Encyclopedia of Environmental Science and Engineering, Volume I and II

AIR POLLUTION SOURCES 109

Part 2. Major Air Pollution Sources (continued)

Mineral products industry Nature of activity Type of air pollution problems

This section involves the processing and

production of various minerals. Mineral

processing is characterized by particulate

emissions in the form of dust. However, most

of the emissions from the manufacturing

process conventional in this section can be

reduced by conventional particulate control

equipment such as cyclones, scrubbers, and

fabric filters.

ASPHALT BATCH PLANTS Hot-mix asphalt paving consists of a

combination of aggregates, coarse or fine,

uniformly mixed and coated with asphalt

cement. The coarse aggregates are usually

crushed stone, crushed slag or crushed gravel,

while the fine aggregates are usually natural

sand and finely crushed stones.

The largest pollutant type is dust, emanating from the

rotary dryers and filtering systems, normally used in

producing asphalt.

ASPHALT ROOFING The manufacture of asphalt roofing felts and

shingles involves saturating a fiber media

with asphalt by means of dipping and/or

spraying.

The major pollutants are particulate emissions from

asphalt roofing plants during the asphalt blowing

operations and the felt saturation. Common methods

of control at asphalt saturation plants include

complete enclosure of the spray area and saturation

followed by good ventilation through one or more

collection devices. Some traces of carbon monoxide

and hydrocarbons are also present in the emissions

from this asphalt process.

BRICKS AND RELATED

CLAY PRODUCTS

The manufacture of brick and related products

such as clay pipe, pottery and some types of

refraction brick involves the grinding,

screening, blending of the raw materials,

forming, drying or curing, firing and ferial

cutting or shaping.

Particulate emissions similar to those obtained in clay

processing are emitted from the materials handling

process in refractory and brick manufacturing.

Gaseous fluorides and nitrogen oxides are also

emitted from brick manufacturing operations.

CALCIUM CARBIDE Calcium carbide is manufactured by heating a

mixture of quick-lime (CaO) and carbon in

an electric arc furnace when the lime is

reduced by the coke to calcium carbide and

carbon monoxide. About 1990 pounds of

lime and 1300 pounds of coke yield 1 ton of

calcium carbide.

Particulates, acetylena, sulfur compounds and some

carbon monoxide are emitted from calcium carbide

plants.

CASTABLE REFRACTORIES Castable or fused-cast refraction are

manufactured by carefully blending such

components as alumina, zirconia, silica,

chrome, and magnesium, melting the

mixture, pouring into molds, and slowly

cooling to the solid state.

Particulate emissions occur from drying, crushing and

handling procedures while gaseous fluoride occurs

during melting operations.

PORTLAND CEMENT

MANUFACTURING

Lime (calcareous), silica (siliceous), alumina

(argillaceous) and iron (ferriferous) are the

four major components used to manufacture

cement. The various substances are crushed in

exact proportions, fired in a klin, and then

ground in gypsum to be bagged for shipment

as cement.

Particulate matter is the primary emission in the

manufacture of portland cement and is emitted

primarily from crushing operations and rotary kilns.

Control systems usually include multicyclones,

electrostatic precipitators or combinations of these

types of control.

CERAMIC CLAY

MANUFACTURE

The manufacture of ceramic clay involves the

conditioning of the basic ores, coolinate and

mont-morillonite (aluminous-silicate

materials), into dry clay products.

Emissions consist primarily of particulates, but some

fluorides and acid gases are also emitted in the

drying process.

CLAY AND FLY ASH

SINTERING

Both the sintering clay and fly ash involve the

firing and burning off of residual matter to

desirable product. In fly ash, carbon is

burned off while in clay, entrained volatile

matter is driven off.

Dust is the major pollutant emitted from the screening

and sintering process.

COAL CLEANING Coal cleaning is the process by which

undesirable materials are removed from both

Particulates in the form of coal dust constitute the major

air pollution problem from coal clearing plants.

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