Problem No. 12: Oil fouling of the high pressure stripper in a urea plant

The efficiency of the high pressure stripper is a very important parameter in the optimum operation of any urea plant. Fouling of the HP stripper can reduce the efficiency and oil is a typical cause of fouling. Oil can originate from, for example, oil seal systems of high pressure reciprocating ammonia and carbamate pumps and carbon dioxide compressors. Oil can easily cause fouling of the liquid distributor system in the top of the HP stripper (where small holes are present) as the oil can become thick due the stripping of the light components. What are the best methods of solving oil fouling problems and cleaning the HP stripper?

Mr Malik Sohail of Agritech Ltd in Pakistan introduces a very interesting practical problem that has a big impact on the performance of a urea plant – oil fouling in the high pressure stripper: We have a TEC ACES plant with a HP stripper of Stamicarbon design. There has been a problem with stripper efficiency and when the ferrules were opened during a shutdown it was found that 150+ tubes (about 10%) had oil in the stripper bottom. The ferrules are OK. No blockage of holes was observed but there was evidence of pitting. The oil consumption at the NH₃ feed pump was high before the shutdown and the HP stripper bottom temperature was on the high side with high NH₃ slippage.