Re: Cooking with Coal-- AJH? Crispin? John Davies?

[AJH <andrew.heggie@dtn.ntl.com>]

On Thu, 28 Feb 2002 02:14:12 -0800, Tami Bond <Tami.Bond@noaa.gov>
wrote:

>
>Stovers & Especially Coalers,
>
>I have been playing with coal burning again. Can somebody tell me why 
>anybody would cook with this stuff?! 

Probably because they cannot afford anything better.
>
>I had previously burned high-volatile (like 40% vol) bituminous. That 
>catches and stays lit pretty well. Now that I am trying some lower-vol 
>coal (at least I think that is the problem) it is hard to get the coal 
>to support combustion. What's the trick? 

Probably to do with size, you need to get the carbon up to its
ignition temperature, at the same time a large lump has a lot of
thermal mass and conducts heat away quite quickly. If volatiles are
present then these are produced and can burn. Wood is a decent
insulator so its surface reaches pyrolysis temperatures quite quickly.
If there is a flame present volatiles catch light and then feedback
more heat into the mass. If the fire only smoulders then there is no
ignition source for the offgas and it vents unburnt, contributing no
heat.

With good coal, anthracite, it is nearly all carbon, once lit it will
glow, to create a flame you need to pump air through it to increase
the fire bed and cause CO to be formed, this then produces the
characteristic blue CO->CO2 flame.
>
>I *could* put the coal in a huge pile and/or start it with lots of 
>wood. Sure, that works. But I can't imagine anyone cooking that way. If 
>you have to use so much wood to get it lit, you might as well cook with 
>the wood. If you have to use so much coal to keep the combustion going, 
>again, one might think people would choose something else. I can see 
>heating with coal, where you ignite once and just keep feeding the fire 
>once it is hot. Starting a coal fire for every meal, though, seems very 
>inefficient.