Biochar -a question or two

[Halcyon Daze]

Ok these may be silly questions but I've never really been 100% sure so here goes.

1. Are the chunky pieces of ash/charcoal that are left over from a campfire essentially the same thing as biochar for all intents and purposes?

2. Do campfire-charcoal and biochar have any fundamental difference in composition?

3. Can these chunks of campfire charcoal be used in place of biochar? (are they interchangeable)

4.What is the main purpose/advantage of making biochar in drums, if you could just light a big fire and rake up the charcoal when the fire has finished burning?

5. If they are indeed one-and-the-same then why call it 'biochar' anyway? -why not simply call the charcoal 'Charcoal'.

Now I think I know the answer to all of these questions (99% sure). Sorry if the questions seem ridiculous but I'm just trying to get to the bottom of some slight confusion I have, so specific answers to these specific questions are much appreciated

[waterboy 2.0]

might help, from the encyclopedia of satan:

http://en.wikipedia.org/wiki/Biochar

for what its worth use a fair bit of charcoal in composting, but the little bit of true biochar I have played with appears to be a much superior soil amendment. Just cant get my hands on enough of it to (without paying premium dollars) really put it to the test.

EDIT - the making of artists charcoal is also an art and science (specific woods used as well), cannot just use fire coals so maybe the same for biochar (?).

Edited October 19, 2012 by waterboy

[tipz]

http://www.instructables.com/id/Make-your-own-BioChar-and-Terra-Preta/

[ballzac]

If you burn it out in the open, it will react with the oxygen (combust) in the air, creating CO2, which is presumably the opposite of what you want. The more oxygen available to it, the more carbon inside the wood will be converted into CO2, so the difference in composition will mostly be the difference in carbon levels, though there are probably many other compounds in the wood that combust.

[Halcyon Daze]

If you burn it out in the open, it will react with the oxygen (combust) in the air, creating CO2, which is presumably the opposite of what you want. The more oxygen available to it, the more carbon inside the wood will be converted into CO2, so the difference in composition will mostly be the difference in carbon levels, though there are probably many other compounds in the wood that combust.

 

OK so once the carbon has converted to C02 (gas) it floats away and all you're left with is less charcoal (aka biochar).

So if you make it in a drum you'll get a lot more but it's essentially the same thing, Right?

or are you agreeing with waterboy that biochar and charcoal are NOT essentially the same thing.

Edited October 19, 2012 by Halcyon Daze

[ballzac]

OK so once the carbon has converted to C02 (gas) it floats away and all you're left with is less charcoal (aka biochar).

So if you make it in a drum you'll get a lot more but it's essentially the same thing, Right?

or are you agreeing with waterboy that biochar and charcoal are NOT essentially the same thing.

 

It's different because you are not just burning a product that is 100% carbon. If that was the case, then if 95% of the carbon combusted, you would be left with 5% of the original mass but it would still all be carbon. But what you're working with is not entirely carbon, so there will be constituents that do not reduce at the same rate as the carbon. There are probably some solid oxides that form as well.

You know the white ashes that are left after a really hot fire? Well any 'charcoal' you make in the presence of significant amounts of oxygen are going to be more like that than real charcoal. It may still be dark, but try using it as a fuel source in place of briquettes and you will see that it's quite different.

[Halcyon Daze]

Ok so there's some differences between the two.

So if I wanted to make some terra perta would campfire ashes be significantly less effective as biochar? (I'm thinking it would not be as good).

Like WB I have found that ashes are an good addition to compost mixes, but I guess biochar must be a whole lot better, whatever you're using it for.

Edited October 20, 2012 by Halcyon Daze

[ballzac]

Well, I guess it depends on what purpose you want it to serve, but considering that the defining feature of terra preta (and what makes it "preta") is its high carbon content. So presumably, whatever you specifically want terra preta for will be less effectively achieved with a substance that is lower in carbon.

[WoodDragon]

I'm going to screw with everyone's heads and contradict some of the comments above.

Charcoal and biochar are essentially not different.

They are generally derived from the anoxic pyrolysis (that is, burning without oxygen) of wood, which is basically a carbohydrate. The lack of oxygen during the process essentially means that there's a chemical rearrangement of the carbohydrate composition to give 'incomplete' combustion products of carbohydrate. I say 'incomplete' in inverted commas because there is a range of products produced, some of which are actually quite combustible (such as hydrogen and forms of solid carbon) and others which are not (carbon dioxide) and some in between (carbon monoxide for example). Overall though there is an increase in the total oxidation state of the collective components of the original wood. The reason for charring rather than just burning wood straight is that the product(s) derived from charring have specific and specialised uses - the loss of some of the calorific content is the thermodynamic price paid for this convenience.

When charcoal is incorporated in soil a la terra preta it's referred to as biochar, but overall the production is not really different from deliberate charcoal production, or from bushfore charring. I say 'overall' because there are possibly some differences - terra preta chars are generally formed at low temperature and with some oxygen present, with the result that the remaining solid is a bit more chemically complex that the more carbonised chars from a bushfire, and probably more 'activated' than charcoals made in a significantly anoxic environment. And in the context of the Amazonian terra preta there is the added influence of physical breaking up of particles by worms and other soil fauna, which further increases the surface area of the overall carbon mass.

I've had good success with campfire and with bushfire charcoals. Probably the one to watch out for is charcoal that might be made from coal-like materials - the latter are not carbohydrates per se, so the end char products are a bit different and especially in the mineral content department. Think coke made from bituminuous coal, for example.

On the matter of minerals, the stuff that is referred to as 'ash' when wood is burned is the non-combustible mineral portion of wood. Basically, that means salts of sodium, potassium, calcium, magnesium, iron and so on. This is why ash can be so good for plants - it's a concentrated burst of the minerals that they use for growth. It's very important to be careful with using fresh ash though, because the same heating process that produces them converts a large portion to metal oxides, which will then hydrate to metal hydroxides when they're mixed with water, causing a high degree of alkalinity in the soil which can harm plants.

And of course, because different trees use different amounts and proportions of minerals to grow, their woods are different, and thus the mineral content can have a big effect on the final char product, in addition to the carbohydrate structure of the wood itself.

Edited October 20, 2012 by WoodDragon

[WoodDragon]

Or the short version to answer HD:

1) Yes.

2) No.

3) Pretty much so, with consideration of specific production contexts.

4) As Ballzac pointed out, charring in drums minimises loss of carbon mass to complete oxidation, thus returning more char for a given amount of wood.

5) 'Biochar' refers to char in soil that is performing a structural/physiochemical purpose in the context of soil biology and soil fertility. But it's still char/charcoal.

[Halcyon Daze]

Confusion reigns!

Thanks wood dragon, Awesome answer. I was hoping charcoal would be interchangeable with biochar for making terra preta, but there are too many contradictions going around the net. Your deeper understanding/ explanation coupled with your own experience is making perfect sense to me!

How did you make your charcoal terra preta? Can you give us the 5 step run-down?

Cheers!

[WoodDragon]

It doesn't need five steps.

I use a hardwood for the charcoal - most eucalpyts are fine - and I crush it up in a fist to about 2-5 mm (perlite) size for adding to soil (there's a lot of powdering in the process, so the finer grades are taken care of), and if I'm using it for orchids I leave it about the size of just over half a sugar cube or a bit smaller.

If there's any worry about alkalinity I will rinse well it with rain water first. I don't bother with pH tests, but a cautious gardener might.

"Clinky" charcoal seems to be best. Not surprising, because it's probably very carbonised and activated.

10-20% absolute max (for some orchids for example), but 5% or even less is fine for many other genera. Experiment and discover.

The rest of the recipe is up to you!

Edited October 21, 2012 by WoodDragon

[WoodDragon]

Dang. Technically, that was five steps.

[waterboy 2.0]

So charring vs burning will give a better "structure" and more effective product. i.e the "clinky" charcoal (which is a very good description ),and in relation to "activation" woody is this in terms of cation exchange or just pure adsorption?

I had just been putting fire coals into compost and running a cycle through there (always have chunks, but become "softer", now I'm think it should just go straight to soil on new ground when broken. Ash is generally used to kill the pear and cherry slugs.

I am keen to really get the most out of the products of heating and vegetation management.

[WoodDragon]

Just to clarify, burning is an oxidation process where most of the carbon is lost as gaseous oxidation product(s), whereas anoxic charring removes much less of the carbon but gasifies (in one form or another and via pyrolysis rather than oxidation) a lot of the hydrogen and hydroxy moieties. Although the charring process leaves mostly just carbon, it's usually not 'activated' - that is, microporous and thus with a high internal surface area. Activation is achieved via some secondary oxidation (either combustive or chemical) which could be said to 'clean out' some of the non-carbon chemicals in the micropores.

Open-fired charcoal is likely to be at least somewhat activated given that it's an oxidative combustion. The snag is that the yield of charcoal is much lower than with charring. I suspect that expert charring would be able to achieve some activation through pyrolysis, but I confess that I'm not so up on the chemistry of the process that I can speak with authority on such subtleties.

But to give it some context, it's about going from solid(ish) carbohydrate wood to porous charcoal to microporous activated charcoal. The first step requires hypoxic or anoxic conditions, the second can be achieved with gentle oxidation, but perhaps also with expert anoxic pyrolysis.

As to the nature of the activated surfaces, there would be many complex chemical interactions occurring, including ion exchange and adsorption (which are sometimes essentially the same thing). Again, this is straying past my level of chemical understanding, but for the purposes of the average gardener any nice clinky charcoal should be fine - after all, the impressive Amazonian terra preta soils resulted largely from campfires and similar, and less frequently from repeated slashing and burning.

And don't forget, it's not just about charcoal. You need decomposing organic matter too, and an ecosystem's worth of microbes, and worms, and mites, and fungi, and...

This is why real gardening is not entirely about the plants, but to a great extent about the husbandry of the soil in which they grow. A real gardener knows when to use a particular soil type and why to use it, whether it's an inorganic limey grit or a peaty mulch or a humusy loam. Some people figure it out by years of trial and error without ever understanding the chemistry and biology of soil, but actually learning these aspects puts a gardener way ahead in terms of effective gardening.

On the matter of when and how to apply the charcoal, I think that running it through a compost heap is a good thing. There's more chance to avoid excess alkalinity, and the nutrients picked up will be there for plants to access when the compost is applied.

And yeah, nuke those cherry slugs with the ash!

Edited October 21, 2012 by WoodDragon

[WoodDragon]

Probably another thing worth pointing out in case anyone's confused is that just because burning as occurs in a campfire or similar is an oxidative process, it doesn't mean that all of the carbon in the wood will be completely oxidised. Things like surface area to volume ratios, temperature and rate of heat loss, gas flow in and out of the combustion vicinity, and mineral content of the wood will all affect the final amount of oxidation, particularly for the centres of larger chunks of wood that may be embedded in ash and in a sustaining envelope of char.

So the charcoal in a spent fire is the stuff that wasn't completely oxidised. It's why we poke at fires, or pile them up, or wave branches at them or blow on them - we're optimising the oxidative conditions. This will lead the thinking pyromaniac to realise that if they disperse/extinguish their fire at the optimum time, before it's completely fizzled out, they'll increase their yield of charcoal without leaving unburned wood. Not as good as char pyrolysis, but it is a way of getting a bit more charcoal if that's what you're after.

[waterboy 2.0]

The pyromaniac in me nearly grabbed the drip torch...lol. Soil gets even sexier when fire becomes involved.

Took me a bit to get some skill burning native veg, going to have to add biochar production to the list.

Got a good old steel drum due for a modification now and play with some millwood offcuts packed in tight.

Very tidy work woody - thank you.

[Sallubrious]

After seeing the price of bagged charcoal in Australia, I decided to to start making my own. My soil in one part of the garden is testing at PH 4 so I'm going to need shitloads of the stuff. I've a added a lot of lime but it can be easy to overdo it because of the timelag between application and complete reactivity of the lime, so I'm not keen to keep liming it much longer.

I've just started and I've made a few small batches that I've started mixing in with my compost.

I've been using a home made TLUD (Top Lit Up Draft) system that I knocked up from a few old baby formula tins I had kicking around (I couldn't find large pineapple juice tins at the supermarket, they would have been a better size). I did it mainly as a proof of concept & I intend to scale it up for larger batches. I'm on the lookout for an old beer keg or a 50 litre drum to upscale the TLUD system.

I,m not sure how the TLUD system will go when applied to a larger batch because of the extra burn time & extra heat generated, I hope it doesn't over burn the charcoal and reduce it to ash.

I've also made a paint tin retort from a 4 litre paint can and it works excellent but it doesn't burn the vented gasses, so it smokes the fuck out of the place. The TLUD system burns very clean and has an afterburner effect that burns off almost all of the smoke/gasses.

A cast iron camp oven also worked very well but it was very smoky too. In a bigger fire or used in a secluded area it would probably be first choice. A lot of the vented smoke would burn off in a large fire so the smoke wouldn't be much of a problem.

Has anyone got any successful designs/systems that are effective and don't produce much smoke ?

[in_spirit]

A charcoal retort is a better concept in my opinion, the enery from the natural turpentines/volatiles etc burning reduces the amount of fuel needed to convert the wood to charcoal, alternatively you could bottle the vbolatiles which is what used to be used before mineral turpentines.

[Sallubrious]

Yeah when I did a batch using a camp oven as a retort & it gave a much higher yield as not as much gets burnt off like it does in the oxygen rich TLUD. The main reason I tried the TLUD was so I don't smoke the whole neighbourhood out.

I saw a good one on youtube that I'm going to try on a smaller scale when I get the materials to make it. It was called Making biochar with Jolly Roger ovens. It uses a TLUD on the bottom section and the top section is a basic retort. The heat from the TLUD cooks off all the smoke so it runs very clean & gives a high percentage of charcoal to wood used (in the top chamber).

 

 

[CβL]

In potentially awesome news - I asked a friend to get me involved with a small biochar company, and he said he thinks he can get me in contact with the owner. It would be unpaid work - but I don't mind (for now), and I think he's giving away shares instead. I'll take those happily. :D

[Halcyon Daze]

Great replies!

You guys might be interested in this. Making biochar in PNG. Biochar is actually an important byproduct of ground oven cooking. In this case it's cooking panda nuts. The benefit of biochar is well known and highly regarded as a soil improver in PNG. As far as I know they have been doing this for centuries and the concept never came form any 'white man'.

They either dig it into the ground or put it into their waste pits (old toilet pits which can be more than 6 foot deep). Eventually crops are grown on the site.

The leaves are mainly there to keep the soil off the food.The hot coals are essentially buried under soil which keeps the oxygen from combusting with the carbon in the coals.

I wasn't there to see this one dug up a couple hours later, but from other ground ovens I did see, they pretty much produce very nice looking biochar this way.

Edited December 22, 2012 by Halcyon Daze

[Sallubrious]

^ I imagine the method they employ up there in PNG must be very similar to the way it was done in the Amazon when they created the Terra Preta de Indio soils that started all scientific interest in biochar.

----------------------------------------------------

I managed to get my hands on a cheap keg yesterday, someone had damaged the connector so it was sold to me for scrap value.

It was still pressurised so I drilled a small hole in the bottom to let the gas out and then went to work with an angle grinder. I cut a 4 inch hole in the top and a series of slits in the bottom for primary air supply.

I loaded it up with with wood and fired it up and it smoked out the whole neighborhood. It did make some nice charcoal though.

My smaller prototype smoked a bit but a few extra holes in the bottom (for primary air supply) fixed that so it looks like I'll need to modify it a bit. I could use a fan to create a forced draft but I really want it to be naturally aspirated.

The keg is stainless steel so drilling and cutting operations are a lot more difficult than they would be in steel, I might have to find a fab shop with a plasma cutter to knock a few more holes in the bottom.

[gecko]

I'm thinking that terra preta originated haphazardly from piles of trash burning.

cassava peelings and trimmings, palm fronds, fruitseeds and skins etc.

generally a food refuse pile that was set on fire and left to smoulder and a bit of soil chucked on it.

Seeing 'biochar stoves and burners' etc. over the years,

they're no different to choarcoal burners

and there's no difference between 'biochar' as it comes out of a retort and charcoal.

the crucial difference imo, between Biochar and charcoal,

is that charcoal becomes Biochar when it is 'charged' with life

and nutrients after extended contact with soil.

or more quickly, as an addition to a hot, aerobic compost pile.

I've used charcoal from various sources to make biochar

Bamboo, grasses, weeds, palm trash, woody fruits

( gumnuts, banksia cones, pine cones almond shells etc)

hardwood, softwoods, woody weeds etc.

then added them to compost piles.

mostly in an open 200litre drum with the bottom knocked out and a tight lid to quell the fire a bit .

when the fire gets roaring, I drop some more fuel in on top of it and snuff it out a bit.

Then quench it all with water when finished.

it stops it burning any more and also washed the ash off.

as with making charcoal for gunpowder, the ideal temp is around 400deg C.

at that temp , the charcoal is not just pure carbon , but consists of a range of compounds.

I don't know what they are exactly, but hotter burned charcoal is different.

you don't want to 'burn the life out of it'.

charcoal burned too hot is no good for gunpowder

and not good for bio-char, but in the case of bio-char, won't be detrimental.

same as pyrolising cotton cloth or cord for tinder...

burn it too hot or too long and it doesn't work as well.

I use pyrolised cotton (with quartz and steel striker)

every day to light a charcoal fueled forge.

I see variations in different batches of charcoal .

some lights up easily and is good for forge-welding steel

some just has trouble getting hot enough.

ie. it may have been burned too hot when being made

[waterboy 2.0]

Bamboo charcoal production manual from China I came across that may be of interest:

http://www.guaduabamboo.com/support-files/bamboo_charcoal_training_manual.pdf