[Gasification] Retort construction, hydrogen embrittlement, and similarity in appearance between the motorcycle gasifer and the gasifier Peter is working with.

[Ken Basterfield]

Drew,
As  an apprentice, I remember we had steel strip annealing firnaces that
used hydrogen for the annealing atmosphere.
The steel had slightly raised silicon content for use in motor and
transformer laminations. I don't recall any embrittlement problems. 
Ken


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-----Original Message-----
From: gasification-bounces at listserv.repp.org
[mailto:gasification-bounces at listserv.repp.org] On Behalf Of drew
Sent: 31 January 2007 20:38
To: snkm at btl.net; gasification at listserv.repp.org
Subject: [Gasification] Retort construction, hydrogen embrittlement, and
similarity in appearance between the motorcycle gasifer and the gasifier
Peter is working with.


Hi Peter and List

    An issue that has been problematic for me in working with retorts is 
that of hydrogen embrittlement in steel.    Especially in thin steel 
sheets it has been problematic.    When you have hot steel (red hot is 
hot enough) and a low oxygen high hydrogen gas present the hydrogen can 
migrate into the steel (the low oxy environment conspires to remove the 
iron oxides which might have reduced the hydrogen penetration), where 
apparently it bonds with the carbon present to create methane at many 
times the constituents original volume.   This leads to cracking and 
rapid corrosion (in steel corrosion rates are directly related to both 
temperature, and strain so the combination of heat, and the tension 
caused by the methane is double trouble).    I suspect that this will 
give any steel retort that passes 450F for extended periods a short 
life.   Most stainless steels are corrosion resistant only because of 
the thin layer of oxides formed on the surface, these oxides are quickly 
stripped of their oxygen in high temp low oxy environments and rapid 
corrosion takes place even at low temperatures.     The use of a easily 
removable, and easily replaceable reduction tube in imbert gasifiers 
shows a good strategy for dealing with this type of corrosion, once a 
system was proved perhaps a ceramic tube could take it's place?   With 
retorts the large surface area needed to transfer the heat and the 
expansion/contraction of that large surface area seem to make that path 
a difficult one, perhaps John F.  would comment on his strategy for 
dealing with this in his continuous retort system?   Systems like his 
would seem to be a great match with micro charcoal gasifiers allowing a 
larger scale controllable process.to do the dirty side of the process 
(extraction of hydrocarbons), with the clean relatively pure char used 
in small gasification plants or returned to the soil as an amendment.   
    I wonder if anyone notice the similarity in appearance between the 
WWII era motorcycle gasifier pics I posted to the Chinese gasifier Peter 
has been testing?    I mistakenly called it a charcoal gasifier, but 
after rereading the article realize the author clearly states it is 
running very well on beach wood scraps.   

http://en.wikipedia.org/wiki/Decarburization

http://en.wikipedia.org/wiki/Hydrogen_embrittlement

All the Best
Drew

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