[Gasification] Fwd: Reg:coal gasification

[Doug Williams]

On Mon, 2 Feb 2015 15:49:04 +0530
Mano Va <gmmanovassm at gmail.com> wrote:

Hello Manova,

I have offered answers in the text to your questions:

 
> *I am manova, I have some doubt on gasification, Last month i took a trail
> on 100 kg coal gasifier (pressure mode (low pressure 3Kpa ) ,Down draft) ,*

Coal gasifiers traditionally work in the updraught mode, so that the
exothermic heat can pass upwards through the raw coal to drive off the
pyrolysis gases first, which then makes the coal more reactive. 
> *Two hours after that  i received only flue so i check the level above the
> reactor bed, *

Charcoal will make gas very easily both in updraught and down draught
modes, so at start-up you will get combustible gas, then just
non-combustible CO2 after the charcoal has been consumed.
> 
> *Again i load the coal and starting gasifier same flue only coming out,*

The  hard raw coal is not very fast to respond to first becoming coal
char, then forming the reduction bed needed to convert the CO2 into CO,
so only hot CO2 comes out in the flu gas.
 
> *Gasifier initial starting time i put 50 kg charcoal and 200kg coal up to
> charcoal bed gas coming out without any flue *

This confirms my explanation and tells you that your testing of coal is
a waste of your time in that design of gasifier.
 
> *After full and full coal reached to reactor flue only coming out*
 
> *gasifying medium : air*

If you gasify with air in the updraught mode, you will usually make
dirty CO gas only fit for burning in heating applications due to the gas
having a high tar content. Steam is usually added to create H2 making a
better quality of gas and to help control the exothermic heat
generation which will melt the grates if the air enters the bed from
the underside. Some WW11 coal gasifiers had only one large bore single
water cooled nozzle, so you should study those historic German designs
if you want to gasify coal reliably.

> *air fuel ratio (coal)1:4(air)*
> 
> *ultimate analysis of coal*
> 
> *C-44%,H-3%,O-10%,Ash-30%,Moisture-13%*

The best coals used for engine applications were Anthracite, a very
hard coal with low volatile content. These are normally expensive
compared to softer bituminous coals. High ash content create flow
problems due to the formation of slag and clinker which displaces the
gas making char. This will block grates in a down draught gasifier, and
clog the ends of air nozzles.

The photos of your flame colour suggest that it has a high carbon dust
content in both photos. The bushy lazy flame is most likely the
start-up gas, and the tighter shorter flame after the bed temperatures
stabilised in the reduction zone.

Hope this is of assistance to you.
Doug Williams,
Fluidyne.