Advanced control strategy for NOx reduction in forced unsteady-state reactors

Mihaela Iancu, Claudiu C. Botar, Paul S. Agachi

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Abstract

The environment safety and climate changes reduction are two important aspects which partially can be achieved by lowering gaseous emissions emerged from chemical industry. These emissions are characterized by low pollutant concentration, high volumes of gases and low temperatures. Their treatment could emerge in economical sustainable technologies only if the reactors used are capable of high yields, high selectivity and autothermal behavior. The forced unsteady-state reactors are an excellent choice for treating this type of emissions because allow trapping of the moving heat wave inside the catalytic bed when exothermic reactions take place; the catalytic bed acts as a regenerative heat exchanger creating the premises of a sustain autothermal behavior even if the temperature of the feed is low. Nevertheless, the forced unsteady state reactors are characterized by a remarkable complex dynamic behavior, as a consequence of the complex interaction between heat and mass transport phenomena inside the reactor. This dynamic behavior gives rise to a set of spatial-temporal patterns, chaotic changes in concentration and traveling waves of heat and chemical reactivity, difficult to deal with. Therefore, an advance control strategy is needed to be applied in order to tackle with all issues that characterize reactors with improved contact between reactants, in which the thermal wave is stored and which allow improved kinetic activity of the catalyst used. The catalytic activity is the main operation concern for processes with low feed temperatures and constraints related to low emissions of unconverted reactants. Therefore, predictions of reactor pseudo or steady-state performances regarding conversion, selectivity and thermal behavior and the dynamic reactor response during exploitation are important aspects in finding the optimal control strategy. Moreover, the switching time and the reagents concentrations in the feeding zone are the main operating parameters that may be adapted or changed to fulfill the condition of zero emissions when using forced unsteady-state reactors. Nevertheless, due to unsteady state reactors characteristics, the adaptation of these parameters to process requirements reveals important control design problems. Therefore, in this paper the possibility of using an advanced control strategy, combining model predictive control (MPC) with an on-off control was studied in order to handle with problems that arise when using a forced unsteady-state catalytic reactor network (RN) in case of selective catalytic reduction of NOx with ammonia. The RN system consists of a network of three plug-flow reactors in series, operated in a closed loop configuration. The RN dynamic model was developed using MatLab/Simulink software. The results revealed that the proposed control strategy (i.e. the on-off control and MPC) can successfully handle the NOx emissions of this kind of reactors.

Original languageEnglish
Pages (from-to)997-1002
Number of pages6
JournalComputer Aided Chemical Engineering
Volume32
DOIs
Publication statusPublished - 2013

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All Science Journal Classification (ASJC) codes

  • Chemical Engineering(all)
  • Computer Science Applications

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