Encyclopedia of Environmental Science and Engineering, Volume I and II

VAPOR AND GASEOUS POLLUTANT FUNDAMENTALS 1213

Oxides of Carbon

The carbon dioxide, CO 2 , concentration threshold for humans

is 5% (5000 ppm) for an 8-hour exposure. This compares with

a normal atmospheric CO 2 concentration of 0.03% (300 ppm).

With a perfect stoichiometric combination of pure carbon

in air, a CO 2 concentration of about 21% could be attained.

Considering the usual dispersion of combustion gases it would

take an unusual isolation to produce a CO 2 health hazard.

A more detailed description of CO 2 consequences may be

found in the Appendix.

Incomplete combustion of fuels is the more serious

problem, since carbon monoxide, CO, will form. This rarely

happens in stationary furnaces for which efficiencies of

combustion are high and oxygen is available in excess of the

theoretical requirements.

It has been estimated (Anon., 1970) that slightly more than

100 million tons of CO are emitted annually in the USA, of

which the major sources are automobiles (59%), various open

burnings (16%), chemical industry (10%) and other transpor-

tation means (5%). New York City, with its acute urban traffic

problem, has established a first alert at 15 ppm of CO over

TABLE 1

Status of Commercial FGD Processes (Adapted from Princiotta, 1978)

FGD Process

Reagent

End Product

Principle of Operation

SO 2 Removal

Efficiency(%)

Limestone Scrubbing Limestone (LS) CaSO 3 /CaSO 4 Sludge LS slurry reacts in scrubber

absorbing SO 2 and

producing insoluble

sludge.

80–90

Lime Scrubbing Lime CaSO 3 /CaSO 4 Sludge Lime slurry reacts in

scrubber absorbing SO 2

and producing insoluble

sludge.

85–95

Wellman Lord Sodium carbonate

(regenerated)

Sulfuric Acid Sulfur Soluble sodium sulfite

absorbs SO 2 in scrubber,

the sodium bisulfite

produced is thermally

regenerated, yielding

sodium sulfite and SO 2

for either acid or S

production.

85–95

Double Alkali Sodium carbonate

(regenerated)

CaSO 3 /CaSO 4 sludge Soluble sodium sulfite

absorb SO 2 in scrubber;

the sodium bisulfite

produced is reacted with

lime precipitating

CaSO 3 /CaSO 4.

85–95

Magnesium Oxide Magnesium oxide

(regenerated)

Sulfuric Acid Magnesium oxide slurry

absorbs SO 2 in scrubber;

the magnesium sulfite

produced is thermally

treated, yielding MgO

and SO 2 for acid

production.

85–95

TOTAL NOx EMISSIONS

(20 MILLION TPY)

NOx EMISSIONS FROM STATIONARY

SOURCES (11.1 MILLION TPY)

NOx EMISSIONS FROM STATIONARY

COMBUSTION SOURCES (10.4 MILLION TPY)

GAS TURBINES

MOBILE

SOURCES

75

50

25

0

75

50

25

0

75

50

25

0

STATIONARY

SOURCES

COMBUSTION

INDUSTRIAL

PROCESSES FIELD

BURNING ENGINESIC

BOILERS

INCINERATORS

FIGURE 1 Sources of NOx emissions.

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