[Gasification] Characterization of waste water from biomass gasification equipment: A case-study from Cambodia

[Doug Williams]

Hi Pete,
You ask:

> So---- what if one allowed the scrubber water to sit still for a couple of 
>days?  Would most of the "condensible hydrocarbons" and the tar rise to 
>the top?  (I assume that most that "bad stuff" isn't water soluble.)  

Heavier tars float but a lot goes into solution and that's the stuff
usually containing benzine and other nasties that are difficult to
filter. 

>Then, could that top layer be sucked off, making for a concentrate that 
>might be easier to deal with?  And, would the remaining "water" be useful 
>in the >scrubber again?

Basically this is how the systems are managed, but the condensate is
carcinogenic and hard not to be exposed to it over a period of time.
Depending on what the condensible is, and there are huge variations, it
can be just very light pyrolysis oil without black tars, or the whole
spectrum of what is commonly referred to as stack gases. These are a
very unstable mix of distillates, and over 200 chemical combinations
have been identified. They don't all survive to condense, but the
outcome is the same of creating toxic black liquor. Sawdust will mop up
pyrolysis oils, and the more activated chars after gasification, can be
used to filter "some black liquor", but having said that, you do need
lab analysis to be sure of the outcomes.
> 
> My reason for asking the original question is this:
>   I have been testing a JXQ-10 for several years now.  I can get it 
>to make enough gas to run an Onan 6.5KW genset for up to about 4 hours 
>per batch, at > about 3KW net, max..  The thing that always ends the 
>run is when the reactor is full of wood chips to the top.

To give you a correct answer, I would need a step by step procedure of
starting it up and operating it over the four hours. It sounds like an
open core principle burning the pyrolysis gases in a very shallow layer
which continually moved upwards towards the incoming air. When it fills
to the top you must have a cylinder of charcoal left that acts like a
plug so it just slowly shuts down as the amount of exothermic heat
drops away.

> As I watch maximum  power, and I see it begin to drop, I can add a 
>thin layer of wood chips and, IMMEDIATELY to power comes back up.  It 
>appears to me that it's the new wood chips that are the "new" energy 
>source, not the (rapid change in) dissociation of CO2 to CO and O2 or 
>the sudden "new" dissociation of H2O to H2 and O2.

The previous set of answers apply, but you are right in that new chips
have the pyrolysis gases to sustain the oxidation band as gas will burn
first turning the wood to char, but as the interface to the flame front
keeps moving up away from the char, it lacks air to maintain oxidation
> of the char. 

I'm pretty sure that is your situation, but give me the fuel operating
info and we can then see if I read your description correctly.

I just remembered (must be getting old) I did a report on condensates
for the Fluidyne Archive with photos. www.fluidynenz/250x.com

Doug Williams,
Fluidyne.