1 October 1997
(1) Chlorinated dibenzo-dioxins (PCDD) and dibenzo-furans (PCDF) can be generated with
small amounts of chlorine present.
(2) The formation of these complex chlorinated hydrocarbons can occur in the combustion
process and during the combustion gas cool-down process. The quantity of PCDD and PCDF is a
function of the combustion process efficiency (see figures 5-3).
(3) The secondary combustion process has a significant affect on the "polishing" of the
combustion gas. The temperature must be maintained above 1500F to assure rapid destruction of
the PCDDs and PCDFs formed at lower temperatures in the primary combustion process (see
(4) Measurable amounts of PCDD and PCDF are formed as secondary pollutants during the
cool-down of gas and condensation of vapors. Therefore, it is important the chlorine be "locked"
into stable compounds during the prior oxidation process or be scrubbed out of the gas stream by
reaction with a chemical sorbent in the high-efficiency gas cleanup system.
(5) There are no current or proposed regulations governing the emissions of PCDD
(commonly called dioxin) and PCDF (commonly called difurans) for incinerators with a unit capacity
below 250 tpd. Federal regulation (40CFR 60.34) specifies a limit of 125 ng/dscm emission of
dioxin/difuran from incinerator units with capacities between 250 tpd and 1,100 tpd. Any release
greater than these levels from unregulated facilities (i.e., capacities below 250 tpd) would likely be
unacceptable to anyone opposing an incinerator project.
(6) Baghouses will not have an appreciable effect on either PCDD or PCDF unless the
exiting gas temperatures are below 350oF. Scrubber efficiency for the removal of PCDD and PCDF
is on the order of 50%. Efficiency is affected by the ability of the mist eliminators to remove the
droplets containing the trapped PCDD and PCDF.
f. Heavy Metals.
(1) The primary sources of toxic heavy metals in MSW incinerators are automobile
batteries, cylindrical batteries, "button" batteries, and electronic devices. Additional control must be
exerted by source separation or a front-end processing/operator to remove car batteries (primary
source of lead), flashlight and electronic device batteries (primary sources of cadmium and
mercury), and any other unusual items from waste prior to incineration.
(2) There are no current or proposed regulations governing the emissions of heavy metals
from either incinerators or fossil-fueled boilers with capacities below 250 tpd. For plants with
capacities between 250 and 1,100 tpd, federal regulation (40CFR 60.33a) specifies a limit of .030
gr/dscf. The lower primary combustion chamber modular SAUs have demonstrated levels of heavy
metal particulate emissions in the range of 0.0046-0.0085 grains/dscf (i.e.,for less than one third of
the acceptable limit).
(3) The best control alternative is a fabric-filter system. As the flue gases cool, the
vaporized heavy metals condense on particulates. Due to their small size (less than 10 microns),
heavy metal particulates are not collected effectively by scrubbing systems (less than 50%
effective). Fabric-filter systems with "seeded" bags create a tortuous path that effectively controls
release of fine particulates.