Suggestions to reduce sparks out of stack

[tjsappen]

I have a custom built arch (2.5 x 8.5) with 5' Smokey Lake raised flue and 4 divided front pan. I run Auf and Aof. I have a 10" stack. Auf is a large squirrel cage blower with a rectangular blast gate I can manually adjust the air from 0 to wide open at 11". If I run over 4 inches open I have quite a spark show out of the stack. The stack is covered with multiple wraps of square mesh to help prevent sparks. I'm looking for any suggestions to help reduce sparks so I can run more air. Typical stack temps are around 600 at 4 inches. I can get more evap if I can run hotter but can't risk the fire hazard.

This year I noticed burning hardwood seems to reduce sparks somewhat compared to popple/basswood.

Any ideas would be appreciated.

Hardinger Sugar Bush
500 taps

[Cedar Eater]

I have a custom built arch (2.5 x 8.5) with 5' Smokey Lake raised flue and 4 divided front pan. I run Auf and Aof. I have a 10" stack. Auf is a large squirrel cage blower with a rectangular blast gate I can manually adjust the air from 0 to wide open at 11". If I run over 4 inches open I have quite a spark show out of the stack. The stack is covered with multiple wraps of square mesh to help prevent sparks. I'm looking for any suggestions to help reduce sparks so I can run more air. Typical stack temps are around 600 at 4 inches. I can get more evap if I can run hotter but can't risk the fire hazard.

This year I noticed burning hardwood seems to reduce sparks somewhat compared to popple/basswood.

Any ideas would be appreciated.

Hardinger Sugar Bush
500 taps

Popple and basswood are both hardwoods, but they are on the softer end of the hardwoods. Hickory, oak, ash and maple are on the harder end and their ash is heavier and less likely to fly out of the stack and more likely to accumulate in your firebox. They also burn colder and slower, but you get more BTUs out of them. I can't help you on the spark arrester though, except to say that if you use a simple mesh screen that minimizes the size of the sparks, it makes it more likely they will be cold before they land on anything.

[maple maniac65]

I have been told the best way to eliminate sparks is to switch to liquid wood (oil)

[motowbrowne]

I was under the impression that AOF reduced or even eliminated sparks. Maybe you need to play around more with reducing AUF and increasing AOF.

[BAP]

Are you running a separate high pressure blower for your AOF?

[lpakiz]

I have an Intensofire clone with one blower feeding both AOF and AUF.
The sparks mine puts out are outrageous. In dryer boiling sessions, I have an extra, separate person designated ""fireman" whose job is to sit outside in a lawn chair with a hundred foot hose.

[maple flats]

Since adding AOF several years ago, we see no evidence of sparks, even when it is pitch dark outside and when the fire is freshly fueled. Maybe you should study the Proctor guidelines for AOF and find what may be different on your's.

[tjsappen]

AOF air is what I was thinking might be part of the issue. I'm not sure what kind of pressure I have. It is on it's own blower which I can control w rheostat. But I tried low and high and monitor sparks and it doesn't seem to matter. I'm thinking of switching blowers to one which is recommended for this application.

I appreciate all the feedback from fellow producers. Thanks.

Tom

[Tater]

Fire requires 3 things: heat, fuel, and oxygen. The purpose of AOF is to inject enough oxygen to thoroughly burn any fuel that remains. If you have enough heat and oxygen, no fuel will leave the stack. The purpose of high pressure and increased turbulence is to ensure mixing so that oxygen and heat will get to all the fuel. If too much air (over or especially under) is injected, it will cause a faster draft and consume more fuel, which may not all get completely burnt before exiting the stack. A major factor is turbulence. Just because there is enough oxygen in the firebox doesn't mean it is all in proximity to the fuel that needs it to burn. If you are not running high enough air pressure (or have too large of nozzles) your AOF may be ineffective. It is adding oxygen and some turbulence, but that is being offset by increasing draft speed, thereby decreasing the length of time the fuel is in the useful area.

AUF can increase the amount of wood burned by a significant margin, but it doesn't immediately turn from wood to ash. I don't completely understand it, but I believe it at least partially turns to a gas that is also a fuel. Without enough oxygen, this gas can actually exit the stack without being burned. In fact, some people have seen this as flames shoot out the top of their stack. In such a case, the oxygen-starved gas has enough heat that as soon as it meets oxygen outside the stack, it has the proper ingredients for fire: thus, flames appear as it finishes burning. It can take a significant amount of oxygen and turbulence to burn all this fuel. Some people who run a single high pressure blower for AUF and AOF find 2/3 or more of the air needs to go to AOF. With an 8.5' pan, you should likely have AOF injected under the flues two feet or so after the firebox to make sure oxygen is there and is not all being consumed in the firebox.

Another thing to watch for is to make sure your air is going where you want it to. Some people find they need to not have AUF for the first 6" or so inside the door because otherwise the air takes the path of least resistance up between the wood and the door rather than up through the wood. Also, some like to minimize the amount of AOF they have on the front of the arch blowing air back toward the stack (you will need some though). It's more important to have AOF in the back where oxygen can be injected as the gas goes into the flues (and again partways back through the flues).

[nymapleguy607]

Soft wood will give off more sparks than hard wood will so that would be an easy fix. Any evaporator that is solely running underfire air is going to produce a huge amount of sparks, its just a matter of adding the air through the coal and ash bed and blowing embers and ash up and the stack draft pulling it through. AOF is going to allow you to get the same amount of heat without running the AUF nearly as hard. Another option would be to add some type of screen in the base stack to catch the larger embers. No setup is going to fully stop the sparks but you can reduece them.

[mainebackswoodssyrup]

We run just AUF in our evaporator with good hardwood and have no issues with sparks so I disagree that in itself generates huge amounts of sparks. Our stack temp needle is buried over 900F when its rolling good. I can't help with AOF because I have no experience with it but Tater is right.............There are 3 elements and finding the right balance of all 3 is what you need.