Advances in Nitric Acid Manufacture

Keywords: Nitric acid.

Although the nitric acid process is a well-known technology, some improvements are still possible. Improvements which are individually small can be combined to lead to significant improvements in terms of costs, reliability and efficiency. Having taken a bull gear type compressor for air services with integrated intercoolers as a package unit, this machine was adapted for nitric acid application. The tailgas turbine was designed as an integral part of this machine. The next step was the application of such a unit specifically for the requirements of a nitric acidplant. In order to improve the total energy balance of the plant, the intercoolers can be partly or completely removed depending on the process selected. This offers not only advantages in terms of energy but also reduces the number of heat exchangers required used with a resultant cost benefit.

A critical heat exchanger within the nitric acid plant is the cooler condenser. Correct selection of the constituents of the stainless steel alloy material is very important in achieving extended life time. Also the design of this exchanger has to be adapted to the special process requirements.

Emission of dinitrogen oxide from nitric acid plants could be critical in future. Krupp Uhde is working on a procedure to reduce this gas component from the current 800-1,500 ppm to whatever value is required by the authorities.

Other further improvements are process air filtration with advanced filter media, use of new knitted catalyst systems in the burner section and some positive changes regarding chemical conversion efficiency and hydraulic behaviour of the absorption tower.

W Freitag and R Maurer, Krupp Uhde GmbH, Dortmund, Germany.

16 pages, 5 figures, 1 table.