Transient simulation of NO_xreduction over a Fe-Zeolite catalyst in an NH₃-SCR system and study of the performance under different operating conditions

Abstract

The NO x reduction in an ammonia SCR converter has been simulated by a 1D+1D model for a single representative channel to parametrically study the characteristics of the system under typical operating conditions. An appropriate model has been selected interpreting the chemical behavior of the system and the parameters are calibrated based on a comprehensive set of experiments with an Fe-Zeolite washcoated monolith for different feed concentrations, temperatures and flow rates. Physical and chemical properties are determined as well as kinetics and rate parameters and the model has been verified by experimental data at different operating conditions. Three different mechanisms for the surface kinetics to model NO x reduction have been assessed and the results have been compared in the cases of steady DeNO x performance and transient response of the system. Ammonia inhibition is considered in the model since it has a major effect specifically under transient operating conditions. Effects of the operating temperature, the gaseous flow rate and the species concentrations such as ammonia dosage and the ratio of NO and NO 2 have been investigated. It has been shown that recently proposed dual site chemical kinetics for Fe-Zeolite catalysts are especially suited to predict the transient operation of the system during ammonia feeding and the inhibition effect after shutting off ammonia. Accurate numerical results for various cases are a strong indication for the validity of the model under the typical operating conditions of an SCR system. This study helps to find the optimum performance of the system under different conditions including a wide range of working temperatures with different flow rates and concentrations.

A predictive control approach to diesel Selective Catalytic Reduction

“…The rate equations taken from [10] have published parameters, which are used directly in the model. The standard and fast SCR reactions remained to be calibrated, and this was completed using emissions cycle data from RICARDO, which contained pre-and post-catalyst NO x concentrations from a 3.0 litre capacity V6 diesel engine fitted with an SCR over the New European Drive Cycle (NEDC) test cycle.…”

“…are taken from [10]. In these rates, concentrations (C x ) are in moles per cubic metre, θ is the ammonia coverage ratio (i.e., proportion of the catalyst filled with ammonia), Φ is the storage capacity in moles, V is the catalyst volume, C N H3 is the concentration of ammonia in the reactor, R and T are the universal gas constant and temperature respectively, K eq is an equilibrium constant that is given for various NO:NO x ratios, and the set {k ads , k des , E des , γ} are constant parameters to be calibrated.…”

SCR Ammonia Dosing Control by a Nonlinear Model Predictive Controller

“…Therefore the filling level can be used as indicator for slip estimation which is indeed important for the SCR dosing control. Although a good model prediction quality is achievable in validation (apart from inhibition effects see Sharifian et al [2011]) with regard to the NMPC the model should be improved to further reduce the model plant mismatch. Hence, in addition to the physical based approach a data based extension is requested to improve the model quality.…”

“…In literature various investigations for modeling and control of the different after treatment devices are presented. The proposed SCR models are in the range from detailed high prediction quality models suitable for system analysis (Sharifian et al [2011]) to control oriented modeling approaches as shown in (Schär et al [2006] and Zanardo et al [2013]). In Willems et al [2007], McKinley and Alleyne [2012] and Hsieh and Wang [2009] different SCR-and an LNT control schemes are discussed.…”

A SCR Model Calibration Approach with Spatially Resolved Measurements and NH3 Storage Distributions

“…The characteristics and performance of Cu-zeolite and Fe-zeolite catalysts have been studied through both engine and reactor experiments [3,5,14]. Numerous SCR models and kinetic studies have also been published for different formulations including Cuzeolite and Fe-zeolite catalysts [6,8,17,20,24]. However, most of the modeling studies focused on only the SCR inlet and outlet emission measurements without considering the spatial measurements in the channels.…”