Hand Feed to Stoker Conversion Slab Heating Project

Merry christmas everyone,

A couple of years ago I bought an old 1983 ??? K8 stoker mechanism to add to my energy king wood coal boiler. Normally I burn nut size and wood as is available. The boiler feeds at this moment a concrete slab 50 ft x 32 ft x 6" insulation between and around slab and ground is 4" styrofoam. A taco 009 and thermo valve feed four loops of 3/4' Pex.
The K8 unit is lightly modified so that it fits in the fire door hole. The door is simply lifted of the hinge.
The stoker unit can be tilted back to start and this is fairly easy.

To increase the efficiency the boiler is connected in counter flow ( the cold water return is on the top and the hot water leaves from the bottom) .It works very well and I have not been able to find information why this could not been done with taking regards of condensing temperatures.

I like to increase the efficiency of the stoker heat transfer since it is placed essential to high in the boiler. Also this firebox is about 36" deep.
I would like to add a squirrel fan rotor ( only the rotor) in front of the stoker unit and run a 1/2" SS drive shaft through the air plenum as to whirl the hot air around in the firebox similar as an AA 130 / 260 . I would use one flange and one pillow block bearing on the cold side and make a 5/8" hole in the flat front surface so some air leakage would occur there. The fan would be driven with a separate motor.

Anybody any ideas about efficiency potential increase and / or problems I might encounter.

Thanks for this great forum.

J

Sorry,I can't answer your question,but would like to see pics. of your boiler mostly to stoker unit in the feed door

joeblack5 wrote:The K8 unit is lightly modified so that it fits in the fire door hole. The door is simply lifted of the hinge.
The stoker unit can be tilted back to start and this is fairly easy.

How about moving the flue opening to a lower location, such as the base?

While the squirrel cage fan would not be in the direct pathof the flame like in an AA boiler, it still shoule be made from Stainless Steel, or some
form of very high temp tolerant steel.

I like the idea, but will the ash falling off the end of the grate interfere with the fan or the fan shaft?

While the firebos is deep, how much additional heated surface would be 'added' by the fan moving the heated air around??

I'll suggest adding a baffle to the back or top of the wood-boier firebox to make the airflow have to make a few turns before exiting the
fire box a fixed piece of steel is maintenance free, and is pretty easy to make up, install and tryout.

Draw us a side view of the firebox and stoker and flue exit with any current airflow baffles.
Then we can see what you are working with..

Greg L

Wow, thanks for all getting back so quickly.
I will make some pictures and try to post.
I like the idea of the baffle plate, will definitely try. There is about 16 " from the stoker grate to the ceiling of the firebox. There is a sliding plate to divert the hot gasses directly out the smoke stack or along the water jacket on top.

I am nervous that the plate would warp or reflect much heat back onto the stoker grate. Could the stoker have a problem with that?
What would you all think a safe distance from the stoker grate?

I thought that the super efficiency of the Axeman A ( 85 % I heard) was partly achieved with whirling the exhaust gasses so that heat exchange is optimal.
Please correct or add about the AA if possible.

I would run the fan about 5 " in front of the K8 so that the ashes do not interfere with the fan itself.

Thank you all.

J

A little update,

Installed a old squirrel cage from a low speed oil gun on a 3/8" shaft and ran that for a test at 1500 RPM and noticed my stack temperature of 650F went way down. Tried it somewhat later and could not repeat the result. The k8 stoker setting was with rice and adjusted ( measured) on 40 lbs coal in 5 Hours. Draft about 0.06. The K8 air flap is at 50% or 45 degree. This test shaft had not any real bearings and I could not get the same RPM the second time ( to much vibration noise because of loose bearings) Unreal how much blast this thing has.
There were no problems warping the fan or shaft and no ashes came into the fan.

Slightly discouraged with the bearing complication in this environment decided to try Greg's suggestion and mounted and 11 gauge SS plate 16" wide and 24 " long horizontal above the fire . This leaves a gap of 1/2" on three sides. A second vertical plate 13" wide and 12" forces the flue gasses to travel down and then up in the rear of the fire box and back up over the installed horizontal plate.
A first test showed with all other settings the same a stack temp of 520F. This is still high in my opinion. I think that the 1/2" gap on three sides leaks to much. So that will be next.

I took pictures that I like to post, what is the max size??
I also am looking for data of boiler that relates BTU and heat exchanger square area, searching on this site did not show anything for me, anybody?

Later J

Hope this works, probably speaks more then all my writing.
J

How do you seal off the air from comming arourd the stoker unit and mano tube.that's some of your problem,but not the worst.
I believe the stoker unit is too high in the boiler,the flames need to sweep the sides in order to absorb the heat into the water.Is there anyway to lower the unit in the door.I thought about doing the same except using a EFM s-30 stoker unit and installing some type of flame defering thing(cast iron window weights) to help sweep the sides of the boiler.
I have now scratched that idea and will be installing an under feed stoker unit that fits in the ash door and brings the ash out

Dennis wrote:I believe the stoker unit is too high in the boiler,the flames need to sweep the sides in order to absorb the heat into the water.

joeblack5 wrote:There is a sliding plate to divert the hot gasses directly out the smoke stack or along the water jacket on top.

can you slide the damper plate closed more.When the stoker unit is runnig it's pushing all the heat to the top and out thru the chimney before the heat can be absorbed.Just make sure you don't close off the boiler too much and gasses excape into the house

How do you seal off the air from comming arourd the stoker unit and mano tube.that's some of your problem,but not the worst.
I believe the stoker unit is too high in the boiler,the flames need to sweep the sides in order to absorb the heat into the water.Is there anyway to lower the unit in the door.

Yeah that is a problem I still have to solve, but this is still experimental. Fire is not going towards the hopper. I do not like to change the fire door since I like to keep this multi-fuel when wood is around.

can you slide the damper plate closed more.When the stoker unit is runnig it's pushing all the heat to the top and out thru the chimney before the heat can be absorbed.

The damper plate does not close the chimney but only forces the heat through a 5" channel and then out the stack see picture 2. Not the blocks I set there to reduce the air speed but are no removed.

I love that underfeed idea. what brand is that, where is it, how much is it , how many are there around,
i have a gentlemens stoker that I wanted to use/ experiment but it feeds the coal from the other side This one seems to feed coal from the front.
What size is the required opening for the ash tray?

Dennis I noticed that did not quote your name in the comments quotes, try to figure "how to" later, my excuses.

J

probably I need to say that this experiment is in my barn, no living beings.

Good Evening folks,

Can anybody help me with finding data about the square area exposed to the flue gasses ( heat exchanger area) together with BTU range of a couple boilers. I have a hard time finding that data. Thanks in advance.
J

PostBy: Rob R. On: Tue Dec 25, 2012 2:17 pm
How about moving the flue opening to a lower location, such as the base?

Rob, your idea turned around and around and the quarter finally fell. This boiler has a wet backwall and I would not want to cut through that especially since I am not a good welder. But I can extend the stove pipe easily inside the stove and force the flue gasses to go to the bottom. It would not be to hard to fabricate a double walled insert and have the water flow through it as an add on heat exchanger at the same time.
I will try the extended pipe tomorrow and play with the add on heat exchanger idea later on.

Thanks for making me think, J

Nice ideas, good to see you trying to improve the heat absorbtion of the boiler.

About the fan, can you turn it around so that the solidback of the fan faces the gtate this way the ash
Won't get in the fan cage and cause your severe imbalance.

Some boilers are VERY simple inside. The Gentleman Janitors are just a plane box with a crosover tube or two. The EFM has added 'comb' ribs or heated tubes. All of these items are 'wet' surfaces, increasing the exchanger area.

I like the idea of adding an elbow or extension to the inside flue exit so the hot air has to
Travel lower in the boiler to reach the exit.

I think one important thing that the AA design does it to sweep the inside of the heat exchager
Surface clean of ash and soot. While the AA is not perfect at cleaning itsself, it does stay relatively clean.
Have you made up a long-handled wire brush to sweep off the interior surface of your boiler??this will probably made a measurable improvement in lower flue temps ??

Just some thoughts,
Greg L

I saw the mention of a .06 draft. That seems really high and may account for the high flue temp also. Do you have a baro and can reduce it further?

Kevin