Improved Evaporation Ideas?

[lmichel]

I'm having so much fun with the new hobby my wife calls
...watching water boil... :-)

I'm using propane (two kingkooker 105k BTU burners) on a 24X36 pan from stainless steel creations. Things are going ok, but I'd like to see if I can "bump-up" the evaporation rate with a few common ideas. Can anyone offer any insight as to how much any of the following ideas might help:

1. Use a fan to move air across the top of the pan?
2. Use a diffused flame or a concentrating one?
3. Circulate the sap in the pan as it boils or just let it sit? Right now it only boils in the two hot spots over each propane burner area. This amounts to two spots about 8" in diameter each.
4. Keep the sap shallow as opposed to deep? Such as 2 inches instead of 6 inches.
5. Let the burners rip, or control them so that the sap is just at boiling?

I'm sure there must be some physics majors out there who could really get into this.

Years ago I had a summer job working at a steel plant when I was in highschool. They were in the process of ripping out some huge natural gas evaporators and replacing them with industrial electrically heated ones. Has anyone considered an electric evap?

Lance
Naples, NY

[Jim Powell]

Lance, my setup is similar, propane fired, and a flat pan. Even though the pans are made with very high sides, I was told by the seller, plus have seen it first hand, the depth should be only an inch or so. The thinner the better for boiling effeciency. But you do need to spend a lot of time getting it as level as possible, otherwise it can be half inch deep on one end and scorching on the other. I tried out these pot watcher gizmo's and posted here about them yesterday. I am not 100% sure they made sap evaporate faster, they do make a lot of noise and made me feel better though. If you don't have a pre-heater I would recommend that highly. This is only my third season, so I'm sure you'll get some more tricks from the more "seasoned" citizens here.

JP

[325abn]

Put bricks around your burners.

Rig your burners so they are about an inch or so from the bottom of your pan. I did this using heavy 1/2 wire cloth. Let your burners rip.

Keep sao level at 1.5 - 2.5 inches. Make sure your rig is level.

Rig up some sort of preheater so you only put sap that is at a rolling boil into your main pan. I did this using brick on both sides of my rig. I just used a backing pan for a pre heat pan.

When you get close to syrup never leave your pan. Things change fast at this point.

[Mac_Muz]

How long does it take to boil off 40 gallons that way?

I just built a rig, and fire it with pine. I don't believe I used a 1/6th cord, and boiled of all I have 41 gallons, in 7 hours. That made 1 gallon and 24 ounces.

I can get my pan boiling like mad at 4.5 inches deep. This pan is 21" x 33 3/4" x 6".

The wood I planned to use I can get out of the ice it is in, not even with a Bob Cat! So I went and cut down about 1/2 cord of dead, barkless white pine. None were bigger at the cut than 8 inch diameter.

[TomE]

Lance,

I am tinkering around on a design for an electric evap pan. The idea is to use several industrial heating elements called a "strip heaters" mounted to the underside of the pan. The limitation I see for the average hobbyist is the power--you can only get 7200W out of a household 30A, 240V circuit. This works out to only 24,576 btu/h, and maybe only about ~3gal/hr--disappointing. If designed correctly, the pan could be set up with multiple temperature "zones" along a sectioned pan. The heat source would be also very controllable. Strip heaters are also not cheap--would cost about $300 to outfut a 24" X 36" pan. Compare this to hot water heater elements at $8 a piece! I will probably build my next setup out of a steam table pan and hot water heater elements. If nothing else, the electric heating elements are very efficient--all the power goes into the liquid and doesn't waste energy heating the surroundings. At my scale (making a quart or so at a time) only costs ~$2.15 in energy costs).

Just thoughts...
Tom

[325abn]

Lance,

I am tinkering around on a design for an electric evap pan. The idea is to use several industrial heating elements called a "strip heaters" mounted to the underside of the pan. The limitation I see for the average hobbyist is the power--you can only get 7200W out of a household 30A, 240V circuit. This works out to only 24,576 btu/h, and maybe only about ~3gal/hr--disappointing. If designed correctly, the pan could be set up with multiple temperature "zones" along a sectioned pan. The heat source would be also very controllable. Strip heaters are also not cheap--would cost about $300 to outfut a 24" X 36" pan. Compare this to hot water heater elements at $8 a piece! I will probably build my next setup out of a steam table pan and hot water heater elements. If nothing else, the electric heating elements are very efficient--all the power goes into the liquid and doesn't waste energy heating the surroundings. At my scale (making a quart or so at a time) only costs ~$2.15 in energy costs).

Just thoughts...
Tom

If you truly get the bug you wont be satisfied!! :) :)

[lmichel]

Thanks Tom,

Hmmm.... Heat Strips... I guess those would work better than my original thought of using spring coil elements in a shallow fire brick bed that the pan would set on. I have a little experience with glass annealers and I know that I can get a 2'X2'X2' chamber at 1950F with about 25Amps using coils.
Can heat strips make direct contact with the pan? Coils are conductive, so I was thinking about how to make darn sure they would never touch a pan even by accident. Maybe heat strips could be used on a pre-heat pan?
I'm also very interested in how you calculate the BTUs provided by an electrical element.

I think I'll stick with propane this year and maybe experiment a little with heating elements next season :-)

-Lance

[TomE]

Lance,

Yes, the strip heaters are meant to be direct surface mounted (BUT NOT SUBMERSIBLE)--the coil is isolated from the strip heater case, and you can even get them in stainless steel as to not let them corrode.

To your question of BTUs for an electric heater element...Most electric heating elements are rated in Watts (which is also the current [in amps] multiplied by the Voltage). The number I mentioned before (24,576 BTU/h) is a direct conversion of Watts to BTU/h (the conversion is 3.413 BTU/h per Watt). Just watch out for the units when dealing with BTUs (note the "/h" I put on the end)--BTU without the "/h" is actually a measurement of Energy as opposed to Power (which is Energy/time)—I think most burners are actually rated in BTU/h even though they leave the "/h" off most of the time.

I am boiling in a HDPE plastic bucket this year (about 1.5 gal/hr), but will also do something different for next year--I would like to get my boil rate up into the 5 gal/h range.

Hope this helps,
Tom