STAC Urea Plant Trip logic on Back End Tripping of Ammonia

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      • Participant


      Typically the source of NH3 is from both NH3 plant and Storage. The flash drum in the NH3 plant provides hot ammonia and the tank storage pumps provide backup. If you have separate Urea plant feed pumps from storage, they should normally be auto-start on low pressure of the feed line to Urea with the block valves open and a check valve to ensure the flow does not return to the storage. Then any interruption in feed from the NH3 plants can be mitigated,

      In some plants, the NH3 from the flash drum has a split range level control. In my experience the level valve to the Urea plant is left on manual and controls pressure anyway while the other level control valve controls drum level. I have always thought the valve to Urea should be a PCV which controls supply pressure to Urea, so when the NH3 plant has an upset it will maintain the pressure as long as possible and give sufficient time for the storage tank pumps to catch up and keep Urea running. Logic manipulation could easily control any scenario.

      The storage tank pumps must be put on line pressure control with the SP somewhat lower than normal line pressure (or the two will fight each other). If there is an alternate need for the storage pumps, this could cause a change in philosophy to be considered. Also be aware the if there is a line break, the supply pumps will detect a low pressure and start to maintain the pressure which could lead to more problems.

      The Urea NH3 pumps can normally take a bit of pressure and temperature fluctuations so they should survive a small upset if you are considering the time to get the storage NH3 up to seal temperature requirements.

      Hope this helps,


        • Participant

        Dear Gentlemen,

        What is the NH3 feed supply source in your STAC technology plants.

        a) From storage after heating.
        b) Or Direct from Ammonia Plant as hot product.

        In case “a” what is your experience regarding energy consumption, temperature control, and reliability of smooth/sustain operation.
        In case “b” what is your experience regarding trip philosophy, if Ammonia Plant Back end trips and NH3 Feed supply discontinues, Urea Plant also forced to SD or not and why?

        Here in SAFCO ( STAC plants only) we are taking hot NH3 feed direct from Ammonia Plant and trip logic is there if back end trips @ Ammonia Plant, the main reason NH3 Feed interruption.

        Due to three urea large Urea Plants with consecutive Ammonia plants, we are suffering un-intentionally with Urea Plant SD due to Ammonia Plant Back End tripping.

        What is your experience and how we can overcome with this situation.????

        Thanks and Best Regards

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