Posted by : sanjay swain Monday, August 5, 2013

STEAM TURBINE INSTALLATIONS HAVE DOMINATED LNG CARRIER PROPULSION AND ELECTRIC POWER GENERATION FOR THE PAST FORTY YEARS. THE EASE WITH WHICH THESE INSTALLATIONS CAN UTILIZE BOIL-OFF GAS AND THEIR APPARENT RELIABILITY HAVE KEPT THEM IN A POSITION THAT HAS LONG BEEN LOST TO DIESEL ENGINES IN ALL OTHER SEGMENTS OF THE SHIPPING INDUSTRY. STEAM TURBINE INSTALLATIONS ARE HOWEVER NOT VERY EFFICIENT. THIS HAS A NEGATIVE IMPACT ON BOTH THE SHIP’S OPERATING ECONOMY AND ITS EXHAUST GAS EMISSIONS. EXACTLY THESE ISSUES PLAY AN INCREASINGLY IMPORTANT ROLE IN LNG SHIPPING TODAY.
ENCOURAGED BY THE LATEST DEVELOPMENTS IN ITS GAS ENGINE TECHNOLOGY, WÄRTSILÄ STARTED LOOKING FOR A MORE ECONOMIC AND ENVIRONMENTALLY FRIENDLY WAY TO POWER LNG CARRIERS. MACHINERY ALTERNATIVES WITH TWO- AND FOUR-STROKE DIESEL, HIGH PRESSURE GAS-DIESEL AND LOW-PRESSURE DUAL-FUEL ENGINES, IN MECHANICAL AND ELECTRIC PROPULSION ARRANGEMENTS, WITH AND WITHOUT BOIL-OFF RE-LIQUEFACTION  WERE STUDIED. DUAL-FUEL-ELECTRIC INSTALLATIONS WERE FOUND TO BE THE MOST ATTRACTIVE ALTERNATIVE TO STEAM TURBINE INSTALLATIONS. 

INTRODUCTION

AFTER HAVING BEEN PREDOMINANTLY FLARED OFF OR RE-INJECTED FOR  DECADES,  NATURAL  GAS  IS  PLAYING  AN  INCREASINGLY IMPORTANT  ROLE  IN  GLOBAL  ENERGY  CONSUMPTION  TODAY. CLEAN COMBUSTION PROPERTIES AND ABUNDANT RESERVES ARE THE MAIN BENEFACTORS FOR THIS EVOLUTION FROM UNSOLICITED BY-PRODUCT OF OIL PRODUCTION TO PREFERRED ENERGY SOURCE.
WITH NATURAL GAS RESERVES OFTEN LOCATED FAR AWAY FROM ENERGY CONSUMERS AND PIPELINES EXPENSIVE OR IMPRACTICAL TO BUILD, SEABORNE TRANSPORTATION OF NATURAL GAS IS ON THE RISE AS WELL. THE MOST ECONOMIC AND COMMON WAY TO TRANSPORT  NATURAL  GAS  BY  SEA  IS  IN  LIQUEFIED  FORM. LIQUEFIED NATURAL GAS (LNG) IS TODAY TRANSPORTED BY A FLEET OF SOME TWO-HUNDRED DEDICATED LNG CARRIERS.
WITH SEABORNE TRANSPORTATION OF LNG EXPECTED TO DOUBLE WITHIN THIS DECADE, A VAST EXPANSION OF THE LNG CARRIER FLEET IS IMMINENT. AT THE SAME TIME, INCREASING CARGO VOLUMES OFFER THE POSSIBILITY TO APPLY ECONOMIES OF SCALE, AND SHIPS ARE ABOUT TO SIGNIFICANTLY GROW IN SIZE. THESE CIRCUMSTANCES CREATE THE  NEED  TO  VERIFY  THE  TECHNICAL SOLUTIONS THAT HAVE BEEN APPLIED IN LNG CARRIERS SO FAR.
FOR THE PAST FORTY YEARS, STEAM TURBINE INSTALLATIONS HAVE DOMINATED ONBOARD LNG CARRIERS. THE EASE WITH WHICH STEAM TURBINE INSTALLATIONS CAN BURN BOIL-OFF GAS AND THEIR APPARENT RELIABILITY HAVE KEPT THEM IN  THE CONTROLLING POSITION  THAT  HAS  BEEN  TAKEN  OVER  BY  DIESEL  ENGINE INSTALLATIONS A LONG TIME AGO IN ALL OTHER SEGMENTS OF THE SHIPPING INDUSTRY.
A TYPICAL STEAM TURBINE  INSTALLATION  CONSISTS  OF  TWO BOILERS, MOST COMMONLY FIRED WITH BOIL-OFF GAS AND HEAVY FUEL OIL (HFO). A STEAM TURBINE IS DRIVING A FIXED-PITCH PROPELLER THROUGH A HIGH-SPEED GEARBOX. TWO ADDITIONAL STEAM TURBINES AND ONE OR TWO DIESEL ENGINES ARE DRIVING ALTERNATORS TO GENERATE ELECTRIC POWER. 



STEAM TURBINE INSTALLATIONS ARE HOWEVER NOT VERY EFFICIENT. THIS HAS A NEGATIVE IMPACT ON THE OPERATING ECONOMY AND EXHAUST GAS EMISSIONS OF THE SHIP. EXACTLY THESE ISSUES PLAY AN INCREASINGLY IMPORTANT ROLE IN LNG SHIPPING THESE DAYS.


MARKET REQUIREMENTS

AN ATTRACTIVE ALTERNATIVE SHOULD BE OUTPERFORMING THE STEAM TURBINE INSTALLATION WITH RESPECT TO ITS APPARENT DISADVANTAGES, WHILE AT THE SAME TIME AT LEAST MATCHING IT WITH RESPECT TO ITS ADVANTAGES. IT IS THEREFORE IMPORTANT TO STUDY THESE ADVANTAGES AND DISADVANTAGES.
THE MAIN REASON TO REMAIN FAITHFUL TO THE STEAM TURBINE INSTALLATION IN LNG CARRIERS IS THE EASE WITH WHICH THEY CAN BURN BOIL-OFF GAS.

BOIL-OFF GAS IS AN UNAVOIDABLE BY-PRODUCT OF THE SEABORNE LNG TRANSPORTATION CONCEPT. A SMALL AMOUNT OF CARGO, APPROXIMATELY 0.13% PER DAY IN LADEN CONDITION, IS LEFT TO EVAPORATE IN ORDER TO CONTROL TEMPERATURE AND PRESSURE IN THE SHIP’S CARGO TANKS. BOTH QUANTITY AND QUALITY OF THE BOIL-OFF GAS ARE SUBJECT TO VARIATION.

  1. OPERATING ECONOMY
ALTHOUGH STEAM TURBINE INSTALLATIONS CAN UTILIZE BOIL-OFF GAS VERY EASILY, THEY DO NOT USE IT VERY EFFICIENTLY. LOSSES IN THE BOILERS, STEAM TURBINE, HIGH-SPEED REDUCTION GEAR AND  SHAFTING  BRING  THE  EFFICIENCY  OF  THE  PROPULSION MACHINERY  TO  A  LEVEL  BELOW 29%  AT  FULL  LOAD.  THE EFFICIENCY OF THE ELECTRIC POWER GENERATION MACHINERY IS BELOW 25% AT FULL LOAD. PART-LOAD EFFICIENCIES OF BOTH THE PROPULSION AND ELECTRIC POWER GENERATION MACHINERY ARE EVEN LOWER.
SUCH LOW MACHINERY EFFICIENCIES LEAD TO A SUBSTANTIAL AMOUNT OF HFO BEING REQUIRED FOR COMPLEMENTING THE AVAILABLE BOIL-OFF GAS. IN LADEN CONDITIONS, SOME 50% OF THE SHIP’S ENERGY REQUIREMENT IS COVERED WITH HFO. IN BALLAST CONDITION, THIS SHARE GROWS TO 80%.
ALSO FOR LNG CARRIERS, LIKE FOR ANY OTHER KIND OF SHIP, FUEL COSTS ARE ONE OF THE MOST IMPORTANT COMPONENTS OF THE SHIP’S OPERATING COSTS.

     2. ENVIRONMENTAL-FRIENDLINESS

THE LOW EFFICIENCY AND THE NEED TO USE LARGE AMOUNTS OF HFO HAVE A NEGATIVE IMPACT ON THE SHIP’S CO2 AND SOX EMISSIONS. CO2 EMISSIONS ARE ALREADY THE FOCUS  OF ATTENTION THESE DAYS, AND CAN BE EXPECTED TO GET EVEN MORE ATTENTION IN THE NEAR FUTURE.

     3. SAFETY

GAS TANKERS ATTRACT LOTS OF ATTENTION FROM SAFETY REGULATORS WORLDWIDE. THE SAFETY OF CREW, SHIP AND ENVIRONMENT IS OF  UTMOST  IMPORTANCE. ONBOARD LNG CARRIERS, STEAM TURBINE INSTALLATIONS HAVE A VERY DECENT SAFETY RECORD. NO MAJOR CALAMITIES HAVE BEEN REPORTED.

   4. MAINTAINABILITY

DUE TO THE NATURE OF THE LNG TRADE, IT IS ALSO IMPORTANT THAT MAINTENANCE OF THE MACHINERY INSTALLATION DOES NOT INTERFERE WITH THE SAILING SCHEDULE OF THE SHIP OR INFLUENCE ITS PERFORMANCE.

STEAM TURBINE INSTALLATIONS REQUIRE A MODEST AMOUNT OF WELL-SCHEDULABLE MAINTENANCE. THE TIMING CAN EASILY BE MADE TO COINCIDE WITH THE WET- AND DRY-DOCKING INTERVALS OF THE SHIP.

MACHINERY ALTERNATIVES

ALTERNATIVE  MACHINERY  INSTALLATIONS  FOR  LNG  CARRIERS COULD POTENTIALLY BE BUILT AROUND DIESEL ENGINES, GAS-DIESEL ENGINE, DUAL-FUEL ENGINES AND GAS TURBINES.

1. DIESEL ENGINE ALTERNATIVES

SINCE THE NINETEEN-SEVENTIES, DIESEL ENGINE INSTALLATIONS HAVE BECOME DOMINANT IN ALL SHIPPING SEGMENTS, EXCEPT LNG  SHIPPING.  EXPERIENCE  GAINED  FROM  THOUSANDS  OF DIESEL ENGINE INSTALLATIONS IN SERVICE HAS RESULTED IN THE DEVELOPMENT OF HIGHLY-EFFICIENT, RELIABLE AND SAFE DIESEL ENGINES. THE LATEST DEVELOPMENTS, LIKE THE APPLICATION OF COMMON RAIL FUEL INJECTION ON BOTH FOUR- AND TWO-STROKE DIESEL ENGINES, ARE TAKING DIESEL ENGINE TECHNOLOGY YET ONE STEP FURTHER.
AS DIESEL ENGINES CAN ONLY BURN LIQUID FUELS LIKE MARINE DIESEL OIL (MDO) AND HFO, THE BOIL-OFF GAS ON LNG CARRIERS HAS TO BE RE LIQUEFIED IN AN ONBOARD RELIQUEFACTION
PLANT AND FED BACK INTO THE SHIP’S CARGO TANKS. THESE RELIQUEFACTION  PLANTS  REQUIRE  A  SUBSTANTIAL  AMOUNT  OF ELECTRIC POWER TO OPERATE AND ARE COSTLY, HEAVY AND HAVE
ONLY BEEN APPLIED IN THE MARINE ENVIRONMENT ON A VERY LIMITED SCALE.

THE  MOST  SIMPLE  AND  STRAIGHTFORWARD  DIESEL  ENGINE INSTALLATION FOR A SHIP THE SIZE OF A CONVENTIONAL LNG CARRIER OR LARGER WOULD BE A SINGLE TWO-STROKE ENGINE IN DIRECT-DRIVE TO A SINGLE FIXED-PITCH PROPELLER. AS THE LNG TRADE SETS HIGH STANDARDS WITH RESPECT TO ‘MAINTAINABILITY’ AND  REDUNDANCY,  THE  MOST  SIMPLE  AND  STRAIGHTFORWARD DIESEL ENGINE INSTALLATION ONBOARD AN LNG CARRIER WILL LIKELY FEATURE TWIN TWO-STROKE ENGINES, EACH IN DIRECT-
DRIVE TO A FIXED-PITCH PROPELLER. IN ORDER TO KEEP THE COMPLEXITY  LOW  AND  THE  OPERATIONAL  FLEXIBILITY  HIGH, ELECTRIC POWER WILL LIKELY BE GENERATED BY A GROUP OF FOUR-STROKE DIESEL GENERATING SETS.
DEVICES FOR LOCKING OR DISCONNECTING THE PROPELLER SHAFTS WILL BE NECESSARY TO ENABLE MAINTENANCE ACTIVITIES ON ONE ENGINE WHILE SAILING.HAVING ONE ENGINE OUT OF OPERATION FOR MAINTENANCE WILL HOWEVER STILL HAVE A SUBSTANTIAL IMPACT ON THE SHIP’S SERVICE SPEED. THIS IMPACT CAN BE REDUCED BY SELECTING CONTROLLABLE-PITCH PROPELLERS, OR BY USING THE TUNING POSSIBILITIES OF ELECTRONICALLY-CONTROLLED, COMMON RAIL TWO-STROKE ENGINES.
THE EXHAUST EMISSIONS OF TWO-STROKE ENGINE INSTALLATIONS ARE REASONABLE, BUT CERTAINLY NOT EXCELLENT.WITHOUT ADDITIONAL EQUIPMENT LIKE SCR UNITS  OR  DIRECT  WATER INJECTION, NOX EMISSIONS ARE SUBSTANTIAL. AS AN INEVITABLE CONSEQUENCE OF USING HFO AS A FUEL, SOX EMISSIONS ARE HIGH TOO.
MORE PROPULSION REDUNDANCY AND OPERATIONAL FLEXIBILITY CAN BE OFFERED BY APPLYING MULTIPLE FOUR-STROKE DIESEL ENGINES  DRIVING  CONTROLLABLE-PITCH  PROPELLERS  THROUGH REDUCTION GEARS. A FURTHER ENHANCEMENT CAN BE REALIZED BY  APPLYING  ELECTRIC  PROPULSION.  THE  APPLICATION  OF ELECTRIC PROPULSION WILL AT THE SAME TIME RESULT IN A HIGHER PART-LOAD EFFICIENCY.

2. GAS-DIESEL ENGINE ALTERNATIVES

GAS-DIESEL ENGINES ACT ACCORDING TO THE DIESEL PRINCIPLE AND CAN VIRTUALLY BURN ANY POSSIBLE MIXTURE OF GAS AND LIQUID FUEL, WITH ONLY A FEW RESTRICTIONS TO THE QUALITY OF THE GAS.
AS THE MIXTURE OF GAS AND LIQUID FUEL IS INJECTED INTO THE COMBUSTION CHAMBER DURING AIR COMPRESSION, THE REQUIRED INJECTION PRESSURE IS HIGH. FOR FOUR-STROKE GAS-DIESEL ENGINES, A GAS PRESSURE OF AROUND 350 BAR IS REQUIRED, WHILE FOR TWO-STROKE GAS-DIESEL ENGINES SOME 250 BAR IS DEEMED SUFFICIENT.



WÄRTSILÄ BROUGHT ITS FIRST FOUR-STROKE GAS-DIESEL ENGINE, THE WÄRTSILÄ 32GD, WITH AN OUTPUT OF 410 KILOWATT PER CYLINDER, TO THE MARKET IN 1987. THE LARGER WÄRTSILÄ 46GD, WITH AN OUTPUT OF 975 KILOWATT PER CYLINDER, WAS INTRODUCED IN 1991.

EXCEPT  FOR  THE  RELIQUEFACTION  PLANT,  LNG  MACHINERY INSTALLATIONS  BASED  ON  GAS-DIESEL  ENGINES  LOOK  FAIRLY SIMILAR TO CONCEPTS BASED ON CONVENTIONAL DIESEL ENGINES.
AS  BOIL-OFF  GAS  IS  GENERATED  AT  ATMOSPHERIC  PRESSURE, LARGE  GAS  COMPRESSORS  ARE  REQUIRED  TO  BOOST  THE  GAS PRESSURE  TO  THE  APPROPRIATE  LEVEL.  THESE  COMPRESSORS REQUIRE A SUBSTANTIAL AMOUNT OF ELECTRIC POWER TO OPERATE AND ARE COSTLY AND HEAVY. ADDITIONALLY, THE PRESENCE OF HIGH-PRESSURE GAS IN THE ENGINE ROOM IS A MAJOR SAFETY CONCERN, ESPECIALLY ON LNG CARRIERS.
EMISSIONS OF GAS-DIESEL ENGINE INSTALLATIONS ARE GENERALLY LOWER  THAN  THOSE  OF  STEAM  TURBINE  AND  DIESEL  ENGINE INSTALLATIONS AS A RESULT OF HIGHER EFFICIENCY AND CLEANER FUEL, RESPECTIVELY.


3. DUAL-FUEL ENGINE ALTERNATIVES

WHEN RUNNING ON GAS, DUAL-FUEL ENGINES ACT ACCORDING TO THE OTTO PRINCIPLE. AS THE GAS IS MIXED WITH AIR BEFORE COMPRESSION STARTS (FIG. 4), A GAS PRESSURE OF ABOUT 5 BAR IS SUFFICIENT. THIS GAS PRESSURE IS IN THE SAME RANGE AS THE GAS PRESSURES IN STEAM TURBINE INSTALLATIONS. CLOSE TO TOP-
DEAD-CENTRE A VERY SMALL AMOUNT OF MDO IS INJECTED IN ORDER TO TRIGGER IGNITION.

PROVIDED THAT AN ADEQUATE GAS SUPPLY SYSTEM IS INSTALLED, DUAL-FUEL ENGINES CAN ACCEPT ALL GAS QUALITIES SEEN IN LNG SHIPPING. IN ADDITION TO RUNNING ON GAS, DUAL-FUEL ENGINES CAN RUN ON MDO. WHEN RUNNING ON MDO, THE DUAL-FUEL ENGINE ACTS AS A NORMAL DIESEL ENGINE.

IN CASE THE SUPPLY OF GAS IS INTERRUPTED, THE DUAL-FUEL ENGINE AUTOMATICALLY TRANSFERS TO DIESEL MODE, WITHOUT LOSS OF ENGINE POWER OR SPEED. THE TRANSFER FROM DIESEL TO GAS MODE IS CARRIED OUT FULLY-AUTOMATIC ON DEMAND.
LOW-PRESSURE DUAL-FUEL TECHNOLOGY IS ONLY AVAILABLE ON FOUR-STROKE ENGINES. THE FIRST WÄRTSILÄ DUAL-FUEL ENGINE, THE WÄRTSILÄ 32DF, WAS BROUGHT TO THE MARKET IN 1996. THIS ENGINE, WITH A POWER OF UP TO  350 KILOWATT PER CYLINDER, IS AVAILABLE IN SIX- AND NINE-CYLINDER INLINE AND  TWELVE- AND EIGHTEEN-CYLINDER VEE-FORM CONFIGURATIONS.
AS  A  RESULT  OF  HIGHER  EFFICIENCY  AND  CLEANER  FUEL,EMISSIONS OF DUAL-FUEL INSTALLATIONS ARE LOWER THAN THOSE OF STEAM TURBINE, DIESEL AND GAS-DIESEL INSTALLATIONS.
IN COMBINATION WITH AN ELECTRIC PROPULSION SYSTEM, DUAL- FUEL INSTALLATIONS ACHIEVE OPTIMUM PERFORMANCE AND HIGH EFFICIENCY AT VIRTUALLY ANY LOAD.

4. GAS TURBINE ALTERNATIVES

GAS TURBINE INSTALLATIONS COULD ALSO POTENTIALLY BE APPLIED IN LNG CARRIERS. THEIR RATHER LOW EFFICIENCY AT PART-LOAD, DIFFICULTY IN COPING WITH HIGH AMBIENT TEMPERATURES, NEED FOR HIGH GAS PRESSURE AND THE REQUIRED SPECIAL SKILLS AND PROCEDURES FOR MAINTENANCE, MAKE THEM LESS ATTRACTIVE.


SELECTION OF ALTERNATIVES

THE FEASIBILITY OF GAS-DIESEL ENGINES FOR PROPULSION AND ELECTRIC  POWER  GENERATION  ONBOARD  LNG  CARRIERS  WAS STUDIED BY WÄRTSILÄ AND OTHERS SOME TEN YEARS AGO. THE NEED FOR GAS COMPRESSION TURNED OUT TO BE A TOO HIGH BURDEN FOR THE OPERATING ECONOMY OF THE SHIP.
THE QUANTIFIABLE CHARACTERISTICS OF THE OTHER ALTERNATIVES WERE COMPARED USING A SPECIALLY DEVELOPED COMPARISON TOOL, WHEREAS THEIR NON-QUANTIFIABLE CHARACTERISTICS WERE DISCUSSED AND COMPARED TOGETHER WITH MAJOR LNG CARRIER OWNERS, OPERATORS, MANAGERS AND SHIPYARDS OVER THE PAST FEW YEARS.
WHEN COMPARING THE OPERATIONAL ECONOMY OF THE VARIOUS ALTERNATIVES, IT IS IMPORTANT TO TAKE THE WHOLE MACHINERY INSTALLATION INTO ACCOUNT. TWO-STROKE DIESEL ENGINES HAVE A HIGH EFFICIENCY, BUT THE NEED TO RELIQUEFY THE BOIL-OFF GAS GIVES INSTALLATIONS FEATURING THIS TYPE OF ENGINES A HIGHER TOTAL ENERGY CONSUMPTION.
THE MOST ATTRACTIVE ALTERNATIVE TO THE TRADITIONAL STEAM TURBINE INSTALLATION TURNED OUT TO BE DUAL-FUEL-ELECTRIC MACHINERY. AS A RUNNER UP BUT AT CLEAR DISTANCE TO DUAL-FUEL-ELECTRIC  MACHINERY,  AN  INSTALLATION  FEATURING  TWIN TWO-STROKE ENGINES, EACH IN DIRECT-DRIVE TO A FIXED-PITCH PROPELLER, A RELIQUEFACTION PLANT, AND A GROUP OF FOUR-STROKE DIESEL GENERATING SETS EMERGED.


DUAL-FUEL-ELECTRIC LNG CARRIERS

CENTRAL IN THE DUAL-FUEL-ELECTRIC PROPULSION AND ELECTRIC POWER GENERATION SOLUTION ARE MULTIPLE DUAL-FUEL GENERATING SETS. THE NUMBER AND SIZE OF THESE SETS OF COURSE LARGELY DEPENDS ON THE SHIP SIZE AND SPEED, BUT ALSO ON THE ENVISAGED OPERATING PHILOSOPHY.



AN LNG CARRIER WITH A CARGO CAPACITY OF SOME 150’000M3 WILL  TYPICALLY  REQUIRE  ONE  SIX-  AND  THREE  TWELVE-CYLINDER WÄRTSILÄ 50DF ENGINES. AN LNG CARRIER WITH A CARGO CAPACITY OF 200’000 M3 WILL TYPICALLY REQUIRE TWO SIX-  AND  FOUR  NINE-CYLINDER  ENGINES,  AND  A  SHIP  OF 250’000 M3 CARGO CAPACITY WILL DO WITH TWO SIX- AND FOUR TWELVE-CYLINDER WÄRTSILÄ 50DF DUAL-FUEL ENGINES.
THE GENERATED ELECTRIC POWER IS FED TO AN ELECTRIC DRIVE FAIRLY SIMILAR TO THOSE USED ON CONTEMPORARY CRUISE SHIPS. TWO  ‘HIGH-SPEED’  ELECTRIC  PROPULSION  MOTORS  DRIVE  A FIXED-PITCH  PROPELLER  THROUGH  A  REDUCTION  GEAR.  TWIN ‘LOW-SPEED’ ELECTRIC MOTORS MOUNTED ON THE SAME SHAFT CAN BE SELECTED TO DRIVE THE PROPELLER WITHOUT ASSISTANCE OF A GEARBOX ALTERNATIVELY. FOR THE LARGER SHIPS, TWIN-SCREW  ARRANGEMENTS CAN BE SELECTED WITHOUT SIGNIFICANTLY INCREASING THE COMPLEXITY OF THE MACHINERY INSTALLATION.
1.       


        1. OPERATING ECONOMY

AS DUAL-FUEL ENGINES HAVE THE ABILITY TO RUN ON BOTH GAS AND MDO, THE CHOICE OF FUEL IS UP TO OPERATOR. SEVERAL INDEPENDENT STUDIES HAVE HOWEVER CONFIRMED THAT FORCING ADDITIONAL BOIL-OFF GAS TO COMPLEMENT THE NATURAL BOIL-OFF GAS IS THE WAY TO PROFIT MOST FROM THE POTENTIAL OF THE DUAL-FUEL-ELECTRIC SOLUTION. FIRSTLY, FORCED BOIL-OFF GAS IS CHEAPER THAN ALTERNATIVE FUELS. SECONDLY, IT IS LIGHTER THAN ALTERNATIVE FUELS. FUEL ‘BUNKERS’ WEIGHT IS THUS REDUCED, AND AT A GIVEN DISPLACEMENT, THE SHIP WILL BE ABLE TO CARRY
MORE  CARGO  WEIGHT.  CARRYING  MORE  CARGO  VOLUME  IS ENABLED BY THE FACT THAT THE DUAL-FUEL-ELECTRIC SOLUTION SAVES ENGINE ROOM SPACE . EVEN WHEN USING A SMALL PART OF THE CARGO AS FUEL, A DUAL-FUEL-ELECTRIC LNG CARRIER WILL DELIVER MORE CARGO TO THE UNLOADING PORT IN THIS WAY.

THE EFFICIENCY OF THE PROPULSION MACHINERY OF A DUAL-FUEL-ELECTRIC LNG CARRIER IS APPROXIMATELY 41% AND THE EFFICIENCY OF THE ELECTRIC POWER GENERATION MACHINERY IS AROUND 44%, COMPARED TO 29% AND 25% RESPECTIVELY FOR A STEAM TURBINE INSTALLATION. A TWO-STROKE DIESEL ENGINE INSTALLATION WILL HAVE A PROPULSION MACHINERY EFFICIENCY OF ABOUT 48% AND THE EFFICIENCY OF THE ELECTRIC POWER GENERATION  MACHINERY  WILL  BE  ABOUT 41%,  BUT  WILL CONSUME A SUBSTANTIALLY HIGHER AMOUNT OF ELECTRIC POWER DUE TO THE PRESENCE OF THE LIQUEFACTION PLANT. ADDING THE CHEAPER FUEL OF THE DUAL-FUEL-ELECTRIC LNG CARRIER TO THE EQUATION, THIS SOLUTION CLEARLY EXCELS IN TERMS OF OPERATING COSTS.


2. ENVIRONMENTAL-FRIENDLINESS

WHEN EXCLUSIVELY USING NATURAL AND FORCED BOIL-OFF GAS AS FUEL, THE DUAL-FUEL ELECTRIC SOLUTION SHOWS UNRIVALLED EMISSION VALUES . ALL OTHER MACHINERY ALTERNATIVES SUFFER FROM THE USE OF HFO, EITHER USED UNIQUELY OR IN COMBINATION WITH NATURAL BOIL-OFF GAS.

3. SAFETY

A  ‘SAFETY  CONCEPT’  FOR  DUAL-FUEL-ELECTRIC  MACHINERY ONBOARD LNG CARRIERS HAS BEEN DEVELOPED BY WÄRTSILÄ TO MAKE SURE THAT THE SAFETY OF THE INSTALLATION COMPLIES WITH CLASS AND AT LEAST MATCHES THE SAFETY OF STEAM TURBINE INSTALLATIONS. THE RECENT INTRODUCTION OF DOUBLE-WALL GAS PIPING ON THE WÄRTSILÄ  50DF WILL FURTHER INCREASE THE SAFETY OF THE SOLUTION. WITH SEVERAL POTENTIAL CUSTOMERS AND CLASS, SAFETY STUDIES INCLUDING HAZARD IDENTIFICATION, FMEA AND HAZARDOUS OPERATIONS STUDIES, HAVE BEEN CONDUCTED TO FURTHER VALIDATE THE SAFETY OF THE SOLUTION.

4. RELIABILITY

THE WÄRTSILÄ 50DF HAS BEEN DERIVED FROM THE WÄRTSILÄ 46, A  DIESEL  ENGINE  THAT  HAS  PROVEN  ITS  RELIABILITY IN VARIOUS DEMANDING MARINE APPLICATIONS, SUCH AS CRUISE SHIPS. THE USE OF GAS IN THE WÄRTSILÄ 50DF AS COMPARED TO HFO IN THE WÄRTSILÄ 46 FURTHER ENHANCES THIS INHERITED RELIABILITY.

5. REDUNDANCY

ELECTRIC PROPULSION SYSTEMS ARE IN THEIR ESSENCE HIGHLY REDUNDANT, AS MORE OR LESS ALL PRIMARY FUNCTIONS OF THE SYSTEM ARE DISTRIBUTED OVER MORE THAN ONE COMPONENT. THE  DUAL-FUEL-ELECTRIC  INSTALLATION  FEATURES  MULTIPLE GENERATING  SETS,  POTENTIALLY  DISTRIBUTED  OVER  MULTIPLE ENGINE ROOMS, HAS TWIN TRANSFORMERS AND CONVERTERS, AND FEATURES  TWIN  ELECTRIC  PROPULSION  MOTORS  WITH  DOUBLE
WINDINGS.

6. ‘MAINTAINABILITY’

CASE STUDIES FOR VARIOUS CUSTOMERS HAVE SHOWN THAT THE REQUIRED MAINTENANCE ON DUAL-FUEL-ELECTRIC INSTALLATIONS CAN EASILY BE CARRIED OUT WITHOUT AFFECTING THE SHIP’S OPERATIONAL PERFORMANCE.  MAINTENANCE  OF  DUAL-FUEL-ELECTRIC INSTALLATIONS IS MORE COSTLY THAN OF STEAM TURBINE INSTALLATION, BUT DOES NO HARM TO THE SHIP’S OPERATING ECONOMY.

7.CREWABILITY’

DUAL-FUEL-ELECTRIC  INSTALLATIONS  CAN  BE  OPERATED  AND MAINTAINED BY DIESEL ENGINE CREWS. THERE IS NO NEED FOR CREW MEMBERS WITH EXCEPTIONAL SKILLS OR EXPERIENCE.

8. OTHERS

THE  DUAL-FUEL-ELECTRIC  INSTALLATION  PROVIDES  EXCELLENT PROPULSION CHARACTERISTICS FOR NAVIGATION IN ICE, DUE TO THE AVAILABILITY OF FULL PROPELLER TORQUE AT ZERO SPEED AND EXCELLENT MANOEUVRING CHARACTERISTICS.
DUAL-FUEL-ELECTRIC INSTALLATIONS CAN EASILY COPE WITH THE POWER  REQUIREMENTS  OF  DYNAMIC  POSITIONING  SYSTEMS. THIS MIGHT BECOME A VALUABLE FEATURE, AS AN INCREASING AMOUNT OF OFFSHORE LNG TERMINALS IS ENVISAGED.



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