Forced draft question

[nymapleguy607]

I'm not sure if any one has ever put any thought into this but would a forced draft work better if you pulled warm air into the fire say from back by the smoke stack. I don't know if by sucking in cool air from the sap house if that might cause cold spots under the pan. Any one have any more knowledge about this?

[maple maniac65]

I think the key is to fuel your fire with as much oxygen as possible. Warmer air might be a plus if you could do it without adding C02 that is already burnt. Leader forced draft adds cold air. The Hurricane uses air from inside the arch and inturn reburns the unburnt gases. Keep in mind that your blower may have a thermal switch built into it so the warmer it ges the more it might just shut off. Nothing is more frustrating then not having a blower work when you need to draw syrup

[Dennis H.]

I may be wrong on this one but I would think cool air would be better.
Cool/cold air is more dense and there for contain more oxygen.

[brookledge]

I don't think it would matter much the fire in the box is over 1,000 degrees and a difference of 50 degree air coming in wouldn't be that significant.
On the other hand I've wondered about those that use airator tubes in the pan whether it makes a difference on the temp of air coming in to the tubes since the sap is boiling at 212 to 219 compareded to over 1,000
Keith

[802maple]

As the designer of the first intens-o-fire's I highly recommend outdoor air which is denser and has more oxygen to it, to allow for better combustion.
The Hurricane is much like my Intens-O-fires and they add air to the top of the fire to keep the unburnt gases burning much like adding oxygen to actetylene on a torch. The only difference between the 2 is the intens-o-fires have more air injection ports and the grates are different.

Keith, I believe although I could be wrong by the time the air in a bubbler gets to the syrup it will be the same temperature as the syrup. I know that sugarmakers up here that have them have noticed increased evaporation although not big amounts.

[danno]

802 - can you give us the basics in building an intens-o-fire, or rig that will put air into the top of the fire box. Drilled galvenized pipe? How do you duct in into your incoming fan? Sounds like a fun project.

[802maple]

Here goes,

You need to put your air into a plenum that you divide to go to 2 places in your arch,then by using dampers to control your airflow to those 2 areas being your grates and your top air. Duct work is built into the arch to carry air to the front to cool and add air to the frame around the door and the door itself. The frame work is usually made out of 3x3 box steel with black iron pipe for nozzles and I use blanket insulation to insulate it so that it doesn't burn the steel. I transfer the air to the door through the hinge that is basically one pipe inside another which has been lathed to fit of which there are 2 of these both top and bottom. The door has a air chamber on the outside to allow air to get to the whole door for cooling purposes. On the inside there is 3 layers of 2600 degree blanket insulation, there are nozzle coming from the air chamber to the fire on 6 inch squares. On the door frame across the top there are air nozzles pointed down at approx. 20 degrees every 3 inches.

The back of the firebox has vertical wall going to the bottom of the flues at 2/3's the total length of the pans. basically rectangular box. Just under the pans, pointed forward are three rows of nozzles built into an air chamber that comes from the same duct work that runs the front air. These nozzles are welded in on 3 centers.

The other air goes to the grates that I make out of firebrick by drilling 3 - 3/4 inch holes in each one of which I have very good luck with. The reason I don't use the cast grates is simply they have to many and to big of holes in them which puts to much air to the bottom of the fire making it very inefficient. A good arch such as the above mentioned Hurricane or the intens-o-fire only put 25 percent of the total air to the fire with the remaining 75 percent going over the fire. The bottom fed forced air units will boil just as hard but their would pile will be smaller at the end of the year.

You have asked me something that is easy for me to build but hard for me to explain as there is shortage of brainwaves between my head and fingers. I hope this helps.

I also use high pressure blowers to run the arch based on 15 to 20 cfm per square foot of arch depending on how many restrictions in the duct work system.

[danno]

Thanks 802 - I've got a general idea, but I think I've got to see it. Care to give me a realistic opinion in the increased gph going from standard forced air under the fire to air over and under the fire on a 3x10?

[802maple]

first let me see if you have one in your area, I don't know where they all went as we only built them and Maple pro sold and delivered them, so I don't know where they all went.

You will notice a 20 to 25 percent increase oer a standard arch with forced draft ,but more important you will use a lot less wood. Not only because of the more evaporation but also from the better efficiency of this style evaporator, whether it is a Hurricane or a Intens-o-fire.

[SUGARSMITH]

Putting hot air into it would make it more efficient. I thought the same that the dense air would make it combust better, ( dense air makes airplanes perform better). I work in the coal fired power plant industry and millions of dollars are spent on air preheaters to make the incoming air as hot as 7-800 degrees. However, for the scale of an evaporator, I think it would not be worth the effort.

[H. Walker]

I was told by the CDL sales rep. that the new Intens-O-Fire draws the combustion air through the inner and outer side walls to pre-heat the air. by doing so he said it increases the efficiancy by something like 5%.

[802maple]

I guess I should restate what I meant is that the air should be coming from outside as there is more oxygen in that air but it is warmed up by the arch itself, There has been some so called improvements in the design of the arch since it has left my hands, but the only thing that I see that has changed is it dressed up a little with a total stainless outside and the damper controls have changed, the inside is basically the same.