Engine RPM for continuous duty generator

[oldfieldguy]

I used to 'know' that one did not use an 1800 RPM (or higher) engine for continuous duty generation.

I have an offshore facility that now has TWO dead 750 kw natural gas fueled generators. Both are forty years old 'big iron' 750 RPM units rated at 750 KW for when this was a major compressor station for an offshore natural gas gathering system. We no longer use it for that.

Total load is in the 200 KW range.

I am looking at replacement, but I'm finding a very small selection of NEW 250 KW units that do not have 1800-RPM engines.

Did we change our ideas about engine RPM in continuous service?

What's the thoughts these days?

old field guy

 

[FacEngrPE]

The discussion about fuel cells seems interesting, I poked around and found some DOE test data. I think from this we could conclude fuel cells will often need a storage buffer (capacitor, batteries, or similar) where they are applied to a system where they are the only source of supply.

The complete document is attached.
The document is talking mostly about hydrogen based systems. The ramping rate for methane fueled systems should be similar.

 

[waross]

The ramp rates are very much better than I had expected.
That graph is both interesting and disappointing.
The heading doesn't match the graph.
Ramp up test
From 25% to 50%, 75% and 100% of rated power should be,
From 25%, 50%, and 75% to: 100% of rated Amps.
Extrapolating from the graph, it should ramp from 25% to 50% in about 0.05 seconds.
It won't take much capacity to buffer 25% for 0.05 seconds.
Motor starting, the Fuel cells may ramp up into a capacitor that is then used to support the starting surge of the motor, in less than a second in most instances.

Wärtsilä engines can ramp at over 100%/minute, much faster than gas turbines, providing ultra-responsive power that is needed to integrate renewable energy.

https://www.researchgate.net/post/What_is_the_typical_MW_minute_ramping_capability_for_each_type_of_reserve[/URL]]What is the typical MW/minute ramping capability for each type of reserve?
NERC Disturbance Control Standard specifies that regulating and supplemental reserves must be able to reach their full capacity within 10 minutes, but since capacities may differ dramatically, this definition will not describe the feasible MW increase within a minute. For instance, a 50 MW unit that meets the aforementioned standard will have a ramp rate of at least 50/10 = 5 MW/min, but a 500 MW will have a ramp rate of at least 50 MW/min. We cannot consider 5 MW/min to be as good as 50 MW/min!

For grid use, fuel cells ramp up incredibly quickly. Fuel cell ramp times may be measured in 1/10s of seconds rather than in minutes.
For small standby sets, as compared to diesel sets, diesel sets respond to block loading with a drop in frequency as rotational inertia helps to supply the sudden load. I anticipate that small scale standby fuel cells will incorporate artificial inertia in the form of capacitors to support block loading.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[waross]

Thanks for introducing us to the Redox technology, Keith.
I haven't been following fuel cell developments and the state of the art is exciting. It looks as if fuel cells are ready for prime time.
For residential use, I foresee combined cycle developments. The rejected heat may be captured and used for home heating, hot water production, clothes drying and absorption refrigeration.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[waross]

Does anyone know the conversion factor for REDOX. Giga-joules to KWHrs?

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[waross]

Genset with a 3406 based engine

A 3412 or a C32, possibly a 3416. (Plus 10% or plus 25% for prime power. Plus 10% is standard but I have seen plus 25% spec'ed for longer life.)

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[itsmoked]

Yes! FacEngrPE thanks for the interesting graphs!
I could easily see an automotive solution of simply limiting the drive accel rate to match the fuel cell ramp while as an aside limiting torque-stress to the drive-train (a money saver)


VFD based motor loads would probably be fine with un-supported fuel cells. The speed of ramping seems to make a pretty good case for only capacitor support being needed.

Does anyone know the conversion factor for REDOX. Giga-joules to KWHrs?

Can you be more specific Bill? Not exactly following your question here.

And yes! A lot of synergy in a residential application. Someone was capitalizing on all these aspects a few years ago in a household drop-in fuel-cell system. I think you then needed only NG plumbed to the home no power. They used some battery to handle things like motors and peak cooking loads.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

I pay $5.77 per GJ for natural gas. How many KWHrs will that amount of gas produce in a Redox Cube?
My house has a 200 Amp panel but the utility limits my demand with a 35 Amp breaker at the pole. It never trips.
35A x 240 Volts /1000 = 8.4 KVA. I keep forgetting to bedevil customer service by asking for a graph of the breaker tripping characteristics. I suspect that it may be very, very inverse time compared to a standard breaker but that's just a guess.
Heating loads are a natural for a co-generation setup. A combination of electric heat and reject heat for absorption A/C and most heating loads. Wait for natural gas cook tops and ovens with electric boost.
Do you have a link to the drop in residential system?

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[TugboatEng]

The cities around me are banning natural gas in all new construction.

 

[itsmoked]

Bill; 6,350 BTU/kWh

1 gigajoule = 947,817BTU

1 gigajoule => 149kWh (no thermal use)



BTW further digging and REDOX is still futzing along not actually selling their product and it only puts out DC!!

However Bloom Energy certainly is. I recall them putting stacks of them in Silicon Valley big hitter campuses. They also serve the marine world.


Saw this:

VANCOUVER, BC and HOBRO, Denmark, Sept. 8, 2020 /PRNewswire/ - Ballard Power Systems (NASDAQ: BLDP) (TSX: BLDP) today announced the launch of the fuel cell industry's first module designed for primary propulsion power in marine vessels. Ballard's FCwaveTM fuel cell product is a 200-kilowatt (kW) modular unit that can be scaled in series up to the multi-megawatt (MW) power level.

Ballard’s FCwaveTM fuel cell module provides megawatts of power for marine vessels, in 200-kilowatt increments (CNW Group/Ballard Power Systems Inc.)
Ballard’s FCwaveTM fuel cell module provides megawatts of power for marine vessels, in 200-kilowatt increments (CNW Group/Ballard Power Systems Inc.)
The FCwaveTM product provides primary propulsion power for marine vessels – such as passenger and car ferries, river push boats, and fishing boats – as well as stationary electrical power to support hotel and auxiliary loads on cruise ships and other vessels while docked at port (also known as 'cold ironing').

I cannot find that house system. It had a "NG reformer", hot water output, needed 30 minutes of maintenance once a year, and I recall they were only going to lease it at first.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

Thanks Keith. That works out to $0.039 per KWHr at my present NG rate, compared to over $0.06 at my present electricity rates, plus about $100 per month fixed costs.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[FacEngrPE]

The residential market may just be too price competitive for the Bloom product. I doubt that the usual tricks used to make small residential HVAC equipment inexpensive would work with a fuel cell stack. It is likely that once the size is dropped below 200kW the installed cost declines slowly with size. The requirement for

https://www.bloomenergy.com/wp-content/uploads/es5-200kw-datasheet-2019.pdf[/URL]]supply natural gas pressure to be a minimum of 10 PSI

creates a building code compliance problem for residential installation.