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First-ever FLNG Vessel to Star Eight Flameproof Motors

Posted June 03, 2016 12:00 AM by Engineering360 eNewsletter

Even as the global market for liquefied natural gas (LNG) slows a bit, industry experts predict long-term growth for the market in the Asia-Pacific and Indian regions. So notes a recent report appearing in the GE Oil & Gas Newsroom. Also noted is the trend to use floating LNG (FLNG) operations to "improve the viability of smaller, more remote or environmentally-sensitive (gas) fields that would otherwise be too costly or difficult to develop." The first tanker to be converted for FLNG operations is the Hilli, whose conversion requires eight flameproof vertical motors.


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Guru

Join Date: Jun 2009
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#1

Re: First-ever FLNG Vessel to Star Eight Flameproof Motors

06/03/2016 12:01 PM

Interesting design but I don't follow the reasoning behind the eight 280KW (375 HP) 11,000-volt motors.

375 HP is easily doable with standard 480 VAC three phase so why the unusually high working voltages for a not a so big of motor system?

Their on a large ship that can hold something like ~125,000 tons of LNG onboard so weight is not a issue.

Add in being at sea plus in a potentially highly flammable environment and going HV for a common size of motors just doesn't seem like a logical combination.

That and getting custom made 375 HP that operate on 11,000 volts plus all the custom switchgear needed to handle that voltage Vs standard 480-volt power just doesn't add up to me.

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Re: First-ever FLNG Vessel to Star Eight Flameproof Motors

06/07/2016 1:01 AM

As you say there are some oddities. (Just a note 125000m3 LNG is typically around 60,000kg)

I assume these are the LNG unloading pumps - it looks like 8 tanks so two pumps per tank to give the required offloading rate.

These will be amongst the smaller big drives on the ship. The really big drives will be for the refrigeration compressors. Normally for on-land LNG these use gas turbines of various types. I have not been able to find out what GoLAR are doing for these compressors but if they have gone with HV motors it might be that the extra risk from these pumps does not significantly change the risk profile. However I am unconvinced by this logic I would want to make every item as low risk as possible so unless its an issue of balancing the power generation?

While these ships are huge, weight is ALWAYS an issue offshore and there is a continuous need to reduce / minimise and eliminate weight and space so even though the weight of standard kit might only change the overall weight but a fraction of 1% the additional cost of bespoke kit might save money overall by reducing the costs of the ship. All the Offshore Platform jobs on which I have worked go through a weight reduction conference stage when you tale a step back and look at the process to see where savings can be made and where changes have put the balance out.

The weight issue in this case is a little different as this is a refurb case so the ship has a fixed capacity - unless you get into the very expensive costs of strengthening hull; adding weight to the keel etc so in this case keeping the weight within the existing envelope is critical. As an existing vessel it must have had off loading pumps (I think this vessel was originally an LNG delivery tanker) so they have replaced those which is expensive and risky unless they are replacing the pumps too.

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