Modeling Of Reverse Flow Catalytic Combustion Process For Air Purification

As a kind of the main atmospheric pollutants, gaseous emissions containvolatile organic compounds (VOCs) lead to many diseases, such as edema,emphysema, cancer and even death at high concentration. Further more, they alsoparticipate in the greenhouse effect, the reduction of the ozone in the stratosphericlayer and the production of actinic smog. In recent years air contaminated witharomatic hydrocarbons released from painting, coating and adhensive industries hascaused many health hazards. More and more attention has been paying to itspurification. Because catalytic combustion of VOCs in a reverse flow reactor (RFR) has highdegree of integration and high thermal efficiency, even inlet temperature and reactantconcentration of waste gas are very low, the reactor can be operated autothermally.Besides, owing to considerable difference in voluminal heat capacity betweengaseous phase and solid phase, the reactor has high stability even the feedcomposition and gas velocity fluctuate frequently in a certain range. Catalyticcombustion in RFR is one of the earliest industrially practiced and the mostextensively used unsteady state reaction techniques. In this work, catalytic combustion of aromatics containing waste gas in a RFR issystematically studied. The influence of main operation parameters and thefluctuation of reactant concentration on the performance of the reactor wasinvestigated in a pilot plant. A heterogeneous one-dimensional with axial dispersionmodel of the RFR was developed. Based on the results of experiments andsimulations, designing and operation strategy of the reactor is discussed. With theexperimental data and simulation results the RBF (Radial Basis Function) artificialneural networks models for predicting pseudo-steady state and transient temperatureprofiles were developed. Real-time control experiments of the reactor under thesevere fluctuation in feed concentration were carried out. First, three kinds of intrinsic kinetic models of catalytic combustion ofaromatics over Pt catalysts were developed with surface-reaction control assumptionand some rational simplification. The intrinsic kinetic experiments of catalyticcombustion of aromatics over a domestic noble metal supported catalyst, NZP-3catalyst, were undertaken in an integral micro-reactor. Model parameters wereestimated with Simplex methods. Statistical test shows that these models are highlyacceptable. Afterwards, a pilot plant packed with a litre of catalyst was designed andconstructed. Some effective measures were adopted in order to keep the reactoradiabatic in radial direction and to reduce the axial heat conductivity along the wallof the reactor. The concentration of VOCs was analyzed by a GC and the transientaxial temperature profile was automatically monitored and collected by a PC.Purification experiments of waste gas containing single aromatic hydrocarbon(cumin) and aromatic mixtures (benzene, toluene and xylene) were carried out in alarge range of experimental conditions. Influence of the parameters, such as the feedcomposition, the components to be purified, the duration of a period and gas velocity,on the performance of the reactor in cyclic steady state was investigated. The resultsshow that the characteristic of thermal wave is the most important property of reverseflow catalytic combustion reactor. Duration of a period is a parameter that influencesthe temperature level of reactor and also could be controlled easily. By adjusting thisoperating parameter, waste gas with different inlet concentrations could be purifiedwith high conversion, autothermally and stably. It was found that the reactor mightpresent saddle shape transient temperature profiles at a very low space velocity and ashort period duration. It was also observed that when the inlet concentration of VOCswas too high and operation condition was improper the reactor could not reach thecyclic steady state and the temperature of catalyst bed would 'run...