Towers, amine strippers

Amine strippers use heat and steam to reverse the chemical reactions with CO2 and H2S. The steam acts as a stripping gas to remove the COo and HjS from the liquid solution and to cairy these gases to the overhead. To promote mixing of the solution and the steam, the stripper is a trayed or packed tower with packing normally used for small diameter columns. 

Tower Internals and Equipment Modification. Tower capacity expansion can be achieved through the use of random or stmctured packing, or through the use of higher capacity trays such as the UOP multiple downcomer tray. Packing has been used in the gasoline fractionator, water quench tower, caustic and amine towers, demethanizer, the upper zone of the deethanizer, debutanizer, and condensate strippers. Packing reduces the pressure drop and increases the capacity. 

The typical stripper consists of a tower operating at 10-20 psig w ith 211 trays, a reboiler, and an overhead condenser. The rich amine feed is introduced on the third or fourth tray from the top. The lean amine i.s removed at the bottom of the stripper and acid gases are removed from the top. 

The entire unit should be cleaned to avoid contamination of the fresh amine, but the customer may not feel the need to do this. As a minimum, the stripper overhead, amine/amine exchangers, and water-cooled exchangers between the towers should be cleaned. 

The stripper tower separates the acid gases from the amine systems, and so its efficiency dictates how effective the system works. Increased pressure drop caused by fouling means higher firing on the reboiler. This condition may lead to corrosion and more amine lost through carryover. 

The cooler on the overhead system of the stripper tower controls the quantity of water and amine that is recovered from the overhead streams. This may be an air- or water-cooled exchanger or combination of these. These must effectively cool if excessive amine is not to be lost. These exchangers will also affect downstream corrosion, because the corrosivity of these acid gases is definitely increased by increasing temperature. 

The amine/amine exchangers and the water-cooled exchangers have a great deal of effect on the operation of the system. As the absorber runs cool and the stripper runs hot, these exchangers must be efficient to exchange the heat. The amine/amine exchangers play a large role in the corrosion found in the stripper tower and reboiler. 

If you think that your tray will be in a foamy service, it s best to double the usual downcomer area from 175 GPM per ft to 90 GPM per ft2. Towers working as demethanizers or de-ethanizers fall into this category. If I have a sour water stripper with hydrocarbon liquids in the stripper feed or water in a hydrocarbon fractionator, I would anticipate foaming. The foaming service I know most about is H S absorption in amine. The greater the concentration of the amine, the greater the foaming. When I noted the 90 GPM per ft value above, 1 had in mind 25 to 30 percent DEA or 20 percent MEA. 

In any refining scheme, the wastewater from the distillation tower is fed to a waste stripper where trace organics are removed prior to the sewer disposal. The organics are recycled to the process. In addition, the process and product storage vents are collected in a recovery system where amines and ammonia are recovered for recycle. Noncondensables are vented. 

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