[Gasification] [biochar] ICM gasifier project comes to a close

[doug.williams]

Hi Mark and Colleagues,

> The question I have (what have I missed?) is why the char from either
> pyrolysis or gasification, from identical feedstocks, would have higher or
> lower ash? 

There would seem to be the old issue of terminology at work here, and added to this all the variations of the processes being used. If the char is being made without air present to oxidize some of the char, then ash is going to be minimal, as will the pH.

 It was been explained to me many years ago, that char resulting from gasification (downdraft in our case), is highly porous and slightly activated. As a portion of the higher up char dropping fresh from the distillation zone is consumed to create the oxidation and exothermic heat to drive the whole process, this ash then cannot avoid entering the porous char as the two descend into the reduction zone. Possibly you could wash it out if there was a need to do so.

>I realize that feedstocks that slag on grates during gasification
> could affect this, but that aside: are we claiming that a ton of chips
> gasified v. a ton of chips pyrolyzed would have substantially different
> effects on soil pH? 

The only time I have seen slagging is when there is dirt or siliceous formations in the feedstock. Fast growing coppice tip wood and leaves are full of potassium and sodium, and these are high ashing fuels. You can also get higher ash in the gasification char if the beds are operating more in a combusting mode rather than oxidation. The amount of pH always affects how the growing medium behaves, so yes, there would be a measurable difference between the char types.

>Potassium hydroxide is hard to gasify; where does it go
> or why is it less available? 

Until the ash forms via oxidation of the char, it's not released, not coated with tar.

Or are we saying because gasifier char is a
> smaller (%) by-product--than pyrolysis char--its ash components will be at a
> lower concentration? 

It depends on who is saying what, and in which context. High density chars produced from a retort for cooking and coking applications should have in most cases, little or no ash at all. High density raw fuels passing through a gasifier, give you the higher quality chars with porosity and ash, which provide the soil bacteria with a habitat to process the nutrients. High density chars probably may not be the perfect bacteria habitat, but would help reduce soil particle agglomeration. There is always more to learn about these things if you need to know(:-)

>Certainly, kg-for-kg of feedstock the  total amount of
> ash will remain constant...won't it?

Without a doubt absolutely correct.

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The above comments have been made as a result of controlling ash formations resulting from high temperature gasification. More recent involvement with char making systems, and the expertise of those involved with end use applications, suggests that chars are not created equal, and we should be careful on how we talk about them, or recommend their application.
Hope this helps.

Doug Williams,
Fluidyne Gasification.




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