Forced Air - the next step.

[danno]

I already have forced air below the grates and am toying with the idea of placing some air nozzles above the grates, a few inches below the pans. Anybody have any experience with increased boil rate and /or burning less wood with this set up?
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[Bucket Head]

I have no experience with forced air above the grates. However I do know some, if not all the evap. manufacturers, have a set up where air is injected above he grates. I am not sure of the exact location though.

Thay say it improves combustion. It must have some merrit, or they would not implement it.

It probably does not "save" any wood. More air means more flame. If anything, maybe same amount of wood, but "more" heat extracted.

Steve

[WESTVIRGINIAMAPLER]

I have air injection all around both sides and top of my archfront. I am looking to add air to the top of the fire a few inches below the pans and may add it to the rear and both sides giving me air injection on all four sides above the fire. This will be probably summer of 2010 if I do it as I am hoping to work on finishing some on the inside of the sugarhouse this summer. I would also like to hear what others have to say about it. I hope it increases my boil rate some. I would like to get it up to 70gph or better, but I am not sure how much this will help with any, but I think it will.

[mfchef54]

go to www.uvm.edu/~pmrc/Combustion.pdf. they have a description. I can't take credit for finding this as someone posted a while back. There is a diagram at the very end of the paper

[danno]

Yup - that's the article I read. The wood saving is really what got me thinking. I assume this is how the inferno arches are built. Looking for someone with some first hand experience about best installation method and whetherr results justify the modifications.

I'm thinking of running 1 or 1 1/2 inch pipe along the back and sides of the fire box a few inches below the pans and drilling the pipe every couple of inches for air release.

Was just looking at my newer wood stove with similar air at the top.

[WF MASON]

The bigger the air flow , the bigger the burn.
Adding air is'nt all that hard , but most don't add enough. Talking to 802maple ten years ago, I learned more about forced air in fifteen minutes than I thought I'd learned in ten years of adding blowers. Jerry is 'the king ' when it comes to adding air. When he posts, learn from it.
There is a forced draft that gives you 5 gph more of evaporation, and there is a forced draft that gives you 15 more gph and can put the sap into the rafters.
As with most things maintance has to happen. On several , at about 6-7 years old,like Brandons but with double doors,I've seen the pipe nozzles burn off and the tube they are welded on will rust and flake from the inside,or Sometimes the flakes will fall down plugging the tube and without the airflow to them , the fire eats them up. But its mostly rust from inside,(the off season) Making sure the pins/washers/blanket or refactory is in place is a must. Or the tube and nozzles must be replaced in the field as were done with these.
More air more burn.

[Beweller]

In solid fuel beds, the oxygen introduced below the grates is consumed very rapidly. If the fuel bed is "deep", the oxygen is consumed completely and above that level the fuel is gasified, a process that consumes energy and makes combustible gases.

If no air is introduced above the bed, the combustion energy of these gases is lost up the stack--and sometimes if the stack temperature is high enough, they burn when they hit the outside air.

With insufficient air you loose two ways--the loss of the combustible gases and the loss of the heat needed to gassify the fuel.

"Deep" is in terms of particle diameters, and more than about three particle diameters is "deep". For the wood fired arch, the appropriate particle diameter is not the diameter of the wood fired but is the "diameter" of the charcoal particles sitting on the grate.

The amount of air introduced below the grate is largely responsible for determining the fuel consumption rate. Increasing the under-grate air will cause the boiling rate, stack temperature and wood consumption to increase, and eventially will begin to blow the fuel out of the rig. This was a real problem with coal-fired steam locomotives.

[RileySugarbush]

It's interesting to me why introducing air above the fuel would be advantageous compared to more air through the fuel. If you had two blowers of equal capacity, would it be better to have one inject air above the fuel or just use the second one to double the air introduced below the grates? Seems to me that if there is more oxygen introduced below the grate, that there would be sufficient remaining above to further combust the gases above.

Yet rather than just putting on bigger blowers, the fancy arches use all those expensive pipes in hot areas where they are at risk of overheating as discussed here.

Why is that?

[swierczt]

How much is enough? Is there a relationship between cfm and square inches of pan?

[danno]

All I know is that "state of the art" wood stove technology is to put air into the fuel AND above the fuel. These units are all very "smoke free" as the combustion is occuring in the fire box, not up the stack.

Also, have you seen the flame caused by air above the fuel? It looks very bizarre. It's not a raging fire, the flame just kind of floats. It's hard to describe.

Where's Jerry?