Article

Effect of reactor configuration on nitric oxide conversion in nitrogen plasma

AIChE Journal (Impact Factor: 2.75). 06/2005; 51(6):1813 - 1821. DOI: 10.1002/aic.10451

ABSTRACT

The configuration of a nonthermal plasma reactor strongly affects the rate of electron collision reactions. Experiments involving the decomposition of NO in N2 were performed in a reactor in which the number of parallel reactor tubes varied from 1 to 10 at a constant pressure of 147.6 kPa and ambient temperature. A previously developed lumped model of the reactions accurately predicted the effects of varying the initial concentrations of NO (from 240 ppm to 593 ppm) and gas residence time (from 1.93 to 7.42 s). With an increasing number of parallel reactor tubes, the rate of electron collision reactions decreases because the energy input per unit reactor volume at unit time decreases, while the energy consumption per molecule of NO converted to N2 and O2 decreases due to electrical and geometric effects associated with the decreasing peak width of the discharge voltage pulses and increasing reactor capacitance. Therefore, increasing the number of parallel reactor tubes provides a viable scale-up method for constructing more efficient pulsed corona discharge reactors. © 2005 American Institute of Chemical Engineers AIChE J, 2005

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    • "All of these reported values of energy consumption represent low energy efficiencies because N atoms, which are one of the main active species responsible for NO x conversion (Zhao et al., 2004a), can be formed from N 2 dissociation at much lower energies (i.e., the dissociation energy is 9.8 eV/molecule). Although many investigators proposed that energy consumption of NO x conversion can be reduced by the optimization of the reactor configuration, [such as changing electrode diameter (Abdel-Salam et al., 2003), reactor length (Namihira et al., 2001), type of discharge (Penetrante et al., 1995), and series/parallel reactor configurations (Zhao et al., 2004b, 2005)], only a few investigators recognized that optimization of reactor pressure is also an important factor for reducing energy cost in conversion of NO using a PCDR. Starikovskaia et al. (2001) investigated the structure of the electrical breakdown in low-temperature pulsed discharges and found that there is an optimal pressure range for the development of the uniform nanosecond breakdown, in which maximum energy (around 60%) goes into gas excitation to produce the reactive species. "
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    ABSTRACT: This work explores the effect of gas pressure on the rate of electron collision reactions and energy consumption for NO conversion in N2 in a pulsed corona discharge reactor. A previous study showed that the rate constant of electron collision reactions, multiplied by the electron concentration, can be expressed as . The model parameter α remains constant with increasing gas pressure, which verifies the previous assumption that the electron temperature is inversely proportional to gas pressure. However, the model parameter β decreases with increasing gas pressure, which indicates that the rate constant of electron collision reactions decreases with increasing gas pressure. The new expression for the rate constant of electron collision reactions, , is more general because it explicitly accounts for the effect of gas pressure that was previously contained in the parameter β. The electron mean energy decreases with increasing gas pressure, which results in thermal dissipation of a larger fraction of the energy input to the reactor that heats the gas instead of producing plasma chemical reactions. Therefore, energy efficiency for NO conversion in N2 decreases with increasing gas pressure.
    Full-text · Article · Apr 2005 · Chemical Engineering Science
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    ABSTRACT: PPM-level concentrations of CO 2 are added to NO/N 2 mixtures to determine the effect of CO 2 on plasma generation and to investigate the mechanism of CO 2 reactions. Addition of 599.9 ppm CO 2 does not affect the electric discharge in NO x in N 2 nonthermal plasma. However, CO 2 slightly dissociates, with CO 2 conversion reaching a maximum of about 5.5% at the power input at which NO conversion ceases. NO(A), the first-excited electronic state of NO, is detected by corona-induced optical emission and is found to contribute to CO 2 dissociation. A kinetic model including 38 reactions is required to adequately model decomposition of NO x and CO 2 in the presence of CO 2 . About 18% of the NO(A) that is formed reacts with CO 2 to form NO, CO, and O.
    Full-text · Article · May 2005 · Industrial & Engineering Chemistry Research
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    ABSTRACT: Both NO x conversion and CO 2 conversion decrease with increasing percent-level CO 2 concentra-tion in nonthermal nitrogen plasma. The rate constants of electron collision reactions of both N 2 and CO 2 decrease with increasing CO 2 concentration because electronegative CO 2 reduces electron concentrations in the reactor due to the electron attachment process. The rate constant of CO 2 dissociation through electron collision is 1-2 orders of magnitude higher than that of N 2 dissociation because of low dissociation energy of CO 2 . Model data for reactor outlet NO x and CO x concentrations agree well with experimental data. The effect of CO 2 on NO, NO 2 , N 2 O, and CO concentrations can be explained on the basis of the proposed reaction mechanism and kinetic modeling.
    Full-text · Article · May 2005 · Industrial & Engineering Chemistry Research
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