Two-Stage Sour Water Stripper

For one of the sour water strippers I worked on in India, the NH3 in the bottoms product was about 200 ppm, even though the NH3 in the 

The problem was not the lack of stripping steam. The problem was also not the excessive pH of the stripper bottoms as my client in India suspected. It is quite normal for the stripper bottoms to have a higher pH than the feed, if the stripping efficiency is inadequate. That is, the acidic H S is stripped out of the sour water more easily than the basic ammonia. The problem of excessive NHj in the stripped water effluent was low tray efficiency. 

Climbing up this tall tower with far too many trays (see Fig. 47.1) (I m more aware of such overdesigned towers at age 70 than I used to be), I observed  

In the Coastal Refinery in Aruba, we used sieve trays with one-half-inch holes, which seemed to work fine. Avoid packed towers. They are subject to vapor-liquid channeling and poor fractionation efficiency due to sloppy installation, fouling, or poor liquid feed distribution. When calculating the required hole area for the trays, don t forget that the vapor loads and hence the required tray hole area will substantially diminish as the vapor flows up the column from the reboiler to the feed tray. This will normally require a reduction in the tray deck hole area in proportion to the reduced vapor flow rate. 

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