Modeling of a Two-Bed Reactor for Low-Temperature Removal of Nitrogen Oxides in Nitric Acid Production

Abstract

In this study, the modeling of the low-temperature catalytic abatement of NOX and N2O from tail gases in a weak nitric acid plant utilizing a single-pressure 0.716 MPa system was performed. A one-reactor concept assumes that in the first bed, NOX is reduced by ammonia on a commercial vanadia–alumina catalyst, and in the second bed, N2O is decomposed on a proprietary nickel–cobalt catalyst. The kinetics of N2O decomposition on a Cs/Ni0.1Co2.9O4 catalyst was experimentally studied in an isothermal flow reactor. The reaction rate constants were determined by varying the residence time and temperature; these data formed the basis for modeling kinetics and heat and mass transport in an adiabatic reactor in which the low-temperature mitigation of nitrogen oxides occurred. Taking into account the given spatial limitations inside the reactor and the allowable temperatures, the layer heights were evaluated to ensure a residual NOX and N2O content of less than 50 ppm. Catalyst loading using layers in a commercial reactor was estimated for the tail-gas flow rates of 46,040–58,670 m3/h. Simulations showed that the optimum inlet temperature was 260 °C; in this case, the NOX and N2O conversion targets were achieved in the range of 46,040–58,670 m3/h while adhering to catalyst bed height and outlet temperature limitations.