[Gasification] Condensing heat exchanger

[Steve Carroll]

Sorry, I think I may have sounded a little flippant in
my response.  It's only because I haven't thought
things out as well as I should have and was wondering
out loud.  Apologies to the list as well for I know
that people wondering out loud can be pretty annoying.
 I think my brain is a little addled right now as I
have started building one part and am trying to design
the next at the same time.

Another person has emailed me off list with some
valuable insight.  He also suggests a direct spray
method but I don't think it is for me.  Truthfully,
what I have is a heat exchanger that I am afraid will
have condensate.  I'm not willing to raise the stack
temperature so I might as well try to make the most of
the condensate.  I think his most valuable input was
that most condensing heat exchangers rely on nucleac
condensation on the clean hydrophilic surfaces of the
exchanger.  The point being that the exchanger
surfaces need to be clean.  On the other hand, I just
read of a company that coats their exchanger surfaces
with Teflon which is hydrophobic.  I think that they
still achieve nucleac condensation but the water
droplets "rain" instead of dripping down the walls. 
They claim benefits from the water dripping onto heat
tubes and the cleanliness of exchanger surfaces.  I
might try spraying on some teflon but I kind of doubt
that I will be able to get any kind of finish similar
to what they have achieved.

What type of burner are you working on?  Is it a
gasifier or close coupled combustor?

Steve

--- AJH <ajh at sylva.icuklive.co.uk> wrote:

> On Mon, 18 Sep 2006 06:25:24 -0700 (PDT), Steve
> Carroll wrote:
> 
> >I'm praying for extremely good combustion.
> 
> I think you have to do a lot of hard work too!
> 
> >  What do
> >you think will be in the condensate?  Could it be
> >pretty toxic?
> 
> Almost certainly as it will have PICs including
> polycyclic aromatic
> compounds, some known carcinogens.
> >
> >I don't know if I would try to cool the exhaust
> stream
> >with a direct spray of water.  Maybe some one else
> has
> >actual experience?  Saturated air at 122°F (50°C)
> has
> >a moisture content of 608 grains per pound of dry
> air.
> 
> 
> I haven't had time to look at the conversion to SI
> units but  there'll
> be no basic difference between the methods as both
> cool the flue gas
> (which is no longer air) to below a dewpoint, So I
> think the only
> thing that controls the absolute humidity will be
> temperature, as the
> remaining gas will be saturated in both cases, with
> the possible
> exception that one may contain more water as an
> aerosol. The loss of
> this water as an aerosol is not a big deal per se as
> the heat has
> still ended mostly ended up in the barrel.
> 
> > It seems like you might be losing more energy than
> >you recover.  You might still be able to recover it
> if
> >you pass though another heat exchanger to preheat
> >combustion air from outside.
> 
> If you think that then perhaps you could post some
> workings, they look
> simple enough once we have a start position of
> ambient temperature and
> humidity , fuel moisture content (given if we know
> it's wood we know
> its products) and exav, as I said my scheme was
> aimed at cheapness and
> avoids at least one heat exchange step.
> 
> AJH
> 


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