Evaluation and Prediction of Deposit Severity in SCR Systems

In this work we extended the findings from a previous study by the authors on the mechanisms and influence factors of deposit formation in urea-based selective catalytic reduction systems (SCR) [1]. A broader range of operating conditions was investigated in detail. In order to quantify the boundary conditions of deposition, a representative set of deposits was studied during formation and decomposition. A box of heat resisting glass was equipped with a surrogate mixing element to monitor solidification timescales, temperatures and deposit growth. A chemical analysis of the deposits was performed using thermogravimetry. The depletion timescales of individual deposit components were systematically investigated. A moderate temperature increase to 350 °C was deemed sufficient to trigger fast decomposition of deposits formed below 250 °C. Above, the amount of temperature-stable components increased noticeably, and temperatures in excess of 600 °C were expected to be required for fast decomposition. Starting from 270 °C deposits were formed within less than 160 s and accumulated rapidly. Based on the combined data, an existent model for the prediction of deposit formation based on CFD simulations of the thermodynamic properties of the wall film [1] was extended to account for the deposit severity. The model accurately predicted the risk of deposit formation. The impact of the applied mixing element, injector and injection rate were represented very well.