70kw Cummins prime power propane generator set fault shutdown… freezing tank starved for fuel?

[707pc50]

Running a low hour 70kw 1800rpm Cummins Gen set at about 75% load on a 1000gal propane tank.
Tank is also supply propane for 4 200k btu boilers running full time. Separate supply lines and high and low pressure regulators for generator and boilers.
In a power outage now from snow storm, relying on generator, Last night at 4am generator faulted “under frequency” and shut down. Propane tank level at 55%
I am assuming starved for fuel, sputtered engine, and turned it self off. My only thought is as tank got lower and air temps hits the high 20s F, the tank froze?
Any ideas or tips? Running now during the day, I lowered the electrical load by half.

 

[707pc50]

 

[Birken Vogt]

BTU demand:

Boilers 800k
Generator 1MM

Total demand 1.8 MM BTU/h

Total max for 1000g tank 745k under INTERMITTENT conditions (continuous is worse).

For continuous loading multiply by .25 = 186 kBTU/h

I would say you are undersized by a lot. Per the book this installation would need 10 tanks for 30F. Really you can get away with less but there it is in black and white.

 

[Birken Vogt]

 

[707pc50]

Thanks for that. I should have done a little more home work.

I don’t think my boilers are a continuous load. Generator is fairly continuous..

I’ll add a second tank and go from there.

Thanks very much for the table, black and white, and very helpful.

 

[Delmer]

A vaporizer is standard on high demand propane installations here, basically a pilot light flame to heat the propane outside to keep pressure up. Like Birken's table says at the bottom, the ice insulates the tank and allows it to get cold enough to drop pressure, so you can see if the tank is frosting up, the tank and propane themselves don't actually freeze.

Usually we worry more when the temp gets cold enough that there's no pressure, -40. So Birken is a better guide for freezing up from condensation, which would be worse in a snowstorm at 20 than at -40. And you're maybe not tested to -40 so the icing is the first to fail.

 

[707pc50]

Ok thanks. You are saying I should add a vaporizer?

Can you provide me a link or part number for a vaporizer?

Or should I try a second tank first?

The boilers are running all winter, generator just as stand by emergency use (but 24hrs a day 75% ish load during those outages).

Thanks for the advise.

 

[707pc50]

Tank gets some frost on it pretty frequently with just the boiler load on it, but no affects on boiler performance is noted.

 

[Birken Vogt]

I would add a second tank. More capacity is always a good thing with this third world thing going on these days. No moving parts. A vaporizer is a mechanical device to fail. It also consumes fuel.

 

[707pc50]

10/4, will do, need the storage anyway to last a week between fills when Gen running.
Thanks & happy new year.

 

[Delmer]

Birken is the generator expert on here. I'm just saying that's what I've seen and maintained here, I don't design them or hook them up. I'd never see one tank with that load though, but again, we can't have the heat go out at 25-35 below, and you might never see that, so icing is your issue.

If you still get icing with 2-4 tanks (what I'd expect or more for that load) then you could look at watering your tank (if you have shallow groundwater etc). It wouldn't take much water at all to keep the tank above 0 and no problems during emergency generator use. Or run a heater hose off your generator and a few loops under the tanks, not approved, but you could make it work somehow

 

[skyking1]

Liquid propane to vaporizer is how they do forklifts, etc.

 

[Delmer]

Good point, even with several tanks, liquid feed to the generator to a vaporizer on the engine would eliminate the generator usage from cooling the tank and would allow it to run on one or two tanks.

 

[hosspuller]

For a temp work around... any way to pipe the genset exhaust to the tank ? It doesn't take high temp to vaporize propane. Any input above 20 degrees will help.

Or stage the four boilers so they don't draw at the same time.

 

[Birken Vogt]

I am generally against liquid feed unless absolutely necessary. The piping can be hazardous.

 

[1693TA]

I am generally against liquid feed unless absolutely necessary. The piping can be hazardous.

When I was installing we were mandated to use liquid withdrawl to the outside wall of the structure with a heated vaporizer enclosed in an armored enclosure. Typically the largest gaseous fuel sets we worked with were 50kw 3ph and larger were diesel. All standby Kohler sets but many went running for days on end in the remote navigation sites.

 

[skyking1]

I am generally against liquid feed unless absolutely necessary. The piping can be hazardous.

I know in a mobile rig it is necessary and indeed poses different hazards.

 

[hosspuller]

I am generally against liquid feed unless absolutely necessary. The piping can be hazardous.

My experience was ultra high pressure low flow as in 3000 psi working pressure, 20 pounds per hour in an industrial process. We used SS tubing in the high pressure and schedule 80 black iron in the 60-100 psi low pressure liquid side.

What hazards had to be mitigated in your piping ?

 

[707pc50]

Generator is 150 feet from tank, supply line burrows underground. Running exhaust heat a now go.

we only rarely see temps below freezing, but power outages do line up with those winter storms.

we can reduce our btu load if 2 tanks still freeze up on us. Don’t think I want to buy more then one more tank.
Thanks for all the help guys.