Half a croissant, on a plate, with a sign in front of it saying '50c'
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High Energy Wood Gasifier

Gasify with steam instead of air
  [vote for,

An ordinary wood gasifier turns wood (or other solid hydrocarbon fuel) into gaseous fuel, for burning in an engine. However, the gas produced has a very low energy density, mostly due to having a large amount of nitrogen in it. (The nitrogen comes from the air that's fed into the gasifier). By using a nitrogen-free oxidizer, we can produce a fuel with higher energy density. If its temperature is high enough, steam act as an oxidizer... therefore, that's what I propose:

Start with a "regular" gasifier, with all of the normal accessory components.

Add the following four components: Two high efficiency counter current heat exchangers (HX1 & HX2), a combined fuel mixer / combustion chamber (C), and a combined boiler / superheater (B).

All of these components (wherever it's reasonable to do so) should be constructed from, or surrounded by, high quality, high temperature, insulating materials (fire clay comes to mind).

In normal operation, there two main streams of fluid and one minor stream of fluid: Fresh air from the atmosphere moves through HX1, C, HX2, HX1 and back to the atmosphere. Water moves through B, HX2, the gasifier, back through B, and onward to the engine (as fuel). Some of the fuel coming out of the gasifier is fed into C.

The air is heated on it's first pass through HX1, and as it goes through C, and cooled going through HX2 and through HX1 the second time.

Similarly, water is heated, boiled, then superheated as it goes through B, superheated some more as goes through HX2, cooled as it passes through G and chemically reacts with the carbon there to transform into "water gas", and cooled further as it passes (uncombusted) through the superheater, then the boiler, of part B.

Of the original gasifier's other parts, the cyclone is placed immediately downstream of the gasifier, before the fuel splits into two streams (to C and B), and the radiator and fine filter are placed downstream of B, after the fuel gas has been cooled by moving it's heat into the feed water.

Wood chips (or whatever) can be added, and ashes removed, via airlocks [link].

After the gaseous fuel has been used, the water that was added at the beginning of the process will have been re-created. Cooling that exhaust will produce liquid water. If the engine and gasifier are reasonably close to one another, that water can be re-used, reducing the total amount of water needed.

goldbb, Mar 08 2010

Gasifier with airlocks for automatic addition of fuel http://www.freepate...ne.com/4029481.html
Credit for this link goes to Twizz, who found it for this idea's original incarnation [goldbb, Mar 08 2010]


       There are, of course, three main purposes for this idea...   

       Firstly, to fuel a vehicle with wood. Since the fuel has at least double the energy density of regular "wood gas," the vehicle would have at least double the power of a vehicle powered by a conventional wood gas generator.   

       Secondly, to produce a fuel for a home's backup power generator. In this case, the higher energy density of the fuel means that a smaller engine could be used, reducing the capital cost of using wood for electricity.   

       Third, to produce feedstock for a gas-to-liquid fuel system... eliminating the nitrogen and increasing the amount of hydrogen should allow a better quality of liquid fuel to be made.
goldbb, Mar 11 2010

       This fuel is extremely dangerous, akin to how electically splitting water into pure hydrogen and oxygen and then storing that mixture could explode with more than twice the force that either gas alone is capable of. Reducing to liquid form may bring risk to an acceptable level.. Will have to dwell on this a bit to understand how the steam will help with anything but making a watered down mess.
AutoMcDonough, Mar 11 2010

       [AutoMcDonough] A stoichiometric (2:1) mix of gaseous hydrogen and oxygen will implode if ignited, not explode, and is perfectly safe to store as long as precautions are taken against the introduction of surplus oxygen from the atmosphere.   

       [goldbb] My impression from recent research is that steam charging of gasifiers is well baked, with the same end goal you propose.   

       I'm not sure the water coming out the other end of the process will be pure enough to be recycled. I assume it would have a substantial load of muck.
BunsenHoneydew, Mar 19 2010

       Actually, an oxygen/hydrogen mix will explode, but will rapidly shrink immediately afterward if the surroundings are cool enough.   

       Regardless, the process I describe is producing a mix of hydrogen and carbon monoxide (not oxygen), which can't burn or explode unless an oxidizer is mixed in.   

       Using steam for gasification might be baked, but compared to what I've found on the web, this is probably the simplest steam charged gasifier that utilizes the sensible heat of the syngas.   

       If all of the soot is removed before the fuel is fed to the engine in which it will burn, then there should be no impurities in the engine's exhaust, and thus no muck.   

       If there are particulates in the engine exhaust in spite of filtering the fuel... well, we can always filter the exhaust before cooling it, or filter the water after it's condensed.
goldbb, Mar 22 2010


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