0707
Petroleum
- Jun 25, 2001
- 3,357
We have a shell & tube exchanger to vaporise hydrofluorydric acid it is the acid vaporizer for the Rerun Tower on a Phillips-licensed HF Alky. Tube material of the exchanger is Monel-SB 163 UNS 04400. Fluid circulation through shell side is steam at 165ºC. Fluid circulation through tube side is HF acid: inlet at 38.8ºC, outlet at 143.3ºC. maximum velocity (tube side) 15m/s. This tube material, from our experience, fails after, 4 to 6 month runs; due to great corrosion thinning on 2º pass. We know that the cause for that high corrosion rate is traces of water on HF acid stream and oxygen contamination through the nitrogen acid blanketing of acid make up feeding. When operating windows are respected, in some runs, we have extended the life of the exchanger up to 18 month! Whenever possible to keep less than 1% of water in HF, maintaining acid purity above 88% and avoiding oxygen contamination seems to be the good operating windows practice. On the other side is hard to convince operation people on this matter, they always say they never exceed the process parameters. The truth is; normal exchanger runs are 4 to 5 month with sporadic runs of 18 month. What are others experience on this subject? Is there any others material practice alternative to Monel in this particular application?
The forum discussion in this matter would be appreciated
Luis Marques
