7/27/2019 Typical PFD for Sour Water Stripper Column

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Typical PFD for Sour Water Stripper Column

In upstream crude oil production and processing f acilities, the produced water f rom oil wells is separated in

the slug catcher . Generally this produced water contains salts, hydrogen sulphide, carbon dioxide etc. Salts

are removed using a desalting unit. Due to presence o f acidic gases present in the produced water,sometimes it is called as sour water. For removal of these gases such as H2S, CO2 etc, the sour water is

sent to sour water st ripper columns.

Even in crude oil ref ining f acilities, steam and water are of ten used in many units such as atmospheric

distillation unit, naphtha hydrot reater unit, kerosene hydrotreater etc. These units produce sour water as a

result o f steam/ water coming in contact with sulphur products in the hydrocarbons. This so ur water is also

then sent to sour water stripper columns f or H2S removal. The H2S removed is sent to sulphur recovery

unit to produces liquid sulphur.

Figure 1 – Typical PFD fo r a sour water st ripper column

Typical process f low in a sour water stripping unit

Typically a sour water f low in crude oil processing facility or in a ref inery is not steady. Sour water is

gathered f rom a number of dif f erent sources and treated in a single column. For upstream oil production

and storage facilities , the produced water comes along with crude oil in a pipeline. During pigging of these

pipelines vast quantit ies of sour water are produced in the slug catcher , which may far exceed the sour 

water stripper f low handling capacity. Hence a buf f er vessel is generally provided upstream to the s tripper 

column to accommodate extra sour water quantit ies in case of a peak e.g. pigging.

7/27/2019 Typical PFD for Sour Water Stripper Column

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Sour water f rom buff er vessel is sent to the so ur water st ripper column under level contro l. In case the f low

to the column sees major f luctuations which may f requently disturb the column operation, f low contro l

valve on the column inlet water line can be used with a cascading signal f rom buf f er vessel level contro l.

Gases f lashed in the buf f er vessel can be f lared or sent to the sulphur recovery unit, if t hey are rich in H2S.

The st ripper column may use either steam or f uel gas to st rip of f the H2S dissolved in water. Water is

introduced f rom top o f the packing or t rays section and steam/fuel gas f lows upwards f rom the botto m of 

the t rays/packing section as shown in the typical PFD in f igure-1. Contact between water and vapor phase

allows t ransf er of H2S fro m water to the gas phase (steam or f uel gas). Gases rich in H2S are removed

f rom the top of the column and treated water is taken out f rom the bottom of the column, under level

control f or t he liquid level of the bottom section of st ripper column.

If steam is used in the stripper column f or removing H2S, then overhead condenser and ref lux drum are

required at the top outlet o f the column as shown in typical PFD in f igure-1. The vapor out let line of the

st ripper column is also equipped with a pressure contro l valve to maintain the sour water st ripper column

overhead pressure. Steam used can be either taken directly f rom the ut ility s team and sent to column or the

treated water f rom bot tom of the column can be sent t o a reboiler to produce steam which is circulated

back to the column f or H2S removal.

If f uel gas is used instead of steam to remove H2S, reboilers, condensers, ref lux drums etc. are not

required. But the gases f rom column overhead out let have a high hydrocarbon content.

 An analyzer is ins talled to detect the H2S content in the sour water s tripper out let. This analyzer generally

transmits s ignal to the cont rol roo m and steam/fuel gas f low can be adjusted f rom the cont rol roo m in

order keep the H2S content in treated water well below the allowable H2S content limit. Alternat ively, a

controller can be used to directly thrott le the steam/fuel gas f low based on a setpoint of H2S content in

the t reated water.