3 replies to this topic

[Abm]

In Double Stage Sour Water stripping unit, stage 1 operates at 7kg/cm2 pressure and H2S is removed from this and Stage 2 Operates at 1kg/cm2 pressure and NH3 is removed from this column.

Based on what criteria this column pressure is fixed.

Kindly Clarify

[Abm]

Anyone Kindly respond

[rizwangoheer]

Hi Abm,

 

Whenever the amount of NH3 is high, a Two Stage Design could be warranted. While an absolute number on the break point for Single Stage vs Two Stage is not fixed, in most cases NH3 content greater than 30 mol% (wet gas basis) can usually justify a Two Stage Design when compared to additional investment required in the Sulfur Recovery Unit.

 

In a Two Stage Design the first column essentially strips out the H2S and operates at a higher pressure but lower temperature than a conventional Single Stage Column, while the second column strips out the NH3 and operates at lower pressure but higher temperature (similar to the Single Stage Column).

 

The principle of Sour Water Stripping is based on the application of heat to reduce the solubility of NH4+ and HS- in the water phase plus the dilution and depletion of gaseous NH3 and H2S on account of the steam vapor. The net result is that the equilibrium is forced to the left and consequently the NH3 and H2S will come out of solution and be easily stripped away as gases.

[rizwangoheer]

In continuation of my previous email. Please see more details below:

 

 

The sour water system with hydrogen sulfide and ammonia consists of a weak base and a weak acid. Addition of strong acid or strong base is used to balance the pH of the exiting effluent and, in addition, the choice of using either a strong base or a strong acid depends on the constituents that are desired to be sent overhead. The addition of strong acid results in the liberation of the weak volatile acids of H2S and HCN (phenol is not considered a volatile acid) and the corresponding holding of ammonia in the liquid phase as a salt in first column. The addition of strong base will result in the liberation of ammonia to the vapor phase and the corresponding holding of the acidic compounds, H2S, HCN, and Phenol in the liquid phase in 2^nd column. When used, a strong base is typically injected towards the bottom of the column since much of the H2S is stripped higher up in the column than ammonia. Thus, injecting strong base towards the bottom will result in less H2S in the column bottoms while still enhancing the stripping of NH3.