VLCC Propulsion, Wärtsilä X82

Transcription

VLCC PROPULSION
WITH WÄRTSILÄ X82 ENGINE FOR LOWEST LIFECYCLE
FUEL COSTS
Contents
Summary........................................................................................................2
Introduction....................................................................................................3
Wärtsilä X82 engine.......................................................................................3
- Wärtsilä’s common rail engine operating system....................................5
- References..............................................................................................6
Propulsion aspects........................................................................................7
- Propeller design point..............................................................................8
- Open water propeller efficiency...............................................................9
- Hull efficiency.........................................................................................10
- Engine specific fuel consumption..........................................................12
- Ballast operation....................................................................................14
- Visibility distance...................................................................................14
- Case study.............................................................................................15
- Lifecycle fuel costs................................................................................17
- Variations in the number of propeller blades.........................................19
Waste heat recovery....................................................................................20
Bibliography.................................................................................................21
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WÄRTSILÄ SHIP POWER BUSINESS WHITE PAPER
VLCC PROPULSION
WARTSILA.COM
Summary
The new Wärtsilä X82 engine with its 65 rpm to 84 rpm speed range is perfectly
suited for VLCC propulsion. The engine offers MCR power of 4750 kW per
cylinder at a speed of 76 – 84 rpm and has a moderate stroke to bore ratio of
4.12.
The open water efficiency of the propeller is affected by its speed and diameter.
As a general rule, the larger the propeller diameter, the higher the propeller
efficiency and the lower its speed becomes. However, the propeller’s diameter
has an influence on the hull efficiency. With a large diameter used to achieve
low propeller speed, the hull efficiency is lower than with a smaller propeller
diameter in combination with a higher propeller speed. Considering this
influence, the impact on propulsion efficiency becomes moderate when varying
the propeller speed and diameter. Furthermore, the engine efficiency (specific
fuel consumption) is lowered with a reduced speed at the same power.
As a result, the gain in propulsion efficiency with a lower engine/propeller speed
and a larger propeller diameter is offset by a loss in the engine’s fuel efficiency.
No difference in daily fuel consumption can be noted when varying the propeller
speed and diameter within the available speed range of the Wärtsilä X82
engine.
In that respect, it needs to be noted that the moderate propeller diameter
solution provides better conditions for ballast operation. This solution, therefore,
provides a concept that offers the lowest annual fuel consumption.
2
Wärtsilä Ship Power business white paper
Introduction
With fuel costs currently responsible for 70 to 85% of the total costs of operating
vessels, it is not surprising that owners and operators are demanding greater
fuel efficiency. From an average HFO price of some USD 150 per ton in 2001,
prices have steadily risen to an average of close to USD 700 per ton in 2012. To
keep running costs at a justifiable level, more efficient ships are needed.
Despite the maritime industry’s claim that shipping is the most environmentally
friendly mode of transportation it is, nevertheless, under considerable pressure
from policy makers, regulatory bodies, and even the general public, to reduce
emissions. Since the level of emissions is directly related to fuel consumption,
it is essential that today’s marine engines achieve the greatest possible fuel
efficiency. In 2013, the International Maritime Organisation (IMO) will introduce
its Energy Efficiency Design Index for new ships according to their CO2
emissions. This again highlights the need for fuel efficiency.
The Wärtsilä X82 engine offers parameters that meet this need.
The Wärtsilä X82 engine
The W-X82 engine is the upgraded version of the RT-flex82T engine. The
W-X82 engine was previously also known as RT-flex82T-B. The RT-flex82
engine series was introduced in 2006; the short stroke version as the RT-flex82C, and the long stroke version as the RT-flex82T.
Following the accumulation of positive service experience with the 82T version,
the W-X82 (RT-flex82T-B) engine was introduced in 2011 as the upgraded
version of the RT-flex82T with the following adaptations:
• Mep increased from 20.0 bar to 21.0 bar
• R1 + speed increased from 80 rpm to 84 rpm
• R2/R4 speed reduced from 68 to 65 rpm
• R4 power reduced to the same mep as R2
Figure 1 indicates where the W-X82 is positioned within the Wärtsilä two-stroke
engine portfolio. Table 1 shows the main parameters of the two engine versions.
Fig. 1:
The Wärtsilä two stroke engine portfolio
Output bhp
100 000
80 000
60 000
Output kW
W-X92
RT-flex82-C
RTA82-C
W-X82
RTA82T-B
10 000
8 000
40 000
RT-flex50-D
RT-flex50-B
RT-flex84T-D
RTA84T-D
W-X72
50 000
RT-flex68-D
RTA68-D
RT-flex60C-B
40 000
20 000
80 000
70 000
60 000
RT-flex96C
RTA96C
W-X62
70
80
90
8 000
6 000
RT-flex58T-E
RT-flex48T-D
RTA48T-D
60
20 000
10 000
W-X35
RT-flex58T-D RTA58T-D
6 000
30 000
100
4 000
W-X40
3 000
120
140 160 180
Engine speed, rev/min
3
Bore
Stroke
Stroke/bore ration
MCR power
MCR speed
R3 speed
Mep
RT-flex82T
X82
820mm820mm
3’375 mm
3’375 mm
4.12
4.12
4’520 kW
4’750 kW
76 - 80 rpm
76 - 84 rpm
68 rpm
65 rpm
20.0 bar
21.0 bar
Table 1:
Parameters of the RT-flex82T and X82
engines
The shape of the RT-flex82T engine is characterized by its slim appearance,
with the fuel supply pumps arranged with good accessiblilty close to the
engine. The electronic fuel injection and exhaust valve control system is
based on the highly efficient, simple and reliable common rail technology.
The common rail platform, with its fuel injection and exhaust valve actuation
elements, is arranged to provide good accessibility at the engine’s upper
platform level.
Fig. 2:
The RT-flex82T engine
The rating field is characterized by the R1+ / R2+ rating points, which offer the
same power as at R1 / R2 but at a higher speed. The R1+ rating point features
a 2 g/kWh lower specific fuel consumption than the R1. This R1+ rating field
allows shipyards greater freedom for propeller tuning. (Fig. 3)
The X82 offers an engine speed as low as 65 rpm at R3 / R4 with a moderate
stroke to bore ratio.
4
Fig. 3:
The rating fields of the RT-flex82T and
5000
X82 engines
R1
4800
4’520kW
4600
Power per cylinder (kW)
4’750kW
4400
R1
R1+
R1+
4200
4000
3800
3600
3400
3200
3000
2800
60
65
70
75
80
85
90
Speed (rpm)
RT-flex82T
X82
Wärtsilä’s common rail engine operating system
Electronically controlled fuel injection and exhaust valve timing enables
optimum combustion under all circumstances. The common rail system allows
the fuel nozzles to be individually activated. They can be either sequentially
operated so as to influence NOx emissions, or alternatively, one or two nozzles
per cylinder can be switched off to achieve an efficient and clean combustion
for low load operation. In single nozzle mode, a stable engine speed of about
10-12% of the nominal engine speed is possible.
To date, approximately 1’000 Wärtsilä RT-flex common rail engines have been
ordered, of which some 600 are in operation. (Fig. 4)
Fig. 4:
The common rail engine operating system
Exhaust valve
actuator
Control
system
Crank
angle
sensor
Fuel
injectors
Exhaust valve
actuating unit
Volmetric
fuel injection
control unit
up to 1000 bar fuel HFO / MDO
200 bar servo oil and control oil
30 bar starting air
5
References
The first engine was contracted in 2007. As of September 2012, 97 engines in
configurations of 6, 7, and 8 cylinders have been ordered. Thus, the RT-flex82T
engine has become the most popular electronically controlled engine for VLCC
and VLOC propulsion.
The first RT-flex82T was commissioned in October 2009 onboard the VLCC
“Crudmed”. The engine was built by Hyundai, and the ship by Hyundai Heavy
Industries in Ulsan, Korea (Fig.5). As of May 2012, 26 RT-flex82T engines were
in service with the first one having accumulated more than 18’000 operating
hours.
Fig. 5:
The VLCC “Crudmed” is powered by the
first RT-flex82T engine
The RT-flex82T engine
is reputedly the most
popular engine for VLCC
propulsion.
6
Propulsion aspects
Fuel efficiency (daily fuel consumption) is defined as a result of the efficiency
of the propulsion system, and the specific fuel consumption of the propulsion
machinery (engine efficiency).
Propulsion efficiency is defined by the following propulsion factors:
• Open water propeller efficiency (η0)
• Relative rotative efficiency (ηR)
• Hull efficiency (ηH = (1-t)/(1-w)
• Mechanical efficiency (ηM)
Propulsion efficiency ηP = η0* ηR* ηH* ηM
Propulsion efficiency is influenced by the propeller speed and diameter. (Fig.6
and Fig.7)
Fig.6:
Impact of propeller speed on the
Propeller diameter
propulsion efficiency
Propulsion efficiency
propeller’s optimal diameter and
Propeller speed
Fig. 7:
Optimum
propeller speed
Propeller diameter
Propulsion efficiency
Selection of the optimum propeller speed
Propeller diameter
limitation due to
draught (ballast)
restrictions
Propeller speed
7
It is assumed that the relative rotative and shaft efficiencies are not influenced
by variations in the propeller speed and are therefore neglected for this study.
The engine’s fuel efficiency (specific fuel consumption) is influenced by the
ratio between the maximum and mean effective pressures. The higher the
ratio, the higher the fuel efficiency, i.e. increasing the pmax/mep ratio results
in a lower specific fuel consumption. Reducing the engine speed for a defined
power increases the mean effective pressure and, therefore, also increases the
engine’s specific fuel consumption.
The following must be considered when calculating the best propulsion
efficiency:
• Any variation in propeller diameter (and speed) affects the open water propeller efficiency.
• A variation in propeller diameter affects the wake fraction w and the thrust deduction t and, therefore, the hull efficiency.
• A variation in engine / propeller speed affects the engine’s specific fuel consumption.
The combination of propulsion efficiency and engine efficiency decides the
daily fuel consumption.
In order to achieve the best fuel efficiency it is, therefore, important to take into
consideration changes in the propulsion parameters (η0, ηH, BSFC) resulting
from variations in propeller speed.
Propeller design point
It is assumed that the propeller is optimized for light running conditions at CSR
power (Fig.8). With that, the propeller design point becomes roughly the CMCR
speed of the main engine.
Fig. 8:
Definition of the propeller design point
120
4.5% LR margin
115
110
105
Power (%)
100
95
90
85
CMCR power
CSR = 90% CMCR power
CSR = 85% CMCR power
80
Propeller design points
75
70
65
60
88
99.0%
90
92
94
96
98
100.9%
100
102
104
Engine/Propeller speed (%)
Nominal propeller curve
8
Propeller curve with 4.5% LR margin
106
Open water propeller efficiency
The open water efficiency of the propeller is basically affected by its speed and
diameter. As a general rule, the larger the propeller diameter, the higher the
propeller efficiency and the lower the propeller speed. Since there is usually
a limitation in the diameter of the propeller due to the draught of the vessel,
the optimum propeller speed is defined by the maximum possible propeller
diameter (Fig. 7).
The difference in the open water efficiency of the propeller can become as
much as 5.3% for a VLCC, such as when comparing a 10.9 m propeller running
at 60 rpm and a 9.4 m propeller running at 76 rpm.
The alpha-factor expresses the relative power at a constant ship speed to
variations in the propeller’s speed and diameter. For the reference case below,
the alpha-factor has a value of 0.23 within a relevant propeller speed range of
60 – 76 rpm for VLCC propulsion. (Fig. 9)
The open water propeller efficiency calculation is based on the following:
CMCR power = 24’000 kW, CSR = 85%, w = 0.316, t = 0.265, 4 blades,
BAR = 0.45, 15.5 knots service speed, 5.5% LR margin
Fig. 9:
Typical open water propeller efficiencies
for different propeller diameters
0.600
0.590
5.3%
0.570
0.560
0.550
0.540
-factor = 0.23
(P1/P2 = [n1/n2] ˄ )
ჲ
0.530
ჲ
Propeller efficiency eta 0 (%)
0.580
0.520
0.510
0.500
0.490
56
58
60
62
64
66
68
70
72
74
76
78
80
82
84
86
Propeller speed at CMCR (rpm)
Diameter 10.9m
Diameter 10.0m
Diameter 10.6m
Diameter 9.7m
Diameter 10.3m
Diameter 9.4m
9
Hull efficiency
Hull efficiency (ηH) is defined by the wake fraction w and the thrust deduction t.
ηH = (1- t)/(1-w)
Wake fraction and thrust deduction can be influenced by the diameter of the
propeller, as proposed by S.A.Harvald (Fig. 10). Due to the larger propeller, the
wake fraction becomes slightly lower and the thrust deduction slightly larger.
Thus, the larger the propeller diameter, the lower the hull efficiency (Fig. 11).
0.10
Fig. 10:
0.10
The wake fraction and thrust deduction
Propeller diameter correction
+
W3
t
W
0
correction as a function of vessel length
S.A. Harvald.
t3
0
0.10
0.02
and propeller diameter, as proposed by
+
0.10
0.03
0.04
0.05
0.06
VLLC Range
0.07
D/L
Fig.11:
The impact of the propeller diameter on
the propulsion coefficients according to
Harvald’s proposal
Comparison of wake fraction 1/(1-w), thrust deduction (1-t) and etaH
Delta (1-t), Delta 1/(1-w), Delta etaH [%]
(as proposed by S.A.Harvald)
4.00
3.50
3.00
2.50
2.00
1.50
1.00
0.50
0.00
-0.50
-1.00
-1.50
-2.00
-2.50
-3.00
-3.50
9200
9400
9600
9800
10000
10200
10400
10600
10800
11000
Propeller diameter (mm)
Delta (1-t) [%]
10
Delta 1/(1-w) [%]
Delta (etaH) [%]
11200
The Hamburg Ship Research Institute (HSVA) has also studied the impact of
variations in propeller diameter on the propulsion parameters. In contrary to
Contrary to Harvald’s suggestion, HSVA proposes that the thrust deduction is
not affected by changes in the diameter of the propeller, but only by the wake
fraction (fig.12).
Propulsion Coefficients
HSVA Values revA
Fig. 12:
Impact of the propeller diameter on the
Influence of Wake Fraction 1/)1-w) and Thrust Deduction (1-t) on etaH
propulsion coefficients according HSVA’s
proposal
(1-t) diff, Delta 1/(1-w) diff. ,etaH
2.0%
1.5%
1.0%
0.5%
0.0%
-0.5%
-1.0%
-1.5%
-2.0%
9.2
9.4
9.6
9.8
10.0
10.2
10.4
10.6
10.8
11.0
11.2
(1-t) diff
1/(1-w) diff
etaH
For further investigations, the mean values from both Harvald’s and HSVA’s
proposals shall be taken into consideration. The impact on the change of
propulsion parameters relative to the propeller diameter is shown in Fig. 13.
Fig. 13:
Mean change of propulsion parameters
Comparison between the wake fraction 1/(1-w), thrust deduction (1-t) and etaH
(mean values S.A.Harvald / HSVA)
3.50
Delta (1-t), Delta 1/(1-w), Delta etaH [%]
3.00
2.50
2.00
1.50
1.00
0.50
0.00
-0.50
-1.00
-1.50
-2.00
-2.50
-3.00
-3.50
9200
9400
9600
9800
10000
10200
10400
10600
10800
11000
11200
Mean Delta 1/(1-w)
Mean Delta (1-t)
Mean Delta (etaH)
11
To ascertain the total propulsion efficiency one should, therefore, not only
consider the effect of the propeller diameter on its open water efficiency, but
also the product of the open water and hull efficiencies η0* ηH, should be taken
into account. With the propeller diameter adapted wake fraction and thrust
deduction, the alpha factor becomes only 0.13, (Fig. 14). This is considerably
less than the 0.23 alpha factor found for the open water propeller efficiency
alone. This shows that the negative effect of a smaller propeller at higher
rotation speed is not as large as one would conclude when considering only the
open water efficiency.
Fig. 14:
Propeller diameter corrected propeller
efficiency
0.650
3.0%
0.620
0.610
0.600
0.590
-factor = 0.13
(P1/P2 = [n1/n2] ˄ )
ჲ
0.580
ჲ
Propeller efficiency (η0* ηH) (%)
0.640
0.630
0.570
0.560
0.550
0.540
0.530
0.520
0.510
0.500
56
58
60
62
64
66
68
70
72
74
76
Propeller speed at CMCR (rpm)
Diameter 10.9m
Diameter 10.0m
Diameter 10.6m
Diameter 9.7m
Diameter 10.3m
Diameter 9.4m
Engine specific fuel consumption
The engine has a defined specific fuel consumption at its maximum power R1.
When the engine is derated within the rating field, the BSFC can be reduced.
The cylinder pressure remains constant within the rating field, and the BSFC
is similar with the same ratio (pmax / mep). Since the mep can be reduced
through engine derating, a more favourable ratio (pmax / mep) is achieved, thus
making a reduced specific fuel consumption possible (Fig. 15).
12
78
80
82
84
86
Fig. 15:
Impact of specific fuel consumption on
engine speed
35000
R1
34000
R1+
167.0 g/kWh
165.0 g/kWh
33000
32000
=
ep
31000
m
29000
R3
28000
167.0 g/kWh
27000
26000
159.6 g/kWh
at 85% load
25000
24000
156.4 g/kWh
at 85% load
- factor = 0.13
ჲ
Power (kW)
30000
0%
10
R2
6%
7
p=
me
23000
22000
R2+
160.0 g/kWh
R4
21000
20000
60.0
160.0 g/kWh
65.0
70.0
75.0
80.0
85.0
Speed (rpm)
7X82
With an alpha-factor of 0.13, the power is 24’830 kW at 65 rpm and 25’340 kW
at 76 rpm, representing a power increase of 2.0%.
The specific fuel consumption increase from 76 rpm (156.4 g/kWh) to 65 rpm
(159.6 g/kWh) is 3.2 g/kWh or 2.0 %.
This means that the gain in propulsion efficiency with a lower propeller speed
and larger propeller diameter, is offset by a loss in the engine’s fuel efficiency.
However, at 65 rpm a propeller diameter of about 10.5 m is required while at
76 rpm, a propeller diameter of about 9.7 m provides optimum conditions.
No difference in daily fuel consumption can be seen, regardless of whether
a speed of 65 rpm or 76 rpm is selected.
Instead, the installation with the 10.5 m propeller
• Requires more aft draught for ballast voyage
• Requires the bunkering of more ballast water
• Increases the investment cost
• Might become critical for the required vessel visibility distance
13
Ballast operation
It is assumed that the forward ballast draught is 8.5 m. The aft ballast draught
depends on the propeller diameter.
Assuming a minimal propeller base line clearance of 0.2m and a minimal
propeller immersion of 0.5m, the aft ballast draught becomes a function of the
propeller diameter.
It is further assumed that by increase the ballast draught aft by 1.0 m, 3.0
% more propulsion power is required for the same ship speed. This is a
consequence of added ship resistance due to the increased draught and trim.
(Table 2).
Propeller
diameter
Aft
draught
Difference
Additional
propulsion power
9.4 m
9.7 m
10.0 m
10.3 m
10.6 m
10.9 m
10.1 m
10.4 m
10.7 m
11.0 m
11.3 m
11.6 m
0.0 m
+0.3 m
+0.6 m
+0.9 m
+1.2 m
+1.5 m
0.0 %
+0.9 %
+1.8 %
+2.7 %
+3.6 %
+4.5 %
Table 2:
The effect on propulsion power and aft
ballast draught resulting from different
propeller diameters
Since a typical VLCC operates for 30 – 50% of its time at ballast draught,
the impact on annual fuel consumption with the large propeller can become
significant.
It can be assumed that for 1.0 m more aft ballast, 9’000 m3 more ballast water
must be bunkered (Table 3).
Propeller
diameter
Additional
water bunker
9.4 m
9.7 m
10.0 m
10.3 m
10.6 m
10.9 m
0.0 m3
+2’700 m3
+5’400 m3
+8’100 m3
+10’800 m3
+13’500 m3
The amount of ballast water which needs to be bunkered is an operating cost
factor. Ballast water needs to be treated and handled, both of which take
energy and time.
Visibility distance
The visibility distance from the bridge over the bow must be 2.0 times the
length of the vessel, or at least 500 metres, whichever is less (SOLAS
Chapter V, Regulation 22).
More draught aft due to a larger propeller reduces the visibility distance. For
1.0 m more aft draught, the visibility distance increases by about 50m.
It might, therefore, be even necessary to raise the wheelhouse should a large
propeller be applied to ensure the correct visibility distance.
14
Table 3:
Ballast water bunker versus propeller
diameter
Case study
The lifecycle fuel consumption of a VLCC having the following data is to be
studied:
• CMCR power: 24’000 kW
• CMCR speed:
65 rpm
• CSR load: 85%
• Service power: 20’400 kW
• Service speed:
61.6 rpm
• Vessel service speed: 15.5 knots
• Propeller diameter: 10.5 m
Main engine options (Fig. 16):
7X82
• CMCR = 24’000 kW at 65 rpm
• CMCR = 24’200 kW at 69 rpm
• CMCR = 24’400 kW at 73.2 rpm
7G80ME-C9.2
• CMCR = 24’000 kW at 65 rpm
• CMCR = 23’730 kW at 60 rpm
Fig. 16:
Engine layout
35000
34000
33000
32000
31000
30000
Power (kW)
29000
28000
27000
26000
25000
CMCR = 24’000 kW CMCR = 24’190 kW
at 69 rpm
CMCR = 23’750 kW at 65 rpm
Dprop = 10.1 m
at 60 rpm
Dprop = 10.5 m
Dprop = 10.9 m
24000
CMCR = 24’370 kW
at 73 rpm
Dprop = 9.7 m
23000
22000
21000
20000
19000
18000
55.0
60.0
65.0
70.0
75.0
80.0
85.0
90.0
Speed (rpm)
7X82
Const speed V = 15.5 kt Alpha = 0.13
7G80ME-C9.2
Design point
15
The specific fuel consumption for the various engine options is shown in Fig.17.
The fuel consumption characteristic is the nominal consumption without
tolerance. It is based on an air temperature of 25°C and a cooling water
temperature of 25°C. The benefits provided by the new FAST fuel injectors are
taken into consideration concerning the X82 engine’s consumption.
Fig. 17:
Specific fuel consumption comparison
Nominal Specific Fuel Consumption
166
Specific fuel consumption (g/kWh)
165
164
163
162
161
160.0
159
158.2
160
158
156.8
157
156
155.6
154
154.5
155
153
152
35
40
45
50
55
60
65
70
75
80
85
90
95
100
Engine load (%)
7X82, 24’000 kW at 65 rpm (Delta, FAST)
7G80ME-C9.2, 24’000 kW at 65 rpm, High Load
7G80ME-C9.2, 23’750 kW at 60 rpm, High Load
Table 4:
Table 4 shows the daily fuel consumption for the various engine options.
Service speed
CMCR power
CMCR speed
CSR load
CSR power
BSFC
knots
kW
rpm
%
kW
g/kWh
Daily fuel consumption
Difference
tons
tons
20’400
156.8
7X82
15.5
24’190
69
85
20’562
155.6
76.77
0
76.78
0
24’000
65
Daily fuel consumption comparison
20’715
154.5
7G80ME-C9.2
15.5
24’000
23’750
65
60
85
20’400
20’188
158.2
160.0
76.81
0.04
77.45
0.69
24’370
73
77.52
0.75
This case study clearly demonstrates that, in the case of VLCC propulsion, a
variation in propeller speed and diameter has no practical influence on the daily
fuel consumption.
16
Lifecycle fuel costs
Daily fuel consumption gives an indication of a vessel’s fuel efficiency. However,
this dimension does not give an indication of the annual or lifecycle fuel costs.
Ballast operation and the vessel’s operating profile are not taken into
consideration as regards the daily fuel consumption.
For the lifecycle fuel cost calculation, the following conditions are assumed:
• 6’720 operating hours per year (280 days)
• 50% loaded, 50% ballast
• Operating profile in accordance with Fig. 18
• HFO price of 700 US$/t
It is assumed that the vessel operates at the same speed in both loaded and
ballast conditions. It is further assumed that during ballast operation, about 1.5
knots more ship speed is achieved than when in loaded condition at the same
power (Fig. 19).
Fig. 18:
Assumed vessel operating profile
3500
Operating hours
3000
2500
3000
2500
2000
1500
1220
1000
500
0
15.5 knots
14.5 knots
13.5 knots
Fig. 19:
Loaded/ballast power/speed assumption
Power / speed characteristic
35’000
Power (kW)
30’000
25’000
1.5 knots
20’000
15’000
10’000
5’000
0
12.5 13.0 13.5 14.0 14.5 15.0 15.5 16.0 16.5 17.0 17.5 18.0
Speed (knots)
Loaded
Ballast
17
Table 5,
Lifecycle fuel cost calculation
CMCR
Servicepower
speed
kW
knots
rpm
kW
mm
rpm
%
kW
g/kWh
CMCR
CMCRspeed
power
Propeller
diameter
CMCR speed
Vessel
speed
CSR load
CSR power
Loaded
BSFC operation
CSR load
%
7X82
7X82
7X82
7G80ME-C9.2
7G80ME-C9.2
24’00024’19024’37024’00023’750
15.5
656973.26560
24’000
10’50010’100
9’70010’50010’900
65
15.514.513.515.514.513.515.514.513.515.514.513.515.514.513.5
85
20’400
156.8
857056857056857056857055857056
76.77
20’40016’70113’47820’56216’83313’58520’71516’95813’68620’40016’70113’47820’18816’52713’338
CSR
Dailypower
fuel consumption
Operating
Differencetime
kW
tons
hours
tons
BSFC
g/kWh
156.8155.6158.2155.6154.4157.3154.5153.3156.6158.2157.2160.0160.0158.9161.4
HFO consumption*
tons
4’2164’1101’3714’2164’1101’3744’2184’1111’3784’2534’1521’3874’2574’1531’385
Total
tons
9’6979’7019’7089’7929’794
Power penalty
%
0.0-1.2-2.40.01.2
CSR load
%
64.451.840.964.251.640.862.950.640.064.451.840.965.252.441.4
CSR power
kW
15’46212’4309’86215’39812’3789’78515’32412’3199’73815’46212’4309’86215’48512’4489’840
Operating time
hours
1250150061012501500610125015006101250150061012501500610
BSFC
g/kWh
156.3159.1162.7155.4158.6162.0154.7158.0161.6158.1161.2164.2159.6162.2165.1
HFO consumption*
tons
3’1853’1281’0283’1543’1051’0193’1243’0781’0123’2223’1691’0383’2573’1931’045
Total
tons
7’3417’2787’2157’4287’495
Total
tons
17’03816’97916’92217’22017’290
Difference
tons
-59
-115
183
252
Difference**
$
-41’083 -80’797128’061176’470
1250
0 150061012501500610125015006101250150061012501500610
Ballast operation
*= HFO with a LHV of 42’700 kJ/kg
** = HFO price = 700 US$/t
The lifecycle fuel cost calculation in Table 5 clearly demonstrates that opting for
a low propeller speed in combination with a large propeller diameter does not
bring any operational cost benefit (Fig. 20). On the contrary, solutions involving
a very large propeller result in:
• Higher total fuel costs
• Higher investment costs
• More ballast water bunkering
• Visibility distance problems
Fig. 20:
12’150’000
Difference in lifecycle fuel costs
Annual HFO (US$)
12’100’000
12’050’000
+176’400 $
12’000’000
+257’600 $
11’950’000
11’900’000
11’850’000
+124’600 $
0
-41’300 $
11’800’000
-81’200 $
11’750’000
11’700’000
7X82
24’000 kW at 65 rpm
dprop = 10.5 m
7X82
7X82
7G80ME-C9.2
24’190 kW at 69 rpm 24’370 kW at 73.2 rpm 24’000 kW at 65 rpm
dprop = 10.1 m
dprop = 9.7 m
dprop = 10.5 m
7G80ME-C9.2
23’750 kW at 60 rpm
dprop = 10.9 m
This case as described is considered as being just one possible scenario.
Depending on the actual hull lines, the actual result might be different. However,
the statement that the propeller diameter has an effect upon the propulsion
parameters is valid for any VLCC hull form.
18
Variations in the number of propeller blades
Traditionally, four bladed propellers are used for VLCC propulsion. Either
5-bladed or 3-bladed propellers could also be considered.. Open water
propeller efficiency calculations show the following results (Fig. 21).
• A 5-bladed propeller has an optimum propeller speed at about five revolutions fewer than a 4-bladed propeller. Only a very slight efficiency improvement can be achieved.
• A 3-bladed propeller has an optimum propeller speed at about six revolutions more than a 4-bladed propeller. An efficiency improvement of up to 1% might be possible.
Fig. 21:
The open water propeller characteristic
with different numbers of propeller blades
Open water propeller efficiency eta 0 (%)
0.60
0.59
0.58
0.57
0.56
0.55
0.54
0.53
54
56
58
60
62
64
66
68
70
72
74
76
78
80
82
84
86
88
Propeller speed (rpm)
3-blade, 10.0 m
3-blade, 10.6 m
4-blade, 10.0 m
4-blade, 10.6 m
5-blade, 10.0 m
5-blade, 10.6 m
Model tests made by HSVA showed promising results. Somewhat more
cavitation and higher hull pressure pulses were experienced, but these were
still within acceptable levels.
Since the optimum speed for the 3-bladed propeller is higher than that of a
4-bladed propeller, it can therefore also profit from better engine specific fuel
consumption. A 3-bladed propeller could well be an alternative for tanker and
bulker propulsion.
19
Waste heat recovery
Only about 50% of the fuel input energy is used productively by diesel engines.
The remaining 50% is wasted, but can be partly recovered through a Rankin
cycle (thermodynamic cycle converting heat into work).
Heat is supplied to a closed loop with water as the working fluid. Heat energy
is extracted from the exhaust gas, scavenge air, and jacket cooling water and
converted into electric power. This takes place by means of a steam turbine.
The engine can be equipped with an exhaust gas bypass to allow an increase
in the exhaust gas temperature at the economizer inlet (Fig. 22).
Fig. 22:
Principle WHR arrangement with exhaust
Ship service steam
Exhaust gas
economiser
gas bypass and turbogenerator
Turbogenerator
Ship service power
Turbochargers
Main engine
Aux. engine
Aux. engine
Since the turbogenerator can also be operated in port, only two diesel engine
driven generators need to be installed.
The engine can be tuned either for engine room air suction or direct ambient
air suction. With direct ambient air suction, it is assumed that the ambient air
temperature does not exceed 35°C.
With that, the turbochargers are tuned at an air temperature of 15°C. At
ISO conditions with direct ambient air suction, the exhaust gas temperature
increases by 15°C and the exhaust gas flow is reduced by 0.2 kg/kWh.
The BSFC increases by 1.0 g/kWh with direct ambient air suction at ISO
conditions. With a dual pressure steam system and direct ambient air suction,
about 4.0% - 5.5% of the engine power can be recovered as electric power
above an engine load of about 50%.
The WHR performance can be further improved by operating a power turbine in
the exhaust gas bypass flow. The power turbine feeds into the steam turbine,
and electric power is generated by a common alternator (Fig. 23). With a steam
turbine / power turbine combination, about 6-8% of the engine power can be
recovered as electric power above an engine load of about 50%.
20
Fig. 23:
Principle WHR arrangement with a steam
turbine and power turbine
Ship service steam
Exhaust gas
economiser
Steam
turbine
Power
turbine
Ship service power
Turbochargers
Main engine
Aux. engine
Aux. engine
Bibliography
• Sv.Aa. Harvald, Resistance and propulsion of ships.
• Dipl. Ing. Hans-Uwe Schnoor HSVA Hamburg, VLCC propulsion – Hull efficiency study.
• Hydrodynamic trends in optimizing propulsion, Dr. Ing. Uwe Hollenbach / Dipl. Ing. Oliver Reinholz, HSVA Hamburg.
• Wärtsilä RT82 Engine Series Technical Review.
Want to know more?
Please contact us:
www.wartsila.com
21

VLCC Propulsion, Wärtsilä X82

Transcription

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