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Start with a device very similar to a wood gas generator, and fill it up with wood chips.
During system startup, supply the device with air, and generate producer gas.
Mix this gas with air, burn it, and use the heat to boil water, and further superheat the steam to very high temperature.
Use
this superheated steam to replace the air being fed into the device.
If the steam is hot enough going in, the charcoal shouldn't cool below the temperatures needed for gasification to occur.
Once the process has switched from air injection to steam injection, the generated gas is split into two streams, one for steam creation (to sustain the process), the other for fuel.
The fuel stream can be (partly) cooled by passing it through a heat exchanger with the air that will be used for combustion.
If the fuel is to be used in an internal combustion engine, additional cooling would be done using a cooling tower.
.
After the gaseous fuel has been used (burnt for heating, or in an engine), the water that was added at the beginning of the process will have been re-created. Cooling that exhaust will produce liquid water, which can then be re-used, reducing the total amount of water needed.
Baked and patented
http://www.freepate...ne.com/4029481.html
like this [Twizz, Sep 24 2009]
[link]
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Does anyone know how hot the steam would have to be heated prior to injection, for this to work? I'm thinking between 600C and 1200C, but that's a very wide range :) |
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Did you google 'blue water gas' before posting? |
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Apologies if I'm missing something, but the patent appears to be for an identical process. |
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I'll admit that I overlooked that patent when searching... however, it's not *quite* the same. |
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Specifically, in the linked patent, a portion of the generated water gas is used to heat the retort that the gasification is taking place in: |
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/An externally heated reflux chamber formed by a sealed retort forming a vertical column is heated to a temperature of approximately 1200° C./ |
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Whereas in my idea, a portion of the generated water gas is used to heat the *steam* that goes into that retort. |
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Although the results are probably very similar, I would expect to be able to heat the steam using a high efficiency counter current heat exchanger, which would consume much less fuel than heating the outside of the retort, since the retort is basically a cylinder, and thus has relatively little surface area. Less fuel burnt equals more fuel for use. |
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Also, by heating the steam, instead of the retort, it becomes easier to insulate the retort. In fact, we could probably build the retort (for my idea) out of refractory bricks... something which can't be done with the patented idea, since refractory bricks are good insulators. |
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Also, there's no suggestion in that patent that the air used for combustion might be preheated in a heat exchanger with the portion of the water gas which isn't going to be used to sustain the process. |
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A further improvement, both to my idea, and for the patented idea: |
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Use pressure swing adsorption (PSA) on the generated water gas, to create two new gas streams. |
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One gas stream from the PSA device would have a higher concentration of hydrogen, and less carbon monoxide, and the other would have a lower concentration of hydrogen, and more carbon monoxide. |
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Burn gas from the stream with the higher level of carbon monoxide to create the heat needed to continue gasification, and send the hydrogen-enhanced stream onward as fuel. |
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The total amount of energy needed to maintain the gasification process will remain the same, but the produced fuel will have a higher ratio of hydrogen to carbon monoxide than it would have without the pressure swing adsorption process. |
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More hydrogen = better quality of fuel. |
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If PSA generates more carbon monoxide than is needed to produce the heat needed to keep gasification going, we can use that extra CO to produce more hydrogen, using the "water gas shift" reaction, where steam is added to CO, and produces H2 and CO2. |
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This could either be done by re-injecting the CO into the gasifier, or by using a separate device. In either case, another PSA device will be needed to separate out (and discard or sequester) carbon dioxide produced by this. |
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