Evaporator Pan Size?

Greetings!

Long time lurker, first time poster. Last year we tapped 15 trees, and ended up with 6-7 gallons of syrup (can't remember, slept since then) and pulled out about 3 or 4 weeks early as we couldn't keep up with our three turkey fryers running every day; they had a measly boil off rate of 3-4 gallons each per day.

So, flash forward to today, were planning on tapping 25-30 trees, and converting an old 275 gallon fuel oil drum to a wood fired evaporator. Weather permitting we're hoping to do 25-30 gallons of syrup, so 1000-1200 gallons of sap?

Dad seems to think a pan measuring 27"x48" would work swell on the top of the fuel oil tank. My question is, is it worth trying to make it a continuous flow pan, or keep it a flat pan based on the amount we're doing? Or would you scale down the pan a touch, and do some form of a pre-heater to feed the the continuous flow?

End goal was to get away from trying to use the turkey fryers every day, and boil just on the weekends.

Also, metal gauge, I'm looking at using 18 or 20 gauge stainless for the pan...I'm not a professional welder, but it appears scrolling the threads that a thicker gauge is less desirable but more forgiving on projects like this, thoughts?

I'll gladly post follow up photos of the project. Did a hog roaster out of one of these fuel oil drums a couple summers ago and built the trailer it sits on...keep diving in head first with these projects.

Thanks for the feed back and input.

Dan

I would put wide rails on the oil tank so that a 2x4 pan will fit. The 2x4 is a standard size and used pans and replacements are easier to find. When it's time to expand a hybrid pan could be used which will increase the evaporation rate considerably. If you have a pan built for it put dividers in it, it will make the pan stronger. Instead of draining it completely you could draw off the sweet that is closer to syrup and finish that on the turkey fryers. That will be faster than finishing the whole contents of the pan.

1 gallon of syrup per tap is quite a bit to expect. The rule of thumb is a quart per tap on gravity and 1/2 gallon per tap on vacuum as goals and most do not quite reach these on average. It depends on the year, spout sanitation and your trees on how much you will get. I would shoot for around 75 taps (1/2 gal./tap) if you want 25 to 30 gallons of syrup. Make sure you finish to the correct density as under density syrup will give you a greater yield but will also mold easier.

Your pan size would give you 9 square feet of surface area and should do 13 to 18 gallons per hour on natural draft. Using AUF will increase that some.

As far as metal gauge goes, thinner transfers heat faster but is a whole different world in welding. If doing it yourself, I would look at 16 or 18 gauge of 304 stainless. With the size and only boiling on the weekends, I would not bother trying to get continuous flow and just batch boil with a couple inches of depth and trickling sap into the pan.

Most of all HAVE FUN with it. If the wife thinks you are acting a little crazy and obsessed with this your head is in the right place.

I second the 2x4 pan idea. Last season you either had super trees or the finished density may have been on the thin side.
While I usually do more taps, for health reasons I was only able to do 225 taps and I got my best ever per tap, 119 gal from 225 taps. That was on 26-27" vacuum. I've never exceeded .38 gal/tap in any previous year and I've had vacuum for over 10 years.
How did you know when the "syrup" was done? Did you use a hydrometer or hydrotherm? To be syrup the sugar % should be at least 66.5% and I go to 66.9% to match Vermont requirements.
It might be best if you study evaporator design ideas on this forum, then build the oil tank evaporator with a lip design to accept a manufactured pan 2' x 4'. Leave room under it that it will fit drop flues in the future and if you start with a flat pan, fill the space with vermiculite and firebricks. Use a 7" stack so you get good draft and make it 10-12' tall for good draft. Use a draft fan to increase the boil rate. For that a 130-150 CFM squirrel cage blower is fine, new or used.
For a pan, look for a used one to start, Craigs list might find one, or look at the classifieds on this forum. Other places to look are at all of the equipment dealers, for a good condition used pan. The closer we get to the 2019 season the higher the prices go and the fewer the choices become.

Man if you got trees that good I'd like to have some. I averaged .20 gallons per tap last year and that is about where I have been for a few years. I was on 3/16th gravity lines. when I first started I done around .35 on new trees that had never been tapped. Within a couple years that dropped to anywhere from .15 -.28 depending on the year. If you started with new trees maybe that is why you done so well, if not then you probably should check density. So I think your plans are a little optimistic. If your batch boiling your going to most likely need to finish on propane in a pot or have a good bit of sap to start, because that pan is going to have to have at least 5-7 gallons of liquid in it at all times to keep from burning (if I done my math right), and at 2" you'll be around 11-12 gal. while boiling.Thats 5-7 gallons finished syrup or at your rate 200 -350 gallons of raw sap to start with. A continuous flow will give you options to finish smaller amounts and shut down and leave sweet for another day. I would go with cont. flow myself.

The op stated 15 trees, not 15 taps. I have 15-20 big yard trees that yield way more than 6 or 7 gallons of syrup per year, hence his problem. I would go with a continuous flow pan or if you could find one, a good condition hybrid pan with some type of flues in it.

Good point Ed R. It would be important to know the number of taps. Sorry I did not catch that, I was assuming 15 taps.

I use a 24x48 inch flat pan on a 275 gal. oil tank arch, it has 1 inch angle iron around the perimeter to support the pan; before that I had built an arch from a very old water heater and used a 16x24 inch flat pan. I've since modified the oil tank arch to incorporate the 16x24 flat pan; then I added a copper coil preheater around the chimney stack, and after that I added Air Under Fire. All were great improvements, but without question the most noticeable improvement is the AUF, so plan to incorporate that from the get-go. I boil with this rig on weekends only; collecting all the sweet, the 16x24 pan does double duty as I use it as the finish pan on an electric range I modified into a six burner unit. I boil about 500 to 750 gallons of sap per season. Insulate the hell out of the oil tank to minimize heat loss/maximize heat to the pan.....ceramic blanket, archboard, firebrick, etc. Did I mention AUF? I really like the set up I have and I think you will really like the step up in performance from the turkey fryer, which I did and it took me only one season to get out the tools and start fabricating. Good Luck and post some pics.

Maybe this will give you some ideas.
The fist pic is the evaporator I made 2 seasons ago. It has a 3 gallon preheating pan and a 2'x4' main pan with 16ga SS. The firebox is double insulated with rock wool and firebrick. The firebox is 24" deep. There is a tray a few inches from the bottom of the pan with firebrick on top of it and narrows down to about 1 1/2" before it gets to the preheat pan. It has a 6" flue.

Attachment 18870

Bigger firebox because of a 2'x6' pan. All complete with a heating oil barrel.

Attachment 18871

The fist pic is the evaporator I made 2 seasons ago. It has a 3 gallon preheating pan and a 2'x4' main pan with 16ga SS. The firebox is double insulated with rock wool and firebrick. The firebox is 24" deep. There is a tray a few inches from the bottom of the pan with firebrick on top of it and narrows down to about 1 1/2" before it gets to the preheat pan. It has a 6" flue.

Attachment 18870

Bigger firebox because of a 2'x6' pan. All complete with a heating oil barrel.

Attachment 18871