Simultaneous Optimization of Operating Conditions and Sizes of Monolith Catalytic Reactors for the Reduction of NOx Emission

ANA M. ARIAS; MIGUEL C. MUSSATI; NICOLÁS J. SCENNA; VESNA TOMASIK; ZORAN GOMZI; SERGIO F. MUSSATI

San Sebastián

Conferencia; 5th-international-conference-structured-catalysts-and-reactors; 2016

Monolith reactors were widely applied to the automobile industry to reduce emissions of undesired products from the exhaust gases. In the last time, monoliths are increasingly under development and evaluation for many new reactor applications. Compared to the traditional catalysts used for gas phase reactions, monolith reactors are preferred to the exhaust gas treatment, because of their high conversion rate, reaction performance and selectivity and elimination of hot-spot [Chen et al. (2008)]. The advantages of monolith converters over the conventional reactors with particular focus on the integral approach to the catalyst and reactor design are clearly pointed out in Tomasicand Jovic (2006).During the last years many research activities in NOx control technologies have been done in different lines from experimental studies at laboratory scale [Tomasic and Gomzi (2004), Rico-Perez et al. (2013), Lumpiañez et al. (2013), Kang et al. (2014)] to the development and implementation of mathematical models in computers [Ghadrdan and Mehdizadeh (2008), Jirát et al. (1999), Shakya et al.(2014), Gundlapally and Balakotaiah (2013), Yun and Kim (2013), Kim et al. (2012), Zukerman et al. (2009), Stepánek et al. (2011)].Simulations and development of mathematical models can be effectively used to gain insights and identify trade-offs between the process variables which help to determine feasible and optimal process designs.Despite of the many publications dealing with the modeling and simulation of selective catalytic reduction (SCR) technology, the state of art reveals that there are only few articles addressing the optimization of SCR technologies for NOx emission using mathematical programming approaches and detailed models [Tronci et al. (1999), Ramanathan et al. (2004), Kim and Kim (2007), Desmet et al. (2003), Kim et al. (2009), Chen and Tan (2012)]. In addition, it is also possible to conclude that there are no articles dealing with the use of robust optimization algorithms applied to the design and operation of catalytic NOx converters.In this paper, a detailed mathematical model to optimize monolith catalytic reactors for the reduction of NOx emission as well as an efficient solution strategy will be developed. The proposed model and the solution procedure should be robust enough in order to guarantee the convergence for any particular input data provided by users. Reactor dimensions (diameter and length) and operatingconditions will be optimized simultaneously. The resulting PDAEs are converted to a set of nonlinear algebraic equations using finite difference approximation (FDM) and are implemented into the optimization environment GAMS (General Algebraic Modeling System). The objective function proposed to be maximized is the ratio between the NOx conversion and reactor volume. The optimal profile of the main operating and design variables (NOx conversion, gas velocity as well as the reactor diameter and length) are obtained simultaneously. In addition, parameter sensitivity is also investigated and discussed in detail.