Improving the Evaporation Rate

[docsmaple]

I built a new evaporator this year out of an old fuel oil barrel. I welded up some 20 gauge stainless pans to put on top. The pans measure 27" x 88" which is pretty good size. I have 3 pans, the last two connected with a valve. They are all flat pans. Here is the problem... Im only evaporating around 12 gallons an hour and its killing me. Not to mention its consuming my wood supply! What are my options to increase my rate? I would like to flue my middle pan eventually but really not sure how to go about that either, especially since my pans are only 20 gauge. Any thoughts or opinions would be greatly welcomed.134361343613436

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[WoznicaSyrup]

I have a 2x5 arch with two pans on top, 28" is taken up by my finish pan (fairly large for its job) and a 25" flue pan on the back with a preheat pan that sits over half of the flue pan. Sap enters my flue pan at 120 degrees and I run my pans about an inch deep maybe a little less. With all of that I boil around 22gph. At 12 gph that's quite slow for your size arch. I would say you would find the biggest difference by getting a flue pan in the works and have it take up the space of two of your pans, with just a single finish pan up front. Also a few questions - How big is your fire box? Have you closed off any of the tank or does the fire have to heat up the entire space? What temperature is your sap entering your pans? How deep are you running your pans?

[TerryEspo]

A few more pics of the inside of your arch would help see what is going on.

Pics from the top down, inside the body of your arch,,,,front pics are good, now a few more from different angles.

[Tater]

Are you using forced air or natural draft? At 12 gph for a pan that's over 2x7, I'm guessing natural draft, because I average 10-12 with our 2x4 flat pan with forced air. Here are some tips to help you out.

1. Dry wood. With natural draft, any moisture will kill your fire. We can force green wood to burn if we mix it with dry, but even with forced air it slows the boil rate.

2. Teeny, tiny kindling size pieces of wood. Coals are not your friend. You aren't needing low, even heat; you need flames, because the more flames you have, the more heat. Chop the wood into too-small of pieces, then split each of those pieces in half.

3. Fire often. With small sticks of wood, your wood will disappear quickly. For max boil rate, you should be firing every 5-7 minutes.

4. More stack. With natural draft, the only thing drawing air in is the vacuum caused by heat expanding the air and rising out the stack. Increasing either the stack diameter or height will help.

5. Enough draft? Have you tried boiling with the ash door open? Perhaps getting more air up through the fire would help.

6. Sap depth. Keep the sap level in the pan as low as you feel comfortable with. A flat pan doesn't have the rapid, violent boil of a flue pan, so don't be afraid to push the limits. Your signature says you have a float system, so if you trust it, run the sap level down to 3/8" or less. We occasionally run lower than that without a float box! :o

7. Forced draft. This will be the single biggest enhancement you can make, and it doesn't have to be expensive. I use two high CFM computer fans each funneled into a 2" pipe that goes right beside the base of the door on either side blowing onto the base of the fire.

8. Preheater. Lots of good ideas here on MapleTrader. Use the search box, study the designs, use your own ingenuity, and work something out.

9. This might be nit-picking, but the first thing I noticed in the pictures was the valve/pipe between the last two pans sticks way out. Copper pipe is an excellent conductor, and that much 3/4" pipe exposed to cold air is cooling your boil somewhat. It may not be that significant, but every little bit helps, right?


Disclaimer: I've only been making syrup for two seasons and have only spent a few months here, but I like to help out as much as I can. Maybe someone with more experience can be of more help.

[WoznicaSyrup]

After looking at the photos the OP posted I can see that there is a piece of tin angled up towards the on at the back of the firebox. That's a solid idea, but do you have anything under that tin to help insulate the firebox and keep the heat where you want it?


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[docsmaple]

The piece of metal that ramps the air up into the back of the evaporator is just roofing steel, and no it isnt insulated behind it. Should I have a smaller firebox with a vertical wall directly behind it that goes maybe 6" from the top before turning it horizontal? What is typically used to insulate behind it? I do trust my float system, but it is bulky and wouldnt allow me to run that shallow. I have never seen what type of floats they use on a professional setup. The other problem is that I had a buddy that welds for a living weld my pipe adapters on the sides an inch and a half up off the bottom. So if I want to draw off any syrup... I have to be at least an inch over that. That will be something ill have to fix in the off season. Also, should my grate be closer to the pan? would that help me not go through as much wood? I'll have to take some more recent pictures when I get home from work. Thanks for all the insight and experience!

[cfenton86]

Defiantly need some insulation in the fire box. Ceramic blanket covering all the walls inside your arch and firebrick around walls where the grate is would be a real improvement. If your arch is to hot to stand next to then your losing a lot of heat that should be going to the pans.

[eustis22]

in a pinch you can use sand or vermaculite underneath your ramp to insulate.

[JDP]

The whole idea is to force the most BTU's to the bottom of the pan to evaporate the most GPH.

Several observations of the pictures.

1. No fire brick of any kind. (your heat goes out the sides and bottom)
Brick the firebox including the walls right up to the pan. (Old red clay bricks are the cheapest alternative to fire brick.)

2. No insulation of any kind . Fill the void behind the arch with sand / gravel - Buy a ceramic blanket and run it up the arch. Also fit it to the sides.
(alternately Roxul insulation will not burn up to 2200 degrees - Ceramic blanket 2400 degrees - Big Price difference considering you likely wont fire over 1000 degrees)

3.Get your rig totally protected from the wind, many GPH are lost to the wind.

4. Fire with small wrist size pieces of (hardwood = most BTU's) wood in a box crib pattern

5. Add a blower..... this is a huge GPH increase (think "Blacksmiths forge")

6. Preheat sap - Get a head tank and run some copper tubing onto the hottest part of your stack or rear of evaporator. The heat transfer from the stack to the copper is tremendous. Use a ball valve to adjust the flow of sap through the tubing. You can gain huge amounts of heat from this. (Copper needs to be in direct contact with the steel for best results) We had ice cold sap (33 degrees) running through about 25 feet of 3/8 copper tubing and we got the temp up to 120 degrees out the end at about 1/2 way on a ball valve. If we get our copper directly on the steel we will hit 180 to 190. That hot sap will not kill your boil and will increase GPH)

7. Enjoy --- Everyone of the previous suggestions will make your rig boil at a higher GPH rate.

[michiganphil]

Filling the arch behind your ramp with perlite or vermiculite will be way cheaper than bricks or blanket. You can get big bags of it at landscape supply stores for cheap, and it's way lighter than bricks. Fill that space up to within a couple inches of the bottom of the pan. This will force the heat next to the pan before it exits the stack.

[Tater]

Nature will also force heat up to the bottom of the pan. Heat rises, ya know. Without forced air chasing the heat all over the place, the heat rises straight up and then works its way toward the stack. Yes, some of it radiates out through the sides and a tiny bit down, but very little goes down (ever see ice fishermen build a fire on the ice?). Insulating behind the roof metal will do virtually nothing.

I boil with a 2x4 flat pan sitting on a 2x4 metal frame. It's insulated on three sides with Johns Manville R-13 batts (yes, it melts when it touches the side of the metal arch when it's cherry red). The insulation is propped in place by cinderblocks and concrete chunks. Our firebox is the full 2x4, and the stack is a six-inch pipe that goes straight out the center of the back of the arch for 3 feet before turning up. In our very unoptimized arch, we can achieve over 12gph with forced draft (with the fans blowing air all over the place and losing tremendous heat out the uninsulated front (can't stand within 3 feet of the door for more than a couple minutes)). Again, I don't think insulating behind the ramp will make a noticeable difference.

[docsmaple]

Okay. I'll have to do some insulating for sure. I cant stand next to my evaporator for more than 10 seconds when she is full bore. That would make a lot of sense to keep that in. I'm in luck bc my father owns an insulating company on the east side of the state. I know he carries the fire proof steel wool looking stuff. Would that be okay to add behind the ramp? or do I need something more dense like sand or vermiculite? Also. Ive always thought about wrapping the copper tubing around the stack but ive got a buddy that says it will flash boil and is more trouble than what its worth. Ever have that happen? I did not get a chance to take any pictures yesterday. I actually had my makeshift shack collapse under all the snow we got in Michigan yesterday. I thought the tarp would have tore first... but it ended up snapping the 2x12 beam I had running across the top! I didnt make it home in time to push the snow off.

[cfenton86]

Yes, "the fireproof steel wool looking stuff" is what you need. Insulate the entire firebox if you can get a bunch of that blanket. As far as the copper tubing around the stack, it shouldn't boil in the tube as long as the sap is flowing into the pan at a steady rate. If you get your boil rate up then you should be calling for more sap which would keep things flowing in the copper tube.

[JDP]

You need to put your tubing on the pipe or the back of your evaporator so you can remove it when you run out of sap. Otherwise the sap will boil and burn inside the tubing and ruin your next batch. Placing the copper coil on the back of your evaporator (if you have that hot metal available) will transfer a tremendous amount of heat when copper is directly held against it!