Problem No. 32: Temperature drop at bottom outlet of HP stripper in a Saipem urea plant

The stripper in a urea plant is a key item of high pressure equipment affecting the overall performance of a urea plant. There is a significant difference between the Stamicarbon CO₂ HP stripper and the Saipem NH₃ HP stripper when judging its performance. The bottom outlet temperature of a Stamicarbon CO₂ stripper is normally relatively low (172- 175°C) and when the performance of the HP stripper reduces (meaning lower stripping efficiency) this temperature will increase indicating an increase in the ammonia content in the bottom outlet of the stripper. However, in a Saipem NH₃ stripper the situation is totally different. The stripper bottom outlet temperature increases with a higher stripper efficiency and an operator in a Saipem urea plant tries to operate the urea plant at the maximum bottom outlet temperature. The maximum value is determined by the acceptable corrosion rates, for example, 224°C for a bimetallic stripper.