environmental
pollution at both global and local scale (assuming also
that this type of pollution cannot be remedied or
mitigated). On the other hand, hydrogen (which if
burnt, produces only water) is regarded as the
definitive solution to free us from fossil fuels and from
the ‘carbon’ economy. Furthermore, hydrogen, whose
storage is simpler than electric energy (at least in
principle), could solve the problems of sporadically
generated electric energy from renewable sources.
Hydrogen can be produced from these sources, then
can be stored and transformed again into e.e. when
desired.
Hydrogen is certainly very abundant in nature,
though it is never present in its free state, but in a
combined form and mostly in very stable molecules
such as water, methane, higher hydrocarbons, etc. To
produce this energy carrier, i.e. to extract it from these
molecules, it is therefore necessary to spend energy
from primary sources. Certainly among the main
advantages of hydrogen are its very clean combustion
(at the most, only a small emission of NOx) and the
possibility (with methanol and ethanol) of direct use in
fuel cells, an extremely efficient energy system that
can obtain zero emissions (in the case of using
hydrogen) and energy yields to partly offset the energy
spent in the hydrogen generation stage.
ENCYCLOPAEDIA OF HYDROCARBONS
FROM SOURCES TO MARKET: ENERGY CARRIERS
Fig. 6.
Hydrogen:
technological
map from
fossil sources.
steam reforming
partial oxidation
natural gas
coal
gasification
waste and
heavy oils
gasification
Production
One of the great advantages of hydrogen is that it
can be produced not only from numerous energy
sources, both fossil (Fig. 6) and renewable (Fig. 7), but
also from nuclear energy, both by means of the direct
thermochemical splitting of water and through
intermediate production of e.e. (as described in Fig. 7
for renewable sources).
Many production methods are well established and
available at a large scale (especially those based on
fossil fuels); the only problem could be their
profitability as far as large-scale energy use is
concerned. On the other hand, hydrogen is already
produced and used on a large scale in the refining and
chemical industry. The sole difference (compared with
an energy use) is that for most uses, it is consumed
immediately after having been generated; for example,
in refining and in syntheses of methanol and
ammonia, thus eliminating the problems of transport,
distribution and storage.
Actually, the syngas itself (a mixture of CO and
H2) is an energy carrier from which hydrogen is often
CO2
syngas
conversion
H2
produced. Indeed, it had already been used as a carrier
known as town gas in cities, but its high rate of
toxicity, caused by its high carbon monoxide content
and its widespread production process (coal
gasification), made its further use inadvisable.
Transport and distribution
A distribution network already exists for the
present industrial uses of hydrogen, consisting in short
pipelines or limited road transport of cylinders. For an
extensive application of hydrogen, you would need an
adequate network of pipelines for the areas of high
demand, and road connections for the areas of low
demand, such as rural zones.
From a physical-chemical standpoint, hydrogen
has similar characteristics to methane and does not
differ greatly as far as problems associated with its
transport are concerned (although its lower energy
density implies a smaller flow capacity); however,
other complications arise linked to the need to use
more sophisticated materials to avoid
embrittlement. Another constraint for the use of
hydroelectric
source
photovoltaic
electric
energy
wind power
electrolysis
turbogas
shift
waste and
biomass
thermochemical
water splitting
gasification
H2
syngas
biological processes
Fig. 7. Hydrogen: technological map from renewable sources.
VOLUME III / NEW DEVELOPMENTS: ENERGY, TRANSPORT, SUSTAINABILITY
309
ENERGY CARRIERS
310
hydrogen in natural gas distribution networks is the
impossibility of using the same compression
stations because of the different behaviour of the
two gases in the compression stage (Bechis, 2003).
Then there are a number of unresolved problems to
be considered, such as the odorization of hydrogen
and the current lack of adequate regulations
(Birgisson and Lavarco, 2004); these obstacles are,
however, not insurmountable.
Stricly regarding distribution, two systems could
be possible. The first centralized one foresees the
production of hydrogen in large plants (if possible,
coupled with CO2 sequestration) and then its
transport in pipelines. The second decentralized
one, however, foresees the production of hydrogen
on a small scale (both by reforming natural gas and
by means of electrolyzers) directly in the service
stations. It is likely that this second system will be
used in the shorter term, then going over to the
centralized one when the hydrogen economy has
become more mature.
problems of cost, recycling, energy efficiency and
infrastructure.
• Adsorption is the emergent technology, but
processes and materials are still in the R&D phase.
Very contradictory results have been obtained with
carbon nanotubes and nanofibres, and at the
moment, scepticism seems to prevail regarding this
approach.
For the innovative solutions, the durability of the
materials and the rate of release of hydrogen still have
to be tested for thousands of loading/discharge cycles;
as the field concerned is basically unknown, the future
is still uncertain.
Storage
Prospects
Whichever distribution system is chosen, it will
be necessary to address the problem of storage,
either on a large or on a small scale, for example in
the reservoir tanks of motor vehicles. Hydrogen
can be stored at high pressure (350-700 bar), and at
the moment, this seems to be the most reliable
method; otherwise it can be liquefied and stored in
cryogenic containers. Some more advanced
solutions are also being studied, such as metal
hydrides which decompose at high temperatures
releasing hydrogen or chemical hydrides, or else
adsorption on activated carbon (Jacoby, 2005).
However, none of these technologies seems yet
able to satisfy the storage criteria that
manufacturers and users want (Zorzoli, 2004); in
fact:
• Storage in the gaseous phase is a mature
technology, but is still too wasteful in terms of
weight, volume and costs, and therefore not
particularly suitable to be used on vehicles.
• Storage in the liquid phase has better volumetric
efficiency which would make it more suitable for
use on vehicles, but the complexity of handling
liquid hydrogen, losses during storage and the
energy required for liquefaction (about 1/3 of the
energy content of the hydrogen) make its
commercial use difficult and, thus, far off.
• Metal hydrides permit storage at a low temperature
and with reasonable volumetric efficiency, but they
are heavy and the question of their heating aboard
the vehicle poses a lot of problems.
• Chemical hydrides (sodium borhydride, etc.) have
In the scientific community and elsewhere, the
future role of hydrogen is much debated (Competing
[...], 2005). It is possible that hydrogen could
eventually become an alternative to the use of energy
sources of fossil origin, but only as a long-term
prospect, since certain problems still have to be
resolved (in particular, the cost of production and
storage); reduction in costs, moreover, requires much
technological innovation. Furthermore, it will still
have to compete, on the one hand, with electric energy
which is far more consolidated on the market from an
infrastructural standpoint (Mazza and Hammerschlag,
2004; Beretta and Pedrocchi, 2005). On the other
hand, it will be in competition with biofuels which
exploit the same principles (derived from renewable
energy) but which, as described below, considerably
simplify the logistics element.
End-use
The other great advantage of hydrogen is its
considerable versatility of use both in the centralized
or distributed production of electric energy and in the
transport field (both for internal combustion motor
vehicles and in fuel cells). Its low discharge emissions
make this type of fuel of great interest.
Methanol
Methanol and ethanol have often been put
forward as interesting synthetic fuels. Methanol,
which is easy to synthetize (from natural gas by
reforming and conversion of the syngas) and
cheaper, has mainly been used in trials, whereas
ethanol obtained from sugar crops (sugar cane,
maize, straw, waste agricultural products, etc.) is
used as a fuel for road transport, especially in
Brazil and the United States.
Being liquid fuels, it is far easier to transport
and store them, even if their hydrophilic nature
may lead to new problems. In the United States,
ethanol has a different distribution network from
ENCYCLOPAEDIA OF HYDROCARBONS
FROM SOURCES TO MARKET: ENERGY CARRIERS
gasoline, and is splash blended into the latter only
prior to final distribution at the pump (precisely to
avoid any problem of water contamination or phase
demixing).
The following discussion is dedicated to methanol,
while ethanol is dealt with among the biofuels.
Methanol looks like being one of the most versatile
intermediates for exploiting natural gas, and is an
alternative to imported gas. The efficient production
technology via syngas, in fact, allows it to be exploited
optimally in terms of carbon and hydrogen use; when
produced on a large scale (7,500-10,000 t/d) from
low-cost gas (⭐1 $/MBtu), the production cost can be
very low (around 100 $/t). Thanks to its liquid nature
(Silver, 2003), it can be easily stored and transported
in vessels of huge capacity (already around 100,000 t,
but even more in future).
At present, methanol is used, above all, as a
chemical intermediate for the synthesis of
formaldehyde and acetic acid. However, it can be
useful for various applications in the energy field:
• As a fuel for power stations: emissions of turbines
supplied by methanol are substantially in line with
those supplied by natural gas, and the use of
methanol could be economically competitive with
LNG, at least in a number of specific cases
(Pollesel et al., 2005).
• As a component for gasolines: although used
directly in the 1980s as an additive and even as
an alternative fuel (experimented in California)
at the beginning of the 90s, methanol came into
the fuel field indirectly as a precursor of
MTBE, a well-known gasoline component. The
MTBE market has recently gone into recession
because of the problems of biodegradability
and aquifer pollution in the United States (Di
Girolamo et al., 2005). However, methanol not
used in the MTBE synthesis could rapidly find
a space in the production of biodiesel, whose
market is, instead, strongly on the upswing (see
below).
• As an intermediate for fuels: as early as the 1980s,
the conversion of methanol was proposed with
zeolitic catalysts in gasoline (Mobil process), but
that approach rapidly became costly because of the
collapse of the price of crude as from 1986. Now,
this process could attract fresh interest following
the pinpointing of catalysts that enable ethylene
and/or propylene to be synthetized selectively and
then converted into quality fuels by means of the
oligomerization of these olefins (Koempel et al.,
2005).
• As fuel for fuel cells in which methanol can
feed the cells directly or indirectly through the
formation of hydrogen; in the case of direct
VOLUME III / NEW DEVELOPMENTS: ENERGY, TRANSPORT, SUSTAINABILITY
supply, various problems still have to be
overcome, above all, due to the large crossover
of methanol through the polymeric membrane
of the fuel cells. A promising market could
open up, especially for ‘portable’ applications
(to substitute batteries for computers, mobile
phones, etc.); at the end of 2004, Toshiba (and
also Smart Fuel Cell) announced prototypes fed
by methanol with a new configuration of the
cell design which should avoid the crossover of
methanol (Baker et al., 2005).
• As an indirect reserve of hydrogen, which could be
easily obtained from methanol through reforming.
Applications of this type can be found, for
example, with the Topsøe Methanol To Shift
(MTS) process, in which the methanol is fed in a
hydrogen plant directly to the water/gas shift
reactor, maximizing the production of hydrogen
(Kane and Romanow, 2004).
Although a new methanol economy has been called
for in the last thirty years (Olah, 2004), this product
has not yet succeeded in establishing itself fully as an
energy carrier, except as a derivative. This is possibly
due to its characteristics as a toxic and poisonous
liquid which have always hampered its penetration of
the market; in reality, many other commercially
available fuels are far more dangerous.
Dimethyl ether
Interest in the use of DME as an alternative fuel for
various uses (Fig. 8) is very recent: as fuel for power
generation, as household fuel, in diesel engines as a
possible substitute of conventional diesel gas oil or as
a fuel for fuel cells (Peckham, 2004; Fleisch and Sills,
2005).
The main boost for using this component is that it
can be produced (similarly to methanol) economically
and on a large scale from natural gas – especially
where there are large quantities of natural gas available
at practically zero cost, or almost (e.g. associated gas
that can no longer be flared), and there are no markets
close enough to make the installation of the typical
natural gas industry feasible. In such cases, it could be
advantageous to transform natural gas into liquids and
to transport these by ship. In specific cases (depending
also on the distance between the place of production
and that of use), it could therefore be convenient to
produce and use DME.
DME has physical-chemical properties very
similar to those of LPG (but less heating power) and
could partly replace it in various uses (for example,
in households), while in other cases, it could exploit
the pre-existing distribution network in theory. As
for LPG, handling DME in cylinders makes it
particularly interesting for use in developing
311
ENERGY CARRIERS
Fig. 8. DME
and its applications.
home fuel
.LPG substitute
.fuel cell fuel
transportation fuel
multi
resources
syngas
.diesel fuel
.fuel cell vehicle
.hydrogen source
DME
power generation fuel
.gas turbine
.diesel co-generation
chemical use
.olefins/gasoline
.methanol chemistry
Production
DME can be produced from natural gas, directly
from syngas with a process very much like methanol
synthesis, or indirectly by means of dehydrating
methanol in large-scale plants (5,000-7,500 t/d of
DME) at extremely low production costs, around 120
$/t, inclusive of transport (equivalent to 4.5 $/MBtu
compared to LPG’s price of 4-14 $/MBtu, according to
variations in the price of crude and seasonal factors). It
312
should be observed that this production cost refers to a
natural gas cost of 0.5-0.75 $/MBtu; it is clear that the
different cost of the raw material and of the scale of
the plant can influence quite significantly the value of
the cost indicated above.
DME does not have to be produced only with
very large investments based on natural gas; in
fact, it can also be produced at a small scale at a
limited cost based on methanol by means of its
dehydration. This type of synthesis can favour a
gradual entry of DME into the market without
excessive investments.
At the moment, world production of DME
stands at about 200,000 t/yr, and is covered by some
twenty methanol dehydration plants; Asia is,
however, an emergent producer with a recent
expansion in China (Nogi, 2005) of about 300,000
t/yr (1 million t/yr by 2009). A project has also been
recently approved for the large-scale production of
DME in Iran (800,000 t/yr) by methanol
50
lower heating value (MJ/kg)
countries where an adequate distribution network
does not exist.
Compared to pure DME, a DME/LPG mix has the
advantage of possessing a higher energy content. As
illustrated in Fig. 9, the heating power of the mix
depends linearly on the proportion of the two
components.
From the standpoint of the different energy content
of the molecules, the same cylinder with DME instead
of LPG (50% C3/50% C4) contains 23% more weight
of product and, in all, weighs 12% more than the same
cylinder containing only LPG, but supplies 23% less
energy; if DME/LPG mixes were used, these
differences would be reduced as a function of the
DME content. The degree to which the cylinders using
DME are filled can, however, even reach 85% (against
80% of LPG), thus partly diminishing the energy gap
between a cylinder filled with DME compared to one
with LPG.
There is consolidated experience of using DME as
a propellant, in lieu of CFC (chlorofluorocarbon), in
sprays. Basically, there are no problems as far as its
behaviour in the atmosphere or stratosphere is
concerned (Ministerie van Volkshukvesting, 1985). In
fact, DME is a non-toxic, non-carcinogenic,
non-corrosive and fairly inert compound.
LPG LHV
45
diesel LHV
40
35
30
DME LHV
25
0
20
40
60
80
100
LPG in the mixture (% weight)
Fig. 9. Lower Heating Value (LHV) of the DME/LPG mixture
(50% C3/50% C4).
ENCYCLOPAEDIA OF HYDROCARBONS
FROM SOURCES TO MARKET: ENERGY CARRIERS
dehydration through the Topsøe technology
(Perregard, 2004). Moreover, various consortia,
especially in Japan, are preparing for the industrial
production of DME. For fifteen months, a
consortium headed by the Japanese company JFE
(including Total) has been experimenting a new
process for the production of DME from syngas in
a 100 t/d demonstration plant, and is preparing to
establish a large-scale industrial plant (probably
around 2 million t/yr) by 2010 (Ogawa et al., 2005).
Transport and distribution
DME can be transported using the same
equipment and the same precautions as for LPG.
The main modifications generally concern the type
of seals and gaskets that have to be used because of
the different ‘solvent power’ of DME. It should be
noted that this aspect is quite general and holds for
every application, both of DME alone and of
DME/LPG mixtures.
LPG vessels (or any type of facility in general) can
also be used for DME with the limits already
discussed; allowing for the smaller energy content, it
would be more convenient to transport DME in special
vessels of about 70,000 t (Hatta, 2004).
Storage and end-use
Like LPG, also DME’s characteristics of a
compressed gas liquid do not seem to present any
major difficulties. The manifold uses of DME are
described below in greater detail.
DME for thermoelectric generation. It can be used
in conventional gas turbines with minimum
modifications and with very low emissions,
comparable to those of natural gas. Although there
have been trials which have verified these
characteristics (with guarantees by the manufacturers
regarding performance), as yet, there is no long-term
experience. Energy can be generated also with
stationary Diesel engines.
DME as substitute/complement of LPG. In this
field, the use of DME does not display any
particular technological difficulties. It seems sure
to undergo rapid penetration, above all, in sizeable
markets, and is of great interest for developing
countries like China and India. Experience in this
field is being gained in China (Weidou et al., 2005)
and in neighbouring countries, and will be
extended also to Iran. It has been demonstrated that
for this use, DME/LPG mixtures (LPG rich) can
also be utilized without altering, in the slightest,
the LPG infrastructure that already exists
(Sanfilippo et al., 2004). DME emissions are even
less than LPG’s which are excellent from an
environmental standpoint.
VOLUME III / NEW DEVELOPMENTS: ENERGY, TRANSPORT, SUSTAINABILITY
DME as an alternative fuel for diesel engines.
The excellent characteristics of DME as an
alternative diesel fuel (high cetane number, high
percentage of oxygen and absence of carboncarbon bonds in the molecule) make it a fuel with
excellent performance and minimum emissions
(particulate is virtually absent). This enables very
severe specifications to be respected without
modifying the engines (except for the injection
system) or the post-treatment systems
(Marchionna, 2002). Use as an alternative diesel
fuel involves a greater added value compared to the
household/industrial type; its nature as a liquefied
fuel makes it more interesting for use in heavyduty motor vehicles. Many technical difficulties
have recently been overcome, but the automobile
industry (with the exception of Volvo and some
Japanese manufacturers of heavy vehicles) should
increase its efforts and, above all, the facilities have
to be built. Despite this, the number of demo trials
is continually increasing (including the
development of prototypes of heavy-duty motor
vehicles, supply stations, etc.) both in Japan
(Matsuda, 2005) and Europe, especially in Sweden
(Landalv, 2005).
Fuel cells. DME, like methanol, can easily be
converted into hydrogen and then supplied in fuel cells
of both membrane and solid oxides type
(Bogild-Hansen, 2005).
DME (as well as methanol) can be derived also
from renewable sources by gasification of biomass and
subsequent conversion of the derived syngas; a life
cycle analysis has recently shown that bio-DME used
in Diesel engines is one of the fuels that has the least
environmental impact at both local and global scale
(Klintbom and Danielsson, 2005).
Biofuels
At present, there is great interest in biofuels: on the
one hand, they give rise to less net production of
carbon dioxide per energy consumed because they
derive from renewable sources – although a lively
debate is still ongoing (Hess, 2005) – and on the other
hand, they partly allow a substitution of petroleum
derivatives.
The main biofuels are ethanol (or its derivative
ethyl-tert-butyl ether, ETBE, homologous to
MTBE) used as an additive for gasoline, and
biodiesel used as an additive for gas oil. The fact
that these products are liquids means that they can
easily be transported and stored (even if ethanol, as
already said, requires an independent distribution
network due to its hydrophilic properties).
Furthermore, they can be used as additives in
moderate percentages (⭐10% vol) and, generally
313
ENERGY CARRIERS
speaking, there is no particular problem when used
in normal internal combustion engines.
Recently, legislation in Europe and the United
States has favoured the rapid expansion of these
biofuels. In Europe, the minimum percentage of
biofuels must be 2% by the end of 2005, and 5.75% by
the end of 2010, while in the United States, the law
establishes that not less than 7.5 billion gallons
(c. 28.4 billion liters) of biofuels (above all ethanol) must
be introduced into road transport by the end of 2012.
The great success of these fuels is favoured also by
the considerable tax subsidies which make them
economically more competitive with fossil fuels, as
their cost of production is generally higher. The high
price of oil and technological improvements in their
production chain could, however, reduce this gap.
Ethanol
Ethanol has always been used as a fuel for
spark-ignited combustion engines, especially in Brazil,
with 4 billion gallons (c. 15.2 billion liters) produced
in 2004 for about one million vehicles running on
gasoline with ethanol or just ethanol; in the United
States, it is used as an antiknock component in
percentages of up to 10%, with 3.4 billion gallons
(c. 12.9 billion liters) produced in 2004.
Ethanol is obtained through fermentation of sugars
from any plant raw material which contains or can be
converted into sugars, such as starch or cellulose (the
production of ethanol from cellulose, presently still in
the experimental stage, promises to appreciably reduce
the alcohol production cost). In Brazil, the main raw
material is sugar cane, while in the United States it is
corn.
After pretreatment, the raw material (Fig. 10) is
subjected to enzymatic hydrolysis which produces
glucose that is transformed into ethanol after
fermentation (Hall, 2005).
Considerable reductions in cost and improvements
in energy yield can derive from using advanced
biotechnological processes and innovative separation
methods (by means of membranes).
Also the oil company Shell is particularly active in
the sector: in 2005, it invested 46 million dollars in the
Iogen project, the purpose of which is to convert straw
and woody wastes (containing cellulose) into ethanol
by using enzymes design in accordance with advanced
genetic techniques. A plant producing 200,000 t/yr of
biomass
feedstock
preparation
hydrolisis
ethanol should come into operation by the end of 2008
for an estimated cost of ethanol of only 1.30 $ per
gallon (c. 3.79 l) (Wechem, 2005).
Biodiesel
Biodiesel is produced from vegetable oils
(rapeseed oil and palm oil), from waste oils and from
animal fat; these raw materials contain triglycerides,
generally triesters of glycerine with fatty acids that
have a long alkyl chain (Lotero et al., 2005). After the
biomass has been processed, the oil is transesterified
with methanol to produce glycerine and the trimethyl
ester deriving from the oily matter, which constitutes
biodiesel. Slightly less than two million tons were
produced in Europe in 2004 (of which one half in
Germany and, in all, another third in France and Italy),
but more than triple this amount should be produced
by the end of 2010. The typical characteristics of
biodiesel are set out in Table 3; it has properties
similar to those of gas oil, although it possesses only
90% of its heating power, on the other hand, it is more
easily biodegradable.
Biodiesel is generally produced by homogeneous
basic catalysis (as a rule, using potash or caustic soda),
although more efficient alternative processes have
recently been proposed by means of using either
heterogeneous basic catalysis or acid or enzymatic
catalysis. The use of supercritical methanol also seems
interesting. Glycerine is, however, an essential product
of this production; at present, it finds an outlet on the
chemical oil market, but the increase in biodiesel
production gives rise to a growing marketing problem
(McCoy, 2005).
Biomass to liquids
Biomass, whatever its nature, has always been used
to produce thermal or electric energy; recently,
different processes have, however, been proposed to
transform it into liquids for the fuel market (as well as
the aforementioned ethanol and biodiesel).
There are basically two approaches, one direct and
the other indirect, for transforming Biomass To
Liquids (BTL). In the direct one, the biomass (often
after pretreatment) feeds a typical refining plant, either
a dedicated one or a co-processing one with oil loads.
In the indirect one, the biomass is gasified to produce
syngas which can then be converted into liquids
through the Fischer-Tropsch synthesis method into
glucose
fermentation
ethanol
recovery
ethanol
Fig. 10. Ethanol production process from biomass.
314
ENCYCLOPAEDIA OF HYDROCARBONS
FROM SOURCES TO MARKET: ENERGY CARRIERS
oxygenates such as methanol or DME, or into
hydrogen.
The direct approach is perhaps more recent, and
has been promoted by the recent European directive on
the minimum content of biofuels in gasoline and gas
oil. It means using the same oils and greases that act
as the basic material for the synthesis of biodiesel to
feed a conversion unit directly (either a cracking unit,
FCC, which causes the molecules of long-chain fatty
acids to break, or a hydrogenation unit in which the
ester bond is broken, mainly producing long-chain
paraffins as well as carbon dioxide and water)
(Buchsbaum et al., 2005).
The direct approach is very simple and has the
great virtue of supplying a product substantially the
same as petroleum. In the case of hydrogenation, the
product can be of very high quality with cetane
numbers as high as 90, and this has led to the setting
up of special plants, as in the case of Neste Oy in
Finland (Neste [...], 2005; Koskinen et al., 2006).
The indirect approach, instead, is more complex as
it requires intensive processes with high investment
costs, such as gasification and the subsequent
conversion of the syngas into liquids. Despite this,
considerable research and development is going on in
this field (Peckham, 2005).
4.1.5 Conclusions
In this chapter, the various aspects that make each
energy carrier more or less interesting have been
analysed, always making reference to its complete life
cycle. The availability of energy sources for its
production and the variety of uses are certainly the
strong points of the carrier; nevertheless, the
intermediate phases of storage and distribution are
even more decisive. On the basis of what has been
stated, it can be inferred that liquid carriers
considerably simplify the transport and storage phases,
and they are, by far, more advantageous than gaseous
and solid ones. This is probably one of the keystones
in the use of oil as a primary fuel, as it is not only
relatively cheap and available in great quantity, but
also able to produce highly appreciated liquid carriers.
To support this, the use of fuel oil (or even emulsions)
in power generation may be recalled. Although it is
surely not the fuel of choice for this purpose, its main
merit is the simplicity of use due to its liquid nature
(as well as being relatively cheap in the past due to the
low prices of crude).
Innovative liquid carriers such as methanol and
ethanol have almost ideal characteristics as energy
carriers: methanol is cheap and can be produced at a
large scale, but its toxicity has so far hindered its
VOLUME III / NEW DEVELOPMENTS: ENERGY, TRANSPORT, SUSTAINABILITY
success. Ethanol is more costly and less available at a
very large scale, but as it derives from renewable
sources, it has often encountered government support,
partly due to pressure from public opinion and
agricultural lobbies. The same may also be said about
biodiesel.
The liquefied carriers (LPG and eventually DME)
can be particularly useful in developing countries
where no adequate distribution network exists.
Gaseous carriers such as methane (and eventually, but
with many complications, hydrogen) can, in any case,
be successful if their use is cheap, eco-friendly, and
justified by the availability of large quantities of
primary fuels (above all gas).
Electric energy, the carrier par excellence, is used
everywhere and has zero emissions in its place of use.
Storage is its weak point, but it should be noted that
every small improvement in this field could lead to an
increase in its use well beyond all imagination.
Competition also exists among the various
carriers (although in some cases, they may even
complement each other), especially between
emergent ones. Hydrogen could have certain
advantages over electric energy, above all,
regarding storage, but at the moment these
advantages are merely hypothetical because
storage is still a weak link in the hydrogen chain.
As it is, biofuels are currently perhaps the main
alternative to a rapid and incisive development of
the hydrogen carrier; they meet many of the
expectations for which hydrogen is desired, even if
not to the same extent and, furthermore, they are
now already in use. Lastly, it must be emphasized
that considerable development of biofuels means
intensive exploitation, above all, of arable land,
making it unavailable for agricultural use.
Precisely these last examples show that the concept
of energy carrier is central in everyday life; this is not
surprising when considered that its task is to reconcile
the use of the various energy sources with the
community’s needs.
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ENCYCLOPAEDIA OF HYDROCARBONS
FROM SOURCES TO MARKET: ENERGY CARRIERS
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Mario Marchionna
EniTecnologie
San Donato Milanese, Milano, Italy
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