[Gasification] Gasification Operational Principles

[Oscar]

Hello Doug and list members.

Thank you very much for your comments. I deeply appreciate them and also the
time you've spent answering my queries.

"My ability to not satisfy everyone with these answers, is clearly evident 
from private criptic e-mails that this Forum never sees. " 

Never mind about satisfying everyone. Experience says that it is IMPOSSIBLE.
Most important is hear, read and try to learn from those, who having more
experience, has something to say even if it does not match our knowledge or
point of view.

...." found that if you use calculations only, you are in for a rude shock,
dealing with the variables of biomass fuels." 

I wholly agree with you that calculation is not all that is needed to make
something work in the engineering field. However having some reliable
estimates to start with, is something I really appreciate in order not to
get lost in the jungle of equations, number, figures etc. Experience and
hands-on the stuff will undoubtedly say the last word. To me, a
baby-beginner in biomass gasification, is important having engineering
guides/estimates capable of helping me in ensuring a good design and
results.

...." If what you suggest is possible, then I would wonder why so few
gasifiers built to calculations by students cannot make a tar free gas. It
is also important to ensure that you are applying the correct calculations
to the appropriate gasifier, because I see students crossing open cores with

information relating to Swedish designs similar to Imbert." 

Well, when I suggested it I never thought about students being capable of
such hard work. Besides my involvement in the biomass gasification project I
am also calculus's teacher at university so I know students very well and I
do know their rather limited boundaries in approaching so complex problems.
I was really thinking on experts/experienced people able to throw some light
on this issue and in position of telling me how far or close I am from
reality of gasification. Such suggestion comes from hours trying to
understand what is behind superficial velocity. Unfortunately I have not yet
the possibility of sustaining it through my own experience. I hope maybe in
the future I can get at it.

..." A gasifier is certainly designed working from a known parameter, but if

there is little or no understanding of how packed carbon beds behave in a 
high temperature environment, what do you change to maintain the tar free 
gas making, or indeed keep it making even dirty gas?  Can you specifically 
state which gasifiers can be built to your understanding of applying these 
principles, and how variations are controlled, or are you referring to it as

a prediction tool, rather than one for proven design?..." 

I wholly agree with you. I am referring to having a reliable estimating tool
to start with, which at the same time MUST BE checked up by experience and
being capable of guarantying a good design which can afterwards be
optimized, of course.

...." At this point, I should say that not all information of how gasifiers
work, or should be designed is in the public domain, and commercial
gasification knowledge has to move on from prior art. It is one thing to
make a gasifier that can work in a laboratory situation for an hour or two,
using calculations, but this knowledge alone rarely makes it fit for
commercial application." 

Right, I got your point. However currently it seems to me there are many
proven technology, for example in the chemical process industry, which start
at a laboratory stage and some years later turned out to be a real thing, a
dream comes true. Of course not before the lab-work being supported by a lot
of hard work experience and hands-on the stuff. 


..." "IF" you are aiming for tar free gas making, all sizing, including
output, revolves around the fuel size in it's raw state, it's then
structural integrity as a charcoal in the oxidation phase, it's size in the
reduction zone, and finally, the amount of heat available for the
endothermic demand of the reduction zone. Flow resistance is more than just
about the interstitial spacing of the fuel, and is the point where gasifiers
work or fail, at least in their ability to make clean gas continuously..."

Yes, absolutely RIGHT.

..." researchers in developing countries tried to build their own from 
literature, not one real success story was reported for tar free  wood
gasifiers.." 

Yes agree with you. Trying to make something really good only having
literature, without any real experimentation at some stages, it only lead us
to no real success.

Thanking you one more time for kindly responding to my request.

Kindest regards.

Oscar.




 





    

  


  

-----Mensaje original-----
De: gasification-bounces at listserv.repp.org
[mailto:gasification-bounces at listserv.repp.org] En nombre de doug.williams
Enviado el: lunes, 03 de marzo de 2008 17:06
Para: Discussion of biomass pyrolysis and gasification
Asunto: Re: [Gasification] Gasification Operational Principles

Hi Oscar,

I will refine my comment:

>" I do not use that measure to establish the correct
>operating parameters, as flow rates are controlled by resistance set by the
>fuel size...."

This comment relates specifically the downdraft gasifiers with multi air 
nozzles and throat, and having had the dubious benefit if spending thousands

of hours upto my elbows in charcoal, ( I really am a slow learner) found 
that if you use calculations only, you are in for a rude shock, dealing with

the variables of biomass fuels.

>As far as my modest knowledge let me see it, I think both are
>linked or strongly interrelated in such a way that fixing one of them the
>other gets automatically fixed.

I agree absolutely, but what I say is that you must establish the fact 
before you can measure the velocity, not the other way around, but in fixing

either, that does not automatically give you a working gasifier.

>Superficial velocity let us get an estimate
>of gasifier diameter along with its height so it should bear influence on
>gas flow rates and its relationship with the resistance sets out by fuel
>size which at the same time should match reactor dimensions.

If what you suggest is possible, then I would wonder why so few gasifiers 
built to calculations by students cannot make a tar free gas. It is also 
important to ensure that you are applying the correct calculations to the 
appropriate gasifier, because I see students crossing open cores with 
information relating to Swedish designs similar to Imbert.

>At the same
>time superficial velocity is a variable which can be quantified for
>predicting gasifier sizing and operating parameters,
..
A gasifier is certainly designed working from a known parameter, but if 
there is little or no understanding of how packed carbon beds behave in a 
high temperature environment, what do you change to maintain the tar free 
gas making, or indeed keep it making even dirty gas?  Can you specifically 
state which gasifiers can be built to your understanding of applying these 
principles, and how variations are controlled, or are you referring to it as

a prediction tool, rather than one for proven design?

> however I don't see how
>easy it could be having a number or quantified estimates of flow rates
.controlled by resistance

At this point, I should say that not all information of how gasifiers work, 
or should be designed is in the public domain, and commercial gasification 
knowledge has to move on from prior art. It is one thing to make a gasifier 
that can work in a laboratory situation for an hour or two, using 
calculations, but this knowledge alone rarely makes it fit for commercial 
application.

"IF" you are aiming for tar free gas making, all sizing, including output, 
revolves around the fuel size in it's raw state, it's then structural 
integrity as a charcoal in the oxidation phase, it's size in the reduction 
zone, and finally, the amount of heat available for the endothermic demand 
of the reduction zone. Flow resistance is more than just about the 
interstitial spacing of the fuel, and is the point where gasifiers work or 
fail, at least in their ability to make clean gas continuously.

 If I may step back to the 1970's, when gasifiers of European origin (built 
using all the known calculations) were sent out to developing countries, and

researchers in developing countries tried to build their own from 
literature, not one real success story was reported for tar free  wood 
gasifiers at the 1985, 2nd International Gasification Conference, held in 
Bandung, Indonesia. If anything, it highlighted the need for other types of 
gasifiers, away from the traditional European systems, and the variations 
you see today originated from that time. What has not changed, is the 
ability to make tar free gas easily despite all the knowledge of 
calculation, so emphasis has changed to gas cleaning, rather than gas 
making.

>Can you please further a little bit more on these aspects. I would really
>appreciate your comments.

My ability to not satisfy everyone with these answers, is clearly evident 
from private criptic e-mails that this Forum never sees.  Gasification has 
many variations to how it might be presented as a written technology, and 
even that has value to someone trying to give explanation to their own work.

I have said many times, that I can share only so much, being restricted by 
commercial obligations, and contribute only as time allows.

Doug Williams,
Fluidyne.




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