After several years in operation, the neutralisation towers of an atmospheric pressure ammonium nitrate (AN) solution plant were replaced during the 2015 maintenance shutdown, due to thickness losses. However, after start-up the plant experienced an unstable operation: level oscillation in the collecting vessel, vibration of AN piping and equipment, intermittent flow and hammer effects in the towers. The plant load could not be increased, and there were signs of iron contamination in the AN solution.
It was clear that there was a flow problem in the towers, so it was decided to use a thermal camera to evaluate the flow profile. The thermal images showed problems just above the second stage distributor, in the area of the ammonia pipe feed. This enabled the possible causes of the problems to be narrowed down. The towers were opened for examination and various dimensions were compared with the drawings and the original towers. This revealed that the new towers were not exactly identical to the old ones, as they were supposed to be. This article will explain the cause of this problem and describe the solution that was implemented.
Rodrigo Dias Gonçalves, Yara Brasil Fertilizantes S.A., Cubatão SP, Brasil
23 pages, 19 figures, 4 plates