[Gasification] Fw: coffee grounds gasification fuel

[Ken Calvert]

From: "Ken Calvert" <renertech at xtra.co.nz>
To: "jim mason" <jimmason at whatiamupto.com>
Sent: Wednesday, October 17, 2007 11:11 PM
Subject: Re: coffee grounds gasification fuel



 Apinun long yutu!   Sorri tru, be mi no save yuhu?
 Jim you will have to fill me in as to where you come from?
 Anyway the story is that dry coffee grounds will gasify very nicely.
 The problem is to get them dry!  For good gasification you need
 a moisture content  of  less than 15% better still 10%.
 Carbohydrate cellulose contains chemically bound water.
Under gasification conditions, the carbon ends up as CO  which is energy 
positive and
the hydrogen ions can get made into molecular hydrogen, which is very energy 
negative.
So, it takes a lot of carbon to get the heat up, and you can only get as 
much hydrogen
as you have surplus carbon.energy.
Add water and  you may get some more hydrogen but  that brings the 
temperature
of the combustion down and you get more carbon dioxide and less carbon
 monoxide.  That is bad news!
he best wood gas is made with around  10% m.c. of non chemical water which 
is
 basically dry wood.
 All the guff you hear about water injection into car engines is with 
petrol,
 which is hydrocarbon and no chemical water content, or with coal or
 charcoal,, which has no hydrogen either. In this case the water can add 
some energy
 If you can get dry 10% moisture content  coffee grounds you are away on a
 fast camel!   The calorific value, per weight, I would guess would be about 
the same
as wood for the same the same moisture level.
If they are say 20% moisture then you will get gas, but it will be of low
 quality with a lot of carbon dioxide and water vapour in it.
Basically the higher the temperature of combustion the better the quality of
 gas up until you start to get different problems,
with the ash melting into 'slag'  which can really gum things up!
You will also have a problem with fuel flow.  The fine granules will
bridge and hold up in the fuel hopper of a classical style gasifier..
 That means you will have to have a rapper, or better still a rotating 
augur
 made of spikes which will keep the fuel moving down into the
hearth throat.  An alternative is to pellet the fuel, like they do with fine
 charcoal.  However, from the top of my head
 coffee grounds don't stick together at all, so you are up for the addition
 of starch or some  kind of cheap adhesive to briquette  the fuel.

   The way we gasified the coffee hulls was to use a cyclone model rather
 than a updraft/downdraft/sidedraft thingo. You may remember  how the Asaro 
burners work,
 with the  husk blown in on a tangent and how they sweep round and round 
inside the
circular firebox and the ashes and char end up as a  cone in the centre of 
the firebox,
until they get so light that they finally get blown up the chimney.  For the
 gasifier we used a tricky modification that allowed us to take the
the ash out from the middle of the base of the fire box.

  The example is when you stir a spoonful of sugar in a glass of water and 
see how the
heavier sugar ends up in the middle.  I guess you could say that it is like
 a fluidised bed, but one where the fuel gets a lot longer to burn by taking
 several times round the firebox.   The term for this style of combustion 
is
 something to do with the way water creates reverse whirlpools when they 
open
 the locks on Dutch canals.  I can't bring it to mind at the moment.

   All O.K. on the  business of  making hollow logs  and burning them up the
 middle.  I think you would also need some low grade starch or  adhesive to
make them.   Haven't done it so maybe Tom R can comment on that.     Come
back to me with your further comments.
I am quite happy to keep thinking about this one, because as you say, there
 is a lot of  instant coffee made these days!
Lukem yu!   Cowboy Ken!