503paper - Laurence Udron Marius Hackel 1 Georg Schaub...

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Laurence Udron Marius Hackel 1) Georg Schaub Engler-Bunte-Institut Universität Karlsruhe (TH) D-76128 Karlsruhe, Germany [email protected] [email protected] [email protected] Thomas Turek Institut für Chemische Verfahrenstechnik, Universität Karlsruhe (TH) D-76128 Karlsruhe, Germany 1) Person to whom correspondence should be sent Catalysis of Reduction and Oxidation Reactions for Application in Gas Particle Filters Keywords: gas cleaning in filters, catalytic reduction of NOx with NH 3 (SCR), catalytic VOC oxidation Introduction Flue gases originating from biomass and waste incineration contain gaseous pollutants such as NOx, volatile organic compounds (VOC), SO 2 , and others, that have to be removed. Catalytic processes are presently applied for selective reduction of NOx (SCR) and oxidation of dioxins in waste incineration, normally after a particle separation step. In this case, the dust-free gas passes through a honeycomb configuration allowing low pressure drop (Janssen 1997, Fahlenkamp et al. 1991, Hagenmaier and Mittelbach 1990). NOx reduction can be seen to occur according to equation 1, at the same time the extent of a parallel oxidation of NH 3 with O 2 (equation 2) has to be minimized. Oxidation reactions of the variety of volatile organic compounds can be represented by equation 3. Catalysts commonly used in industrial applications are based on titania-supported vanadia (and tungsten) oxides. 4 NO + 4 NH 3 + O 2 4 N 2 + 6 H 2 O( 1 ) 4 NH 3 + 3 O 2 2 N 2 + 6 H 2 2 ) (CH x O y Cl z ) + O 2 CO 2 + H 2 O + HCl (3) Integration of these catalytic reactions in gas particle filters has recently been proposed as an attractive solution, either separately for NOx reduction (e.g. Hübner et al. 1996, Saracco 1999) or for VOC oxidation (e.g. Saracco 1999, Gore 1999, Saracco and Specchia 1998). The simultaneous occurrence of reduction and oxidation reactions in a catalytic filter can be envisaged in the same way as it is proven in today's honeycomb reactors in waste incineration (Frings et al. 1994, Schaub 1996).
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2 Objectives and Approach The present study is a first part of an investigation addressing the simultaneous occurrence of oxidation and reduction reactions in catalytic filters. It has the objectives a) to assess the state of knowledge regarding suitable (types of) catalysts for reduction and oxidation, b) to collect and analyze published information about reaction rates of both NOx reduction and VOC oxidation, and c) to adjust a lab-scale screening method to the requirements of an activity test with various oxidation/reduction catalysts. Results Effects of simultaneous reduction and oxidation reactions with a V 2 O 5 /ZrO 2 -Al 2 O 3 catalyst were investigated experimentally by Jones et al. (1997) using a model flue gas with N 2 , NO, NH 3 , and Cl-Ethane as VOC model compound. For the conditions applied, complete conversion of NO was achieved in a fixed bed reactor at 300 °C, of chlorethane at 340 °C, both for a GHSV of 19000 h -1 . As can be seen in Figure 1, conversion-temperature profiles were practically identical
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503paper - Laurence Udron Marius Hackel 1 Georg Schaub...

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