Another Homemade Evaporator Question

[sandman6921]

OK, here's my latest brainstorm..After firing on a plain steel pan on a block arch, I'm building a real rig.
Basically a thru the pan tube similar to a Mason thru tube pan. My rear pan is going to be 30x36 with 12 -- 2.375"
tubes in a 7" drop area. One problem, is my stainless is a bit heavy - 18ga +.
My real dilemma though is I started my arch with a big old heavy woodburner -- BUT I'm considering using a hard coal stoker or two to fire it with. Somewhere along the line, I came by 2 keystoker firing units that are rated at 144,000 btu ea. --Do you guys think one of these coal stokers would suffice, or should I go ahead and figure on using two of them, pumping out real close to 300,00 btu's. I don't want overkill, and thats what I usually do when I build!! Thoughts? ( Pic's shortly when it looks like something)

[spencer11]

pics whould be awesome.(i plan on building a pan like that for next season, but bigger) are you chosing to fire it with coal or propane? i would use wood. i use to use propane and it was so expensive. then i went to wood last year and it was practically free! i hope you dont mind if i steal your pan idea! :D

spencer

[sandman6921]

I'm planning on firing with hard coal. I use it to heat my place with, so I have it on hand. I use wood in my block arch, and have a basically free supply, but I think I can control the coal fire easier. When I post pic's anyone can feel free to use and improve. I don't have the best welding skills, and I'm pretty cheap, so I use what others throw away..

[spencer11]

i would fire with the coal or wood then.

spencer

[Ecnerwal]

By rough calculation, each 144,000 BTU/hr stoker should be providing enough heat to boil 17+ gallons per hour. That ignores inefficiencies, and involves some rounding to not ignore them quite that much. Depending on how well you insulate, guesstimate perhaps 15 gallons per hour worth of heat - whether that's anywhere near what you actually get out of it probably depends more on the pan design and overall insulation. How big is the whole rig/pans going to be? My first guess would be that one should suffice, but most folks are prone to cranking the heck out of things (and blowing a lot of useful heat up the stack) so that would lead you to the road of overkill. If you are going to overkill the front end, do yourself a favor and design some extra length in too, so you get more use out of all that coal you'll be burning before you send it up the stack. Might also want to take extra care to make sure the coal smoke and syrup never meet - woodsmoke can be an acceptable "note" in syrup flavor, but I don't think coal smoke works the same way.

[sandman6921]

The back tube pan is going to be 30" x 36". If I calculated correctly, I'll have 26.5 sq.ft. in the tubes and 7.5 sq. ft. in the pan so I should have an effective area of 34 sq. ft., front syrup pan 30x30. Anthracite does not smoke like regular coal, actually less than oil fire. beside lining the whole thing with firebrick, I wasn't planning on insulation. Just didn't know how much the thicker stainless was going to hurt. Of course I guess it just takes longer to heat up, but also longer to cool down. I can always install both stokers and run on one. If you've never seen one of these, think forge -- air is forced thru burning coal from below, and they are pretty efficient, about half the cost of fuel oil.

[Ecnerwal]

Sounds similar to some of the pellet burners (which probably stole technology from the coal stokers, as they were around first.) I've never seen a coal stoker - closest would be a coal furnace retrofitted with an oil burner, or the pellet boiler I just looked at (also about half the cost of oil.)

With 34 square feet you probably really want both, if my boiling rate ballpark calculations are correct. As you say, no need to run both if that turns out not to be true, on on slow days. Get a preheater and hood on there at some point, as that helps your boiling rate "for free" (well, for the price of building it) and provides clean hot water to boot.