Passivation air in the Synthesis loop

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  • #102064
    redagalih
    Participant
      • Participant
      quote Naemat123 post_id=10110 time=1618635085 user_id=5346:

      Can anyone have data about ” How to calculate % oxygen (Total air mixture we are injecting in CO2). ”
      if anyone have kindly do share will be highly obliged.
      Thanks…

      You can simulate it using DWSIM (open source software simulation) including dehydrogen column/reactor reaction

      #102058
      pbaboo
      Participant
        • Expert

        The oxygen analyser installed in CO2 compressor 3rd stage which is reflecting in control room with Low oxygen alarm. The sample also analyze by lab twice in each shift.
        However you can calculate by following example
        Passivation air flow to CO2 compressor is 450 Nm3/hr
        CO2 Flow in 3rd stage=25000 Nm3/hr
        O2=(450 /25000)X 0.21 X100=0.378%

        https://www.ureaknowhow.com/ukh2/round-table-1/7/1813.html

        Regards,

        #102057
        naemat123
        Participant
          • Participant

          Can anyone have data about ” How to calculate % oxygen (Total air mixture we are injecting in CO2). ”
          if anyone have kindly do share will be highly obliged.
          Thanks…

          #102030
          Mark Brouwer
          Keymaster
            • Expert

            The relation between dissolved oxygen and the oxygen content in the gas phase under equilibrium conditions follows the Henry Law.
            Refer to:
            https://www.ureaknowhow.com/ukh2/photo-gallery/gallery/4-graphs/773-oxygen-partial-pressure-gasphase-atm-versus-ppm-liquid.html
            So adding more oxygen in the gasphase will hardly help as almost in all equipment there are no equilibrium conditions with exception of maybe the urea reactor.

            quote amir_tafazol post_id=10064 time=1615814602 user_id=3834:

            Moreover, as I know the dissolved O2 in liquid will affect passivation layer and if we add more O2 which is more than saturate condition based on thermodynamics, it would not help. Is it correct?
            #102029
            Mark Brouwer
            Keymaster
              • Expert

              Two issues are relevant here:
              1. stay away from crystallisation temperatures
              2. avoid thermal shocks when restarting the plant

              quote amir_tafazol post_id=10063 time=1615814391 user_id=3834:

              Hi all
              In Stamicarbon SAFUREX plants we should have at least 0.3 Vol.% O2 in CO2 gas injected to synthesis in normal operation. It is mentioned that blocking-in of the synthesis section can be extended as long as the wall temperatures of the urea reactor and HP pool condenser are above 125 °C. No time limit is mentioned but blocking in is not allowed if the Nickel content in the end product was more than 25 % above the base line value. So I think the time limit is obtained based on experience. Would anyone can help about the philosophy of the 125 °C ? What will happen if the temperatures drop below 125 C?
              #102027
              amir-tafazol
              Participant
                • Participant

                Moreover, as I know the dissolved O2 in liquid will affect passivation layer and if we add more O2 which is more than saturate condition based on thermodynamics, it would not help. Is it correct?

                #102026
                amir-tafazol
                Participant
                  • Participant

                  Hi all
                  In Stamicarbon SAFUREX plants we should have at least 0.3 Vol.% O2 in CO2 gas injected to synthesis in normal operation. It is mentioned that blocking-in of the synthesis section can be extended as long as the wall temperatures of the urea reactor and HP pool condenser are above 125 °C. No time limit is mentioned but blocking in is not allowed if the Nickel content in the end product was more than 25 % above the base line value. So I think the time limit is obtained based on experience. Would anyone can help about the philosophy of the 125 °C ? What will happen if the temperatures drop below 125 C?

                  #102023
                  Mark Brouwer
                  Keymaster
                    • Expert

                    For normal austenitic stainless steels like 316L UG and 25-22-2, the max blocking period is 72 hrs, but please get confirmation and information about all pre-conditions from Stamicarbon: henri.smolenaers@stamicarbon.com, VP Services

                    #102018
                    salem842
                    Participant
                      • Participant

                      What is the latest time limit of blocking in by STC.

                      Regards

                      #98099
                      mnmudassar
                      Participant
                        • Participant
                        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?

                        We are also in process of installing dedicated passivation air compressors to ensure reliable operation in the event of short of passivation from the Co2 system itself, as we are experienceing severe corrossion issues in HP stripper. I believe that it is an added advantage based on Urea synthesis sensitivty towards the corrossion resistivity

                        #97281
                        Mark Brouwer
                        Keymaster
                          • Expert

                          correct in my point of view.

                          #97280
                          norozi1972
                          Participant
                            • Expert
                            quote umar30:

                            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.

                            Hello dear umar
                            As we know for pasivation of diffrent kinds of material that used in the high pressure equipments we need diffrent percentage of O2.If O2 content in the synthesis reduce less than licensor advise.The equipment will be corroded.but my opinion about the effects of the excess O2 in the synthesis is reducing the capacity of the plant because of increasing in the amount of inert and also increase the range of flammability area and it donot have any effect on corrosin rate.
                            Dear Mark and all friends please correct my information if anything is not right .

                            with best regard
                            khpc-iran
                            norozi

                            #97269
                            wasi
                            Participant
                              • Participant

                              Hello every one, I am wasim anjum, process engineer in Engro Fertilizer..

                              On 3835MTPD Snam urea plant, we use to maintain .25 to .3% oxygen in reactor through CO2 compressor feed. Howeever, ammonia %age is kept high before shutdown for liquid hold up in reactor to avoid corrosion as otherwise high oxygen contents in the loop may lead to explosive mixture formation.
                              In addition, we have a separate air compressor for stripper passivation.

                              Regards,

                              Wasim Anjum,
                              Process Engineer l Engro Corp, Pakistan

                              #97263
                              Mohammad Farooq
                              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

                                dear all,

                                Although , it has been explained well by friends, just to add that when synthesis loop goes under shut down , passivation layer will break and by adding air in this case will not help . Hold -up period can be prolonged(Max as described by licencer) and in this case addition of ammonia is more useful in order to prevent corrosion . system needs repassivation before star -up
                                one friend has mentioned that black hard scale at carbamater condenser tube, in my opinion it is not oxygen percentage impact. . but it may be due to erosion of other internal in the loop or somewhere else

                                regards

                                #97260
                                protyai
                                Participant
                                  • Participant
                                  quote mark.brouwer:

                                  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.

                                  1. Our high pressure reactors are made of 25-22-2 material. What is the recommended (industrially used) % O2 in CO2 feed. We use 0.3%. Is it low?
                                  2. Black and hard (Fe2O3) corrosion product is formed frequently on the top of the tubes of our carbamate decomposer (material – 316). Is it because of the low passivation air flow rate or high passivation air flow rate?

                                  h

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