blower vs. open draft

[7810hunting]

Could I get close to the same results by keeping my bottom draft wide open
rather than installing a blower on my 2x61/2 maple pro evaporater?

[Bradenfish]

I'm no expert but i doubt it. I run my 3x10 draft wide open with no blower. I assume that most people always run their's wide open.

[Sugarmaker]

7810
Like Brandefish, what ever you have you pretty much run wide open or as fast as it will boil. I would say the execption to that is that you can get too hot of a fire in your evaporator. A blower system can raise your stack temp and possibly have a stack melt down. NOT a good thing.
Natural draft may not allow that to happen?
Anyway I think you will boil more sap with a blower than without. But you need to fire consistently too.
With a blower I get a good boil in all areas of the evaporator. It feels like I am boiling faster. I can get about 80-90 GPH. I have not boiled much on this rig with out the blower. But I would estimate 60-70 GPH without the blower going???

[3rdgen.maple]

No is the simple answer. If you add a blower I would first check with manufacturer about voiding warranty. They are gonna probably tell you to buy different grates and a new arch front made for this application. And there is good reason for it.

[Brent]

you will get a hotter fire if you put a blower on it

BUT

a huge part of that heat will go up the stack AND you'll burn a lot more wood per gallon evaporated.

The US Dept of Ag Forest Service and Vermont University have both published studies that show that you need to blow about 80 of the air above the fire and only 20% up through the grate. Under normal circumstances with a blower or natural draft below the grate, you are not burning all the wood gasses. The fire is starved of O2 above the visible flames. Adding air under significant pressure above the fire causes turbulence to mix the gasses and get more efficient use of the wood. This is exactly the same basic principal as modern wood stoves. They have no grate at all.

There are lots of other threads on this subject.
To read the articles go to our web site and at the very bottom of the "making syrup" page there are links to 3 important articles
http://www.duffyslanemaple.ca

Also what is arguably the most efficient evaporator made is the new Hurricane and it has no grate whatsoever. It injects air at high velocity throughout the firebox and does it so well that the fine ash left over blows clear the other end and is removed under the stack.

[Fred Henderson]

I have found that for my operation it is best if I pull the coals and ash after each firing. With no ash buildup it leaves more space for air to come into.

[KenWP]

I finally found a sorce of a small fan I am going to try on my evaporator for the top of the flames. I took apart a old micro wave last night for the transformer and the fan on it blows a resonable amount of air for a small evaporator. I am looking for a little extra just to make it burn hot especially on those dasy when the barometric pressure causes it to stop boiling. I have to find one more microwave for another transformer so should have a couple of fans to use.

[dano2840]

so how do you duct the air from a blower above the fire on a convetional evaporator with a draft door?

[bison1973]

I was thinking of adding forced draft to my arch. Evrything you see about them claims to save wood (in cataogs, etc). But on this message board I've seen where people say it will actually make you use more wood (like mentioned above). So what gives? I liked the idea of forced draft grates but not so much if wood consumption will go up.

Will people with forced draft grates tell of their experiences with and without it?

[Amber Gold]

This is my experiance. Keep in mind this is one year's worth of experiance, so don't have years of data to back this up.

I have a 2.5x8 with a blower and forced draft grates. Last year burning a combination of dry/partially dry/wet wood I was able to max out around 65 gph. I think this year with nice dry wood I'll do about 75gph. There's another trader w/ the same evaporator but it's bone stock and he averages 55 gph. I'm not positive, but I believe our wood per gal of syrup numbers were about the same and my sap ranged from 1.2% to 1.8%. I don't recall what his was, but it was better than mine. I believe you will burn more wood per hour, but you're also increasing your gph.

You don't need the forced draft grates. You can use fire brick and drill holes in them. They work well and are far cheaper.

[WESTVIRGINIAMAPLER]

I have went from 35 gph stock to 60 to 65 gph with a pressurized inferno arch and the air is only from the underside. Yes, I burn significantly more wood but I evaporate significantly more gph. In the long run, I get more syrup per cord that I did before, not much, but I wouldn't care if it was less syrup per cord, I don't have forever to boil.

As far as stack meltdown Chris mentioned, not sure what that is. I run my stack usually from 1400 to 1750 degrees. Hopefully one of these days I get get high pressure air mainly over top of the fire and cut down on wood usage.

[Sugarmaker]

Brandon,
I agree with the fact that more wood is used. but I also like you believe that I am boiling at a faster rate.
"Stack melt down" which could be catastrophic to anyone's operation. is when the stack gets so hot that it glows cherry red and it looks like you could poke a hole through it with a stick. I am speaking from experience here. This was due to aggressive firing and running the blower at full output for many hours. My point was that with a blower on a wood fired arch it is approaching the same process as a forge, which is to get a much hotter fire. Blowers under the grate will do just that. They also are forcing a lot of heat up the stack and if you have a conventional front on the arch it may get hotter too. Probably a lot more than a air over fire unit.
I have a external stack thermometer and try to keep the stack temp under 900 F. with 750 F seeming to be a good avg boiling temp in the stack for our rig.. Your stack temps are twice as high as mine but you may have a different method of measuring compared to mine being attached to the exterior of the stack.

I built my own lost cost blower grates from angle iron and they are still working but have warped somewhat. I have fired other evaporators with cast grates and no blower and they did not boil in all areas of the the pans.

Chris

[Paddymountain]

Today I ran the first test boil with my refurbished 2.5 x8 evaporator.
I have two 2x4 box beams running along each side of the arch above the grates. Each has a 110 cfm squirrel cage fan on it. I rebuilt the doors and
made them airtight. I don't know about wood consumption yet as I was using
2x4 cutoffs and such, but I evaporated about 50 gal an hr without really firing it very hard. Last year I had a 275 gal evap with flat pans, but also had air over fire. When the fire is going good it sounds just like an oil furnace
and there is no smoke coming from the stack.

[Brent]

When I put a blower under the grate with my Half Pint 3 years back we boiled a lot faster too. No question about it. My guess is we went from about 7-8 GPH up to 10-12. But you couldn't turn your back on it for very long. It ate an ungodly amount of wood... flat pan of coarse. And I think it takes far more than an hour to cut, split, move, stack etc than it takes in wood to boil for an hour. Besides, my bush is pretty much cleared of beech and ash. I don't want to be cutting the ones that give the golden eggs so wood efficiency is getting more important to us.

I also think that last year our 2 x 6, with tiny blowers above the fire, ate less wood per hour than the Half Pint.

[WESTVIRGINIAMAPLER]

Chris,

I am using a Condar internal stack thermometer that is magnetic on the outside and probe that senses temperature goes about 3 to 4 inches inside the stack. Here's the link if anyone wants to buy one, mine seems very accurate:

http://www.condar.com/stovepipe_meters.html

It is the 2nd one down from top and is called the Flue Guard and it registers to 1700 degrees.

[slammer3364]

Stop out and check out tje little blower we made for ours improved boil time and I dont think we used any more wood:) :)

[ibby458]

I used a belt drive furnace blower that had air intake on only one side. I control the air by partially blocking the intake with a piece of plywood. The output is adapted from 10x10 inches to 4x24 to insert in the back of the ash box. (Had to put a bottom in the ash box first) I sealed the ash door with gasket and pipe clamps. (Makes it easier to clean it out.) The grates are still the original Grimm style. They did warp pretty bad in one corner where the ash built up enough to block the air in that area. I used SS bolts to secure some arch blanket to the existing doors.

By keeping the blower intake about 1/2 blocked, I can still fire the arch without shutting off the air.

My stack temperature (with an industrial stem thermometer inserted in the stack) maintains 750 - 1000 degrees.

My evaporation rate went from 50-55 gph to 90-100 gph using bone dry hardwood. The wood consumption dropped almost by half. You do have to fire it ALOT. If the fire drops much at all, it takes quite a while to get back to where you were. I found every 10 minutes to be right.

Not all the improvement can be credited to the blower. I also put another layer of bricks under the flue pan so there's only 1/4" clearance. THe wood was better too, no softwood at all, dried 2 years and split pretty fine.

To ensure the improvements were real, I kept meticulous records, writing down every firing time, drawoff and head tank filling. (As I had for every boiling since I got a real evaporator) The gph was calculated for the entire 8-10 hour boil, including startup and shutdown. The average sap was 2.5%. (season average) (high of 5.8 on some old roadside trees, low of 1.2 on some younger deep woods trees, all on buckets)

I also recorded sap totals from each section of woods and percentage. Very handy to determine what to tap. Syrup grade and amount was recorded for every draw. I also recorded container size, grade and price for every sale. All this makes planning for the future a lot easier.

Unfortunately, I lost all my records when our house burned. Gotta rely on memory and start a new set of records.

[vtsnowedin]

This is my first post at mapletrader.com. I',m glad to meet you all. Currently I am setting up a 3x8 Grimm lightning that my Wonderful wife gave me for my last birthday. It has SS pans that may not be original as the arch dates to the sixties. The arch has an original equipment blower and there is a rheostat that mounts on the wall between it and the power source that lets you control the speed of the fan. The blower is mounted under the flue pan and feeds into the ash pit under the grates. The front is conventional cast doors uninsulated. This setup lets you mount the rheostat on the wall near the front of the rig so you can turn the fan down or off while loading wood and control the burn to keep all of the flue pan boiling without over doing it and super heating the stack. I never saw this rig run but I have boiled on a 5x14 that had conventional front and a fixed speed blower mounted in the same place. It would blow sparks and smoke out the edges of the doors if the fire was too close to them or the weather was turning towards rain. Had to shut it off at each firing. PITA. Apparently technology has moved ahead and now it's best practice to inject some air (cold or preheated) above the fire to add oxygen later in the burn cycle. I don't know how I could modify this rig to add that. I think that for now I will set it up like I found it and see how it works and go from there. A steam hood over the 3x5 raised flue pan with preheater is also on the want list but will have to wait until I've made some syrup.

[Sugarmaker]

vtsnowedin,
Welcome to the trader!
If you have boiled on a 5 x 14 then you are in a league above me. Thats a large rig. BTW nice gift from the wife! I may drop a few hints to the little MRS.:) I could use a shiny new unit.
We run our 550 CFM blower on our old 3 x 10 King on low most of the time to avoid over heating the stack and do not shut it off during firings which are about every 5-6 minutes. Using pallets as fuel.

Regards,
Chris

[smitty76]

welcome aboard vtsnowedin

good luck with your new pan as well. My wife can't stand how much time I spend at the sugar house and will never purchase any sap stuff for me, but she sure loves the syrup.

Have Fun and Good Luck