copper tubing pre-heater

[sap-evap-orrator]

I saw an idea for a sap preheater using a coil of flexible copper tubing wrapped around the flue pipe. Is this a good idea? Is it safe to heat the sap in copper? Is there any concern about off-flavor being passed on to the syrup or for that matter, contamination from the copper? Any thoughts or input would be appreciated

Thanks and best of luck to everyone this season

[BreezyHill]

Copper is fine, used in our preheater in the steam from the flue pan for over 30 years. It was the heavy wall 1.5" and it finally corroded thru in the end of the 2013 season and I changed it to SS 1.5" dairy pipeline. Still have the same temp at the float box.

Ben

[Pibster]

Coiling copper around the stack won't boost the cold sap temperature very much. I did it one year and it wasn't worth the hassle. Switched to a copper preheater inside a hood and what a difference. The sap was extremely hot coming out of the preheater.

[Lukie]

I did that for a few years and with enough coils i was going from cold sap to Luke warm BUT the problem was that you could not turn the flow off because it would burn the sap in the tubing! and would cause the sap to boil into the line and back feed steam into the sap tank or bucket.The way i solved it was never turn it off and when i ran out of sap i would flush it with water so the the sap would not burn in the tube.Run the water into a bucket and it gives you warm water to work with

[Sugarmaker]

Lots of folks have tried it. Results vary. Most effective preheater is in a enclosed steam hood over the rear pan.
Regards,
Chris

[optionguru]

As already mentioned it works ok but not great. I did 10 wraps around my 6" stack and then took a section of 8" pipe and put it around the whole thing. I did have hot sap coming out but the problem like Lukie mentioned is that once you're out of sap you have to switch it to water and have that flowing somewhere else so you don't burn the tubing or the sugar inside of it.

[sams64]

This is how I preheat as I do not have a hood. If you just wrap the copper around the stack it will do very little. But, if you wrap it around the stack and then insulate over the copper it will get between warm and very hot. MY biggest issue is when I don't maintain my header tank level and the the copper starts to boil sap in the the preheater and then vapor locks. It takes me a while to cool it down enough to run clean sap and then flush the burnt stuff out. I am going to change the arrangement a little this week so that I can add a vent, hopefully this will stop any vapor locking.

I have a valve to regulate flow and not a float box. If you have a float box that tends to completely stop the flow you will most likely end up with lots of boiling in the preheater. (not good) if I need to stop adding sap I just run the preheater into a bucket.

When I have the system balanced just right the sap is entering my pans at about 160F. This makes a huge difference in boil rate as compared to sap that enters at ambient temps. I would guess that it adds 3-4 gph to rate of evaporation.

Sam

[11-Nick]

I'm going to beat this dead horse.
I know this type of preheater has been hashed through and through, but I'm still going to ask a question.
I looked for the specific thread, but couldn't find it.... someone made a copper coil around the stack. the sap entered the bottom of the coil and wound upwards around the stack. At the top, they put a tee with one leg going up above the head tank, and the other leg going to a valve just before dumping into the pan.
This setup seems to solve the problem of vapor locks.
The problem of getting more heat into the system (if you are only getting luke warm sap out of the preheater) is to insulate around the coil. A removable layer of insulation and/or flashing added after the boil gets going good would seem to get the heat up. Taking the insulation off during fire up and shut down should allow the coil to stay cooler, reducing (not eliminating) concerns of boiling whatever is in the line.
The only question I have is with shutdown. Once you run out of sap, and you run 5 gal of water through the coil... does it hurt to leave the copper sit empty? Uninsulated on the outside of the stack, the copper wouldn't melt even with the evap at a full boil, much less during shutdown. The only thing I can imagine being effected would be soldered fittings, or an off taste when fired up the next time due to the copper coil sitting empty while hot during previous shutdown. I didn't see this specifically addressed in any threads I looked at tonight.
Apologies for the dead horse. I don't have a hood, so preheating options are very limited. I'm boiling on a 2x4 pan and have little to no boil in almost the full half of the pan where I'm currently trickling sap in. Would love to gain some boil there, as the bubbles in the front half of the pan are looking incredibly lonely.
The only question remaining to me is the issue of