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Tom Reed,
(Tom has been baiting me on the feeding issue for
some time so I guess it's time to respond.)
Your conclusions regarding the pressurized
gasification of bagasse in Hawaii are rubbish.
Your cost figure is, I believe, grossly
exaggerated. It's like the fish that grows in the
telling.
Your comment implies that it was all "wasted"
public funding and does not recognize the investments and contributions made by
private companies to the technology development. The experience was costly, there are aspects of the project that appear
to be wasted, but I wouldn't say that the whole effort was
"wasted." Since 1997 I have seen the experience from Hawaii productively
applied to both research and industry in a variety of applications, including
some of your own. Other publically funded projects have also benefitted from the
experience that people involved in the Hawaii project have carried forward. For
those who participated in it, and for others who have never heard of it, the
project was useful. For those who had nothing to do with it but watched
from the sidelines I'm sure that it was considered a wasted
effort. As you well know there are
technological risks in pressurized gasification. I happen to believe that it is
an appropriate use of public funds to help find ways to offset those risks.
The Hawaii project was cancelled for a combination
of reasons: political, economic and technological. The economic circumstances
that made the project look interesting in 1989 had changed significantly by
1997. Today the host facility, a sugar mill, is permanently closed. The ultimate
goal of combined cycle power generation at some of the world's 900 sugar mills
began to dim even by 1995 when the gasifier first operated. What began as a
promising Princeton "thesis" in the late 1980s began to lose its glow. How many
commercial biomass gasification IGCC plants are operating today, let alone on
bagasse? All current efforts are publicly assisted development
projects.
On the technology side there
were modifications in several areas that had to be addressed to continue
the project: gasification and feeding, hot gas handling, and in the service
island, the utilities that keep the plant going. The feed system was a
convenient scapegoat. The principal technology participants (GTI and
Westinghouse/Siemens) felt that we had practical solutions and wanted to
continue the work. But without a host (among other things Hawaii was in an
election year, hence no support there) or convincing economic benefits, the
political hurdles couldn't be overcome.
It is possible to feed gasifiers under pressure but
it can be complex and somewhat more costly than most projects can afford.(That
is also true, by the way, for pressurized pulping and chemical processing of
biomass.)
In the first phase of the Hawaii project we (TR
Miles) designed and built the 75 MMBtuh enclosed flare which by all
accounts performed as expected. The feed system was a (Sunds Defibrator) plug
screw system with almost no feed preparation ahead of it. In retrospect the
designers in Phase I would have benefitted from the modifications that we made
to prepare the fuel in Phase II. To credit the feed system suppliers, there was
no opportunity for them to improve on the pressurized plug screw
system with the experience obtained in the first phase of testing.
In the second phase the project was under different
management. We (TR Miles) modified the feed system to a lockhopper with a
pressurized metering bin, subject to some constraints that turned out to be
crippling. We had used the lock hopper systems successfully in a dozen
applications up to 125 tpd and 300 psi. Successful systems have
redundancy, which we were not afforded in Hawaii due to budget limitations. We
had just five months to almost completely modify and test the gasification
system so that when feed system (or other) failures tripped the
gasifier during the first several tests we had no time to make the
appropriate modifications. Nor could we make essential changes to other parts of
the system. We had to vacate the site and await the next phase, which never
came. We did, however, have several productive runs that allowed us to
document the performance of the system and plan the necessary
changes.
In my opinion, after several years of experience
with commercial scale gasifiers, melters and combustors, the gasifier (GTI
RENUGAS) worked extremely well during the many hours that we did operate. The
scaleup was successful. Gas quality, BFB control, etc. all eventually
worked very well. The (Siemens/Westinghouse) hot gas cleanup system also worked
very well. We also came away with a clear concept of how we would design a
pressurized feed system for bagasse.
Many organizations have worked on feed system
designs. We can design feed systems that will operate at turbine
pressures. There are good gasification systems available. But is there a
need? More than one company has backed away from pressurized biomass
gasification system development after substantial investments. When you look at
the real costs of IGCC systems I don't think you'll find that the feed system
is the principal constraint. For the
next several years BFB and travelling grate boilers will be the
investors principal choice. Low pressure gasifiers will be used
for difficult fuels, cofiring or for NOx reburn.
Regards,
Tom Miles
----- Original Message -----
Sent: Tuesday, February 05, 2002 5:20
AM
Subject: Re: GAS-L: maximum
pressure
Dear Leland and all:
Many projects have gone belly up because of feeding problems (ie
Hawaii, cost ~ $50 M and 15 years of wasted technical effort, sunk by bagasse
feeding problems).
If we pelletize all biomass for high pressure use
first, it can probably be fed using the reliable coal pressure feeding
technologies that have been standard for 100 years.
While most pelletizing today is for sawdust for the new automatic
pellet stoves, there is also significant pelletizing of peanut shells and
bagasse - both excellent candidates for high pressure feeding.
Onward... TOM REED
BEF GASWORKS
In a message dated 2/1/02 12:25:08 PM Mountain Standard Time,
LINVENT@aol.com writes:
Dear Bill,
The high pressure
gasification of biomass has been done on a large scale
at the Hawaii
project where sugar cane bagasse was fed into a high pressure
system
with oxygen feed. The recent offerings from the DOE have requested low
pressure gasification technology to deal with the material handling
problems
into and out of the gasification system at pressure.
Considering that the DOE
was a major sponsor of the Hawaii project, this
is an interesting
philosophical change.
The major
benefit to high pressure is not having to compress the gas to
feed into
a turbine which operates at 150-350 psi. Compressing the gas after
gasification is a significant parasitic load.
There are ways to deal with the power generation
without having to worry
about pressurized systems which work out very
economic.
Sincerely,
Leland T. Taylor
President
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