Q & A > Question Details
Recently we have suffered some problems of Cupper Corrosion test failure in LPG. The LPG came from a caustic treatment for mercaptan sulphur removal. After caustic treatment, the LPG pass through a decanter (with NaOH/MEA solution) and sand filter, which are supposed to remove any caustic carryover from LPG. We do not see any caustic collected in the sand filter, however we have detected Na and nitrogen in LPG, so we suspect that it is not working properly. The sand filter seems not only not working, but also accumulating some contaminants: we have seen sometimes that LPG pass the cupper corrosion test in the inlet, but not in the outlet of the sand filter.
We are evaluating the possibility of substituting the sand by any other more effective adsorbent for caustic / nitrogen (amines). The possibilities are: activated carbon, Anthracite or alumina.
Has anyone experience with adsorbents for contaminant (caustic, amine, etc..) removal in LPG? Any idea / recommendation regarding the operation of the sand filter?
04/09/2014 A: keith bowers, B and B Consulting, kebowers47@gmail.com
Failing 'copper strip corrosion' quality tests on LPG can be caused by many things. Trace H2S is a bad actor (it has nearly the same boiling point as propane.) In your situation, it is likely the 'caustic wash' caustic needs to be replaced more frequently, or a 'final rinse' with fresh make-up caustic may be enough.
Sand filters are a good, low cost, but low capacity 'final filter' so to speak, 'suspenders after the belt.' Uniform liquid distribution is necessary for the maximum effectiveness to be achieved. Sometimes the loading of the sand improperly creates a dense zone in the middle diverting most flow to the edge.
The sand filter IS catching something, but remember the strength of retention is low. Stuff WILL leach off and into the LPG once it is loaded. The 'loading' will not be visible, but can be inferred. Precise measure of 'sulfur in' vs 'sulfur out' on a routine (daily?) basis will show declining efficiency as loading approaches completeness.
Look at how well the sand is being 'regenerated' to ensure that is effective at restoring the capability.
25/08/2014 A: Egbert van Hoorn, Hocon B V, Egbertvh@hotmail.com
LPG treatment is more difficult and has more problems than most people realize. I strongly suspect that this is an FCC refinery. FCC refineries frequently have problems with the LPG quality which are not understood. The are related to sulphur and nitrogen contamination of the LPG. The test methods used are regularly not adequate to correctly measure the sulphur and nitrogen content of LPG. This results in downstream deactivation of TAME/MTBE/alkylation or isomerisation units.
The key point is to understand which contamination occurs and how it happens. Detailed measurements of the composition of the LPG are required to understand this. Understanding the problem is the most important item.