joy677-ga,
Thanks for posting such an interesting question. I was aware of DCFC
technology, but this was a good opportunity to dive in more deeply to
its potential.
The main obstacle to developing DCFC is informational. There is so
little actual working experience with the technology -- and what is
there is fairly small scale -- that it's difficult to envision what
the main technological challenges of a full-scale DCFC would be.
Consider the following:
--A Google search for the exact phrase, "Direct Carbon Fuel Cells"
returns slightly more than 100 independent results:
://www.google.com/search?sourceid=navclient&ie=UTF-8&rls=GGLD,GGLD:2005-04,GGLD:en&q=%22Direct+Carbon+Fuel+Cells+
(There are about 1,000 results all told, but most are duplicates of one another)
This is a very meager collection of literature, and provides little to
go on in terms of evaluating the overall potential of the technology,
or the key stumbling blocks to its commercial viability.
Although the public labs like Lawrence Livermore have published some
good technical information on DCFC, the private companies treat their
technologies as proprietary, and have provided very little detailed
information on just what they have -- or haven't -- accomplished.
But whatever they've managed, it's still a very long way from
commercial scale operations.
--Here is a link to one of the actual working prototypes of a DCFC power generator:
http://www.esnips.com/doc/7d481846-52c4-46dc-a9ef-08efd4b15091/DCFC-celltech-power.jpg
--And here is another:
http://www.esnips.com/doc/1c0b3fc6-190d-443c-b4c8-b4d0f3abfc7c/DCFC-SARA.jpg
Click on [Original Size] to see the images at their largest resolution.
Again, it's obvious these are nascent technologies, with little
experience on which to evaluate the obstacles to scaling up to
commercial operation.
Having said that, several themes do emerge from the literature as to
some of the key challenges facing DCFC as a viable power technology:
--Beneficiation. The fuel that is most often envisioned as a source
of carbon for a commercial DCFC is coal. However, in order for the
coal to be suitable for use in a DCFC system, it must be cleaned of
ash, volatiles and impurities (chiefly sulfur), and must be prepared
as microfine particulates. Both these steps are energy-intensive,
that is, costly.
The energy demands for beneficiation impact the overall efficiency of
the technology. Many beneficiation processes that are effective
enough to de-ash coal to the required levels are themselves
demonstration technologies, so the overall costs and effectiveness are
not well documented.
In addition, beneficiation is also a fairly "dirty" operation, from an
environmental standpoint. Even if DCFC is as clean as its proponents
suggest, it's cleanliness must be viewed in the context of
'transferring' pollution to the beneficiation stage.
Similarly, DCFC enthusiasts talk about being able to achieve energy
efficiencies of 80% or higher, but these figures do not generally take
into account the energy demands of the coal clean-up steps. The cost
of beneficiation also adds to the overall costs of any coal-based DCFC
power generation system, making it more difficult for the technology
to achieve cost-competitiveness with convetional technologies.
--Agglomoration. Conditions within the DCFC fuel cell are such that
there is a tendency for the microfine coal particulates to cluster
together and form agglomorates. This is particularly true when
volatile gasses are released from the fuel feed...the interaction of
the relatively cool fuel and the hot gasses leads to reactions that
can cause clumping.
There has not yet been any large-scale demonstration that DCFC-type
particulate fuels can be fed into a system on a large-scale and over a
long period of time without serious problems occuring from
agglomeration of particles.
--Contaminants. No matter how clean the fuel stream, there will
always be some amount of impurities present that will produce sulfur
and nitrogen gasses, and other pollutants. Carbon monoxide generation
is also a concern. Again, there has been no large scale demonstration
that a DCFC system can operate successfully without producing
excessive pollutants that can add considerably to operating expenses,
and could conceivably render the technology non-competitive.
Another factor to consider regarding the viability of DCFC is CO2
emissions, though this may be more a policy than a technological
issue.
DCFC produces a concentrated stream of relatively pure CO2, and
because of the relatively high efficiency of the system, has lower
overall CO2 generation per MWH of power than with conventional
technologies. This gives DCFC a potential advantage over other
technologies *if* nations agree to set stringent limits on CO2
emissions from power generation. Currently, the move to limit such
emissions is more talk than action. If and when such limits are put
into place, these might provide a boost to DCFC technology
development.
Currently, DCFC technology does not yet offer such clear-cut economic
advantages as to have attracted large-scale attention and funding as
an alternative source of power generation. This is perhaps the
largest obstacle that DCFC will need to overcome if it is to become
the preferred energy technology of the future.
Here are some sources of information that may be useful to you if you
wish to read further on this topic:
http://www.llnl.gov/tid/lof/documents/pdf/307238.pdf
Direct Carbon Fuel Cells: Assessment of their Potential as Solid Carbon Fuel
Based Power Generation Systems
http://www.osti.gov/bridge/servlets/purl/891068-h5oSTE/891068.PDF
Carbon-based Fuel Cell
Final Report
http://www.llnl.gov/tid/lof/documents/pdf/322858.pdf
Direct Conversion of Chemically
De-Ashed Coal in Fuel Cells
I trust the information here fully answers your question. However, if
there's anything else you need, don't hesitate to ask. Just post a
Request for Clarification, and I'm at your service.
All the best,
pafalafa-ga
search strategy -- Google search on [ direct carbon fuel cell ] |
