I have been asked to look into using a natural gas engine generator vs diesel engine, 1000kW for hospital use.
By the manufacturers I was told that the NG is a lot more expensive and it needs to be a lot bigger to provide the same power as a smaller diesel engine gen.
I am on an OSHPD project (California) and the emergency loads need to be picked up within 10 seconds, besides the obvious cost reasons can anybody else tell me why not to use a NG gen?

What is the starting time?
Can NG pick up emergency loads within 10 seconds as required by OSHPD? (I know diesel can)

Thanks

Diesel can be stored easily and you can realistically bunker enough for an extended run without any support from the outside world. You could store enough LPG if you have a large pressurised tank, although it would be considerably more hazardous than a diesel tank, and fairly expensive. As for large-scale storage of methane... certainly not easy or cheap.
  

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

Thanks Scotty,

my main concern between these two types is the emergency load pick up.  Per code in california emergency loads need to be picked up within 10 seconds so if we have 2 or more diesel generators we've seen them being able to synchronize and pick up all the loads within 10 seconds.

Is that the case with the NG Gens, how fast do they turn on and how fast do they synchronize?

Thanks,  

I'll let Bill or Mike answer that one - they know more about relatively small recip machines than I do.
  

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

I worked on a small installation years ago where GM automotive V-8s were converted to natural gas and used for standby generators. This was a department store where the POS terminals would lose their memory in about 8 seconds. The sets regularly came on-line fast enough to save the POS configurations.
As for larger natural gas engines, Let's hope Mike posts in.

Bill
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"Why not the best?"
Jimmy Carter

I have been peripherally involved in manufacture of fewer than a dozen 1MW or smaller NG generator sets, mostly destined to provide all of the electrical power on Gulf of Mexico oil rigs, where they are preferred because the natural gas is 'free'.  

They are typically specified with heaters to prevent condensation in the generator shells, and oil and/or coolant heaters and circulation pumps to keep the block temperature above ~100F for quick starting, exactly as are Diesels used in similar circumstances.

I am not aware of starting or synchronization issues unique to natural gas engines, but I wasn't invited to every meeting, and I claim no great expertise in this field.

 

Mike Halloran
Pembroke Pines, FL, USA

My past design experience has been that the issue is the reliability of the fuel source for emergency power use.  Starting and synchronizing never came up as I recall. The NG engine will be larger.  For most of the situations we looked at, the AHJ would not allow NG engines to be used for emergency power unless there was a lot of on-site storage, which is never going to be practical with NG.  

I can't imagine anyone accepting an NG engine for a hospital in California.  But I've been wrong before. Diesel engine should be cheaper.  

 

David Castor
www.cvoes.com