Takeo Urabe* and Akio Motoi**

* The Tokyo Metropolitan Research Institute for Public Cleansing
** The Tokyo Metropolitan Industrial Technology Center

+ Correspondence should be addressed to Takeo Urabe:
(3 Yumenoshima, Koutouku, Tokyo 136 Japan)

Abstract

Boiler tube thinning at up to about 30cm top of caster-equipped edge of combustion chamber in a refuse incinerator, where exhaust gas recirculating operations were employed for about five years, was especially large and lots of cracks were found in the scale. CaSO4, NaCl, KCl, etc. were identified in the ash which adhered to the boiler tube and Fe2O3, KPb2Cl5, K2ZnCl4, NaCl, Na3Pb2 (SO4) 3Cl, etc. were identified in the scale. There is a possibility that these chlorides and sulfates are related to high temperature corrosion of the boiler tube. A survey on the high temperature corrosion environment, including gas tempera ture and concentration of gas components according to the location of the combustion chamber in the refuse incinerator, was undertaken under four operating conditions of the air blow rate (O2 6.2-10.2% at chimney). The results show that operation of O2 concentration of about 10% makes high temperature corrosion environment mild, but low air ratio operation of O2 concentration of about6% makes vaporization of salts increase owing to the rise of gas temperature near the stoker. There is a high concentration of CO, H2, H2S, etc. owing to long frame of fire and thus the high temperature corrosion environment of the combustion chamber boiler tube becomes considerably severe.

Key words: refuse incinerator, boiler tube, high temperature corrosion, combustion chamber, corrosion environment