ExxonMobil

200’000 m3 LNG carrier

Propulsion system alternatives
with
Sulzer type low speed engine

With boil-off reliquefaction and

heat recovery considerations

Marine
H.Schmid, 24.2.2003 / 1
 ExxonMobil, 200‘000 m3 LNG carrier
Low speed engine propulsion with BO reliquefaction

Parameters:
• Average boil-off rate 0.12% per day
• Maximum boil-off rate 0.17% per day
• Boil-off at ballast 45% of loaded boil-off
• Lower heat value of LNG 49’300 kJ/kg
• Density of LNG 458 kg/m3
• Lower heat value of heavy fuel 40’500 kJ/kg
• LNG price 5.2 $/MMBtu (245 $/t) *
• Heavy fuel price 4.3 $/MMBtu (165 $/t) *
• Specific power for reliquefaction plant 0.95 kW/kg/h

* As specified by ExxonMobil

Heat recovery.ppt / 2 / 5.11.2002/ H.Schmid

 ExxonMobil, 200‘000 m3 LNG carrier
Low speed engine propulsion with BO reliquefaction

Propulsion power and voyage profile:

• Vessel service speed 19.5 knots
• Service power loaded, incl. 21% sea margin 31’365 kW
• Service power ballast 28’229 kW
• Suez channel speed 10 knots
• Suez channel power 4’000 kW

• Time per roundtrip trip 620 hours

• Suez channel passage 20 hours
• Manoeuvring and harbour 60 hours

Heat recovery.ppt / 3 / 5.11.2002/ H.Schmid

 ExxonMobil, 200‘000 m3 LNG carrier
Traditional steam turbine propulsion system

Ship service steam Boiler

Heavy fuel

G Boil-off gas
0.12% per day
Turbogenerator

G
LNG
Turbogenerator 200'000 m3
-162°C

G Diesel
generator

Ship service power

Heat recovery.ppt / 4 / 5.11.2002/ H.Schmid

 ExxonMobil, 200‘000 m3 LNG carrier
Low speed engine propulsion with BO reliquefaction
Single engine alternative with FPP

Ship service power

Reliquefaction
Plant

Boil-off gas
G 8L26 0.12% per day
2'480 kW / 900 rpm

8L26
G 2'480 kW / 900 rpm
9RT-flex84T-D LNG
36'900kW / 76 rpm 8L26 200'000 m3
G 2'480 kW / 900 rpm -162°C

8L26
G
2'480 kW / 900 rpm

Heavy fuel

Heat recovery.ppt / 5 / 5.11.2002/ H.Schmid

 ExxonMobil, 200‘000 m3 LNG carrier
Low speed engine propulsion with BO reliquefaction
Twin engine alternative with FPP

Ship service power

Reliquefaction
Plant
6RT-flex68T-B
17'640 kW / 94 rpm
Boil-off gas
G 8L26 0.12% per day
2'480 kW / 900 rpm

G 8L26
2'480 kW / 900 rpm
6RT-flex68T-B LNG
17'640 kW / 94 rpm 8L26 200'000 m3
G
2'480 kW / 900 rpm -162°C

G 8L26
2'480 kW / 900 rpm

Heavy fuel

Heat recovery.ppt / 6 / 5.11.2002/ H.Schmid

 Twin screw propulsion with fixed pitch propellers

Super container vessels.ppt / 7 / PAD / 20.3.01 / H. Schmid

 ExxonMobil, 200‘000 m3 LNG carrier
Low speed engine propulsion with BO reliquefaction
Propulsion system with auxiliary propulsion drive and FPP

Ship service power

Reliquefaction
Plant

Boil-off gas
8L26 0.12% per day
Thrust transmitting G 2'480 kW / 900 rpm
disconnecting device

8L26
G 2'480 kW / 900 rpm
9RT-flex84T-D LNG
M
36'900kW / 76 rpm 8L26 200'000 m3
G 2'480 kW / 900 rpm -162°C

8L26
G 2'480 kW / 900 rpm

Heavy fuel

Heat recovery.ppt / 8 / 5.11.2002/ H.Schmid

 ExxonMobil, 200‘000 m3 LNG carrier
Low speed engine propulsion with BO reliquefaction
Typical 3’000 kW shaft generator / motor

Heat recovery.ppt / 9 / 5.11.2002/ H.Schmid

 ExxonMobil, 200‘000 m3 LNG carrier
Low speed engine propulsion with BO reliquefaction
Thrust transmitting disconnecting device

Heat recovery.ppt / 10 / 5.11.2002/ H.Schmid

 ExxonMobil, 200‘000 m3 LNG carrier
Low speed engine propulsion with BO reliquefaction
Annual operating cost comparison
Single low speed engine
US $ Steam turbine plant
with reliquefaction

Fuel cost 13’146’000 7’778’000

Lube oil cost 425’000

Maintenance costs 72’000 337’000

Total 13’218’000 8’540’000

Difference 4’678’000

Net present value* 29’000’000

Based on a LNG price of 5.2 $/MMBtu and a heavy fuel price of 165 $/tone

* With a pay-back period of 8 years and 6% interest rate

Heat recovery.ppt / 11 / 5.11.2002/ H.Schmid

 ExxonMobil, 200‘000 m3 LNG carrier
Low speed engine propulsion with BO reliquefaction
Annual operating cost steam turbine versus low speed diesel engine
with boil-off reliquefaction
Relation LNG cost versus Heavy Fuel cost ($/MMBtu)

2.0

1.5

1.0

0.5

0.5 1.0 1.5 2.0

Relation of operating costs of steam turbine versus diesel and reliquefaction

Heat recovery.ppt / 12 / 5.11.2002/ H.Schmid

 ExxonMobil, 200‘000 m3 LNG carrier
Low speed engine propulsion with BO reliquefaction

Heat recovery.ppt / 13 / 5.11.2002/ H.Schmid

 ExxonMobil, 200‘000 m3 LNG carrier
Low speed engine propulsion with BO reliquefaction
Rotterdam 380 cSt Heavy fuel price, January 2002 - January 2003

$ / tone $/MMBtu
200 6.80

180 6.00

160 5.20

$ / MMBtu
$ / tone

140 4.40

120 3.60

100 2.80

80 2.00
Jan Feb Mrz Apr Mai Jun Jul Aug Sep Okt Nov Dez Jan

Heat recovery.ppt / 14 / 5.11.2002/ H.Schmid

 ExxonMobil, 200‘000 m3 LNG carrier
Low speed engine propulsion with BO reliquefaction
NYMEX Henry-Hub Natural Gas price and Rotterdam 380 cSt Heavy fuel price
January 2002 - January 2003
$ / MMBtu LNG $ / MMBtu HFO
6

4
$ / MMBtu

0
Jan Feb Mrz Apr Mai Jun Jul Aug Sep Okt Nov Dez Jan

Heat recovery.ppt / 15 / 5.11.2002/ H.Schmid

 ExxonMobil, 200‘000 m3 LNG carrier
Low speed engine propulsion with BO reliquefaction
Operating costs of steam turbine vessel* versus diesel vessel
depends on LNG price versus HFO price

HFO price LNG price

165$/tone 245 $/tone 201 $/tone 142 $/t

4.3 $/MMBtu 5.2 $/MMBtu 4.3 $/MMBtu 3.03 $/MMBtu
4.07 $/GJ 4.97 $/GJ 4.07 $/GJ 2.87 $/GJ
100% 122% 100% 71%

Steam turbine plant 13’218’000 $ 12’045’000 $ 8’540’000 $

Diesel engine plant 8’540’000 $

* For the missing boil-off energy, the turbine is operated with heavy fuel when gas price is higher then the
fuel price and with forced boil-off when the gas price is lower then the fuel price.

Heat recovery.ppt / 16 / 5.11.2002/ H.Schmid

 ExxonMobil, 200‘000 m3 LNG carrier
Low speed engine propulsion with BO reliquefaction

Added value with Sulzer RT-flex engines

• Simplified engine maintenance
• Smokeless operation over the entire load range
• Improved fuel consumption
• Stable dead slow engine speed (~ 12 rpm)
• Improved crash stop / reversing performance
• Three years TBO (Tribo Pack)

Heat recovery.ppt / 17 / 5.11.2002/ H.Schmid

 ExxonMobil, 200‘000 m3 LNG carrier
Low speed engine propulsion with BO reliquefaction

Engine waste heat recovery system

A considerable amount of the engine’s waste energy can be
recovered from the exhaust gases.

Exhaust energy can be recovered through

• A turbogenerator operated with steam generated from a
exhaust gas economiser
• A power turbine operated with exhaust gases branched-off
before the engine’s turbochargers
Realistic engine operating conditions need to be considered
for the potential of recoverable energy
Heat recovery.ppt / 18 / 5.11.2002/ H.Schmid
 ExxonMobil, 200‘000 m3 LNG carrier
Low speed engine propulsion with BO reliquefaction

Realistic engine operating conditions need to be considered for the

evaluation of the potential of recoverable energy.
Influence of engine operating conditions on exhaust gas
temperature, exhaust gas flow and specific fuel consumption

ISO tropical ISO tropical ISO tropical

Exhaust gas temperature change (°C)

Change in specific fuel consumption

100 Change in exhaust gas flow (kg/kWh) 0.2 6
90
0 5
80
70 -0.2 4
60

(g/kWh)
-0.4 3
50
40 -0.6 2
30
20 -0.8 1
10 -1 0
0
-10 -1.2 -1
new engine new engine average aged maximum new engine new engine average aged maximum new engine new engine average aged maximum
maximum engine aged engine maximum engine aged engine maximum engine aged engine
conditions conditions conditions

Operating conditions Operating conditions Operating conditions

Heat recovery.ppt / 19 / 5.11.2002/ H.Schmid

 ExxonMobil, 200‘000 m3 LNG carrier
Low speed engine propulsion with BO reliquefaction
Alternative 1:
Main engine exhaust gas heat recovery with turbogenerator
Ship service steam
Exhaust gas
economiser

Ship service power

Reliquefaction
G Plant

Turbogenerator Boil-off gas

G 8L26 0.12% per day
2'480 kW / 900 rpm

G 8L26
2'480 kW / 900 rpm
9RT-flex84T-D LNG
36'900kW / 76 rpm 8L26 200'000 m3
G 2'480 kW / 900 rpm -162°C

G 8L26
2'480 kW / 900 rpm

Heavy fuel

Heat recovery.ppt / 20 / 5.11.2002/ H.Schmid

 ExxonMobil, 200‘000 m3 LNG carrier
Low speed engine propulsion with BO reliquefaction
Principle heat recovery system

158°C L.P. sevice steam

3.5 barg
147.9°C
L.P.
Low pressure Drum
evaporator

Low pressure
superheater Condensate
3.2 barg / 180°C heater
95°C
H.P.service steam

High pressure H.P.

evaporrator Drum Charge air cooler
7.0 barg
170.4°C
Charge air receiver

High pressure
Engine
6.5 barg / 260°C
superheater Exhaust gas receiver

Turbocharger
~
G Gas turbogenerator

Steam turbogenerator G
~

Heat recovery.ppt / 21 / 5.11.2002/ H.Schmid

 ExxonMobil, 200‘000 m3 LNG carrier
Low speed engine propulsion with BO reliquefaction
Heat recovery Alternative 1, Annual operating cost comparison
Single low speed
Heat recovery
US $ engine with
Alternative 1
reliquefaction
Required electric power 5’500 kWe

Recovered power 2’100 kWe*

Fuel cost 7’778’000 7’253’000

Lube oil cost 425’000 412’000

Maintenance costs 337’000 290’000

Total 8’540’000 7’955’000

Difference 585’000

Net present value ** 3’630’000

* At loaded condition
** Assuming a pay-back time of 8 years and 6% interest rate
Heat recovery.ppt / 22 / 5.11.2002/ H.Schmid
 ExxonMobil, 200‘000 m3 LNG carrier
Low speed engine propulsion with BO reliquefaction
Alternative 2:
Main engine exhaust gas heat recovery with turbogenerator and
power turbine
Ship service steam
Exhaust gas
economiser

Turbogenerator
Ship service power
Reliquefaction
G Plant

Boil-off gas
Power turbine G 8L26 0.12% per day
2'480 kW / 900 rpm

G 8L26
2'480 kW / 900 rpm
9RT-flex84T-D LNG
36'900kW / 76 rpm 8L26 200'000 m3
G 2'480 kW / 900 rpm -162°C

G 8L26
2'480 kW / 900 rpm

Heavy fuel
Heat recovery.ppt / 23 / 5.11.2002/ H.Schmid
 ExxonMobil, 200‘000 m3 LNG carrier
Low speed engine propulsion with BO reliquefaction
Heat recovery Alternative 2, Annual operating cost comparison
Single low speed
Heat recovery
US $ engine with
Alternative 1
reliquefaction
Required electric power 5’500 kWe

Recovered power 3’000 kWe *

Fuel cost 7’778’000 7’098’000

Lube oil cost 425’000 406’000

Maintenance costs 337’000 270’000

Total 7’833’000 7’774’000

Difference 766’000

Net present value ** 4’760’000

* At loaded condition
** Assuming a pay-back time of 8 years and 6% interest rate
Heat recovery.ppt / 24 / 5.11.2002/ H.Schmid
 ExxonMobil, 200‘000 m3 LNG carrier
Low speed engine propulsion with BO reliquefaction
Alternative 3:
Main engine exhaust gas heat recovery with turbogenerator and
power turbine
Ship service steam
Exhaust gas
economiser

Exhaust gas
heater
Turbogenerator Ship service power
Reliquefaction
Plant
G

Boil-off gas
8L26 0.12% per day
G
Power turbine 2'480 kW / 900 rpm

G 8L26
2'480 kW / 900 rpm
9RT-flex84T-D LNG
36'900kW / 76 rpm 8L26 200'000 m3
G 2'480 kW / 900 rpm -162°C

8L26
G 2'480 kW / 900 rpm

Heavy fuel

Heat recovery.ppt / 25 / 5.11.2002/ H.Schmid

 ExxonMobil, 200‘000 m3 LNG carrier
Low speed engine propulsion with BO reliquefaction
Heat recovery Alternative 3, Annual operating cost comparison
Single low speed
Heat recovery
US $ engine with
Alternative 1
reliquefaction
Required electric power 5’000 kWe

Recovered power 5’000 kWe

Fuel cost 7’778’000 7’260’000

Lube oil cost 425’000 397’000

Maintenance costs 337’000 235’000

Total 8’540’000 7’892’000

Difference 648’000

Net present value * 4’020’000

* Assuming a pay-back time of 8 years and 6% interest rate

Heat recovery.ppt / 26 / 5.11.2002/ H.Schmid

 ExxonMobil, 200‘000 m3 LNG carrier
Low speed engine propulsion with BO reliquefaction
Alternative 4:
Main engine exhaust gas heat recovery with turbogenerator and
power turbine, PTO system
Ship service steam
Exhaust gas
economiser

Turbogenerator
Ship service power
Reliquefaction
G Plant

Boil-off gas
Power turbine G 8L26 0.12% per day
2'360 kW / 900 rpm

8L26
G
2'360 kW / 900 rpm
9RT-flex84T-D LNG
G
36'900kW / 76 rpm 200'000 m3
8L26
G -162°C
2'360 kW / 900 rpm

8L26
G
2'360 kW / 900 rpm

Heavy fuel

Heat recovery.ppt / 27 / 5.11.2002/ H.Schmid

 ExxonMobil, 200‘000 m3 LNG carrier
Low speed engine propulsion with BO reliquefaction
Heat recovery Alternative 4, Annual operating cost comparison
Single low speed
Heat recovery
US $ engine with
Alternative 1
reliquefaction
Required electric power 5’500 kWe

Recovered power 3’300 kWe *

PTO generator power 2’200 kWe

Fuel cost 7’778’000 7’046’000

Lube oil cost 425’000 413’000

Maintenance costs 337’000 237’000

Total 8’540’000 7’696’000

Difference 844’000

Net present value ** 5’240’000

* At loade conditions
** Assuming a pay-back time of 8 years and 6% interest rate
Heat recovery.ppt / 28 / 5.11.2002/ H.Schmid
 ExxonMobil, 200‘000 m3 LNG carrier
Low speed engine propulsion with BO reliquefaction
Comparison of heat recovery alternatives

Alternative 1 Alternative 2 Alternative 3 Alternative 4

Required electric power 5’500 kWe 5’500 kWe 5’000 kWe 5’500 kWe

Recovered power 2’100 kWe 3’000 kWe 5’000 kWe 3’300 kWe

PTO generator power - - - 2’200 kWe

Operating cost saving 585’000 $ 766’000 $ 648’000 $ 844’000 $

Net present value * 3’630’000 $ 4’760’000 $ 4’020’000 $ 5’240’000 $

* Assuming a pay-back time of 8 years and 6% interest rate

Heat recovery.ppt / 29 / 5.11.2002/ H.Schmid

 ExxonMobil, 200‘000 m3 LNG carrier
Low speed engine propulsion with BO reliquefaction
Operational and economical most attractive concept:
PTO / PTI drive in combination with heat recovery through
turbogenerator and power turbine
Ship service steam
Exhaust gas
economiser

Turbogenerator
Ship service power
Reliquefaction
G Plant

Boil-off gas
8L26
Power turbine G 0.12% per day
2'360 kW / 900 rpm

8L26
G
2'360 kW / 900 rpm
9RT-flex84T-D LNG
G/M
36'900kW / 76 rpm 8L26 200'000 m3
G 2'360 kW / 900 rpm -162°C

8L26
G 2'360 kW / 900 rpm

Heavy fuel

Heat recovery.ppt / 30 / 5.11.2002/ H.Schmid

 ExxonMobil, 200‘000 m3 LNG carrier
Low speed engine propulsion with BO reliquefaction

Operating modes:
•Normal open sea mode (19.5 knots loaded)
➪ Propulsion power is provided by the the main engine
➪ E-power is provided by the heat recovery system and the PTO generator
• Emergency propulsion mode
➪ Propulsion power is provided by the 3’000 kW shaft motor
➪ E- power is provided by auxiliary engines
• Maximum ship speed mode (20.5 knots loaded)
➪ Propulsion power is provided by the main engine and the shaft motor
➪ E-power is provided by auxiliary engines

Heat recovery.ppt / 31 / 5.11.2002/ H.Schmid

 ExxonMobil, 200‘000 m3 LNG carrier
Low speed engine propulsion with BO reliquefaction

Heat recovery.ppt / 32 / 5.11.2002/ H.Schmid

 ExxonMobil, 200‘000 m3 LNG carrier
Low speed engine propulsion with BO reliquefaction

Single engine propulsion system with auxiliary propulsion

drive / PTO and waste heat recovery system
• Propulsion redundancy up to a vessel speed of about 9 knots
• Maximum vessel speed of 19.5 + 1 = 20.5 knots
• Electric power demand can be covered by waste energy recovery
and PTO generator.
• Annual operating cost saving of about 840’000 $ can be achieved

Heat recovery.ppt / 33 / 5.11.2002/ H.Schmid

 ExxonMobil, 200‘000 m3 LNG carrier
Low speed engine propulsion with BO reliquefaction

Single engine with

Twin engine
APD

Vessel cost 3’000’000

Clutch system 550’000

Motor system 2’000’000

Total 2’550’000 3’000’000

Economiser 950’000 150’000

Turbogenerator with
2’000’000
power turbine
NPV 5’100’000

Net investment 400’000 3’150’000

Heat recovery.ppt / 34 / 5.11.2002/ H.Schmid

 ExxonMobil, 200‘000 m3 LNG carrier
Low speed engine propulsion with BO reliquefaction

Conclusion:

Status
• If the value of boil-of gas is higher then the value of heavy fuel, the heavy fuel
operated low speed engine in combination with a reliquefaction system provides
an interesting solution.
• The single engine propulsion system with a fixed pitch propeller provides the
most economical system with regard to operating costs and investment costs.
However, this system does not provide propulsion redundancy. Engine
overhauling can not be made during loading and unloading of the vessel.
• The twin engine plant provides the vessel with propulsion redundancy. If equipped
with fixed pitch propellers, about 50% engine power is available in the single
engine mode. The twin skeg ship is more expensive then the single skeg ship.

Heat recovery.ppt / 35 / 5.11.2002/ H.Schmid

 ExxonMobil, 200‘000 m3 LNG carrier
Low speed engine propulsion with BO reliquefaction
Conclusion:

Proposal
Single engine propulsion system with APD / PTO and waste
energy recovery system
• The single engine vessel combined with a APD system provides the vessel with a
second propulsion power source. Engine overhauling is at any time possible
without restrictions.
• The fuel bill is reduced by about 10%.
• If needed, the vessel speed can be increase by about 1 knot to 20.5 knots by
using the APD system as propulsion power booster.
• Electric power for ship service and reliquefaction plant is generated by the waste
energy recovery and the PTO generator. No auxiliary engines are in operation
while the vessel is at sea.

Heat recovery.ppt / 36 / 5.11.2002/ H.Schmid