Generator LP 100lb tank

[Huntinguy]

I am kinda off to my next project/conundrum.

I have a " whole house" (7,5kw) generator for my pump house. It calls for a maximum draw of 130,000 BTUs. I need to run it off 100 lb tanks. They have the standard valves like the 20 lb tanks. I have seen some regulators that claim to provide the BTUs but they are all 3/8 hose fittings for 3/8 hose. That size hose only flows 80,000 BTUs.

I really do not want to put a 250 gallon tank there for lot's of reasons.

Has anyone done something like this and made it work? How did you do it and what parts did you use?

 

[jaxs]

I've done similar many times. Other than pol fitting in tank valve, everything else is common plumbing sizes/threads. Run 3/8 lines from 2 (or as many as you like) tanks into Y with 1/2" outlet. A 100 pound tank will only run the genny for 15-20 hours so you often need more capacity anyhow. There's a second but more hassle and expensive way for sub-freezing weather. Special tank with liquid withdrawal or invert conventional tank with proper regulator. Some gennies come from factory equipped with vaporizer allowing liquid use without special regulator.
Are you using new or used tanks? FYI used forklift tanks sell much cheaper than 100 pounders and can supply both liquid and vapor.

 

[SPYDERLK]

You will have to do something clever to keep the tanks warm as you draw from them. Maybe duct waste engine heat over/around them. ... Unless your usage is typically brief and in warm weather.

 

[Huntinguy]

I kinda figured I would have about 20 hours of run time with the 2 tanks. I hadn't planned on using them in tandem... guess I will need to.. Cold could be an issue. I will have to solve that this summer.

Is there such thing as a 1/2 inch braided line I could use? I haven't seen one.

 

[hayden]

Others here may know the details, but another limiting factor for propane is the vaporization rate of the propane. It's liquid in the tank, and vaporizes off the liquid surface filling the space above in gas vapor. It's the vapor that's drawn off and burned. If you draw off the vapor too fast, new vapor can't evaporate off the liquid fast enough to replace it and you starve the appliance. The evaporation rate depends on the surface area of the liquid, and the temperature.

I have a 4kw RV generator that runs on propane and they caution that it will not run a full load off a 20lb tank. I ran it off a 1000 gal tank so no problem, but I don't know what the minimum would be for portable tanks, nor that the requirements would be to power a 7.5kw generator.

 

[hayden]

Here's some more info Products include generators, heaters, fireplaces, chain saws, power washers, transfer switches, etc....

 

[Huntinguy]

Thanks Hayden. Wish I would have known that last year. It is good information.

We don't often get below 0 out here. So I guess I should get another tank thus summer.

Out the 2 outages we have had in the last 2 years, the longest was 14 hours.

My manual also says not to run off of a 20lb tank. Probably because of starvation.

Now to find the proper hardware...

 

[workinonit]

3/8" will run it. I run my 6500 on my RV with 3/8" line. I would just get me a couple of tank heaters.

 

[triptester]

Nearly all 20,30, 40, and 100# vertical tanks are the same diameter so vaporizing area is the equal the only difference is liquid storage capacity.To get larger vaporizing area a vertical tank has to have a larger diameter or you need to get a horizontal tank.
POLs are not all the same they have diffrerent maximum BTU capacities which are seldom clearly indicated.

 

[RayIN]

Thanks Hayden. Wish I would have known that last year. It is good information.

We don't often get below 0 out here. So I guess I should get another tank thus summer.

Out the 2 outages we have had in the last 2 years, the longest was 14 hours.

My manual also says not to run off of a 20lb tank. Probably because of starvation.

Now to find the proper hardware...

LPG evaporates until tank pressure reaches the limit of evaporation. A tank too small cannot evaporate/boil liquid into gas fast enough to supply demand due to insufficient surface area.

 

[hayden]

Nearly all 20,30, 40, and 100# vertical tanks are the same diameter so vaporizing area is the equal the only difference is liquid storage capacity.To get larger vaporizing area a vertical tank has to have a larger diameter or you need to get a horizontal tank.
POLs are not all the same they have diffrerent maximum BTU capacities which are seldom clearly indicated.

I suspect this is why forklift tanks are horizontal.

 

[LouNY]

You can flow quite a bit of propane through a POL fitting, a couple, or3-4 of tanks and POL fittings tee'ed into a high capacity regulator.

 

[Shawn T. W.]

Nearly all 20,30, 40, and 100# vertical tanks are the same diameter so vaporizing area is the equal the only difference is liquid storage capacity.To get larger vaporizing area a vertical tank has to have a larger diameter or you need to get a horizontal tank.
POLs are not all the same they have diffrerent maximum BTU capacities which are seldom clearly indicated.

While the surface area of the top of the liquid propane is the same ... The taller tanks allow for larger exterior surface are to "warm" the "boiling" propane inside, larger capacity tanks hold more liquid, so they don't cool off as fast as smaller one do ...

A 420 Lb tank is vertical, hold 100 gallons at 80% fill and uses the same POL fitting as the 20 pounder, and the horizontal 1000 gallon tank ...

The POL is not restricting the gas vapor flow. It's either the vaporization rate due to cold (propane starts to vaporize at -44°F at 0 PSI) or the regulator(s) are not up to the task, they make them for different BTU loads ...

 

[bigtiller]

I think a 420 lb propane tank, sometimes called a 120-gallon cylinder, that holds about 100 gallons when filled to 80% would be a good choice.

 

[Shawn T. W.]

Yeah, the "420's" are a "DOT" certified tank, and must be recertified after so many years, but can me transport full at 80% capacity ... Propane weighs 4.2 Lbs per gallon at 60°F, so holds 100 gallons ...

They also make a 120 gallon ASME certified tank, that looks almost identical to the 420's, but doesn't have the recertifications needed later, but must be down to 5% to transport over public roadways ... 120 gallons full at 80% is 96 gallons ...

In Vermont in tight alley ways where we didn't have the required 10' set back from property lines to set a 500 gallon tank for say a pizza place ... We could legally set 4 of the 420's, tied the POL's together with pigtails, then hooked the last one to a high pressure regulator, which reduces tank pressure down to 10 PSI, put a secondary regulator at the entry point to the building, which dropped it down to 1/2 PSI which is close to the 11" of water column (wc) that most appliances require ...

 

[chim]

When we built our house we used a propane generator for power running it on BBQ tanks. On really cold days it would sputter. One rainy day it began to run rough. Thinking it was running out of gas I went to check the tank. It was heavy. Partly because it still had a good bit of fuel and partly because of the big ice donut that formed around it

 

[RayIN]

You will have to do something clever to keep the tanks warm as you draw from them. Maybe duct waste engine heat over/around them. ... Unless your usage is typically brief and in warm weather.

Yep, the liquid surface area determines the amount of gas available for use. A 100# cylinder will not have the surface area required to boil off the liquid into gas to supply enough gas to run that genset.

reference: https://www.lbwhite.com/application/files/3317/0931/0356/Propane-Tank-Sizing.pdf

 

[LouNY]

Of course there are work arounds that are not endorsed by the safety czars;
As you use your propane you can tip the cylinder sideways a bit to get more surface area,
as long as you don't tip it so far that you get a liquid slug into your vapor system.

 

[Huntinguy]

Hmm, this seems to be much more complicated than I thought or expected.
Seems like I am seeing comments to run tank preassure to the generator then step it down...
Do you think this sounds reasonable: run 2 100lb tanks each having a regulator with a 6 foot 3/8 line and connect them via T to the 3/4 pipe at the generator.

I really don't want to start over and use a 250 gallon tank. This is setting in the front yard about 50 feet from the house. Not sure the "HOA" would not like looking out the front window and seeing the tank. Pump house is already pushing her humor limit and I am still hopeful that I can put in a chicken coop next spring.