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 » Mon. Nov. 02, 2015 8:59 pm

Keepaeyeonit wrote:Nice work :cheers: , I am building sorta the same thing for my 983 but mine doesn't have the length that yours does so the air won't get as hot and I'm using 3/4" pipe(I have it laying around) not Sq tube. I will see if it makes any difference.
Cheers back at ya.
I don't want to wish away the warm weather here but I'm anxious to see how these work. The daytime highs here are supposed to be in the low seventies until next Monday. (I know, whine whine whine...right?)
Good luck. I'll be curious to hear how your's work.

 
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. Nov. 23, 2015 9:30 am

Edit; just a heads up, this is a long read, sorry. But I'm not sure I could have written it differently without leaving out necessary detail...

Here's an update on my secondary air project:
I've been burning on and off for 11 days now. I say on and off because I had to let it go out a couple of days last week due to the outside temps last Tuesday and Wednesday (highs in the 70s and lows in the 50s).
I've been burning anthracite for the most part with a little bit mixed in (that's another thread I need to update...lol).
Based on my experiences so far, the design of my secondary tubes pulling air from the primary air is NOT ideal. It works, but it's very temperamental. There is a very fine line for when and how it works.
With anthracite, I originally couldn't tell when and if it was working. I spent the first couple of days fiddling with the ash door and the load door trying to get the fresh anthracite going. I used a lot of combinations of doors half open, partially open, one closed and one open, secondary tubes open, with doors closed, etc.
Here's the best combination I've found so far; shake-down, leave ash pan door wide open, secondary tubes closed and load door closed. Allow the coal bed to get really hot. Then add a layer of anthracite. Dig a hole through the fresh ant coal to get some flame. Open the secondary air tubes completely up, open the primary control all the way and then shut the load door completely.
At first I get a single "blow torch" looking flame coming up from the hole that goes down through the new coal into the hot coal bed. This was pretty much what I would have expected. Nothing remarkable...but after about 5 minutes I started noticing the ghostly looking blue flames soaring around up in the TOP of the firebox right underneath the baffle plate. They were really hypnotizing...
In another 4 or 5 minutes the ant coal bed ignites and looks pretty typical. BUT, what I hadn't noticed the first couple of times is that I have a completely different fire burning up above the coal bed at the baffle plate...I don't mean a few random flames, it's a a separate fire burning there. I've tried to get pictures of the two different fires burning but the picture doesn't really show a distinguishable difference between the two fires.
If I close the secondary tubes off, the upper fire goes away. With the secondary tubes half open the only difference I see is the fire on top of the coal bed gets taller.
If I leave the tubes completely open for about twenty or thirty minutes the entire firebox turns into one great big gorgeous fire. It's really spectacular. But ironically, it doesn't seem to translate into a lot of additional heat. ??? The stack temp will climb. I've seen it get up to 240 or so. But the stove temp is 250 or 260. If I mess with the secondary controls It basically puts out the upper 2/3rds of the fire box.
Another interesting thing is with this setup, I rarely get anything that looks like the "blow torch" look coming out of the secondary air holes that I've seen pics and videos of that some of you all have posted. I sometimes see that a little in the first part of the burn. Then, at least this is my assumption, as the secondary tubes start to heat up, the semi blow-torchy looking flames start kind of releasing and and head up towards the baffle plate and keep burning for a several seconds. Then shortly after that is when the upper fire begins really burning.
As the fire burns for 45 minutes to and hour it settles down and looks like any other ant fire I've seen.
At that point is when I turn off the secondary air tubes. After the secondary tubes are off, the stack temp goes way down but the stove temp climbs way UP.
In order to get any benefit of the secondary tubes with my setup, I have to leave the primary control wide open. When they're closed, you have to quickly shut the primary air down to 1 to 2 turns open or the stove temp starts to go crazy.
As for bit coal, I can pretty much just leave the secondary tubes completely open and control the entire fire with the primary air control. The bit fire is very stable with these tubes. Again I don't get the blow torch look coming out of the air holes in the secondary tubes... I basically just get a firebox full of flame that isn't crazy hot. After and hour or two when all the volitales have burned off I shut off the air tubes and burn as normal.
Due to my setup, I have to always open and close the ash pan door to make adjustments.
My next goal is to cut a couple off holes in the area between the load door and the ash pan door and turn the tubes out there. That way I can make adjustments easier and can take advantage of the difference in pressure between the inside of the firebox and the outside of the firebox. Not just the difference between below the grates and above the grates...

 
User avatar
Keepaeyeonit
Member
Posts: 1680
Joined: Wed. Mar. 24, 2010 7:18 pm
Location: Northeast Ohio.( Grand river wine country )
Baseburners & Antiques: Glenwood #8
Coal Size/Type: Nut & stove
Other Heating: 49 year old oil furnace, and finally a new heat pump

Post by Keepaeyeonit » Mon. Nov. 23, 2015 11:44 am

Good write up and very informative, it would be my guess that when you move your air pick up outside the the furnace you will see a difference. I also get crazy fire in the firebox with the tubes, slow rolling and it comes and goes.

 
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. Dec. 18, 2015 10:52 am

Finally it cooled down enough for me to fire up the Hotblast furnace and try out the modified secondary burn tubes. My original design had the secondary burn tubes pulling air from the primary air intake from below the ash pan. I tried it this way first to avoid cutting holes in the front of my stove.
This first setup definitely changed the burn characteristics of the stove. The biggest benefit that I found is that it seemed to make refueling a bit fire more stable and help burn off some of the volitales that were baked out. The secondary air control on my stove was originally a slide damper on the load door. It worked okay but only allowed air into the front of the firebox. There always seemed to be a lot of un-burned gasses escaping out of the flue and lots of smoke (typical of bit). That control has since been removed and a piece of glass installed there.
My first modification was tough to regulate when burning anthracite. Only on a couple of occasions did I feel like I had the right balance of primary air and secondary air. I had no way to independently control the two. It was hard to idle the anthracite fire. It either wanted to burn very warm or go out. My assumption is that the air was trying to bypass the bottom of the ant fire via the secondary air tubes. With my setup, I could only moderately control some of the air that entered these secondary tubes. I did not have a way to completely shut them off.
The newest modification has the secondary tubes pulling in air through holes I cut into the front of the stove and a better control on each tube that allows me to almost completely shut off the secondary air if I want.
The fire has not been burning 24 hours yet. I started a bit fire last night because it starts so easy. Within 20 to 30 minutes the fire was coming along nicely so I decided to close the load door and see how she was going to react. Instantly I could tell that the new modifications had made some drastic changes. As soon as the firebox got some serious heat in it the secondary tubes literally roar to life. I could actually hear the fire inside making a subtle "roaring" sound. The whole firebox looked like a fireball. I didn't have my phone with me at this point to take a picture. I started working the primary down. I didn't want to mess to much with the controls on the secondary burn tubes in fear of choking it down so much it would create a nasty puff. After a couple of minutes the barrow was bouncing and the fire would darken a little and then get bright again. To complicate things even more, soot was blacking out the glass and I couldnt clearly see what was going on inside. I didn't really like the way it was behaving. It appeared to be starving for air even though the secondary tubes were wide open. I was trying to figure out how to give it a little more without letting it get out of control. I decided to remove the 1 1/4" pipe plug in the rear that caps where you would add a draft induction blower. This port dumps air directly into the firebox...but not a lot. Fortunately that worked really well. It seemed to stabilize the mad fire I had.
I'm not entirely sure what all I had going on there. My assumption is that I let it get to hot to begin with.
The way a Hotblast is designed originally only allows secondary air into the front of the fire box from the load door. The baked out gasses in the back half of the fire box just went up the chimney in the form of soot and smoke.
For a short period of time while the glass was clear I could see that the secondary tubes were putting oxygen right over the fire (which is what I wanted) and trying to ignite all of the gasses. Obviously this makes more heat, AND VERY QUICKLY.
The next time I use bit I will close her up a little sooner and let it self regulate air and heat.
Things stabilized very nicely after the first 40 minutes or so. For a while I had a 250 degree spread between the over the door temp and the flue temp. 453 over the door and 199 just out of the breech.

As for anthracite; I shook the fire down this morning and added about 60lbs of anthracite on top of the hot bit coals.
Well all I can say is wow! I'll let the pics below do most of the talking. It got up to 440 over the load door at one point and 300 in the flue pipe. The nice part was I could adjust the primary control down and brought it right back under control.
I shut the door and the fire literally leaves the top of the coal be and jumps up to the height of the burn tubes. Not like it's just burning with the air right where it comes from the tubes, but the entire upper firebox, above and below the baffle plate, is engulfed in a blue flame. It was really something to see.
The first picks are right after the coal bed ignited. The primary control was about 3 turns open and the secondaries 100% open.
The first pic kind of shows what I was describing but because of the angle of how I have to take the picture (from above) it looks like the fire is on top of the coal... it's not. Also, those bright orange flames in the rear under the hot water coil are where I had banked some bit coal to the rear so it wouldn't completely smother it when I added the anthracite.
After the secondary tubes heat up the blow torch takes over...

It will take a couple of days to get the feel for these changes but I like what I've seen so far...

I just checked, a little more than 4.5 hours in to the anthracite burn and she's idling along at 280* over the door and 136 in the pipe. So far so good.

Attachments

fire9.jpg
.JPG | 112.2KB | fire9.jpg
fire2.jpg
.JPG | 63.9KB | fire2.jpg
fire4.jpg
.JPG | 115.1KB | fire4.jpg
fire6.jpg
.JPG | 79.6KB | fire6.jpg
fire5.jpg
.JPG | 86.5KB | fire5.jpg
temp.jpg
.JPG | 59KB | temp.jpg


 
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. Dec. 18, 2015 10:59 am

Here are a couple of videos from the previous post...
The first is after the secondary tubes heat up.
The second is about an hour into the burn and he primary control is only open about 1 turn.

Attachments

IMG_0954.MOV
.MOV | 1.2MB | IMG_0954.MOV
IMG_0961.MOV
.MOV | 1.4MB | IMG_0961.MOV

 
User avatar
Lightning
Site Moderator
Posts: 14659
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. Dec. 18, 2015 11:46 am

Wow! That is freakin ridiculously awesome! Good work :D

You are burning the Kimmel's from Tractor Supply, right? That stuff seems to have a hair more volatiles than the average run of the mill coal. I just saw the vids. Very good!

Hows that water coil working out for you? Did you write a thread for it?

 
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 » Tue. Jan. 19, 2016 10:32 pm

Here is a little video of the secondaries burning bit. Sorry for the dirty glass. I should have spent a little more time with a razor and scraped it all off. I
Over the door temp 638* The flue 211*
It will burn like that for about an hour and a half or so. I can hold 450+ degree temps for about 4 hours. It will stay 300+ for about 7 to 8 hours. Not bad for bit.
It almost has eliminated the bit smoke. Instead of getting the harsh black locomotive looking smoke coming out of the chimney it's now very light and gray.
Pretty happy with the secondaries so far.

Attachments

trim.4E39C388-52C0-4CF2-8118-E2D0B492CD92.MOV
.MOV | 41.5MB | trim.4E39C388-52C0-4CF2-8118-E2D0B492CD92.MOV

 
User avatar
SWPaDon
Member
Posts: 9857
Joined: Sun. Nov. 24, 2013 12:05 pm
Location: Southwest Pa.
Hand Fed Coal Furnace: Clayton 1600M
Coal Size/Type: Bituminous
Other Heating: Oil furnace

Post by SWPaDon » Tue. Jan. 19, 2016 10:40 pm

That's pretty cool, thanks for sharing.


 
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 » Tue. Jan. 19, 2016 10:52 pm

While burning much more of the smoke, what has that done to your consumption and heat produced?

 
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 » Tue. Jan. 19, 2016 11:33 pm

franco b wrote:While burning much more of the smoke, what has that done to your consumption and heat produced?
It has pretty much done what I had hoped. We are burning close to the same amount of coal per day on cold days. Maybe a touch less. But, we are heating more square feet this year. We had an adult daughter move back home for the winter. She is living upstairs. It is a converted attic area. This area was closed off last year when it was just the wife and I. It's nice and warm up there now. There are no ducts on the second floor. We just leave the door open at the bottom of the steps and heat moves right on up. It's worked very well.
Last year I had issues with trying to regulate the burn. It either wanted to go nuclear or it smoked and sooted, had watch for some nasty puff backs and lost temp quickly.
It is now very stable. This bit from eastern KY that I burn LOVES secondary air. After leaving the ash pan door open for a couple of minutes and then letting it burn with the spinner all the way open for about 5 minutes, I can close the primary all the way down to about 1.5 turns and it does it's magic. With my high chimney draft it starts pulling that air into secondaries and you saw what it does...
The one thing that I have noticed is the ash...there is less of it. Maybe 25 to 30 percent less ash. I'm not sure if this coal just burns more completely than what I was using last year or if the hot longer burns are more efficient. Probably a little of both I imagine.

 
fig
Member
Posts: 1137
Joined: Fri. Feb. 12, 2016 2:36 pm
Hand Fed Coal Boiler: Harman SF360
Hand Fed Coal Stove: T.O.M (Warm Morning converted to baseburner by Steve) Round Oak 1917 Door model O-3, Warm Morning 400, Warm Morning 524, Warm Morning 414,Florence No.77, Warm Morning 523-b
Hand Fed Coal Furnace: Clayton 7.1/DS Machine basement stove/ Harman SF1500
Baseburners & Antiques: Renown Parlor stove 87B
Coal Size/Type: Bituminous/anthracite
Other Heating: Harman Accentra, enviro omega, Vermont Ironworks Elm stove, Quadrafire Mt Vernon, Logwood stove, Sotz barrel stove,

Post by fig » Sat. Dec. 14, 2019 4:53 pm

Digging up an old post of yours about the stove glass turning black when burning bit. I was wondering if you were able to overcome that and keep the glass clean? I ask because I’m about to put a window in my hotblast and I too will be burning bit. I don’t know if it’s worth the effort if it just immediately soots up.

 
User avatar
Lightning
Site Moderator
Posts: 14659
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. Dec. 14, 2019 5:38 pm

It will help if you mount the glass on the exterior of the door. Make the hole in the load door slightly smaller than the glass, so that the glass overlaps the hole by a 1/4 inch. Then put gasket material around the top and bottom to reveal an 1/8 gap on the sides. Fresh air will enter thru the 1/8 gap on each side of the glass to create an "air wash" that will help keep it clean. Although it will eventually get sooted up, it cleans off easy. At least the Anthracite fly ash did, not sure about bituminous soot. Seems like a razor would clear it if needed. Put the window in, you'll wanna be able to see the secondary air combustion so you can tweak the flow.

Load Door Window Installation

Post Reply

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