3 replies to this topic

[Frederick34]

Hello to all!

 

I have a question about washing water injection systems and hope someone here can help me with it. I have noticed that several distillation columns that have water injection systems at the top for washing, operate at temperatures of 120-125 °C (248-257 °F) and pressures that can be 0.5-1 kg/cm2g (7-14 psig). What is the point of injecting water if in those conditions the water evaporates (I know this because the vapour pressure of the water at 120-125°C is much higher than the pressure of the tower)? If all the water is transformed into steam, it is not possible to wash any salt and the whole washing system does not make sense...

 

I performed a simulation in HYSYS considering the currents and their respective compositions. I hoped that when considering the hydrocarbon-water mixture, the dew point of the aqueous phase varies, but it did not occur. The simulation predicts that under column top conditions, the entire mixture is in a gaseous state.

 

I’m making a mistake in the calculation methodology or did I miss something?

 

Thank you very much!

[PingPong]

 

 

I have noticed that several distillation columns that have water injection systems at the top for washing, operate at temperatures of 120-125 °C (248-257 °F) and pressures that can be 0.5-1 kg/cm2g (7-14 psig).

I have never seen distillation columns that have water injection systems at the top for washing.

Or do you mean water injection into the overhead line upstream the condenser?

 

What kind of distillation columns are you talking about? What service?

Edited by PingPong, 09 January 2024 - 06:54 AM.

[Frederick34]

 

 

 

I have noticed that several distillation columns that have water injection systems at the top for washing, operate at temperatures of 120-125 °C (248-257 °F) and pressures that can be 0.5-1 kg/cm2g (7-14 psig).

I have never seen distillation columns that have water injection systems at the top for washing.

Or do you mean water injection into the overhead line upstream the condenser?

 

What kind of distillation columns are you talking about? What service?

 

 

You’re right. I said it wrong: it’s not a water injection at the top, but the overhead line upstream of the condenser.

I’ve seen this kind of injections in topping units and some main FCC fractionators.

[PingPong]

Injected water that vaporizes lowers the temperature of the overhead vapor.

You have to inject so much water that there will be free water left at the inlet of the condenser.

 

In your simulation you must use an adiabatic flash for that, not simply fixing the temperature at that of the column top.