A Good or Not So Good Idea?

 
User avatar
nortcan
Member
Posts: 3146
Joined: Sat. Feb. 20, 2010 3:32 pm
Location: Qc Canada

Post by nortcan » Mon. Nov. 29, 2010 7:24 pm

Hi all, I would like to know if someone has already made a path or a sort of channel to bring air to the top of the coal bed? The purpose of it would be to ignite the gases when reloading the stove?
All comments, ideas or advices are welcome.


 
User avatar
LsFarm
Member
Posts: 7383
Joined: Sun. Nov. 20, 2005 8:02 pm
Location: Michigan
Stoker Coal Boiler: Axeman Anderson 260
Hand Fed Coal Boiler: Self-built 'Big Bertha' SS Boiler
Baseburners & Antiques: Keystone 11, Art Garland

Post by LsFarm » Mon. Nov. 29, 2010 7:39 pm

It's really not needed for anthracite coal. However with the huge volumes of volitiles from Bituminous coal, there were a few Bit-burners with over-the-fire hot air vents..

I made a hot air vent for my hand fed boiler when I was burning Bit. coal in it. It worked very well for about two weeks, then the very high temperatures, corrosive environment cause the steel to just flake away to nothing. I literally broke the steel parts with my fingers like a soup cracker.

So even if you could make a metal chanel to add air over the fire, it wouldn't last very long..
I would think just adding an over the fire air vent in the loading door would be sufficient if your stove doesn't have one already..

Greg L

 
User avatar
nortcan
Member
Posts: 3146
Joined: Sat. Feb. 20, 2010 3:32 pm
Location: Qc Canada

Post by nortcan » Mon. Nov. 29, 2010 10:23 pm

Hi Greg, thanks for the comments. The reasons I wanted an over the fire air vent were that: after I reload the stove, I open the top loading door (the stove is a Vig 11) just a little and the blue flames arrive and the second reason is that I saw these vents on the glenwood stoves. Maybe as you said these vents could be for bit burning. I was thinking to make the channel from thick stainless st. to support the heat???
Pierre

 
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 » Mon. Nov. 29, 2010 11:13 pm

I think you are on the right track. You could get an extra 10 or 15 percent heat. Also to be considered is the burning of the CO gas which occurs primarily when the coal bed is air starved. If you can, take a look at how some of the new wood stoves handle secondary air. I think stainless will hold up well or you could consider a hollow cast refractory baffle or perforated tube.Careful matching of air and fuel is what has led to the higher efficiencies in auto engines, oil burners, and wood stoves.

Possibly the air could be controlled by a bi-metal strip to open when the right temperature is reached. The reverse of your primary air thermostat.

 
User avatar
nortcan
Member
Posts: 3146
Joined: Sat. Feb. 20, 2010 3:32 pm
Location: Qc Canada

Post by nortcan » Tue. Nov. 30, 2010 9:49 am

Hi, thanks for the infos,
Salutations

 
User avatar
LsFarm
Member
Posts: 7383
Joined: Sun. Nov. 20, 2005 8:02 pm
Location: Michigan
Stoker Coal Boiler: Axeman Anderson 260
Hand Fed Coal Boiler: Self-built 'Big Bertha' SS Boiler
Baseburners & Antiques: Keystone 11, Art Garland

Post by LsFarm » Tue. Nov. 30, 2010 11:47 pm

Cast iron might work, but how are you going to hook up air to the vent, and control it?

With Bit coal, up to 30% of the heat in the coal is from the volitiles.. only a few percent in Anthracite.. and most Anth volitiles are burnt off in a normal fire.

I built my in firebox vent a second time from low grade stainless, it only lasted a few days longer.. I was burning at very high temps.. the two vents were always bright red.. I never figured out a way to make a piece of cast iron do the job, and I switched to anthracite soon after..

Careful use of over the fire air will do the same with a small anthracite fire.

Greg L

 
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 » Wed. Dec. 01, 2010 4:39 pm

Though hard coal has only about 4 percent volatiles they can account for 20 percent of the heat available. The dramatic rise in stack temperatures when gasses are burning illustrates this. Also to be considered is the formation of carbon monoxide from the incomplete combustion of the fixed carbon portion of coal. A burning coal bed contains ash and pieces of coal of different sizes. Some parts of the fire get plenty of air while other parts starve resulting in the formation of CO. Without secondary air it doesn't burn. The difference is burning a stove at 60 or 70 percent efficiency or getting up to the high 80s or better.


 
User avatar
nortcan
Member
Posts: 3146
Joined: Sat. Feb. 20, 2010 3:32 pm
Location: Qc Canada

Post by nortcan » Wed. Dec. 01, 2010 10:29 pm

LsFarm wrote:Cast iron might work, but how are you going to hook up air to the vent, and control it?

With Bit coal, up to 30% of the heat in the coal is from the volitiles.. only a few percent in Anthracite.. and most Anth volitiles are burnt off in a normal fire.

I built my in firebox vent a second time from low grade stainless, it only lasted a few days longer.. I was burning at very high temps.. the two vents were always bright red.. I never figured out a way to make a piece of cast iron do the job, and I switched to anthracite soon after..

Careful use of over the fire air will do the same with a small anthracite fire.

Greg L
Hi, I wanted to know if it was worth the job before beginning. I think I can reach a hole beside the ash pan and use it for the air inlet. Sometimes after reloading, when I go outside, I can smell the sulfur smelt, so I was thinking that with some air could help.
Thanks

 
User avatar
nortcan
Member
Posts: 3146
Joined: Sat. Feb. 20, 2010 3:32 pm
Location: Qc Canada

Post by nortcan » Wed. Dec. 01, 2010 10:34 pm

franco b wrote:Though hard coal has only about 4 percent volatiles they can account for 20 percent of the heat available. The dramatic rise in stack temperatures when gasses are burning illustrates this. Also to be considered is the formation of carbon monoxide from the incomplete combustion of the fixed carbon portion of coal. A burning coal bed contains ash and pieces of coal of different sizes. Some parts of the fire get plenty of air while other parts starve resulting in the formation of CO. Without secondary air it doesn't burn. The difference is burning a stove at 60 or 70 percent efficiency or getting up to the high 80s or better.
Hi, thanks for the infos. Does your stove have that over the fire air spray? I think it would be great to get that heat from these gases.

 
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 » Thu. Dec. 02, 2010 3:49 pm

nortcan wrote:Hi, thanks for the infos. Does your stove have that over the fire air spray? I think it would be great to get that heat from these gases.
No, but I have added air by drilling three 1/4 inch holes which makes an obvious difference. After shaking I get three blue jets opposite the holes. The stove is hopper fed so the fresh coal is already very hot.

 
User avatar
nortcan
Member
Posts: 3146
Joined: Sat. Feb. 20, 2010 3:32 pm
Location: Qc Canada

Post by nortcan » Thu. Dec. 02, 2010 9:27 pm

Hi francob, do you leave the 3 holes always open or do you close them later?

 
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 » Thu. Dec. 02, 2010 10:58 pm

When I made the holes I threaded them so I could close or partially close them if I wished. I wound up leaving them open.

Too much air will lower draft through the coal bed and too little will fail to burn the gasses. I think some should be present all the time to also burn CO. But you also need a high enough temperature to ignite the gasses.

I have also been burning a small Buderus stove which is batch loading and has an adjustable secondary air fixture. There have been times when I have opened the loading door to see the blue flames ignite only when I opened the door, this in spite of the secondary air being open. The reason I think is that the air openings are higher than the coal bed was at the time and the air was going straight out the vent without mixing with the gasses. Stove was set for a low burn so opening the door allowed a large volume of low velocity air to enter. At a higher heat setting and a full load of coal it is apparent the secondary air openings are working well. So things can vary with temperature and also with primary air setting and also with the load of coal. When burning a stove very hot and primary air is open fairly wide then probably very little if any secondary air is needed. It is when the stove is set for a low heat output that incomplete combustion is more likely to occur.

 
snuffy
Member
Posts: 532
Joined: Fri. Jan. 25, 2008 11:55 pm
Hand Fed Coal Stove: Harman SF250 & Mark III backup
Other Heating: Oil Hot Water

Post by snuffy » Thu. Dec. 02, 2010 11:10 pm

For my own knowledge, isn't that the purpose for the secondary air valves on the Harman Magnafire loading door?

 
User avatar
VigIIPeaBurner
Member
Posts: 2579
Joined: Fri. Jan. 11, 2008 10:49 am
Location: Pequest River Valley, Warren Co NJ
Hot Air Coal Stoker Furnace: Keystoker Koker(down)
Hand Fed Coal Stove: Vermont Casting Vigilant II 2310
Other Heating: #2 Oil Furnace

Post by VigIIPeaBurner » Fri. Dec. 03, 2010 12:31 am

Norcan, your stove already has a secondary air inlet, totally cast iron and controlable too. I've usually kept it closed but recently began to open it when I start recharging.
When the damper is closed this port lets air into the secondary burn chamber inside the right side of the stove and then to the back secondary chamber . When the Vigilant is in updraft mode (damper open), the air is sucked into the main fire box chamber. There's always a little air feeding directly into the firebox from the glass in the to front doors. Like Harman glass windows, the gasket is only on the sides and top, the bottom does not have a gasket.

I wouldn't use this port in low fire/warm weather conditions. I'm concerned it saps too much draft under these low draft conditions. With it closed, the additional draft would draw O2 from beneath the fire and a more complete combustion. It's also the most direct path into the room from the fire box area so it would be the first source for CO to back draft, damper open or closed. Remember, the Vigilant was once a wood stove.

 
User avatar
nortcan
Member
Posts: 3146
Joined: Sat. Feb. 20, 2010 3:32 pm
Location: Qc Canada

Post by nortcan » Fri. Dec. 03, 2010 11:32 am

franco b wrote:When I made the holes I threaded them so I could close or partially close them if I wished. I wound up leaving them open.

Too much air will lower draft through the coal bed and too little will fail to burn the gasses. I think some should be present all the time to also burn CO. But you also need a high enough temperature to ignite the gasses.

I have also been burning a small Buderus stove which is batch loading and has an adjustable secondary air fixture. There have been times when I have opened the loading door to see the blue flames ignite only when I opened the door, this in spite of the secondary air being open. The reason I think is that the air openings are higher than the coal bed was at the time and the air was going straight out the vent without mixing with the gasses. Stove was set for a low burn so opening the door allowed a large volume of low velocity air to enter. At a higher heat setting and a full load of coal it is apparent the secondary air openings are working well. So things can vary with temperature and also with primary air setting and also with the load of coal. When burning a stove very hot and primary air is open fairly wide then probably very little if any secondary air is needed. It is when the stove is set for a low heat output that incomplete combustion is more likely to occur.
Hi, thanks for infos. If possible for you, can you post a photo of you air vent holes? I love your idea of igniting these gases at the load top. If they don't burn they go outside and their combustion heat is lost.


Post Reply

Return to “Hand Fired Coal Stoves & Furnaces Using Anthracite”