Efficacy of biochar as a carbon offset

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Dan Hartas

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Aug 17, 2010, 5:58:04 AM8/17/10
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Hi, I'm in the UK, working for a company interested in implementing a
common-sense and small-scale approach to carbon offsetting. Kilns such
as the one demonstrated here - http://www.biochar.info/index.cfm?view=52.19&lan=en
- look very promising, as we are based in a rural location and are
fairly small.

I was just wondering, as an initial inquiry into whether it's even
feasible to do this, if anyone had any information as to what extent
this is a good carbon offset. Would it actually have a net carbon
negative effect on such a small scale, with building materials and
such? Also, is the cost of doing this likely to be prohibitive? This
basic information is just for comparison to alternatives at this
stage, and we would appreciate any help that might be available.

Thanks much,

Dan Hartas

Nando M. Breiter

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Aug 17, 2010, 8:25:08 AM8/17/10
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Hi Dan,

I built this kiln.

In answer to  your basic question, yes, carbon is offset, as long as the offgases are flared and the feedstock scenario makes sense. I'm not completely happy with the design as it stands, because the afterburner is difficult to light and maintain burning (although this can be solved fairly easily, it's just not as simple and straight forward as I would like it), and energy is wasted in the one batch at a time approach. I built it for a somewhat different purpose, to experiment with low temperature biochar in our agricultural trials.

One should realize from the onset that once pyrolysis is complete, a barrel will contain perhaps 20 kgs or less of char, which equates to about 20 x 0.8 x 3.66 = 58.5 kgs of CO2, if you use woody feedstock. If you utilize the energy wisely to offset fossil fuel use you might be able to squeeze 100 kgs of CO2 abatement out of each batch. Is that worthwhile?

There is a lot of excess energy in the gas that is released. Ideally, that energy should be used to heat a building or water or in some other useful way.

There are of course caveats to the notion that this approach offsets carbon. If you cut down perfectly healthy trees and char them, one should note that the carbon in those trees was already sequestered and you've accelerated the release of about half of it (the half in the syngas that was flared). It will take decades until the other half that is now stabilized in the char exceeds the amount of time the carbon that was in the tree would have remained sequestered.

However, it should also be realized that almost every other claim of a carbon offset is simply a reduced rate of GHG emissions against a theoretical baseline rate of emissions. That sort of math doesn't work in finance, nor does it work in the physical world of carbon balances. Offset is a term that makes it sound like carbon is being taken away to counterbalance carbon that was added, but in most cases, it's simply not true. Biochar is the only simple way I know of that actually removes carbon from the active carbon pool and stabilizes it in the inactive carbon pool.

It should also be realized that if you try a simple approach to make biochar, you might come up with a better way of doing it. Or your neighbor will. Or you might inspire someone who is interested in larger scale production and has the feedstock stream so that it makes sense to invest in an industrial pyrolysis reactor.

I'd experiment with alternate designs to make it more efficient if I planned on using this approach. Perhaps the barrels could be reduced in height to about 1/3 of the height of a standard barrel, lowered in the top of the enclosure, and pulled out the bottom. A few small holes in the bottom of the barrel would allow the offgas to escape while preventing oxygen from entering. One barrel would initiate pyrolysis in the next above it, and the flaming gas rising up the sides of the enclosure would ignite the gas that begins to evolve in containers further up. This is actually an old design that worked relatively well.

Kind regards,

Nando

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Dan Hartas

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Aug 17, 2010, 9:29:22 AM8/17/10
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Nando,

Thanks very much, it's fantastic to receive that quality of
information so quickly. That's a lot of very useful food for thought:
this would seem to be a significantly cheaper way of counting your
carbon than micro-generation, even before you account for savings from
using the heat or the char itself. As long as the trees come from
managed forests and are replaced, then I think this is a genuine
carbon offset: the government over here would give you a grant for a
wood-burning water boiler which was 'carbon neutral' in that way, and
(though I may misunderstand) this is much more likely to be a genuine
carbon offset than that.

Thanks again,

Dan

On Aug 17, 1:25 pm, "Nando M. Breiter" <na...@carbonzero.ch> wrote:
> Hi Dan,
>
> I built this kiln.
>
> In answer to  your basic question, yes, carbon is offset, as long as the
> offgases are flared and the feedstock scenario makes sense. I'm not
> completely happy with the design as it stands, because the afterburner is
> difficult to light and maintain burning (although this can be solved fairly
> easily, it's just not as simple and straight forward as I would like it),
> and energy is wasted in the one batch at a time approach. I built it for a
> somewhat different purpose, to experiment with low temperature biochar in
> our agricultural trials.
>
> One should realize from the onset that once pyrolysis is complete, a barrel
> will contain perhaps 20 kgs or less of char, which equates to about 20 x 0.8
> x 3.66 = 58.5 kgs of CO2, if you use woody feedstock. If you utilize the
> energy wisely to offset fossil fuel use you might be able to squeeze 100 kgs
> of CO2 abatement out of each batch. Is that worthwhile?
>
> There is a *lot* of excess energy in the gas that is released. Ideally, that
> > biochar+u...@googlegroups.com<biochar%2Bunsu...@googlegroups.com >
> > .

Geoff Beacon

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Aug 17, 2010, 9:51:09 AM8/17/10
to bio...@googlegroups.com
Nando

What was the weight/nature of the feedstock?

Thanks

Geoff Beacon


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Geoff Beacon
geoff...@sent.com

----- Original message -----
From: "Nando M. Breiter" <na...@carbonzero.ch>
To: bio...@googlegroups.com
Date: Tue, 17 Aug 2010 14:25:08 +0200
Subject: Re: [Biochar] Efficacy of biochar as a carbon offset

Hi Dan,

I built this kiln.

In answer to your basic question, yes, carbon is offset, as long as the
offgases are flared and the feedstock scenario makes sense. I'm not
completely happy with the design as it stands, because the afterburner is
difficult to light and maintain burning (although this can be solved fairly
easily, it's just not as simple and straight forward as I would like it),
and energy is wasted in the one batch at a time approach. I built it for a
somewhat different purpose, to experiment with low temperature biochar in
our agricultural trials.

One should realize from the onset that once pyrolysis is complete, a barrel
will contain perhaps 20 kgs or less of char, which equates to about 20 x 0.8
x 3.66 = 58.5 kgs of CO2, if you use woody feedstock. If you utilize the
energy wisely to offset fossil fuel use you might be able to squeeze 100 kgs
of CO2 abatement out of each batch. Is that worthwhile?

There is a *lot* of excess energy in the gas that is released. Ideally, that

Kind regards,

Nando

www.carbonzero.ch

> biochar+u...@googlegroups.com<biochar%2Bunsu...@googlegroups.com>

Nando M. Breiter

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Aug 17, 2010, 10:13:05 AM8/17/10
to bio...@googlegroups.com
I used scrap untreated construction wood in the last batch I made, kept the retort under 450 C, and you can expect about a 30% weight to weight conversion ratio in this case. For a feedstock like straw, with a lower lignin content, the conversion ratio will be much less.

Nando M. Breiter

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Aug 18, 2010, 3:48:55 AM8/18/10
to bio...@googlegroups.com
Geoff,

A further note. To maximize yield for any feedstock, keep the pyrolysis temperature low, under 450 C, and keep oxygen out of the retort. Volatiles will be left in the char that will initially prevent both absorption and adsorption, so to best prepare the char for soil, it should be composted first to provide an ideal environment for bacteria to consume the volatiles and gently oxidize the surfaces (to facilitate adsorption of cations). Crush the char down to a maximum of a few millimeters in size before composting so bacteria have better access.

Nando
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