detnorskeveritas

8/4/2019 DetNorskeVeritas

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Slide 1

INTERTANKO,ATHENS 13th April

PROPULSION ALTERNATIVES, LNG

By

Wilhelm Magelssen

Associate Members Committee



Slide 2

Propulsion power for LNG carriers

20,000

30,000

40,000

125,000 150,000 175,000 200,000

Size (m3)

Engine Power (kW)

21 knots

20 knots

19 knots

Source: MAN B&W



Slide 3

Thermal efficiencies

35

30

40

25

50

45

Medium speeddiesel engine

20

Capacity (MW)501 10

55

Thermal efficiencies %

Gas turbine

Combined cyclegas turbine

Steam turbine

Low speed diesel engine

5

LNG carrier

Source: MAN B&W



Slide 4

Handling of boil-off gas

• Use as fuel in boilers

• Accumulation during voyage

• Use as fuel in gas engines

• Use as fuel in gas turbines

• Re-liquefaction

• Burn in oxidizer (incinerator)



Slide 5

Means for disposal of boil-off gas

Steam turbine propulsion:

• Two boilers + main and auxiliary condenser

Gas engine propulsion:

• One oxidizer with redundant auxiliariesDiesel engine propulsion:

• One re-liquefaction unit + one oxidizer

Gas turbine propulsion:• One oxidizer with redundant auxiliaries



Slide 6

Propulsion alternatives for LNG carriers

• Steam turbine/dual fuel steam boilers

• Dual fuel high pressure gas/diesel engine

• Dual mode low pressure gas/diesel engines

• Low pressure gas engines and diesel engines

• Gas turbine & combined gas turbines/diesel

engines

• Diesel engine/boil-off re-liquefaction



Slide 7

Steam Turbine Propulsion - Simplified

Furnace

Condensate

pumps

MainCondenser

Red gear

H.P

L.PShaft

Feedpumps

Deareator

Super-heater

EconomiserFlue gas uptake

Downcomers

Boiler casing

Water wall



Slide 8

DNV Rules for gas fuelled engine installations

• The Rules define two concepts for safety against

gas hazards in machinery spaces:

– Inherently gas safe machinery space

The two-barrier concept as known from the IGCCode with an additional requirement for fitting

excess flow shut-off in the gas supply

– ESD protected machinery space

Single wall gas piping accepted. Applicable for lowpressure gas engines only



Slide 9

Gas engines - piping

• Low pressure gas engines have gas supply

piping which is difficult to arrange with

complete jacketing

• There are no low pressure gas engines on the

market at present having fully jacketed gas

piping. However,Wärtsilä, is claiming that they

are in the position in the near future



Slide 10

ESD Rule conditions (Emergency Shut Down)

• Conditions for acceptance of ESD protected

machinery space:

– Gas supply pressure to be < 10 bar

– Automatic de-energising of all sources of ignition ondetecting of low concentration of gas and shut-off of

gas supply to the engine room

– Automatic shut-off of gas supply on loss of engine

room ventilation, detection of fire or excess gas flow



Slide 11

ESD protected engine rooms

• Because of the shut-down requirement for an

ESD Protected engine room, the power

generation for propulsion and manoeuvring

must be divided between two or more enginerooms independent of each other



Slide 12

Dual Mode Gas/Diesel Engines



Slide 13

ESD protected engine rooms



Slide 14

Diesel engines + Re-liquefaction

BOG FEED

VENT

TO TANKS

2 3

1 E

COOLING

WATER

-200

-100

0

+100

-200

-100

0

+100

-200

-100

0

+100

-200

-100

0

+100

MAX

MIN

-200

-100

0

+100

MAX

MIN

-200

-100

0

+100

-200

-100

0

+100

-200

-100

0

+100

-200

-100

0

+100

R E S E R V O I R

BY-PASS

SUCTION THROTTLE

N I T R

O G E N

RECYCLING



Slide 15

Re-liquefaction plant for LNG boil-off

• At present there is experiences only from oneshipboard LNG re-liquefaction plant (NYK)

• Power consumption is high (3,5-5,0 MW)

• For LNG cargo tanks with permitted filling ratioof 99.5% (spherical) overfill protection

arrangements should be considered



Slide 16

LNG carrier with oxidizer



Slide 17

Coastal LNG carrier: “Pioneer Knutsen”

delivered 2004, 1100 m3 cargo carrying capacity

2 x engines for gas fuel only + 2 diesel engines , - diesel electric propulsion

2 pods for main propulsion

redundant propulsion



Slide 18

Gas Turbines

• Rolls Royce MT30

– 36 MW flat rated @26C

– 42% thermal efficiency

– 201 g/kWhr on gas

– Dual fuel capable



Slide 19

Cargo

Tank

Steam Turbine Propulsion – Engine Room Arr’t



Slide 20

Cargo

Tank

Gas Engines/Electric Propulsion – Engine Room Arr’t

+

~

~

Reduced length



Slide 21

General Arrangement – Gas Turbines



Slide 22

Gas emissions from LNG carriers

Fuel NOx SOx CO2

Steam turbineHFO +

LNG200 2.400 180.000

Low speeddiesel

+ re-liquefaction

HFO 3.950 1.800 120.000

Dual fuel

electricLNG only 240 0 100.000

Gas turbines and

COGESLNG only 850 0 108.000

Source: ALSTOM Emissions: Tonnes / year / ship



Slide 23

Economics of LNG Re-liquefaction and

Slow Speed Diesel Propulsion

• Low Fuel Consumption for Propulsion, but powerrequired by the re-liquefaction plant adds another

10 – 20 tons of heavy fuel oil

• Unknown Initial Cost for the Re-liquefaction

Plant, but Assumed to be Significant

• High Power Requirements for Re-liquefaction, inthe order of 3-5 MW at max. load

E i f D l F l G /Di l E i /G



Slide 24

Economics of Dual Fuel Gas/Diesel Engines/Gas

Turbines and Electric propulsion

•Electric Propulsion Plants Require Higher InitialCosts

• Gas/Diesel Engine Plants Have Lower Fuel

Consumption - Thermal Efficiency 42-44% v.s.

31-33% for Steam Propulsion

• Gas/Diesel Engines Have Higher Maintenance

Costs

•Fuel Cost Savings for Gas/Diesel PlantsIncrease With Higher Fuel Oil Price



Slide 25

LNG carrier propulsion - Conclusion

• The traditional steam turbine propulsion has

served LNG carriers well for over 30 years

• Future operating modes will require flexibility

and efficient propulsion plants able toaccommodate different ship speeds

• Operating economy and environmental issues

have to be considered carefully when selecting

propulsion power plant

• Safety and redundancy are important features

required from the propulsion power plant



Slide 26

Offshore re-gasification and discharge



Slide 27

Experienced personnel, - a serious challenge !

.. insufficient supply of

competent people may

have a knock-on effect onother shipping sectors ?



Slide 28

LNG Trade in cold Climate

• Cold climate: Is this the future environment for LNG

carriers? What kind of impact will this have on the

Propulsion system?



Slide 29

End of Presentation

Thank you!

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