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Unmanned Offshore Platform Power Supply

Unmanned Offshore Platform Power Supply

Unmanned Offshore Platform Power Supply

(OP)
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 !

RE: Unmanned Offshore Platform Power Supply

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

Two gensets may even be economic

RE: Unmanned Offshore Platform Power Supply

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

RE: Unmanned Offshore Platform Power Supply

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

RE: Unmanned Offshore Platform Power Supply

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.

RE: Unmanned Offshore Platform Power Supply

Is it a Wellhead Platform?

RE: Unmanned Offshore Platform Power Supply

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. wink
  

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

RE: Unmanned Offshore Platform Power Supply

(OP)
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 ?

 

RE: Unmanned Offshore Platform Power Supply

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

RE: Unmanned Offshore Platform Power Supply

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.

RE: Unmanned Offshore Platform Power Supply

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

RE: Unmanned Offshore Platform Power Supply

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.

RE: Unmanned Offshore Platform Power Supply

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

RE: Unmanned Offshore Platform Power Supply

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

RE: Unmanned Offshore Platform Power Supply

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.
   

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

RE: Unmanned Offshore Platform Power Supply

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

RE: Unmanned Offshore Platform Power Supply

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

RE: Unmanned Offshore Platform Power Supply

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.
  

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

RE: Unmanned Offshore Platform Power Supply

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

RE: Unmanned Offshore Platform Power Supply

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

RE: Unmanned Offshore Platform Power Supply

With only 60 kW load, the micro turbine & UPS assembly with a small wind turbine providing some extra battery charging capability may be a viable answer, despite my making fun of it.  The political benefits and tax exemptions may help with the added costs.  The technical challenge will be to put a complicated, sophisticated system together with reasonable reliability in a remote area.

How are the maintenance costs on the micro turbines?  Do they provide an advantage over standard diesel piston units because they have fewer moving parts?  There was a lot of press on them a few years ago.
 

RE: Unmanned Offshore Platform Power Supply

The micro turbine mfgr claims low maintenance costs, because of alleged simplicity.

The air compressor for the bearings adds some complexity.

The battery bank and high power four quadrant inverter add more complexity.

You may have noticed that microturbines are not, e.g., arrayed so as to cover every bit of available land in the USA.

 

Mike Halloran
Pembroke Pines, FL, USA

RE: Unmanned Offshore Platform Power Supply

Several years ago I worked on a project for some offshore environmental monitoring instrument platforms.  PV was not a cost effective option at the time, the maximum load was 45 ekW, but there was a fairly large change in demand depending on what was running.  The systems installed ended up having a 25 ekW diesel unit, a 45 ekW diesel unit, and four small wind generators with a total capacity of about 22-24 ekW.  There was a large battery bank that could be charged by the wind gens or a set of chargers (rectifiers and alternators).

The platforms had a scheduled visit every 30 days, but the design required unattended operation for up to 90 days, in case someone could not get to the platform because of weather or sea conditions.

We installed external sumps with bypass filtration, and a rather elaborate fuel supply system. We sized everything for quarterly services, and the engines we selected had an average 12,000 between major service.

We had to develop a load management system because of the type of sampling the platforms did, they started and ran some fairly large pumps periodically.

Before you make a decision on what type of power source you're going to use I'd suggest you'd understand the types of loads and load profiles you're going to deal with, how often between visits, type of monitoring and emergency response the system will require, and since it's offshore, what regulatory requirements do you face?

We provided the generators, control and fuel module, the shipyard in Japan assembled the platforms and they were positioned offshore, I spent about 8 weeks getting the first one ironed out, the last one I spent 4 days on.

The control system was based on three Allen Bradley SLC500 plc platforms, and redundent HMI platforms using Rockwell's RSView32, generator controls were Woodward and Basler based.
The platform sampling control system was controlled by a Toshiba PLC, all the interface was digital, a lot of wiring but we had a good working relationship with the owners controls vendor and it was a solid system.  The platform transmitted data twice a day and had redundent tape backups.

I made a visit to two of the platforms two years later, at the expiration of the system warranty, for an inspection by the owner and a marine safety agency.  There were no reported operational problems except for an oil leak on one unit contained by the secondary containment and the unit shutdown by the control system.  The small units had about 6500 hours, the large units had about 4000.  We determined the engines would likely go the recommended overhaul interval of 12,000 hours based on the inspection, oil sample reports, and fuel and oil consumption records.  Two of the wind generators required bearing replacements, and some of the batteries did not test well and were replaced.  In general the end user felt it was a success. I don't know if the platforms are still operating.

As I remember the overall power system price, including genertor units, power system module, battery module, wind generators, and monitoring and control system was about $350,000 in 1999.

Hope that helps.

RE: Unmanned Offshore Platform Power Supply

I have a hard time thinking of what monitoring you would need 50kW for.   A lot of my experience has been attributed to remote sensing while achieving low average power consumption.  1W avg can do a whole lot of sensing. With a 100W I can't think what couldn't be sensed.  And 50kW?!?

As you get these larger drains I bet the wastage sky rockets due to the ensuing mentality, "we can add this and that too".  Waste like using a PLC.  Gawh!

Keith Cress
kcress - http://www.flaminsystems.com

RE: Unmanned Offshore Platform Power Supply

"Waste like using a PLC.  Gawh!"

Standard interface, readily available spares, (I nearly said cheap, but someone mentioned A-B lol ), maintainable by field technicians...
  

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

RE: Unmanned Offshore Platform Power Supply

The mentality of offshore is not so much "we can add this and that", as it is, "Wal-Mart is not ten minutes, or even a day, away."

Beyond the actual sensors, some loads are unavoidable:
Navigation lights.
Redundant navigation lights.
Anticondensation heaters for idle generator.
Anticondensation heaters for sensor electronics.
Floodlights for boarding.
Signal recording equipment.
Satcom equipment.

Some loads may not be unavoidable, but would not be surprising:
Air conditioning for sensor electronics.
Surveillance cameras and:
  Remote positioners.
  Washer/Wipers.
  Surveillance recording equipment, armored.
  Satcom equipment.

Some loads would only be needed during maintenance, but are best left aboard:
Hoist.
Seawater wash pump.
Desalination system for fresh water wash and/or survival.

 
 

Mike Halloran
Pembroke Pines, FL, USA

RE: Unmanned Offshore Platform Power Supply

Clearly the most economical answer in this case is the local generation in any of the several possible ways. Only as a theoretical exercise, we can try an a.c. solution with underwater cable. At 50Hz it happens approximately as follows:

1) 10kV, 3x120mm2 Cu, 100kW + 40kvar load, 2 reactors of 560kvar at the beginning and the end of the line, du=2.5%, DP=25kW, Scc=5MVA

2) 30kV, 3x120mm2 Cu, 1MW + 0.4Mvar load, 2 reactors of 2.6Mvar at the beginning and the end of the line, du=2.7%, DP=90kW, Scc=42MVA

Data for cables are taken from underground types. It is only an approximation.

JMM (Spain)

RE: Unmanned Offshore Platform Power Supply

(OP)
Thanks a lot guys for all your inputs !

JL

RE: Unmanned Offshore Platform Power Supply

Because of the disparity between peak demand and minimum demand, a hybrid system actually can make sense.
E.g.
2 x xxkW gensets
plus
nn kWh of batteries + inverter + charger
...
where the battery bank and charger would be sized to keep either of the gensets very busy charging, for a relatively short time at relatively infrequent intervals, and the gensets would be sized so that either one can run everything continuously, and the inverter would be sized to run just the steady loads, and to start a generator when it couldn't keep up.





 

Mike Halloran
Pembroke Pines, FL, USA

RE: Unmanned Offshore Platform Power Supply

You know, a term like "offshore platform"  can bring to mind anything from a small instrument platform operated by a research or regulatory agency, to a really big oil and gas production platform. Is it a jack-up, floater, flip, or what?

Also depending on where someone wants to put it can bring all kinds of issues up, as pointed out, redundent running lights, security and intrusion prevention systems, lighting and housekeeping loads like ballast and bilge pumps.

As for the PLC's, well it was the best solution I could come up with based on customer requirements, and frankly in that time frame I did a lot of projects with AB SLC's and Woodward/Basler controls and I never had issues with the hardware, I could respond to customer demands for customization or site changes, and the support in my area at the time for the AB products was excellent.  So with all that the difference in hardware price really wasn't all that great, of course now days I'm not the fan I was of AB, but isn't that evolution?

Mike, your list is near dead on, except we also had two sets of collision avoidance radars with automated messaging and the anchor handling system. These were floaters with four point anchoring.  These platforms were actually pretty interesting, as they sampled water from various depths, looked for oil slicks and floating debris, and also did some air quality monitoring.

Maybe the OP can provide some details on the platform, like what it's doing, types of loads, expected load profiles, etc?
 

RE: Unmanned Offshore Platform Power Supply

Yeah Mike thanks for the list.

I was envisioning something like the buoys around here.  Solar panels and batteries add a semi-custom computer and the needed sensors.   Oh well.  

Keith Cress
kcress - http://www.flaminsystems.com

RE: Unmanned Offshore Platform Power Supply

Hi Folks
I am new to the forum, but saw your question re unmanned platform power generation.

If you go to www.genexdesign.com you will see some information there which might be of help.

we deal with this type of equipment based on a high specification enclosures designed for offshore environments.

the diesel drive units are modified to accommodate extended sumps to lengthen standard service intervals to 2000 hours.

Machines are usually configured in dual or triple configuration to provide back up, and allow cycling of the duty unit to further extend platform attendance periods.

Microturbines are a good solution with advertised service intervals of up to 8000 hours, however they require very specfic operating conditions, mainly good stable gas supply, with set gas pressures.

Solar Sytems are effective but require large footprint areas to produce low outputs.

I am not too experienced in wind power systems, but again at 60kVA thats going to be a large footprint area.

The Ormat System mentioned in another reply is very efficient, but only prodcues low power output, I think they have just released an upgraded unit from 500W to 2000W, so you would require multiple arrays.

The footprint of a typical 60kVA Diesel set in a High IP rated enclosure with extended sump to 2000 hours service intervals would be approximately 3.2 mtrs long, by 2 metres wide, by 2.4 mtrs high.

Catserveng,s comments on the diesel system with Allen Bradley PLC etc was correct in my view, and Gen Ex can provide such a system.

Hope this helps.




 

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