No.004 ; Reduction of SO2 and Offensive Odor from Process Exhaust Gas

No. 004

Classification of Technology:: Air Pollution Control
Type of Industry:: Food
Subject:: Reduction of SO2 and Offensive Odor from Process Exhaust Gas

1. Purpose
In addition to reducing SO2 discharged from stacks in the product drying process from 250ppm to under 15ppm, dust from 200ppm to under 60ppm, odor density of 30,000 to 70,000 will be reduced to 500 to 1,500.

2. Applied Technology and the Time
Since the factory is located near a residential district, there was need to reduce offensive odor ( odor generated when drying the product ). A exhaust gas deodorizing device which make use of sodium hydroxide and sodium hypochlorite solution was therefore installed. ( Oct., 1992 )

3. Principle
SO₂ + 2NaOH + NaOCl -> Na₂SO₄ + NaCl + H₂O
Deodorization, desulfurization and reduction of dust are carried out on the exhaust gas by passing it through a cooling tower, alkali washing tower and oxidizing tower arranged in series. Process flow is described on the next page.

4. Effect and Achievement

	Before Application	After Application
Dust discharge	80 ~ 110 ppm	12 ~ 18 ppm
SO₂ discharge	220 ~ 260 ppm	4 ~ 5 ppm
Odor density	About 30,000	About 600

Better results were obtained over the original plan as for exhaust dust and SO2.

5. What to do next ?
Establishment of a maintenance system for the tower packing material. Introduction of a deodorizing and desulfurization system in other drying equipment.

Implementing company:: Shikishima Starch Co., Ltd. Suzuka Factory

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