Two-stage exhaust gas for urea using the full-circulation aqueous solution method
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In the two-stage absorption of urea using the full-circulation aqueous solution method, complete absorption is achieved in terms of design; therefore, there are no components from the exhaust gases in the material balance. But in practice, the control of the second-stage exhaust gas, that is, the second-stage pressure, still involves some degree of openness; its ammonia content is generally less than 10%. Many manufacturers send this second-stage exhaust gas to a scrubber tower, where it is absorbed and washed using ammonia solution at a concentration of around 3%. I would like to ask fellow experts for their opinions: can ammonia solution at a concentration of around 3% effectively absorb and remove the ammonia content from the second-stage exhaust gas at normal pressure? By how much can the ammonia content in the two-stage exhaust gas be reduced?
Ammonia water at around 3% has an ammonia partial pressure of about 50 mmHg at temperatures over 40 degrees, which is slightly below 0.1 atmosphere (corresponding to a 10% ammonia content in the gas phase by volume), and it can be absorbed. The absorption efficiency depends on the flow rates and temperatures of the gas and liquid phases; in general, not much absorption should occur.
It can be absorbed, but the effect is not very good; after all, it is absorption under normal pressure, and traditional processes involve feeding the exhaust gas in two stages into the absorption tower. The exhaust gas level for NH3 is 1.5–3.0%. Our factory is able to keep this level under control during the cold seasons, but it can rise above 12% during the hot summer months. You might want to consider using a polishing unit; it can yield good results.