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• Are there options for online cleaning a preheat exchanger network?

  Jun-2021

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Answers

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• Marcello Ferrara, ITW Technologies, mferrara@itwtechnologies.com

  One common cause of corrosion is the formation of heat stable salts (HSS). HSS cause an irreversible consumption of amine with subsequent loss in acid loading capacity and increasing the level of contaminants, causing corrosion in the amine unit and operating problems in the SRU.

  Additional corrosion is due to HSS penetrating the protective FeS layer on the metal surface exposing the metal to further attack.  Several HSS anion species have been directly related to increased corrosion in carbon steel in amine solvent systems; in particular they appear to act as corrosion accelerators by displacing the iron sulphide film.

  The corrosion rates increase with higher concentrations of all of the HSS species. The corrosion from HSS occurs in hot areas of the plant, wherein the liquid and vapour phases are present: the reboiler, reboiler outlet line, the regenerator column between the lean amine level and the bottom trays. HSS start causing evident corrosion problems when the total HSS level exceeds 2%.

  ITW has developed and patented technologies, together with proprietary know-how, to dissolve HSS and hence remove them from the equipment.
  A pro-active approach has also been developed for preventing HSS formation.
  ITW technologies’ applications range from normal run to turnaround.

  Equipment can be cleaned online without having to open the same. This is particularly beneficial in severe applications such as heat exchangers placed at elevated location or columns/vessels.

  The ITW cleaning method involves the injection of a proprietary chemical that transforms the fouling into a fully reusable liquid, thereby removing deposits from metal surfaces.

  Avoidance of opening the equipment is particularly important at unit start-up and during maintenance turnarounds because of pipe scale/rust formation; this readily forms when carbon steel is exposed to air, especially in the presence of moisture. Any pipe scale or rust is immediately converted to iron sulphide when H2S is introduced in the unit. Because FeS is not bonded to the pipe it will be carried by the circulating solution and contribute to fouling.

  This is an important additional benefit of ITW Online Cleaning in that it will improve performance upon restarting.

   

  Jun-2021