biochar and sorghum syrup question

This thread brought me to Permies, and now I'm a member

Here's the problem I'm trying to solve:  If I'm making sorghum syrup, how can I turn the bagasse into biochar and also use the heat to cook the syrup?

I'm thinking of having a burn box with two shelves:  the bottom one for a wood fire, and the top one for the bagasse contained in lidded restaurant steam table trays.  I saw someone using them to make biochar in a wood stove, and it seems like a great solution.  The gravity-held lid is basically a giant check valve.  It lets the gases out during pyrolysis, but won't let much oxygen in afterwards.  So, I'm thinking I would have a fire going, swap in some trays of bagasse (the trays hold 4-5 gal each), send the gases either up or back (not sure yet) for full combustion, and use the heat to cook my syrup.  When there doesn't seem to be anymore combustible gas coming out of the trays (in this setup, you should be able to see some burning of the gases as they come out from under the lid), then swap in new full trays of bagasse.  Would love to hear any thoughts or suggestions on making this work.  Thanks

Hi Curtis, welcome to permies!

I'm not familiar with sorghum processing.   Is the bagasse dry when you'd be cooking your sorghum?  If so, I think this would work fine.  The heat from the biochar pyrolizing is about half of the heat if it was fully burned (or so I hear).  Just so you aren't hoping to get more heat from the material than is realistic.

Plus it takes a little while for the fire to heat up the contents of the retort (steam table pan) to get it to off-gas.

In any case, it sounds like a fun combination of functions.  Good luck!

Thanks,  Mike -- the bagasse is definitely green, probably about 25% residual moisture.  The nice thing, though, is that the juice is already 15-20% sugar,  so there's nowhere near as much boiling required as there is for things like maple syrup.  (Usually target around 80 Brix for the finished product)

Welcome to Permies!
I like how you are thinking.
It sounds like you have been watching Edible Acres, a great channel.
A full steam table pan should fit inside of a file cabinet, and you could set another into the top to evaporate the syrup in.
Wrap the outsides in insulation for greater efficiency.

To increase  productivity you could heat the stainless steel retort with a TLUD(top-lit up draft) charcoal producing  gasification  stove.
They burn best on regular sized fuel,  like wood pellets.
If you dry the bagasse first, it might work, I'm not sure how broken up it is.


What kind of climate do you live in?
Is there a call for space heating?
If so,  consider if this could be an indoor process.
There is a channel called Permaculture Playground that has done some great work using TLUDs indoor.

If not using a TLUD ,  a small rocket stove might be the way to go for very efficient use of fuel,  and clean burning.
I wonder,  would it be worth while to capture the steam from the syrup, since it will be a distilled  water.

If you need stainless steel containers, don't forget stock pots and mixing bowls as cheap alternatives.
Corrugated stainless steel natural gas lines might find a place in your design,  if you want to direct gasses from the retort to feed the fire below.

I am going to rephrase what you said for my comfort. I want to make bio-char from sorghum/sugarcane residue/bagasse. (I am going to ignore the pot ontop the exhaust because, I think you have that part down).

So you would have to 1st build a biochar retort and also get the bagasse as dry as possible. There are quite a few different bio-char 'retorts' out, but letting us know the size/scale will help us to determine which one works best. How much sorghum reside will be available. How much time do you have available.

Personally I think a good 1st step would be to just burn all the bagasse leaving no biochar behind, with say a rocket stove. With this you will be able to figure out how to dry your bagasse (you could just sir/sun dry them or use the rocket stove heat to dry them). You might realize that you don't even have enough bagasse to sorghum juice into sorghum syrup. Now a rocket stove converts 100% of the carbon in the feedstock to heat, but with a retort 50% of the carbon is turned to heat and the other 50% is left as biochar. So it would be nice if you after using a rocket stove you still had 50% of the bagasse sitting in a pile. Lets say that is the case.
TLUD GASIFIER STOVES
RETORT STOVE
KON-TIKI OPEN FLAME-COVER PYROLYSIS
LARGE BRICK KILN (could be earth bermed for easy access to cook on top)
Here is a wonderful resources https://biochar.international/guides/biochar-reactor-to-meet-needs/#introduction

Here is a $500 setup for a 30lbs of feedstock
https://www.biochar-international.org/wp-content/uploads/2018/04/backyard_biochar_kiln_instructions.pdf




It looks like fermenting the bagasse before helps
https://www.sciencedirect.com/science/article/pii/S0960852410010692

Thank you, all -- this is already helpful!

Here's the typical breakdown on sweet sorghum:

Around 20-30 tons fresh weight biomass per acre

Fresh biomass is ~90% water; after juice extraction, the bagasse usually has ~25% residual moisture

Juice contains 15-20% sugar, finished syrup is around 80%

Average yield is about 200 gallons finished syrup per acre

So there's an abundance of crop residue available, but because of the moisture content I see it more as a supplement to the wood than a full replacement.  If I can get some of it dry enough, then I might be able to run the process almost entirely on bagasse, but boiling away that much water is obviously pretty energy intensive and it usually takes several hours to boil down a batch of juice.

Right now I run the bagasse through a shredder to break it down, and in a BioCharlie it seems to char nicely.  Don't know if I'll be able to close the energy loop on the shredder, but the perfect is the enemy of the good.  Harvest is in September, so the temperature outdoors can be either warm or cold (I'm in upstate NY), depending on the year.

Could you lay out the bagasse for a year to dry out and then burn it the following season?  

Mike Haasl wrote:Could you lay out the bagasse for a year to dry out and then burn it the following season?  

That might be an option, but the high residual sugar content means it's likely to decompose fairly easily if it doesn't dry out fast enough or gets wet before the next harvest comes around.  Kind of like dealing with pomace, it's likely to start fermenting and decaying pretty quickly :-(

A secondary product occurs to me.
I have a friend who makes vinegar from spent brewery grains.
The high sugar content in the bagasse might be enough for vinegar making.

Back to biochar, a solar drying arrangement might speed the process.
Drying racks have multiple uses, and a solar dryer can be pretty simple.
Even if it's too humid where you are to dry food to  preservation state,  it might be fine for bagasse.
A proper vented hoop house might be the way to go, plus it could be a place for the syrup boiling operation.

OTOH you might not want to build a solar dryer/hoophouse in addition to the sorghum/biochar  system, plus September in New York isn't ideal solar drying time anyway.
So maybe just start with a  wood fire to dry bagasse, which can be burned to dry more bagasse, which can be used to make bagasse charcoal, and boil the sorghum syrup.
Build up your store of dry feedstock with wood fires,  to the point where it becomes self sustaining.
When you get low on fuel,  stop biochar/syrup production and build up your store of dry bagasse.
Or just dip into your charcoal reserves.
If the char hasn't been inoculated,  it will be a great fuel.
Burning charcoal to make more charcoal and syrup, seems like an efficient  choice.



If you are making lots charcoal, fueling your chipper with it would  be relatively simple,  compared to a woodgass system.
But one thing at a time, right?

BTW,  that BioCharlie is pretty damn cool!
Seems like it could be made DIY , but a great idea none the less.
Right now I use an old steel toolbox in my fire pit,  for much the same effect.
The BioCharlie will probably last longer .
I made my TLUD from a stainless steel stock pot, and there are some DIY stills made from SS mixing bowls, so consider them as you look reasonably priced yet durable  parts.

William Bronson wrote:The high sugar content in the bagasse might be enough for vinegar making.

I'd love to hear more about the vinegar idea when you have a chance.

Solar drying did cross my mind -- I was thinking of either a large kiln-type; or even a large drum made from hardware cloth painted black, with a simple roller system with a solar-powered worm gear to rotate and aerate it.  But yeah, Sept sun in NY (like me) isn't always the brightest :-)  As you say, my best bet may be to get the cycle started with wood, but then feed with bagasse as conditions allow.

My BioCharlie is homebrew, since there's no way I would spend $60-80 on such a thing.  I basically cut a length of 6" stovepipe, crimped the cut end and threw on a couple of off the shelf end caps.  I then drilled a couple of rows of small holes along the  seam of the pipe to let the gases escape.  My crimping job wasn't great, which was a blessing in disguise -- it created a gap through which I can see the initial steam escape, then nothing, and then a stream of flammable gases.  After those have gone away, I wait a little bit longer for good measure, and then set it aside and cover the drilled holes with ash from the fire to prevent oxygen from entering.  Gives me about a gallon of biochar each run.

Curtis,  the business is called Madhouse Vinegar and this is their website :
https://www.goodvinegar.com/

As you can see from their selection, anything goes!

For your sorgum mash, I suggest a recipe from this page:

http://nordicfoodlab.org/blog/2013/10/vinegar-science-pt-5