Re: Wood is wood, biomass is biomass, check the density

["Paul S. Anderson" <psanders@ilstu.edu>]

Stovers,

Below is my attempt to understand an earlier message.  My words
might be very simplistic, and certainly common knowledge to anyone who
ever had a university class on combustion (and some on the list serve are
the professors of such classes).  But in the end, I think I ask a
couple useful questions.  

Paul

At 06:24 AM 5/30/02 -0600, Tom Reed wrote:

> From a practical
> viewpoint the real and bulk Volume energy density and Mass energy
> density  is MUCH more important in evaluating fuel value, handling
> difficulties, combustion properties etc.... 

More important than what?  I believe you refer to being more
important than "the
carbon content of the woods", but I would like confirmation of
that  belief.

Tom also wrote:
> For combustion (T
> >1200 C) the ash content and properties can be all important, less so
> for gasification (T < 1000 C), even less so for pyrolysis (T< 700
> C).  

Teacher, please help the neophyte.  Am I correct is saying:
1)  that pyrolysis ("the chemical decomposition by heat,"
ala Webster dictionary) that occurs at temperatures (unstated minimum) up
to about 700 C actually would not (or probably would not) product gases
that would be driven off from the biomass fuel.   In other
words, the biomass changes composition, but all of the molecules stay
within the mass.  

2)  that gasification (where gases are created and liberated from
biomass) occurs approximately between 700 C and 1000 C.  

3)  that what we regularly (commonly) think of as full
"combustion" really only kicks in when the temperature gets
above 1200 C.  

4)  And let me try to state how combustion is different from
pyrolysis and gasification:  
   a)  clearly pyrolysis and gasification are occurring
simultaneously with full combustion because they occur at lower
temperatures that must be reached prior to combustion taking place.

  b)  The gases created by gasification can
"combust", as is seen in the "secondary combustion"
in a gasifier stove.  We note that char (as in charcoal, which is
essentially just carbon) is a byproduct of that gasification
process.  And I assume that the temperature of the flame of the
secondary combustion is greater than 1200 C.  (Tom or others: What
is the average temperature range of the flame of secondary combustion of
the "typical" gases from gasifying of wood and other
biomass?  And is that flame temperature similar to the temperature
of burning LPG or other processed fuels used for cooking?)

  c)  Therefore, where Tom said "combustion", I want
to break down that word (or get a better word) to refer to ONLY what
happens as the temperature reaches and passes the 1200 C level.  I
BELIEVE (please correct me if I am wrong) that we witness the change of
the solid called carbon (as in the charcoal but also as in other carbon
compounds) into gasses that, with a subsequent mix with oxygen, will
yield CO and CO2 (and we gain the heat energy).  (I am sure there is
a formula for this, but I am trying to understand it in less technical
terms.)

  d)  Only then is any solid NON-combustible residue left
behind, and we generally call that "ash".

So, when Tom wrote:
>For combustion (T >1200 C) the ash
content and properties can be all important, less so for >gasification
(T < 1000 C), even less so for pyrolysis (T< 700 C).  

he was also saying:  for the gasification process, the ash
content and properties of biomass are less important.  

I would like to know "how much less important".  Multiple
choice:
a.  not much less important 
b.  meaningfully less important
c.  major-ly less important
d.  extremely less important.

I assume that the answers a,b,c,d will vary depending on the selected
biomass (maybe).  So please comment on some main ones like:
wood products (twigs, chips, sawdust pellets, etc)
seed-hulls 
other

My enquiry is rather qualitative, but someone might have quantitative
data about this.  The issue at hand can have significant meaning
concerning the usefulness of gasifier stoves.

Paul

Paul S. Anderson, Ph.D.,  Fulbright Prof. to Mozambique 8/99 - 7/00

Rotary University Teacher Grantee to Mozambique >10 mo of 2001-2003

Dept of Geography - Geology (Box 4400), Illinois State University

Normal, IL  61790-4400   Voice:  309-438-7360;  FAX:  309-438-5310

E-mail: psanders@ilstu.edu - Internet items:
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