Verbundvorhaben: Hocheffiziente Biogas-SCR-Systeme - BiNOred; Teilvorhaben 1: Experimentelle Untersuchung der Eindüsung von Harnstoff-Wasser-Lösung für SCR-Systeme von Biogas-BHKW, Teilvorhaben 2: Entwicklung eines CFD-basierten Auslegungstools für die SCR - Abgasnachbehandlung in Biogas-BHKW, Teilvorhaben 3: Feldvalidierung und Begleitung der Entwicklung einer computergestützten Auslegung zur SCR Abgasnachbehandlung von Biogas-BHKW

Abstract

As part of the project, the complete SCR process chain was investigated both experimentally and numerically with the aim of generating a digital image of the SCR process, which should enable reliable predictions for the design of biogas CHP exhaust gas systems. Prior to the experimental investigations within the hot exhaust gas flow, a basic characterization of commercial two-fluid nozzles was carried out. In order to assess the influence of manufacturing-related deviations in nozzle geometry on the spray pattern, ten identical nozzles from an established manufacturer were measured in terms of spray angle, droplet velocities, and droplet sizes. It was found that the spray angle near the nozzle is significantly influenced by differences in the geometry of the atomization air ring gap. However, the droplet distribution in terms of velocity and size remained largely unaffected.

In order to generate sufficient validation data for the numerical investigations, extensive measurements were then carried out on spray parameters, evaporation behavior, and ammonia concentration and distribution under different boundary conditions with the influence of a hot gas cross flow. For this purpose, a hot gas section was set up in advance. The burner module available at ITV was used for this purpose. The following module for optical investigation of the spray area and the other modules for integrating mixers and catalysts were newly manufactured. Within the scope of the investigations, the measurements of ammonia distribution upstream of the catalyst inlet are particularly noteworthy. A high atomization air flow proved to be particularly advantageous for improving uniform distribution. In combination with a mixing element, high degrees of uniformity can be achieved even at high gas velocities or short mixing distances. A reduction in exhaust gas temperature has little effect on uniform distribution, but has a significant influence on the conversion rate of urea to ammonia. This means that at lower exhaust gas temperatures, less ammonia is present upstream of the catalyst. In this case, incomplete conversion of the urea leads to undesirable side reactions and solid deposits. Overall, comprehensive generic data was generated, which enabled the project partners to validate all process steps within the digital model.