[Gasification] Making char vs producer gas

[Peter Davies]

Thanks Doug, given the level of prior art reinventing the wheel is an 
occupational hazard. Yes we have observed what you describe, the point 
of differentiation though is where we were starting on straight (dry) 
wood chips each run rather than charcoal from the previous run. It 
became clear that substantial improvements in gas calorific value and 
useful volume were possible that we seemed to be missing out on. It was 
study of this that led to the refinements in design we now enjoy the 
benefits of.

Cheers,
Peter


On 3/13/2014 6:37 PM, Doug wrote:
> Hi Peter and Gasification Colleagues.
>
> On Thu, 13 Mar 2014 10:22:02 +1100
> Peter Davies <idgasifier at gmail.com> wrote:
>
>> snip<
>>   Part of
>> the development path we followed was understanding why with our early
>> pilot systems gas the quality was higher in the period immediately after
>> start-up when the system had first settled, then declined to a lower
>> equilibrium, conventional wisdom being that this was a bed porosity
>> change over time (ash/fine particle build up). We found this was only
>> part of what was going on, hence the advances we have made.
>> snip<
> You describe a normal behaviour for packed bed gasifiers. They start up on quality char made overnight from the endothermic heat released on shut down. There are always situations where fuel moisture will condense as it cools then run down the hopper walls and saturate the start-up char. It's good reason to use fuel as dry as possible, then stop the gasifier at a lower fuel level, never with a full hopper.
>
> Dry start-up char will get the exothermic heat going quickly to be available to carbonise the incoming raw fuel, then as the heat budget begins to build, the whole gasifier must then become heat soaked before the exothermic heat can return to the gas making. If you had a gas analyser on line with appropriately placed T.C.'s, you can watch the two lines of data swapping places in almost real time. Gas analysers measure after the event, while T.C.'s are as it happens. The trick is to correlate this data by watching the bed movement and it's colours.
>
> Bed dynamics like you describe do cause problems, but these are also factors of poor design and process understanding. How individual development programmes deal with this decides their fate, but pleased to hear that all this is behind you. We need winners, not egg on our faces(:-)
>
> Hope this might be of assistance.
>
> Doug Williams,
> Fluidyne Gasification.
>
>

-- 
Peter Davies
Director
ID Gasifiers Pty Ltd
Delegate River, Victoria
Australia
Ph: 0402 845 295