Passivation air in the Synthesis loop

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  • #95195
    muhammad-adnan-hanif
    Participant
      • Expert

      Assalamo Alaikum

      Nasir, in my opinion the normally added O2 i.e. ~ 0.32-0.35 % of total CO2 flow is sufficient to passivate the HP section equipments in normal operation and same we are practicing on our three SP based plants and the results are quite well satisfactory.

      However, during reduce load operation before shutdown, we do not increase O2 to HP section in view of avoiding to enter the mixture in explosive range. We try to reduce corrosion rate by increasing NH3 concentration which also helps to keep mixture away from explosive limits and it is a part of standard operating procedure on our all three plants.

      quote nasir410:

      hi to all my friends my question is
      In the shut down condition when the solution is in hold position in synthesis loop what is the condition of Passivation air/layer?when the feed is cut in the reactor how can we ensure maximum Passivation air in reactor?
      tell me for the Snam technology

      Nasir Hussain
      Pak Arab Fertilizers Multan Pakistan

      #95194
      muhammad-adnan-hanif
      Participant
        • Expert

        Yah, we were experiencing the same problem in our SP based plants and after installation of additional compressors for passivation of stripper bottom part the issue has significantly decreased. So, based on our experience i shall recommend you to install the same as soon as possible.

        quote cboyda:

        Our facility is a 2100 MTPD Snam plant. We currently only have one passivation air injection point (CO2 Compressor). Based on some corrosion we are seeing in the Heat Affected Zone (HAZ) of the stripper bottom channel liner welds, we are considering installation of an additional air compressor to supply air to the bottom of the stripper. The HAZ corrosion is evident in both the liquid and vapour space of the bottom channel. Would somebbody be able to tell me that there is significant benefit for us to install this additional passivation compressor to inject air in the bottom of the stripper?
        #95193
        cboyda
        Participant
          • Participant

          Our facility is a 2100 MTPD Snam plant. We currently only have one passivation air injection point (CO2 Compressor). Based on some corrosion we are seeing in the Heat Affected Zone (HAZ) of the stripper bottom channel liner welds, we are considering installation of an additional air compressor to supply air to the bottom of the stripper. The HAZ corrosion is evident in both the liquid and vapour space of the bottom channel. Would somebbody be able to tell me that there is significant benefit for us to install this additional passivation compressor to inject air in the bottom of the stripper?

          #95192
          engahmed84
          Participant
            • Expert

            hi all
            as mr. mark mentioned there will be a limit time before passive layer break down and complete drain become nessc. , in stamicarbon plant 72 hrs is the max. limit before passive layer break
            and i think that providing high oxygen % before shutdown will not benefit as most of it will be vented through inert valve and still we are regulated with nature of the st.st that will suffer from corrossion cells after the design limit time away from supplied oxygen just before shutdown
            e.x : as long as oxygen % is above 0.6% vol. just before shutdown it is o.k
            please correct my information if anything is not right

            thanks

            #95130
            nasir410
            Participant
              • Expert

              Omar actually i was talking about the special case of plant shutdown.Is this not good practice of having much amount before shutdown?when the synthesis loop is in hold position?

              Nasir Hussain

              #95129
              nasir410
              Participant
                • Expert

                Ok thanks provide me this graph

                Nasir Hussain
                PAk Arab Fertilizers Multan Pakistan

                #95128
                umar30
                Participant
                  • Participant

                  optimum oxygen is required for urea reactor passivation if we increse the % of oxygen from optimum value than reactor corrosion will increse
                  reactor corrosion will increse with low and high % of oxygen. if you need a graph showing this phenomenon i will provide you.

                  #95095
                  nasir410
                  Participant
                    • Expert

                    In our plant when we reduce the load to reactor for shutdown, we maximize oxygen in the CO2,in this way we ensure maximum oxygen as much we can.

                    Nasir Hussain
                    Pak Arab Fertilizers Multan Pakistan

                    #95092
                    Mark Brouwer
                    Keymaster
                      • Expert

                      Stainless steels need oxygen to form a passive layer and in the urea synthesis continuously oxygen needs to be added to assure the passive layer remains there.
                      The Snam processes also adds oxygen via the CO2 on the reactor.

                      Ofcourse during blocking in no oxygen can be added (in all types of technologies) and there is a risk the passive layer will be depleted. Therefore there a time limit that one can block in the synthesis without major corrosion risks

                      #95091
                      brijlalgupta
                      Participant
                        • Participant

                        As per my knowledge, for Snam Urea process, passivation air is not needed in HP part of urea synthesis.

                        #92324
                        nasir410
                        Participant
                          • Expert

                          hi to all my friends my question is
                          In the shut down condition when the solution is in hold position in synthesis loop what is the condition of Passivation air/layer?when the feed is cut in the reactor how can we ensure maximum Passivation air in reactor?
                          tell me for the Snam technology

                          Nasir Hussain
                          Pak Arab Fertilizers Multan Pakistan

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