Indoor biochar producing TLUD gasifier

Hi there,

Even though I know many people on this forum are all about RMS and they are amazing I have to say that they are sustainable at best.
In my opinion the real magic starts with biochar producing systems which can truly be called carbon negative. Yes their energy output is obviously much lower since the biomass is pyrolized instead of burnt down to ashes but that is a small price to pay.

So the idea of putting a top lit up draft (TLUD) gasifier indoors came soon after I first started playing with TLUD's nearly 4 years ago now but the very first prototype was only realized in the second half of 2016. It was what I call a thermal mass gasifier and even though it burns amazing it wasn't really doing a good job of heating my 187sqft house because it just took too long to warm up all that thermal mass. The 12mm thick steel cookplate does get up to a good enough temperature (200-220C) that combined with a ceramic dome it cooks a decent pizza. For real cooking though it's a bit weak.
With pellet stove pellets the stove burns for a little over 3 hours but obviously the most environmental fuel is homegrown fuel and for that I mainly use carob pods which give me a burn time of about 1h20m per batch, since carob pods pack much looser there is a bit more air in the system so there is some ash formation on the surface of the char as well but still less than for example in open pit burns.
Char production when burning stove pellets is 10liter per batch.


So with the first stove not quite cutting it in terms of heating my house I went on to build a second stove all out of metal, two old propane bottles to be precise, and boy does this heat the space! I fitted a tiny cookplate on top from some sort of cast iron disk and this gets up to about 340C, that's more like it :) Also because the whole stove is made out of metal the radiant heat is just so much better.
A tiny downside to this first all metal prototype is that the fuel cylinder I'm using is only 60% of the volume of the first stove and since carob pods need a more combustible starter fuel such as some scrap pallet wood on top of it it makes "burning" carob pods a bit too laborious so I tend to use pellet stove pellets which give a burn time of about 2h10m, almond shells work excellent as well.
Char production with stove pellets is 6 liter per batch.


I'm sure people will ask this but no I do not have any plans available at this stage since there are many points of improvement that I have already identified on the second stove which will be implemented on the next build. And yes this system could also be hooked up to a thermal bench although the height of the flue exit might make this less practical.

WARNING:
Keep in mind that building a gasifier system inside your house is entirely at your own risk and I cannot take any responsibility for any injuries that might occur if anyone attempts to replicate this system.
The house I'm running this stove in is a very old stonewall house with plenty of natural ventilation. Gasifiers work by purposely producing all kinds of gasses (including CO) in an oxygen starved environment to then burn them in an oxygen rich part of the stove but this secondary combustion can sometimes fail if the fuel cylinder hasn't been loaded properly of has been loaded with the wrong material. This has happened to me and although the smoke has never entered into the house it is not something that is impossible to happen either.

Nice! 2 hours of untended burn time and a load of biochar. Tlud's don't get much love around here it seems. I play with charcoal gasifiers and that is how many of us make our fuel. Efficiency wise they rate about the same as a RMH except for the roughly 25 percent left as biochar. They do burn very clean thanks to the secondary burn and glowing char layer. I would love to see some metered tests done putting them head to head. I think the only suggestion I would have would be to run your air intake from outside to the stove. Two things will happen. You will not depressurize the building and force it to pull cold air into the house. You will eliminate the risk of backdrafting into the structure.
Cheers,  David

Thanks for your reply David,
I haven't seen any videos of people putting a TLUD inside besides a video of an old guy burning one in a garage without a flue (can't recommend this) and that might be the reason why they aren't getting much love because how much use are they really if you are not using as much as the heat as possible?
Also the hassle of taking the glowing char outside for quenching isn't for everyone although you could snuff the embers by putting a lid on it as well but personally I prefer the higher quality of water quenched char. I wouldn't snuff the embers with a lid though without having a good carbon monoxide detector closeby to see if this method doesn't create a potentially dangerous situation. Snuffing with sand is another option but then things become even less practical

A quick video on the difference between water quenched and sand snuffed char, hydrophilic vs hydrophobic.

I don't think they are up there with RMH in terms of how clean they burn, I think their soot production is a bit higher simply because the temperature that is reached in the combustion zone is much lower, although I will use an insulated heat riser in my next burn or maybe even insulate the riser in my metal stove because I want to put in a bigger hotplate anyway which will allow me access to the riser. Having said that they are for sure much cleaner than conventional wood burning stoves and the entire burn from start to finish is smokeless. In my opinion the biochar production makes up for the slightly higher pollution of this stove vs a RMH and as long as open burn piles are still a common thing in my country it is not something that one could be worried about :p

I have thought about drawing in air from the outside but decided that is wasn't worth the extra work, the walls of my house are 50cm thick stone wall so not the easiest thing to drill a hole into, so far I haven't had any issues with backdrafting into the structure, even on very windy days or when opening the door relatively fast. Also I like to move things around so I'm not sure the stove stays where I have it now and perhaps I'll still make a thermal bench for it as well. Still debating myself on this because as mentioned previously the house is quite tiny.

I think you might have seen Gary Gilmore's keystone stove... He had an exhaust fan in the garage for his videos by the way... I did notice in your videos the kind of lazy flame.  That would account for the low temp you are talking about. I don't get that at all when I do my double 50 gallon barrel tlud burns or my 5 gallon propane tank tlud. I think you are on to something insulating your riser. Maybe increase the diameter as well to force more updraft. A super heated charcoal layer should clean up that soot. With that high temperature come metal fatigue of course... Charcoal gasifier users for running engines are less concerned about the heat capture then running the engines cleanly. I make most of my engine charcoal in a wood stove myself and cover it in a pot. I had a co monitor next to it all winter just in case. Never had a problem. I don't quench it because I don't use it for biochar. For engines the charcoal is better if not fractured from quenching.
Lots of tlud talk and charcoal enthusiasts at www.driveonwood.com


Cheers,  David Baillie

This is the video I saw, the garage door is open in the video but like that the stove won't do all that much for heating I think.


Thanks for mentioning Gary Gilmore's stove, I had not seen the video before (and now my illusion of being the first to have an indoor TLUD that vents to the outside is broken :p)
I'll post the video here as well for the convenience of other Permies



Where in my video are you seeing the lazy flame? If its at 7:30 into the second video then its because that is at the very end of the burn when gasification is nearly done.
And yes a bigger fuel cylinder diameter will give a more intense flame. Something else that would definitely improve the draft is using an insulated flue pipe or at least having the part outside of the house insulated, although here in the South of Portugal we barely get any freezes so it is less important then if you'd be in a much colder climate.
Another option would be to keep the ventilator running the whole time and not just the first ten minutes to get the stove going but since I'm already reaching 340Celsius up top that would probably make things uncomfortably hot.

Thanks for sharing the link about the woodgas cars but I think I have to stay away from that one or it might spark my interest in getting a car, doing everything on bicycle helps keep me in shape xD

Cheers,
Martijn

thanks I had not seen the bill Knauss unit before... Yup you have to watch out for the dark side... Once charcoal gets a hold of you it does not let you go.  I meant upsizing the riser not the fuel canister. As you mentioned though you are achieving a good hot burn anyways. Keep on cycling
Cheers,  David Baillie

Quick little update, I am currently working on a brick version that uses the 20 liter fuel cylinder of my first stove and will have the same steel plate up top as well.

The all steel stove was putting out way too much direct heat and soon after the stove was out the heat would be gone as well. The first stove had too much mass around it and was poorly insulated from the walls so it took too long to properly heat up and radiate that heat out into the space.

The new stove is made with 5 cm thick bricks standing upright and has a dimension of roughly 50x70x170cm with a proper bell and depending on the initial exhaust temperature might even get a stratification bench as well.

Nice to see you are working on the design. Best of luck with the improvements. I've settled on my method for now. I'd love to experiment but certification and insurance requirements restrict what you can do here. For now I will continue to produce my char in the stove.
Cheers,  David

Hi David,
Have you considered using a small retort inside your woodstove?



I've done this myself using a small (about a quart or so) stainless steel can with a few tiny holes punched around the edge of the lid and then placing it upside down onto a bed of embers inside my dads tiny Jotul 602n stove. This works great and gives you 100% ash free char. The char being ash free is quite important to me since the soil here is already leaning towards the alkaline side so I rather not add any ashes to it on purpose.

Retorts are especially nice to pop into your stove at the end of the evening because you don't have to worry about the stuff inside them to smolder down to ash if you leave the retort in your stove overnight.

I've used retorts in the stove and they are useful but I find them slower and the metal does wear out. When I grind and sift the ash is removed. Here soils are acidic anyways.

If your soil is acidic anyway then a bit of ash is nothing to worry about, I wish I had that luxury.

The OP has some newer videos out at his : Permaculture Playground Youtube Channel