[Gasification] reducing temp. of gasification

Anand Karve adkarve at gmail.com
Thu Sep 15 22:25:47 CDT 2011

Dear Jim,
from your message it appears that it is not possible to lower the
temperature of gasification if we wanted to produce producer gas in an
oven-and-retort system. We developed, at the end of the last century,
an oven-and-retort process for producing charcoal from agricultural
waste. At that time, a researcher from the National Chemical
Laboratory, Pune, India, tested some catalysts in our oven-and-retort
system to show that one could produce active charcoal even at the
relatively low temperature of 300 to 400 C. This led me to thinking
that one may discover a catalyst which might help us in getting
producer gas from agricultural waste at this temperature. Some
preliminary experiments were conducted by us with the help of a
pyrolyzer being used for producing fuel oil from plastics. The same
proprietory catalyst was used in this process, which was being used in
the plastic to fuel oil process. We obtained a fair quantity of
combustible gas, which we could collect over water, like biogas. We
burned it in a biogas stove. The success of these experiments lead me
to think that it might be feasible to produce producer gas in an
oven-and-retort system.

On Mon, Sep 12, 2011 at 2:25 PM, jim mason <jim at allpowerlabs.org> wrote:
> On Sun, Sep 11, 2011 at 8:08 PM, Anand Karve <adkarve at gmail.com> wrote:
>> Dear Henri,
>> yes it is too complicated. I give below my basic reason for using this process.
>> India generates
>> When we heat the biomass in a closed vessel, can we add a catalyst to
>> the biomass so that the producer gas is generated at a lower
>> temperature? In this way, we would require much less material for
>> burning outside the reactor vessel. If anybody has already done this
>> kind of work, is the catalyst known? Once we get producer gas without
>> nitrogen, we can look at filling it into cylinders and supplying it to
>> rural people as high grade fuel for using in internal combustion
>> engines.
> a.d.
> it would be wonderful to have a conversion route like this.  sadly i
> think the thermo-chemistry is against us here.  but you should prove
> us wrong ;-)
> however even if solved, the result would still be marginally able to
> be compressed economically in low tech situations.  think of the
> difficulty in even ch4 compression for fuel volumes.  now, 2-3x that
> difficulty with pure h2 and co? (btw, what is the actual energy
> density difference here?)
> here's some challenges for the "magic retort" that i see.
> first, you have both a volatile gas/liquid and char conversion
> problem.  pyrolysis is going to give you both.  yes, we can easily
> complete pyrolysis at 300c or so with common ic exhaust heat exchange,
> or other relatively low grade heats.  don't need catalysts to do this.
> by well controlling the temp, and having lots of time, you can make
> the tars less nasty to deal with later.  however, they will still be
> tars needing cracking and/or combustion and reduction.  we usually use
> the rule of thumb of 1000c to crack them.  if you keep their
> generation to only primary tars via low temp pyrolysis, it will take
> somewhat less temp to do this conversion.  how much less i don't have
> good numbers on yet.  wish i did.
> however, it is very unlikely that could get down to 300c.  most of the
> catalytic tar cracking assists i've read about are in the 700c and up
> range.  mostly really 900c and up.  here's a page from reed's handbook
> that give results for some common routes, including dolomite:
> http://wiki.gekgasifier.com/w/page/6123685/Catayltic%20Tar%20Cracking%20Methods
>  (thank you tom)
> it is also known that putting dolomite in the biomass during pyrolysis
> will make the tars produced a bit more benign and more easy to deal
> with downstream.  this is a method used in pyrolysis to oil situations
> where control of the liquid / gas output is desired.  its still a
> mess, but a bit less so.  under highly controlled lab conditions,
> everyone gets excited.  DOE soon writes big checks.  tragedy usually
> follows.
> assuming you do somehow solve the tar cracking problem at low temp,
> either through pyrolysis control or tar cracking, now you have to get
> rid of the char.  well, you can just agree to use that for biochar too
> of course.  but if you want that to be fuel you need to get up into
> temps where reduction happens at useful rates.
> in a typical reactor situation the usable bottom end temp for
> reduction ends around 650-700c.  it is usually much higher with
> smaller reduction volume reactors.  in our units we're usually still
> 800c at the bottom of reduction.  this is non-ideal, as you are
> wasting reduction potential.  however you are gaining fines purging
> out the bell, which is needed to prevent bell packing.
> as you approach infinite reduction times you can get reduction down
> into the 500c range.  that is where it stops chemically under atm
> conditions.  you can use vacuum to assist reduction, but that is hard
> to gain under temp.  though with batch load the reducing temps will
> reduce volume and increase vacuum which will help drive more
> reduction.
> here's the gas equilibrium charts that reveal some of this.
> http://wiki.gekgasifier.com/w/page/6123723/Gas%20Equilibrium%20Charts
> i don't know of any catalysts that alter reduction temp curves.  there
> must some.  i'd be very interested to know too.
> but really, you are trying to do this all in one step in a barrel, so
> separating them like the above isn't fully helpful.  what you are
> describing here is really a pyrolysis retort, not a gasifier.  it is a
> magic retort that goes "biomass to gas" in a manner that many have
> wanted a magic retort that goes "biomass to oil".  the gas in this
> case being the controlled output, not the oil.  relatively high temps
> are needed to increase the gas fraction vs liquid fraction, and you do
> this at the cost of them going progressively nasty and difficult to
> post process.  this also works against the original desire for low
> temps.
> so there's some problems.  you knew all this.  not sure that helped
> any.  unfortunately, i don't have this magic catalyst in my
> possession.  if you find it, please do send me a can!
> jim
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Dr. A.D. Karve
Trustee & Founder President, Appropriate Rural Technology Institute (ARTI)

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