RE: Terms used in incineration

[ttweed@wildrockies.org (Tony Tweedale)]

>He sent the following response:
>
>No. They don't represent a source of combustion of aromatics in the presence
>of chlorine compounds.  ESPs are used to control very small particles, and
>work at high temperatures, so they tend to be used to control  emissions
>from municipal waste incinerators, ore smelting furnaces and cement kilns,
>all of which themselves can generate dioxins at varying rates.
>
>ESPs actually catch the particles on which dioxins attach themselves, so
>they reduce emissions of dioxins.
----

hi--as I understand it, ESPs create significantly more dioxins than other
a.p. control eqpmnt, becuase flue gas residency times are greater, which
also favors lowering the T to the range where they are created (~200-500 d.
C).  Those wopould be the key variables for creating dioxins in the air
flow.  Particles whose surface (especially if metals are adhered)
contribute to the creation of dioxins play a role, and I believe a lot of
dioxins are created on ESP particulate that spends more time escaping the
ESP, thus magnifying those key variables.  I can't speak for the
differences in dioxin formation in the trapped ash of different control
devices.

Compared to a cyclone, where the airflow escapes rapidly at higher T, and
perhaps the C & Cl disperse in the atmosphere before they can form dioxins.
I imagine simpler, smaller o-cl's are formed, along with greater amnts of
HCl, the predominant chloride (Cl-) salt that exists in the energetic
envirinment f a combustor.

BTW, this brings up another mistake or severely misleading implication in
the above, that aromatics are necessary for doxin formation.  I wont bother
citing any literature since it is totally accepted that dioxins form 'de
novo' from chloride reacting w/ carbon.  My guess is that their formation
from ceratin aromatic (ring) precursors that favor di-benzo dioxin & furan
dual ring systems are much more imortant in lower T environments such as
chlorphenoxy herbicide (an ideal aromatic precursor) reaction vessels...
--

I know little about smelting, but I see the USA's Dpt of Energy's publicity
for modern Al smelting talks about the imprtance of removal of chloride
(and other) salts to reduce need for recasting.  Perhaps this is the
chlorine industry's permanent nighmare rearing its head again--the
corrosivity of chlride salts (such as HCl) to industrial equipment (a
problem that prevents chlorine using pulp bleachers from reusing any of
that waste water, a major expense (both in pumping water and in biological
wastew ater treatement for discharge)).  In any case, the brochure speaks
of a Selee Corporation detection probe and chloride salt filtering system
being developed for the AL industry.  BUt as to magnessiou,. I guess if it
is processed in the form of MG shloride, the amounts of chlorine might be
overwhelming...

Tony Tweedale

Causality is a concept not subject to empirical demonstration. -David Hume
(1711-'76)

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