[Gasification] engine

[doug.williams]

Toby,

I cannot discuss something without first knowing what you parameters are for 
you idea.

You say:

>Thanks for the information.  If the nitrogen is as high as 50%,  wouldn't 
>the engines power be much less than if it were at >15%.

Less nitrogen improves the gas quality, so the power would be more, not 
less.

>You missed my point about the second stage.  The thermal energy is there, 
>if that first stage is dry fuel and directly fires a >second stage at 
>higher temperature.

You can only produce higher temperature if you use air containing the 
nitrogen.
Dry fuel can mean anything, and in practice is hard to control the moisture 
content. Usually if you can get the wood to 15%, then you can get the higher 
oxidation temperatures, depending on the gasifier design. If you oxidize the 
wood to the best possible temperature, you will get about 12-1500C, and this 
gas will be CO2. If this enters a second stage containing wet wood, the 
temperature will drop considerably, bearing in mind that the wet wood has to 
be constantly replaced. The problem here is, that you will not be making any 
CO, and the hot CO2 will only drive off pyrolysis gas, not hydrogen. If at 
best you could get it to work to that stage, then what you get is a charcoal 
build-up in this secondary chamber, because there would not be enough 
exothermic heat available to drive the reduction process, and consume the 
charcoal to make CO. You would have a lot of CO2, CH4, possibly some H2, and 
nitrogen.

 > I don't mean to overdo it, but instead control the feed so stage two bed 
temp is 1500 or so.  Building a cracker will >obviously need refractory and 
insulation and more gas cooling.

I can only conclude you are thinking of some other sort of process, as there 
is only one source of oxidation, air and it's nitrogen diluents, and this 
has to provide the exothermic heat for all the process. You would be hard 
put to crack producer gas in a separate cracker, no matter how you build it.
Hope this helps,
Doug Williams,
Fluidyne.




Thanks,  Toby Seiler



"doug.williams" <Doug.Williams at orcon.net.nz> wrote:

Hi Toby,

You ask:

> Is the compressability of the gas affected by the amount of nitrogen in
it?

The short answer is no, if talking specifically about producer gas. On
average, there can only be about 50% nitrogen in the gas. The combustible
gas, CO, and H2, will ignite when the compression temperature reaches 1128F
for CO, and 1060-F for hydrogen. As a mixture, it will ignite at around
600C, and you should not forget, that you must take into consideration the
operating temperature of the engine, as over heated engines will increase
the risk of pre-ignition.


> If the gas had higher hydrogen content and lower nitrogen, would you
> expect it to precombust more or less? How would >compression ratio be
> affected?

The same answer applies as above, and the only way to prevent premature
ignition, is to lower the compression ratio. This is why most purpose gas
engines are around the 12.5:1 ratio.

> Jim, how about putting another stage in your setup? Setup a chamber that
> feeds wet fuel into a hot zone created by the >hot gas of stage one,
> under very precise manual control. Flare it off and compare. I think the
> higher water content can be >made into an advantage in reducing nitrogen
> and increasing hydrogen for your engine feed gas.

You cannot add water to a wood gasifier to increase the hydrogen content of
the gas. Even at 15% moisture content, a surplus of water exists that cannot
be cracked into H2, and this ends up as condensate when the gas is cooled.
As Greg Manning pointed out, it takes heat energy to thermally crack water,
nothing less than 1,000C, or all you get will be steam.

Hope this sorts your thinking.

Doug William,
Fluidyne Gasification.








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