Warm up steam and flash steam admission to ACC

ACC Users Group ACC Users Group Discussion Forums Design Warm up steam and flash steam admission to ACC

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    • #1599

      Dear Experts,
      Request your views on the following query

      Normally steam is admitted to the ACC, after gland steam seal is established to the ST, and SJAE is put in service and vacuum pulled to required levels. However, we would like to know if it is advisable to admit flash steam (steam/ flash steam from external flash vessel receiving condensate/steam generated during steam line warm up before charging of auxiliary steam header and establishing required auxiliary steam header pressure and temperature) to the ACC before vacuum ejector is in service and vacuum pulled to the required levels and gland steam seal established for the ST.

    • #1600
      Martin Cyr


      If I understand you correctly, you are asking if it is OK to dump flash steam to an ACC that is at atmospheric pressure. Short answer is NO. The ACC is a heat exchanger. When any heat exchanger is full of air it cannot exchange heat ie. condense steam.

      My questions to you are; Why do you want to dump flash steam to the ACC prior to ACC start-up? How long would you want to dump steam to the ACC prior to ACC start-up?

      Marty Cyr
      SPX Dry Cooling USA, Inc.

    • #1601

      Marty Cyr,

      You are right.

      To answer your questions raised, the flash steam is generated from the process warmup and heating up of main steam line and auxiliary steam header (a tap of from main steam line), prior to attaining steam header conditions suitable for gland seal system charging and steam to ejector. Normally, for main steam and auxiliary steam line warmup,condensate and steam are drained through a atmospheric flash tank, but in the preliminary design proposed in this case, there is no such atmospheric flash tank and all start up drains are flashed through a flash chamber which is connected to the ACC duct.

      From plant startup and achieving steam conditions for auxiliary header 10 bar, 250 degC we expect it to take about 30 minutes. So during this duration, the condensate/ steam generated will be dumped to the flash tank connected to ACC while the ACC is atmospheric.

      we have couple of other queries as well.

      1. if the flash steam is admitted to the ACC while it is atmospheric, the steam entering the ACC would probably pressurize the duct as it is not possible to condense the steam. Normally, the ACC is designed at 1.5bara or so. This leaves a very small margin, and may cause unwarranted rupture of the relief device. Am I correct in my understanding?
      2. Suppose, it is acceptable to admit the flash steam, is there any duration limitation.
      3. If we are able to start vacuum pulling in parallel with flash steam admission. Is this OK. How will it be ensured that all the non – condensibles are positively removed from the system.

      WorleyParsons -Power, Oman

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