Influence of disturbances in municipal waste incineration plants on catalytic converters

Forced by legislation, a series of catalytic converters have been installed in German municipal waste incineration (MWI) plants to reduce nitrogen oxi des and/or polychlorinated dibenzodioxins/furans (PCDD/F). The catalytic ma terial is usually based on TiO2 doped with V2O5 and WO3. During the past 2 years, problems arose especially in new installations in connection with di sturbances in the combustion chamber. The emission of great amounts of carb on monoxide and other products of incomplete combustion caused fast tempera ture excursions in the catalytic converters. As a result, some of these ins tallations were heavily damaged. For this reason the oxidation of pyrolytic gases was investigated with several types of catalysts in the laboratory. The gases detected during periods of low oxygen concentrations in an incine rator behave quite differently when they pass a catalytic converter. While hydrogen and some unsaturated hydrocarbons like benzene or ethyne are easil y oxidised at the operating temperature of about 300 degrees C, others like carbon monoxide or methane are rather inert at this temperature. Oxidation of the compounds first mentioned will produce enough energy to rise the te mperature of the catalytic converter up to values where even CO and CH4 wil l react. In this case, temperatures will exceed 700 degrees C, which can be concluded from the changes in the physical properties of the catalytic mat erial. Under certain conditions, these changes may result in a complete des truction of the catalytic converter. The first measure to prevent such dama ge could be a bypass and additionally catalytic materials that withstand hi gh temperatures better than catalysts based on TiO2 could be used. (C) 1999 Elsevier Science Ltd. All rights reserved.