Detoxification of Dioxins Using E-beams
Introduction
Detoxification of dioxins found in the flue gases emanating from waste incinerators can now be done with the use of electron beams. The Radiation Chemistry Research Establishment of JAERI has developed a system for this process. Japan is going to amend its law for preventing air pollution later this year. The amount of toxic equivalents (TEQ) permitted in flue gases would be sharply reduced from the present emission standard of 80 ng/m3. Typical amount of TEQ/m3 in the flue gas emitted by the existing incinerators vary between 10 ng for small incinerator with a capacity of < 2 ton/hour and 1 ng for large incinerator with a capacity of > 4 ton/hour. Incinerators using the new process may reduce these amounts to 5 ng and 0.1 ng respectively.
Flue gases from waste incinerators are released into the atmosphere after smokestack pollutants are eliminated through electrostatic precipitation and/or filtration. Currently, bag filters require subsequent detoxification. The gaseous dioxins in the flue gases can be eliminated or decomposed through charcoal absorption columns or catalytic reduction process towers. However, both processes also require subsequent treatment and their efficiency varies with the temperature.
In the new process, electron beam is applied to flue gases, generating highly reactive activated gases such as activated oxygen from the ingredients of flue gases, which decompose the chemical structure of dioxin. The EB process system uses a shielded irradiation chamber accelerator, which is superior to current bag filters on two main counts. First, the process does not produce any toxic residuals and can eliminate dioxins at a low concentration. Second, it can be easily installed in existing waste incinerators. Experience with radiation-chemical technology using e-beams such as the decomposition of voltaic organic chlorides at factories, and the de-sulphurization of flue gases from thermal power plants has been used to develop this process.
An e-beam system with 300 KV, 40mA accelerator and an irradiation chamber has been giving demonstration tests since Dec 2000 at Takahama Clean Centre in Haruna, Gunma. Using real flue gas flowing at 1000 m3/h at 200 oC, it reduces dioxin levels by 50, 80 and 90% with absorbed doses of 3, 10 and 15kGy respectively. Its running cost is about two-third of the system using bag filters. The system may be commercialized by JAERI.
For further information please contact
Science & Technology Wing Embassy of India
2-2-11, Kudan Minami, Chiyoda-ku
Tokyo 102-0074, Japan
Tel: +81-3-3262-2391 to 97,
Fax: +81-3-3234-4866
E-mail: tandonus@hotmail.com
