Preheater.

[vach50]

I'm looking at different options for a homemade preheater. I know about wrapping copper tubing around a chimney. This won't work for me for a couple reasons. Instead I was thinking about running copper pipe or tube, or galvanized pipe inside my exhaust stack. Anyone else try this? How much tube or surface area will I need to heat up the cold sap as much as possible? Last year I average 15 to 18 gph evaporated. Thanks.

[maple flats]

Do not try galvanized, you would ruin the syrup.

[NhShaun]

I've heard that people scorch their sap In copper lines wrapped around the outside of single wall stove pipe. I can only imagine it would be even worse with copper coiled on the inside of the stove pipe. I suppose if you kept it flowing constantly it wouldn't be as bad, but still the risk of exploding boiling sap.

[McKenney Maples]

I'm looking at different options for a homemade preheater. I know about wrapping copper tubing around a chimney. This won't work for me for a couple reasons. Instead I was thinking about running copper pipe or tube, or galvanized pipe inside my exhaust stack. Anyone else try this? How much tube or surface area will I need to heat up the cold sap as much as possible? Last year I average 15 to 18 gph evaporated. Thanks.

I’m not sure I would try this, but it would be a fun experiment. I would build a shell and tube style heat exchanger with the smoke traveling through the tubes and sap in the shell.

[Johnny Yooper]

I'm wondering if locating the pipes inside the chimney stack would get sap in the pipes too hot and possibly lead to scorching/vapor lock, but if the flow was fast enough you might be ok, as said above would be a good experiment. One test is worth a thousand opinions. The last several seasons I've been running 40F sap through copper tubing coiled around the outside of my single wall chimney pipe and it comes out at 160F so been working good for me.

[Bucket Head]

I wouldn't bother experimenting with an 'inside' version. It will only lead to scorching and vapor lock. 160F with your current set up is really good in my opinion. You know, if it's not broke, don't fix it- kind of thing.

Also, with any style pre-heater, flushing it with water immediately after running out of sap is the only way to prevent scorching of leftover sap and an overall buildup of "crud" that you'll never get out. Most folks would be shocked if they could see the inside of their tubes. Right when the last of my sap gets to the float box is when I rinse the feed tank out and then I send a few gallons of water through the preheater while it's still hot/warm. A clean preheater is a happy preheater.

[misterclassic]

I did it last year on my stack but coiled it on the outside, then covered it with 1/2" ceramic insulation held in place with wire. I ran the sap from the top down but will run it from the bottom up this year so I don't get air pockets. And I rinsed it each time I shut down. I put an extra valve at the top and bottom of my coil for this purpose.

[Sugarmaker]

I'm looking at different options for a homemade preheater. I know about wrapping copper tubing around a chimney. This won't work for me for a couple reasons. Instead I was thinking about running copper pipe or tube, or galvanized pipe inside my exhaust stack. Anyone else try this? How much tube or surface area will I need to heat up the cold sap as much as possible? Last year I average 15 to 18 gph evaporated. Thanks.

You can try various options; having a hood and a conventional preheater system is pretty tried and true. What ever you do put in a thermometer port so you can see what temp your getting from your preheater. a std in hood preheater should give you about 190 deg F sap into your boiling pan improving the efficiency about 10-15%.
Regards,
Chris

[RileySugarbush]

You can try various options; having a hood and a conventional preheater system is pretty tried and true. What ever you do put in a thermometer port so you can see what temp your getting from your preheater. a std in hood preheater should give you about 190 deg F sap into your boiling pan improving the efficiency about 10-15%.
Regards,
Chris

I agree with Chris, but would like to point out that 15% efficiency gains are only possible if you get near boiling sap out from near freezing raw sap in. I point this out because I feel the benefits of preheating, while good, are often much less than most people think. In many cases, the cost and effort may be better spent on combustion efficiency. For example, adding a blower or drop flues can give 100% greater evaporation rate in some cases.

I find the biggest benefit of our preheater in the clean distilled condensate since we don't have water at our sugarhouse.

[wlatrout]

Before I had an RO I used copper around the stack. It worked well. I tried it with RO sap and it would burn the sap and vapor lock. Going to do something different this year just haven't decided jet.

[Zucker Lager]

I've been toying with the idea of using a chimney stack heat reclaimer like they sell for wood stoves then duct it to a small heat exchanger like this one
https://www.ebay.com/itm/Water-to-Air-Heat-Exchangers-/301705624921?_trksid=p2385738.m4383.l4275.c10
feed that contraption with a variable speed blower to adjust temperature. You would have from no heat up to what the chimney heat exchanger could deliver depending on the speed of the fan. That might fix the problem of burning / vapor lock????? just a thought Jay

[Sinzibuckwud]

I run a 3\16ths copper line twice around the inside wall of the sap pan submerged. keeps boiling sap coming out up to 5gph and hot sap up to about 8 or 9gph. Have left sap in the system for up to 30 min with no scorching, I do get air lock, generally when the head tank gets low, opening the valve wide open for a second or filling the tank will clear it out.

[Mark B]

I've got an idea for a preheater that involves using two pieces of stove pipe one the same size as your stove pipe and the other one inch bigger... and sandwich a copper line between the two pieces of pipe and then seating it over the first foot or so of your stove pipe.

Say that you have a 6-inch stove pipe from your evaporator... so you buy a 1-foot piece of 6-inch pipe and a 1 foot piece of 7 inch pipe. wrap your copper around your 6 in to give the copper its shape and then set this inside the 7 inch pipe. at the same time unlock the 6 so that it compresses out against the seven and holds your copper in place.

There should still be enough room now inside that unit, the unlocked 6 inch piece of pipe, to fit that copper line sandwich down over the 6" stove pipe from the evaporator and enough transfer of heat that it should preheat the sap running through your copper line. Hopefully with the additional space and layer of metal between the copper line and the chimney pipe it will not allow the sap to scorch inside the copper line. I will have to try to make one of these and take a picture of it. the idea is very clear inside my head.

[maple flats]

I think if you want to preheat using the stack pipe you are best copying what Johnny Cuervo did. Look in his posts, he made a wrap around preheater that can be adjusted for the amount of contact with the hot stack.