thanks steve, thats really helpful, and gives me a lot of material to work through.
yes, it is a divorced process, Brandt style system. I knew someone would have done something similar, I just couldn’t find it. The only thing I was taking from the gek was using exhaust heat to drive pyrolysis.
Thinking about Bob’s implication that I might not have enough temp from the exhaust gas to fully drive pyrolysis, made me think that perhaps this isn’t exactly right, and maybe it would be more accurate to say that the gek (v.4+) uses exhaust heat to support an extended pyrolysis zone, and I probably need to think about being a bit more thermally efficient than my 2 barrel idea.
So, my next idea is to start with a tube full of charcoal, in a tube, in a barrel full of woodchip, in a barrel, in a barrel, in a barrel. I will ignite the charcoal through an ignition port, and enough of it will burn to ash to create an open tar gas combustion/cracking chamber, by the time the wood chip is hot enough to produce tar gas. It will have an insulated lid, top and bottom, so that I can empty the charcoal out, and fill with woodchip (and refill the combusted bit of charcoal that started the whole process).
I guess the critical thing is going to be the diameter of the tube full of charcoal, so that it can produce enough heat to get pyrolysis going, whilst leaving enough charcoal for thorough reduction.
Hi Jono, looking at the drawing. The wood chips are all in a common area right?
How does the tar Gas get to the bottom of the container and how do the wood chips flow up with the targas and then down into where the charcoal level is. The charcoal level will be used up and needs to be replaced but wood chips do not flow up hill with out a mechanism help.
Or I am just not under standing the drawing very well.
Bob
The woodchips don’t move. The idea is to size the system such that the tar gas burns all the oxygen, such that the charcoal does not combust so will not need to be replenished. The woodchio vestle is a single open vestle, with a tube in the centre, with the tube connected to the sides with pipes, so that tar gas can flow around.
I heard that 80% of the energy in biomass is in the volatiles, with only 20% in the fixed carbon. The challenge is going to be to get the heat out of the core, and into the chip fast enough to start pyrolysis, to arrest the combustion of the charcoal
Okay the engine exhaust is going to be running on petroleum fuel to get it started. At best I see the heat being 200 °f . The combustion area is the coldest area with out side air coming in. In order to get it up to pyrolysisation temperature the charcoal in the tube will start to burn. There needs to be a way to replenish the charcoal from above the top. And as it burns there is not place for the ash to go but into the bottom and plug things up. It has to be up to 2000 °f temperature in the tube to crack the tars into a good syngases. Charcoal is white hot in this area and it is turn into ashes and being used up fast.
Also this is causing a lot of moisture to be released and it will go upwards causing a lot of steam to be released.
Bob
No petroleum. Its started with fire through the ignition port on top. Some charcoal burns, at this point it is functioning like a down draft charcoal gasifier. At some point, heat from the charcoal combustion propagates through the walls of the tube to start pyrolysis in the woodchip, sending tar gas into the combustion tube and arresting the combustion of the charcoal. Then the whole barrel is gradually brought up to pyrolysis temperature over the next hour, mainly from the core, supported by the exhaust gas heat in the outer jacket. Once the woodchip is all turned to charcoal, the tar gas will stop flowing, oxygen will get into the charcoal core, and the charcoal will start to combust again. I will need to detect this to tell me it is time to refuel
Oh, also, diesel engine exhaust gasses are typically in the region of 400-1200 Fahrenheit, depending on load. Gasoline engines vary less as the air intake is restricted, but similar temperatures over a narrower range. I don’t know how syngas affects exhaust temperature on either a converted diesel or Gasoline engine, but Jim mason seems to think he is getting good pyrolysis temperatures out of his set up, which is a natural gas engine running on syngas
Not sure I understand. I would have assumed it would depend on how much tar gas was getting produced, and the air flow through the system, as to whether or not the oxygen gets consumed before getting to the charcoal.
What is the limiting factor? As in, a retort kiln can convert 100% of its biomass into charcoal from the combustion of tar gas, excluding the fuel required to bring it up to temperature. Why can’t a gasifier? What is the ratio of charcoal that has to be consumed to charcoal that can be produced through gasification? Maybe I could size my charcoal stage to contain sufficient material for the process
It takes a lot of charcoal at 2000 °f and higher temperatures to convert or what we call to crack the tar gases into good gases. If you could have a large amount of charcoal coming down from the top into the combustion chamber it would keep the process going until the full pyrolysisation temperature is reached and the wood is completely turned into charcoal. This takes a lot of time to do.
Meanwhile the ash from the charcoal burning prosses is going straight downward into the bottom, then you have the gases going up. What is driving this vaccum force of movement. Is it a diesel engine running? If it is how is it going to run to get this process going in the first place but on diesel fuel.
I still see a problem with all the wet moisture coming off the wood. It has no place to go but through the whole system. This will stop the good gases from being made to run the diesel unless it has another source of fuel. Now when running a diesel engines you have to be running on some diesel anyways for lubrication of the parts. So it will never be running on 100 % charcoal gases and converted tar gases.
When you run any wood type gasifer or retort you need to deal with the moisture coming out of the wood. Even wood at 18% moisture content needs to be manage in the system to make good gases. And that does not happen until about the halfway point through the pyrolysisation of the wood when most of the moisture is finally cooked off and just gases coming from the wood.
Bad tar gases going through the gasifer system could mean a tared up diesel engine temperature are not maintained.
So in your drawing there needs to be ash management in the bottom area to collect ashes and fines.
Filtering of the gases still has to be done too.
Is this system going on a diesel generator system? Or motorized vehicle? There is a big difference in how the systems work.
Bob
Ah, thats the bit of information that I was missing. I did not realize that charcoal was chemically involved in tar cracking, I had thought it was mostly just a thermal process, though I knew h2o can act as a catalyst.
Jono one way you can produce extra charcoal from a regular gasifier is to use a grate that only holds up the charbed sufficiently, size the diameter of the grate to just big enough. It will slip a lot of char. Only issue would be making sure that the system is producing enough char to replenish the bed as it’s slipping.
Thermal efficiency of preheating the air going to the nozzles definitely helps, lowers wood consumption and drives more heat into the system to pyrolyze faster. Wayne Keith’s book shows methods that work very well to preheat the incoming air.
But even in a regular system you get lots of charcoal slipped from the grate. Great for composting, and sifting out the bigger stuff and running in a charcoal gasifier.
If you plan to run a tractor on woodgas it will shake the grate plenty with all the ruts and hills you have to drive over. Shaking the grate let’s it sift char out.
Ah, good Jono.
You are arriving at woodgas-as-a-fuels understandings.
Read Jim Mason here: www.driveonwood.com/library/basics-of-woodgas/
His explanation is very technical accurate. For understanding. For those who have to know why first. Before building. Before Operating. Before DOing.
Mine was to make-easy-inspire. Then learn from Try-Doing, again and again. Growing into understandings.
The woodcharcoal is not actually a catalyst. It does get used up contributing a HOT, made active oxygen stealing carbon molecule.
The wood carbons get bound to a HOT oxygen molecule ripped away from made HOT H2O molecules. Making then remaining H2 and two CO fuel gases. The wood ceelular minerals, with heat and time acting as a catalyst to make some wood methane CH4 fuel gas.
In real world applications the wood volatiles contributes only ~20-30% of the energy. The woods cellular carbons the other 70-80 % of the total energy.
You can confirm this air tight wood stoving. The real intense heating energy released in the gone to hot glowing coals stage.
The wood charcoal guys confirms this with their pre-made charcoal engines powering.
S.U.
Regards
Steve unruh
I found something pretty interesting in Tom Reeds “handbook of biomass downdraft gasifier engine systems” in the library. On page 45 of that document there is a design that has a tar gas burner in a tube. Only very superficially similar to my idea, as the key to that design is that the open tar gas combustion chamber is surrounded by the char bed, to insulate it, as opposed to my idea of having the drying and pyrolysis zone around the tar gas burner that would suck heat away from it. The point made in that design review, however, is pretty interesting. Because the tar gas burner is separated from the charcoal bed, it is isolated from the endothermic process of reduction, which enables it to reach higher temperatures (1200c/2200f) and achieve more effective tar cracking.
I should warn everyone, I have a farm to run, so it is going to be winter before I can spend a month in the workshop with a welder testing out whatever I end up deciding to try and make.
Jono if you want something just to test out, @Matt has made a no weld ammo box charcoal gasifier.
If you read it before I edit it in, I’m going to link some posts of the build. You’d have to make the charcoal and size it down but that’s as easy as burning wood in a barrel and snuffing it with the lid, then breaking it up with a shovel.
Since he made these videos he’s updated the nozzle design. Use this nozzle style in that build with the videos.
I want to say Matt has powered a 420cc Harbor Freight engine with this design but I can’t quite remember.
I have a simple question; when people put a grate shaker in, or something similar, what do people find is the best way to make a temperature resistant air tight seal around a rotatable shaft that penetrates the wall of the gasifier? I was thinking of an oil soaked fire rope, like the big end rope seal on my old tractor (but smaller, obviously).
Hi, i once used the sealing end from an old water pump (centrifugal, water-ring pump), this was the type with stainless axle, and graphite rope seal, “stuffing box” with a big cap-nut to put pressure on the seal. Only drawback’s it was made of cast iron, but with little “innovative” welding it hold up well.
It’s also possible to make a seal like this from a ordinary compression fitting, for hydraulics for example, it’s easiest to drill them out so pipe or axle shaft goes right through, then some turns with stove rope and high temp grease, or graphite string (often available at plumbing supplies) where the little compression conical ring should be.
Many also uses fully-threaded rod, and nut welded in the side of gasifier, then a loose locking nut, for when it not in use.
Just some ideas.
Water pump! What a brilliant idea! The Cummins diesel engines have a super simple 2 bolt water pump that would be a shoe-in swap, add length to the inside impeller up to the grate, gasket surface and factory 2 bolts and however you want to actuate it on the outside
