…here I continue,… the scientific discussion,… coal gasification is therefore carried out at a high temperature in an area filled with coal, which turns into gas and ash, as I previously stated, there must always be enough coal in stock in the direction towards the exit, but be careful, it is good that the heat reaches all the way to the exit and that there is still enough oxygen before the exit to convert carbon gas into CO, so we avoid unpleasant things with the formation of soot further on in the pipeline and cooler. Supplying oxygen to this area can be carried out in the form of water vapor or CO2, if there is too much heat, this would apply to coal gasifiers, but when gasifying wood we usually run out of heat here, due to the conversion of pyrolysis gases higher in the process, so I supply to this area fresh air, but beware, it’s walking on the edge, … 
Tone in the Pegasus book that idea was fleshed out in some Henschel gasifiers. Updraft(correction edit) with a second very small diameter nozzle located below the clean out(correction edit), it’s purpose is to clean the grate and eliminate bridging.
Here basically, i was going to write out a simple explanation but because wood itself is made of a lot of different chemicals, and the gas produced by gasification is syngas (or synthesis gas) and contains a mixture of various gases… it started to get long and complicated. I will defer to a potentially eye glazing paper on the subject, but it isn’t that bad and I assume the papers it references are eye-glazing, but go into much greater detail:
https://pubs.acs.org/doi/10.1021/acs.iecr.9b01219
If you read the paper, you see several cracking reactions, that use heat energy thus heat conservation inside the reactor will help to produce cleaner burnable gas.
Then because of Charles law of gas, if you lower the temperature of the gas, not only do you condense out things like tars. You increase the density of the gas. It also increases the time for things like fly-ash to drop out.
It is essentially a heat driven cracking reactor. Monitoring tools even if they are the clever, simple ones like WK has, are important to get a ballpark idea of what is going on in the reactor. (certainly you can use digital ones, but SHTF folks are worried about EMP events would rather use analog, electronics are a mysterious black box for a lot of people, and you don’t need precise accuracy.) But certainly things like monitoring and displays and alerts are possible)
The object is clean (tar free) burnable gas, not perfect efficiency. If you want efficiency, you have to jump to industrial sized reactors, which use processes that don’t scale down to lab/hobby-size reactors like the ones on this site. Unless it is easily and cheaply achievable, it typically isn’t worth it and the extra couple of chunks of wood are no big deal compared to tar reaching the engine.
The other consideration is safety, since it is a mobile reactor and it bounces around on the road, and accidents do happen. You are basically carrying around a contained fire.
Has anyone here built a system like this? From the diagram it seems the lower jet is short, almost below and away from the grate. Should this not be above the grate? I would think within the restriction/reduction zone where char is still hot activated and could utilize the extra oxygen coming in to then convert more char? This low in the burn tube in my head we have a charcoal gassifier built underneath a functioning raw wood gasifier…
It’s an updraft charcoal gasifier, not meant for raw wood. It’s one of the early adopted systems in Europe.
yes but isnt this also a rough implementation of the idea @Tone used in his design with the lower central nozzle as a down draft wood/chip gasifier as well?
So, perhaps Tone is not the first to have thought of this.
Rindert
But maybe the first to implement it in a down draft raw wood system
I made the joke before to Tone that his system is more like a refinery to make charcoal for his tractor. Retort and gasifier all in one.
Friends, there are certainly many people who are smarter than me and have tried and made various good gasifiers, but at the moment my understanding of the processes is such that I have adapted the construction of the gasifier to this… Well Marcus, if I try to explain the gasifier from Cody’s picture, air and water vapor are fed through a water cooled nozzle into the lower part where the coal is gasified, the resulting gas travels up to the outlet, and the ash and remaining fine coal collapses onto a grate that has the possibility of shaking. In addition to the ash, there is certainly some amount of fine coal that falls to the bottom, this part is lost, the designer probably focused on the coal above the grate, so he added a side nozzle that supplies oxygen under the grate, so this fine coal has the possibility of gasification … Otherwise, the wood gasifier is first a dryer, then a charcoal cooking stove, a charcoal gasifier downstream and a tar gas catalyst.
Well I am still making steady progress making a few improvements and upgrading my gasifier project, sealing up detected leaks and building a nozzle ring - but my wife has been sick this week which has kept me from getting as much done as I would have liked to. She is feeling better and went back to work today, so maybe I will get enough done to have another test by Sunday
In the meantime, the process of gasification is still on my mind and I thought of another “science” type question about gasification process that I thought of.
Does anyone have any input about char in the recovery zone? I am curious because obviously the hottest part of the fire would seem to be at the choke point and perhaps above it upstream - but I am curious, once past the choke point and into the recovery zone downstream, does that char cool down to the point that it is burning at a lower temp or not burning at all around the outer edges and is just used for absorption of the free O2 molecules or is it always an active part of the burn also? I am just curious, when I get into a project I tend to go all in and try to understand as much as possible about what I am doing and everything about the processes that are involved.
Depending on how hard you’re drawing on the gasifier, it can burn all the way down to the grate. Which is not a good sign, because then you’d be consuming the charcoal faster than it’s making.
Others should be coming in with a more refined answer than what I just gave.
Good morning Derrick .
The hot spot is constantly moving up and down . There are several factors that cause this .
How hard the motor is pulling the gasifier , width and depth of the restrition ( choke ) that also can be adjusted , wood size and moister content .
Very easy with a steel rod or heavy wire to find the hot spot of the gasifier .
Derrick the area/volumn below the choke point is called scientifically, historically the Reduction zone. Calling it the Recovery zone is a newer being accepted terminology.
And that is O.K.
In the DIY world we should call things for the best common language understandings.
The dedicated air entry points are properly, historically called tuyeres. We all struggle with the French spelling and pronunciation of these air nozzles. Air jets naming is used too indicate a forced steam of air.
On your question the HEAT energy in the glowing HOT charcoal is the very real active energy we are to passive chemicals potentials converting and delivering to the engine to be it’s fuel. Compressed with air oxygen and re-ignited converting back from passive stored chemical energy potential to real alive active HEAT gases expanding energy.
So your below the choke point decreasing charcoal temperature did not just bleed off, or go poof, disappear. It was converted stored. The actual shrinking charcoal down there is not magic disappeared either. It is giving up carbons atoms to make CO; and in a raw wood gasifier CH4 fuel gasses. HOT H2O steam getting delivered down there is stripped of it’s O’s by the more powerfully HOT heat energized greedy Free C’s to make more CO fuel gas. The poor H2’s left lonely looking for free O’s. They find these under controlled condition downstream in the engine combustion chamber.
And in the traditional Four conceived Zones explanations these lower two zones are ridgdley defined at the restriction/choke point.
Except in real life usages they are not! They float up and down; and across, in and out as Wayne said.
Pictorial graphics of dedicated wood charcoal gasifers usually show this expanding and contracting Oxidization/Reduction zone well.
Down below where you are questioning proves a wood gasifier at it’s hot-as- hell core is a charcoal gasifer.
The difference as a raw wood fueled gasifer it in place makes it’s own charcoal. And within itself is internally takes care to the majority of the raw woods nasties of acids, toxic phenols and such.
Turning the majority into just more engine grade fuel gasses. It needs a physical narrowing restriction/choke area to ensure no upper system nasties can bypass escape the conversion HOT hell area.
Residence TIME in zone plays a predominate factor too.
Regards
Steve Unruh
ok so in this understanding the restriction point is the point of you shall not pass to the unwanteds, converted to usable energy by the power of hot hell, or else. The restriction is in theory the last line of defense to prevent tar making. Hot heats needed at all times to purify sent through gasses. So, besides engine demand flow, what keeps the fire hot in this zone? Available oxygen correct? And in turn, depth of the restriction would be insurance to good gas made. More depth more activated hot char fire white to burn up or convert to better made fuels coming out the others side. But this only works if the heat stays within the restriction correct? Or that if it moves up is still hot active enough for passing through gasses to be usefully converted. This ever moving hot lobe of heat up down and around, so is this how the drizzler gassifier works? With minimal fuel feeding, tamping down to force heat zone to stay right at the restriction and always purify gasses? Seems the theory at least to me.
Norman, I early on I.D.ed the WK as essentially “just a big pot of charcoal”. I was not saying that as a slam.
Later a couple of other fellows smarter than me, better defined the WK as actually doing the majority of it’s thermal-chemical Reduction above WayneK’s choker plate. Kristijan said this. Joni iffered this. And one other guy saying. . . name?, name?, name? . . . damn brain. (mine)
Anyhow they were comparing the active area volumes to a more traditional restriction down draft. Above and below the restriction/choke area VOLUMNS.
The WK much more above than below. The traditional downdraft closer to a 50/50 split above and below. Note those traditional guys are always stating in velocities, velocities, velocities. Actually a base necessity for those systems.
You are a WK builder user. Not so overly velocity thinking are you. Temperatures? Temperatures. Temperatures! Right.
Interesting conceptualizations.
I have come to think more in Times-in-residence in each phase step.
You brought up the DriZzler system. Where does that fall into the thermal-chemical concepts and equations?
I do not care. No eyes open Practicalist should. It is not practical for anything other than a fixed loaded stationary system. And a system that must have a finely graded fuel particles that can be automated dribbled in across a wide area to maintain it’s thin shallow, shallow reaction beds. Always, always, start with the fuel input factor!!!
Much more interesting to me would be Stephen Abbadessa’s 60 and 30 degrees downward jets system. The Swedish guy Jonas with the multiple chipped fuel systems. Tone’s dual level all char eater system. These have all shown real wide range Practical usages. Small stationary, to vehicles.
But hey. Remember I am the as direct as possible from trees and brushes woods to a real working producing engine shaft power guy.
Now isn’t that a WK??
S.U.
Thank you Steve you always clarify the random thoughts in my head. Yes each gasifier has to operate on different principles, to get the same outcome produced usable gas. Each has a specific or set of specific needs, some that can cross over some that don’t. And each can be dependent on the fuel source utilized, which in my opinion the less input of my body energy spent processing the fuel is the better for me. Whenever I get a permanent home and a wood stove I will be back to PLENTY of energy input into wood preparation between house heating AND 2 woodgas trucks! And then I get the passive energy input of charcoal cleanouts as a benefit as well from the trucks for tinkering. Though most of it get recycled back for bob’s rocket mix or lunch time bbq use as of right now. Only down side of that use is char is small in size so 15-20 minute cook time at max before reloading the bbq. Hard to slow cook a big slab of meat with quick dissipating heat source… Not the same as a quick burger for that use it is just fine. Borderline long enough burn for a pack of bratwurst which is my common favorite lunch. Reminds me I’m low on sauerkraut need to run to the store
I felt like adding some insight into the inner workings of a gasifier, hope some of you can appreciate it.
One misconception in reactor design is overemphasis on the importance of nozzle and hearth velocity.
Nozzle velocity does help with mixing the pyrolysis gases and tars with fresh air by creating localized turbulent flow and depositing air over a larger area, we all know this. However in the end for a specific vacuum load, a corresponding specific amount of air is drawn in regardless of nozzle configuration. Remember the equilibrium feedback loop. Drawn in air causes combustion which creates heat which increases the rate of pyrolysis which increases pressure which reduces the need for air draw. Nozzles are a means to distribute air, not to change how much of it is drawn in in total.
So how do some wood gasifiers work with just a single nozzle? Let’s go further into mixing.
When designing a reactor remember these are not open areas with straightforward flow paths. The geometry of fuel and charcoal acts as a massive maze that is in huge part responsible for mixing, by separating flow paths into smaller and smaller sections and then crossing and overlapping those with paths of the other gas to be mixed.
Flow separation is the fundamental basis of mixing. A mixture gets exponentially more uniform with every division. From two streams of different gases (like fuel and oxidizer) with a width of 10 units to four alternating gas streams 5 units wide to eight alternating streams 2.5 units wide to sixteen alternating streams 1.25 units wide and so on. We can keep doing this until the streams are undistinguishable from each other down to the molecular level, creating a truly uniform homogenous mixture. Of course there is an upper limit to how much mixing is worth it as every mixing element adds resistance to the flow.
In our gasifier oxidation zone this happens countless times with random shapes leading to very turbulent flow. Turbulent flow occurs upon flow separating and different velocity flow streams meeting behind an obstacle, for example when a plane wing aerofoil stalls. Due to the random geometry there will be a wide range of velocities, which causes turbulence in the spaces between solid fuel.
This is the reason why particularly wood chip and pellet gasifiers can work well with a single large nozzle. There are so many more flow separations for mixing due to the finer fuel size so they can afford to just dump the same air in one point and let the contents of the firetube do the mixing. Hence why they usually have longer and narrower firetubes so that initial air spread area via the nozzle does not need to be wide. There is also the factor of smaller passages between fuel leading to a higher locational velocity to move the same volume of gas through in accordance with Bernoulli’s principle.
As for the restriction it is not just to increase flow velocity and concentrate heat in the center but also to increase the distance the gas travels within the firetube.
In short: Velocity is not the main factor in mixing, and turbulence is still created at lower velocities within randomized fuel geometry. The amount of flow separations plays a greater role for mixing, and air mixing with pyrolysis gas is key to thorough combustion of heavier hydrocarbons like tars.
If anyone here had the patience to read through all that, you are a trooper and have my utmost respect 
Antero, you wrote it nicely, it is actually true that the amount of air sucked in through the nozzles is determined by the pressure difference at the place where the nozzle is installed, but this difference is primarily determined by an engine with suction of the generated gas, then gas expansion during pyrolysis, steam condensation in the upper part,… if we have several nozzles arranged in the direction of the gas flow, it arises due to the resistance of the gas flow between the fuel and the diameter of the pipe, the pressure difference between them, so it is on the nozzles closer to the engine, the pressure difference is greater, so the air penetrates here faster. With such a design of the gasifier, the size of the nozzles is important, as this determines the possible amount of air under certain conditions… just as you wrote Antero, I also respect everyone who has the patience to read this
Great example of a situation where nozzle sizing matters more. Naturally said by the man with a central auxiliary nozzle in their gasifier 
I did not mention many variables relating to the pressure difference in that part of the previous post as it was already getting long but I do think there are situations where nozzle size has effects other than the ones mentioned, such as upon sudden change of load where the fuel mass may not have enough time to heat up due to limitations in thermal conductivity of the gases and solids, so it would take a short while for pyrolysis rate to increase. During this time more charcoal carbon would be oxidized directly as less pyrolysis gas would be available.
Of course ideally for maximum fuel efficiency charcoal would never be oxidized directly by air and would instead be used for reduction of either pyrolysis gas and tar combustion byproducts, recirculated exhaust gas or injected water/steam.
This has me thinking about nozzle angle again. Naturally as load increases nozzle velocity, the air ‘jet’ range increases but so does to some extent the strength of it being pulled down towards the restriction. Angling nozzles upwards should have a positive effect for pyrolysis ramp up and pyrolysis gas combustion during a sudden load increase. Some systems here already do this.