Unmanned Offshore Platform Power Supply

[JLuc]

Hi all,

do you have any suggestion for the power supply of an unmanned offshore platform:

distance from shore: 100km
load: 50kw

How about using DC with a rectifer/inverter combination?

Thanks !

 

[Hoxton]

How about a small genset (think of the cost of installing / maintaining 100km of cable! Reliability etc?)

Two gensets may even be economic

 

[raithrovers1]

What are the suggested maintenance manning times? Once a week , once a month?
Are there any other platforms close by that you could maybe tie into their generation?
It would be recommended that whatever system you go for is backed up by a suitably rated UPS. An industrial unit of about 60kVA what probably do the job and wouldn't break the bank.
Whereabout is the unmanned platform located?

UPS engineer

http://www.calibrepower.co.uk

 

[rcw retired EE]

For only 50 kW you should be able to put up some windmills, solar cells and wave power generators all charging a battery bank that feeds the UPS for the same cost as the cable. If it's in deep water you could add an OTEC system to run a turbien off the water temperature difference.

Aren't those renewable power sources supposed to be cost effective and reliable according to the critics of our current power generation systems?

My apologies for making fun- your project sounds interesting. On site generators is probably the way to go.

Good luck

 

[alehman]

Despite rcwilson's tongue-in-cheek comments, there probably are some situations where PV or wind would make sense. Obviously you have to look at first costs, and your costs for maintenance and fuel transportation.

This is a handy and free tool for comparing life-cycle costs.

http://www.retscreen.net/

Alan
“The engineer's first problem in any design situation is to discover what the problem really is.” Unk.

 

[ctpt]

Is it a Wellhead Platform?

 

[ScottyUK]

On the information presented - which ain't much! - I'd agree with Hoxton that a generator or group of generators with a large fuel reserve would make sense. Of course other factors like expected life of the installation, availability and proximity of personnel to maintain and refuel it, and so on would all need to be taken into account.

How is commercial fuel cell development going these days? I'm not sure if this is a serious possibility or something that rcwilson maybe forgot to include on his list.


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If we learn from our mistakes I'm getting a great education!

 

[JLuc]

Thank you all for your inputs !

I looked at the cost of procurement and installation for a MV 100km submarine cable, and we are in the range of $40,000,000 USD! and it would be technically challenging, with reactive compensation issues, steady-state voltage rise, transients, charging current, etc... not simple !

i don't think solar panels would be suitable, but wind generator sounds good for an environmentally friendly solution.

I agree with you guys. I think that dual diesel generators, with a large fuel tank, would be the way to go. Combined with a 60kVA UPS.

I need to look at maintenance issues for generators. How long can a small diesel generator run, between maintenance ?

 

[itsmoked]

The military uses micro turbines that put out 75 ~ 100kW and are the size of a small trash can. Probably 20X more reliable than a DG. They're 400Hz so all your motors could be substantially smaller too.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[davidbeach]

Internally the micro turbines produce something far higher than 400Hz, feed that through a rectifier and then an inverter. The same micro turbine machine can produce most any frequency because output frequency has nothing to do with machine speed.

 

[itsmoked]

Not the ones I saw and discussed with the operator. These were the ones they run field hospitals with. Probably a bunch of planetaries.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[davidbeach]

Wow. Take something with one moving part and two bearings to support that part with no need for accurate speed control and make it far more complex with a requirement for precise speed control. Makes sense to me - not.

 

[MikeHalloran]

I am somewhat familiar with a particular line of microturbines that generate AC power, which is rectified and inverted to feed an AC bus. They contain no gears, and because the turbine is supported on air bearings, no lube oil supply. There is an air compressor for the bearings.

The turbine and alternator idle at 25k rpm and run at 45k to 75k rpm depending on load.

The box also contains a bank of batteries, for starting, but mostly to supply or absorb bus power while the turbine is spooling up or down to match demand.

The box also contains a recuperator that recovers some of
the turbine's exhaust heat and uses it to preheat the incoming combustion air. Given that, the turbine generator consumes only about 20 pct more fuel than a Diesel at equivalent power, over its entire operating range.

The box occupies about twice the volume of an equivalent Diesel generator in a sound control enclosure.



Mike Halloran
Pembroke Pines, FL, USA

 

[rmw]

Is that 40 Million with a "M"? Wow that is a lot.

Also, think about fuel delivery and storage issues. I suspect you would like to deliver as least often as possible, but diesel in long term storage can develop issues which have been discussed repeatedly on this site. Do a search if you are interested.

Plus, for generators in that size range, you better get something with good reliability if you don't want to have to go out there often.

rmw

 

[ScottyUK]

Mike H,

Why would anyone want to pre-heat combustion air at a turbine intake? Turbines love cold dense air, some installations spend a lot of money on intake cooling systems to improve efficiency and power output. Seems kinda strange to deliberately heat it up.


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If we learn from our mistakes I'm getting a great education!

 

[MikeHalloran]

If I'm understanding it correctly, the recuperator is the critical item that brings the GT's specific fuel consumption into the same order of magnitude as the Diesel's.



Mike Halloran
Pembroke Pines, FL, USA

 

[Hoxton]

Recuperator: It seems odd as scottyuk says to go from cooling a GT inlet to heating it up! Think of it a recycling energy, then you see the point. Caterpillar Solar do them. Not sure about power ststion size GT's though

 

[ScottyUK]

Interesting - not something I've ever heard of on a utility-class machine, but these micro-turbines are obviously very different animals even though they work on the same principles. I guess the lack of an HRSG makes the micro-turbine's exhaust a waste of otherwise useful high grade heat energy.


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If we learn from our mistakes I'm getting a great education!

 

[waross]

I have had a lot of experience with 15 KVA to 50 KVA sets used for residential standby in an area with weekly or more frequent grid failures. It was common to see these sets run a year or more between service.
Admittedly there is a difference between standby and prime power, One start and 9000 hours a year versus 75 to 100 starts and 100 to 200 hours a year. Both services are tough on lube oil in their own way.
I would be spec'ing oversized oil sumps and filters and investigating methods of automatic oil changing for one year service intervals. For that duty I would consider swapping out and rebuilding sets every two years.
Two sets, about 4500 hours per year each. That is probably doable with oversized filters and sumps and possibly one automated oil change a year.
Rather than rebuild, you may consider replacing the sets with new sets every year. One year old sets with 4500 hours should have a reasonable resale value. They would make a great standby set for a small business.
Rather than oversized sumps you may consider auxiliary sumps and filter housings. The sumps and filter housings could be left in place and replacement sets could be standard designs to reduce replacement costs. There was a time when used lube oil could be added to the fuel supply. It would increase the average specific gravity and give better economy. These days with very fine injector spray patterns and the fine filters needed to protect the injectors, lube oil addition is no longer a good idea. The cost of supplying and changing fuel filters that have been prematurely loaded up by impurities in the lube oil costs more than you save.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[rmw]

Scotty,

Some googling might be in order. Recuperators are used to heat the air after compression but before fuel addition using exhaust heat in order to bring up the turbine efficiency. A recuperated CT could be inlet cooled at the same time as well in order to increase throughput.

I saw them used a lot about 30-40 years ago on mechanical drive frame type GT's used for compressor drives at natural gas pipeline transmission stations.

I don't ever recall seeing them on similar sized (Frame 3 and Frame 5, typically 2 shaft machines when used in NG transmission but single shaft machines of the same size in power generation) electric utility machines.

It may be that the economics are there for pipeline stations since they are 24-7 base loaded machines where as CT's used in power generation are usually not base loaded unless they are in CC service. They are usually last on, first off when used in simple cycle configuration.

Also, I suspect that the output shaft RPM is quite a bit higher in a compressor drive than in a generator drive, even though on the same sized Frame machines, 3's and 5's (back then) the output shaft speed was 5120 and the generator speed was set by a gear between them.

Ormat, an Israeli company has a system where they now put a waste heat boiler on the pipeline GT's stacks and use the exhaust waste heat to make a little steam to drive a turbine generator to sell power off the wasted heat.

rmw