HP carbamate pumps seal water and HP NH3 pump seal oil

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Viewing 15 posts - 1 through 15 (of 20 total)
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  • #101087
    mocznik-police
    Participant
      • Expert

      Dear All,

      We have changed NH3 pump seal to ammonia water. We use 5-6% ammonia water with 0,2% urea content on enter. On exit from plungers we have discovered increase of ammonia and urea in the ammonia water (20-40% ammonia content and 4-6% urea content).

      What can be the reason? Modification was made by Flow Serve. Our pump is 5-plunger type.

      #97041
      technolog
      Participant
        • Expert

        Thank you for your Stamicarbon’s contact.
        We find oil fouling on the top of the stripper of course in that sensitive place with liquid divider ferrules.
        I wonder if this contamination could come from CO2 compressor by accident.

        Best regards,
        Janusz

        #97040
        Mark Brouwer
        Keymaster
          • Expert

          Stamicarbon had in the past a specification about the quality requirements of oil to be used in urea plants. Important is here the residu content the oil contains when heated (simulation of stripper conditions).
          Please contact: john.oostveen@stamicarbon.com (after sales).

          Where you face oil fouling problems ?
          There are design optimisations developed to avoid oil fouling in the top of the HP stripper, radar level measurements and in control valves (stuffing box).
          Let me know in case you need more information.

          Mark

          #97039
          technolog
          Participant
            • Expert

            Thank you Mr. Farooq for information.

            Another topic:

            How can we check if lubricating oil for rotating equipment (especially HP ammonia pumps) may be used in urea plant?
            What is correct specification (requirements) for such lubricating oils?

            Best regards,

            Janusz Maćkowski

            #96915
            m-farooq
            Participant
              • Expert

              hi,Maćkowski

              you can check with M/S peroni which is an Italian company and they can also give you the record of desired modification
              regards

              #96914
              joeg
              Participant
                • Participant

                Dear Mr. Chin,

                Regarding your two questions:

                #1: Carbamate as we know is a diffucult medium being highly corrosive and quite abrasive. As such in order to prolong packing and plunger life URACA has incorporated in their carbamate pumps a timed flush injection. That means the small PD pump coupled directly to the main pumps crankshaft must be installed so injection occurs when the main pumps plungers are in suction stroke. When timed correctly the small PD pump injects a small amount of condensate directly on the plunger while it is retracting to BDC (bottom dead center). The small PD pump must only overcome suction pressure to inject condensate which will flush clean the plunger and also prevent carbamate from contacting the packing. This design works and packing life should be 1 year or more depending on how well you maintain your pump.

                #2: Regarding seal oil for low pressure packing, this is an old design however many customers prefer this due to the fact that the packing will last longer sometimes up to 2 years or more. The seal oil must be metered such that you only overcome the suction pressure so oil can enter the chamber. Adding too much oil is a waste. If you want to eliminate the oil flush you will need new stuffing boxes designed for condensate only.

                #96913
                technolog
                Participant
                  • Expert

                  We would like to change oil seal system to water seal system for reciprocating HP NH3 pumps.
                  Which company in Europe could make such modificatin?
                  Could I know where such modifications were performed?

                  Best regards,
                  Janusz Mackowski

                  #96077
                  girish-prakash
                  Participant
                    • Expert

                    Dear Mark,

                    I fully agree with you however in case of ammonia feed pump the contaminated seal water quantity though theoritically is close to 0.5 m3 / pump (for 3-plunger pump) but practically (for higher packing life) it is close to 0.75-0.8 m3 / pump and often compromises are also made for higher ammonia content in the seal water outlet. All water collected is processed in waste water section and increases the ammonia load in the top section of the column. As a result very marginal increase in process water recycle to Synthesis section is observed. But its impact on conversion is very little and cannot be measured for all practical purposes.

                    Regards,
                    Girish

                    #96072
                    Mark Brouwer
                    Keymaster
                      • Expert

                      Please be aware that there are two type of water systems.

                      For reciprocating HP NH3 pumps one applies a water seal system: water acts as a seal between packing rings on the process side (high pressure side) and packing rings on the the atmospheric side of the plunger (low pressure side). Any water entering the process side is caused by leakage through the high pressure side packing rings, which is a minimal amount and not visibly influencing the conversion figures in the reactor.

                      For reciprocating HP carbamate pumps one applies a water flush system: here water needs to flush along the spindle between high pressure side and low pressure side in order to wash away carbamate crystals. Here one can expect more but still a limited amopunt of water entering the process side.

                      #96071
                      suzakuseikun
                      Participant
                        • Participant

                        Dear All,

                        For the effect on Urea conversion, the argument made was that currently we are using oil sealing so only oil gets entrained into the HP stripper, HPCC and finally to the reactor. If we switch to water, instead of oil, now water will be entrained to the synthesis instead. So we will have more water in the mixture and it will reduce the Urea conversion.

                        Will this actually happen? What is the conversion of Urea obtained in plants that are using water as their sealing water? any reduction?

                        Thank you.

                        Regards,
                        Chin MP.

                        #96070
                        mahmoodraufzafar
                        Participant
                          • Participant

                          Dear All

                          In my opinion sealing by water for ammonia pumps have following advantages over oil.

                          1- No recycling arrangement is required.
                          2- Oil passing in process can not be eliminated.
                          3- Whenever you open exchangers that found clean.
                          4- No environmental problem of vessels draining.
                          5- No inventory problem with water.
                          6- And finally improve exchanger capacity especially in process condensate treatment section.
                          In my experience try reduce No. of equipments and machines, this will help for both plant operation and maintenance.

                          #96068
                          m-farooq
                          Participant
                            • Expert

                            dear chin mp,

                            hp carbamate pump ,

                            judging from the drawing it means that your ( pd )injection and centrifugal pump are both in service when carbamate pump is in operation (pl correct me if i am wrong) .

                            it means that cylinder arrangement is in such a way that it requires sealing at both ends as one pump may not be sufficient to lubricate (water seal) for complete cylinder . moreover most probably there are outlets at both ends.
                            if you needs to keep one pump in service then you might need to modify cylinder sealing arrangement (mechanical expert can give better opinion)

                            h.p ammonia pump ,

                            1-for h.p ammonia pump many friends are agreed that it is better solution than oil sealing

                            2-we are also planning to change from oil to water sealing near future at one of pd ammonia pump at our plant . The quality of water ( steam condensate ) is important .mostly vendor adopted this application in 90 ies and initially they have oil sealing . As for as material of construction is concerned we need to contact vendor . however it requires only stuffing box/lantern ring modification

                            3-provision of filter may also be considered for sealing water injection application.

                            4 leakage rate in minimum and possibly very minor impact on desorption section . and since water is taken out from desorption section as process condensate ,hence in my opinion its is not going to affect reactor conversion
                            Best regards

                            #96067
                            Mark Brouwer
                            Keymaster
                              • Expert

                              Most important is to use solid free water. If it contains some ammonia it is not a problem.
                              Better is to have therefore stainless steel lines for the water supply.
                              Also the stuffing box need to be changed when one switches from oil to water seal.
                              Please contact the vendor for more details.

                              #96066
                              girish-prakash
                              Participant
                                • Expert

                                Dear Mahmood,

                                BFW requirement is roughly around 0.11-0.15 cu.m/Hr. / plunger. so if you have 3 plungers then the total requirement is around 0.45 cu.m/pump. The temperature should be around 40 deg. C.
                                You can modify existing oil sealing pump to water sealing one. You should preferably use clean and cold condensate for sealing purpose

                                #96063
                                suzakuseikun
                                Participant
                                  • Participant

                                  Dear M. Farooq,

                                  Attached is the PID indicating the sealing points at the plunger for the carbamate pump. Hope it can paint a clearer picture.
                                  Remark UreaKnowHow.com: PID is deleted because of its confidential nature. Please include a sketch and respect secrecy agreements.

                                  As for the ammonia pump,
                                  The idea of changing from seal oil to seal water is not readily accepted by some and therefore I hope to get more clarification from the floor.

                                  It is indeed delightful for me to hear that is standard feature now to use seal water instead of seal oil. My question is:
                                  1) When it is mentioned as standard feature does it mean it came with new pumps? Or were you able to modify existing pumps by changing their seal system from oil to water?
                                  2) are there any difference of material for construction of pumps between that of using seal oil compared to using seal water?
                                  3) For the seal water, we can only use demin water? Our desorption system is already overloaded due to a number of revamps and the idea was to use ammonia water from the ammonia water tank so that no extra water is introduced into the system
                                  4) For those using seal water for the NH3 pump, is there any effect on your urea conversion at the reactor? (The point made by other engineers is that more water to NH3 water tank, more water will be sent back to the synthesis, reducing conversion) Were you able to handle the extra ammoniacal condensate without pumping more to the synthesis via carbamate pump?

                                  Regards,
                                  Chin MP


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