[Gasification] Ash to land?

[Tom Miles]

The principal mechanism for thermal fractionation or separation of the
inorganics in gasification and combustion is the volatilization at
relatively low temperatures and condensation to submicron particles (or onto
particles). As Jan knows you can trace the inorganics all the way through
the gasification or combustion process as they tend to stay in different
locations depending on the conditions. 

We have used this in staged combustion (gasification followed by air added
in stages) to separate the more refractory phosphorous from potassium in
animal manure. We collect the phosphorous rich ash which is heavier in a
boiler or cyclone and the potassium downstream in a baghouse. The two ash
fractions have different economic values. So far we have no industrial
applications but we know it works.  

We have not seen that pyrolysis systems do much better at retaining alkali
than gasification. In simple reactors even though you are carbonizing the
organic fraction at a relatively low temperature you still volatilize
significant amounts of alkali which condenses in the oil. In the case of
gasification the alkali make sticky particles when you burn the gas.  

Lead sometimes reacts with alkali and stays in the cooler parts of the
furnace or boiler.  Zinc, cadmium and other metals tend to go with the light
submicron fraction into the back half of the convection sections, into the
ESP  or out the stack.

It's a challenge to use a gasifier or boiler as a way of turning an ash
disposal problem into an asset. 

Tom Miles        

-----Original Message-----
From: gasification-bounces at listserv.repp.org
[mailto:gasification-bounces at listserv.repp.org] On Behalf Of Pels, J.R.
(Jan)
Sent: Thursday, May 10, 2007 7:03 AM
To: Discussion of biomass pyrolysis and gasification
Subject: Re: [Gasification] Ash to land?

I would say so. When you make charcoal and burn it elsewhere, then
dispose the ash safely. 

Depending on the temperature you make or lose active groups that can
bind metals. Char made at high temperature does not bind metal very
well. pH is also critical for heavy metal mobility.

Jan

========================================
Dr. Jan R. Pels
ECN - Biomass, Coals and Environmental Research
P.O. Box 1, 1755 ZG Petten, The Netherlands
telephone: +31-224-564884; fax: +31-224-568487
mobile: +31-6-10923218
e-mail: pels at ecn.nl
========================================
 
> So if I understand this correctly, we would want a gasifier 
> that produces charcoal NOT ash. Thus the heavey metals would 
> be locked in the charcoal...

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