Need more air!!! I think...

[swierczt]

Hello,

This is my first post. First I've got to tell you that I've been sugaring in central Connecticut for about 12 years at the hobby level (35 taps) and learned mostly on my own...but I think I've learned more about sugaring in the last few months by reading the posts on this site than I've learned in the last 12 years on my own! Keep up the good work!

Now to my question...I have a home-build barrel evaporator with a 28 x 36 pan on top and a forced draft system on the bottom. I have a 8" stovepipe out the back with no damper with aprox. 10' of stovepipe. One problem I've always had was that to get the most gph out of my rig I have to keep the door cracked to let more air in. I know I am loosing heat out the opening in the door. For my forced air, I have two- 2.5" squirel-cage blowers with 3000 rpm motors on them. I had one, blowing through an iron pipe with .5" holes blowing up through the bottom of the fire. It helped, but still had to crack the door to keep the fire cranking. I added a second blower low on the door blowing right at the fire along with an asjustable air intake with a 6" x 2" opening to take in air and STILL have to have the door cracked! I know I am loosing heat this way. Is my stovepipe too long or too short? Is there something else I'm missing? Thanks in advance!

[3% Solution]

swierczt,
I had mine on a barrell arch, til it rotted out.
I had two 4" fans blowing into mine and still have them blowing into the new arch.
I have a 6" pipe coming out.
This thing cranks right up pretty good.
If you close the door and let the heat build up, does it chug?
If so, you need air, lots of air.
Just my two cents.

Dave

[RileySugarbush]

Does your firebox run all the way to the back of the pan? If so, try shortening it up so its only 18 inches long. Build a wall with firebrick to within an inch or so of the pan bottom to force the combustion gasses up to the top of the arch and avoid them racing out the stack without doing any good. For your rig, the airflow should be mostly through the grate, up through the fire and up and out along the bottom of the pan.

If it still seems like you need more air, try an experiment with a leaf blower. Even a cheap electric one should give you plenty of air for that size arch. If it works, you can keep using it or find a quieter equivalent blower.

Let us know what works for you.

[swierczt]

Thanks for the replies.

I have tried closing the door and leaving it alone for about an hour. Usually what happes it that it boils along for 15 min. or so then the boil dies off. When I open the door after an hour, the wood is still there, but smoldering away, kinda line a wood stove. My arch does go all the way to the back of the barrel and then out through an 8" hole to another chamber I added to the back for a preheater pan. There is a half wall in the preheater chamber, but I have often thought about buiding this up a bit and even as you suggested shortening my arch with firebrick or even just dirt for this coming season and making a more perminent fix next year. The leafblower is an idea. The little fans that I have blow pretty hard..like a supercharged hairdryer...but a leafblower has to be even better than that.

[OGDENS SUGAR BUSH]

sounds like to much wood, i have to fire mine at least every 10 minutes. do like RILEY says and shorthen for fire box

RICH

[RileySugarbush]

Another thought:

If you have enough combustion air, you should be able to see down through your fire to the grates about 5 minutes after you add wood. The goal is to have a lot of wood surface area burning with plenty of air all the time. If you end up with a bunch of coals on the grate, there is not enough air flow up through the fuel.

For reference, with our 2x6, the firebox is probably much smaller than yours and we blow in about 200CFM under the grate. We charge with wood about every 6 minutes.

[swierczt]

I usually add wood every 10 min. I cut it small, 12" long and no more than 3" across. I use mostly hard sheet metal skidwood...comes on 10' long skids w/ 4"x4" runners...I split those in half. I have learned to keep the fire small and never pack it in...like you said, to be able to see through to the grates. I only add 4-5 pcs at a time and let it burn until it's almost gone to coals, which usually takes about 10 min.

[Sugarmaker]

swierczt,
I may have missed it but what gph are you expecting and or getting?
My first thought was your wood size/ type/ dryness.
The blowers you have should do the job. That thing should roar. Sounds like you have plenty of stack size and height too.
Can a stack be too large 8 inch sounds big , but?
I would make sure the blowers are really getting the air to the fire. and maybe try firing every 5 minutes with 1/2 the amount of wood? When you say 3 inches across? How big are these pieces in cross section? We burn almost all pallets but the bulk of the wood is slats which are only 1/2 to 3/4 inch thick and catch and burn hot and quick. Just a thought that the wood might be just a little big for that size fire? Big kindling might work better? The bigger the fire the bigger the wood it will /can take. I may be using smaller sized wood in our 3 x 10 than you are? I can tell when I switch to split stick wood 4 inch dia. that it doesn't catch as quick and the boil dies a little too.
Good luck and welcome!
Chris

[RileySugarbush]

I really think the blowers are inadequate. We ran a half pint around here with a couple of small blowers through 2 inch pipes for a while and it was impressively hot right where the air comes in, but overall the fire didn't burn that well. When we replaced them with one bigger, high volume blower connected over the draft door, it made all the difference. I think if you get high volume air under the grate and block up the firebox to force the combustion up to the pan you will see huge improvements.

Then you can fine tune the size and firing schedule.

[swierczt]

On the best days, I get maybe 8 gph, but it's probibly closer to 6 gph. I can remember getting close to 12 once, but that was one of those days when everything was going just right, bright sun, high pressure and super dry air and wood. (and the door was open about 4"!). I had a 6" pipe to start, but that seemed to choke the fire and got lots of smoke backing up, so I opended it up to an 8" and everything seemed to work better. I'll agree, that the fire seems to burn really hot at the grates, but I don't exactly see the flames blasting all the way to the bottom of the evap. pan. Do you think that bigger holes in the pipes would help?

[RileySugarbush]

A bigger flow path to the area under the grate is best. My blower connects to the plenum through a 6" diameter duct, transitioning into a rectangular area about 4"x10". No restriction at all. Might as well get all the flow you can. The small holes increase jet velocity, but that doesn't really buy you anything.

[HHM-07]

sounds to me like you don't have enough space between your gratesfor the air to pass up tru. is it better after you shake it down ??

[maple flats]

I think your firebox is too deep. When i had a half pint (2'x3') the firebox was 20" deep. At the back of the 20" was a brick partition that was full width of the arch and was up to the bottom of the pans leaving just 1.5". I had a 6" stack and no forced draft. The stack was 12' high. I added wood to the fire every 7 minutes, just 3 or 4 wrist sized pieces and the fire roared. I regulated it with the draft door which was about 12" wide and the best boil came with an opening of about 4-5" (x12). The fire was like a blow torch. I think you should make a fire brick wall about 20" in from the door and what I now know I suggest only leaving 1" below the pans. Behind the wall fill it with vermiculite and then a thin layer of morter or even half bricks flat to keep the vermiculite from going up the stack. Be sure to leave more room before going to your preheater section and ultimately up the stack so as not to restrict flow. Now put all the air to it you can get out of your blowers. If the door also needs to be open you need more blower.
My 3x8 only has a 24" deep firebox, a wall up about 2/3 to pan and then tapers rearward and up at about a 60 degree angle. When it gets to the pans there is only 3/4" space all the way back until I am almost to the stack. At that point it drops down to get better air flow. I now fire every 5 minutes, 4-5 pcs 20" wood split wrist size. I fire one side and then the other half 5 minutes later. I have the wood ready to go in before i open the door so it does not need to be open any longer than necessary. I have a full rolling boil within about 15 minutes of start up and if i do my part it does not slow til I want to shut down. Try these ideas and you will see a big improvement.

[peacemaker]

well put maple flats well put i agree 100 %

[TapME]

swierczt, have you checked your wood for being dry? Just a question.

[Valley View Sugarhouse]

Do all of you guys fire, alternating doors?? I fire only one side, the side I am drawing from, never gets opened, I fire about every 5-7min. open dorr, push good hot stuff over throw in a arm full, close door. If I open the side I am pulling syrup from, I have to slow the pull, and or stop it, If I fire one door only I can eventually get it adjusted so it will run syrup continus..

[Sugarmaker]

VVSH,
Getting lazier in my old age and so the pieces of pallets are a little bigger. If I need to open both doors to fire then thats what is going to happen. I have fired many a day just opening one door as you mentioned. Probably helps keep the syrup coming more steady as you say. I do have some pine slabs and pine split chunks that I will fire with just one door open.
Chris

[peacemaker]

thats interesting i have only one door on my homemade arch and i wonder if teh way the door opens to where i am pouring off matters ... sugar maker how are u cutting your pallets

[Valley View Sugarhouse]

Yah I can see with pallets, I have to open both when disposing of bodies too..

[peacemaker]

your a mad man vvs never thought of getting rid of them tha way with all there polyester and colone and hair jell the burn nicely

[swierczt]

I think your firebox is too deep. When i had a half pint (2'x3') the firebox was 20" deep. At the back of the 20" was a brick partition that was full width of the arch and was up to the bottom of the pans leaving just 1.5". I had a 6" stack and no forced draft. The stack was 12' high. I added wood to the fire every 7 minutes, just 3 or 4 wrist sized pieces and the fire roared. I regulated it with the draft door which was about 12" wide and the best boil came with an opening of about 4-5" (x12). The fire was like a blow torch. I think you should make a fire brick wall about 20" in from the door and what I now know I suggest only leaving 1" below the pans. Behind the wall fill it with vermiculite and then a thin layer of morter or even half bricks flat to keep the vermiculite from going up the stack. Be sure to leave more room before going to your preheater section and ultimately up the stack so as not to restrict flow. Now put all the air to it you can get out of your blowers. If the door also needs to be open you need more blower.
My 3x8 only has a 24" deep firebox, a wall up about 2/3 to pan and then tapers rearward and up at about a 60 degree angle. When it gets to the pans there is only 3/4" space all the way back until I am almost to the stack. At that point it drops down to get better air flow. I now fire every 5 minutes, 4-5 pcs 20" wood split wrist size. I fire one side and then the other half 5 minutes later. I have the wood ready to go in before i open the door so it does not need to be open any longer than necessary. I have a full rolling boil within about 15 minutes of start up and if i do my part it does not slow til I want to shut down. Try these ideas and you will see a big improvement.


I like the idea of shotening up the firebox. The wood that I've been using is good and dry...seasoned for at least a year or two and under cover once its cut up. I've been sticking to the 12"/wrist-size rule, so I don't think my wood is too big. I agree that the firebox is probibly too deep. Raising the grates would probibly help also. Any suggestions as to where to get vermiculite? Maple Flats, how many gph did you get with your 2x3 rig?

[Sugarmaker]

Peacemaker,
I cut the pallets with a chain saw. And pallet holding bench.
Chris

[gmcooper]

You can get vermiculite at any masonary supply. Also some garden centers will have it.

[peacemaker]

sugarmaker i guess i meant not the method of cutting as more so how like when i need to cut them fast i cut down the middles of rhe slats then split the 2x materila to make the pallet in 6 oieces with the tops attached to the 2x still but normal cut i run down along the 2x make a pile of slat and a pile of 2x ...as far as vermiculite lol punch a hole in alot of old house and fill bags full lol right supper sappy ...

[Sugarmaker]

Peacemaker,
I used to compress them a lot more by cutting out most of the slats but its just to much small stuff to handle. So I cut then so the slats are attached to a section of side rail about 12 inches long. More air space but a lot less moves.
Chris

[peacemaker]

thats what i was think as well i think i boiled better on the pallets whole as compared to cut up ... but this year i have some wood working projects for the slate wood so i started cutting them off saving them and burning just the 2x .... but gonna cut some both ways ...

[peacemaker]

swierczt,
i was reading another post and i remind me of this one and something from way back where are u drawing the air from for your forced draft ... there was a thread about that cold air verses warm air ...

[peacemaker]

i cant find that thread anyone remeber that one was way back thought it was about not getting the back pan to boil ...?

[swierczt]

I have the blower pumping air into the bottom of the firebox in a box about 3' away from the evaporator. The other one is attached right to the door, but about 6" away so as not to melt the wiring or the motor windings. I have an aluminum dryer hose from the fan box to the evaporator. I have a cover and walls on three sides of my sugarhouse...so I guess you would call the air going into the firebox cool, but I wouldn't call it cold. I can usually get 1.5" of sap up to a boil in 20 min. or so once the fire it lit. It's a rolling boil across all three chambers of the pan, but the sap isn't exactly jumping out of the pan. I know I went through a lot of wood last season...a lot more than I think I should have based on the ammount of syrup I made.

[Jeff E]

Just a thought, could your preheater be creating to much restriction, creating a situation where the blowers become necessary?

I used to use a 2x4 flat pan (GBM) and would do 10-12 GPH. I would get a good jumping boil on the whole pan. The fire box was only in the first 24", then a taper up to the back. I had about 4" of space between the vermiculite and the pan. Probably to much space...

I moved it at one point and went from the old 7" stack, 8' high, to a 6", 10' stack. It was shiny and new, so I thought it would be better!!!

When I started boiling I could not make it boil hard, I had smoke coming out through little gaps in the arch, had a smokey exhaust, all bad. My memory of night boils when the top of the stack would look like a jet engine (wasted heat, but boy did it boil) was not happening anymore.

I went back to the old rusty 7" stack and 'Shazzam!', no more smoke, but kickin' boils.

All this to say, a slight restriction on the exhuast side made a huge difference.

On my new (to me) 3x12 drop flue, I am sticking with a clean, standard 14" stack, 20' long and expect to not need a blower. I am bricking the arch now in fact.

Here is a question: In the flue section on my 2x8, I have had vermiculite right to the flue bottoms. Should I leave a 1" gap so heat is getting to the bottom edge as well? Seams like it would help. Also, the flues start in the angle section of the arch, so the hot gasses don't get entirely squeezed into the flue area until about 2' into the flues of the 3x8 flue pan. Any concerns with this?

[royalmaple]

Jeff-

The gov and I ran into that on my 2.5x8 and what we did to fix that was to stuff a bunch of loose bricks on the ramp to force the flames into the flue pan sooner. Major difference in boil. Before flue pan wouldn't really get going. Now I can keep a serious wave going from front to back. Try stuffing some bricks in there if you need to, after you test it and if you don't like the boil. You can always take them out or add more to get a different effect.

[swierczt]

I don't think the bricks in the preheater section are really hurting anything. They only come up about 1 split high so only about 3" of the 8" is partially obstructed when the smoke/fire comes from the main chamber into the preheater chamber. I ran it without the bricks for years...added them two years ago...and the only difference I saw was a little faster preheater warmup. I've seen no differece in the main pan.

[peacemaker]

the other thing i just caught u said u run your sap level at 1 1/2 try running them lower

[RileySugarbush]

Warning! Controversial opinions of arch design to follow! This is not meant to cause a fuss, its just what I followed when I designed my arch for my 2x6 drop flue. Results in 40 to 45gph with preheater.


Grate size: width=90 to 100 % of the pan width, Length 110% of your wood length to about equal to pan width. No deeper than needed to get the wood in.

Combustion air: up through the grate at a flow rate to give an average air velocity of 1 to 2 feet per second through the firebox. Example: 2x6 Firebox is 2 feet wide by 20 inches deep = area of 2'x1.67' = 3.33 sq feet of firebox area. The fan should be sized at: 3.33 ft^2 * 1 foot/sec*60sec/minute = 200 CFM. Up to 400 would be better, with greater stack base temp and evaporation rate, but lower fuel efficiency. [Brandon would probably double it again to 800cfm! ;) ]

Flue air injection not considered but would definitely help.

Flue section. Vertical back wall to the firebox to force the combustion gasses to the pan as quickly and for a long a distance as possible. With forced combustion and/or a good stack length, there is no need for a slope in the back of the firebox. It decreases heat transfer and evaporation rate.

Flue area = about 1/10 of the firebox area. (less that 0.5sq. feet in the above example. Flue gasses expand about 3 times when heated to 1000 degrees, so the volume flow rate is up to 600CFM in this area. That plus the restricted area accelerates the flow to higher velocity, encouraging turbulence. The wide and shallow slot under the pan keeps all the heat near the exchange surfaces of the pan for good heat transfer.

Stack base: Full width of pan transitioning to 1/10 of firebox area, or an 8" diameter stack for the 2x6 example above.

Stack height , 2 x arch length as a minimum, though this is less important when forced draft is used. Better stack draw will minimize the need for an airtight arch.

Other opinions or comments?

[peacemaker]

john explain what is meant by flue air injection ?and where did u get this info

[RileySugarbush]

By flue air, I am referring to air introduced above the flames to allow more complete combustion of the flue gases. I've never tried it but plan to. Many here have talked about it and some commercial rigs have it.

All the info there is a kind of hodge podge of conventional wisdom culled from various threads here, and my experience and calculations with my home made rig. I wish I had all these numbers right away when I started building. It certainly is not textbook stuff, and I expect some will disagree. but I throw it out for you all to kick around and discuss. A few items, like slope or no slope, size of the gap under the flue pan and CFM for good combustion have been discussed pretty completely. One thing I'm pretty sure of is how well my rig runs and the evaporation rate, which is constantly monitored with an sap flow meter.

[Jeff E]

John, you note that the space under the flue pan has been discussed. I have not seen it. Is it conventional to leave a gap under the drop flues?

[Gary R]

RSB,

I guess I should have asked for that kind of input before I built my rig:) . Good details for the home built guy to follow. It's hard to find a thread that has all the pieces to making a decent rig. I'm adding a little more blanket under my pan so I don't have to cut the whole forest down to feed it;)

Thanks

[RileySugarbush]

I've seen 1" or less recommended for under the flues and I have about half an inch. It makes sense to me to minimize it to force most of the flue gas through the flues but not insulate the bottoms.

[tuckermtn]

just catching up on this tread...I spent yesterday afternoon doing exactly what Royalmaple did- making an earlier and steeper ramp to force the flue gasses up into my raised flue earlier...When I talked to Leader a few weeks ago they reccomended that the top of the ramp be 12" back from the front of the flue pan. mine was closer to 24" back...when we ran it that way in years past there was a noticeable line where the boil really started- about a 1/3 of the way back from the front of the flu pan. I'm looking forward to seeing how she runs now...

in terms of spacing between bottom of flues and top of blanket- I run about a half-inch gap to start the season and then the ash seems to close the gap by the end of the season so there is no gap...might try keeping some of that in there to have no gap...

[Brian Ryther]

Gary,

When I rebuilt my arch last summer I posted Pics when I had about 2.5 inches from my bricks to the bottom of the flues. Every response was to close the gap. I went with the 2.5 for the first few boils. I had good results. Then I put three rows of bricks in. One at the front, middle and back of flue pan to close the gap to within 1/8" at those three spots. Maplecrest drew me picture of this set up. He explained that the forcing the gases up in a few spots would create tirbulance under the pan = good heat exchange. I gained about a 20% increase in GPH.

Brian

[Uncle Tucker]

john explain what is meant by flue air injection ?and where did u get this info


I tried this with my 2x6 and the boil is the same the whole length of the flue pan. I never tried it without it but from what guest in my sugar say it is ripping. I would say I am getting about 35-40 GPH. I have two separate blowers, one for the grates, one for the air injection. I have pictures in my signature.

[Gary R]

Brian, I don't have a flue pan. It's a 3 section flat pan. I will close the air gap a bit. I also understand about the bricks for turbulence. Easy to add. I might put them under the blacket to keep some heat retension down.

Thanks