H2SO4 injection in urea melt

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  • #102289
    Mark Brouwer
    Keymaster
      • Expert

      Refer for the phase diagram urea – sulphuric acid to:
      https://www.ureaknowhow.com/ukh2/photo-gallery/graphs.html?i=scan0038-1

      This phase diagram shows two eutecnica (E1 and E2) with a melt point of 10 degC.

      Urea and sulphuric acid form the following complexes:
      Urea.H2SO4 and 2urea.H2SO4
      source: Dalman, L.H., 1934, “Ternary systems of Urea and Acids”, JACS 56:549-553

      #100419
      Mark Brouwer
      Keymaster
        • Expert

        Dear Chaudhari
        This reaction is very exothermic, also have you inspect the prilling bucket, becasue MOC of prilling bucket is Al. Alloy. I feel that H2SO4 might harm your prilling bucket.

        Can you share performace pre and post dosing of H2 SO4.

        (NH2)2CO + H2SO4 —-> (NH2)2CO.H2SO4
        Very exothermic (explosive reaction if excess heat is not controlled)

        #100418
        dinakar
        Participant
          • Participant

          We have a dedusting system to collect urea and ammonia in the prill tower off hot air …which will be best treating with h2so4 r dedusting in

          #100370
          i-g-chaudhari
          Participant
            • Participant

            Dear Le ,
            In understand that you have done this experiment in year 2010 so you have very long experience which none of company has tried. I wish to suggest injection of sulfuric acid before concentration section to my company with many benefits of
            1.0 Increasing crushing strength of prills
            2.0 Lowering ammonia content in waste water
            3.0 adding ammonium sulfate in urea product to prevent misuse of subsidized fertilize urea as industrial product.
            4.0 adding AS in urea may increase nitrogen use efficiency of urea along with additional nutrient of Sulfur in urea.

            Kindly share your experience for interest of all members.
            Regards.

            I G Chaudhari

            #98458
            vsridhar
            Participant
              • Participant

              One more effect of dosing sulphuric acid in to urea melt will be
              1.Presence of Ammonium sulphate (AS)content in urea will reduce the Nitrogen content to less than 46%
              2.Presence of AS will make urea more hygroscopic in nature.The relative critical humidity will come down from 74% (@30 deg C for normal urea granule) to around 69%(@30 deg C for urea containing AS content).
              In other words urea handling/loading cannot continue once the RH increases to 69% in case of urea with AS where as in the case of normal urea it can continue till RH increases to 74%.
              Regards
              Sridhar

              #98454
              girish-prakash
              Participant
                • Expert

                Dear Friends,

                Is there any adverse effect of acid dosing on the Prilling Bucket, which is usually of Aluminium?

                Regards,
                Girish

                #98453
                niranjanmurthyp
                Participant
                  • Participant

                  Dear All

                  can any one tell me the effect of H2SO4 injection to urea melt on dust and ammonia emission.

                  Regards,
                  Niranjanamurthy P

                  #98449
                  Mark Brouwer
                  Keymaster
                    • Expert
                    #96220
                    vsridhar
                    Participant
                      • Participant

                      As you know,biuret formation, in urea melt ,is favoured by three conditions namely
                      1.High concentration
                      2.More residence time
                      3.Less partial pressure of Ammonia
                      In the above mentioned reaction which is exothermic ,the temperature must be increasing more thus producing liquid bubbles leading to two phase flow ultimately resulting in pump cavitation.
                      Since the acid is being injected as extra quantity,the residence time experienced by urea melt is increasing thus leading to more biuret formation.In addition,since the acid is consuming whatever excess Ammonia is available,the biuret formation is rapid due to condition no. 3 mentioned above.

                      #96216
                      imran-idris
                      Participant
                        • Participant

                        Mr. Ting Nguk Sing, as per your experience decrease in flow definitely indicates cavitation which we all know results in developed head of the pump, flow rate and finally amperage, but it seems from previous discussion of Mr. Inban that decrease in flow has not been experienced which means that there is least possibility that the pump cavitates in this case.

                        #96212
                        ting-nguk-sing
                        Participant
                          • Participant
                          quote lnban:

                          Dear all!
                          Today i inject H2SO4 98% into urea melt solution to prilling top, injection point is suction of urea melt pump, but the problem is the current and discharge pressure of the pump decrease gradually when acid flowrate increasing gradually, what happen with the melt pump? does it cavitate? do you have experience about this?
                          Thank all!

                          Urea melt temperature I believe is 133 degC at the melt pump suction and H2SO4 is at ambient temperature. Injection of the acid to the high temperature melt will cause the acid to vaporize leading to melt pump cavitation. We had experienced, while injection of CPL (hot condensate) to clear blockage for the sampling valve located at the pump suction caused the same effects i.e. current and discharge pressure/flow of the pump decrease.

                          #96211
                          imran-idris
                          Participant
                            • Participant

                            Dear MR. Le Ngoc Ban, I have few queries regarding reduction in pump discharge pressure & amparage.
                            1- Have you observed any drop in melt flow through pump as a result of your experiment?
                            2- Have you experienced any abnormal sound through pump or there was any rise in pump vibrations?
                            If you have not experienced any of the above symptoms then it is not cavitation, its just that either
                            1- the density of the pumped fluid has decreased, but this fact cannot be supported because of the fact that decrease in density would result in increase in volumetric flow rate for the same plant load. So this change can be considered minimal (as required power is directly proportional to cube root of increase in flow through pump). However
                            2- change in viscosity of the pumped fluid can change significantly be the addition of ionic compunds like H2SO4 which would ultimately result in low pressure drop in the discharge line.

                            Please also look at this aspect of the issue as well which is quite positive one if the above mentioned observations are not captured during your experiment.

                            Regards,
                            M. Imran Idris

                            #95646
                            Mark Brouwer
                            Keymaster
                              • Expert

                              when you add H2SO4 in urea solution a highly exothermic reaction occur which produce ammonium sulphate and caynuaric acid which generate NH3 and more vapors collect at inlet which causes cavitation in molton urea pump and resultantly flow comes down.

                              #95640
                              girish-prakash
                              Participant
                                • Expert

                                Dear Inban,

                                As far as I know, yours is a Snamprogetti plant and you can contact them directly for this. They do recommend H2SO4 dosing as a option for reducing NH3 from Prill Tower but for this you need to have acid proofing of top portion (where the exhaust is in contact with concrete walls). Other finer details like rate of dosing and its expected impact can be discussed with your licensor.

                                Also can you please let me know the method applied by you for the measurement of NH3 from Prill Tower and how consistent are the results specially in view of the large diameter of the tower and impact of wind direction and velocity on the samples collected?

                                Regards,
                                Girish

                                #95637
                                Ban
                                Participant
                                  • Expert

                                  @ serpoush1: The plant load when i did the test was about 99 ton/h, you can calculate H2SO4/Urea mole ratio.
                                  Now we are waiting result of prill hardness test, we hope the hardness will be improved.

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