Poor man's preheater

[jfroe939]

Here's an idea to pre-heat sap in a big pan on a homemade rig: if you have a non-insulated stack. Buy copper tubing a shade size smaller than regular sap line is. Have your sap tank elevated about 7-8 feet in the air on a stand then have a fitting that runs sap out of the tank's bottom to go through the regular sap line. Next, connect the end of the plastic sap line to the copper tubing about 2 feet away from the evaporator's stack so heat won't screw up the plastic tubing. Wrap the copper tubing tight as possible around the stack in a coil. Let the sap flow. The resulting sap that comes out of the low end of the copper tubing should be pretty darn hot now. To keep the copper tubing in place, use regular wire like on an electric fence to tighten it up. Further, use regular aluminum foil and wrap a few, long sheets of it around the tubing kinda like insulation. The trick is to keep the copper as tight and as close to the stack as possible because you're looking for the metal to be in physical contact with each other. Radiant heat resulting from not wrapping the copper as tight and creating gaps will mean cooler sap than a nice tight wrap would create. I had 40 feet of copper on an 8" stack and that did well when the copper was tight. That made sap that was painful to the touch when it came out. The only problem you'll have is that at the end of the day, you'll have to disconnect the sap line from the copper so it doesn't melt the tubing. Leave the copper in place. The problem that develops is that the tiny remaining amount of sap still inside the copper tubing boils and the sugars turn into a black crisp on the inside and it can plug your copper line. Solution: use your air compressor to blow it out. Hope this helps somebody.

[KenWP]

Wonder why we never thought of that before. You could swing the end out and run water thru when you finish up.

[Gary R]

Ken, that "We" should be an "I":) . Quite a few people have done that on this site. That will work for the very small producer. Say a guy that can remove his pans if the preheater gets clogged. Others have experienced vapor locks and of course the black stuff plugging the line. I would hate to have my preheater clog up inthe middle of a boil when you need to be drawing off.

[petersp22]

Kinda like this?
http://stevepetersen.smugmug.com/Other/2009-Sugar-Season/IMG1417/510457356_LkHHE-M.jpg

I used 10 feet but might add another ten for this season. Another thing I was thinking about was wrapping it with some flashing, like you suggest. When I'm at the end I just dump a few gallons of water in the tank and swing the end of the preheater tube over a bucket and let it run while the fire goes out.

[lpakiz]

Yep, got the same thing. I wired a piece of tin over the coils before insulating with fiberglass building insulation. Worked pretty good.

[Jim Schumacher]

Steve, is that .375" tubing?

[petersp22]

Quarter inch.

[Jim Schumacher]

Quarter inch.

Quarter ID?

[KenWP]

Ken, that "We" should be an "I":) . Quite a few people have done that on this site. That will work for the very small producer. Say a guy that can remove his pans if the preheater gets clogged. Others have experienced vapor locks and of course the black stuff plugging the line. I would hate to have my preheater clog up inthe middle of a boil when you need to be drawing off.

That should be WE when I am being fastidious as there has to be 40 threads on this already. And if you put a way to swivel the tube or if you run a bit of water thru it and clear the sap it will not burn. The temp of the stack will not get hot enough usually to melt the copper unless it's red hot but just in case I made a swivel so that I can just run plain water thru and not get the copper two hot..

[mtbguy]

Why not snake the coil without going all the way around the stack. Then you could just wire the preheater to the stack and remove it when you don't need it. I don't know how else to describe it but the coil would only be on the front or rear of the stack in a back and forth pattern. This isn't my idea I think I saw it on this site in someone's pictures.

[petersp22]

I tried that but couldn't get the coils tight enough to the stack to make much of a difference. Even the bare coils didn't seem worth it so I wrapped the insulation around. It's not a big deal for me to pour a bucket of water in the tank and turn the tube so it runs into a bucket while I'm shutting down. I saw that same picture and didn't they use springs to pull the coils of the "snake" together? Didn't seem worth my effort.

[petersp22]

Jim, for your reference. While I was at the hardware store I checked on my tubing particulars - 1/4 inch refrigerator supply line. 1/4 inch is the OD. When I flow 5-6 gph through 10 feet around a 500-600 degree stovepipe I gain about 60-70 degrees. It helps keep the boil going. When I throttle it back I can make steam pretty easy. So I'm thinking if I add another 10 feet it will still be manageable.

[maplesyrupstove]

Check out ( Johnny Cuervo ) site, for pictures of his preheater.You can take it off when sap is all gone. Darrell

[Maplebrook]

I made a preheater like this from 50' of 3/8" copper tubing. I cut it into 2- 25' pieces, made a manifold on the end of the supply line from the tank, and put a valve on the 2 outlets. It would boil the sap in the tubing if the flow was slowed down too much. Had a problem wrapping the copper tight around the 8"pipe, but...wrapped it around a length of 7" then slipped it off that and jammed it over the 8" stack. Worked great.

[maplesyrupstove]

Maplebrook , were are you in N.S. Darrell

[tylerj]

I'm thinking of doing this also as a preheater. One thing I'm not sure of is if the shutoff was between the holding tank and flue pipe if you turned off the tap for whatever reason and the flexible copper around the flue was empty, what would happen when you opened it up again later when you are ready for more sap? I'm thinking of the empty copper tubing being very hot and then all of a sudden you add some sap to it. Any safety concerns there??

Would it work to have the shut off after the coiled tubing around the flue so that the tubing is always full of sap? Would the heat migrate upwards into the holding tank or would the sap in the tubing boil and scorch in place if the valve was turned off? I realize the idea would be to always have a steady trickle of sap going into the pans but being new at this I can see that I might run into times when I don't want more sap going in. Any thoughts?

[KenWP]

When you cut down the flow of sap going thru the copper tubeing it boils real quick and you get bubbling back the supply tank. It sounds like the old hot water heater lines in school. I found it was better to have a way to divert the sap to another container so it keeps running and does not get to hot. That and when you run out of sap it helps to run water thru it to clean the sap out and to not get the tubeing to hot untill you have pure water going thru. You also have to have good valves on the tubeing. The first valves I used would shut down when I had sap trickling thru them and I had to constantly regulate the flow. I got better 1/4 turn valves and then stopped that problem.

[Maplebrook]

Good thinking Tyler
I have had both of your scenarios happen with my preheater. If the tubing sits empty and cold sap enters, it sputters for a few seconds as the cold sap works it's way down. Some burnt sugar will come out the pipe, I caught it in a dipper and tossed it. Once the pipe cooled, everything was fine.
If the flow was stopped with the tubing full, it would boil, create pressure, and in my case blow out the coupling where the flexible sap tube met the copper. to solve these issues, which only happen at start up or when you run out of sap, was to leave them trickle into the pan, dip it out and dump it back in the tank.
Good idea Ken had to divert the sap.

[tylerj]

Thanks for the info guys. What about adding a return line back to the holding tank to create an closed loop system? So after the coil there would be a tee with a shutoff on both sides. One to the sap pan and one back to the holding tank. When the valve is open to the evaporator the return line is closed to bring the sap down the preheater and into the evaporator. If you want to turn the sap off close the valve and open the other to create the loop. Then the heat should circulate the sap within the holding tank. Would that work ok?

[KenWP]

Well if the holding tank is above the evaporator you would have a problem on gravity to get sap to go downhill and then back up hill. The feed line for the preheater would already be at the bottom of the tank.

[Maplebrook]

Tyler,

A closed loop system would work, but as Ken alluded to, don't forget about gravity. I'm assuming your sap tank is high to allow the sap to flow down through the preheater.
In my experience, it's a small amount of sap (less than 10 litres) that would flow during the times when you don't want sap coming into the pan. To make it easier, could you divert it into a sap collection jug and pour it back into the tank?
I tried to attach some pictures of my old rig but ran into problems. Looks like I'll have to consult inhouse tech support (wife or son) to do this.

Happy Remembrance Day fellow Canadians!
Darren

[tylerj]

Actually I think gravity is what would make it work.

From google..."The principle of the thermosyphon system is that cold water has a higher specific density than warm water, and so being heavier will sink down. Therefore, the collector is always mounted below the water storage tank, so that cold water from the tank reaches the collector via a descending water pipe. If the collector heats up the water, the water rises again and reaches the tank through an ascending water pipe at the upper end of the collector."

It would be a thermosyphon system similar to a batch style solar water heater described above. No pumps just natural convection. As long as the heat source is below the storage tank. I was going to have the tank above anyways to provide the drop for the sap to flow into the coil.

Emptying into another pail would be probably simpler but hey where's the fun in that lol??? I have some extra valves anyways so I think I might try it. It would be very self contained that way at least.

Yes happy Remembrance day!


my g.grandfather.... http://www.vac-acc.gc.ca/content/collections/virtualmem/photoview.cfm?casualty=563943&photo=21629

[Maplebrook]

Sounds interesting enough.

I wouldn't run it continous due to running hot sap back into the storage tank. You want the raw sap to stay cool so bugs aren't growing in a nice warm sap tank and then the tank sits between boils and allows them critters to mutiply.

[KenWP]

Actually I know it won't probbably work because I already tried it. It does send a tiney bit of sap back to the tank but not a whole lot. It spurts out and then stops and then spurts a bit more. At least it dosn't get burnt. If some how you could put a one way valve in the tube it would give you constant flow as the hot sap could only flow the one way. But where to find such a critter except on a coffee maker tube I have no idea.

[tylerj]

Sounds interesting enough.

I wouldn't run it continous due to running hot sap back into the storage tank. You want the raw sap to stay cool so bugs aren't growing in a nice warm sap tank and then the tank sits between boils and allows them critters to mutiply.

Yes I was thinking of just doing this for the preheater tank only. Sap that would be used up during that days boil. I shouldn't have referenced it as a storage tank as that would be outside staying as cool as possible.

Ken thats interesting it didn't work for you. I wonder if both lines to the tank were at the same level possibly? So that the heated sap was able to go in either direction which would stop it from creating a current in one direction only. I was thinking if the cold supply line was lower than the lowest point of the heated coil that the heat would only go up and create the convection current. I'll give it a shot and see what it does.

[Brent]

The thermosyphon would kick in - backwards

The hot sap would end up back in the overhead tank.

[DanE.]

Since I'm waiting for my fire bricks to dry, well the cement in between them. I was thinking on how to improve my pre-heater.

Has anyone create a water (or sap) jacket opened on top around their base stack? This would have excellent heat transfer and no vapor lock issues. add a float valve to it and your all set, of course a second float valve on your flue pan.

I thought about doing this last spring, but forgot when I made my new stack base.

any thoughts?

[Toblerone]

In my first year, I tried this coiled-copper-around-the-stack type of pre-heater. I thought it was more trouble than it was worth. It kept sputtering when I'd least expect it, and I had trouble with burned sap. They guy I was sugaring with was pretty good at getting it to work well, but for me I felt like I had better things to do than fiddle with it.. and I love fiddling with things.

Now I use a turkey fryer burner (just burner, not the pot) under my preheater pan.. one of the ones that is supposed to sit on top of the evaporator pan. I never understood that, by the way. The only way any significant heat can be extracted from the steam is to condense it, but if the condensation water just drips back into the evaporator, you've not gained a thing.

DanE, I've thought about that too. You'd have to have a special pan that curved away from the stack before it reached the top. Then always have sap above the line where it curved away so no sap would scorch. I'd rather look at ways of extending the arch itself another 2 feet. That's essentially what you'd be doing anyway.

Dave

[Otterguy]

I have been reading this and other treads on preheaters and think I have a solution which I will try shortly and let you know how it works out. First I will make a U shaped removable coil to fit at the base of the stack. The top and bottom tubes will be attached to a cheep stainless steal 12 qt stock pot. When full of sap this will create a closed loop sap heater. The cold sap at the bottom will thermo syphon up the coil and go back into the pot and continue doing so.

A line will feed sap from the storage tank to the preheater pot and a line will feed sap from the pot to my back pan. As I use a float valve in the back pan to keep a constant sap level in my pans I will need a second one in the preheater pot to maintain it's level. Therefore as sap draws down in the back pan it will slowly but steadily be replaced with warm sap from the preheater and the preheater will refill as well. I presume that the draw off will be slower than the circulation of the sap going through the 3/8 coil and therefore heat up. This way the sap will never stop flowing in the coil and not burn or require a steam pressure vent. I guess I will have to put the pots outlet near the top of the pot as cold sap will go straight to the bottom. But manageably slowly as the flow through the preheater should be a lot slower than the flow through the coil.

It will have to sit it on some sort of sliding table so at the end of the run I will be able to slide it back off of the stack to so as not to burn. The remaining sap in the pot can than be added manually. Once my pans get down to scorching level I have to stop and finish anyway but I won't have any issues with the preheater over heating.

Any thoughts or suggestions?