GAS-L: Re: Coal cooking summary

["Thomas Reed" <tombreed@attbi.com>]

Dear Dan and All:

I enjoyed Dan's extensive comments on coke.  (I am used to the name "coke"
as the product of coal pyrolysis.  Maybe Dan can tell us if there is a
difference between Coke and Rock coal.)

At the turn of the century a product "coal oil" was in widespread use in the
U.S. and England (and probably everywhere else).  It is the product of low
temperature coal pyrolysis.  What is the name for the remaining carbonaceous
material after low temperature pyrolysis?  Does "coal oil" exist anymore?

Coal tar is the product of high temperature coal pyrolysis (as in making
coke).  Coal tar is the resulting high temperature pyrolysis condensate
(over 700 C).

I look forward to some expert opinion here...

Yours truly,                    TOM REED           BEF



----- Original Message -----
From: <Carefreeland@aol.com>
To: <tami.bond@noaa.gov>; <stoves@crest.org>
Sent: Thursday, February 28, 2002 9:06 PM
Subject: Re: Coal cooking summary


> Tami, Stovers,
>        We are all more familiar with wood and charcoal.  We now want to
apply
> our skills to coal to improve the combustion.  Let's look at the primary
> differences between charcoal and rock coal.
>       1. Rock coal has more ash, similar to a briquette with clay binder.
>       2. Rock coal has higher density, more like the ceramic stove than
the
> ticanium stove.
>       3. Rock coal has almost zero porosity unless chipped or powdered.
>       4. Rock coal can be high or low volatility, but generally is lower
in
> volatile than wood or char.
>        The first feature gives more heat retention as the resulting ash
> insulates the burning embers much more quickly. This also enables
reflection
> back into the burning coal.
>        The higher density holds more heat once properly warmed. Higher
> density acts like a heat sink while trying to ignite, requiring more
initial
> heat.
>        Lower porosity allows less surface area which slows the burning
rate
> without sufficient movement of oxygen. The higher heat retention
> characteristics somewhat offset this in open burning. This is because of
the
> higher resulting internal temperatures producing CO instead of CO2. The CO
is
> then emitted and burned as more oxygen becomes available away from the
ember.
>
>        The more volatile rock coal has, the more hydrocarbon gas emitted
at a
> lower temperature.  This gas can be useful or not just like the gas from
> wood.  The exception is that rock coal produces sulfur compounds, nitrogen
> compounds and heavy metal oxides.  For this reason I also recommend
outside
> ventilation of flue gasses.
>        The Chinese undoubtedly have used some sort of bellows or even
> blowpipes just to establish their pit fires.  The lack of air circulation
> would probably kill the flames from CO2 suffocation without extra oxygen.
A
> sizable fire built from wood would also give sufficient air circulation.
>        Since early man, bellows of all sorts have been used.  Some made of
> skins, some just blowpipes to enhance the lungs. By directing the air into
> the coals, less starting fuel can be used.
>        There are two kinds of reflectivity spoken of here.
>        1. Direct reflectivity, where the infrared and visible light are
> reflected off of a shiny surface.
>        2. Secondary reflectivity. This is where the radiation from
combustion
> of fuel heats a surface such as the inside of a stove. This surface then
> reradiates the infrared light waves back to the fuel. The heat retention
is
> required to steady the intermittent pulses of combustion.
>        With the rock coal, the combustion tends to be self contained once
> started.  The problem is the lack of initial combustion heat to
sufficiently
> raise the temperature of the entire grain of coal.  If powdered coal is
used
> it helps, but still does not match the porosity of wood char or the
volatile
> content of wood.
>        Anyway you look at it you need more air.  Direct reflectivity would
> help, but how do you keep a white or polished surface?  High temp
firebrick
> has a high alumna content keeping it's walls white during combustion.
>        Thin cast iron seems to be a compromise.
>       1. It heats quickly enough not to conduct too much heat away from
the
> starting fire.
>        2. It retains enough heat to be secondary reflective.
>        3. It insulates enough not to draw heat away from the beginning
fire.
>
>        4. It can be thin and still not burn through unlike any other
material
> known to man.
>        I return to the thought that we threw away the perfect material for
> combustion stoves when we forgot how to make certain types of iron
materials.
>  Every time I start my potbellied stove I am reminded of this. My stove
has
> both of the iron and brick materials and was made very long ago.  In our
> stoves today, the secret is all in the grate. It is the only high carbon
> silicon iron (wrought iron) used in combustion.
>        Rock coal was the common term until 1900.  The "rock" name was
dropped
> after charcoal was almost made obsolete. That was back when the "Collier"
was
> the most important person around.  He was the skilled tradesman who made
your
> coal for you.
>        The best stoves I have known for coal burning, had the these same
> features.  Secondary air is not as important for coal once up to
temperature
> because the burning temp is hot enough to completely combust everything.
> This is provided  enough primary air is present.  Draft is far more
> important.
>            Dan Dimiduk
>
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