6 replies to this topic

[ToddT]

Has anyone seen the latest issue of Popular Science? On page 44 (August '09 issue) they have a drawing of a biochar producer. Hmmm... looks a lot like a gasifier! It even generates gases containing H, N and CO. They talk about the positive effect of adding biochar to the soils. No question about that.

My question is this: how would we go about intentionally generating more char without generating more tar or liquid condensate? What would be the goal as far as temperatures and vacuum inside the gasifier? How would feedstock choice and configuration affect this? Large blocks, clean chips, dirty chips?

The BioMax line seems to do a good job of avoiding any liquids. Their char is as black and rich as any laser printer toner cartridge. How can we achieve similar results on our GEK?

[jimmason]

ToddT said:

My question is this: how would we go about intentionally generating more char without generating more tar or liquid condensate? What would be the goal as far as temperatures and vacuum inside the gasifier? How would feedstock choice and configuration affect this? Large blocks, clean chips, dirty chips?

The BioMax line seems to do a good job of avoiding any liquids. Their char is as black and rich as any laser printer toner cartridge. How can we achieve similar results on our GEK?

todd, while is it possible to get char out of an imbert type or stratified downdraft gasifier, the char is not going to be of the type most would argue is optimized for biochar.

biochar is best produced at lower temps that leave some of the original volatiles in the char. a downdraft gasifier is trying to do exactly the opposite. and to the degree you do not remove all the volatiles from the char in pyrolysis, you are going to cook them out in the combustion or reduction zones, and thus end up with tar problems in the gas.

also, the basic architecture of a downdraft means that the char has to pass through the combustion/cracking zone on the way to the reduction zone. thus the char is exposed to the highest temps in the gasifier. if you want lower temp char, this is working against you for biochar making.

finally, the ratio of tar gas to char output from pyrolysis is already out of sync with the combustion needs internally in a gasifier. our mass balance work to date suggests there is about 2.2x the amount of tar gas produced than we can directly burn and have enough char to reduce the results. the rest of the tar gas has to be thermally cracked, thus all the temp, geometry and void space sensitivities of a downdraft gasifier. you can't just internally burn all the tar gas or you will overrun the amount of char available. if you start removing char from the gasifier, these challenges only get more extreme.

i realize people are suggesting to do exactly this, but i think we are going to find it to be a relatively poor path for combined energy and biochar making. there are ways around this problem of course, but starting with a typical downdraft gasifier is not the way to do it.

there are other bolt in reactors for the gek that will do pyrolysis in more controlled manners for biochar. both direct burn and indirect retort. the auger fuel feed add-ons for the downdraft are repurposed for fuel feed and ash removal in the pyrolysis forms of the gek.

we will likely have these at the IBI conference in colorado next month.  these have long been in process in house, but we've yet to have them ready to distribute out in the world.  we should have them ready to go very soon.

in the interim, you can run the v3 gek as an updraft pyrolyisis unit, via putting the ejector-venturi/mixer/burner tree right on top of the reactor and pulling up through the bed.  light it on the bottom through the ash grate post.  this is one reason why that post is hollow.  it can transport air as well as instrumentation.


jim

[tomasobertoli]

picking up on this old yet very relevant thread

agreed on the fact that other technologies are better at charring rather than gassifying

not agreed on the fact that biochar needs to have a high content of volatiles ... research is very disputed and inconclusive to assume such a thing without debate

what is the expected percentage of (bio)char left among the ashes of a current power pallet ? is it safe to assume a number higher than 5% ?

now that the heat from the engine is recovered thanks to the TOTTI shacking the grid more frequently wouldn't make the gas production become smoother and the percentage of biochar increase to 10 or even 20 percent ?

[fuel spiller]

Last month at the workshop, I was amazed how little ash was produced. 5% was a number used in the past, but it looked more like 1- 2% to me.  I imagine over use of the shaker would lower the size and temp of the char bed, more so than the TOTTI could compensate.

[fuel spiller]

It seems better (easier) to run a TLUD gasifier for char production.
It could run on less than ideal GEK feed stock and the waste heat could be used to dry chips for the GEK. Running too cold (pulling too much char) would never foul any filtration... there is none!
Fair warning! this is logic from a guy who climbs a tree to cut it down! :)

[tomasobertoli]

thanks for the updated info on left over

to avoid confusion when you mention 1-2% char and ashes is it
- compared to the mass of the input feedstock (30% humidity) or  
- in terms of carbon content ?

regardless of this detail my question remains, could a more frequent shacking of the grid increase the production of left over (bio)char to 10% without compromising temperatures for tar cracking ?

I'm looking for a balance between electricity and (bio)char because a farmer could have a good use of both to make operations really sustainable.

With a 20kW power pallet in a year a farmer could process as much as 100 tonn of waste wood. At 10 % it's a very respectable 10 tonn of ash and (bio)char that could be mixed with the manure and go back to the field or orchard.

Considering a good application rate is between 10-20 tonn per hectar (for example look at (http://iopscience.io...315/6/37/372052)) a farmer could gradually apply the available (bio)char back into the fields with little extra costs and great benefits.

[fuel spiller]

Hi again

compared to the mass of the input feedstock

We removed it from a 10kw unit and used it to first fire a new 20kw pallet that we put together at the workshop.

I'm sure Bear has info on 'over shaking' I know the GCU can be set at many rates. Perhaps a grate with larger holes would be more 'wasteful' with char.
I still feel that bio char production without filtration would be a better way to go (use the heat to dry the gek fuel). It could run on less than ideal gek fuel.