[Terrapreta] torrified wood vs. charcoal (Robert Flanagan)

[Robert Flanagan]

Hey Bill,

I'm really sorry for the delay in my response but I had to go overseas
during the week and I'm running a little behind.

To try and answer the first question, you could certainly use your excess
heat to take the moisture content down to around 20% then gasifiy your
biomass to insure you get all the energy from your biomass plus the extra
energy from the cracked water. You could also preheat your primary and
secondary combustion air to give your gasifier better over all combustion.
There is a company in India that sell different gasifiers for heat or
electricity called http://www.ankurscientific.com/ and I'm sure they could
make the modification to produce biochar if requested.

The stove you describe in the last part is just an open fire from what I can
make out. If you start a fire and add fuel to the top and have air flow from
the bottom you just doing complete combustion (Reduction to ash) and you
will always have lost energy as the moisture will make your gas very wet.
When all the moisture is driven off and you start burning the off gases have
finished burning then you could in theory quench the char but it sound
dangerous!

Hope this answers your questions,

Regards,
Rob.

On Sat, Feb 16, 2008 at 8:12 AM, info at biorealis.com <info at biorealis.com>
wrote:

> Hi Rob,
>
> Thanks for the great explanation of pyrolysis v gasification.  You
> wrote "why waste all the energy taking biomass to just under it's
> exothermic curve just so you can burn it for heat?"  -- which
> prompted a further question:  What if I already have a source of
> readily available heat that is presently being wasted? How would that
> change the equation? Or would it?
>
> I have a source of "waste" energy available, with temperatures
> ranging between 370C and 400C.  Could these temperatures be used for
> pyrolysis (or gasification? or torrification?) of biomass?  If
> feasible at all, what type of biomass (or moisture content) should I
> be considering?  Ideally, I'd like to be able to extract usable fuel
> gas (H2 and CO) plus biochar.
>
> You also wrote:
>
> "Now with gasification, the lowest possible jump is from around 280C
> to 600C (Depending on air flow), due to primary air (Fresh oxygen)
> flowing through the reactor the whole time (enough to strip the gases
> off, but not enough to reduce the carbon to ash). So with
> gasification stoves we exploit this law and use the excess energy to
> crack the gases and water as they pass through this hot carbon zone."
>
> What if it is *not* a gasification stove, but a completely closed
> (except for a vent to release the gases generated within) vessel
> filled with biomass and heated to 400 degC? What could I expect to
> get out of such a reactor?
>
> Regards,
>
> Bob Crosby
>
>
> >So to answer your question, or ask the question "What happens to the
> >pollutants while it's been turned from wood to torrified wood?" Again I
> say
> >why waste all the energy taking biomass to just under it's exothermic
> curve
> >just so you can burn it for heat?
> >
> >A little back ground on pyrolysis "V" gasification,
> >
> >In pyrolysis your feedstock is typically high in moisture (50%, called
> green
> >waste) and little or no oxygen is added during the process (depending on
> the
> >process time and desired charcoal) so typically you have a very wet off
> gas.
> >There is a direct relationship between temperature, duration, carbon
> content
> >and charcoal yield. With slow low temperature pyrolysis (400C) it's
> possible
> >to have charcoal yields of around 33% but not much higher with a low
> carbon
> >content. When you reach higher temperatures, your charcoal yield can drop
> to
> >10-15% (the typical yield for traditional charcoal kilns used in Brazil
> is
> >about 15%). The highest possible charcoal conversion obtainable today is
> via
> >flash carbonization (http://www.hnei.hawaii.edu/flash_carb_biomass.pdf).
> >
> >Gasification on the other hand uses biomass with much lower moisture
> content
> >(Optimum 20%). The biggest difference between the two is the natural
> >exothermic jump in the flaming pyrolysis zone. These figures change a bit
> >for different biomass streams but to avoid confusion, I will keep it
> simple
> >and not get too bogged down with the finer details. When you heat up
> biomass
> >to around 280C it goes into an exothermic reaction (begins to give off
> heat)
> >and the temperature jumps to around 400C. Now this energy jump causes the
> >next layer of biomass to heat up and also go into the exothermic zone and
> so
> >on and so on, until you're left with a pile of char. Now with
> gasification,
> >the lowest possible jump is from around 280C to 600C (Depending on air
> >flow), due to primary air (Fresh oxygen) flowing through the reactor the
> >whole time (enough to strip the gases off, but not enough to reduce the
> >carbon to ash). So with gasification stoves we exploit this law and use
> the
> >excess energy to crack the gases and water as they pass through this hot
> >carbon zone. This then provides fuel that we can burn directly whilst
> also
> >producing charcoal (wood gas (CH4) + water + high temperature carbon,
> reacts
> >as follows H20+C=H2+CO; end gas= (CH4+H2+CO))
> >
> >  Where gasification is concerned, a 20% charcoal yield is considered
> high
> >but you have to remember the higher the temperature of the charcoal the
> >higher the carbon content, so although you might have less charcoal, your
> >overall fixed carbon yield might be very close.
> >Better to get all the energy from the biomass plus the energy from the
> >hydrogen in the water using a Top Lit Up Draft (TLUD) stove!
>
>


-- 
Robert Flanagan
Chairman & President
Hangzhou Sustainable Agricultural Food & Fuel Enterprise Co., Ltd.

Skype "saffechina"
Tel:   86-571-881-850-67
Cell:  86-130-189-959-57
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