1 October 1997
(3) The 1996 federal regulations mandating low levels of specific species of emissions, will
necessitate the use of particulate control devices for all incinerator technologies.
b. Acid Gases.
(1) Sulfur Dioxide. Based on the limited literature available, an average uncontrolled SO2
emission rate of 45-87 ppm can be expected from municipal waste incinerators. In normal SO2
scrubbing systems for solid fuel boiler systems, an actual operating removal efficiency of 90-95%
can be assumed.
(2) Hydrogen Chloride.
(a) Under 40CFR Part 60, the scrubbing system must also control hydrogen chloride
(HCl), acid gases, and NOx. Control of NOx will reduce the removal efficiency SO2 to an anticipated
80%. Fortunately, most municipal-type waste has a low sulfur content and SO2 emission levels of
50 ppm or less are readily achieved with a scrubber.
(b) Hydrogen chloride (HCl) is the primary form of acid gas produced in municipal waste
incinerators. PVC plastics, paper, and putrescible garbage are the major contributors of chlorine in
the refuse stream and are considered the primary source of HCl emissions at refuse-burning
(c) HCl emissions from burning IIA Type 2 waste (municipal) in starved-air or excess-air
incinerators have ranged from 53-724 ppm before the exhaust gas is treated.
(d) HCl emission levels vary widely and reflect variations in feed stock. Plastics and
paper have been found to be the major contributors, while food waste and untreated wood products
are minor contributors of HCl. Typically, food waste and wood products make up only 8% of the
source of chlorine. Because military waste streams have high paper content, an aggressive paper
and plastic recycle program can drastically reduce the source of chlorine and reduce HCl emissions
to the low end of the 50-725 ppm HCl range for an incinerator with a materials recovery facility.
(e) Because PVC plastics contain 40% chlorine, removal of all PVC plastics from the
waste delivered to the incinerator may be a significant factor in helping achieve low HCl emissions.
(f) The recommended process for removal of HCl is a spray dry scrubber followed by a
bag house (emission limits in the Federal Regulations were established on the basis that the limits
could be achieved by a spray dryer/bag house system).
(g) In all systems, uncaptured acid vapors (e.g., H2SO4, H2SO3 or HCl) will condense on
surfaces at temperatures below 275F. Resultant corrosion on equipment and structures can be
detrimental. If scrubbers are not used, the equipment and structures downstream must be kept at
temperatures above 300F or designed to withstand the acid attack.
(1) Oxides of nitrogen (NOx) are compounds consisting of nitrogen and oxygen and are