Pre-heat wtih coil around chimney pipe

[Woodsrover]

I have a Mason XL with a pre-heat box and for the most part it boils very well. Though it has the pre-heater, that only takes the chill of the sap and doesn't really warm it. When I'm boiling well and in turn feeding sap pretty quickly, only the rear 1/3 of the first channel will boil if I'm lucky. Turn the feed off and the whole channel will boil nicely after just a minute or so. If I can feed near-boiling sap into the first channel I should be able to boost the efficiency of this pan by 20%.

I was thinking of T-ing off my feed pipe and wrap a 1/2" coil of soft copper around the chimney and feed that into the evaporator. Will have valves on both ends of it so I can adjust the flow and will maintain the original pre-heat tank so I can adjust or flood if necessary. I try to maintain a 700-degree chimney so there's a lot of heat to use there.

Has anyone done this with any success?

[claystroup]

I have thought about doing the same thing but only then wrapping the outside of the chimney pipe/copper tubing with ceramic blanket attached with big hose clamps. That would really force the heat into the copper tubing with sap running through it. Thoughts?

Clay in Michigan

[Tweegs]

2 words: vapor lock.

Stack temp will be higher than the boiling point of sap.
If sap starts to boil in that copper…

[Woodsrover]

2 words: vapor lock.

Stack temp will be higher than the boiling point of sap.
If sap starts to boil in that copper…

I could see that happening but with a little tweaking should be easy to prevent. Even if I play it save and introduce even 150-degree sap into my pan instead of 50-degree sap I'll gain a good deal of boil in the pan. I think its worth a shot.

[Woodsrover]

I have thought about doing the same thing but only then wrapping the outside of the chimney pipe/copper tubing with ceramic blanket attached with big hose clamps. That would really force the heat into the copper tubing with sap running through it. Thoughts?

Clay in Michigan

I have a roll of header-wrap sitting here on my desk as we speak....

[sams64]

I have been running a set up like claystroup described for 2 years. It does get the sap nice and warm, it can vapor lock. Some things that i am going to change this year to prevent vapor lock are:

1) I am going to wrap the coils going up the stack, so cold sap enters low and warm sap exits high.

2) Move my vented loop from the inlet side to the outlet side.

3) raise the height of my header tank.

The purpose of these changes is to allow any bubbles that from to travel out of the system with ease, instead of locking up the system. By coming in low and out high the bubbles will want to travel with the flow of sap, instead of fight it. Moving the vent will give the bubbles a place to escape in the direction they want to go. Elevating the header tank will create more static head to push any air bubbles along, instead of stalling.

sam

[Tweegs]

Had trouble with my preheater vapor locking. Was trying for temps around 190. Backed off to 150 and had no further trouble. Still had a good boil in the flue pan, too.

Start up and cool down could cause problems for you.

At start up, it seems the stack is going to get hot long before you reach a boil and start moving sap through the copper.
This is one time you could have sap boiling in the tube.

If you run out of sap at the end of the boil and the copper goes dry, you will burn the residue inside the tube.

Not saying it can’t be done, those are just a couple of things to think through.

[lpakiz]

Wrapping your coil with ceramic blanket, while efficient, is messy. You could probably accomplish the same thing with a tin (SS) shield around the coils. Pretty sure you will need something like that to achieve high enough sap temperature.
When you run out of sap, be ready with water. Have a way to divert the water to a pail so it doesn't go back into the pan.