How much biochar to offset 1 tonne of CO2?

I've been looking into carbon offsets I can do myself, and biochar is one of them.
I would like to implement it first of all in my garden, and then use my contacts with local farmers to scale up.
Can anybody give me some pointers as to:
- studies that show how much t/ha of biochar draw down how much CO2?
- biochar kilns fed with wood chips or corn cobs that make use of the waste heat (integration into heating circuit of a house)

Google tells me:

The atomic weight of carbon is 12 atomic mass units, while the weight of carbon dioxide is 44, because it includes two oxygen atoms that each weigh 16. So, to switch from one to the other, use the formula: One ton of carbon equals 44/12 = 11/3 = 3.67 tons of carbon dioxide.

So around 250kg of pure carbon, in the form of char, would be roughly equivalent to 1000kg of CO2 in the atmosphere.

This doesn't take into account any of the other possible side effects of using biochar in soil - for example improving soil life, which itself draws down some CO2 from the atmosphere, in the form of plant roots etc...

That is a lot of biochar!

This is what I know about reducing CO2:

My dear hubby always said, "Plant a tree, plant lots of trees".

Make lots of compost, use compost tea instead of using fertilizer.

These might help:

https://permies.com/t/153498/Measuring-soil-carbon

https://permies.com/wiki/44396/Cows-Save-Planet-Judith-Schwartz

Biochar production releases/burn about half of the carbon in the starting woodstock, turning it from CH2O + O2 into CO2 +H2O+ heat.

Carbon capture per year varies between an area that is moist and frost-free and a cold zone 3 desert.  

The amount of carbon that you can harvest from a forest with 100ft (300yr old) tree is alot more than you can harvest from a 10ft(1yrs) cornfield. For bio-char production we don't count carbon that is captured as sugar/oil/starch/resin/etc we are mostly looking for at lignin/hemicellulose, at the very lease cellulose.

Temperate forest store 4x more carbon underground than above ground whereas tropical forest store twice as much carbon aboveground when compared to belowground.

I would compare the carbon in CO2 directly to the carbon in biochar vs using the 1:4 ratio.

Plants capture about 123 carbon per year, but only 2 carbon makes it to next year stored as biomass, due to night-time respiration, trading with pollinators/fungi/animal/etc.

But to give a short answer to your question we can get about 10ton of carbon per acre.

Here is an article that you might find relevant: https://www.fs.usda.gov/sites/default/files/fs_media/fs_document/wo-95-consideringforestandgrasslandcarboninlandmanagement-508-92517.pdf

[quote=Susan Wakeman
- biochar kilns fed with wood chips or corn cobs that make use of the waste heat (integration into heating circuit of a house)


This is the holy grail of making biochar, isnt it? Capture the heat and put it to work. I remember seeing this interesting video a while back:



If you can make a clean flame, then I would think it would be pretty easy to put a heat-exchanger of some sort above a retort. Maybe an old radiator, with a thermosiphon up to a big water tank? It would not capture heat very efficiently, but I suspect without really engineering something you are going to have be content with capturing only a little bit of the heat.

Unless you automate something like this, it is going to be a lot of work, though. So unless you enjoy tinkering, welding, and building contraptions it will likely ultimately be a frustration. If your goal is to capture a LOT of carbon, then I would advocate for using the pit method. With enough brush to burn you can make hundreds of pounds of charcoal in a few hours, and all you need is a hole in the ground. Is your goal to offset your own carbon footprint? If so, reducing your consumption is the easiest place to start.

I have thought long and hard about how to integrate heat recovery with biochar making. I've background with a chemical engineering degree, so this is something right in my area of training.

My immediate instinct is that this is going to be pretty hard to make viable on the scale of a single property. Clean consistent burns need feedstock of consistent size and moisture content as an initial starting point. The larger the system you are using the larger the chunks it can cope with, and the less consistent it needs to be. On a domestic scale you'd probably need to be using something like compressed sawdust pellets - free flowing, consistent size etc... Without this consistent feedstock it will need a lot of human micromanagement on a daily basis to ensure it continues to burn cleanly.

But if you scale it up to community size - for example for generating electricity, or for large scale piped hot water for domestic heating - you could benefit from lots of economies of scale. Both in terms of infrastructure, but also in terms of the tolerance of the system to more varied feed stocks. It liberates every homeowner from the chores associated with managing a biochar furnace, and provides a convenient central location for processing the waste material and then dealing with the bulk biochar produced.

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On the other hand, I have thought for a while that small scale rocket-style cookstoves would be really well suited to adaptation to collecting biochar. I have used camping version of these, and a set of dry twigs or firewood split small (sub 1cm) will boil a pan of water, fry a meal etc. It makes a ferocious heat, comparable to a powerful gas ring. It needs some micromanagement but you are standing by the stove cooking anyway.

Over ten minutes or so, the stick char away in the burn tube, building up a reasonable pile of char. If you keep going too long the char ends up blocking off a decent amount of the burn tube.

If you were to modify the burn tube so that you could push char back and then have it drop down, it could land in a catch pot to be quenched at the end of cooking. The flame front protects the char from oxygen reaching it until cooking is done, which is why the char builds up to start with. You wouldn't generate much char from each meal, but if you were using it regularly it would add up.

I look at it this way. Lots of folks take 100carbon that is in woodchip/straw/manure/etc and then turn it into compost that only has 10carbon left in it after the composting process is complete with the other 90 carbon going back into the atmosphere, and they then take that compost and use it to help the farm crop. But when you make biochar you aren't releasing 90 carbon back into the air, you are only releasing 50. You can even reduce the 50 that make it into the air by making wood vinegar that farmers can use on their crops.

Over a 10yr+ period if you were to collect all the dead/fallen wood in a forest and turn it into bio-char. You would actually end up with more carbon on the forest floor, than if you had just left it to become compost that mostly just cycle right back into the atmosphere. So at times I even think it makes sense to just make bio-char just for bio-char sake.


As for offsetting your heating CO2, If you grow your own heating fuel/firewood with zero biochar production, then you are already offsetting your heating CO2 needs and doing good with net zero. If you grow extra so that you can turn some of the firewood into biochar then you are not just doing good, you are doing great, at least in my book.

A clean burning biomass space heating furnace that produces char is what I'm  building.
Mine will need processed fuel, like pellets or chips because it is a TLUD.
This also makes it a batch operating system.

There is something much better out there, it really blew my mind.
Matt Ryder is a woodgas experimenter that posts on driveonwood.com.
His charcoal producing gasifier furnace not only accepts unprocessed wood, it also allows for continuous feeding.
He has a small business manufacturing woodgas equipment but like many in the fire arts he is generous with his knowledge.
Check out his char producing gasifier furnace here:


https://youtu.be/K20l6WF7xBw

I asked a Swiss Pyrolysis expert and got the following reply concerning producers of biochar systems at farm scale with heat recovery. Just for reference in case somebody finds it useful.

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Wir kennen die folgenden Anlagenbetreiber:

Biomacon
https://www.biomacon.com/
Stephan Gutzwiller
Vertretung Biomacon Schweiz, baut eigene Anlagen für Beheizung von Gebäuden - der Experte zum Thema Pflanzenkohle und Kaskadennutzung in der Schweiz
http://www.kaskad-e.ch/
061 534 68 86
s.gutzwiller@kaskad-e.ch
Biomacon baut auch kleinere Anlagen, die am ehesten Ihren Anforderungen entsprechen.

Pyreg
https://pyreg.com/
Philipp Reichardt
PYREG GmbH - Trinkbornstraße 15-17 - 56281 Dörth
Mob:     +49 1520 19797 65
E-mail:   p.reichardt@pyreg.de

Syncraft
https://www.syncraft.at/
Dipl.-Ing. (FH) Marcel Huber
Geschäftsführung / CEO
Syncraft Engineering GmbH
Münchnerstrasse 22, 6130 Schwaz, AUT
Mobil: +43/(0)699-10020585
marcel.huber@syncraft.at

CTS - Carbon Technik Schuster GmbH
https://ct-schuster.de/
Fleinheimer Str. 1
89561 Dischingen
Reimund Schuster
+49 7327 - 920 17 80
info@ct-schuster.de

Carl - thanks for sharing that video. It's a really neat design. Continuous flow is where it is at for heat capture for domestic use combined with biochar production. The auger arrangement is very nice. I'm curious about the lack of quenching it seems to need. It must cool sufficiently in the length of the auger to drop below combustion temperatures. Automating would definitely be key to use for long periods of time, which would presumably require some kind of industrially processed feed stock.

Albert Bates wrote a book on this topic.  I liked it.  It's called "The Biochar Solution". He says that yes, we need to use biochar in the soil for farming and gardening, but we need to use it in many other areas as well. Cement making was a huge one. I think he talked about using it in paint as well.

JohN S
PDX OR