This is normally rust that was either left in the system after a turnaround or entered with the feed gas and not indicative ofactive corrosion.
detected by passing a magnet over the filtered
solid before acid is added to the solid.
Add 0.1N hydrochloric acid to the well and note any reactions. Notice whether the solid is slightly, moderately, or fully soluble in the acid. Stir the solid gently with a spatula and observe if the solid persists. Carbon fines, organic solids (such as asphaltenes, waxes), and magnetite will not dissolve. Test for carbonate (CO 3 ² - ) Immediately after adding the hydrochloric acid to the solid, observe if any ‘fizzing’ occurs. If carbonate is present, it will be liberated as bubbles (of CO2). The evolved gas will not cause lead acetate paper to discolour as it will in the sulphide test. Test for presence of sulphide (S 2- )
Feed gas Iron sulphides that foul amine absorbers are usually created in-situ, and counter-intuitively, ar a result of regenerator corrosion. When the regenerator (or reboiler) corrodes, free iro (Fe+2) ions are released into the amine. When amine enters the absorber and encounters th sour gas, a reaction between Fe and H 2 S occurs andFeS is formed. Iron sulphide isno soluble and therefore becomes potential fouling material as soon as it develops. How iro circulates around amine systems is called “the iron pump”, a term coined by Shell. It i illustrated in Figure 3: Contactor Flash tank Regenerator Fe+2 reacts with H S 3 Corrosion of the reboiler/regenerator results in Fe+2 release 1 Figure 2: Positive Tests for Fe 2+ using Potassium Ferricyanide and Fe 3+ using Potassium Thiocyanate Iron Sulphide Formation The most common fouling material in amine systems, especially in refineries, is iron sulphid (FeS). Figure 2 Positive tests for Fe 2+ using potassium ferricyanide and Fe 3+ using potassium thiocyanate Lean amine
Immediately after the acid has been added to the solid, hold a piece of lead acetate paper close to the fizzing acid. The paper will discolour to brown when sulphide is present. This is due to the formation of lead sulphide (PbS). The darker the discolouration, the higher the sulphide content. Test for presence of iron (Fe 2+ , Fe 3+ ) Figure 3 Add 1-3 drops of potassium ferricyanide (III) aqueous solution to one well. If the solution turns blue/green, the sample contains Fe 2+ , a product of active corrosion. Add 1-3 drops of potassium thiocyanate aqueous solution to the second. If the solution 4
Rich amine contains FeS
2
Fe+2 in lean amine
Figure 3 The ‘iron pump’ cycle
turns pink or red, the sample contains Fe 3+ , which is iron that has been exposed to oxygen. This is normally rust that was either left in the system after a turnaround or introduced with the feed gas and is not indicative of active corrosion. Iron sulphide formation The most common fouling material in amine systems, especially in refineries, is iron sulphide (FeS). Iron sulphides that foul amine absorbers are usually created in situ and counter-intuitively
Refining India
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