Block Arch Efficiency

[maple flats]

If the damper is fully open and held there, it is unlikely the cap is the issue. Is the cap sort of like a Chinaman's hat? That should be OK, but if you think it might be restricting the draft, remove it. I think just adding more stack and making sure there is enough air feeding the fire under the grates. For grate height, any height you can maintain without building up with ashes and coals is good.
On a small commercial evaporator with a 2' x 3' pan, the draft door is usually covering a 6" x11 or 12" opening and that door is generally opened all the way or almost all the way. As you add stack make sure you brace it safely to prevent it from falling over and God forbid, hit one of your "4 little ones".
3 Steam pans is about 5 S.F. and 5x1.5=7.5. You are at about the limit , while the warming pan helps it will not give the same as the 3 main boiling pans. Just do all you can to keep the rate at 7.5, maybe even 8 or 8.5, I don't think you will beat that. When you keep the air open enough, the wood dry and split fine enough, fuel the fire by using a timer and find the best interval for your set up, and have enough stack, you are not likely to beat that. Enjoy this addiction, there is no cure.

[Big_Eddy]

Wow, that's amazing! I never knew how much that would affect the boil rate. Ironically, we just got done splitting some nice dry ash into wrist size pieces for the next boil too.
I'll see what I can come up with to extend that stack height. Another thing to note is this used pipe we found and are using, not only had a damper but also a rain cap. Maybe the rain cap and damper both are choking off the draft???

Get rid of the damper and the cap. Add some extra stack if you can. Make sure you have some kind of door and leave at least 2" gap below it for air to enter. Your grate bottom should be above the bottom of the door. You want air to come in under your door, up through the grate and then to the fire. Keep your fire at the front (20") and keep the gap under the rear pans to 2" or so. 1 gph avg per square foot for natural draft is typical. You will be hard pressed to get to, never mind average 1.5 without a blower.
Less wood more often boils harder than more wood less frequently. Toss your wood in angled or cross wise to maximize air flow.

[Matt H]

As stated earlier the block arch has gotten 5.5-7.5gph. A few changes were tested last weekend on the block arch. Overall the block arch averaged 6gph with a change in wood and grate height.

Burning the split wrist sized dry ash definitely increased the temperature and could be felt when the "door" was removed.

The grate height is proving to be a challenge. When the grate was 3" high we got anywhere from 5.5-7.5gph and sometimes would boil in the 3rd pan (at 1" sap depth). This time I raised the grate height to 8" high total. At 8" high, the 3rd pan would not boil (at 1" sap depth) even with the added heat from better wood. After trying different sap depths the best the 3rd pan would do was a simmer (at 3" depth only). Keep in mind the pans are set inside a frame work, not on top of the frame. I'm thinking the heat is taking the path of least resistance and going around the sides of the 3rd and 4th steam pans instead threw the flue area (1-2" gap) under the pans....just a theory. Any thoughts on this???

The coal base seemed a little too deep at 3". Does this sound right? Maybe the grate height caused the intake air to bypass above the coals? BTW...I haven't raised the exhaust stack yet. For the next boil I think I'll raise the stack to the suggested 4' and lower the grate down to 6" high.

[Trapper2]

Good post Dave.

[CampHamp]

For your upgrade, you might consider using siphons (if you’re not already). Then you have a continuous flow pan with gradient and no ladling.

See here.

[Matt H]

Good post Dave.

No doubt! I appreciate you this forum's willingness to help.

[Matt H]

For your upgrade, you might consider using siphons (if you’re not already). Then you have a continuous flow pan with gradient and no ladling.

See here.

Jamie, these siphons do look interesting. Right now we're transferring from pan to pan with a hydrometer cup....over and over and over. Then after that we do it again. Definitely would be an arm saver. Thanks!

[Matt H]

3 Steam pans is about 5 S.F. and 5x1.5=7.5. You are at about the limit , while the warming pan helps it will not give the same as the 3 main boiling pans. Just do all you can to keep the rate at 7.5, maybe even 8 or 8.5, I don't think you will beat that. When you keep the air open enough, the wood dry and split fine enough, fuel the fire by using a timer and find the best interval for your set up, and have enough stack, you are not likely to beat that. Enjoy this addiction, there is no cure.

Thanks again Dave! I just got done getting 8gph. I put the grate at 6" and used the wrist size dried wood. I'll get to the stack height change sometime.
I also experimented with sap depth at 4-5" deep in the pans, due to my pans being submerged in the arch. This seemed to work even better than 1" deep. I'm assuming the heat from the sides of the pans is now going into the sap.

[KJamesJR]

Not sure if any of this has been mentioned yet.

Second year boiling on a block arch. Have a 16"x40" divided flat pan. Thanks to some of the folks here I have seen good results but there's still major room for improvement. After lots of note taking Here's my take on it...

Fire grate/ash cleanout: You want this tall. When I rebuild next year I'm making my fire grate and ash cleanout at LEAST 6" tall. Currently it's about 16" wide by 2" tall and fills with coals which destroys efficiency I've found. Doesn't let enough air into the combustion chamber. Re-loading, no matter how seasoned the wood, will just smolder on top of a pile of hot coals. No flame at bottom of pan = no boil. I'm constantly having to stick my poker in there and scoop the coals out on to the ground. As soon as I do, low and behold the fire ignites once again and I get a good boil. Also find a grate that wont melt/warp. I used rebar and it melted rather quickly.

Fire box: This doesn't have to be huge for a smaller hobby pan. I started with a 18" or so fire box. Wasted a lot of wood. Most of the heat was pushed further back and I was only getting boils in the middle/center of my pan. Reduced to 12" and smaller splits with much better results. Front of the pan boils, less wood used and the whole pan gets hot. Also the gap between the arch and back of your pan (where the hot gases need to travel before leaving up the stack) should be about 1"-2". Mine was 6" and I wasn't getting enough heat to the back of my pan.

Door: A front door helps. With smoke, embers and heat loss. A piece of sheet metal works fine. A piece of sheet metal hinged and screwed into the block with a ceramic insulated blanket works even better to keep the heat in. You'll lose A LOT of heat from the front of a block arch.

Pan: Next year I'm recessing my pan into the arch. Boiling outside sucks 50% of the time. Wind, rain, snow... Lost of surface area from a raised pan is exposed to the outside and basically acts as a huge heat sink. Sucking up heat and expelling it into the cold open air. Also get some kind of rail gasket or ceramic gasket for your pan. Smoke and heat will stop rolling out between your pan and the blocks, or steel frame. Less heat loss, better draft, better tasting syrup.

Blocks: Also soak up a lot of heat. I would imagine a block arch takes a while to heat up, holds heat better than steel but if the inside isn't insulated, waste a lot of heat. Just sucks it up and radiates it outside. Good for keeping warm I guess. Consider insulating your arch next year with ceramic fire blanket or fire brick. Or both.

Blower: Good thing about boiling outside, at least if the front of your arch is facing north, you get the random wind gusts that shoot into your firebox. Yeah it cools your pan down but your fire comes back a lot hotter. You'll notice this specifically when you open your door to reload with wood and you instantly lose your boil because all the heat comes out the front. A blower would help to ignite the new fuel much faster. The heat will come right back as soon as you close the door. I would suggest looking in to a blower. I know I'm going to next season.

Flue: You wont need a damper. I'm doing fine with a smaller diameter stack but it's also twice the length of my arch. I would imagine a 6" stack about twice the length of your arch should do well considering your pulling enough fresh air in.

Pre Heater: Next year I'm extending my arch for a dedicated preheater. Putting a pan or something onto of your main pan doesn't help with your GPH as the steam collects of the bottom of your preheater and just drips back into your syrup. Also, the preheater sap doesn't get THAT hot. Being outside, maybe 60-70 degrees. Putting it directly over hot gas I would think is much better.

These are all pretty low cost or free tweaks you can make aside from maybe the blower. I'm sure there's some kind of fan you can rig up however on the cheap and make it work. The insulating blanket, or even pan gasket can be expensive but it seems you can get it by the roll which is more bang for your buck. The fire brick will be expensive.

EDIT:

One last thing is sap depth. Run at 3/4" if your feeling good. Block arches are typically too inefficient to keep a good boil going at 1". The shallower, the better. When you start getting syrup near the draw off, open the drip valve, flood the pan a bit and draw off the finished.

I also just noticed your using steam pans. You can disregard all the stuff about continuous flow methods but hopefully the rest helps you out.

[Fravy]

I run about the same set-up.

I run 3 steam pans and a 4" vent pipe. One thing I did this year was to run my little Ryobi leaf blower under my sheet metal door once I had re-stacked more firewood or when I was just getting started. That little leaf blower made a great blower vent. I had some metal mesh I bought from Home Depot wedged between the first row and 2nd row of block for my fire grate. That gave me an 8" lift. When I fired that blower up, I got nearly an instant and very heavy boil. With only 2-3 inches of sap in the pan the bubbles were foaming up to over the top of the pan. It made me worry I was providing too much air/heat, so I only used it after adding sap or wood to get things back to a strong boil. That being said, I finished 30 gallons of sap down to about 2 gallons in about 5 hours. That would be roughly 28 gallons / 5 hours or 5.25 gallons per hour on three steam pans. Since then, I stacked up some pavers in the back of my arch so that the heat coming off my woodfire would hit that 3rd pan better. My 3rd pan was barely boiling unless I had the blower on. I'm hoping that will get me three full-boiling pans tomorrow.