Mardi Gras engines started for the first time

[chengkp75]

1 hour ago, ALWAYS CRUZIN said:

Very interesting indeed. How safe is the refueling compared to diesel?

About on par, but LNG requires more work.  When fueling a cryogenic tank, you can't pump -260*F LNG directly into the tank, or it will shatter.  You first have to "squirt" some fuel into the tank and let it flash to gas, absorbing heat and cooling the tank slowly.  Once the tank is around -160*F (IIRC), you can then start to bulk load the tank with liquid LNG.  LNG tanks also have to have an inert atmosphere in them (diesel fuel tanks, when you draw out fuel, air replaces it in the top of the tank) to prevent any possible combustion, so the ship has a nitrogen generator to remove nitrogen from the atmosphere, and pump pure nitrogen into the tanks as they are emptied.  As you bunker this tank, they recollect the nitrogen into storage tanks for reuse.

 

While LNG has a much lower flash point (the temperature where vapors will ignite if an ignition source is present) than diesel (-306*F for LNG, 143*F for diesel), the flammability range for LNG is higher than diesel.  The LEL (lower explosive limit) and UEL (upper explosive limit) are the concentrations of vapors that will sustain combustion.  If the vapor concentration is below the LEL, then even with a flame or spark, there will be no combustion, and if it is above the UEL, the same thing, there isn't enough oxygen to combust.  Diesel has a flammability range from 0.6% to 7.5%, while LNG is 4% to 15%.  So, leakage can lead to combustion in both products, but the concentration has to be higher with LNG, and typically LNG gives a more visible indication of leakage (a frost plume, and frost accumulation at the leak).  Leakage during bunker operations is one example of "methane slip" present when using LNG.  This is the amount of methane (an ingredient of LNG) that escapes either during the extraction process, the handling process (where the natural gas is refrigerated), the transport process (pipelines, bunker barges, bunkering operations), or the combustion process (low load operation of the engine).  Methane has 84 times the global warming potential over a 20 year span than carbon dioxide, and 24 times CO2 over 100 years, which makes it a considerable greenhouse gas (remember cow farts), and is one of the drawbacks of LNG use.

[PhillyFan33579]

1 hour ago, chengkp75 said:

About on par, but LNG requires more work.  When fueling a cryogenic tank, you can't pump -260*F LNG directly into the tank, or it will shatter.  You first have to "squirt" some fuel into the tank and let it flash to gas, absorbing heat and cooling the tank slowly.  Once the tank is around -160*F (IIRC), you can then start to bulk load the tank with liquid LNG.  LNG tanks also have to have an inert atmosphere in them (diesel fuel tanks, when you draw out fuel, air replaces it in the top of the tank) to prevent any possible combustion, so the ship has a nitrogen generator to remove nitrogen from the atmosphere, and pump pure nitrogen into the tanks as they are emptied.  As you bunker this tank, they recollect the nitrogen into storage tanks for reuse.

 

While LNG has a much lower flash point (the temperature where vapors will ignite if an ignition source is present) than diesel (-306*F for LNG, 143*F for diesel), the flammability range for LNG is higher than diesel.  The LEL (lower explosive limit) and UEL (upper explosive limit) are the concentrations of vapors that will sustain combustion.  If the vapor concentration is below the LEL, then even with a flame or spark, there will be no combustion, and if it is above the UEL, the same thing, there isn't enough oxygen to combust.  Diesel has a flammability range from 0.6% to 7.5%, while LNG is 4% to 15%.  So, leakage can lead to combustion in both products, but the concentration has to be higher with LNG, and typically LNG gives a more visible indication of leakage (a frost plume, and frost accumulation at the leak).  Leakage during bunker operations is one example of "methane slip" present when using LNG.  This is the amount of methane (an ingredient of LNG) that escapes either during the extraction process, the handling process (where the natural gas is refrigerated), the transport process (pipelines, bunker barges, bunkering operations), or the combustion process (low load operation of the engine).  Methane has 84 times the global warming potential over a 20 year span than carbon dioxide, and 24 times CO2 over 100 years, which makes it a considerable greenhouse gas (remember cow farts), and is one of the drawbacks of LNG use.

Could you go into more detail about this process?  😊

 

Very informative post. 

[ALWAYS CRUZIN]

I would think the piping would be flexible from tanker to cruise ship. How are those made to constantly monitor the gas? Are they double walled? Sounds like transferring the LNG will take longer to fuel the cruise ship vs diesel.

[chengkp75]

27 minutes ago, ALWAYS CRUZIN said:

I would think the piping would be flexible from tanker to cruise ship. How are those made to constantly monitor the gas? Are they double walled? Sounds like transferring the LNG will take longer to fuel the cruise ship vs diesel.

Of course they are flexible hoses.  They are corrugated stainless steel, and they are double wall.  There is no constant monitor of the gas in the hose.  Well, given that LNG has less energy per gallon than diesel (diesel has 1.7 times the energy per gallon, and residual fuel 1.8 times), you need more LNG to get the same energy you would get from diesel, so it will take longer to fuel at the best of times.

[jas1178]

On 9/24/2020 at 11:29 AM, chengkp75 said:

 

@chengkp75 Just want to thank you for sharing your vast knowledge, expertise, and insights here.  Your posts are fascinating, and I really appreciate you.