more contaminants, and if the gas enters just below the tower internals, the bottom of the lowest tray or packing support tray can become fouled. Deflection devices will stop contaminants from impinging directly on the trays or packing, but the deflectors themselves can become fouled, hindering their intended purpose. The inlet gas feed rate must match the KO drum design capacity; otherwise, overloading may entrain contaminants, and the bottom of the absorber is at risk. Fouling contaminants in the lean amine Solids that contaminate amine can enter through the inlet gas, make-up water, amine make-up, maintenance activities, turnaround cleaning, activated carbon, or erosion. The appearance of the lean amine is an important factor for gauging the quantity of solids it is carrying; the amine should be clear and transparent. If it is grey, brown, or black, then suspect solid contamination. Two quick ways to determine if this is the case: Let the sample sit for a couple of hours and observe if solids precipitate. Filter the amine; observe if it appears cleaner and if the filter contains solids. Although lean filters can prevent solids from fouling the absorber, determining the nature of the solids and their origin is the most effective way to prevent fouling without having to rely on frequent filter changes. Solids identification Filtering contaminated amine provides valuable information about the type of contamination and its origin. Amine experts use the device shown in Figure 1 to test the amount and composition of solids in amine samples. A pump creates a vacuum below the amine in the beaker and pulls it through the microfilter paper into the flask. After filtering the solids from the amine, there are tests that will help determine the composition of the solids. For each of these tests, transfer a small amount of the solid to form a well in a ceramic spot plate. Do not fill the well; leave room to stir the solid without spilling. Tests for inorganic ions Magnetite (a product of FeS or FeCO3 after it has been exposed to oxygen) is magnetic. It can be
Figure 1 Solids microfiltration setup
the treated gas H 2S specification, or it ultimately carries amine over the top. To prevent fouling, the solids causing the problem must be identified and their presence in the absorber mitigated. Before these symptoms appear, however, the fouling risk of the absorber can be predicted by monitoring both the feed gas separation equipment and the lean amine. Fouling contaminants in the feed gas The feed gas flows through a knockout (KO) drum before it enters the absorber. This vessel is designed to remove contaminants from the gas, which can promote fouling if allowed to enter the absorber. KO drums should have reliable level instruments and good control strategies so that the operator knows the vessel is draining properly. Carryover from a feed gas KO drum has a very high potential to foul the bottom of an amine absorber. To remove contaminants from the gas, the KO drum must be sized properly (0.1-0.15 m/s gas velocity in the vessel) and have a demister pad on the outlet. Improper design will hinder the separation of contaminants and allow them to pass through the drum. Whether contaminants entering with the feed gas will foul the absorber depends on the design of the feed gas distributor and the velocity of the gas. With more gas will come
Refining India
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