How many cfm needed?

[islandviewpeter]

I have a 2x8 raised flue Phaneuf with an air tight arch running natural draft. Smoke seems to be black/grey so I think I need more air. 9" stack over 16'. Boils good when it gets up and going, but smoke stays dark. Been playing with a squirrel cage blower directed in the draft door. Wondering if I should cut a plate to cover the door and only let the air in with the fan? Or would this not be enough air? How do you figure how many cfm you require for AUF.
Burning dry ash, split small, firing every 7 minutes. Good ripping fire heading back arch.
Thanks,

[boondocker]

I have a 30X8 CDL and I added a blower and a airtight door, insulated the front and blocked the draft door. I find it odd it only has a 9" stack? Mine has a 12" stack. Only time mine blows black is just after firing but I have a hard time keeping a consistent hard boiled is what my issue is. Add the blower to the back of the firebox and block the draft door. It could be the wood or lack of air. My blower is a 450cfm Dayton.

[islandviewpeter]

Found a piece of heavy walled 4" pipe in the shop. Thinking about cutting a piece and laying in in the ash space. Planning to drill holes in it to direct air flow up into fire. Considering drilling equivalent air space as we have in the draft door and then sealing the draft door. Not sure of the cfm of my fan.

[islandviewpeter]

So I found an earlier thread where it was suggested (Big Eddy) that for a low pressure blower that one should have half the area of the stack in air inlet openings. So my stack is 9" which is 64 square inches then i would need around 32 square inches of opening in the pipe we are placing below the grates. Which we will obtain with around 55 7/8" holes drilled in the top half of the pipe.
Does this sound right to get a good fire burning?

[BreezyHill]

Our 2x6 grimm came with a 140 cfm fan. two years ago I added another 70 cfm fan and it helped a bunch.

Last season I hooked up a fan that was to a semi truck exhaust suction system. 8" fan on a 1750 direct drive system. I have had to slow it way down and find that there is a point where you will have no smoke and the ash is supper fine. I can boil for 5 days for 3-5 hours each day on 12% sap and make 3 gallons of ash.

I would cut out a cover and use forced air. Look on ebay for fans. the other place is bounce house fans on clist. I have seen them go for $20 and they will have plenty of air supply.

I saw a catalog from bascoms and a 2/6 to 3/10 had a 500 cfm fan that was adjustable. This was back about 4 -5 years ago.

[islandviewpeter]

Thanks for info. We are going to try the forced air route. I have a squirrel cage fan off an old grain aerator. Just trying to figure out how many cfm it moves. label shows 1450rpm, .08hp, 2.3amps it has about a 8" diameter cage on it. We'll give it a try and see how it goes. Just blowing the fan straight in the ash door had a visible effect on the smoke exiting the chimney and seemed to help even out the boil.

[Mini_Maple_Men]

We found a $50 floor drying fan in Home Depot and built a duct to go in our ash door, it really increased our evap rate but on the lowest setting I still have to block the intake half way or it will just blow flames out the top of the stack. And we really have to watch our stack temps on our little arch!16195

[BreezyHill]

Just remember black smoke is to little air
and blue to a light gray is to little heat.

You can blow to hard and to early to get a good burn. Stack temp gauges are a great tool when using forced air.

With my modification I don't need air over the fire as I have so much pressure below air is making it up thru and completing the combustion cycle.

No smoke, less soot on the flues to brush off each day and the ash is super fine.

Good Luck!

Ben

[islandviewpeter]

Thanks, Ben.
What do you have directing the air under the fire?
I installed a digital stack thermometer last night so we have that covered now.

[BreezyHill]

I just have the standard grates and the blower comes in the ash pit thru a plenum that is v shaped to supply air to the entire width of the ash pit.

The grates have a3/8 to half inch opening that the air shoots up thru. They glow and I have cracked one of them. I need to weld that one before next season.

[islandviewpeter]

So now I need help
Interpreting today's data. Put the pipe down the centre of the ash pit with 52 7/8 holes in it . Then blocked the ash door and connected my fan. It was pretty obvious the fan wasn't putting out enough air. Pretty slow fire, wood was turning black. Stack temp barely to 500. Opened up ash door and left fan running and things got moving. Boil got going, stack temp got up into the 900 -1000 range. But then I shut fan off and stack temp went to highest of the day. 1080. Boil seemed to get moving especially in back pan.
I didn't have enough sap to more closely compare boil rates. In both cases the smoke was still blacker than I would like.


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[Super Sapper]

What size of pipe did you use? These fans fo not put out any pressure and any restriction will decrease your cfm. I mounted mine to the back of the ash box and let the grates diffuse the air.

[DocsMapleSyrup]

I agree with Super Sapper. The low pressure fans move air but any resistance reduces cfm substantially. I had a similar instance and was trying to use a 550cfm fan to blow air up through holes drilled in firebrick which line the floor of my arch. Didn't work. I drilled as many holes into the firebrick as possible, didn't work well, so I ended up going to to a bouncy house blower which is a high pressure blower. Now I've got something! If I were to redo my arch, I would pull out the firebrick floor and use 2" angle iron "V" up to hold ash and insulate the angle iron and would space them 3/8' - 1/2" apart to allow the air move freely under the grates and through the grates. If I did that, I would not need the high pressure blower. In your case, if you can get rid of the pipe and blow air under and through the grates, that my improve things for you.

[islandviewpeter]

We used a 4" id pipe. See attached picture. We slide it in from the front and then cut a plate to close up the rest of the ash door area. It was quite obvious that there was not enough airflow so I just slid the plate back and let the natural draft work along with the fan.
Interesting thing was with both the fan and the natural draft running the stack temp would go up when I opened the door to fire. Is this normal?16221

[BreezyHill]

Let the fan put the air to the ash pit. the grates will allow air to go into the fire box where it is least restricted by wood blocking the grates.

As one said the pipe as a diffuser is restricting the fans out put.

My fan is a Chicago style fan (paddle fan) it produces good amount of pressure. so the air will blast up thru the grates and mix with any unburnd gases. The black is carbon that has not burn oxidized.

Your goal is to have no carbon in the exhaust pipe of the evaporator(Rig).

If you have an air leak under the pan and the stack is pulling air in then your stack temp can go up with the burn of carbon in the stack.

Sight glass on the rig to see where the burn is occurring is helpful.

The ideal situation is that the stack temp will be at a moderate level. Too high and you are still burning gases/carbon in the stack or at least near the probe.

Think of it like this...if the exhaust going by the probe is 1000 degrees how much more pan length could did you need to have sap pulling the heat out of the exhaust.

The other side of that coin is am I getting the most out of the fuel burned.

My youngest son has the boiling rate record for our family. I have sat and watched him load the rig and it goes against everything that I have ever read or seen. He fuels every couple minutes. The fresh wood is an inch from the pan and the coal bed is deep. Stack is not that hot 700-800 and the smoke is clear, just heat. When he fuels you see a little black for maybe 20 seconds and its gone. The pans are rolling very well except for the last foot of the flue pan.

After days of contemplation I think I figured it out. He has the front pan boiling from the front to the rear. This gains him the advantage. He is pulling of more syrup per hour thus raising the sap inflow rate. The way the rest of us fuel the flue is doing the bulk of the work with a fast boil across the entire pan and heat escaping thru the stack. The front pan is boiling from the rear to the front and while we have acceptable pull of rates it is reducing our boil rate by the 2-3 gallons an hour in boiling rate.

I am sorry to say that the plan as of now is to install an oil burner in the rig to facilitate my post accident level of activity. The saving of time of loading the rig will be used to keg the syrup immediately and have one person running the operation with the most efficient use of time. I plan to just install a plate over the grates so that the rig can go back to wood in the future. But three sons still in college and another 2 years of recovery was not what I had hoped to hear.

Keep a note book or clip board pad of notes. Dates gallons of sap, hours of burn, wood used, syrup pulled off, stack temp, outside pressure, and if you can figure a way to get an inches of water on the ash pit, you can make your rig a super efficient unit.

The inches of water will be able to help you get the perfect timing of fueling the rig...when the reading reaches a point, that is a low reading of when there is the least amount of restriction you will see your stack temp fall from the air that was not used to burn fuel. This will lead you to a point or pressure that you need to fuel the rig.

Stack temp is a crucial source of info but it is not the set point we need for optimum efficiency. I think it is a combination of factors and a large factor is your fuel source. How dry is the wood, type of wood, and size of the wood will all play a factor is your final reaching your optimum boiling rate.

Yup these are the things I think of when boiling at 1 am. And yes it is tough to not be in the thick of it this season...addiction is a good description of our passion. LOL

[islandviewpeter]

Thanks, Ben
It all makes sense. I'll keep monitoring and making notes to see what happens. It's all part of the fun. Setting up the stack thermometer has already yielded some interesting information. I do have a piece of glass in the door but it's usually so dirty you cannot see much thru it. Overall I feel my unit needs more air, natural draft has quite dark smoke, I just need a way to get more in there. I'm shopping for a stronger fan and in meantime will go without the pipe for a try. Freezing rain today, not enough sap to bother firing up. Looks like mid week we will get going again up here.

Sorry to hear you are recovering from a mishap. May I ask what sort of accident you suffered?

[BreezyHill]

I was the one that was not expected to live when a drunk driver was doing an estimated 60 mph in a 35 thru a red light. I was returning from a rodeo where my youngest son was team roping. Our Ford Explorer had everything from the font tires forward removed. I caught him in the corner of my eye and I laid down about 8" of rubber according to an investigator. I had a broken back, left hip blown out of joint and most of the ribs on the left side were broken length wise. Bruised lung, spleen, small intestine and liver, right shoulder was all stretched appart and pulled my sternum apart, and a TBI tramatic brain injury. We spun so fast we hit the back of the other suv for a second impact and then went around a couple more times to come to a resting point about 50 feet from where we were hit. My wife also caught a glimps of the car and relaxed. She got a broken two and pulled muscles in her back. Oldest son got a separated shoulder and his girl friend that was asleep got a bad concussion.
week in the spine unit and then home to live on ice for about 8 weeks. I was in our towns squad for 4 years and know that morphine and the lot are not good to be on so I opted for the less addictive drugs and ice. When I went in to our feed store 4 weeks later for a visit I could not make change to save mylife. Pretty odd to know quarters nickles and dimes and pennies and not be able to add them together.
Prior to the accident and it is starting to work again I could do math in my head for several digits.

The secreat to life is to live every minute to its highest potential, Love and be loved and to share knowledge with others. It is a pretty dark road to travel if you cant help your friends and soon to be friends. Friends= a stranger you have not meet yet.

Live life like you were dying has a lot of meaning to me know.

I just got back from a walk in the sugar bush with my youngest to check the squireel population. 20 minute hike took an hour plus. I have no concept of time now. So days seem super short. I can recall the past very well it is just the present. Wife brought lunch to the store a few Saturdays ago and I had the super sized sweet tie. several hours later took a customer back to the paroit feed isle and there was a sweet tea on the shelf. I was not happy that DA Fool left their drink there. Well that Dumb *** fool was me. LOL

When you are to the point you can laugh at yourself you are in a good place in life.

Drive defensively it will save your life!

[maple flats]

Found a piece of heavy walled 4" pipe in the shop. Thinking about cutting a piece and laying in in the ash space. Planning to drill holes in it to direct air flow up into fire. Considering drilling equivalent air space as we have in the draft door and then sealing the draft door. Not sure of the cfm of my fan.
I did exactly that but it was on a high pressure blower when I added air over fire/air under fire. I think it will still help under the fire with the right amount of air input. On a squirrel cage I just bon't know what size blower is called for.
If you have any smoke after the fire initially gets started you need more air. You should not be able to see the exhaust except for maybe a few seconds when you add wood.

[islandviewpeter]

Under natural draft I always have had dark smoke, but I do need a fan with more push to get that extra air into the rig. I am going to try just the squirrel cage with no restrictions into the ash drawer along with the natural draft until i can source a stronger blower. I'm working in from the front this year and hope to move it around the back next year.

[mellondome]

Ditch the pipe... just blow into the ash area under the grates. Also, block off the fiest 6 inches of the grate by the door and the last 6 inches by the ramp. This will ensure the air is going up through the wood. If you don't it will take the path of least resistance .. up the door and across the pans killing your boil. Same for the back... it will push up the ramp putting cooler air under the flues. You want all the air to have to go though the burning lumber.
When i used wood, i found a squirrel cage blower that fit the ash/draft door opening. Full on @465cfm was a little much for a 2x6... but you could see in the shack without lights due to the base stack glow!

[islandviewpeter]

Had a good boil last night. 250 gal in 5 hours from match strike to shut down. When rolling good stack temp stayed in the 970 to 1070 range. Smoke is starting to clear was still black at firing but changed to whitish when rolling good. Set up was squirrel cage blowing in ash door from a 6" piece of duct, ash door completely removed. Blocked area of grate inside door with a row of fire brick and also area at back of grate as well. Good even boil. Consistent draws. Once going good was firing based on stack temp. Average from start-up around 50 gal per hour, was above that at peak boil. Boiling 3.2% sap.

Thanks for all suggestions. Might try a bit stronger fan in the future as I still feel we are lacking a bit of air.

[BreezyHill]

I would bet another 25%-35% mor cfmx and you will have her.

It does take a good amount to get the last of the carbon fully burned but a dimmer switch on the unit or an intake adjuster will help you throttle the air volume to just right.

[islandviewpeter]

Thanks, Ben

I really appreciate you taking the time and energy to respond and provide advice. Sounds like a a horrible experience for you and your family. I wish you and yours a continued recovery.

Peter

[islandviewpeter]

So confession time.

Wanted to get some more air out of the fan so my Dad found a motor and turbine off an old furnace which looked like it would fit. He took our squirrel cage apart to assess the switch and discovered the fan was put together wrong. Motor could mount on either side, it was mounted on the wrong side. Switched it around and voila! massive increase in air flow. I started up up to check before firing and blew all the little bits of loose ash in the pit all around the milk house. Had to block remainder of draft opening but it really got it up to boil fast, clear smoke, nice even boil. Wonderful.

I had thought that there was not much flow out the fan and it was low pressure, but it really was low pressure! We inherited the fan when we bought the farm 30 years ago so we can't be held responsible for original assembly problem. Only used it once to try and aerate some moist grain but it kinda sucked (haha) so we set it aside. Solved the grain drying issue with bin floors and fans.

Now I just need a good run of sap to really get things steamy.

[BreezyHill]

I had a similar issue. Motor was wired backwards form manufacturer and it sure did make a difference when I got that cage spinning in the right direction. :lol: