INTERNATIONAL JOURNAL OF ENERGY RESEARCH
Int. J. Energy Res. 2008; 32:1058–1064
Published online 25 February 2008 in Wiley InterScience
(www.interscience.wiley.com) DOI: 10.1002/er.1411
SHORT COMMUNICATION
Potential applications using LNG cold energy in Sicily
Antonio Messineo*
,y
and Domenico Panno
Department of Energy and Environmental Researches (DREAM), University of Palermo, Viale delle Scienze, Palermo 90128, Italy
SUMMARY
According to previsions, natural gas could be the main energy source worldwide, inducing relevant geopolitical
changes. Most likely, such problems will be solved with the development of a gas transportation mode alternative to
traditional pipelines: liquefied natural gas (LNG). The global LNG trade has increased rapidly during recent years. A
significant amount of energy is consumed to produce low-temperature LNG, which has plenty of cryogenic exergy/
energy. Therefore, the effective utilization of the cryogenic energy associated with LNG vaporization is very important.
Sicily, with more than five million inhabitants, is the second biggest region of Italy and in this region will be realized two
of the 11 gasification plants planned in Italy according to the regional energy master-plan. This paper shows some
interesting applications for the cold produced in gasification plants, e.g. for seawater desalination and for fresh and
frozen food production and conservation. These applications seem very interesting for Sicilian situation and also can
contribute to energy saving and greenhouse gases reduction to match Kyoto Protocol targets. Copyright # 2008 John
Wiley & Sons, Ltd.
KEY WORDS: LNG; energy recovery; seawater desalination; cold chain
1. INTRODUCTION
The combustion of fossil fuels has played a
dominating role in the build up of greenhouse
gases in the atmosphere. It is estimated that the
energy sector accounts for about half the global
emissions of greenhouse gases [1].
The Kyoto Protocol commits the signatory
countries to undertake measures finalized to
reducing greenhouse gas emission, in order to
reach the set goals. For Italy, the commitment is
the reduction in the greenhouse emissions by 6.5%
below 1990 levels over the commitment period
2008–2012 [2].
It requires the introduction of suitable political
strategies and programs aimed at establishing a
sustainable energy system together with the
application of a set of actions either at national
scale or at regional one [3].
Local authorities are called to play a remark able
role in carrying out environmentally oriented
strategies to manage energy resources efficiently
*Correspondence to: Antonio Messineo, Department of Energy and Environmental Researches (DREAM), University of Palermo,
Viale delle Scienze, Palermo 90128, Italy.
y
E-mail: messineo@dream.unipa.it
Received 26 July 2007
Revised 2 January 2008
Accepted 13 January 2008
Copyright # 2008 John Wiley & Sons, Ltd.
and to address the life quality towards the
sustainability.
Hence, the energetic efficiency of industrial
plants and equipment must be increased. Thus,
the use of primary energy derived from fossil fuels
will be reduced and the energy management in
industrial activities will be improved.
In industrialized countries, about 15% of
electric energy is used for air conditioning and
refrigeration. In order to solve the problem of
exhausting fossil fuel, there are many attempts to
utilize the waste energy more effectively. Energy
can be saved in this field, for example, recovering
the cold energy produced in gasification plants
when liquefied natural gas (LNG) is gasified, thus
contributing to rationalize energy and achieving
the Kyoto Protocol aims [4–8].
2. LNG LIQUEFACTION PLANTS
Natural gas is one of the most widely used
conventional mineral energy resources. In contrast
to other mineral resources, such as coal and
gasoline, natural gas has higher combustion heat
and produces much less pollution. The disadvan-
tage is that it is in a gaseous state under ambient
temperature and pressure; hence, it must be
usually liquefied to LNG for long-distance trans-
portation and storage.
LNG is produced by cryogenic refrigeration of
natural gas after removing the acid and water.
Liquefying natural gas is a high-energy consump-
tion process, producing one ton of LNG consum-
ing about 850 kWh of electric energy. In addition,
it should be gasified for normal use at the receiving
site. Gasification also consumes energy. If we can
make use of the cold heat of LNG, it is evident
that the overall efficiency will improve.
LNG is a low-temperature multi-component
liquid mixture. Its main component is methane,
whose concentration is usually above 80% in the
mixture. It also contains nitrogen, ethane, pro-
pane, normal butane and isobutane, normal
pentane and isopentane. Its exergy depends on
the system pressure, temperature, ambient tem-
perature and component concentrations [9].
Natural gas liquefaction requires relevant in-
vestments and conspicuous amounts of energy that
is furnished by the same gas and by other fossil
fuels. The used plants utilize several industrial
processes; the most common types are as follows :
*
cascade cycles with several fluids (i.e. for
decreasing temperature: propane, ethylene,
methane);
*
cascade cycle exploiting binary or tertiary
hydrocarbon mixtures;
*
turbo-expansion cycles.
Liquefaction is carried out through cascade cycles:
at the higher temperatures through a propane
cycle, latter through an ethylene and ethane cycle
and in the end through a methane cycle. Natural
gas, cooled from top to bottom by propane, ethane
and methane, liquefies and drops to 1588C; later,
through a lamination valve, flows into the
cryogenic tank where it keeps cooling down to a
temperature of 1618C:
Figure 1 shows the scheme of a cryogenic plant
where the following processes are carried out:
natural gas liquefaction, methane, ethylene and
propane cryogenic cycle.
3. LNG GASIFICATION
Most of the gasification processes occur in plants
located on coasts where there is a wide availability
of seawater to be used as heating water for LNG
gasification. The equipment is made of a series of
open vaporizers (open rack vaporizers) constituted
by several heat exchangers where seawater flows on
the outside surfaces and vaporizes LNG flowing
inside the ducts at pressure between 80 and 85 bar.
A plant using seawater for gasific ation processes
works through a therm al gap equal to 4–88C
between the entrance and the exit of the heat
exchanger and with a water load between 100 and
180 l s
1
:
Another gasification system is the submerged
combustion types (submerged combustion vapor-
izers); these use send-out gas as fuel for the
combustion that provides vaporizing heat.
Growing costs and environmental problems
linked to energy conversion processes lead to
POTENTIAL APPLICATIONS USING LNG COLD ENERGY IN SICILY 1059
Copyright # 2008 John Wiley & Sons, Ltd. Int. J. Energy Res. 2008; 32:1058–1064
DOI: 10.1002/er
recover a good portion of the energy used during
the liquefaction process.
Gasification produces about 840 kJ kg
1
of low-
temperature energy [9, 10]; hence, it is possible to
use this cold energy for several applications, such
as nitrogen, oxygen and argon production through
air liquefaction, frozen food production, fresh
and/or frozen food storage, fresh water production
through seawater desalination, etc.
According to previsions, the demand for natural
gas will increase about 2.1% yearly reaching a
value of 4800 10
9
Stm
3
year
1
in 2030. This
growing gas demand requires increasing invest-
ments in gas pipeline building, in liquefaction and
gasification plants, and for the transport from the
producer to the consumer countries. Figure 2
shows the growing reliance on gas imports for
2000–2030 period [11].
LNG transportation plants are needed both for
an adequate diversification of the supply sources
and to satisfy the consumption of those countries
unreachable through pipelines.
The gasification potentiality existing on our
planet (August 2005) is equal to 22:7 10
6
m
3
shared among 50 plants distributed as follows: 13
plants ð2:84 10
6
m
3
Þ in Europe, 30 plants ð18:54
10
6
m
3
Þ in Asia, 1:00 10
6
m
3
(5 plants) in
North America and 0:32 10
6
m
3
(2 plants) in
South America.
Compressor GN
GN Treatment
P
ro
p
a
n
e
Ethylene
M
e
t
h
a
n
e
Liquid
Separator
Heavy Fractions
LNG Flash Tank
Storage
LNG
Boiler
Boil-off line
Alternator
Seawater Heat Exchanger
enahtem .rpm
oCe
na
p
o
rp
.
r
p
mo
C Compr. ethylene
Ethylene
Methane
Seawater Heat Exchanger
Figure 1. Cryogenic plant scheme.
Figure 2. Growing reliance on gas imports for
2000–2030 period in Billion cubic feet per day.
A. MESSINEO AND D. PANNO1060
Copyright # 2008 John Wiley & Sons, Ltd. Int. J. Energy Res. 2008; 32:1058–1064
DOI: 10.1002/er
Italy has only a rather small gasification plant
(Panigaglia, Liguria) in function since 1971.
Eleven gasification plants, of which three are
offshore, are planned in Italy. In Sicily, the two
gasification plants planned will be realized in Porto
Empedocle (Agrigento) and Priolo (Siracusa)
according to the regional energy master-plan [12].
4. LNG COLD ENERGY FOR SEAWATER
DESALINATION PROCESSES
The first proposed application concerns the
possibility of producing fresh water through sea-
water desalination recovering LNG cold energy.
In the last decades of the 20th century, the
problem of drought has significantly affected
Sicily, giving rise to the construction of a number
of desalination plants for civil, agricultural and
industrial uses.
Although the northern part of Sicily has always
been helped by the presence of mountain chains
that have significantly contributed to the water
needs, in the southern part of Sicily the availability
of water sources has been continuously worsening
due to a decrease in rainfall, which reached, in some
areas, values of only 400 mm of water per year.
The population affected by severe water scarcity
can be estimated in as many as 500 000 inhabi-
tants, distributed along the southern and western
coasts in the districts of Caltanissetta, Agrigento
and Trapani. However, almost 50% of the island is
actually characterized by very low rainfalls [13].
Scientific studies and experiences carried on
different countries allowed developing separation
systems and processes through freezing that have
not yet had an adequate spread on industrial scale.
It is known that the separation of salt contained
in solution can be carried out through both
freezing and vaporizing water. The latter case
(liquid–vapor passage), working at normal pres-
sure, requires 2257 kJ kg
1
; whereas the liquid–
solid passage requires about 334 kJ kg
1
: The
second process ap pears energetically economical,
even if separating pure liquid water from the salt
solution is more complex and requires greater care.
The huge amount of cold energy from gasifica-
tion plants makes freezing desalination procedures
more appealing. It essentially consists of three
basic operations: freezing, washing and melting.
Other au xiliary operations, as filtration and air
removal, are needed to remove the amounts of
solids in suspension.
High salinity water is sent to a heat exchanger
where it is progressively cooled down to almost
freezing temperatures. Next, the suspended
solids are screened out in the filtering section,
whereas the dissolved gasses are separated by
rest of the fluid to obtain better freezing. The
cooled and pre-treated water is sent to the
next freezing stage where crystal formation takes
place.
Crystal size is very important in order to obt ain
an effective salt–water separation. If the crystal
size is too big, it could trap within saltwater sacks;
otherwise, if the crystal size is too small, the next
washing procedure may be too difficult.
Since their formation, the crystals are covered
with salty wat er; therefore, before undergoing the
fusion stage, they will have to be washed to remove
the high amount of salt stuck on the solidified
mass. After the washing procedure, the cleaned ice
goes in the fusing section. Figure 3 shows the
scheme of a plant using LNG cold energy for fresh
water production.
The availability of LNG cold energy may
undoubtedly contribute to make desalination
processes less expensive. The possibi lity of placing
these plants next to gasification stations facilitates
the use of the available cold energy and constitutes
a stimulus to develop this technology.
5. LNG COLD ENERGY IN THE
COLD CHAIN
The second proposed application utilizes LNG
cold energy in some loops of the cold chain as
storage warehouses for raw materials and finished
products, frozen food manufa ctures and hyper-
markets. Productive settlements or big commercial
centers in need of cold energy could rise near
gasification plants.
Both cases require building pipelines to transfer,
through a secondary fluid, some of the cold energies
recovered in the gasification plant to users.
POTENTIAL APPLICATIONS USING LNG COLD ENERGY IN SICILY 1061
Copyright # 2008 John Wiley & Sons, Ltd. Int. J. Energy Res. 2008; 32:1058–1064
DOI: 10.1002/er
Among the secondary fluids, carbon dioxide
seems to be interesting since it, due to its
thermo-elastic characteristics (low specific volumes
and good thermal exchange properties) [14, 15],
lends itself to work as a good thermal vector in
transferring the recovered cold energy to users.
Liquid CO
2
is carried to the gasification plants
and, through adequately insulated tubes, to the
different stations where heat exchangers, working
as vaporizers, are set up.
Carbon dioxide pro duces the needed cold by
passing from the liquid to the vapor state, and
through a feedback loop if returns to the gasifica-
tion plant, thus restarting the cycle.
Using CO
2
as a secondary fluid allows reaching
the users’ required cold temperatures, whi ch in
the case of frozen food production may reach
408C:
The above-described type of cold distribution
system means a remarkable reduction in energy
consumption since refrigerating equipments are no
longer needed. This means significant saving in
electric energy since electricity is required only to
pump the secondary fluid.
The advantage is significant enou gh even for big
hypermarkets, where electricity consumption to
produce cold is over 50% of the general consump-
tion. Choosing CO
2
is also convenient due to
its good safety properties (A1, classification
ASHRAE).
Figure 4 shows the scheme of a system using
LNG cold energy to store fresh and/or frozen food
Figure 3. System using LNG cold energy for fresh water production.
A. MESSINEO AND D. PANNO1062
Copyright # 2008 John Wiley & Sons, Ltd. Int. J. Energy Res. 2008; 32:1058–1064
DOI: 10.1002/er
