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cutting and welding on a diesel fuel tank-Now how to build a heat exchanger

Started by OneWithWood, September 21, 2006, 08:51:52 AM

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OneWithWood

My adventure into firing the outdoor boiler with bio-diesel has lead me to the point where I need to modify a 275 gal home heating oil storage tank.  I need to do some cutting with a drill and sabre saw and then a bit of welding to weld studs with a stick welder to provide a method to secure a gasketed access cover.  (I am pumbing the return line of the boiler through the tank to keep the bio-diesel temp around 150°F).
I could use some advice on the best way to proceed.  It is my understanding that diesel fumes are not explosive like gas.  Is this true?  I know I cannot start a fire with diesel fuel.
Thanks for the help  :)
One With Wood
LT40HDG25, Woodmizer DH4000 Kiln

Modat22

the fumes aren't but if it turnes to a white smoke it is. And that white smoke will go boom trust me on that one :)

What I do when welding on gas tanks (which should work for you as well) is run a flex pipe from a lawn mower engine's exhaust into the tank at the bottom and allow it to escape from the top out creating an oxygen staved purge. Keep the lawn mower running while you weld.

No oxygen = no ignition.
remember man that thy are dust.

scsmith42

Ditto Modat's comments.  A couple of years ago I had to weld uup the fuel tank on my Dresser Scraper after an operator put it on it's side (see my photo gallery).

Instead of exhaust fumes, I used the argon bottle from my TIG welder to fill up the tank.  I thoroughly emptied the tank first and rinsed it out with water several times, before filling it with argon.  I then taped off the openings and welded away.

Good luck.

Scott
Peterson 10" WPF with 65' of track
Smith - Gallagher dedicated slabber
Tom's 3638D Baker band mill
and a mix of log handling heavy equipment.

DanG

I'm a lilly-livered, yellow-bellied chicken when it comes to cutting and welding on tanks.  Is it possible to place the work area such that you can fill the tank with water?  I've noticed that water rarely explodes.
"I don't feel like an old man.  I feel like a young man who has something wrong with him."  Dick Cavett
"Beat not thy sword into a plowshare, rather beat the sword of thine enemy into a plowshare."

Modat22

I never could get a good weld with water in the tank, I'd get done, fill er up and get a drip, drip. Really any non non-oxydating gas works, I just use lawn mower exhaust because its cheap.
remember man that thy are dust.

Reddog

I have always steamed em. My dad and grandfather both welders told of exhast filled tanks still blowing up. This was because the engine was running to rich and dumping gas fumes in.
To stema them we would put water in the bottom and place the tank on a heat sorce. once it starts boiling let it go for a few hours steaming a way. Then weld it up. if I was not doing that I would use a inert gas like scsmith42 said.

bitternut

I once had a oil furnace replaced with a gas unit. Furnace installer removed the old oil tank from the basement by cutting it up in the basement with a sawzall. Had the whole tank removed lickity split. Yes they drained it good before cutting. ;D

I think I would use both water and inert gas. If you fill the tank partially with water and then add the inert gas you will save quite a bit of gas. Water is cheap plus it will help to keep things cool if needed. Ain't cheap filling those bottles these days.

Fla._Deadheader


Just a note. Steel is porous enough, that the fuel does penetrate a little. Heat drives the fuel out as FUMES. That's what causes the explosion.
All truth passes through three stages:
   First, it is ridiculed;
   Second, it is violently opposed; and
   Third, it is accepted as self-evident.

-- Arthur Schopenhauer (1788-1860)

Ianab

What FDH said...
Diesel is in some ways worse than petrol becuse the heavier residue doesn't evaporate like the lighter petrol and more of is trapped in the metal and seams of the tank. Once you heat it with the welder it becomes an explosive vapour just like petrol.

The argon, nitrogen, CO2, exhaust fumes or water precautions are needed.  :P

Cheers

Ian
Weekend warrior, Peterson JP test pilot, Dolmar 7900 and Stihl MS310 saws and  the usual collection of power tools :)

Furby

If ya remember the piggy roaster...........
I had that drum laying here open for 3 or 4 years. No telling how many years it sat emty and open before I got it.
StumpJumper cut it with a torch if I remember right. Also did some welding on it.
Jeff B fired it up after getting it made and said it was smoking a lot and you could see the residue on the metal burning.

Harold, what was that you have said before about building a brush fire around a tank to burn it all off before cutting?

OWW, I start fires with diesel all the time. :-\

Fla._Deadheader


BIG Propane tanks, Furby.  ::)  Throw 'em on a Dozer Deck and sweat 'em dry. I have welded gasoline tanks by filling them COMPLETELY full. All that MIGHT happen is, it will burn. A wet rag will put the fire out. FUMES is where the problem is.

  I know a couple guys that cut fuel tanks with a torch, without sweating them. NOT ME. NO SIRREE

  I priced installing a trailer hitch for a guy, one time, in Arkansas. Guy said TOO MUCH. He went elsewhere, and they burned a hole in his gas tank. Never thought to smother it. Jumped in the car and figgered the high speed wind would blow out the fire.  ::) ::)  Yeah, RIGHT. Asked him if the price was cheaper than me. He got mad. Tsk, tsk.  ::) :D :D :D :D
All truth passes through three stages:
   First, it is ridiculed;
   Second, it is violently opposed; and
   Third, it is accepted as self-evident.

-- Arthur Schopenhauer (1788-1860)

OneWithWood

Maybe I can come up with a no weld solution.  It sounds like drilling the initial hole and cutting the opening for the access panel with a sabre saw or sawzall might be safe enough.  Then I would only need to drill holes for the studs to secure the new plate.  I was going to tack the studs in but maybe I would be better off using some type of epoxy to hold them in place.
Any suggestions for an appropriate epoxy?
One With Wood
LT40HDG25, Woodmizer DH4000 Kiln

Fla._Deadheader


Doing a small spot at a time would probably be safe. The problem occurs when a LOT of fumes are generated. Cut the hole, then wait a little before drilling. How big is the hole to be ?? If it's pretty big, do part and then wait. Use a shop vac to pull what fumes are in the tank, to the outside. ??
All truth passes through three stages:
   First, it is ridiculed;
   Second, it is violently opposed; and
   Third, it is accepted as self-evident.

-- Arthur Schopenhauer (1788-1860)

OneWithWood

The hole will be approx. 10"x6".  I need to stub out two 3/4" ID black iron pipes through the cover, or two brass nipples attached to the black iron.  The pipes will extend down the inner face and along the bottom of the tank to provide heat via hot water ( I need to keep the bio-diesel above the cloud point and ideally around 150°F to keep it flowing, atomizing and burning well).  I think I can maneuver them through a 10x6 hole.
One With Wood
LT40HDG25, Woodmizer DH4000 Kiln

Modat22

I agree with deadheader.

I thought you where going to be doing more welding than that.

If you go the epoxy route. Use JB weld 24 hour curetime. Clean the areas with a wire brush and solvent and let her sit till hard.
remember man that thy are dust.

Murf

OWW, if you make a seperate plate, slightly larger than the hole you need, then all you have to do is make a brace or something that will slip in behind the tank wall bridging the opening and have it threaded to pull it in tight and seal around the edge. A little gasket material cemented to the cover plate will seal it up fine, especially if it's at the top where it is at or above the fluid level.

Of course the other alternatives that require no cutting or weldeing at all.....

Such as to wind a coil of pipe around the tank, and then wrap that again in an insulated blanket.

Or just put a T-fitting on the output line, run it through a heat exchanger (hydraulic fluid cooler plumbed to a small pump) and then just dump the heated bio-diesel back in through the filler cap or vent. This would also give you some circulation of the liquid in the tank.

Or put a T-fitting on the fill and vent openings and insert the return line down one over to and up out the other. It would slow the speed at which, but then again you dont get bio-diesel delivered by truck with a high volume pump either.
If you're going to break a law..... make sure it's Murphy's Law.

OneWithWood

Murf, that heat exchanger idea is a good one.  Now if I can just think up a way to use natural convection so I don't need a separate pump . . . :P ::) :P ???
One With Wood
LT40HDG25, Woodmizer DH4000 Kiln

Quartlow

you only need one pump OWW.   2T'S the return from the house  run on line to the oil tank, and one  back to the furnace hard to explain


    |         |
    |         |
-------------------

bottom line is the return hot water from the house
top to vertical lines go to the fuel tank, put a ball valve between the two T's and one in the return from the fuel tank.
with the one between the ts open and the on ein the return closed you get no heat to the tank. open the return from tank a little and close the one between the ts some and some return flow will go to the tank and some will go back to the boiler.
Breezewood 24 inch mill
Have a wooderful day!!

sandman2234

One drawback to using a gasoline powered engine exhaust fumes, is if the engine is running a little rich, you are making an even more volitile situation. Gas fumes, on top of diesel, now that ought to light off nicely...

  I prefer H2O, and even that will still allow small popping when cutting a propane tank. (did a 350 gallon one, that had been open for years and it would still pop a little, just enough to make me sweat!)

  Considering I have cut several thousand actylene tanks with a torch, I guess you can't call me a coward. (a few other words, yes, but not a coward). My partner and I used to do it for a Navy contract, but as most good things, they ended. I typically made $85 an hour back in late '80s with no overhead. Really hated to see that contract go...
    David from jax

Murf

OWW, if you mounted the heat exchanger level with the bottom of the tank of oil, it would circulate by convection, just not very effectively.

A lot of small Japanese diesel tractors have no water pump, the work strictly on convection. The problem you would have is the temperature difference wouldn't be as much as an infernal combustion engine and ambient temps.

That said, you could always just use a T off the output of the heat exchanger as the feed for the burner, then at least what you were sending to the burner would be warm enough.
If you're going to break a law..... make sure it's Murphy's Law.

OneWithWood

Murf, you really stirred up my grey matter.   ???
The new plan is to install the tank in the small greenhouse next to the furnace ( I was really surprised when my sweet wife suggested this - floor space in the greenhouses is closely guarded  ;) )
I am thinking about the heat exchanger, I think to maximize the surface area and thus the heat transfer a coil in a tube would work out well.  I can easily plumb the return hot water line to run 180°F water through the tube.  The problem is finding the correct fuel line to use.  B100 and copper do not get along very well so I need to use steel.  (The copper reacts with the bio diesel and degrades the fuel )
Does anyone know of a steel 3/8" OD line that is easily bent?  Or can I use heat to soften the steel to wrap it around a pipe without crimping it?  I want the coil to fit into a 4" maximum tube.  The water from the boiler has a conditioner in it that prevents the steel from rusting.

How do I modify the title of this thread to read: Cutting and Welding on a diesel fuel tank - Now how to build a heat exchanger  :)

and we haven't even gotten to food or guns yet  :D
One With Wood
LT40HDG25, Woodmizer DH4000 Kiln

scsmith42

OWW - re steel lines that are easily bent, see if a local trucking parts supplier has bulk steel brake line.  Typically it comes in lengths up to 6' or so; I hope that  you don't need much!

Steel lines are also used on heavy equipment, and some speciality metal suppliers may stock small steel tubing that is a mild steel. 
Peterson 10" WPF with 65' of track
Smith - Gallagher dedicated slabber
Tom's 3638D Baker band mill
and a mix of log handling heavy equipment.

Murf

OWW, phone around your area to all the hydraulic shops and see if one of them has an old heat exchanger they have taken off a piece of heavy equipment or something.

Typically they are large tube style excchangers that go in line with the radiator hose. They are usually stainless or plated steel with a 3/8" or 1/2" steel line wound around on the inside terminating in pipe thread fittings on the outside at each end.

If you can find one of those all you have to then do is make up reducers to go from the oil line size up to, and back down from the heat exchangers size.

You may also get lucky and find a small hydraulic resrvoir with provisions for a heat exchanger coiul to be inserted. This may be less work and fiddling in the long run. Besides, doing it that way would give you a few gallons of hot oil always standing by for use.
If you're going to break a law..... make sure it's Murphy's Law.

Don_Papenburg

Seamless hydraulic tube.  Farm and industial machinery scrapyards would be a good place to start.    Also use a couple runs of 1/4 or 1/8 " black iron pipe scedual 40 or less . I made a heat echanger for my blast hood that I stuck in the exhaust pipe on the compressor . It worked too good ,burned the rubber right off the hose.  anyway it was easy to bend and two smaller pipes would provide more exchange surface.
Frick saw mill  '58   820 John Deere power. Diamond T trucks

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