Updated: July 2002

1. Purpose

To remove HCl and SOx in the flue gas from municipal refuse incinerators through their reactions with aqueous solution of caustic soda.

2. Performance

HCl concentration at the outlet: 10 ppm or less
SOx concentration at the outlet: 10 ppm or less

3. Characteristics

1) The high efficiency in the harmful gas removal
2) Removal of mercury is also possible.

4. Principle

The system is normally installed downstream to the electrostatic precipitator and the like dust collecting system. Flue gas cooled by spraying the circulating solution is allowed to contact the circulating solution containing caustic soda via the packed filler material, so that the harmful gas will be removed through the following reactions:

NaOH+HCl -> NaCl+H2O
2NaOH+SOx -> Na2SOx+H2O

5. System Configuration

1) Scrubbing tower
The scrubbing tower consists of the cooling section and the absorption section. A counterflow type spray tower is used for the cooling section. To protect against corrosion, inner surface of the tower is applied with the resin lining, and the inlet part is lined with the natural fire-resistant stone. The absorption section is provided with the packed bed for removing the harmful gas contained in flue gas.
2) Dehumidifying cooler
This is for cooling the circulation hot water fed from the absorption section. An indirect type heat exchanger using finned steel tubes, or a cooling-tower type direct heat exchanger is used for the purpose.
3) Steam heater
This is used for heating air or flue gas in order to reduce the amount of white smoke produced. In addition to those mentioned above, the system includes also the pumping unit for circulating the absorbed liquids, the caustic soda (the absorbent) storage unit, the waste water treatment unit for processing waste liquids from the scrubbing tower, etc.

6. Application

For flue gas treatment on municipal refuse incinerators and industrial waste incinerators.

7. Examples of Installation

Twenty seven units of the system are now in operation for the municipal refuse incinerators, and additional six units are now under designing stage.