Q & A > Question Details
We have hydrotherapy unit , consisting of cobalt molybedium (s-7 and s-120) reactor, reaction temperature 610 F system pressure 24 bar.We have a problem for two months that is the reflux drum of stripper got very low thickness observed, its boot water has PH 2.0----2.5, iron greater than 100 ppm while chloride was 1000 to 2000
condensate injection 8bbls/h from condenser inlet.
We have already done the cleaning of all heat exchanger , overhead condenser, overhead reflux drum.
Then start up of the unit was performed but condition remains the same.
Please share your opinion regarding this problem.
16/06/2015 A: Ganesh Maturu, Self, maturu.ganesh@gmail.com
Almost all the chlorides can be removed from cold high pressure separator using water wash. Since it reaches below the NH4CL desublimation temperature in cold high pressure separator, most of the chlorides dissolves in water and separates from boot. Following are some verifications can be done.
1. Since stripper overhead boot water observed as highly acidic and contains high chlorides, confirm whether enough wash water is added before reactor effluent air cooler by checking the cold high pressure separator boot water concentration.
2. Check the water balance across the stripper. If stripper receiver boot contains water flow higher than stripping steam and wash water injection at stripper overhead line, water-HC separation is not happening properly in high pressure separator in reactor section. Necessary modifications should be done to take care of this separation at high pressure separator.
3. Since you have mentioned, continuous injection of condensate at condenser inlet, make sure that enough water is present in liquid form (around 20% injected water should be in liquid). This can be checked by using a simulator. Again this may not solve your problem of reflux drum corrosion. But increasing wash water flow dilutes the chloride concentration and reduces corrosion issues.
13/06/2015 A: Narendra Naidu, Bapco, nbpnnaidu@gmail.com
In normal operation the Hydrotreater should not see any Chloride salts in the Stripper overheads, it should all be washed with Wash water at the Effluent exchangers and be dissolved in Sour water.
You may have some Ammonium bisulphide salts formation but the deposition temperature would be very low based on the concentration.
So in short if you have Chloride salt deposition in your Stripper overhead than the problem exists in the sour water separation in the Cold High pressure separator and there is physical carry over of Sour water with salts to the downstream Stripper oil. check the levels and rectify that. Check the interface levels in the separators?
Where is the source of extra Chloride? some of the sources could be, check your Naphtha feed Chloride content has it increased? H2 make up Chloride content if this is coming from a Platformer? Stripped Sour water used as wash water in Hydrotreater chloride content. you have to eliminate the source of the problem
this is same problem in the earlier query raised on this forum.