Page 167 - Wastewater Solids Incineration Systems

134 Wastewater Solids Incineration Systems

amount of particulate matter captured, so it is important that the state testing and
reporting requirements are fully understood during the permitting process.
Particulate matter is the portion of incinerator ash that is carried out in the flue
gas. The uncontrolled particulate emission rate can readily be calculated using the
percent inert fraction of the feed solids on a dry basis and the type of incinerator. In a
multiple-hearth furnace (MHF), approximately 85% of the ash exits the incinerator as
bottom ash; the remaining 15% is carried out as particulate matter in the flue gas.
Thus, a 45-metric tonne/d (50-dry ton/day) MHF with a feed cake that is 75%
volatile and 25% inert on a dry basis would have an uncontrolled particulate matter
emission rate of 71 kg/h (156 lb/hr, i.e., 50 dry ton/d 2000 lb/ton day/24 hr
0.25 lb inert/dry lb 0.15). In a fluid bed incinerator, all of the incinerator ash is
blown out of the incinerator (with some of the fluid bed sand); hence, the uncon-
trolled particulate matter emission rate in the above example would be 473 kg/h
(1042 lb/hr, i.e., 50 2000 1/24 0.25).
The primary emission criteria for particulate matter are the new source perfor-
mance standards (NSPS) for municipal incinerators (40 CFR, Part 60, Subpart O),
which require that particulate emissions be controlled to not more than 0.65 g/kg (1.3
lb/dry ton) of solids incinerated. This standard sets minimums that all incinerators
have to meet. The NSPS also delineates another particulate emission rate, namely
0.37 g/kg (0.75 lb/dry ton) of solids. If an incinerator can demonstrate particulate
matter emissions equal to or less than this limit, the incinerator is exempt from cer-
tain monitoring and reporting requirements. Hence, the lower particulate matter
limit is a typical design objective for new incinerators.
Control methods for particulate matter include cyclones, Venturi scrubbers,
impingement tray scrubbers, wet and dry electrostatic precipitators (ESPs), and
fabric filters (or baghouses). On existing installations, Venturi scrubbers, tray scrub-
bers, and wet ESPs are most commonly used. On newer installations, however, dry
ESPs and fabric filters have been used.

1.1.1 Opacity
The NSPS for incinerators also limits visible emissions to 20% opacity. According to
the NSPS, opacity is “the degree to which emissions reduce the transmission of light
and obscure the view of an object in the background.”
Hence the greater a plume’s opacity, the more it will obstruct light and the more
difficult it will be to see through. It should be noted that white plumes as well as
black plumes can exhibit high opacity. Opacity measurements can be made by a