Catalytic reduction of nitrogen oxides by ammonia

Abstract

Of all the methods for treating gases to remove nitrogen oxides, the most widely used are methods based on catalytic reduction. The capital expense required for such methods is relatively small, and the equipment can be simpler and at the same time quite efficient. Among these methods, the most promising is the catalytic reduction of nitrogen oxides by ammonia, forming nitrogen and water. The chief advantage of this method is the capability for reducing nitrogen oxides in the presence of excess oxygen in stack gas. The catalysts may incorporate one or several oxides of manganese, copper, iron, chromium, cobalt, nickel, molybdenum, and vanadium, giving a 90-100% removal of nitrogen oxides at 250-500{degrees}C. Here we are reporting on an investigation of the activity of commercial catalysts based on the oxides of such metals as chromium, zinc, iron, cobalt, nickel, calcium, and aluminum (K-16, K-16U, GIAP-19, Pd/C, NTK-4, NTK-10, TO-2, IM-2204, STK, K-24, Ni-Cr) in the selective reduction of nitrogen oxides. The catalyst activity was investigated in a flow-type laboratory unit consisting of a section for the preparation of gas mixtures with the required composition, a single-pass flow reactor with a fixed bed of catalyst, and a saturator for injecting water vapormore » into the reaction stream. A model gas mixture was prepared by feeding each component in the required quantity by means of flow regulators. The required content of water in the gas was established by passing part of the gas through the saturator, which was heated to the appropriate temperature. The streams of the individual components were mixed in a pipe cross; the model mixture, similar in composition to stack gas, was fed to the reactor, which was mounted in an electric furnace.« less