I saw this many years ago and even exchanged some emails over it with fellows because I thought there was something here that could be useful, and I still do…
Problems we bump up against in solid fuel gasification are related to efficiency and power loss.
We lose power to pumping losses in the engines as we use the engine itself to drive the process.
We are limited to how hot we can run the systems because the combustion air expands as we heat it and our fuels can not take the heat without pyrolizing before they should in the bunker.
We need to operate at higher temperatures and pressure.
We need to run under boost.
Drive an undersized turbo off a large enough engine to develop as much boost pressure as possible and force feed the gasifier hot air ( and super heated steam ).
Make everything smaller form the tuyers to the combustion and reduction zone in order to concentrate that heat.
Regulate that heat with the correct amount of steam to prevent a melt down.
Now things become a little simpler.
A waste gate control can keep the system under regulated boost.
A demand regulator can lower the pressure from filter outlet and feed the gas to a proportioning valve.
The calorific value of the fuel can be regulated by increasing or decrease steam injection.
The combustion air is kept at atmospheric pressure and mixed with the above combination into the naturally aspirated engine.
Higher efficiency, less power losses better consistent quality fuel gas…
I know it will function, but I am not sure about the efficiency.
Kohen is the only one with an engine that can take full advantage ( his high compression SI converted diesel ), and dollars to doughnuts I am willing to bet it has an easily accessible oil gallery and he might find a turbo in that shipping container.
If you remember the video posted where he showed the calorific value of the fuel gas increased with the addition of water imagine how much further than could be improved by drastically increasing the available heat energy in a more compact reduction zone.
There is a historical precedent for how this would work.
A few Town gas plants used to draw air to heat their coke beds, then spray oil or water ( or both as required ) on the super heated coke to make gas until the coke bed cooled then they would do a reheat.
We could skip this reheat by making everything smaller and hotter under pressure.
The result was richer gas than a straight run through the gas plant without.
When you think about it we are trying to make gas in partial vacuum with the current thinking and this is counter productive
By using a small turbo we always have a turbine wheel under power and a compressor working.
We might lose some power to increased exhaust pressure but we would certainly gain more by reduced pumping losses through the gas system to the engine.
I have been tinkering since I last was doing any significant posting and I am not going to follow through to build this, but others might have the parts ready to go.
I would start with a water moderated Charcoal system, then go to a conventional down draft wood system.
A fluid bed large system might even be possible if you had a big enough engine and a supply if fine biomass feed stock.
This is open source no one has a patent on the idea ( I put some protection in place to snarl up a patent in Canada if someone tries but I have no intention to follow through and build one for profit or any commercial interest).
I don’t have any issue with anyone trying to make a commercial product of it as long as they do not try and patent it and prevent others from using the idea.
One of things to think about when turbo boosting with a waste gate vs. vaccum is the connections of the piping. I have had loose connections develop and have been alright going down the road. The next day when starting up have found them when using my pusher blower. Positive pressure on the gasifier system is going to call for different ways to connect piping, then just using simple hose clamps. Helping to get the vaccum lower helps, but you will still need some vaccum up to the engine, or into a turbo charger then into the engine.
Running bigger piping or redundant piping will do more, also bigger hay filter for more flow less vacuum drag down. What a difference I have notice just keeping my hay filter and cooling rails and related piping cleaned out of soot has done for efficiency on my woodgasifier.
In a Charcoalgasifer, Koen has mentioned over a over again that he starts with a new batch of clean dust free charcoal on every start up. Dumping the cooled charcoal out before the next start up run. That alone does more for efficiency then anything. Less vacuum at start up and when running.
Maintenance cleaning in the hopper and tar gutters, condensation tanks, ash nozzle area, or grate, drop box, cyclone filter, hot filter, cooling rails, hay filter, and other piping is the key to making a gasifier work more efficiently going down the road, for charcoal or wood gasifiers.
Maintenance does not use up engine shaft power, but it does add to it, and it always eliminates hauling weight.
using a supercharger to put the gas-generator under pressure was already done in the forties during WW2 in some cases. You get a higher peak output of power and a better specific fuel consuption, as you use the energy of the exhaust gases.
But the system gets more complicated and has to be absolutely air tight, as it is running under pressure.
Some information can be found in the swedish gengas book (here in the library) on the pages 227 to 229 and in the Book from Switzerland pages 344 to 363.
In general, you need a larger gasifier, as the volume of gas increases and you get a higher load on the system. In a charcoal system, the basic principles of lowering the temperature with EGR or steam injection are both applicable.
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
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.
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…
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.
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?