9542
Ind. Eng. Chem. Res. 2005, 44, 9542-9548
Multifunctional Filter for Treatment of the Flue Gases from Municipal Waste Incinerators D. Fino,* N. Russo, G. Saracco, and V. Specchia Dipartimento di Scienza dei Materiali ed Ingegneria Chimica, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Torino, Italy
The simultaneous catalytic removal of NOx and volatile organic compounds and filtration of dust or sorbents injected for the treatment of incinerator flue gases can be achieved by means of an innovative catalytic filter concept based on the combination of a high-temperature-resistant polymeric filter bag, enclosing a catalytically activated ceramic foam structure. Improvements in catalyst nature and deposition described in the present work allowed improvement of the performance of an earlier developed catalytic filter. Particularly, the adoption of MnOx‚CeO2 + V2O5‚WO3‚TiO2 prepared by a wet impregnation route and its deposition in suitable amounts (6 wt %) within a zirconia-toughened-alumina (ZTA) foam by a microwave-assisted preparation method, allowed achievement of abatements of NO and benzene higher than 90% and 50%, respectively, at an operating temperature of just 200 °C. As some dioxins and furans are normally oxidized at lower temperatures than benzene, higher conversion rates can be expected for at least some of these harmful compounds. Higher catalyst loadings are not useful since they lead to plugging of the pores, thus hiding portions of the catalyst and severely lowering the effectiveness factor. I. Introduction Incineration plants for municipal wastes are widely spread all over Europe, which requires a careful evaluation of their environmental impact. The major pollutants emitted are dust (silicates, aluminates, salts, metal oxides, carbon, ...), acid gases (HCl, HF, SO2), nitrogen oxides (NO, NO2), carbon monoxide (CO), heavy metals (Hg, Cd, Pb, As, ...), polyaromatic hydrocarbons (PAH), dioxins (PCDD), and furans (PCDF). According to the second version of the European BREF manual on the best available techniques for waste incineration (BAT Reference Manual1), the following treatment routes are recommended: Dust should be preferably removed by electrostatic precipitators after the heat recovery systems (400 µm pores) and a new catalyst based on the mechanical mixture of MnOx‚CeO2 and V2O5‚WO3‚TiO2 powders, NO abatements of at least 85% and benzene conversions close to 80% were obtained when operating at superficial velocities up to 60 Nm3 m-2 h-1 (1 Nm3 equals the m3 of flue gas at 0 °C and 1 bar). However, pathways to further improve the performance of the multifunctional reactor were also enlightened, aiming at more active catalysts and a more even catalyst distribution inside the foam structure. The present paper describes the results obtained in improved catalytic filters. II. Experimental Section
Figure 1. Scheme of typical mobile grates municipal waste incinerator with progressively simplified flue gas treatment routes: (A) conventional “wet route”; (B) conventional “dry” route; (C) “dry” route with low-temperature SCR and CATOX reactor; (D) “dry” route with catalytic baghouse filters.
II.1. Catalyst Development. As detailed in ref 6, currently adopted SCR units employ V2O5‚TiO2 catalysts that operate at 320-400 °C in honeycomb catalytic converters fed with space velocities of about 20 000 h-1. To cope with the significantly lower operating temperatures required for the envisaged application, an innovative catalyst was developed in ref 4. It was based on the mechanical mixture (1:1 mass basis) of powders (
