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Submitted Chris Haslego, Nov 21 2011 11:21 AM | Last updated Nov 21 2011 01:29 PM




Category: Refining
Question: What is a good method of cleaning a crude tower?
Keywords: v1i8,crude,tower,distillation,column,cleaning,procedure
Answer: Here is a typical progression:1. Steaming: The steaming is done after all liquid hydrocarbons have been drained from the column and associated piping. The objective of steaming is to make the column and associated piping free of residual hydrocarbons. The column vent and pump strainers in the side draw piping are de-blinded and steaming is started from utility connections at the bottom of the column. Generally, steaming is continued for about 20 to 24 hrs, ensuring the column top temperature remains more than 100 ??C throughout the operation.2. Hot Water Washing: When clear steam is observed exiting the column vents, water washing of the column should be started. With steam still in commission, water is sent to the column, usually via reflux lines, and it is drained from the column bottom, associated pump strainers, etc. The water flow rate should be adjusted so that steam still comes from the vent (i.e. water should not result in condensing of all steam before it reaches the column top). Water flow should be stopped for 2-3 hrs and then resumed. This cycle of steaming and washing should be repeated several times for a total of about 15 to 20 hours. Injection of a turpene-based detergent into the steam can also be considered. The condensate-soap solution can be collected and circulated through the various side cuts. 3. Blinding: When clear water is observed at side draw pump strainers, etc., associated piping should be isolated by installing blinds wherever isolation is possible.4. Cold Water Washing: The hot water wash should be followed by a cold water wash (i.e. steam should be fully closed). The cold water washing is done for about 20-24 hrs. 5. Chemical Injection for Removal and Neutralization of PIS Deposits: During the cold-water wash or after washing is over, chemical injection for removal of pyrophoric sulfides should be considered. The various options for chemical treatment are discussed below: Acid cleaning - This procedure involves pumping in an acid with some corrosion inhibitor. The acid dissolves sulfide scale and releases hydrogen sulfide gas. It is effective and inexpensive, however, disposal of hydrogen sulfide gas can be a problem, as can corrosion (when the system contains more than one alloy). Dilute hydrochloric acid solutions may also be used. The resulting iron chloride turns bright yellow, acting as an indicator for removal of the iron sulfide. Acid plus hydrogen sulfide suppressant - Additional chemicals can be added to the acid solution to convert or scrub the hydrogen sulfide gas. Chelating solutions - Specially formulated, high pH, chelating solutions are quite effective in dissolving the sulfide deposits without emitting hydrogen sulfide, but this is an expensive application. Oxidizing chemicals - Oxidizing chemicals convert sulfide to oxide. Potassium permanganate (KMnO4) has been used commonly in the past to oxidize pyrophoric sulfide. Generally the potassium permanganate is added to the tower during the cold water washing as a 1% solution. At various intervals, samples are taken and checked for color. The colors of the fresh KMnO4 and the spent MnO2 are purple and brown respectively. If the color of the solution becomes brown, additional KMnO4 is needed. The reaction is judged complete when the solution color remains purple. It takes approximately 12 hours to complete the job. In recent times, the use of potassium permanganate as an oxidizer has raised serious safety and health concerns. A very good alternative to explore is the use of a cleaning agent called Zyme-Flow from United Laboratories (see link below).Reference: Pryophoric Iron Fires, www.cheresources.com/ironfires.shtml
Links: Zyme-Flow Website

Pryophoric Iron Fires Article
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