Q & A > Question Details
I have a problem with my sour stripper column

Feed :
NH3 = 796 ppm
H2S = 324 ppm
pH = 8,7

Product (Sour Water Stripped)
NH3 = 136 ppm vs max 50 ppm
H2S = 5 ppm vs max 10 ppm
pH = 5,8

Why does the pH of sour water stripped (product) decrease significantly with the NH3 content still high? What happens with this process? I have added to the ratio of the reboiler but NH3 still is high. And now, my temperature reboiler sour water stripper cannot increase (indicating fouling). Anyone help me?
 
Answers
13/05/2020 A: Morgan Rodwell, Fluor Canada Limited, morgan.rodwell@fluor.com
You probably need to analyze the water for other acids that are present. If those are ppmw then you have far more than equimolar amounts of NH3 to H2S indicating that another acid species is present. Weak acids or heat stable salts are species that won't strip based on the conditions in the column, often organic acids, HCN or HCl. One solution is to inject a small but metered amount of caustic soda into the column below the feed stage to bind with these acid species and drive up the pH, releasing the NH3. There is a good article on this here: https://www.digitalrefining.com/article_1000543.pdf