Ignition of coal

[op9]

I am well experienced with burners using gas and oil of varying grades and qualities.
However I have been asked if it is feasible to use a gas burner or burners (permanent installation) to be used to do the initial ignition of coal on a travelling grate stoker. The stoker is about 4mtrs wide. Obviously this is instead of the more manual way of initially starting a fire!!!

Has anyone had any exposure/experience with this?

Thanks in advance,
Rod

Rod Nissen.
Combustion & Engineering Diagnostics

 

[Flareman]

op9
I have no direct experience but there's no reason you shouldn't be able to do this. Ignition of coal is variable according to the type of coal you have, but the bottom line is that you need to have enough heat in the flame to hold the coal above 800 degF (or thereabouts - above red heat) for long enough for it to aquire that temperature. Remember, big pieces and clumps of powder take longer to heat up. Once the solid achieves a red heat it is in a condition to begin to gasify and burn, sustaining the temperature on its own.
Waving a small flame across the top of a pile of coal doesn't do it. You have to have a positive heat transfer time or time and a big enough pilot flame contacting the coal.

Good luck
David

 

[IRstuff]

Sounds like it's not different that starting up the charcoal in your BBQ, except that it's moving ;-)

Presumably, you're simply interested in getting the coal to the point of ignition, so that the main burner doesn't waste its heat output on heating up the coal. So, it should be, in the first order, a straight heat capacity problem, i.e., how many BTUs does it take to get the coal up to the ignition temperature? So, something like 0.3 BTU/lb-°F. This book may prove useful:

http://www.archive.org/details/ignitiontemperat00armsrich

TTFN

FAQ731-376

 

[rmw]

I can't see it. Not that gas or oil isn't capable of burning hot enough to ignite the coal, but how do you do it with permanently mounted burners unless they impinged directly on the coal pile? What about the air coming through the grates all the while tending to cool the coal as the gas or oil (above it I assume) tries to heat it? Now if you are talking about putting the burners below the grates and burning the gas or oil up through the grate, then I could see it, although I wouldn't want to comment on what would happen to the grate while all this was going on.

 

[op9]

Hi rmw,
Well what I envisage are burners which do impinge their flame on the coal at the bed entry to heat it above ignition temp (say 800degC). I assume thats how you normally start firing a cold bed with maybe additional combustables (timber) and a gas torch, when the fires haven't been banked. When the coal starts burning it heats the refractory arch. Then when the grate starts moving the new coal is ignited as it comes through. The under fire air could be reduced and would not be significant until the main burning commences.

I was assuming that this manual task of basically starting a coal fire, could be more automated. The burners may have to be of a type which can be withdrawn, removed or retracted out of the way in normal operation.

Appreciate any coal burning specialists to comment.
Rod.

Rod Nissen.
Combustion & Engineering Diagnostics