Block Arch Efficiency

[Matt H]

We have about 30 taps out and am looking to increase our new cinder block arch's boil rate beyond the current 5.5gph. Is this a fairly normal rate?
I'm hoping to get it more efficient on a LOW BUDGET....a single income family with 4 little ones requires a tight ship! LOL

I'm looking for help finding the most cost effective options for under $50. Here are some spec's:
*3 course cinder block arch
*4 full size, 6" deep steam pans held by an angle iron frame
*19" wide X 24" deep fire box lined with paver sidewalk bricks
*1-2" between bottoms of 2 rearward steam pans and bottom of flue also lined with paver sidewalk bricks
*steel, non-insulated cover for door - air is able to seep around sides
*raised fire grate (3" high I believe)
*6" diameter, 8' tall stove pipe with damper (only run with at wide open)

Ceramic Insulation for the "door", pan frame, etc. looks like it should be my next step, but is too pricey.

Ideas are much appreciated!
Matt

[barnbc76]

One of the problems I ran into with my block arch was not having enough room under the grate, 3" may not be enough because it often fills up with coals and airflow is affected. A blower will help A lot burning the coals all the way into ash.

[ecolbeck]

Back when I had a block arch I got a cheap bathroom exhaust fan and some round metal ducting and blew air in under the fire. It melted the grate that I had but I got 9 gph out of a 2x3 pan.
Make sure your wood is split really small and add small amounts of wood every 5 min to keep it ripping!

17987

[maple flats]

What is the actual surface area of the pans total? If you get somewhere near 1.5 gal/sq ft of surface for your evaporation, you are good, if much below that look for ways to improve it.
Fire needs 3 things, fuel, heat and oxygen. If the fuel is dry and split fine, figure how to get more air to it. Air just seeping thru the cracks is likely too little. The next thing, you might be choking the fire with a 6" stack, either add 2' height or go to 7" or 8". You do not want a damper, for now try to wire it at the knob to prevent it from even slightly closing. Once the fire is lit heat is not an issue, regulate the air and fuel.

[Big_Eddy]

You're not likely to get much better. Smaller wood, more frequent firings, blower. Keep it ripping.
Best thing you could do would be to lengthen the block arch and add some extra pans at the end. Extra length = extra evaporation for the same amount of effort and wood.

You haven't mentioned sap depth. If you dare - run 1" deep. You'll need to watch for scorching on the sides and you will need to add sap often - but shallow pans evaporate sap significantly faster.

[Matt H]

Thanks for the input!

Talk about a shot to a man's ego...my wife ran the rig today and got 7.5gph instead of my measly 5.5gph! LOL She used some drier wood and kept the first 3 pans right around 1" deep. The 4th pan was used for preheating. What a great wife!

Unfortunately the 6" pipe is all we have on hand. I did notice that the stove pipe is not all that hot. Also pots sitting on steel surrounding the stove pipe aren't getting even warm. This seems odd to me.

No electric power near the block arch for a blower. :( So hopefully a change to the grate height will do the trick. Is 6" about right?

Each pan is roughly 12" X 20" for a 4 pan total of 6.7 square feet. We've got a way to go to reach the optimum 1.5 gallons/square feet.

[Matt H]

You're not likely to get much better. Smaller wood, more frequent firings, blower. Keep it ripping.
Best thing you could do would be to lengthen the block arch and add some extra pans at the end. Extra length = extra evaporation for the same amount of effort and wood.

You haven't mentioned sap depth. If you dare - run 1" deep. You'll need to watch for scorching on the sides and you will need to add sap often - but shallow pans evaporate sap significantly faster.

Thanks that made a 2gph difference between proper wood and sap depth....was 5.5 now 7.5!

[Matt H]

What is the actual surface area of the pans total? If you get somewhere near 1.5 gal/sq ft of surface for your evaporation, you are good, if much below that look for ways to improve it.
Fire needs 3 things, fuel, heat and oxygen. If the fuel is dry and split fine, figure how to get more air to it. Air just seeping thru the cracks is likely too little. The next thing, you might be choking the fire with a 6" stack, either add 2' height or go to 7" or 8". You do not want a damper, for now try to wire it at the knob to prevent it from even slightly closing. Once the fire is lit heat is not an issue, regulate the air and fuel.

As I reflect on the lack of heat in the stove pipe, I believe the arch might be losing too much heat to create a good draft. Initially the first boil went well and stove pipe was noticeably hotter. Last night was the 3rd boil and I could almost leave my hand on the pipe! Overall, I'm guessing the problem is a stack up of issues??? Some we fixed on the 3rd boil last night (using smaller, drier wood and keeping the sap level lower increased 5.5gph to 7.5gph) and some issues still need to be resolved (raise fire grate this year, stove pipe size and add blower next year). As each boil continues, I also see where the pans are warping and creating gaps between each other...some gaps are now 3/8".

I'm thinking this should be my strategy for this year...
1. Raise the fire grate and/or modify door - Is there an ideal height/setup for the fire grate and door combo? Maybe some dimensions or guidelines to follow? This should be fairly easy, as I have scrap steel, metal fab experience, and equipment.
2. Find heat loss and fix - Your 1.5gph/sqft guideline coupled with lack of heat in the stove pipe indicate to me there is a major heat loss somewhere in the system. Do you think the pans' gaps and a lack of insulation would cause that much heat loss?

[barnbc76]

A taller stack can create more draw, maybe add another 4'. Try to use very dry wood, last week I used a bunch of real old 2x4's they were so dry they burned real fast, taking us from our normal 8gph to 10gph.

[Matt H]

A taller stack can create more draw, maybe add another 4'. Try to use very dry wood, last week I used a bunch of real old 2x4's they were so dry they burned real fast, taking us from our normal 8gph to 10gph.

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???

[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 (http://mapletrader.com/community/showthread.php?18050-Siphoning-between-pans&p=198282#post198282).

[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 (http://mapletrader.com/community/showthread.php?18050-Siphoning-between-pans&p=198282#post198282).

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.

[CaptT820]

We run a block arch in the driveway as well with 4 steam pans. The arch portion of the firebox area is lined with firebrick. My blocks are filled with sand as I have a ready supply. The sand helps the thermodyamics of the blocks and helps keep the heat in. Its very rustic but very effective. 6-inch diameter flue pipe with damper is 10-feet tall, supported by guy wires. The firebox is just cinderblock, you can fancy it up with fire bricks and help the efficiency as i did last year, just didnt have the time this year. Our "door" is just a piece of 1/2" concrete board that I had lying around, this could be improved, but it was free. The firebox has a grate I made from high strength rebar. The grate has never even warped with proper welding and has 6-inches of clearance underneath. The biggest key to burning hot and keeping the pans boiling is to add a blower. I use a Vent-Tech 6-inch inline blower with a piece of 18-inch long stove pipe directly under the grate with a rheostat to control the fan. We went from a ~4 GPH evaporate rate to 8-9 GPH evaporate rate. You do have to feed the fire more often, but it burns much hotter, and even after 10 hours of boiling I never cleaned the coals out once, as they burn almost completely. Hope this helps.

[woodsy]

We run a block arch in the driveway as well with 4 steam pans. The arch portion of the firebox area is lined with firebrick. My blocks are filled with sand as I have a ready supply. The sand helps the thermodyamics of the blocks and helps keep the heat in. Its very rustic but very effective. 6-inch diameter flue pipe with damper is 10-feet tall, supported by guy wires. The firebox is just cinderblock, you can fancy it up with fire bricks and help the efficiency as i did last year, just didnt have the time this year. Our "door" is just a piece of 1/2" concrete board that I had lying around, this could be improved, but it was free. The firebox has a grate I made from high strength rebar. The grate has never even warped with proper welding and has 6-inches of clearance underneath. The biggest key to burning hot and keeping the pans boiling is to add a blower. I use a Vent-Tech 6-inch inline blower with a piece of 18-inch long stove pipe directly under the grate with a rheostat to control the fan. We went from a ~4 GPH evaporate rate to 8-9 GPH evaporate rate. You do have to feed the fire more often, but it burns much hotter, and even after 10 hours of boiling I never cleaned the coals out once, as they burn almost completely. Hope this helps.

I like that idea of filling the blocks w/sand. Hadn't thought of that. Should make good insulation and maybe moderate the heat on the blocks.
My 3' x 4' long unmortared block arch on a slab in its second year is showing a lot of heat damage/cracked blocks . It holds together OK still but
looking to improve on it some. Good boil rate 7-8 gal. hr cranking . Firebrick is pricey though . Probably $150.00 to do a 2 1/2 rows sides and back.
Was wondering about furnace cement on the block faces if that would hold on or not.
Like the OP, we are trying to save money by boiling our own, only about 3 gals syrup year

[CaptT820]

I found a guy on Craigslist in Woburn, MA that supplies high end firebrick and insulation to the commercial boiler industry. His prices were good and he has an amazing selection. You can buy the firebrick rated for a number of different temperatures from 2200 to 3200 degrees F. He also has an impressive supply of commercial grade insulation in all different thicknesses, a little of this goes a long way. The sand in the block arch helps along with some vertical rebar pieces anchored to the ground. The sand and the firebrick together allow the blocks to last longer before cracking. I also add a 4-ft long piece of aluminum angle iron (1"x1") that is screwed to the top layer of blocks along each side of the evaporator to set the steam pans on. It makes it much easier to get the pans in and out.
Still block arching for now, but we went from 2.4 gallons of syrup last year to 6.25 gallons this year. Thank god for the new homemade RO unit.

[Matt H]

It's been a few weeks now. Thanks again to your suggestions and experience offered! Anyway, I got a chance to try a leaf blower this weekend and it created some wicked heat. During a non-blower scenario and dry wrist size wood only the 2 front pans boil and the 3rd pan might slightly simmer. With the blower idling and mixing dry and green wrist size wood, all 4 were boiling and the stove pipe was too hot to touch. Things kept me busy and I didn't get a chance to measure gph, but am guessing it was somewhere north of 11gph.

Most cost effective features so far have been the leaf blower (maybe $2 per hour), using dry wrist sized wood (free), lining cement blocks with landscape pavers (free), and 4-5" depth in steam pans (free). The first 3 make fairly good sense but I may need to further explain the 4th. Most folks suggest using a 1-2" depth and this is best for most setups (just bottom of pan contacts arch's hot air). These steam pans are sunk into the arch using a framework. This, by no planning of mine, has created more heated surface area. So by maintaining a 4-5" sap depth we've been able to take advantage of the sides of the pans being heated.