Technological and operational concept of an LNG carrier

Scientific Journals
Zeszyty Naukowe
Maritime University of Szczecin
Akademia Morska w Szczecinie
2010, 21(93) pp. 28–33
2010, 21(93) s. 28–33
Technological and operational concept of an LNG carrier
Koncepcja techniczno-eksploatacyjna gazowca LNG
Monika Bortnowska
West Pomeranian University of Technology in Szczecin, Faculty of Maritime Technology
Department of Oceanengineering and Marine Systems Design
Zachodniopomorski Uniwersytet Technologiczny w Szczecinie, Wydział Techniki Morskiej
Katedra Oceanotechniki i Projektowania Systemów Morskich
71-065 Szczecin, al. Piastów 41, e-mail: [email protected]
Key words: liquefied gas, membrane tanks, cargo capacity, marine power plant, cost structure
Abstract
In connection with the current investment project of building an liquefied natural gas (LNG) terminal in
Świnoujście, an analysis of design solutions and operational features of the potential variant of an LNG
carrier supplying gas from the Persian Gulf areas has been conducted. As a result of studying the waterway
restrictions on the assumed route, the article presents the concept of the optimum LNG carrier size – its
overall dimensions – along with an analysis of design parameters. A hull shape model was used to examine
the hull resistance and propulsion system. Besides, the size of the ship engine room was estimated and the
power demand of the main propulsion system was determined. The cost patterns of LNG carrier construction
and operation was included as well as the estimated mean value of its construction unit cost.
Słowa kluczowe: gaz skroplony, zbiorniki membranowe, objętość ładunkowa, siłownia okrętowa, struktura
kosztów
Abstrakt
W związku z rozpoczętą inwestycją budowy gazoportu do obsługi skroplonego gazu ziemnego w Świnoujściu przeprowadzono analizę techniczno-eksploatacyjną potencjalnego wariantu gazowca LNG, dostarczającego gaz z obszarów Zatoki Perskiej. W wyniku przestudiowania ograniczeń drogi wodnej na założonej trasie
w artykule przedstawiono koncepcję optymalnej wielkości gazowca LNG – jego wymiary wraz z analizą
parametrów projektowych. Dla zamodelowanego kształtu kadłuba statku przeprowadzono wstępną analizę
oporowo-napędową, oszacowano wielkość siłowni okrętowej i wyznaczono zapotrzebowaną moc napędu
głównego. Zamieszczono strukturę kosztów budowy i eksploatacji gazowca LNG wraz z oszacowaniem
średniej wartości jednostkowego kosztu jego budowy.
Introduction
In order to become independent of gas supplies
from Russia, Poland undertook the construction
of a gas terminal in Świnoujście. Such investment
project had been offering opportunities for building
LNG carriers at Polish shipyards. This, in turn,
would have given the shipbuilding industry
a chance to improve their financial standing.
Unfortunately, the present economic situation and
the collapse of leading Polish shipyards has
probably shattered this chance for ever. As a result,
gas will be transported to Poland by ships launched
at foreign shipyards.
At present the natural gas is planned to be transported to Poland on board ships in a liquefied state.
Out of various LNG shipping technologies, LNG
carriers are still the most widespread means of
transportation. Natural gas is at present the most
desirable source of energy in the world, and the
development of the LNG technology has caused
that trading in gas started to have a global dimension. No wonder that the number of this type of
ships being ordered and built keeps growing,
together with a single ship cargo capacity now
reaching 266 000 m3 of liquefied gas. According to
analysis, in the year 2030 the LNG global trade
28
Scientific Journals 21(93)
Technological and operational concept of an LNG carrier
 land-based infrastructure, i.e. LNG receiving
terminal and transfer piping system,
 limitations of the waterway where LNG carriers
will be operating:
• Limitations of the LNG terminal in Świnoujście
according to [2]:
Length overall
Loa  300 m,
Maximum draft
T  13,5 m,
Cargo capacity of LNG carrier
VŁ  200 000 m3
• Navigational restrictions in the Danish Straits:
Transit traffic in the Danish Straits moves along
two routes – figure 1:
 route T – for ships with deeper draught
through the Kattegat Strait and the Great Belt
– Lmax = 285 m, B = 43 m, Tmax = 15 m [3],
the strait through height of the Great Belt
Bridge is equal to: h = 65 m;
 through the Sund Strait – for ships with shallower draught, the strait through height of the
bridge along this route is equal to: h = 57 m.
figures shall exceed gas supplies carried out in
a conventional manner – via gas pipelines. A dynamic development in the construction of gas
carriers has also contributed to the downward trend
in the cost of building these vessels – due to strong
competition, especially from Korean shipyards.
In comparison, according to [1] in recent years the
unit cost of gas carrier of Q-flex ship size has
amounted to about 1015 $/m3, while in the end
of the 1990s it amounted to 1200 $/m3 (for typical
145 000 m3).
In the present article the concept of the optimum
LNG carrier size is presented for the Świnoujście–
Qatar shipping line, taking into account the waterway limitations concerning draught, breadth and
depth as well as an analysis of design parameters.
For the modelled hull shape of the ship the preliminary analysis of the ship hull resistance and propulsion system was conducted, and the cost pattern of
the LNG carrier construction and operation was
included.
Selection of the gas carrier type and size
For this consideration the LNG carrier with the
system of membrane tanks has been chosen; its
construction engineering has been known and
applied for more than 40 years on well-proven
standards. It confirms their high reliability and
safety levels. The percentage of membrane tanks in
the gas carriers market for 2009 was nearly 70%.
All the largest newly built gas carriers, and those
built in the past two years, Q-Flex (216 000 m3) and
Q-max (266 000 m3), are fitted with membrane
tanks.
The system of membrane tanks shows advantages over spherical tanks, first of all owing to:
 higher safety due to the double hull,
 good visibility from the bridge due to flat deck
construction,
 easy access to all spaces,
 better use of hull space through full integration
of the cargo space with the hull shape,
 better use of cargo tanks capacity,
 quicker precooling due to smaller mass of cargo
tank material.
The size of the LNG carrier with membrane
tanks and of the whole fleet will depend on many
factors, such as:
 import direction, i.e. the distance between gas
deposits and the final consumer – assumption:
the Świnoujście–Qatar route (ca 6800 nautical
miles = 12 600 km),
 volumes of natural gas imported,
Zeszyty Naukowe 21(93)
Fig. 1. Shipping routes in the Danish Straits
Rys. 1. Trasy żeglugowe w Cieśninach Duńskich
Cargo carrying capacity and ship principal
dimensions
For a selected technique of gas transport based
on collected technical data of the ships built, the
regressive relationships between a particular design
and operational parameters were elaborated, which,
in turn, were used for estimating the LNG carrier
size.
Considering the limitations of principal dimensions, resulting from the necessity of the ship to get
through the Danish Straits, and the port terminal
parameters in Świnoujście, the maximum cargo
carrying capacity of the ship should not exceed
VŁ = 150 000 m3. In table 1 the results of analyses
of design parameters are presented for two potential
variants of LNG gas carriers that can be handled by
the terminal in Świnoujście.
29
Monika Bortnowska
The concept of LNG gas carrier
Table 1. Main dimensions and design parameters of two LNG
carrier variants
Tabela 1. Wymiary główne i parametry projektowe 2 wariantów gazowców LNG
Parameter
Length overall Loa
Length between
perpendiculars Lbp
Breadth B
Hull depth H
Height of the cargo
tank Htruk
Module volume LBH
Draught T
Block coefficient CB
Displacement D
Deadweight DWT
Light ship MSP
Gross tonnage GT
Draught – light ship TSP
Water ballast
[m]
Both the silhouettes of LNG carriers and their
design solutions have been similar for many years.
The general subdivision of spaces is similar to that
in other tankers. The spatial arrangement of the ship
has not undergone any essential modifications and
in the hull shape one can notice only attempts at
elongating the cargo compartment, in order to increase the cargo carrying capacity – which is of
economic importance.
LNG carriers belong to a group of highly
specialized ships, due to the applied technology of
cargo transport. The priority issue is ensuring
continuous cargo cooling as well as avoidance of
cargo evaporation to the outside atmosphere. The
average daily cargo evaporation (boil-off) ranges
from 0.15 to 0.2% of the gas cargo weight – this
amount depends mainly on the insulation effectiveness degree. Therefore, shipping of liquefied
natural gas requires very good thermal isolation of
the tanks from the environment. The highly
complex construction with specialized tanks and
equipment results in very high construction and
operational costs. Despite a downward trend in the
unit cost of 1 m3 of LNG cargo space, the cost of
building average size LNG carrier still amounts to
more than $ 200 m.
Cargo capacity of LNG carrier
VŁ = 150 000 VŁ = 200 000
[m3]
[m3]
285
300.0
[m]
[m]
[m]
[m]
[m3]
[m]
[–]
[t]
[t]
[t]
[–]
[m]
[m3]
273.5
288.0
43.0
26.7
48.0
28.5
34.0
38.0
314 005
11.85
0.745
106 894
75 500
31 400
99 076
3.8
55 000
393 984
12.5
0.762
135 615
95 615
40 000
128 952
4.7
69 800
The obtained result of optimizing calculations is
that the gas carriers fleet of cargo carrying capacity
VŁ = 150 000 [m3] and the ship operational speed
v = 19.5 knots for the assumed navigation line shall
consist of three ships.
In order to carry out the preliminary analyses of
design parameters, based on the existing ships data,
the range of basic design parameters of LNG
carriers has been determined. These parameters
have an impact, inter alia, on: ship hull resistance
and propulsion system characteristics, developing
the required ship speed, ship stability and its
behaviour in waves, safety, damage stability etc.
Determining the lengths of main compartments
in an LNG carrier
According to the International Code for the
Construction and Equipment of Ships Carrying
Liquefied Gases in Bulk (IGC Code) and the analysis of subdivision solutions of the ships in operation
the following parameters have been assumed
(Fig. 2):
 double bottom height h = 3.2 m,
 width of ship’s double side w = 2.5 m,
 thickness of insulation layer of membrane tank
t = 0.3 m.
Cargo compartment of gas carrier (ca 66% Lbp) –
spreads out over the area from the front engine
room bulkhead to the back bulkhead of fore tanks.
It is separated from the environment and from the
rest of the ship with double bottom, double sides
and deck. This compartment has been subdivided
into four cargo tanks of different lengths (Fig. 3).
Cargo tanks have been separated from each other
with a cofferdam, each tank is equipped with cargo
reloading / handling installations fitted with two
high-duty pumps.
Volumes of particular cargo tanks – filled at
98.5% are equal to the values given below, respec-
Table 2. Ranges of the identified basic design parameters of the
LNG vessel based on existing ships
Tabela 2. Zakresy podstawowych parametrów projektowych
gazowców LNG wyznaczonych na podstawie statków zbudowanych
LNG vessels
Design
parameter
min
max
 = DWT / D
0.62
0.8
Ł = VŁ / D
1.23
L/B
B/T
H/T
CB
6.0
3.3
1.7
0.68
l = L / 1/3
Fn = V / (Lw g)
*
1/2 *
Existing ships
VŁ = 150 000 VŁ = 200 000
m3
m3
0.706
0.705
1.47
1.4
1.47
6.4
4.6
2.32
0.82
6.36
3.63
2.25
0.745
6
3.84
2.28
0.76
5.53
5.84
5.81
5.66
0.18
0.22
0.2
0.195
ship speed v = 19.5 knots
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Scientific Journals 21(93)
Technological and operational concept of an LNG carrier
Size of the ship engine-room and the power
of the main propulsion system
LNG
The size of the engine room of the LNG carrier
depends on the type of ship propulsion system –
first of all on the main engine. A relatively recent
alternative to the steam turbine power plant, the
most common in gas carriers, (on account of high
reliability of the turbine, ease of using boil-off gas
as fuel, and relatively low cost of maintenance), is
the dual fuel diesel electric plants – DFDE plants
(two kinds of fuel: heavy fuel oil and gas vapours)
as well as DRL (only heavy fuel oil, possibility of
re-liquefying of cargo vapours).
Based on overall dimensions of power plants of
gas carriers built to date, an analysis of the power
plant size for the newly designed ships has been
conducted. Table 3 presents the percentages of
length of the power plant and that of the cargo
compartment within the length between perpendiculars Lbp.
It is notable from the data in table 3 that certain
advantages may be achieved by applying new solutions of the propulsion system.
The use of, e.g., a DRL type power plant in an
LNG carrier (instead of steam turbine) contributes
to the lengthening of the cargo compartment by ca
6%, which yields in addition 10 000 m3 of LNG
(gas carrier of 150 000 m3), see figure 5.
tank
Fig. 2. The midship section of the cargo tank (the autor`s
study)
Rys. 2. Przekrój poprzeczny zbiornika ładunkowego (opracowanie własne)
tively: VŁ1 = 22 938 m3, VŁ2 = VŁ3 = 42 655 m3,
VŁ4 = 41 791 m3.
On the LNG carrier being designed in way of
the midship, along the length of middlebody, the
three (out of four) cargo tanks (counting from the
aft) have the constant cross-section area, forming
the parallel body, equal to: Fzb = 975.34 m2,
whereas the tank no. 1, due to the shape of waterlines has a variable surface area along the length.
The general design concept in form of a 3-D
model of the LNG carrier under design is presented
in figure 4.
LNG tank
No. 4
Wheelhouse and
accommodation
After
peak
Gas
combustion
unit
LNG tank
No. 3
Vent mast
Manifold
Compressor
Engine room
T/S
Fig. 3. Profile of LNG carrier (the autor`s study)
Rys. 3. Widok boczny gazowca LNG (opracowanie własne)
Fig. 4. 3-D model – the concept of LNG carriers 150 000 m3
Rys. 4. Model 3D – koncepcja gazowca LNG 150 000 m3
Zeszyty Naukowe 21(93)
31
LNG tank
No. 2
Cofferdam
LNG tank
No. 1
Fore peak
tank
Diesel oil
tank
Monika Bortnowska
Table 3. The percentages of the marine power plant length and
the cargo compartment length for the design concept of an
LNG carrier
Tabela 3. Procentowy zakres długości siłowni okrętowej i przedziału ładunkowego dla koncepcji projektowej gazowca LNG
Types of propulsion
system
Steam turbine S / T
Dual-fuel diesel
electric (DFDE)
Slow-speed diesel
with reliquefaction
(DRL)
Length of engine
room
(16.6 ÷ 17.7%) Lbp
45 ÷ 48.5 m
(14.5%) Lbp
39.5 m
Length of loading
space
(64 ÷ 65%) Lbp
175 ÷ 178 m
(66%) Lbp
180.5 m
(13 ÷ 14.5%) Lbp
35.5 ÷ 40 m
(69 ÷ 70%) Lbp
188 ÷ 191.5 m
PB 
Fig. 5. Slow-speed diesel with reliquefaction (DRL) – reduced
length
Rys. 5. Siłownia DRL z możliwością ponownego skraplania –
redukcja długości
The hull resistance and effective power calculations according to the Holthrop method have been
carried out, using the Hullspeed program, to determine the the propulsion system power of the LNG
carrier. The results are presented graphically in
figure 6.
RT [kN], PE x 10 [kW]
PE
3500
3000
RT
1500
1000
500
15
17
19
ship speed v [w]
21

17 951
 27 600 [kW]
0.65
(4.1)
The exact determination of construction and
operating [service] costs of an LNG carrier is
a rather difficult task. It results i.a. from the fact
that relevant source materials are hardly available,
the documented data are lacking, which is connected with trade secrets of the companies operating on the market. Therefore, this author presents
just basic components of an LNG carrier building
and operating costs.
The following components make up the LNG
carrier construction costs:
 materials;
 labour;
 documentation;
 shipyard maintenance;
whereas the following factors have an impact on
the LNG carrier operating costs:
 shipping route length;
 fuel (diesel) oil, depending, i.a., on: current fuel
oil prices, specific fuel consumption, ship speed
etc.);
 shipping capability (cargo carrying capacity) of
the ship and kind of the propulsion system used;
 type and number of the cargo tanks used;
 costs of the crew – freight rates;
 other, i.a.: additional charges, costs of repairs
and overhauls, costs of port services etc.
According to statistical data for the year 2008
[4] the unit cost of LNG carrier construction,
broken down into kind of propulsion system used in
years 2005–2008 amounted to:
 for the steam turbine power plant (S/T): 1018
÷ 1450 $/m3,
 for DRL power plant: 1000 ÷ 1120 $/m3,
 for DFDE power plant: 1190 $/m3.
In figure 7 the average value of the unit cost of
building of the LNG carrier is presented, as well as
its level reached over the past 14 years.
According to the obtained data – figure 7, the
cost of building an LNG carrier of 150 000 m3
capacity will amount to $ 175 m.
As per [1], the following factors, have a significant impact on the LNG carrier operating costs
reduction: its shipping capability (cargo capacity)
and the shipping route length. In figure 8 the relation of the relative shipping costs of the LNG carrier and the route length for various sizes of LNG
carrier is presented.
reduced length
2000

Basic components of the LNG carrier
construction and operation costs
DRL- slow -speed
diesel with
reliquefaction
2500
PE
23
Fig. 6. Hull resistance RT and effective tug power PE as
a function of ship speed
Rys. 6. Opór kadłuba RT i moc holowania PE w funkcji prędkości statku
Assuming the general propulsion system efficiency η at 65% level, the power demand of the
main engine on the LNG carrier for the ship speed
v = 19.5 knots is approximately equal to:
32
Scientific Journals 21(93)
Specific costs LNG carrier 
mean value [$/m3]
Technological and operational concept of an LNG carrier
2000
1800
1600
1400
1200
1000
800
600
400
200
0
Summary
1800
From the economic point of view, larger LNG
carrier cargo capacity results in the reduction of the
operating costs, owing to the higher shipping efficiency of a given fleet of ships. In case of the port
in Świnoujście, the allowable principal dimensions
of ships capable of sailing through the Danish
Straits to the Baltic Sea determine the maximum
cargo capacity of the ship, which according to the
analyses conducted should not exceed 150 000 m3.
However, if the investment project of the
Northern Gas Pipeline (which according to recent
information would be located on the Baltic Sea
bottom) is completed, the restrictions on LNG
carriers draught will certainly be tightened. It may
force a reduction of the maximum displacement of
ships navigating along this route. As a result, their
cargo capacity will have to be reduced, which in
turn will necessitate a larger number of gas carriers
to be built, consequently, higher construction and
operating costs.
1389
1152
1994–1999
2000–2004
2005–2008
years of building
Relative LNG shipping costs, [%]
Fig. 7. Average unit cost of building of an LNG carrier [4]
Rys. 7. Średni, jednostkowy koszt budowy gazowca LNG na
podstawie [4]
120
110
100
90
80
VŁ = 145 000 m3
VŁ = 200 000 m3
70
60
VŁ = 200 000 m3
50
References
40
1. CHO J.H., KOTZOT H., VEGA F., DURR CH.: Large LNG
carrier poses economic advantages, technical challenges.
Kellogg Brown & Root Inc., Houston.
2. GUCMA S.: Wybór optymalnej lokalizacji terminalu LNG
na wybrzeżu polskim. Inżynieria Morska i Geotechnika,
2008, 2.
3. HAJDUK J.: Bezpieczeństwo żeglugi na akwenie Bałtyku
Zachodniego. IV Międzynarodowa Konferencja Naukowo-Techniczna Explo-Ship, Szczecin 2006, ZN AM w Szczecinie, 2006, 11(83).
4. The World Fleet of LNG Carriers. 8 November 2008.
30
20
1000 2000 3000 4000 5000 6000 7000 8000 9000
Shipping distance [Mm]
Fig. 8. Relative LNG shipping costs and the route length for
various sizes of LNG carrier [1]
Rys. 8. Względne koszty transportu LNG w zależności od
długości trasy dla różnych wielkości gazowca [1]
Within a distance of 7000 nautical miles the cost
of transport can be reduced by nearly 10% in the
case of 200 000 m3 ship, and by nearly 20% if
a ship has still higher cargo capacity of 250 000 m3
(compared to LNG carrier of 145 000 m3 capacity –
figure 8).
The scientific study financed from the funds
planned for research and science in the years
2007–2009 as a research and development project
no. R10 003 02.
Recenzent:
prof. dr hab. inż. Jan Szantyr
Politechnika Gdańska
Zeszyty Naukowe 21(93)
33