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.
NOx reduction in a single representative channel of an SCR converter is modeled accounting for convective mass transfer along the channel, diffusive mass transfer and chemical reactions within the catalytic layer, coupled via mass transfer boundary condition at the wall. The proposed 1D+1D code for the channel has different parameters involving rate expression constants for the surface chemistry and properties of the catalytic and washcoated layer. A comprehensive set of experimental data on the Fe-Zeolite washcoated monolith was available for different feed concentrations, temperatures and flow rates. A genetic algorithm was used as an optimization technique to calibrate the model parameters by minimizing the error between simulation results and transient responses of the real system. Dynamic tests showing the response of the system during fast transients were subsequently used to assess the predictive quality of the model with the calibrated parameters. In particular, different rate expressions for the surface reactions were compared to find the best fit for the tested catalyst, providing insight with respect to the importance of the different reaction pathways and the chemico-physical properties of the system. Based on the findings, an optimization strategy could be proposed both in terms of sequence as well as minimum required experimental tests for each sub-system according to the parameters which can be determined separately.
NOx reduction over an Fe–zeolite catalyst is simulated for highly transient conditions representative of automotive diesel engine operation. A transient 1D convection + 1D diffusion (1D + 1D) model for a single channel of a catalytic converter is developed, including a set of the most recently proposed kinetics for Fe–zeolite catalysts. The parameters specifying the characteristics of the selective catalytic reduction system are introduced, and an efficient calibration procedure is proposed that exploits the specific structure of the experimental dataset, consisting of a total of 90 operating conditions with varying space velocities, temperatures and inlet concentrations.
Parameterization of the system is carried out by studying the system response to single step feeds in the inlet ammonia up to steady state (slow transient). Experimental data for highly dynamic ammonia dosing is subsequently employed to assess the model performance at highly transient conditions typical of diesel engine operation. Excellent agreement is reported for a total of 90 operating conditions; differences between the predictions and the experimental data in cumulative converted NOx after 20,000 s of operation are less than 2%.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.