4 replies to this topic

[ravi.s]

Dear Experts,

Generally, Sour water stripping unit consists of Feed Preparation tank – Sour water Storage Tank. This sour water storage tank provides sufficient residence time for liquid HC separation, HC that has not separated in the surge drum. These also essentially helps in downstream processing & have the benefit that:
 Much less oil, if any, will reach the sulphur plant
 Minimum oil removal will be needed from either stripper as liquid.
 Longer sour water mixing to minimize feed composition fluctuations due to many sources of refinery sour water

Based on the above, it is decided to provide the Sour Water Storage tank in the sour water stripping unit (SWS)

1. This tank will have a large volume approximately 14000 m3 normally & first estimate measures this tank to be 30 m in diameter and 20 m height.

2. If the tank will be at lower pressure than the Collection Drum, there will be a pressure differential between the off gas of the collecting drum and the off gas of the Sour Water Storage tank. This will result in the flashing of NH3 and H2S from the tank. We cannot plan to route this to the SRU incinerator stack as this will result in H2S and NH3 emissions & will not be acceptable based on the environmental regulations at site.

Considering the environmental regulations, shall I expect expert comments on the:

1) Lower tank pressure than the collecting drum: use of BLOWER to suck the gas from the tank & discharge at 1.05 kg/cm2g so that same can be routed to SRU.

Or

2) Design of the tank: designing the large volume tank for internal pressures not more than 15 psig so that tank vent can be routed to SRU through pressure controller.

Or

Any additional information / comments?

Attached Files

•  SWS_FLOW_SHEET.XLS   64KB   224 downloads

[Zauberberg]

It is a mystery why do you need buffer tank at all? Have you analyzed this system properly?

I have designed one SWS unit and operated 3 different types in my past (direct steam stripping, reboiled stripper with pumparound circuit, and one with top reflux). Surge drum is the key issue in separating hydrocarbons and highly volatile gases. If this is designed the way as it should be, there is no need for any intermediate buffer tank.

The news for me is that you are routing flash gases to SRU. This is bad practice, since the flash gas will contain substantial amounts of NH3 and hydrocarbons, which adversely affect Claus operation. I don't know the sour water feed composition and relative flowrates, but (usually) you can burn this stream safely in refinery flare.

Feed fluctuations can be an issue, but surge tank is provided exactly for these purposes. If this is an existing unit, try to perform laboratory tests and analyze both individual sour water and SWS feed streams and watch for differences. I believe they cannot be so drastic. The key is how to adjust stripper operation, and not to mix the feed perfectly. The way how you described it, it will always be different at some extent.

Best regards,

[fallah]

It is a mystery why do you need buffer tank at all? Have you analyzed this system properly?

I have designed one SWS unit and operated 3 different types in my past (direct steam stripping, reboiled stripper with pumparound circuit, and one with top reflux). Surge drum is the key issue in separating hydrocarbons and highly volatile gases. If this is designed the way as it should be, there is no need for any intermediate buffer tank.

The news for me is that you are routing flash gases to SRU. This is bad practice, since the flash gas will contain substantial amounts of NH3 and hydrocarbons, which adversely affect Claus operation. I don't know the sour water feed composition and relative flowrates, but (usually) you can burn this stream safely in refinery flare.

Feed fluctuations can be an issue, but surge tank is provided exactly for these purposes. If this is an existing unit, try to perform laboratory tests and analyze both individual sour water and SWS feed streams and watch for differences. I believe they cannot be so drastic. The key is how to adjust stripper operation, and not to mix the feed perfectly. The way how you described it, it will always be different at some extent.

Best regards,

Normally, what is the pressure of sour gas exitting from stripper? Is its pressure so much enable us conducting to SRU(with operating pressure normally higher than sour water stripping unit)?If not, how do we do?
Regards

[fallah]

Normally, what is the pressure of sour gas exitting from stripper? Is its pressure so much enable us conducting to SRU(with operating pressure normally higher than sour water stripping unit)?If not, how do we do?
Regards

[NAJAF]

HI DEAR FRIENDS
ICAN NOT FIND FLASH POINT OF SOUR WATER IN SOUR WATER TANK
PLEASE HELP