Need some pointers and critique for my Arch Design

[82cabby]

Hi gang-

My barrel evaporator has finally boiled its last batch and its time to build the next generation. I am going to build an arch for a 2x4 pan. I would like to incorporate AOF and AUF. Additionally I am going to build in a 'shelf' where my preheater pan can sit and be heated by the flue gasses. As this is only the second evaporator I have built, I am working out the design in Autodesk Inventor, trying to figure out as much as possible before actually cutting into some otherwise perfectly good steel! Below is an image of the model so far with a couple of basic dimensions. Any feedback would be appreciated. Obviously it is a work in progress and I haven't added the doors or the fire brick yet, although the arch board insulation is in there.

Thanks, Dave

Evaporator DWG.jpg

[Super Sapper]

Do you have your pan already? If not why not build a 2 x 5 and forget the preheater. This will be more efficient than a 2 x 4 with a 1 foot preheat pan. AUF will help a lot but with that size AOF is probably more of a fun thing to play with, which is a big part of why we do this.

[Bricklayer]

I would do away with the cross angle just behind the firebox. It will warp like crazy since it it fully exposed to extreme heat. and it's really not needed as long as you have a good solid frame.
I used 3/16 angle for my build and she's held up well. I used 1/2" plate steel for the back section where the transition stack is.
I used Ceramic blanket to insulate mine and it barely gets warm to the touch except for the front get a little hotter then the rest. One mistake I made was that I wish I had of used high temp silicone on the inside where the skin attaches to the rails and frame. I fully welded the skin on but I get leaks here and there when I'm lighting it and get some smoke comming out of the leaks. But once she's rocking and up to temp no leaks.
Your sizes look almost exact as mine.
You could probley go a little wider with the arch.26.5" is good for a 24" pan. Gives you room for valves and float boxes. 3/4"-1" is ok for the pan to sit on. I made mine to rest on 1/2" and it scares me sometimes. I'd rather it be 3/4"
If you sit on the rails too much you lose a lot of pan space that's not in contact with the flames. And that will decrease your gph rate.
Also a big thing to consider is that you have a couple inches beteeen the back of your pan and your stack. I made this mistake and I get sap burning on the pan sides when I get it rocking. I solved this with a shield but it still bothers me.
And another thing is to have something to secure your pan. I welded 4 small pieces of threaded rod to the front rail of my arch and cut slots into a 3x3 angle. Once pan is in place. I put angle tight against pan and tighten nuts. Keeps pan nice and tight.

[maple flats]

1/2" to 3/4" is plenty for the pan to sit on. The more overlap the less heat transferred to the outer edges. In fact mine only overlaps 3/8". The less overlap the better the heat transfer. As said above, do not put a cross angle, leave it open.
AUF/AOF, AUF helps get a hotter burn at the expense of more wood, AOF helps get much higher use of the potential from the wood gases generated. As such AOF with a high pressure blower is a huge benefit, but maybe not worth it on a 2x4, if you build it as a 2x6 (you'll want to grow anyways) the AOF will cost the same as on a 2x4 but you will capture far more of the potential from the AOF. Also, if you do go with 2x6, make sure to have both flat syrup pan and a flue pan, either drop or raised flue. Start looking now for a set of pans , then build the arch to fit. Pans are generally cheaper now until early fall, then prices climb as more and more buyers enter the market.
On a used pan, if soldered be certain to avoid leaded solder, must be labeled leadfree. The older ones were at first 50/50 solder, then later they were low lead before lead free was made.

[mol1jb]

How many taps do you currently have and how much growth is possible in the future? Last year I built a 2x4 oil tank arch and this year I am building a 2x6 arch to handle my tap increase. I found a good set of used pans from bascom. If I hadn't I would have gone with the smokey lake hybrid pan.

[82cabby]

Thanks all for the replies!

I widened the design by an inch to 25" overall and deleted the cross member at the rear of the firebox. I happen to have a fair amount of 1 1/2" x 5 foot angle iron that is 3/16 thick so that is what I would like to use for the main portion of the frame. I have a 24 x 8 preheater from my 2x2 barrel evaporator that I would like to continue using. My reason for building the support for it was to open as much of the pan as possible. I hate to see condensate dripping back into the pan! However, I was thinking it wouldn't be too hard to cut off that support and go to a 5 or 6 foot pan eventually.

I used ceramic blanket in the barrel evap and it insulated very well but wasn't terribly durable. Would the arch board hold up better and does it insulate as well as the blanket?

For the past several years we have run 65-75 taps on a combination of buckets and tubing. I will eventually to 100 but due to the hilly nature of my property, and the fact that the evaporator (and house, and garage) are at the TOP of the ravine, going to more than say 125 would be a major challenge.

The opening from the firebox into the angled flue portion is 8 1/4 inches which will drop to about 6 with the firebrick in place. That will angle down to about 2 inches or so at the far end. Does that sound about right?

Thanks for the feedback gang,
Dave

Revised Drawing:

Main Frame Assembly Solo.jpg

[Ghs57]

I used all arch board on my home built. It's OK unless it comes into contact with items heavier or harder. Therefore, I will be rebuilding my firebox this fall because a good deal of the board above the firebrick, which was hit by errant chunks of wood over the past two seasons, has chipped away.

I started out with a 2x4 pan on this rig, but now am running a 2x6. I made it for a 2x6, and had covered the back two feet for one season. Wish I had just started with a 2x6 pan because it would have saved a lot of time and money. 100-125 taps is a lot to ask of a homebuilt 2x4 without forced air, hood and a preheater. Sorry, don't mean to be negative, but that's my experience. Good luck with your build.

[82cabby]

Thanks Gary. I will make sure that all the arch board any where near the firewood is covered by firebrick. That is the problem I had with the insulating blanket, it really got torn up pretty quick where it was not sandwiched between firebrick and the evaporator.

There will be forced air as I can use the blower from my barrel evap and the preheater as well and I should also mention I have a home built RO. Best thing ever. I will look at pricing on 2 x 6 pans. If they are not too much more than 2x4 then I really should consider it. I really like the idea of building the arch so I can easily convert it to a 2x6.

And I guess a related question would be, what are the minimum number of gallons of sap needed to fire up a 2x4, 2x5 and 2x6?

If I do only tap 75-85 trees will I even be able to fire up a 2x6 on a slow week? On a good run, of course, I couldn't keep up with the barrel evap and would end a 16 hour day of boiling with more sap than when I started! However on a slow week, I might only get 45 or 60 gallons of sap. Looking back on 2017 I had 78 taps and I had one day of 110 gallons and two days in the 90s. The rest of my collection days were 55 to 75.

Design wise, I am working on the door currently, so if anyone has any further suggestions there I would appreciate it.

Sorry for all the questions. This is going to be a major expense for me and I really want to get it right.

Thanks, Dave

[Ghs57]

Man, I gotta build an RO.

With that, you have changed the equation on when to go bigger. Depending on your GHP, you may be fine with the 2x4. What concentration are you boiling?

I like to fill my IBC tote (275 gals or so) before I fire up the 2x6 and sweeten the pans. After that, I usually run every few hundred gals, depending on the temps. How frequently you run is decided by many factors. Sap spoilage is a concern, so is letting the pan sit for a long stretch. And your evap rate. This is all non-RO sap for me, and I boil at 25-30 GPH. I like to run for at least 4 hrs. It can take about an hour to get everything up to temp.

I got so far behind with my 2x4 that I would have to dump sap. This was with under 75 taps. I've only had over 100 with the 2x6. There were some heavy runs in there, but I have not dumped anything since the 2x4 days.

I managed to get some money back on the 2x4 by selling it on CL, but it would have been far to cheaper to buy the 2x6 first. And I'm not sure the hybrid was the way to go. A separate flue/syrup pan rig has greater potential.

Unfortunately, I'm not sure about getting it right either.

[82cabby]

Yeah, the RO is great! I usually get about 1.5% -2% sap from the trees and can bump it to 6-8% with the RO. I priced 2x6 pans and I think they would break the budget at this point. But, building the evaporator so it can be easily converted to 2x6 makes a lot of sense.
I need to reconsider the width to make sure I am not covering too much of the pan with the rails and find high temp silicon for sealing the skin.