Half a croissant, on a plate, with a sign in front of it saying '50c'
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Electric wood gas cooker

Battery powered "engine" takes raw wood turns it into gas to run engine
  [vote for,

Instead of warming up wood with tons of smoke and tar, for a wood gas motor,

a. you put the wood into a compartment.

b. In the compartment the wood is cut down into saw dust, using electric power.

c. Then the compartment is warmed electrically to above 100 degrees with air evacuated from compartment.

d. a small amount of liquid nitrogen is introduced, causing all humidity to turn to water and be extracted at bottom of compartment.

e. extremely dry sawdust with nitrogen (and presumably no oxygen), now heated by microwave. Mostly clean gas is produced and immediately burned, creating energy that can be used in a motor or for generating electricity.

f. Presumably the energy received from this system far exceeds that put into the process.

g. The produce is charcoal, which can be sold or used in modern clean-burning charcoal electric plants.

f. The CO2 emissions can be fed into a vegetation area, to be consumed by plants, or caught in water and fed to algae. (Using the Aerovator invention for consuming all bubbled gas in water)

[Edited: d.SMALL amount of nitrogen and e.ENGINE or GENERATING ELECTRICITY]

pashute, Oct 30 2012


       I don't really see the point of "d. liquid nitrogen is introduced, causing all humidity to turn to water and be extracted at bottom of compartment."   

       By the time you've raised the temperature above 100 degrees and evacuated the air, the moisture will almost all be gone.   

       Generating liquid nitrogen is also going to make "f. Presumably the energy received from the far exceeds that put into the process."
rather less likely.

       The key to efficiency for heating using electricity is to move heat around, rather than generating heat resistively then throwing it away.   

       If you are burning the product gas to create electricity on-site, then you have low-grade heat to spare, and could give the wood a preliminary drying before doing anything more aggressive.
Loris, Oct 30 2012

       [Loris] thank you for your input.   

       The point is that I cannot allow for escape of any gas (smoke) while drying the wood. I'll be happy to dry it using any other method. A very small amount of nitrogen should be needed for this, since the compartment is at low pressure in advance.   

       There is a discrepancy between the idea in the headline (at least the description line) and the idea body. I wrote in the beginning "to run car" and in section e wrote: immediately creating electricity. I meant "can be used for running an engine or generating electricity". I'm editing that.   

       You are correct about the latent heat.
pashute, Oct 30 2012

       Heating dry sawdust by microwave will still produce tons of smoke and tar. That's what happens when you heat lignin to destruction. The idea is to burn most of it in the engine.   

       Getting the wood extremely dry may be misguided. Wood is mainly carbohydrates and lignin, which contain hydrogen and oxygen. Water is therefore produced during pyrolysis of wood.   

       What [Loris] said. You are using extremely wasteful and expensive energy (electricity stored in batteries) to replace cheap, low grade energy (wood, or even better, waste heat).
spidermother, Oct 30 2012

       I glanced through a TV program last week that cameo'd a guy who was superdrying wood in a furnace. The process didnt look very efficient, but IIRC they said that seasoned dried wood contains 20% water, compared with 2-3% for the furnace dried sort. And the seasoned wood burns at 200-300C whereas the superdried stuff goes up at 300-400C or figures to that effect.
FlyingToaster, Oct 30 2012

       I completely agree, your toastiness. Drier wood burns more completely, at a higher temperature, and with greater net heat output, which are all good things. The mistake here is to obsess about getting rid of the very last bit of water, using very high-grade energy (electricity, liquid nitrogen), when abundant water is formed during pyrolysis anyway. It's a teacup in a storm.
spidermother, Oct 30 2012

       The idea stems from experience. I'm working with some partners on an existing gigantic coal cooker (holds about a ton of wood each time) with an invention of mine for de-smoking, which is working pretty well now after a few first attempts. But until it reaches 300C and for 3 hours, most of the "smoke" is steam.   

       I figure that removing the moisture would bring me to the cooking stage much quicker. The whole process should be done without combustion, and thus, much less smoke and pollution.
pashute, Nov 04 2012

       Instead of heating & nitrogen cooling...   

       Depressurize the chamber down to about a quarter atmosphere (or whatever it takes to boil water at ambient), and every time the pressure rises too much, evacuate it back down. The water coming out will be at 100C which may be useful for something.   

       This is preferable to completely evacuating the chamber because heat lost from the wood during the process can be replaced by convection from the walls of the chamber (which may be passively solar heated if not indoors to speed things up a bit).   

       When the pressure doesn't rise anymore, then the only water left in the chamber is in the form of vapour. Evacuate that, and replace with air.   

       If sawdust is your end goal it may or may not be easier to wait until after the wood has dried.
FlyingToaster, Nov 04 2012

       //The whole process should be done without combustion, and thus, much less smoke and pollution.//   

       Are you sure? I thought heating wood without combustion gave the most smoke possible - what with smoke being the unburned product of pyrolysis and all. That's not a problem, though, as long as you deal with the smoke - such as by burning it with plenty of air - rather than let it escape.
spidermother, Nov 04 2012

       I seem to remember reading somewhere that heating wood in an airtight chamber is one of the ways of producing methanol, wood alcohol, one of the simplest alcohols and an excellent fuel.
cudgel, Nov 05 2012

       Separating the methanol is the tricky part. Fortunately, you don't really have to. Just condense most of the water; the mixture of more volatile components (including the methanol) burns well enough.
spidermother, Nov 05 2012

       You should be able to get most of the water out but keep the smoke in. Just don't heat the wood to the point where it starts to decompose.   

       Lowering the pressure lowers the boiling point of water; that's a more efficient way than simple heating.   

       Or you could run just a dehumidifier in the sealed compartment. This can take out the water and return the air. The heat generated is returned with it, so it's a much more efficient use of electricity than simple heating.
Loris, Nov 05 2012

       But most of the water (about 400g per kg of wood) is produced during pyrolysis, not present as water in the wood. Please, pyrolysis and gasification are mature technologies. Details such as 'dry the wood first' have all been thought through.
spidermother, Nov 05 2012

       Well, I was going by pashute's comment that he only got steam for the first 3 hours as implying that no actual gasification was taking place.   

       Water produced during gasification is a different matter, of course. One could still salvage heat from it, as condensing boilers do, I suppose.
Loris, Nov 05 2012

       Why bother? You need some water vapour for the water gas reaction to take place, which is quite important if you want to turn the carbon into carbon monoxide. This is also a reason why (if done properly) you shouldn't have charcoal left at the end.   

       It is very easy to condense the water vapour out of the gas as well further down the line. This would represent some energy loss, since this normally involves cooling the gas, however I think that loss in some form is inevitable (if left hot, the difference in temp in the engine is probably reduced unless the cooling system is very effective). Most engines will cope with the amount of water vapour in the gas anyway, however this does require the gas to be fed in when hot and thus with a low density, so less in the cylinder.   

       Also, I assume the last paragraph is intended to be an eco-friendly move. The woodgas should be carbon neutral anyway.
TomP, Nov 05 2012

       [TomP] You're describing a wood gasifier, where a controlled flow of air is introduced; the combustible products are mainly CO and H and, indeed, no charcoal remains at the end.   

       [pashute] is talking about pyrolysis - a different process, done with little oxygen, producing alcohols, phenols, hydrocarbons etc., and leaving plenty of charcoal.
spidermother, Nov 05 2012


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