1214 VAPOR AND GASEOUS POLLUTANT FUNDAMENTALS
at 8-hour period. High temperatures favor the equilibrium
dissociation of CO 2 to CO, with the latter being very stable
at high temperatures. Thus is a CO 2 –CO mixture is quenched
from its high temperature zone the percentage CO may remain
high, since at lower temperatures longer times are required to
reach equilibrium. Rich fuel-air mixtures favor the formation
of CO over CO 2. A complete description of CO control meth-
ods may be found in the section Mobile Source Pollution.Miscellaneous GasesCompounds of fluorine are known to have negative effects
(Fluorisis) at concentrations as low as 5 × 10−3 ppm. They
are generated as waste gases of fertilizer aluminum and
ceramic processes, but are present to a lesser extent in most
flue gases. A concentration of 0.1 ppm (vol.) of fluorine has
been set as a maximum permissible value by the American
Conference of Governmental Industrial Hygienists; USSR
standards are roughly one tenth as stringent.
Ozone, O 3 , is one of the strongest gaseous oxidants and is
formed naturally from oxygen during electrical discharges in
the atmosphere and at the high temperatures of combustion.O 2O
O O O2
2 3→ ⋅
⋅→Taken as oxidants, New York City classified an ozone level
above 0.03 ppm as unsatisfactory and above 0.07 ppm asunhealthy over a 6 hour period. Eye irritation commences
at concentrations of about 0.1 ppm. Interestingly enough
ozone in the lower stratosphere affords part of the protective
shield against ultraviolet radiation from the sun, which could
destroy land vegetation.O O + O^3 →^2.Some scientists are concerned that nitric oxide formed by
supersonic jets may deplete the ozone supply in the lower
stratosphere, eroding the barrier to the destructive rays.
High temperature processes involving metal recovery
from ores emit mercury vapor in addition to sulfur dioxide.
Mercury is available at concentrations up to a few hundred
ppm (Kangas et al., 1971) during zinc sulfide ore process-
ing for example. Hydrochloric and hydrofluoric acids also
appear in the roaster gases of such processes. No danger
levels for mercury vapor have been officially established
in ambient air quality standards.
A few limits have been established for less common pollut-
ants of the process industries in USSR standards given below.
The US ambient air quality standards call for hydrocar-
bon concentrations below 160 mg/m^3 (0.24 ppm) between
6–9 am.
Aldehydes and other oxygenated hydrocarbons are
formed by the action of ozone on unburned hydrocarbons in
the presence of sunlight. For example,O 1-3 Butadiene A crolein Formaldehyde.^3 → In the above reaction both products have been linked to the
severe eye irritation encountered in urban environments.TRANSPORT OF POLLUTANTSThe feed and waste materials of any combustion or chemi-
cal process travel through ducts or pipes. Control devices
may be placed at various stages of the process, depend-
ing on the separation technique to be employed. It will
be valuable to review the flow and transport behavior for
fluids and then the separation methods. The important pro-
cess variables to be considered are the mass flow rate of
the waste gas, its temperature, pressure and composition.
The raw material feed rate variables may also be of sig-
nificance, as in the desulfurization of fuel oil. Control
devices may broadly be classified according to the physi-
cal separation process being used, adsorption: absorption:
extraction: distillation: or to the chemical process, homoge-
nous or heterogeneous catalytic reaction. In each instance,
equations which account for the transport of material and
energy must be developed.
In a sense almost any process may be considered as
taking place in a pipeline. The simplest model of flow is
called plug flow and assumes that no mixing takes place
along the axis of the pipeline, but that lateral mixing is com-
plete. Also, this assumes a flat velocity profile exists at each0 .1 .2 .3 .4 .5110100.610 –510 –410 –310 –210 –1PERFECT DISSOCIATION(1/T°R) x 10^3FIGURE 2C022_001_r03.indd 1214 11/18/2005 2:32:41 PM