Solving NOx Production Problems in Nitric Acid Manufacting Plants

The NOx content of tail gases from a standard nitric acid manufacturing plant depends on the absorption efficiency; in other words, mainly on the pressure factor. Initially, the NOx cleansing problem was tackled simply by increasing the absorption pressure; although it is an efficient method, it cannot be applied to old plants and it demands a high energy input. Variousprocesses were then proposed for solving the problem of old plants, that is, low-pressure absorptions. Only selective catalytic destruction of NOx with amonia is used on an industrial scale today. Although efficient with respect to pollution control, this method involves a loss of ammonia yield which is not insignificant; in order to reduce this loss, RHONE POULENC have developed a High Efficiency Absorption, based on a liquid-phase oxidation of NOx and used in combination with the catalytic destruction: these two techniques used together enable the most stringent standards for NOx levels to be met in each case and at minimum cost.