Re: GAS-L: Dechlorinated char

[LINVENT@aol.com]

In a message dated 9/25/02 9:25:13 PM, graeme@powerlink.co.nz writes:

<< 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 >>

Dear Doug and others,
    Dioxins are created under the conditions which Doug stated and include 
the necessity of particulates of a certain size and residence time and 
temperature to form in a full combustion system. Oxygen is needed for the 
chlorine dioxide formation. 
    These conditions do not exist in a gasification system. Research has sho
wn that gasification of liquors from pulp mills actuall destroys dioxins 
already present in the feed stream. The reason for this is that hydrogen 
strips the oxygen from the oxygenated chlorine present and forms hydrochloric 
acid as opposed to dioxins. 
    We have demonstrated gasification of MSW ( from San Diego) with no 
dioxins in the ash. Determination of dioxin content in the ash is an 
indicator of it's presence in the reaction. Although no gas analysis was 
performed on this test, the lack of dioxin in the ash showed no dioxin 
formation. 

Leland T. Taylor
President
Thermogenics Inc. 
7100-F 2nd St. NW Albuquerque, New Mexico USA 87107 Phone: 505-761-5633, fax: 
341-0424, website: thermogenics.com. 
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