Pre-Heated Secondary Air Modification…Is This Possible?

 
User avatar
Ky Speedracer
Member
Posts: 492
Joined: Sun. Dec. 21, 2014 9:38 pm
Location: Middletown, Kentucky
Hand Fed Coal Stove: Florence HotBlast NO.68 & Potbelly
Hand Fed Coal Furnace: HotBlast 1557M
Coal Size/Type: Ky Lump & Anthracite Nut
Other Heating: Oil

Post by Ky Speedracer » Fri. Feb. 27, 2015 6:57 pm

I have been curious about pre-heated secondary air for burning bit coal. From everything that I’ve read, it seems this is the most efficient way to burn bit.
My stove is a Hotblast 1557M. I know there are people that view this as a substandard coal burning stove but I’m not looking to debate that here. That is what I have. My intent here is to see if there is a way to make a relatively minor modification to this stove to take advantage of the benefits of a preheating secondary air.
Lightning, Hotblast and probably others have made modifications to their stoves to add and more evenly distribute secondary air to their units (which are similar to mine). The modifications seem to work well for them. They burn anthracite which maybe doesn’t benefit as much from “preheated” air as, at least from what I understand, bit would.

So here goes an attempt to describe a concept for a modification to my stove that would require only one hole to be drilled into the outside of my stove.

The primary concept is to run two pieces of tubing in the bottom of the fire box (one on each side of the grate) starting from the liner that is just inside and under the load door. These tubes will run under the fire brick (the fire brick would actually sit on top of the tubing) along side the coal bed. When the tubing reaches the back of the stove I would turn it up with a 90 so it will travel between the last fire brick and the back of the stove to the top of the fire brick. Another 90 and then run the tube all the way back to the front of the stove. Basically sitting on the top of the fire brick at the top of the fire bed where all the volitale gasses are baking out of the heated bit coal. The entire tube would be “C” shaped essentially framing the outside of the fire bricks. The top of the tube would have evenly spaced holes drilled from front to back to distribute the air.
I would cut a hole in the front liner, one on each side, just big enough for these tubes to pass into the void that this liner creates between the fire box and the front of the stove. The liner will need to be sealed off from the rest of the stove with some insulation or something.
Then I would cut a hole through the front of the stove in the area that is just under the load door and just above the ash pan door to allow air into the area behind the liner where these two tubes have access to it. I would need to put some sort of slide control or spinner over the hole in order to control the air flow into these “secondary air tubes”.

I have attached below some drawings to try and illustrate what my concept is. The “secondary air tube” is in red.
The first drawing is kind of a “cut-away” view of the fire box. The second shows the liner removed. The last one just shows the tube.

The biggest question that I have is - will this “secondary air tube” running under the fire brick and essentially down in the coal bed heat up the secondary air enough to make a difference. The next question is – what material would this tube need to be made of so as not to melt/crack/breakdown and fall apart?

Attachments

FIREBOX 1.pdf
.PDF | 441.1KB | FIREBOX 1.pdf
FIREBOX 2.pdf
.PDF | 431.1KB | FIREBOX 2.pdf
FIREBOX 3.pdf
.PDF | 199.9KB | FIREBOX 3.pdf


 
User avatar
carlherrnstein
Member
Posts: 1536
Joined: Tue. Feb. 07, 2012 8:49 am
Location: Clarksburg, ohio
Hot Air Coal Stoker Stove: combustioneer model 77B
Coal Size/Type: pea stoker/Ohio bituminous

Post by carlherrnstein » Fri. Feb. 27, 2015 7:15 pm

You need to remember that the pressure inside of the firebox is only slightly less than the room. So if there is much restriction in the over fire airways the volume of air that enters the firebox will be very small. Then there are puffs if you have a puff (everybody has them)then you will have raw bit coal smoke in your living space.

I recommend a metal device that would replace one or more firebricks that mimic the function of the warm morning corner firebricks. Some Ds Machine stoves have what the call a louver that accomplishes this.

The finial solution is a stoker they are wonderful machines. :D

 
User avatar
Lightning
Site Moderator
Posts: 14658
Joined: Wed. Nov. 16, 2011 9:51 am
Location: Olean, NY
Stoker Coal Boiler: Modified AA 130
Coal Size/Type: Pea Size - Anthracite

Post by Lightning » Fri. Feb. 27, 2015 7:20 pm

I think that's a fantastic idea. I've considered something similar to deliver primary air at the bottom of the fuel bed.

The only thing that might happen is ash build up having an insulating effect on the tube. What do you think about running the tube halfway up on the slope instead of at the bottom of the fuel bed?

 
franco b
Site Moderator
Posts: 11416
Joined: Wed. Nov. 05, 2008 5:11 pm
Location: Kent CT
Hand Fed Coal Stove: V ermont Castings 2310, Franco Belge 262
Baseburners & Antiques: Glenwood Modern Oak 114
Coal Size/Type: nut and pea

Post by franco b » Fri. Feb. 27, 2015 7:34 pm

I like your skill in generating an illustration.

I think it would work, but is too complex. The problem is very similar to burning wood gas, so a look at modern wood stoves might give some more ideas. I think your stove has a baffle; if so the front edge is a good spot where the gas makes a turn to go to the breech. With an established fire there is plenty of heat and with coal it is long lasting.

Stainless would be the best material, but I don't know the best alloy.

 
User avatar
warminmn
Member
Posts: 8108
Joined: Tue. Feb. 08, 2011 5:59 pm
Location: Land of 11,842 lakes
Hand Fed Coal Stove: Chubby Junior, Efel Nestor Martin, Riteway 37
Coal Size/Type: nut and stove anthracite, lignite
Other Heating: Wood and wear a wool shirt

Post by warminmn » Fri. Feb. 27, 2015 7:47 pm

My mod made a big difference burning bit and seemed to help with wood but I havent burnt enough wood with it yet to come to a conclusion. Im going to have a bunch of wood to burn next year as I have to cut a couple trees down. I had 2 separate pipes that were each 3/4" in size. I will be redoing it this summer to 1" so that is one recommendation I would make as the bigger the better as you can always restrict it if you need too. Mines just a box stove type. not like yours. I did manage to take a couple videos of them working but havent tried to upload them yet. I will try to do that. I just used black pipe but Im sure that could be improved on.

When they kick in they have a low roar and the temp shoots up real fast. Flames shoot up my stove pipe sometimes and its fun to watch thru my baro door :lol:

 
franco b
Site Moderator
Posts: 11416
Joined: Wed. Nov. 05, 2008 5:11 pm
Location: Kent CT
Hand Fed Coal Stove: V ermont Castings 2310, Franco Belge 262
Baseburners & Antiques: Glenwood Modern Oak 114
Coal Size/Type: nut and pea

Post by franco b » Fri. Feb. 27, 2015 7:51 pm

The purpose is to burn the gas to take advantage of the heat and to eliminate smoke as much as possible.

Mixing the air with the gas as evenly as possible is key to best performance. Tubes to the sides may not be the best spot. Directly over the fire I think would be better. If you have a baffle you could consider adding a plate spaced about 1/2 inch from the original baffle on top or below and directing air through what has become a hollow baffle to exit at the front edge just at the point where the gas has to make a turn.

 
User avatar
Ky Speedracer
Member
Posts: 492
Joined: Sun. Dec. 21, 2014 9:38 pm
Location: Middletown, Kentucky
Hand Fed Coal Stove: Florence HotBlast NO.68 & Potbelly
Hand Fed Coal Furnace: HotBlast 1557M
Coal Size/Type: Ky Lump & Anthracite Nut
Other Heating: Oil

Post by Ky Speedracer » Fri. Feb. 27, 2015 10:04 pm

Lots of good stuff here guys!
carlherrnstein wrote:You need to remember that the pressure inside of the firebox is only slightly less than the room. So if there is much restriction in the over fire airways the volume of air that enters the firebox will be very small. Then there are puffs if you have a puff (everybody has them)then you will have raw bit coal smoke in your living space.

I recommend a metal device that would replace one or more firebricks that mimic the function of the warm morning corner firebricks. Some Ds Machine stoves have what the call a louver that accomplishes this.
I have crazy, I mean CRAZY high draft. It might possible be able to suck a tennis ball through these pipes. Lol
I already have a secondary air control that stays open most of the time on my load door to help burn off gasses. So if I have a puff back it would not be much different than my setup now from that perspective.
I will look into the Warm Morning deal you are referring to. I'm not familiar with that... Thanks!
Lightning wrote:The only thing that might happen is ash build up having an insulating effect on the tube. What do you think about running the tube halfway up on the slope instead of at the bottom of the fuel bed?
Good point. But the most important time, at least as I understand it, that this is a benefit is during initial burn off of gasses after loading. At that point, after a good shake down, I should have cleaned most of the ash away. Does that make sense?
franco b wrote:I like your skill in generating an illustration.

I think it would work, but is too complex. The problem is very similar to burning wood gas, so a look at modern wood stoves might give some more ideas. I think your stove has a baffle; if so the front edge is a good spot where the gas makes a turn to go to the breech. With an established fire there is plenty of heat and with coal it is long lasting.

Stainless would be the best material, but I don't know the best alloy.
franco b wrote:
The purpose is to burn the gas to take advantage of the heat and to eliminate smoke as much as possible.

Mixing the air with the gas as evenly as possible is key to best performance. Tubes to the sides may not be the best spot. Directly over the fire I think would be better. If you have a baffle you could consider adding a plate spaced about 1/2 inch from the original baffle on top or below and directing air through what has become a hollow baffle to exit at the front edge just at the point where the gas has to make a turn.
To be honest, my main thing I'm looking to do is burn off those gasses as completely as possible to prevent smoke and smell. I can get super high stove temps now if I'm not carful controlling the stove after loading. 800+ degrees if I don't watch it.
As I said, I'm primarily looking to burn off those volitales with better control. I'd like to try and burn them off more completely at a lower temp if that's possible. I have some neighbors that are close enough to me I don't really want to offend them. No one has complained yet and may never complain but I don't want to be an irritant.
Interesting concept of moving the the pipe to the edge of the baffle. I need to think about how to do that.
warminmn wrote:My mod made a big difference burning bit. I had 2 separate pipes that were each 3/4" in size. I will be redoing it this summer to 1" so that is one recommendation I would make as the bigger the better as you can always restrict it if you need too.
I did manage to take a couple videos of them working but havent tried to upload them yet. I will try to do that. I just used black pipe but Im sure that could be improved on. :
Good to know about the tube sizing. Also, would like to see the vids if you get them up sometime.


 
User avatar
Ky Speedracer
Member
Posts: 492
Joined: Sun. Dec. 21, 2014 9:38 pm
Location: Middletown, Kentucky
Hand Fed Coal Stove: Florence HotBlast NO.68 & Potbelly
Hand Fed Coal Furnace: HotBlast 1557M
Coal Size/Type: Ky Lump & Anthracite Nut
Other Heating: Oil

Post by Ky Speedracer » Sat. Feb. 28, 2015 7:43 am

franco b wrote: I think it would work, but is too complex. The problem is very similar to burning wood gas, so a look at modern wood stoves might give some more ideas. I think your stove has a baffle; if so the front edge is a good spot where the gas makes a turn to go to the breech. With an established fire there is plenty of heat and with coal it is long lasting.
What if I were to maybe connect the two tubes together at the back of the fire box after they run the length of the fire bed and then bring a single tube up to the bottom of the baffle, then run it towards the front of the stove the length of the baffle and just below it. At this point I could evenly space holes on the tubing that runs right over the center of the fire. OR, I could put another peice on the end of the tube, creating a T right at the end of the baffle plate and putting the holes in that piece.
I haven't come up with an idea for the "double baffle" concept yet.

 
hman
Member
Posts: 90
Joined: Sun. Aug. 29, 2010 4:08 pm
Location: Chillicothe,Ohio
Hand Fed Coal Stove: D.S.Machine 1400 (sold) looking for another stove
Coal Size/Type: Lump/Bituminous

Post by hman » Sat. Feb. 28, 2015 10:35 am

I agree,that I would set up your secondary air tubes the same way as the new wood stoves.
The reason I say this is,I am burning bit coal in a epa wood stove,that has a baffle and secondary air tubes.
I am mixing with wood and I am not loading the stove up with coal.Their is no smoke at all and the heat output is a lot higher and a lot longer than just burning wood alone.

I would have the tubes above the fire under the baffle plate.Instead of using tubes,use a 2x3 or 2x4 tube,and cap the end off at the door, "like a box beam". Drill holes in both sides the full length.Bring pipe into the back of that tube for your secondary air.

On you tube, their is a fellow that done an englander 28-3500 wood furnace with secondary air tubes,like you are talking about.I don't think he put a baffle above his tubes though.
On my wood stove, they use firebricks as the baffle.

I think this would work very well to burn bit coal cleaner and get more heat from the gases being released and you would not have to give so much air at the time when you load the stove.

 
User avatar
warminmn
Member
Posts: 8108
Joined: Tue. Feb. 08, 2011 5:59 pm
Location: Land of 11,842 lakes
Hand Fed Coal Stove: Chubby Junior, Efel Nestor Martin, Riteway 37
Coal Size/Type: nut and stove anthracite, lignite
Other Heating: Wood and wear a wool shirt

Post by warminmn » Sat. Feb. 28, 2015 11:59 am

Im going to see if my video links will work. The milder burning one was with ant and the wilder one was with bit. Taken thru a 2 inch window so its hard to get. I think you will have to copy/paste the links.

http://vid1196.photobucket.com/albums/aa419/conce ... %20ant.mp4

http://vid1196.photobucket.com/albums/aa419/conce ... %20bit.mp4

 
User avatar
Ky Speedracer
Member
Posts: 492
Joined: Sun. Dec. 21, 2014 9:38 pm
Location: Middletown, Kentucky
Hand Fed Coal Stove: Florence HotBlast NO.68 & Potbelly
Hand Fed Coal Furnace: HotBlast 1557M
Coal Size/Type: Ky Lump & Anthracite Nut
Other Heating: Oil

Post by Ky Speedracer » Sat. Feb. 28, 2015 12:30 pm

if I understand what you guys are saying about the newer designed wood stoves, the air is being introduced above the fire and just below the baffle? Which in my case is approximately 12" above the fire bed.
The reason I ask is that after going back and doing some research, most of the recommendations from a while back on other threads seem to indicate that the air should be introduced just above but fairly close to the fire bed. Maybe it doesn't make a lot of difference as long as it's evenly distributed between the firebed and the baffle...
warminmn wrote:Im going to see if my video links will work. The milder burning one was with ant and the wilder one was with bit. Taken thru a 2 inch window so its hard to get. I think you will have to copy/paste the links.

http://vid1196.photobucket.com/albums/aa419/conce ... %20ant.mp4

http://vid1196.photobucket.com/albums/aa419/conce ... %20bit.mp4
Warminmn-Those videos are badass! What is the approximate heighth of your secondary tubes?

 
User avatar
warminmn
Member
Posts: 8108
Joined: Tue. Feb. 08, 2011 5:59 pm
Location: Land of 11,842 lakes
Hand Fed Coal Stove: Chubby Junior, Efel Nestor Martin, Riteway 37
Coal Size/Type: nut and stove anthracite, lignite
Other Heating: Wood and wear a wool shirt

Post by warminmn » Sat. Feb. 28, 2015 12:56 pm

They are on top of the firebrick which I think is two firebrick high, so I think 15". They are a little uneven height wise. I think this next summer I will do some more work on the inside and they may be a couple inches lower then. I have to slice the ash and its kind of tough if I fill it up with about 100 pounds. I'd like to have the pipes closer to my level of coal.

 
User avatar
Lightning
Site Moderator
Posts: 14658
Joined: Wed. Nov. 16, 2011 9:51 am
Location: Olean, NY
Stoker Coal Boiler: Modified AA 130
Coal Size/Type: Pea Size - Anthracite

Post by Lightning » Sat. Feb. 28, 2015 2:14 pm

Warminmn, that is some kick ass secondary air burn, man!!
Wow, nice work! :D

 
User avatar
warminmn
Member
Posts: 8108
Joined: Tue. Feb. 08, 2011 5:59 pm
Location: Land of 11,842 lakes
Hand Fed Coal Stove: Chubby Junior, Efel Nestor Martin, Riteway 37
Coal Size/Type: nut and stove anthracite, lignite
Other Heating: Wood and wear a wool shirt

Post by warminmn » Sat. Feb. 28, 2015 3:30 pm

Thanks! I need a bigger window so I can watch it easier. Part of the summer project too.

 
User avatar
Ky Speedracer
Member
Posts: 492
Joined: Sun. Dec. 21, 2014 9:38 pm
Location: Middletown, Kentucky
Hand Fed Coal Stove: Florence HotBlast NO.68 & Potbelly
Hand Fed Coal Furnace: HotBlast 1557M
Coal Size/Type: Ky Lump & Anthracite Nut
Other Heating: Oil

Post by Ky Speedracer » Mon. Mar. 02, 2015 3:54 pm

After a couple of days of research and reviewing the recommendations of several replies to this thread, I have started looking at a re-design.

Franco and hman both recommended that I look at the newer style wood stoves with secondary burn capabilities. I’m glad they did.
I was trying to preheat my air by running it through the coal bed. It appears to me that the newer style wood stoves preheat the air in their secondary burn tubes by suspending the entire tube structure above the fire. Based on what I’ve seen by watching videos, this appears to work very well.
So I started thinking about that concept and how to incorporate it in my furnace.
One of my goals was to try and keep this as minimally invasive as possible. My stove is setup with a port in the rear to add a forced combustion blower. It appears to me that this port comes in over the top of the fire bed. It looks like the place that it comes in is just under the baffle on the back wall of the firebox. (If anyone can confirm that this is how it is designed that would be appreciated).
So, assuming that the box on the back wall of my firebox is where the combustion blower distributes air then my new design is based on trying to utilize that. I would not use the blower (I think there is a good chance that using the blower would melt this furnace down into a puddle using the type of bit I burn...lol). The port on the outside looks to be 1 1/2" pipe and is threaded so I would probably just thread a pipe into it of some configuration and add a gate valve or something to control air flow. The outside opening looks to be about 12” below where it actually exits into the firebox. I assume this would assist in air flow?
My questions now are more along the lines of; 1) is this port big enough to allow enough air into the secondary burn system? 2) what sizes of tubing should be used to hold enough air inside the firebox to preheat? 3) how many holes should be drilled and what size?
Lightning, I know you added this type of burn tube to your Clayton. Was there a formula to this or a bit of trial and educated guessing? Same question to you Warminmn?
My primary goal is to burn the volitale gasses off as completely as possible to minimize smoke and soot. And, burn efficiency. Based on Franco’s recommendation I am trying to keep most of the secondary burn close to the edge of the baffle. That seemed to me like the best area for burn off.

Attachments

firebox2.pdf
.PDF | 356.6KB | firebox2.pdf
fb2.pdf
.PDF | 398.9KB | fb2.pdf
fb4.pdf
.PDF | 362KB | fb4.pdf
fb3.pdf
.PDF | 426.2KB | fb3.pdf
fb2nd tube.pdf
.PDF | 209KB | fb2nd tube.pdf


Post Reply

Return to “Hand Fired Coal Boilers & Hot Air Furnaces/Stoves Using Bituminous”