1/4 inch preheater

[wobbletop]

I retried with my last boil (I'm a small backyard guy with 20 taps on a barrel evaporator).

I was mainly worried about the sap flash scorching in the tube. I used 10' of 3/8" copper tubing wrapped about 6 times around the stove pipe. It was wrapped as tightly as I could but it was not 100% in contact since the stove pipe isn't completely round. I also made sure to have a constant downward wrap as I was worried about having a place where something could just sit in the tube and boil. This would make sure the tube would drain by itself.

I used the aquatec 8800 from my RO system to provide the flow. I used 1/4" line to connect the pump to the copper with about 18" of wrapping coming off the stove pipe to try to prevent the heat from the stove pipe from melting the plastic 1/4" tubing.

Initially I had the wrapping high on the stove pipe as that's less hot, but I pulled it lower as I got more comfortable using it.

I had the sap recirculating to my 32G sap storage, but it was obvious that that would not raise the temperature very much or quickly.
I switched to recirculating in a 5G bucket with about 1G of sap in the bucket. This allowed be to increase the sap temp.
The sap was about 50F in the storage, and it would raise to about 85F by the time I needed to add more to the evaporator (about 5-10 minutes).

I don't have a way to trickle into the evaporator yet, so I would add 1G sap to the 5G bucket, wait for it to come up to 85F, then add that to the evaporator, and repeat. I made sure to never have the pump draw air so the flow would stall and potentially flash the sap in the heater tubing.

I could probably double the tubing wrapped or insulate it better to the stove pipe to increase the performance. I could try to add a couple taps from the line to feed both my evaporator trays, but that would be a lot more tubing and connections.

Once I was out of sap, I just filed the 5G bucket with permeate and let it circulate until the stove pipe was cool enough.

image-20190329_120026.jpg

[wobbletop]

One more update....

I was using the RO pump to circulate the sap around the preheater, but I didn't complete my RO the night before my boil, so I was running the RO instead of the preheater during my boil. The next time I tried to use the preheater, there were a lot of copper flakes coming off the inside of the coil into the fluid, so I did not use the stove pipe preheater.

So a warning if you use this method: You either need to always use this method and keep fluid going through the coil, or remove the coil from the stove pipe if you're not going to use it.

I'm not sure if I can recover the coil my running a lot of water through it.

[Aaron Roy]

This is what I did. https://youtu.be/jV5CUXEv6HA. I have added to that since but that is the first video that I made with the tubing. There is another video with tubing and and somemore from this year with my new setup

[Mark B]

I never got back with my follow up. My 3/8 copper wrap worked great. 25' of 3/8 copper sandndwiched between two pieces of stove pipe and placed over the actual chimney pipe. Between placement of the warming tank and the coil my preheat system held the sap at 110f at a minimum. This was from cold concentrate to the warming tank.0418191754c.jpg

[wobbletop]

Thanks for the update.

Are you using forced air or natural draft? Did you happen to measure what your stack temp was near the tubing?

Maybe your insulation idea is what is making it work for you.

[Johnny Yooper]

Previous to this season I was using ten wraps of 1/2 inch copper around the chimney pipe, that took 40F incoming sap to 160F. This year just for grins I doubled the wraps to see what would happen and I hit 178F. I have the tubing wrapped fairly tight so virtually no gaps to the chimney pipe but I think if I cover the tubing with some kind of insulation I could get it somewhat higher, I don't necessarily want to go much higher though. I also did some boiling without running any liquid through the preheater, my soldered coupling joining the two lengths of copper wraps remained intact, then ran sap through the preheater during later boils and didn't notice any issues. I like to experiment and try new things each season, to see what works and what doesn't. Also built a 3'x8' aluminum hood exhausted through ceiling (first year boiling inside the log sugar shack and was concerned with steam buildup), a few tweaks for next year but overall it worked pretty good.

[Mark B]

Thanks for the update.

Are you using forced air or natural draft? Did you happen to measure what your stack temp was near the tubing?

Maybe your insulation idea is what is making it work for you.

I found that without the piece of stove pipe between the actual functioning stove pipe and the copper, it tended to boil the sap in the pipe, scorching sometimes. The extra pipe buffers the heat transfer a bit. Then by wrapping the whole thing with a third pipe it traps the more even heating and helps to push it into the copper without boiling or scorching.

My setup has a draft vent in the door, as well as an air under fire vent I added 2 years ago. I'm still tweaking the auf, but as it all sits, my little homebuilt 2x4 boils at about 14gph. I didn't measure stack temp this year, but I know I need to add 1-2' to my stack this next year to increase my draft.