Entwicklung eines Katalysators zur Abgasreinigung für Biomassekraftwerke

The integration of biomass based fuels is leading the way towards reliable energy supplies, but still high emission values are observed during the energy conversion (NOx, SOx, H3PO4 and soot), due to the Nitrogen, Sulphur and Phosphate contained in biomass [1]. Additionally, mineral content and heterogeneity of biofuels lead to high concentration of particles in exhaust gases, which can reach up to 60 mg/Nm3 [2]. To address this problem, robust exhaust gas treatments can be installed at firing systems, however for small and medium systems (<10 MW) economical and fitted solutions are still needed [3]. Previous approaches are based on catalytic coating of porous bodies, i.e. [4][5]. In this technique, the external surface of a filter body is coated with a catalytic solution. This method is also called impregnation [6]. Through this process, a particle filter and catalytic material are merged into one product. Although this technique has shown efficiencies of up to 80% at over 250°C in dusty conditions like biomass combustion, the impregnation method is limited by the porosity of the support [7]. On one hand, low porosity bodies efficiently retain particles, but at the same time this property limits the impregnation method because these bodies filter most of the catalytical particles. This inhibits the deposition of the catalyst in the internal bulky structure of the porous filter. On the other hand, supports with good porosity get easily coated, which also increases the amount of deposited catalyst [8]. However, these filters are clogged later under operational conditions. For instance, pores get plugged with dust particles, which increases the pressure drop and subsequently minimizes the catalytical effect [9]. An acceptable balance between porosity of the filter and activity of the catalyst calls for alternative fabrication methods. Besides, the active material should catalyze under dusty, wet and corrosive conditions. Moreover, other parameters such size, cost, mechanical stability and chemical resistance must be kept under the standard values [10]. Therefore, a new fabrication method for catalytic filters was developed and tested in this project to satisfy the requirement of small and medium firing plants, see figure below To achieve this, an organometallic compound based on copper was synthesized by a solvothermal process, see left side of previous figure. Stabilization of the active sites was achieved through addition of silicoaluminate precursors and an organic template as mesoporous structuring agent. This process encapsulated the catalytic material for upcoming steps. As illustrated in the middle part of the previous figure, integration of filter material and catalytic material was done by mixing and shaping the catalytic filter in a mold. Adjustment of the molding process and porosity were attained by addition of inorganic binder. Finally, the shaped body was calcinated and activated in a controlled atmosphere for the final operation in the SCR test stand. Validation of the process was linked to the NOx reduction capacity of the catalyst. Therefore, adjustment in the formulation was done by analysis of the NO conversion, depending on temperature. Additionally, a particle filtration test was run on the catalytic filter in order to analyze the simultaneous performance during dust filtration and NOx conversion. Lastly, the optimal formulation was tested under real exhaust gas and characterized based on temperature and pressure. Finally, to evaluate the synthesis, detailed spectroscopy measurements were implemented on the catalytic filter. By doing so, active centers and absorption sites of the catalyst were revealed by using several analytical techniques, such as STEM, XRD, TPR, TPO, EPR and NMR. Based on the analytical measurements, a catalytic mechanism is proposed.Die Entwicklung von biologischen Brennstoffen zeigt realistische Wege für erneuerbare Energien auf. Trotzdem gibt es weiterhin gefährliche Abgasemissionen während der energetischen Verwandlung. Diese Emissionen (NOx, SOx, HPO3 und Ruß) werden von Stickstoff, Schwefel und Phosphaten generiert, die in der Biomasse enthalten sind [1]. Noch dazu führen mineralische Inhaltsstoffe und chemische Heterogenität der Rohstoffe zu hohem Staubanteil in den Abgasen, welcher bis zu 60 mg/Nm3 erreicht [2]. Um diese Tatsache zu vermeiden, sind an Feuerungsanlagen robuste Abgasnachbehandlungssysteme installiert. Dennoch werden für mittelgroße sowie kleinere Anlagen (