Low temperature in the medium pressure decomposer

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  • #96687
    engr-thescent
    Participant
      • Participant

      Mr. Joao Amilton
      I think sudden decrease and then increase in MP section pressure may be attributed to sudden closing and opeining of HP section off gases valve to MP decomposer during shutdown activities. As in the case on snamprogetti plants HP off gasses from carbamate separator directly goes to the bottom of MP decomposer. In case of casale technology i’m not confirmed, you can check this as casale technology is a CO2 stripping plant with LP decomposer as for i know or your plant have been revamped by the casale.

      Regarding low bottom temperature of MP decomposer it may also be due to higher opening of strpper bottom level control valve and gasses from HP section are by passing to MP section from there. this will also effect the MP condenser performance and will also be indicated by high discharge pressure of carbamate pump.
      Also as per Mr. Imran Idress advice you should first conform that this temperature decrease is actual or not.

      #96204
      imran-idris
      Participant
        • Participant

        Dear joão amilton, in order to identify if there is an actual deterioration in MP decomposer performance, you need to compare the following parameters.
        1- Steam consumption in LP decomposer before and after the change in MPD conditions
        2- Valve opening of level controller of Stripper & MPD against the same plant load.
        3- Change in operating conditions of MP absorber (Reflux Ammonia flow, Top tray temperature, and flow of absorbent from LP section to MP absorber)
        We have experienced a carryover from MP decomposer top when all the liquid in MPD coming from Stripper shifter to MP absorber along with vapors from MP decomposer. This happened due to high flow of inert gases from HP section to the bottom of MP decomposer.
        We also have experienced choking of packed bed in Decomposer bed, but that was in LP decomposer.
        See if you find any signs for erratic temperature indication in MP decomoser

        #96199
        dppandey
        Participant
          • Participant

          Dear friend.
          Some times the temperature of MP Decomposer comes down due to solution carry over from HP Carbamate Seperator. It may be due to faulty indication of level in HP Carbamate Seperator (showing zero at full) or some flow restriction through ejector.
          Any damage in MP Decomposer, it will reflect in MP Amonia Absorber.

          #96198
          m-farooq
          Participant
            • Expert

            hello,

            can you please share what technology of urea plant are you dealing with ?
            is your stripper is working normal . i mean all the composition and solution outlet conditions are normal before the decomposer like pressure,flow, temp etc? .
            A little elaboration about h.p decomposer drawing ?

            is there any restriction checked with heating media in H.P decomposer ?

            #92553
            joao-amilton
            Participant
              • Participant

              After the shutdown in the last Friday (09/02/2011), the urea reactors were drained at a rate of 30 kgf/cm2h, less than Urea Casale recommendation (50 kgf/cm2h). During the start-up (09/04/2011), we realize that the temperature of Medium Pressure Decomposer Tower didn´t reach the normal condition (156 ºC). We adjusted the reactors conversion and checked the steam and condensate conditions in the reboiler of the Decompose Tower, but the temperature didn´t change, staying in 143 ºC.
              We realize that when the capacity of the plant increase, the Decomposer temperature increase during some time, but it soon falls to 143 ºC.
              We suspect that the Decomposer´s internals (trays , downcomer) may have been damaged. By Plant Information (PI) data, we saw a strange behavior in the internal pressure of the Decomposer. After 25 minutes of the reactors were drained, the pressure in the Decomposer fell quickly in some seconds. After that, the pressure increase quickly and the temperature fell quickly at a same time. Apparently, this behavior may be associated to washing procedures of the system. We think a strong flash of the water used to wash the tower may have damaged the trays or downcomer.
              Who has had this kind of experience?

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