Dual fuel diesel electric propulsion systems LNG carriers
LNG shipping : Since the beginning of the 21st century, LNG has been very much in the picture. Oil majors are expecting that LNG will be taking a much larger share in the energy mix in the next 25 years. The LNG value chain necessarily involves LNG shipping. It’s in this part of the value chain that we’ve seen some major technology changes recently. .
The introduction of the dual fuel diesel electric (DFDE) LNG carrier (LNGC) and the slow speed diesel driven LNGC with onboard reliquefaction (DRL) are radical departures from the currently dominant steam turbine drive technology. The introduction of the dual fuel diesel electric drive systems could also open the door for dual fuel gas turbine electric (DFGTE) propulsion systems, as they are based on the same electric drive concept.
Electric propulsion systems for LNGC’s include the following components:
•Prime movers, i.e. dual fuel diesel engines;
• Prime mover driven generators;
• Main switchboard to distribute the generated power to the various consumers;
• Propulsion transformers;
• Frequency converters;
• Electric propulsion motors;
The introduction of electric drive in LNGC propulsion might seem like a radical step, but in fact the move toward electric propulsion was an evolutionary process. With the LNGC growing in size, the onboard power requirements increased so much that 440 V installations couldn’t handle the load safely. This led to the introduction of medium voltage switchboards and pumps motors. This familiarization with medium voltage systems was the first step towards electric propulsion. In cruise vessels, medium voltage propulsion systems were introduced more than a decade earlier and have since gained an excellent track record.
Fig:Dual Fuel Diesel Electric Propulsion Systems for LNG carriers
The advantages of the dual fuel electric propulsion system over the conventional steam turbine drive system are:
• Improved thermal efficiency of the propulsion plant, both at sea and in port;
• Lower installed power, as the power plant serves both the propulsion load as well as the harbor load;
• Increased redundancy with 4 prime movers and two (almost) independent drive lines;
• Increased cargo capacity within the same overall dimensions of the vessel;
• Crews with diesel electric experience are more readily available the crews with steam certification;
• Electric propulsion system is easier to operate and faster to start up and to shut down;
However, there are also a few disadvantages:
• Steam turbines have proven to be very reliable over time, more reliable than diesel engines;
• Steam turbine plants need less maintenance than diesels;
• Diesel engines have higher lube oil consumption than steam turbines;
• Electric driven vessels need additional equipment to handle excess boil-off gas;
• Steam turbines are very flexible in terms of fuel types and fuel mixing ratios, whereas dual fuel diesel engines operate either in gas mode or in diesel mode;
Benifits of compressed gas technology
Transporting economically viable compressed gas liquids from remote fields
Advantages of the dual fuel diesel electric propulsion & crew training
Increased Cargo Capacity for LNG ships & Advantages of the dual fuel diesel electric propulsion
Procedure for transporting remote gas
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