[Gasification] Getting both heat and char .....

[Doug]

Hi Paul,Rolf and Colleagues,

This is to clarify Paul's questions. I hope the separations do not 
confuse too much.


 >Pyrolytic  gas can be quite wet so precise temperatures are risky to 
quote.
> Yes.  There is no scrubbing or drying or other preparation of the 
> pyrolytic gas.  In the TLUD world, the gases are usually created in 
> the 500 C to 650 C range.  And the raw biomass fuel might enter with 
> as much as 15% to 20 % Moisture Content (MC).
>
> If the MC of the raw fuel was lower (such as 5% MC), would that help 
> raise the temperature?

The short answer is yes, we don't need steam to displace gas volume.

>
> Hypothetical question:  Part A.   if the pyrolytic gases were cooled 
> to below 100 C, water could be removed by condensation, and we would 
> have lots of wood vinegar.   However, there would also be massive 
> amounts of tars and "gunk" being deposited also. However, the final, 
> non-condensed gases just might have the desired temperature when 
> combusted.   Those gases would be H2, CO, methane-and-related-gases, 
> and what else?
Cooling the gas is a waste of the heat that it contains. Any condensed 
tars, hydrocarbons, or vinegars may have applications, but also add to 
the technical difficulties for their collection. Their removal, other 
than moisture best removed by drying the wood, reduces the calorific 
energy of the pyrolysis gas. Difficult to calculate, but also adding to 
the gas heating value will be carbon particles. Normally we would seek 
to minimize these by using a cyclone, but ceramics need reducing 
atmospheres, or read that as carbon rich heated atmospheres, so carbon 
dust is great.
>
> Part B.  Alternatively, after the removal of the wood vinegar, perhaps 
> the remaining gases plus the reheated tars, etc. could be reheated to 
> become a dry, quality gas for higher burning temperatures.   All of 
> this would be with losses of thermal energy during condensation and 
> then the need to add thermal energy. Could this have benefits that 
> could justify the expense?
I think the previous answer covered this, but I see no benefit at all to 
this suggestion. At a later date after there is a system working, you 
will then have opportunity to extract condensates. Our experience tells 
us that as toxic black liquor, the less you have the healthier the 
working site. No exaggerating, it's a health and safety hazard.
>>
>> What I can tell you from experience, is that it always burns hotter 
>> than clean producer gas, upwards of 1,050C,
>>
> If that is the maximum, will this be sufficient for Rolf and his 
> friend to use?    There is no way to turn 1000 C into 1300 C, correct?
Not well explained, sorry. Clean tar free gas will not burn over 1,050C, 
but if the system design produces pyrolysis gas which has all it's 
hydrocarbons, then the temperatures will be upwards and over 1,050C, a 
basic tar test for cleaner specification gas,

>
> But your next words I do not understand.
>>
>> 13-1500C is a rough rule of thumb for gas exiting the combustion 
>> chamber.
>>
If you combust pyolysis gas full of hydrocarbons, then the flame 
temperature will be 1,300-1,500C.  One of the most difficult areas of 
combustion is that thermo-couples start going crazy over 1,300C. 
Expensive ceramic ones damage too easily, so once the TC melts, you know 
the higher temperatures are present, possible over 1,500C.


 >I am not understanding what that means.   The combustion chamber is 
the "burner" of the pyrolytic gases?

The short answer is yes if we were just creating heat. Ceramics like 
Rolf is seeking to fire, are done in a tunnel kiln, and the tunnel 
becomes the combustion chamber. The geometry is important to create the 
combustion phenomena, but to design this we first need a tunnel kiln to use.

 >>It has a very high radiation factor useful for refractory 
application, but the price for this is that you will get a high ash 
content in the kiln and flue dust emissions.

 >Something in the above sentence is not clear to me.   The "kiln" is 
part of the gasifier or is it where the materials are being heated?   
And the pyrolytic gases of TLUDs do not >have ash in them.   And I am 
not understanding the source of any flue dust emissions.

The gasifier is close coupled to the kiln, and the burner is mounted in 
this case, on the end of the tunnel kiln which forms it's own combustion 
chamber containing the ceramics. The spent gas has to exit the tunnel at 
some point, above the condensation temperature. May be the ash from the 
carbon dust will settle in the tunnel depending on combustion gas 
velocity. Usually, a correctly sized flue stack is required to assist 
with removing the exhaust gas, and this is where ash dust can become an 
emission. It would be good to put aside TLUD understanding, as they work 
on a totally different principle not relevant to this project need.
>
> Are your comments somehow referring to the FULL gasification processes 
> in downdraft gasifiers (pyrolysis AND char-gasification are both 
> occuring)?
No, Downdraft gasifiers more often than not make pyrolysis gas and need 
char extraction to work. Full gasification as you say, need minimum bed 
disturbance and between 1-4% of the fuel drops out as char. Rolf only 
has a downdraft engine gasifier for his first trials, and we should get 
plenty of pyrolysis gas out of that, at least for the first tests to 
fire the ceramics. Maybe we will have to extract char as well, but all 
that is still a long way off at this point.
>>
>> The actual combustion is complex, but achievable in a non regulated 
>> situation, emissions being the issue, both dust and toxic gas CO,CH4, 
>> and Dioxins. Combustion of these gases have been our focus for some 
>> 6-7 years, and current work at CalForest in California, is to use 
>> this gas to dry the incoming fuel to the charmaker.
>>
> The above sentences seem to indicate that your explanation is about 
> FULL gasification and not about only the pyrolysis process with 
> resultant charcoal creation.
We take raw producer gas from the Shasta gasifier, meaning hot cycloned 
hydrocarbon free downdraft  gas for the boiler green house application. 
This has high carbon dust content which burns to ash. This is a problem 
for the boiler, but just needs more cleaning cycles than anticipated.

The Charmaker is an updraft system and burns to waste the very dirty 
pyrolysis gas. The gas flare vertically from high stacks making them 
safer, as we have no space to work with them on the ground. The radiant 
heat cooks you from about 3-4ft, so the chances are, unless you have 
stood by an oil rig flare, many researchers just haven't acquired this 
type of experience from pyrolysis gas flares.

You might like to look again at the Fluidyne Archive last update showing 
the charmaker and gas flares in action. The bigger flares at higher 
output are not shown mainly due to us too busy keeping up with the input 
fuel flow.   Earlier updates show the Cyclomix burners and combustion 
chamber hooked to a heat exchanger, so there is plenty of info to brush 
up on  as we developed these larger gas making system components. When 
operational, we collect data from those points important to both the 
gasifier and process, including continuous gas analysis, which cannot be 
used for pyrolysis gas. (to dirty)
http://www.fluidynenz.250x.com/

Doug Williams.










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