I am not making myself well understood here am I.
The turbo runs the gasifier under high pressure and temperature and the engine only supplies the power through the exhaust.
Exhaust heat we normally waste so its less of burden on shaft power yes, but its not driving the compressor wheel to force feed the engine.
What I want to do is use the engine to power a turbo and run the gasifier at higher than atmospheric pressure so you can run it much hotter for tar cracking and gas water shift.
Less water left in the gas, more complete reduction of CO2 to CO and water to H2 and CO.
Not talking about forced induction at all, but we are off in the weeds and no one is looking where I am pointing
Hi Wallace,
well, I start to get what you are after - hopefully
Maybe a sketch of your idea can help?
The WW2 turbos were made to turbocharge the engine and thus get nearly pertrol power. The gasifier were run the same, they were just a bit bigger as the needed woodgas volume increased with greater engine power compared to a normal suction gas intake.
For you, the turbo is “just” or primarely there to supercharge the gasifier, right?
Well, there is a big but from my point of view. This is only theoretical knowledge, maybe someone else can give more practical experience.
With a higher pressure you can create a higher draft and a higher throughput on a gasifier. But you can’t change the fundamentals of the water-gas-shift.
A certain amount of charcoal only releases a given amount of excessive heat, no matter how fast and under which pressure you burn it. Thus the amount of water you can reduce to hydrogen is also limited. Besides best possible heat economy and recovery of the gasifier, the only way to increase the hydrogen yield is to introduce heat from outside to the system. This was done in town gas plants by heating up the coke with air alone first, as you wrote above.
The large amount of hot glowing coke acted as a heat reservoir to fuel the water reduction, but after cooling down by the heat consuming water reduction it has to be brought back to high temp with air alone again and again.
The background of charcoal gasification and with and without steam is well explained in the book “Driving on wood. The lost art of driving without gasoline” in the library section. From this description and the balance of heat creation and consumption of this processes, I would say that your idea will not work as you intended.
Now you are getting it.
We can not preheat incoming air beyond a certain point because it expands too much but compress it even a little and you gain more heating value for a given amount of air.
Now you can start to shrink things because you are running under boost.
How much?
I am not sure, but the throat can shrink a little a we can increase the velocity through the char bed.
This will intensify the heat and allow more water gas shift and so on until we find a new equilibrium.
We also gain the advantage of not sappy engine power by sucking on the gasifier and lowering our VE.
We can now use a counter flow heat ex changer to reduce our outlet temperatures and not worry about the increased flow resistance because we are under pressure.
We can strip more heat off the gas outflow because the more efficient heat ex-changer design and this will result in a higher inlet air temperature to the tuyers ( and I reminder you a higher density ).
Feed this cooled gas now to a demand regulator and its simpler to regulate gas flow and mixing ratio.
The gas is probably richer too because the higher temperatures allow you to make more gas with less oxidation because we are not using as much heat in the gasifier itself to drive the process.
Exploiting as much excessive and otherwise lost heat as possible is definitely the right way and allows to come closer to the theoretical equilibrium, which won’t change and thus can never be exceeded.
For optimum power this is the way to go.
My suggestion: Use the turbo both for pressurerising the gasifier and the engine the way they did it back in WW2. Compress only air, use a part of it as primary air for the gasifier and the other part as secondary air for the gas mixer of the engine. As you have the same pressure niveau for both primary and secondary air, mixing is nearly as easy as with a normal mixing device relying on engine suction
Benefit: You avoid both the pressure losses of the gasifier to suck on the engine and you have a still a little supercharge in the intake.
Again the old dilemma: Simplicity versus better economy and higher power.
look at the video
Its a really bad fluid bed gasifier, but its self powered…
Add a re-generator to improve efficiency and build a proper gasifier about the internal bits and maybe it could generator enough power in its own right to run the gasifier/filter/cooler apparatus and we feed the gas from it to a gasometer for a stationary application…
Simplicity.
If you are using the same parts to do one thing as to do another then one is no simpler than the other.
But if you are going to turbo charge an engine you need an engine to start with that was built stout enough to run on boost.
Down side to this is it was optimized for gasoline and runs at a low compression ration and we are producing a low heating value fuel that is high octane.
That’s a big miss match…
You say you have seen WW2 systems that pressurized the gasifier and the engine at the same time.
Can you post a link, that would answer a lot of questions and probably raise new ones too!
Only partly true, as you have to built the whole gasifier and system sturdier to deal with the pressure. All connections have to be really tight, as small leaks will lead to escaping gas. Different if you run on underpressure caused by engine suction.
Woodgas can be used with compression ratios (CR) up to 17:1 (Koen has a research paper in his google drive that stated this), so using a normal CR of a petrol engine with a slight supercharge on woodgas should be possible, as you won’t exceed the original petrol power.
Hi Wallace, the light bulb came on in my head. Okay we are running our gasifier plus atmospheric pressure. At the grate in my gasifier I have seen 1670f. I try not to get it that hot for every long. So are we looking at running the temperature up to 1700f at the grate with a positive atmospheric pressure?
Or keeping the temperature the same but under a positive pressure, which then will cause we a more complete cracking of H2O and converting the gases.
One other thing is the pressure released if you have a puff in the hopper. Positive pressure means no leaks. It much easier to seal the hopper with a vaccum and if you have a puff in the system to release the pressure hopper spring loaded seal on the lid.
Bob
I have mixed thods about this. The mad sciencetist part wants to say “let the turbo spin!” but the realistic says “wohaa let safety, simplicity and experiance take the lead”.
Ok. Lets listen to the mad sciencetist
Both of you are right. Til says you can not exceed a certain amount of gas per carbon atoms, yes, that is true. But you can substitute air oxigen with water oxigen with less nitrogen dilution, richer gas. Fuel moisture. Dont waste it, use it. Its there all along. But thats easyer sayd thain done.
Raising pressure in a gasifier will only speed the reactions, but it will not change product gas reaction equalibrium! Sayd differently, pressurise the gasifier, you wil need a smaller hearth gasifier, but the gas WILL be the same composition as a athmospheric one.
Now, the way l wuld do it.
First compress the air with a turbo. It will allso heat due to pressurisation. Heat it eaven further with exhaust gases. Then, heat it eaven further with gas from the reduction zone and you shuld end up with air preheated to near 800c. At this temperature, the efficiancy of the gasifier will be much much enlarged. No hopper condensation wuld be neaded or wanted, becouse at this energy recirculation, the extra water is neaded to substitute the air-make richer gas.
Then, the unreacted moisture will condense easyer due to pressure, resaulting in dryer gas-richer gas.
A contra working vacuum automixer-pressure equaliser mixes pressurised gas with athmospheric air in perfect ratio. The engine has no problems sucking it.
But is all this worth it? I dubt it sadly…
Well thats enough midnight brainstorming for today
Edit: in order to crack more water, one needs to add more enthalpy. Pressure does not add enthalpy! Only heat does.
Its the same as in kitchen. Salt doesent add any nutritional value to the food, but it does make it more tasty
a lot of energy is lost in the exhaust gas (30%) I think)
it is very tempting to try to reintroduce into the system. but how to do this simple?
a turbo is relatively simple (turbinate hot and pressurized gases to produce mechanical energy)
if the turbo drives an electric generator, instead of a compressor, it can, by electrolysis, produce HHO to feed the gasifier
What level of efficiency can we expect?
I think that, by this choice, we avoid the difficulties related to positive and variable pressure in the gazogene
moreover, as Til and Kristijan explains, compressed air does not really improve the gasification, it intensifies it (acceleration of the process)
The injection of HHO enriches, in quantity and quality, the gas.
What do you think of this?
Using the high temp of the exhaust gases to preheat the primary air as Kristijan suggests is one of the easiest ways.
If you use EGR, try to feed the exhaust as hot as possible into the gasifier (insulated pipes).
Another use of the hot exhaust gasses was done by the DEUTZ-company. They built a tractor, were the spare wood was stored in big tight bucket in cages. The hot exhaust was led through this buckets and dried the wood. A picture of this tractor can be found in the PEGASUS-book (Library / Pegasus Gasifier | Drive On Wood!) on page 29. The long bucket lies on the rear fender. A smart idea in my point of view.
Using a turbine to drive an generator sounds nice. You could also run a thermoelectric element to create electric energy.
Creating HHO sounds nice first, but it is not without reason called “detonating gas” in German. Feeding it into the burning zone of the gasifier might not a good idea, better instead directly into the engine manifold.
But here we are more in the field of a thought experiment again, quite impractically for mobile applications in my point of view. What we discuss here might be of more interest for stationary applications, where space an weight is not a question and you run under more stable load.
My choice for mobile applications: Find a good balance between heat economy/recovery and compact build/weight for the gasifier to get rich gas with reasonable effort. And try as much inner streamlining of all the piping to avoid unnecessary pressure and thus power losses.
Keeping it simply simple (KISS) in the build, the way it operates, less moving parts, air and gas flow is okay as long as it is not restricted to much to keep a good vaccum flow not ranging to high. Control valves as few as possible. But still making a good rich gas production. Hearted air 600*f at the nozzles from waste heat from the exhaust is really good.
Removing excessive unneeded water and tars is another important thing.
Removing soot, ash from the rich gas is also needed.
Reheating gas for final filtering through paper if used.
Doing all these things with out any moving parts and delivering the rich gas up to the engine compartment is the goal for the KISS build.
Yes, and even mixing the air and gas before going into the engine.
Why, just look at who is driving the most miles day after day.
Bob
I think Roger Blomli has pointed out an effective use of process heat to raise system efficiency in the Weiss system, to pre-pyrolize incoming fuel without introducing all the oxygen and nitrogen needed to produce syngas from cold fuel.
do the exhaust gases contain water vapor? do they manage to dry the wood?
The injecting HHO into the gasifier (vs intake manifold) would allow a better synchronization of the flow of gas with the needs of the engine (in my opinion)
Yes, they do from the combustion of the hydrogen. Temperature is the key of drying the wood. If the temp of the exhaust is above 100°C, the steam fraction is kind of superheated and can dry the wood. If the temp is too low, you get condensation and thus the opposite effect of moisting the wood.
Tractors often run at high loads (ploughing etc.) at low speeds, so you get a high exhaust temp with low cooling effect of airflow. Because of this, this predying method might work good on tractors or stationary engines, but moderate on trucks.
Yes the first part is right. Hotter. But l am afraid just heat it self will do the job.
Say you inject air in at 1 bar and 500c, or atm pressure and 500c, you will get the same gas composition. But a smaller reaction zone in the gasifier!
Now, 500c and 800c air will make a hell of a difference!
But thats just chemical theory. For sure you will have to do a test
