Prill combustion air

Re: Prill combustion air

PostBy: BigBarney On: Thu Nov 13, 2008 12:46 pm

Steinkebunch:

I had a hand fired stove of this type years ago and the tubes look just like your

picture that seems to be normal combustion for bit coal.The carbon is exactly

where you would expect,the coolest tubes in the heat exchanger near the

center bottom where there is the most cooling from the air flow.

The heated secondary can be located anywhere that could be easy to

install and regulate with with a flapper valve to the coal you are burning,

each coal has different needs based on the % and type of volatiles contained

in it.

Could you show an outside picture of your stove and any place you already have

easy access to add the preheated air,somewhere on the bottom would be best

near the ash pan.


BigBarney
BigBarney
 

Re: Prill combustion air

PostBy: europachris On: Thu Nov 13, 2008 2:17 pm

You can also try a refractory "reflector" that hangs above the firepot. Get some refractory castable cement and make a mold about 8 or 10" diameter and 4" thick, wire reinforced. Pour it and make sure to have a method of attaching a chain to it cast in also. Then, hang that from the center tube above the pot and adjust by trial and error, but start about 8 or 10" above the pot. That will reflect heat back down on the fire and assist in making sure the volatiles get enough heat to light off.

Use some stainless steel chain or cable so it will last a while.....
europachris
 
Stove/Furnace Make: EFM 350/Iron Fireman
Stove/Furnace Model: Custom bituminous burner

Re: Prill combustion air

PostBy: steinkebunch On: Thu Nov 13, 2008 3:51 pm

BigBarney: Photo shows outside of stove. I was actually thinking of tapping into the forced combusion air though - just rob a little of that air since it's already inside the firebox. I could drill a 1" hole in the air duct prior to the burner, bolt on a pipe flange, and screw some steel pipe and fittings together to get through the flames a few times before releasing the air near the heat exhange tubes. Judging by how the heat exchange tubes and firebox walls have lasted (mild steel I presume), one would think the steel pipe would last a few years.

Refractory cement is an interesting idea. Sounds like a simple idea to try. Maybe even suspend a firebrick or two for a really quick trial.

Steinke
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steinkebunch
 
Stove/Furnace Make: Homemade Bituminous Hand-Fed
Stove/Furnace Model: Prill underfed stoker Model M8


Re: Prill combustion air

PostBy: Berlin On: Thu Nov 13, 2008 4:32 pm

better than secondary air in a stoker setup is the use of ceramic fiber board (can be bought online) get 1" thickness cut it into a circle and suspend it above the firpot just below the air tubes; this will dramatically reduce soot and be much much simpler and more effective in a stoker.

I don't understand how this thing is not working properly. it is normal for some soot to develop in the firechamber during idle, then burn off after a hard firing and repeat. there shouldn't be flames in the smokepipe. if you have flames in the smokepipe w/too much air and EXCESSIVE soot in the heat exchanger w/ too little air then you simply have to much fuel for the furnace.

please post some pictures of the fire while stoking; this would help.
Berlin
 
Hot Air Coal Stoker Furnace: Will-Burt Combustioneer 77B
Coal Size/Type: Ohio BITUMINOUS pea stoker coal

Re: Prill combustion air

PostBy: steinkebunch On: Thu Nov 13, 2008 5:05 pm

Berlin: You could be right that I have too much fuel for the furnace. I need to get a smaller pulley to slow the feedrate down and see how that works. I'll try to get some photos of the burn too. At any rate, a ceramic fiber board or other secondary air improvement couldn't hurt.

Steinke
steinkebunch
 
Stove/Furnace Make: Homemade Bituminous Hand-Fed
Stove/Furnace Model: Prill underfed stoker Model M8

Re: Prill combustion air

PostBy: BigBarney On: Fri Nov 14, 2008 10:38 am

All:

This idea of a plate over the fire is another excellent one that is used in European Boilers to help

burn up the volatiles with the intense heat reflected back into the fire pot. Maybe a combination

of reflection and additional air would be even better.

Steinkebunch: The idea of using the forced draft to the firepot for the extra air is doable by the

splitting the air off,and ducting it above the fire to complete the combustion process.Now you have

to see how this can be done with the least modification to the stove.Can you send a picture of the

air feed and stoker side of the stove?


BigBarney
BigBarney
 

Re: Prill combustion air

PostBy: steinkebunch On: Fri Nov 14, 2008 11:38 am

First pic is fire stoking with air open too much - flame is whiter

Second pic is with fire stoking, air close quite a bit, yellower flame. But the flame is still 18" long or more.

Photos were taken on different cameras, so they are hard to compare. Still quite a few sparks go up the chimney even with this lower air setting.

I'll try to hang a firebrick inside this weekend to see what it does.

Steinkebunch
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steinkebunch
 
Stove/Furnace Make: Homemade Bituminous Hand-Fed
Stove/Furnace Model: Prill underfed stoker Model M8

Re: Prill combustion air

PostBy: LsFarm On: Fri Nov 14, 2008 12:46 pm

I think you have the explaination right here.. I'd slow the feed and see what happens.. you have a very big fire for a fairly small heat exchanger.. Or you can try some PRB coal like you mentioned..

Let us know what you find out.

Greg L


steinkebunch wrote:I cannot adjust the feed rate. The stoker/auger just turns at a constant rate. No step pulleys. Some could certainly be added. But to lower the feed rate, I'd need a smaller pulley on the motor, or a larger pulley on the gearbox, I think. I'll have to give that some thought. These stoves were made in Sheridan, WY, which has local Powder River Basin coal, more in the 8,000 btu range. I'm using coal on the other side of the BigHorn mountains. It is way different. Maybe i need to do some tweaking, or just try a few weeks of the PRB coal.


Steinke
LsFarm
 
Stoker Coal Boiler: Axeman Anderson 260
Hand Fed Coal Boiler: Self-built 'Big Bertha' SS Boiler
Baseburners & Antiques: Keystone 11, Art Garland

Re: Prill combustion air

PostBy: BigBarney On: Fri Nov 14, 2008 1:23 pm

Steinkebunch:

Like LSFARM said it looks like you have a excessive feed,too much coal on the grid at one time,with the

lower feed you may have enough air. How many heat exchanger tubes are in the stove?

For the plate above the fire I'd use a steel plate 1/2-3/4 inch thick which would last a long time,no

need for fire clay or cement.Just suspend 2-3 inches below the heat tubes and try out.

BigBarney
BigBarney
 

Re: Prill combustion air

PostBy: BigBarney On: Fri Nov 14, 2008 1:26 pm

Steinkebunch:

Put a timer on the feed and run on a cycle to get the burn you need,adjustable for

daily temp.

BigBarney
BigBarney
 

Re: Prill combustion air

PostBy: steinkebunch On: Fri Nov 14, 2008 5:54 pm

BigBarney: The stove has 3 heat exchange tubes, each about 3" in diameter.

Having never seen an underfeed stoker in operation before this, I did not know that my flame was too high. I could guess that it was too high when I had flames in the chimney, but I thought the lower photo (above) was about right. Guess I'll find a smaller pulley and give it a shot.

Gettin' colder out, stove is running more now, so the flame does not take too long to get to full fire now.
steinkebunch
 
Stove/Furnace Make: Homemade Bituminous Hand-Fed
Stove/Furnace Model: Prill underfed stoker Model M8

Re: Prill combustion air

PostBy: Berlin On: Fri Nov 14, 2008 6:34 pm

I have almost the same stove you have. I can tell you with a certainty that your feed is way, way too high. the flames even in the pic with "more air" don't have enough air. the flame shouldn't be white, but it should be about 8" tall max and bright, bright yellow, almost white. yes you'll get flyash, but that's due the the lighter ash coal that your burning, it's simply the way it is with western coal.
Berlin
 
Hot Air Coal Stoker Furnace: Will-Burt Combustioneer 77B
Coal Size/Type: Ohio BITUMINOUS pea stoker coal

Re: Prill combustion air

PostBy: steinkebunch On: Fri Nov 14, 2008 10:06 pm

I bought a new pulley - 5/8" arbor and 2" diameter. Turns out that the old pulley was a variable pulley - you could adjust the width of the pulley to allow the belt to ride deeper in the pulley. It was already adjusted to the minumum, which was about 2". So the new pulley didn't change anything.

I had the stove down for a few hours to change the pulley, and when I started it up, it ran for about 15 minutes. I again had fire in the smokepipe.

I need a smaller pulley, but I don't think I can find a smaller one, 1-3/4" is about as small as I see on the web. I'm sure I need to go way smaller. I don't have alot of room to put a bigger gearbox pulley on.

Seems that I really need a slower motor. This one spins at 1725 RPM. Maybe I cannot get much slower unless I go with a DC motor?

If I'm going to mess with the motors, I should probably separate the stoker drive from the combustion air drive.

Not sure where to head next.

Steinkebunch
steinkebunch
 
Stove/Furnace Make: Homemade Bituminous Hand-Fed
Stove/Furnace Model: Prill underfed stoker Model M8

Re: Prill combustion air

PostBy: LsFarm On: Fri Nov 14, 2008 10:46 pm

Steinke, you may want to try the repeat cycle timer that Big Barney suggested... If you want to try one, I can mail you one so you can see if it will help.. you can set the timer to run a percentage of a minute, or a percentage of 10 minutes etc.. I'll need to find the directions :D :mad:

Greg L.
LsFarm
 
Stoker Coal Boiler: Axeman Anderson 260
Hand Fed Coal Boiler: Self-built 'Big Bertha' SS Boiler
Baseburners & Antiques: Keystone 11, Art Garland

Re: Prill combustion air

PostBy: LsFarm On: Fri Nov 14, 2008 10:54 pm

I forgot to mention, in some of my literature for my Iron Fireman and for other underfeed bitum stoker units.. there was a lot of discussion about sizing the stoker to the boiler,, they had dimensions for minimum distance to the top of the firechamber.. There was a statement that you never want the actual flame to touch the top or the heat exchanger.. that the flame is incomplete combustion and it will deposit soot and unburnt products on the heat exchanger lowering efficiency and heat transfer..
The discussion went so far as to recommend digging pit under the boiler to drop the firepot down low enough below the heat exchanger..

Greg L.
LsFarm
 
Stoker Coal Boiler: Axeman Anderson 260
Hand Fed Coal Boiler: Self-built 'Big Bertha' SS Boiler
Baseburners & Antiques: Keystone 11, Art Garland