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How to convert PPMw (by weight) to PPMv(Volume) for H2S & moisture(H2O) in gas mixture?
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Submitted Chris Haslego, Nov 21 2011 11:21 AM | Last updated Nov 21 2011 01:29 PM

Category:	Refining
Question:	What are some potential causes of plugging in a waste water treatment unit seal drum?
Keywords:	seal,drum,plugging,ammonium,salts
Answer:	BACKGROUND The plugging occurs in upper bridle taps (vapor phase). The gas contains approximately 50-100 ppm ammonia and similar concentrations of hydrogen sulfide. The drum is at ambient temperature (~70-90 ⁰F). ammonium sulfide salts are suspected.RESPONSE Try to get a sample of the material that is causing the plugging. If it is a powdery white salt then ammonium bisulphite salts may be causing the plugging problem.There are two ways you can keep ammonium salts from precipitating :1. Dissolve them in water2. Raise temperatures above 145 ⁰C by using steam or electrical tracing.A rule of thumb regarding the formation of ammonium salts is as follows:"Multiply the ammonia partial pressure in the vapor phase by the hydrogen sulfide partial pressure in the vapor phase. If the result exceeds 140 psia squared, then the ammonium bisulfide salt will form"If the above rule-of-thumb is correct, it doesn't sound as if ammonium bisulfide salts would form in your wastewater treatment plant seal drum unless the drum is a a very high pressure. Water injection in the upper taps may be a good solution since this may help guard against the plugging regardless of how it is forming.