purge a oil tank for safty

For blowing yourself up, or for heat-treating steel?

-- Ed Huntress

Wash with the hot water/degreaser/alkaline cleaner leave it vented and then get on with the bloody welding fergossakes! A clean oil tank/gasoline tank/propane tank is _not_ an explosion hazard. There may be the odd flicker of flame. But there is that if you weld near painted metal and no-one gets their shorts all knotted up over that do they?

Mark Rand RTFM

I don't know what you are talking about.

:)

--Winston

Was it Mark Twain who said that it is possible to have an enjoyable conversation only if all participants are unfamiliar with the subject?

Thanks for ruining a perfectly enjoyable conversation, you weasle.

:)

--Winston

Winston, ships have been using flue gas to provide an inert atmosphere in their tanks for years. Here are a couple of references: First a long, rather drawn out discussion about ships:

Second, a for sale advert which shows a vessel listed for sale with the inert gas system: In short, you are making an assertion that I am wrong with no proof, while I am showing you how wrong you are.

I assume that as you don't know what you are talking about when you attempt to refute my statements you probably don't know what you are talking the rest of the time and it seems ridicules to engage in a debate with a fool. So as far as I am concerned the contest is over. Please feel free to feel that you have "won" if it strokes your ego.

Bruce-in-Bangkok (correct Address is bpaige125atgmaildotcom)

Flue gas has almost no CO (70 - 160 ppm) It is a mixture of about

94% nitrogen and carbon dioxide and a little oxygen.

I think we can agree that flue gas, popularly used to displace air in the fuel tanks of ships is non-flammable.

Can we also agree that that the carbon monoxide (CO) component of exhaust gas as emitted from the tailpipes of most pre-1975 cars is both poisonous and flammable?

Thassall I was saying. Sorry to ruffle ya.

--Winston

I'm a bit curious as to how the combustion process has increased the nitrogen percentage, from about 80% in the air going in to the 94% of the flue gas.

John Martin

You use all the oxygen in the air for combustion, and don't generate all that much carbon dioxide in return. And you generate water vapor (H2O), that doesn't count as a gas. That's how the nitrogen content increases, because the other stuff decreases or converts.

Now note that the "flue gas" they are using is from a Diesel engine, NOT Gasoline. Or they could be burning bunker oil in a big Wartsilla bazillion-CID marine diesel if they preheat it first.

Gasoline engines built pre-catalyst can have significant CO in the exhaust (not to mention some unburned gasoline ftrom incomplete combustion at idle) and that's what has everyone here worried enough to NOT use it as a blanket suggested method of purging a tank.

-->--

That is a good question. Any Chem E's want to help us with an answer?

--Winston

Actually. Even with a somewhat rich running, non catalyst petrol engine. The exhaust won't support combustion even of hydrocarbons. The oxygen depletion takes care of that. The 1-4% CO is poisonous and the unburned gasoline is flammable, but they won't support combustion.

Indeed. If the modern catalyzed engine is cold, the catalyst is going to have no effect on the CO output of the engine.

As I implied before. JFDI :-)

Mark Rand RTFM

Chemist, not Chem E., I assumed complete combustion with 78% N2, 21% O2, and 1% other gas with a CH2.2 hydrocarbon to only H2O and CO2. If you condense the water, I get 80% N2, 19% CO2, and 1% other. Plus the water doesn't condense in the flue gas, so that'd make it 74% N2, 18% CO2, 8% H2O, and 1% other. 1% rounding error. This also discounts CO, NOx, unburned fuel, etc. I don't know how you'd get 94% N2.

You lose the O2, but get CO2, mole for mole. The only loss in mass is the O2 to H2O, and only if it condenses. Otherwise, you gain the mass of the fuel. I figured it on mass, not volume. Gas volume is 22.4 L / g-mole at STP.

Pete Keillor

(...)

(...)

Thanks Pete.

I put that very clumsily by adding the fractions of N2 and CO2 to indicate how much of the flue gas becomes completely non-flammable.

Nitrogen approx. 78 to 80% Carbon Dioxide approx. 12 - 14% Oxygen: 2 - 6%

--Winston