Hi don is this project a wood gas or char fueled machine,Or vehicle?
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this one will be wood, Kevin
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Don,
I was wondering, if the pre-heat is coming from the hot gas, is it possible for the soot in the gas to stick / cake up around the nozzle manifold over time like in Waynes “Drop Boxes”? Possibly enough to actually insulate this area and reduce the preheating effect? It would seem to be a tough place deep in the system to keep cleaned out and monitor. Maybe clean out would be accomplished from the ash dumps periodically?
I was just wondering how this would affect things if at all. Maybe there is enough heat in this area to keep it all burned away from the nozzle manifold or bumps in the road to keep it all shaken down…
Bryan
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Bryan that area may well plug up with soot but it was not designed for preheating the incoming air but just as a manifold to get air to the nozzles. If it tempers the air a little that is fine. I am going with unheated air to the nozzles with this build to see how much difference it makes. I can always add heat with exhaust if I need it.
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Ahhh, okay Don I hadn’t thought about the exhaust preheat possibility.
There’s always more than one way to skin a cat!
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As always when reading Max´s posting there are things mentioned that you need to sleep on. Being a bit slow I took a 2 week nap on this one.
I´ve mentioned before my little system has to work hard keeping up with traffic on the big road and that my vacuum ratio lowers when long term high load. I know it takes a full 40 min hopper before my whole apparatus is fully warmed up and preheat in full bloom. I expect the preheat to then at least double the volume of the incoming air. My thinking is that the extra drag this creates over the nozzles is also contributing to my lowered vacuum ratio - not only insufficient char making.
The other day the hopper lid accidentally closed a bit offset. I discovered a bit lower vacuum than usual but I was a bit late for work so I didn´t stop to correct it. I experienced about 10-20% power increase but also about 20% higher rail temp.
I think I´ll try two separate fully up to temp experiments: 1) Let some air into the hopper through my vacuum guage port. 2) Partially bypass the preheat by letting some air in my light port.
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Jan, this will be a good test for you, and us all. I’m positive we all can benefit from some cold dense air coming in to our gasifiers from time to time, once the temperature is up to the operating norms for each individual gasifier. This will help going down the hi ways and keeping up with traffic. Now if we can just which it back at lower speeds and idling times to keep the temperatures up. Balancing on the gasifier temperatures is the KEY to good performances. Not to hot, Not to cold.
May be installing a valve on your lighting port to control it from the cab of the truck would work.
Bob
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I like the results of your naps JO, Makes a lot of sense.
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Hello guys; I understand the “sleeping on it” bit. I am pretty much reading this for the first time so not a lot of pre-thought. I sit here with my nose 5 ices away for the screen so I see EVERY WORD clearly. My thought on what Max has said;
Ok you calculate the orfice or nozzle for a certain velocity of cold air. Now when you start pulling hot air through that same nozzle — the hot air is thinner, so it is like the difference of sucking a thick syrup through a straw or sucking water through that straw. The water will flow through the straw much faster. If you want to slow the water down to the syrup velocity, you have to go to a larger diameter straw. Same thing with the air, larger orfice or nozzle for to slow the speed of the hot air down to the speed of the cold
The term “Absolute Zero” is important to remember. This makes it possible for us to run one nozzle for both hot and cold air. If you double the temperature of the air going through the nozzle you don’t double the area or diameter of the nozzle to keep the same velocity. If memory serves me, absolute temperature in my system is -460 degrees F. So if we start with cold air at 70* F and go to 140* F we have NOT doubled the temperature and thus do not double the nozzle size. We have gone from 460 + 70 - 530* to 460+140- 600* That is an increase of 13% and probably a 13% increase in nozzle size. TomC
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Tom, good comparason with that syrup. But the oposite.
Hot air has a bigger volume, so you have to make nozzles bigger for hot air intake in order to achive the same velocity.
JO,
An interating absorvation indeed.
But be carefull about fuffs with extra oxigen in the hopper!
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JO You probably are going to find me to be all wet on these comments, but it is how I see what you are saying.
See my post about Absolute Temp and volume.
When you are pulling hot air through the nozzles, the air is thinner and flows through with LESS drag and thus the vacuum decreases. ( again sucking syrup through a straw requires much more vacuum than sucking water).
Then the lid situation. The open lid allow an easier route for air to come into the hopper so the vacuum dropped. The added air might have raised the height of the pyrolysis zone, burning more wood and raising the temp in the pyrolysis zone generating flammable gases faster. The added flame also probably raised the rail temperature. I believe this is saying for running when up to temperature, you could use larger nozzle orfices. TomC
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Tom,
You´re right about the syrup - water. Why jets fly higher - less drag.
In this case I think the more important factor is that air contains less molecules of O2 per volume when hotter. A larger volume has to enter to satisfy the fire - increased nozzle area needed. Still with smaller nozzles total vacuum on the system about the same, only a larger proportion of it over nozzles due to a larger volume of air entering => increased drag.
You´re right about the absolute temp as well. I expect my preheated air going into the nozzles to be in the 300 C (600 F) neighbourhood, thus the doubled volume. I might just check my numbers. The TC can easily be put into the nozzle jacket through the lightport.
Kristijan and Tom,
With my double wall monorator hopper and its internal cirkulation I expect the added air to go down the void and enter below the funnel fingers. That´s only 1-2 inches above nozzles. Adding this air will temporary increase my oxidation zone. I guess I could just as well use smaller fuel for those occations, but experimentation is experimentation.
I know Wayne once tried this and didn´t notice much diffence, but I want to have some fun too 
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I did it too, the FEMA from an imbert incident 
At my static tests l often run without the lid for longer times. Runs quite constant.
As for hot air volume; one mole of air at 0c holds 22,4l. The same air heated to 300c holds 46,3l so about twice the volume. A big big difference in nozzle diameter!
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Preheating charcoal air would let you run more steam in the system.
I wonder if this means you need less air for a given load and the tuyer size could be kept smaller.
That would be an interesting experiment.
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The opposite, since the water tips the energy balance to the decreasing temperature, you’l need the extra oxy per volume to keep it in balance.
I have some old boring books about it, did put it to a test, and the results are as expected/predicted in the book.
closest thing to making water gas: heating with air, cooling with water…
in my experience, the hotter the reduction with colder air. also the least/lowest CO2 in the gas, the coolest gas out…
but thats dark side… black magic 
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It is a heat driven process.
If we strip heat from the output gas and put it back into the input we need to generate less heat for the reduction zone and we have more available energy for hydro cracking.
Theoretically that is…
Too much heat after the reduction process might have something to do with the increase you see in CO2 Koen.
CO is an unstable gas and I am wondering if there is a temperature range where the instability is higher causing some gas to revert to Co2 and carbon black
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Hi, Wallace!
20. of November 2016
Some old books state, that the gas should be quickly cooled down to <500*Celsius after the grate to stop this deteriorating.
So, by all means keeping the gas hot and “process-willing” for reduction, and then abrupt cooling it down to preserv the result!
Also, this tells about having enough reduction char for the motor’s top demand. When temperatures below the grate start going abowe normal, the bells should be ringing.
Undoubtly, this trimming cannot be made completely by changing fuel size.
To assist in keeping a big enough top performance char volume, you need a means of sieving it (at tanking manually) or by a remote electrical motor during driving.
Remote mechanical grate shaking from the cabin was used in Germany under the WWII. (Zeuch)
The sieving mechanism can also be formed to regulate the active char volume.
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Thanks Max for confirming something I could only guess at.
There is a lot of process hat here that should be looked at very closely.
I have another question now.
I read someplace ( I think it was Doctor Reed or something ) a paper on velocity of gas through the char bed.
He had created some tables to calculate this for best gas…
Does temperature of incoming air change this ( need longer to heat therefore we need a longer or shorter char bed ).
Another Canadian ( names are lost to me today ) posted some pictures and video on the gasification digest about temperature effects on his Imbert down draft.
Extremely cold inlet air was denser but was putting too much of a burden on his machine making bad gas.
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I think we have to be careful making blanket statements when we have different styles of gasifiers. I am betting that with the WK style that the large char bed and long dwell time will overcome some of the problem with introducing cool air in the nozzles. I hope I am not wrong because that is the way I am building this time.
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Hi, Wallace!
21. of November 2016
The “easy” thing with Imbert-like construction is that you can start with imaginary passage velocities on 3 levels and use the motors maximum gas consumption per second for scaling the process volumes. Including ~fuel size.
Ditto for the nozzles.
First, everything as cold, then the “heatexpansion” as requiered.
Still, hardly ever you hit the nail on the head… first time.
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