Page 120 - Fundamentals of Air Pollution

90 6. Sources of Air Pollution

The most widely used pulping process is the kraft process, as shown in
Fig. 6-11, which results in recovery and regeneration of the chemicals. This
occurs in the recovery furnace, which operates with both oxidizing and
reducing zones. Emissions from such recovery furnaces include particulate
matter, very odorous reduced sulfur compounds, and oxides of sulfur. If
extensive and expensive control is not exercised over the kraft pulp process,
the odors and aerosol emissions will affect a wide area. Odor complaints
have been reported over 100 km away from these plants. A properly con-
trolled and operated kraft plant will handle huge amounts of material and
produce millions of kilograms of finished products per day, with little or
no complaint regarding odor or particulate emissions.

L. Noxious Trades
As the name implies, these operations, if uncontrolled, can cause a seri-
ous air pollution problem. The main problem is the odors associated with
the process. Examples of such industries are tanning works, rendering
plants, and many of the food processing plants such as fish meal plants.
In most cases, the emissions of particulates and gases from such plants are
not of concern, only the odors. Requiring these industries to locate away
from the business or residential areas is no longer acceptable as a means
of control.

Fig. 6-11. Schematic diagram of the kraft pulping process (6). 1, digester; 2, blow tank;
3, blow heat recovery; 4, washers; 5, screens; 6, dryers; 7, oxidation tower; 8, foam tank;
9, multiple effect evaporator; 10, direct evaporator; 11, recovery furnace; 12, electrostatic
precipitator; 13, dissolver, 14, causticizer; 15, mud filter; 16, lime kiln; 17, slaker; 18, sewer.