Multi-fuel boiler?

[fredrosse]

A LP Gas (Propane) tank behaves very similarly to a steam boiler. The only difference is that the pressure-temperature relationship for Propane is different than the relationship for steam.

With a steam boiler, holding pressure of several atmospheres (say 100 PSIG), you can open a valve and let off steam. If there is no heat source to the boiler (no fire), then steam pressure will decrease, and eventually the boiler will reach one atmosphere absolute pressure( 0 PSIG, 212F, 100C), and no more steam comes out. If you want to have more steam come out, and you want to maintain any pressure, you have to add heat to the boiler. In the case of a steam boiler, this heat is supplied from the fuel/fire.

The Propane tank has the same type of relationship, except the propane tank will get well below 32F (0C) when the pressure reaches one atmosphere absolute ( 0 PSIG). At ordinary ambient temperature, the propane in the tank will be at several atmospheres pressure.

Normally the heat to keep the propane tank warm enough is ambient air heating the tank, typical ambient temperatures in the range of 60-80F (15-25C) .
However the heat available from the ambient air has limits. If you want to draw large quantities of propane from the tank, the ambient heat transfer to the tank is not enough, and the propane boils away at lower and lower temperature & pressure. Eventually the tank gets very cold, and the available rate of drawing off propane is very limited.

With a high capacity burner, you need to supply extra heat to the propane tank. One good method is to flood the tank with ordinary lake or sea water. This water is capable of supplying adequate heat to keep the propane near ambient temperatures, which gives an available propane pressure of several atmospheres. The maximum temperature that the propane tank can experience is only the lake (or sea) temperature, and the corresponding propane pressure is within the safe limits of the propane tank.

Another method mentioned earlier is to use a steam coil or hot water jacket surrounding the propane tank. This method allows the potential to overheat the propane tank, which raises the pressure above the safety limits of the propane tank. As previously mentioned, this method is wrought with danger, and should never be used.

[87gn@tahoe]

Stevey, you forgot waste motor oil at 153,000 to 180,000 BTU per gallon and usually the cost of FREE, it is a great fuel.

On my father's 21ft "George H. Sandin" we can burn without any smoke or noxious fumes. The "day" fuel tank is next to the boiler to keep it warm so there is no need to "water down" with diesel fuel. We have cusioned seats that are built around plastic milk crates that fit four 1/gal windsheild washer bottles perfectly. We then transfer the oil from the seats to the 9/gal "day tank". We have six seats at 4gals each, 24 gals total and the 9 gal "day tank" (33gallons TOTA), at 3gal/hr MAX (more like 2-2.5gal/hr) we have approx 11hrs of FREE steaming, plus bunkers with firewood.

It CAN be messy if you're not careful. Also, finding a source that doesn't get tainted with water can be tricky. But if you get in good with a couple of your local mechanics and DIY neighbors, and let them know your terms, you will have an unlimited source of free fuel for years to come.

Over the nearly 30 years my father has had his boat, he has spent a TOTAL of $25.oo on fuel, only because he bought diesel a couple times.

[stevey_frac]

Indeed, I didn't include waste oil.

Personally, I'd shy away from it, as there is some risk of breathing the fumes of that concoction, and it's going to contain heavy metals from it's time in an engine crankcase.

That being said, i'm sure if treated properly it burns well, and you can't beat the price!

With regards to the lake water propane tank heater... that's exactly how I would do it...! Wouldn't take much water at 50 degrees to keep the propane tank from freezing up. You couldn't go in the winter would be be my only complaint, but then, you can't boat in the winter around here anyways... so it's not really a valid complain.

[artemis]

Indeed, I didn't include waste oil.

Personally, I'd shy away from it, as there is some risk of breathing the fumes of that concoction, and it's going to contain heavy metals from it's time in an engine crankcase.

That being said, i'm sure if treated properly it burns well, and you can't beat the price!

If you live where there are fast food places, used deep fryer cook oil is just great! No problem with water, heavy metals, etc. A few less BTUs per lb, but... if you're selective in your storage you can smell McDonalds for lunch, Skippers seafood for dinner, etc.

[stevey_frac]

That's an awesome idea Artemis!

*Sets off labeling 50 gallon drums with restaurant names*

[farmerden]

Some of the heavier oils don't pump as well at colder temps and I was going to install a steam loop in my tanks so I could take the chill of the fuel.Probably would have a shut off as well and the loop would return to the hotwell.If I spent that much time I might as well install a temp gauge as well so I could take scientific readings!! For fuel pumps I use an automobile fuel pump running off of an eccentric on the driveshaft.I 'm thinking about upgrading to a Dodge truck diesel fuel pump as I think that would move the fuel easier than the gas pump I am presently using. Den

[artemis]

Some of the heavier oils don't pump as well at colder temps and I was going to install a steam loop in my tanks so I could take the chill of the fuel.Probably would have a shut off as well and the loop would return to the hotwell.If I spent that much time I might as well install a temp gauge as well so I could take scientific readings!! For fuel pumps I use an automobile fuel pump running off of an eccentric on the driveshaft.I 'm thinking about upgrading to a Dodge truck smelly long-chain hydrocarbon fuel pump as I think that would move the fuel easier than the gas pump I am presently using. Den

Be aware that some fuel pump diaphrams deteriorate when used with "biodiesel" and other waste oils

[stevey_frac]

Just make sure you get a relatively new fuel pump, and you should be ok. Anything made after 1996 should be ok, but to be safe, try and get something made in the last 10 years.

[farmerden]

So far so good! The pumps are pre 1990 ,I can't cross them with anything as there are no parts numbers which is why I will upgrade one day. One pump pumps fuel and the other pumps sludge from the pan under the engine to a gallon jug which saves the bilge from oil contanimation and the great outdoors as well! After all we share this water with these guys and they might not take kindly to having bilge oil pumped on them![/img]

[stevey_frac]

I'm envious Den. You live in a truly beautiful part of the world.




When it's not raining anyway. I have no idea if a gasoline pump degrades with bio-oils. I've never heard of anyone doing that before!