preheated secondary air

preheated secondary air

PostBy: carlherrnstein On: Sat Oct 27, 2012 6:13 pm

Does anyone have a idea how hot secondary air needs to be to ignite coal gas cooking out of coal? Im just looking for a rough number Im thinking it would be at least 300 or so.
carlherrnstein
 
Hot Air Coal Stoker Stove: combustioneer model 77B
Coal Size/Type: pea stoker/Ohio bituminous

Re: preheated secondary air

PostBy: Lightning On: Sat Oct 27, 2012 7:22 pm

I don't think it quite works that way.. For combustion you need a fuel (coal gas) and oxygen and a source of ignition, such as a flame. I don't think a hot secondary air of 300 degrees will ignite anything :( Somebody fix me if I'm wrong lol
Lightning
 
Hand Fed Coal Furnace: Clayton 1537G
Coal Size/Type: Nut/Stove Size Mix

Re: preheated secondary air

PostBy: McGiever On: Sat Oct 27, 2012 7:44 pm

This may give you a clue... ;)


Code: Select all
Coal >  Ignition Temp/* >   Volatiles Initially Released Temp/*

Bit        400-500*C                   200-300*C
Ant        700-800*C                   380-400*C
McGiever
 
Stoker Coal Boiler: AXEMAN-ANDERSON 130 "1959"
Hot Air Coal Stoker Stove: HARMAN MAGNUM
Hand Fed Coal Stove: RADIANT HOME AIR BLAST
Baseburners & Antiques: OUR GLENWOOD 111 BASEBURNER "1908"
Coal Size/Type: PEA / ANTHRACITE, NUT-STOVE / ANTHRACITE
Other Heating: Ground Source Heat Pump
Stove/Furnace Make: Hydro Heat /Mega Tek


Re: preheated secondary air

PostBy: LsFarm On: Sun Oct 28, 2012 10:17 am

The preheating of the secondary air is to prevent cooling down the volitiles so the won't burn. If you introduce cold, outside air, the volitiles will remain as soot, and wasted, unburnt energy.

The air above a fire is usually too low on oxygen to burn all the volitiles, and it takes the right combination of oxygen, heat and volitiles to create a fire. This 'right' combination often results in a 'puff-back' in handfed stoves.

With the hot blast stoves, the secondary air usually comes in through a duct that is located alongside the outside of the firepot, so the firepot is doing the preheating. The vent ring around the upper perimeter of the firepot is also very hot, so the air probably is heated to ??? 300-500* ?? just guessing, it would depend on the fire, firepot liner, airflow rate etc.

The design for the HotBlast stoves is well thought out, and I'd love to watch one light off the volitiles.. it would be an impressive sight I'm sure.

When I was burning Bit coal in my big hand fed boiler, I created a preheated air source, and when the conditions were right, the secondary fire was very impressive. and it reduced the soot buildup quite a bit.

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: preheated secondary air

PostBy: Lightning On: Sun Oct 28, 2012 12:06 pm

OK that makes sense :D The heated secondary air helps combustion :idea:
Thanks for the detailed answer, learn something everyday!
Lightning
 
Hand Fed Coal Furnace: Clayton 1537G
Coal Size/Type: Nut/Stove Size Mix

Re: preheated secondary air

PostBy: carlherrnstein On: Mon Oct 29, 2012 11:20 am

I figured it wouldnt need to be super hot. Im seeing with my vigilant I sometimes have a good bit of unburnt coal gas going up the flue, and Im toying with the thought of replacing one or both of my glass windows with a steel plate with a vent and baffal to heat the air with a small window to see how its doing.
carlherrnstein
 
Hot Air Coal Stoker Stove: combustioneer model 77B
Coal Size/Type: pea stoker/Ohio bituminous

Re: preheated secondary air

PostBy: Berlin On: Mon Oct 29, 2012 3:21 pm

on lower heat output you'll always have unburned gas entering the flue; even with secondary combustion air, you'll lose most of that because at low burn, even with preheated secondary air you will not have enough temp to ignite the gasses. I wouldn't do anything about it, It doesn't cost you greatly in terms of efficiency and secondary air at lower burn rates won't improve things.
Berlin
 
Hot Air Coal Stoker Furnace: Will-Burt Combustioneer 77B
Coal Size/Type: Ohio BITUMINOUS pea stoker coal