[Stoves] How to make smokeless coal?

Darpan Das darpandasiitb at gmail.com
Mon May 22 00:22:51 CDT 2017


Dear Mr Andrew

Thanks for your answers. Some comments:

I asked: If I remove the volatiles then will the emissions reduce?
You said: Perhaps but you will still have to burn the smokeless coal
completely. What will you do with the volatiles you have removed?
My reply: I do not understand what you mean by 'burn the smokeless coal
completely'. Burning a fuel completely is achieved when they are provided
with a stochiometric amount of oxygen to produce completely oxidised
product of CO2 and H2O. This can never be the case for uncontrolled
combustion devices like stoves.
Further, I agree the process of carbonisation involves the removal of
volatiles at a certain temperature. These volatiles, when removed have
certain calorific value and usually when emitted from coke oven batteries
are collected as 'tar' as can be used for commercial application.

I asked: How do I decide at what temperature should I carbonise?
You said: The higher the temperature then nearer the coal will get to be
coke.
My reply: So ideally you mean the temperature with infinite value is the
one where coal would get converted to coke.Coking plants would try to
reduce their cost by reducing the temperature at which to carbonise. This
is basically that temperature, where most of the volatiles get removed.
Will it not vary from coal to coal, size to size? How can I optimise this
temperature?


I asked: Why is low temperature carbonisation of coal meant for domestic
use and high temperature for metallurgical use?
You Said: The reason coke is made at a high temperature is so that it is
nearly pure carbon, domestic smokeless coal just needs the more
volatile substances
removed but leaving higher tars in the coal to retain more of the initial
energy in the coal plus make it easier to light.
My reply: Usually literature report of 600 C for domestic coke and 800-1000
C for metallurgical coke. Why this distinction? Why can they be
interchangeably used?  You said 'domestic smokeless coal just needs the
more volatile substances removed but leaving higher tars in the coal to
retain more of the initial energy in the coal plus make it easier to
light'. So does this mean by heating the coal at lower temperature for
domestic application the low molecular weight volatiles are removed,and tar
with high molecular weight remain which provide enough calorific value to
the fuel to make it a easy fuel to light. If this theory to be hold true -
they why metallurgical coke are heated at higher temperature? We would want
the same thing there too.

Regards
Darpan

On Mon, May 22, 2017 at 3:13 AM, Andrew Heggie <aj.heggie at gmail.com> wrote:

> On 20 May 2017 at 19:33, Darpan Das <darpandasiitb at gmail.com> wrote:
>
> >
> > 1) Is carbonisation of coal the major step to make it a smokeless fuel
>
> I'm no expert but my take is yes and more below.
> >
> >
> > 2) Is pyrolysis/carbonisation/ devolatalisation the same thing?
>
> Yes
> >
> >
> > 3) Are volatiles the main reason for emissions from coal cook stoves?
>
> Not being able to completely burn these volatiles in the time the
> molecules remain in the flame leads to Particles of Incomplete
> Combustion leaving the flame, these are a mixture of soot and
> Polycyclic Aromatic Compounds.
> >
> >
> > 4) How can i remove the volatiles?
>
> By heating up the coal in the absence of air
> >
> >
> > 5) If I remove them then all the emissions will reduce?
>
> Perhaps but you will still have to burn the smokeless coal completely.
> What will you do with the volatiles you have removed?
> >
> >
> > 6) How do I decide at what temperature should I carbonise?
>
> The higher the temperature then nearer the coal will get to be coke.
> >
> >
> > 7) Why is low temperature carbonisation of coal meant for domestic use
> and
> > high temperature for metallurgical use?
>
> What do you mean by low temperature?
>
> The reason coke is made at a high temperature is so that it is nearly
> pure carbon, domestic smokeless coal just needs the more volatile
> substances removed but leaving higher tars in the coal to retain more
> of the initial energy in the coal plus make it easier to light.
> >
> >
> > 8) Is the size of the coal not important factor to be taken into
> > consideration when carbonising the coal?
>
> I don't know
> >
> >
> > 9) Why is coke for domestic purpose also called semi-coke?
>
> Because it is only part way to being coke as the pyrolysis is at a
> lower temperature (typically 650centigrade rahter than 1100c when
> making producer gas.
> >
> >
> > 10) Coke obtained from Low temperature Carbonisation same as Semi Coke?
>
> Probably
> >
> >
> > 11) What are the specification for quality assurance of the domestic coke
> > products? Are there any standards?
>
> I would think there are bound to be but  I don't know them.
>
> There are similariiities between pyrolysis of coal and making charcoal
> but the by products from coal are nastier.
>
> I suspect this is because the coal contains volatiles which are more
> phenol (ring like carbon structures) like whereas wood has more chain
> like structures and the lignin, which is phenol like structures are
> not as complex so can burn out more completely without giving rise to
> many PAHs, Also coal gives of amoniacal liquids and sulphur compounds.
>
> Andrew
>
> >
>
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-- 
Darpan Das
Research Scholar
IIT Bombay
India
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