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Reply To: Compressor Vibration

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#30158

Mike Kimbrell
Participant

One of the products from thermal decomposition of resid is ammonia. To prevent ammonium chloride salt forming, the amount chlorides entering with the feed should be limited. This goes back to the desalter performance in the crude unit. The chlorides in the feed will hydrolyze into HCl which will react with the ammonia to make a salt. A water wash on the overhead of the main fractionator vapors should capture all of the HCl in the aqueous phase. Keeping the operating temperatures above the salt point until the water wash should allow all the HCl to be removed by the water wash. That should prevent the HCl from reaching the wet gas compressor suction. Without HCl no ammonium chloride can be formed. If you thought that you were getting ammonium chloride salts into the wet gas compressor, increasing the amount of water injected into the main fractionator overhead condensers should limit the amount of salt that could form in the compressor.

The dienes in the light hydrocarbons in the overhead vapors can polymerize at the temperatures in the wet gas compressor. This usually requires some oxygen as a catalyst to start this polymerization. A few ppm oxygen is enough to initiate this polymerization. Some operators inject some liquid naphtha into the wet gas compressor suction to prevent the compressed vapors from going through a dry spot as that appears to be where this polymerized material begins to attach.

If there are ammonia salts on the compressor wheels, injecting some water into the wet gas compressor suction should be enough to dissolve it and move it to the first stage discharge coolers where the water wash at these condensers should remove those salts.

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