Another practice run not boiling as expected

[mathprofdk]

Hi folks,

The image below is a new custom evaporator I designed based on other barrel evaporators here. A friend who welds professionally did the work. Because I live in the suburbs on a small lot, heating with wood wasn't practical. (Firewood is very expensive, and I don't have space to store free pallets.) So my friend recommended natural gas, and ended up using 3 furnace burners. We have a 1/2" line from the house, so there should be plenty of pressure.

I left 10" at the back of the drum for a raised pre-heater. (I use a stock pot with a valve to drip in - I'll use the same pot to bottle.) The pan is roughly 2x2. The burners have nice blue flames reaching about 4-6 inches high, with the concentrated part of the flame only about 1" high. (The openings are linear, so they kind of burn in a parabolic shape along the length of the burner. Then there's a much less concentrated flame that goes the rest of the height.) There's about 4" of space between the burner and the pan. I have a 6" stack with a damper that I left completely open. It wasn't complete in this picture, but the stack is 6' tall.

So my problem - my friend quoted 300,000 BTUs in the burners, so I was expecting a roaring flame and rapid boil. After 20 minutes or so, I did get a boil going, but just barely. Definitely no rapid boil. The only bubbles were along the three furnace burners, with the hottest temperatures at the far end near the pre-heater. The temperature near the front never got to boiling.

Thoughts for the next test: I plan to fill the space below the burners to force the heat up against the pan. I'm also planning on putting a regular house fan near the openings to force more air inside. I'm hoping to ask my friend to weld some aluminum on the bottom of the pan to distribute the heat better, too. The SS he used is fairly thin.

Any other ideas? Was I wrong to expect a roaring boil with this set-up? Am I missing something obvious? I used a turkey fryer last year, and I really don't want to boil for 20 hours to make 1 gallon again. Plus my friend spent a ton of time making this (it looks sexy as hell), and for his sake I really want it to work.

~DK

5492

[berryrd]

Hi DK. Maybe you have too much draft and its pulling the heat past the pan which explains why the pans are hotter in the back. Think more like a kitchen stove. You dont need the draft like a wood fired evap. Good luck, Clay

[500592]

I would close the damper up and try again

[mathprofdk]

Thanks for the tips. To Clay's point, I forgot to mention that all three burners have taller flames to the back, even without the pan in place. The system originally had 5 burners, but my friend only used 3. Could that be factoring in?

The damper is an easy thing to try, though. What about air going in - should I try to restrict the amount of air? There are openings for the burners that I can mostly block with the ceramic insulation if it would help.

~DK

[Russell Lampron]

If you haven't already done so, insulate the inside of the barrel with ceramic blanket. Also with gas burners like that you don't even need a stack. Gas finishers and canners don't use them. They just have air space so that the burners can get oxygen and so the exhaust can vent out. I wouldn't do any mods to the pan it should work just the way that it is.

[ACollette]

DK,

Here is my thought.

You are connecting to your home natural gas line... that being said, your natural gas is regulated at your meter to below 1/2" lb or less than 14" water column. You have 3 big commercial burners there, they are not getting enough fuel flow to convert to the amount of BTU's required to bring your product to a boil. As an example, your turkey fryer that you were using last year, when you fired it had a "roaring" sound to it - Right? That is because that regulator on the fryer set up is probably running between 15-30 psi range, therefore supplying you with a lot of fuel. A lot of fuel = a lot of fire = a lot of BTU's. BTU's factor your evaporation rate. My guess is your furnace burners have lazy flame, not the blow torch flame that you saw on your Turkey fryer. Ask your friend who quoted you the 300,000 BTU's from the burners what he/she thinks. I'm not a gas technician... only a Vermonter! Good Luck.

[PerryW]

300,000 BTU is more than double my home oil furnace. It should really crank. I think my home furnace is jetted at 110,000 and it heats a whole 1600 sq ft house + basement/.

[maple dayes]

how deep is the sap in the pan?

[mathprofdk]

@maple dayes - About 1.5". I don't want to run any shallower until I get a better idea of the evaporation rate. I'm just doing batch processing, do I do have a pre-heater set up. It can get a little chaotic with two little kids to check up on, though.

I wonder if that BTU number is a mistake, though.

@ACollette - My guy says that it shouldn't be the pressure from the house.

[802maple]

Like Russ says you shouldn't need a stack on that type of burner. probably sucking the heat out. I would run at an inch or less also.

[PerryW]

I wonder if that BTU number is a mistake, though.

@.

I searched on this site and 300,000 btu might be about right. 300,000 BTu would would be equivalent to a 2.1 GAL/Hr Nozzle on an oil burner, which looks about right for a 2x3 or 2x4 sized evaporator.

Guess I leaned something today. Even a small evaporator puts out more heat than a house furnace!

[maple dayes]

we run 3/4 to 1 inch on our small rig any depth much more than that and the boil really slows down. i would try at least 1 inch

[ACollette]

PerryW,

I don't think he is producing the 300,000 BTU's. That evaporator would be really boiling if he was. He is not getting enough fuel supply to feed the size burners that he has on the rig. Just because he has three big burners doesn't mean that they are being supplied the way they would in a commercial boiler set up. He only has a 1/2" feed of Natural gas at less than 1/2 psi. You can have a truck engine rated at 500 hp but if you only have one injector supplying it you will not get the rated capacity, same theory applies here.

[mathprofdk]

Based on the flames I've seen, I think ACollette is likely on to something, even though my welder friend doesn't agree. Would moving to 3/4" pipe (probably for next year - too busy to make that change this year) make a significant difference? It'd more than double the cross-sectional area, but will that mean double the fuel, since the pressure isn't very high? Are there any other options, assuming I still want to hook up to the house natural gas line?