Nitric acid (HNO3) is needed to manufacture ammonium nitrate for fertilizers and the mining industry, and for plastics and dyes. Its industrial production involves oxidizing ammonia (NH3) with air over a platinum/rhodium gauze catalyst to nitrogen oxides. The nitrogen oxides are almost all absorbed in water to form nitric acid, the desired product. Unfortunately, the ammonia oxidation step also generates unwanted nitrous oxide (N2O) which passes unchanged through the plant and enters the atmosphere in the plant’s tail gas. Some residual NOx, which even the most efficient process cannot entirely turn into nitric acid, is also emitted with the N2O. While limits on NOx emissions have long been in force because of concerns about acid rain and smog, N2O emissions have for a long time not been subject to effective restrictions. However, in the meantime N2O has been recognized as the powerful climate killer it truly is. One ton of N2O emissions has the same impact on global warming as 265 tons of CO2. As an estimated 400,000 tons of N2O are generated annually in nitric acids plants worldwide, this is a potent problem. Fortunately, the thyssenkrupp EnviNOx® abatement process for nitric acid plants provides an effective solution.
The EnviNOx® N2O and NOx process is a so-called end-of-pipe technology because it is installed in the waste gas stream of the plant and thus entails no risk of product contamination, nitric acid production loss or fouling of equipment (such as the process gas cooler). A proven solution already installed in multiple nitric acid plants worldwide, the EnviNOx® process is remarkably effective: N2O removal rates of up to 99% and above, and virtual elimination of NOx down to nearly zero ppm. It is also a highly practical solution as abatement of both pollutants can be combined in a single reactor vessel and only limited quantities of the N2O and NOx reducing agents are consumed in the process. EnviNOx® technology employs highly active zeolite catalysts that have a long service life and contain no toxic components, ensuring easy handling and disposal.
thyssenkrupp’s wealth of experience and expertise has enabled the development of N2O and NOx abatement solutions that are optimized for particular process conditions and temperature ranges. With this proven technology to remove harmful greenhouse gases, thyssenkrupp is helping nitric acid plant operators make a key contribution to climate protection.