[Gasification] r.e. Optimising gasification

[Mark & Elena Gallmeier]

Jonathan,

I've been physically working a lot with charcoaling in smaller scale retorts 
recently.

>but maybe in the long run charcoal
> is a better fuel anyway at least
> for mobile applicaitons

I think this is very likely.  As far as I can tell from "The Literature", 
all of the early European WWII era gasifiers were charcoal burners, as were 
all the Japanese gasifiers and the post-war Korean and Filippino vehicle 
gasifiers.  True wood gasifiers - fueled with centrally prepared 'car 
wood' - didn't appear in quantity until 1942.

>much
> reduced filtration (tar mitigation)
> requirements.

This depends on what grade of char one uses.  The worst tars aren't removed 
from char until well above exothermic carbonization temperatures.  Gas made 
using a lower grade brown-black char prepared at 627 F maximum (end of 
exothermic carbonization) will still need a robust filtration scheme since 
the heaviest tar volatiles will still be present.

I have examples in my shop of 3/4" Schedule 40 pipe elbows that became 95% 
blocked with tar produced AFTER the end of exothermic carbonization.  i.e. 
retort temperatures were well above 627F when those tars were produced. 
The idea of putting this stuff through an engine system without very 
aggressive filtering goes away fast.

Moisture up to 10% can still be present too, depending on how carefully the 
char is stored between preparation and use in the gasifier.

My outlook now for fueling gasifiers with 'char' is either a) use torrefied 
wood for fuel or b) use a much higher metallurgical grade char to ensure the 
volatiles are gone.    I expect low grade char is a very unsatisfactory 
half-way house because of the remaining volatiles content.

>high efficiency retorts
> at central plants to process
> wood+various ag wastes first to make syn methane & charcoal, and sell the
> charcoal as a byproduct
> for transportion  & other uses may be viable.

Other viable uses include metallurgical applications such as iron melting 
cupola furnaces.  If metallurgical char were to become common then small 
cupola foundries to melt locally available scrap iron would likely 
experience a revival, too.

>From what I've learned, back when charcoal 'retorting' - as opposed to 
'kilning'  - was common in the 1940s & earlier , the retorters were 
primarily after chemicals recovery.  Char fuel sales were a secondary 
byproduct for char retorters.  Primary char fuel manufacturers of the same 
era relied on charcoal *kilns* operated with controlled amounts of inlet 
air.

Best Wishes,

Mark


> Message: 7
> Date: Sat, 25 Nov 2006 11:37:09 -0500
> From: "Jonathan F. Pratt" <jonpratt76 at hotmail.com>
> Subject: [Gasification] Optimising gasification
> To: <gasification at listserv.repp.org>
> Message-ID: <BAY101-DAV18DB5B084B51647DB0C561C6E00 at phx.gbl>
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>
> Admittedly you can't have too high a moisture content flowing through the
> reaction zone or the temps
> will drop too low and kill the reaction BUT if you start with superheated
> air or steam at 500C plus
> pre-heated intake air in the gasifier the extra heat inputs should
> compensate for the extra thermal load
> going into the endothermic water gas reaction.  Your producer gas is going
> to be richer in H2 and CO
> and much less proportion of nitrogen so the output gas may be double in
> heating value than regular
> producer gas diluted with 60% nitrogen.
>
> I don't think there is a 'holy grail' here either but it seems like
> recycling the engine heat outputs of both the
> coolant and exhaust will result in significantly higher overall 
> efficiencies
> with this gasifier+ICE combo.
> It seems like the efficiency would come from a lower fuel consumption
> (charcoal or maybe wood) for
> a given power output.  If there is more power per stroke because of the
> higher caloriffic gas that would
> equate to lower fuel consumption (enriched producer gas) for a given power
> level right?
>
> Or does it all end up the same efficiency because you end up consuming as
> much carbon with steam as
> you would with atmospheric O2?
>
> As you said wood may not work with this waste-heat recycle because it
> already has moisture content and
> 25% native moisture content is optimum, but maybe in the long run charcoal
> is a better fuel anyway at least
> for mobile applicaitons because of it's higher energy density and much
> reduced filtration (tar mitigation)
> requirements.
>
> So looking down the road, maybe an infrastructure of high efficiency 
> retorts
> at central plants to process
> wood+various ag wastes first to make syn methane & charcoal, and sell the
> charcoal as a byproduct
> for transportion  & other uses may be viable.
>