Ni content in process reaction mixture in HP urea synthesis

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  • #101085
    mocznik-police
    Participant
      • Expert

      Dear Mark,

      Thank you for constructive discussion and sharing your and yours’ colleagues experience. It has helped us to understand what could happened a lot.

      Hope to read more interesting case studies on Round Table!

      #101084
      Mark Brouwer
      Keymaster
        • Expert

        Dear All,

        Further discussions lead to the conclusion that the changes in Ni likely are related to turnaround activities (the T/A was from 12 July to August 16).

        #101078
        mocznik-police
        Participant
          • Expert

          Dear Mark,

          Please see via below link the trends of Ni content in synthesis and HP carbamate pump. We have increased oxygen content on 19th October.

          https://www.ureaknowhow.com/ukh2/round-table-1/8/1739.html?p=8627#p8627

          Any conclusions?

          #101075
          Mark Brouwer
          Keymaster
            • Expert

            In the HP scrubber one has relatively high partial oxygen levels in the gasfase, so one would not expect that going from 0.8 vol% (which is already high) to a higher figure would give benefits in the HP scrubber.

            One should look at trends as the analysis is not very accurate. Did you do this ?
            How the delta-Ni looks over the HP scrubber trendwise at 0.8 and 1.1 vol% O2 ?

            yes, one can also measure Ni in the LP section as also there the stainless steel are passivated by the oxygen dissolved in the liquid coming from the HP stripper.

            Nice and interesting case is this !

            #101074
            mocznik-police
            Participant
              • Expert

              Dear Mark,

              Yes, we talk about a Stac CO2 stripping plant with falling film HPCC.

              We noticed that Ni level started to decrease in HP Scrubber, in other equipment we have stable Ni level. We started measure Ni level in HP carbamate pump and we have noticed high level as well.

              Can it be a reason of high Ni level in HP Scrubber? Do you measure Ni level in LP section as well?

              #101073
              Mark Brouwer
              Keymaster
                • Expert

                At which equipment you mean the passive corrosion decreased ?
                How did you conclude passive corrosion rates decreased when you increased the oxygen content
                We talk about a Stac CO2 stripping plant with falling film HPCC, right ?

                #101072
                mocznik-police
                Participant
                  • Expert

                  Dear Mark,

                  Thank you for quick reply! We decided to increase amount of oxygene in urea synthesis from 0,8 to 1,1%. We have noticed that passive corrosion started to decrease.

                  Do you have any advice what could happened?

                  #101070
                  Mark Brouwer
                  Keymaster
                    • Expert

                    Dear Krzysztof,

                    One measures in Nickel to check if one has active corrosion.

                    In case one has active corrosion it cannot become passive anymore unless one shuts down the plant, drains the synthesis and re-passivates.

                    This means one should look for increasing trends, not peaks.

                    Then one should know what is ones normal Nickel levels, to know if one has an increasing trend.

                    It does not make a lot of sense to compare with other plants as it depends on for example the applies materials. For example 316L UG and 25-22-2 have completely different Nickels contents…

                    Let us know when anything is unclear

                    Mark

                    #93750
                    mocznik-police
                    Participant
                      • Expert

                      Dear Friends,

                      I would like to ask what is your standard Ni content which you measure in urea synthesis. When we should worry for corrosion? In which vessels you check Ni in your plants? We are worry because our Ni content in HP scrubber has increased compared to earlier years more than a standard level .

                      What can be a reason? Have any idea?

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