GAS-L: Dechlorinated char

["Graeme Williams" <graeme@powerlink.co.nz>]

Dear Mr Fujiura

Your question regarding how to dechlorinate Refuse Derived Fuel (RDF) char
hasn't had much response from the Gasification List, possibly you have had
private responses.  There should be much more awareness of RDF disposal and
conversion technologies, and more importantly the potential environmental
problems that can be created in ignorance.

We know you plan to pyrolise the RDF but that doesn't tell us if this is
achieved via partial combustion or external heating of the fuel mass.  This
is important, as it determines the toxic nature of the char and could become
really hazardous waste.

If partial combustion is used, the chlorine bonds to the benzine ring a
process that is enhanced in the presence of moisture and an alkaline
environment.  If this chemistry (now dioxin) enters or passes through the
low temperature combustion zone the dioxin becomes fixed as an ash particle,
toxic, soluble , and impossible to separate out of the char.

When the pyrolysis is achieved by indirect heating, the chlorine still bonds
to the benzine and becomes locked into the char.  In both cases the char
should be considered toxic, and to my knowledge thermal separation is the
only way to render the char to a safe state.

However, having said that, for it to work in a gasifier as I stated in my
first response to your question, you need carbon.  By removing the
volatiles, the remaining carbon will be proportionally less than the clay
fillers and other non-combustibles found in RDF, making it difficult or
impossible to gasify, or dechlorinate.

Although a number of reports exist stating that pyrolysis and gasification
are superior technologies for RDF disposal, you don't find much actual
useful information in the public domain on how to achieve it.  Those
companies who claim success in RDF disposal naturally wish to protect their
commercial interest and are unlikely to offer advice to a potential
competitor.  If pyrolysis is your choice then you may find that you will
have to develop your own separation or waste stabilization technology.

As an alternative to pyrolisation, gasification of  RDF seems to resolve the
dioxin problems, but then the size of the process is smaller and technically
demanding, but it makes great gas.

The above information has been acquired  from our work with RDF that began
first in 1977, again in 1986-7,and continues today in Canada (along with all
the tests).

This doesn't help you much but it does, I hope, give you a better
understanding of the potential toxic problem you are endeavouring to create.

Doug Williams
Fluidyne Gasification.


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