Encyclopedia of Environmental Science and Engineering, Volume I and II

AIR POLLUTION SOURCES 107

Part 2. Major Air Pollution Sources (continued)

Food and agricultural industry Nature of activity Type of air pollution problems

MEAT SMOKEHOUSES Smoking is a diffusion process in which food

products are exposed to atmosphere of

hardwood smoke, causing various organic

compounds to be absorbed by the food.

Emissions from smokehouses are generated from the

burning hardwood, and included particulates, carbon

monoxide, hydrocarbons (CH 4 ), aldehydes (HCH) and

organic acids (acetic).

NITRATE FERTILIZERS Nitrate fertilizers are the product of the

reaction of nitric acid and ammonia to form

ammonia nitrate solution or granules.

The main emissions from the manufacture of nitrate

fertilizers are the ammonia and nitric oxides lost in the

neutralization and drying operation.

PHOSPHATE FERTILIZERS Nearly all phosphate fertilizers are made from

naturally occurring phosphorous-containing

minerals such as phosphate rock. The

phosphorous content of these minerals is

not in a form that is readily available to

growing plants so that the minerals must be

treated to convert the phosphorous to a

plant-available form.

Emissions from manufacturing phosphate fertilizers

include vent gases containing particulates ammonia,

silicon tetrafluoride, carbon dioxide, steam and sulfur

oxides. The sulfur oxides emissions arise from the

reaction of phosphate rock and sulfuric acid.

STARCH MANUFACTURING Starch is obtained through the separation of

coarse starch in corn to a fine dry powder

form ready for marketing.

The manufacture of starch from corn can result in

significant dust emissions from cleaning, grinding, and

screening operations.

SUGAR CANE PROCESSING The processing of sugar cane starts with

harvesting crops, then through a series of

processes (washing, crushing, milling,

diffusing) into the final sugar product.

The largest sources of emissions from sugar cane

processing are the open burning in the harvesting of the

crop and the burning of bagasse as fuel. Emissions

include particulates, CO usually large, HC and nitrogen

oxides.

Wood processing industry Nature of activity Type of air pollution problems

WOOD PULPING INDUSTRY Wood pulping involves the production of

cellulose from wood by dissolving the lignin

that binds the cellulose fiber together. The

three major chemical processes for pulp

production are the kraft or sulfate process,

the sulfite process and the neutral sulfite

semi chemical process.

The kraft process involves cooking wood chips

in sodium sulfide and sodium hydroxide to

dissolve the lignin. The excess pulp and

impurities are washed away and the

remaining clean pulp pressed and dried into

the finished product.

Particulate emissions from the kraft process occur

primarily from the recovery furnace, the lime kiln and

smelt dissolving tank. This characteristic kraft mill

odor is principally due to the presence of a variable

mixture of hydrogen sulfide and dimethyl disulfide.

Some sulfur dioxide emissions result from the

oxidation of the sulfur compounds. CO emissions may

occur from the recovery furnaces and klins.

PULPBOARD Pulpboard manufacturing includes the

manufacture of fibrous boards from a pulp

slurry. After the pulp is washed, it is entered

into a board machine and subsequently,

dried and ready for fabrication.

Emissions from the paper board machine consist of only

water vapor. Little or no particulates are emitted from

the dryers.

METALLURGICAL INDUSTRY

The metallurgical industries can be broadly divided into primary and secondary metal production operations. Primary metal industry includes the

production of the metal from ore; among these industries are the nonferrous operations involved in aluminum ore reduction, copper smelters, lead

smelters, zinc smelters, iron and steel mills, ferro alloys and metallurgical coke manufacture. The secondary metals industry includes the recovery of the

metal from scrap and salvage, the production of alloys from ingot, secondary aluminum operations, gray iron foundries, lead smelting, magnesium

smelting, steel foundries, and zinc processing.

Metals industry Nature of activity Type of air pollution problems

ALUMINUM ORE REDUCTION Bauxite, a hydrated oxide of aluminum

associated with silicon, titanium, and iron, is

the base ore for aluminum production. After

preliminary purification using the (Boyer)

process, the new oxide (Al 2 O 3 ) is reduced in

the Hall-Heroult process and pure aluminum

is produced. Four tons of bauxite are

required to make 1 ton of aluminum.

During the reduction process, the effluent released

contains fluorides particulate and gaseous hydrogen

fluoride. Particulate matter such as aluminum and

carbon from the anodes are also emitted.

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