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The High Pressure Stripper is a key equipment item in a urea production plant using the carbon dioxide stripping process. The design drawing of such equipment item states that the perpendicularity deviation of the stripper tubes after installation shall be less than 0.5‰, while not more than 3 mm. The perpendicularity is very critical. If perpendicularity of the tubes can not reach the requirements, synthesis fluid entering the tubes will be distributed unevenly. Bias flow at the lower part or local dry zones of the tubes will finally lower the stripping efficiency, increase the bottom fluid temperature of the stripper and increase the corrosion rates of the tubes. Thus the load and efficiency of the whole plant may be affected. During the construction of some urea production plants using carbon dioxide stripping process, only the levelness of stripper tubesheet is measured or perpendicularity of the outer wall of the HP stripper is measured by level meter, while strict alignment of the stripper tubes is not carried out. Therefore, the bottom fluid temperature of the stripper will be high after start-up, while the load and efficiency will be low.
In conclusion, perpendicularity of the stripper tubes is an important factor affecting the stripper efficiency, so strict alignment of the stripper tubes shall be carried out on the new urea production plants using carbon dioxide stripping process. As for old units, if the bottom fluid temperature of the stripper is persistently high, the related inspection shall also be carried out. In addition, perpendicularity of the stripper tubes shall be remeasured and realigned after the overhaul.