7 replies to this topic

[dhrubabasu2013]

Our Amine regeneration unit has a design temperature of 92 degree Celsius, but on calculation, water dew point is found from steam table at 108 degree Celsius.

 

The calculation is derived from 331 kg-mols of water and a total of 990 kg-mols in the overhead vapor from the stripper column. The top design pressure is 1.05 kg/cm²( gauge).  Thus, the partial pressure of water vapor in the overheads from the stripper column is 0.35 kg/cm²( g). This absolute pressure is 1.35 kg/ cm²( g).

 

From the steam tables, the corresponding saturated temp. is around 108 degree Celsius.  Is this calculation correct?   But then how can the dew point be greater than the design temperature.  Please clarify.

[Profe]

Hi Dhrubabasu2013

 

About your question:

 

The amine regeneration unit works at a top pressure or operative pressure. This pressure will define the top temperature of the regenerator.

The saturation pressure of water is a function of temperature (see chart attached)

But we must also consider to determine the top temperatureof the regenerator, the mass balance and energy balance: amine regenerator and associated equipment such as:

Cooler top (top for cooling and condensation of water vapor)

Heat input to the regenerator (by reboiler and process stream - rich amine)

The top temperature is iteratively determined assuming a temperature until mass and energy balances are met in the amine regenerator.

 

I think this will be useful

 

Good luck

 

Fausto.

Attached Files

•  Water saturation pressure.png   16.44KB   2 downloads

Edited by Profe, 05 October 2015 - 04:42 PM.

[breizh]

Hi ,

another resource to add to Fausto's chart .

 

Hope this helps

 

Breizh

[PingPong]

The calculation is drawn from 331 kg-mole of water in overhead column and total of 990 kg-mol in overhead column.The top design pressure is 1.05 kg/cm2 ( gauge).Thus partial pressure of water vapor in overhead column is 0.35 kg/cm2 ( g). Thus absolute pressure is 1.35 kg/ cm2 ( g).

That is not correct.

 

1 atm = 1.03 kg/cm²(abs) however in reality the atmospheric pressure varies somewhat and can be higher or lower than that.

 

Partial pressure of water vapor is (331/990) * (1.05 + 1.03) kg/cm² ABS = 0.70 kg/cm² ABS.

That corresponds with about 90 ^oC in a steam table.

Edited by PingPong, 06 October 2015 - 01:30 PM.

[dhrubabasu2013]

But Mr Ping Pong, if I take

Partial pressure of water vapor is (331/990) * (1.05 + 1.03) kg/cm² ABS = 0.70 kg/cm² ABS,

 then converting it back to gauge pressure will be 0.7-1.03=-0.33 kg/cm²(gauge), how partial pressure can be negative.Please clarify

 

Regards

Dhrub

[breizh]

Hi ,

All your calculation should be based on Absolute Pressure !

 

Breizh

Edited by breizh, 15 October 2015 - 09:29 PM.

[dhrubabasu2013]

Yes I agree , here I m just giving illustration that how partial pressure can be - be,in case I convert back to gauge pressure .

[shan]

Partial pressure definition:

Partial Pressure = (Total Absolute Pressure) x (Volume Fraction of Gas Component)

 

There is no possibility of negative value of partial pressure as defined because both total absolute pressure and volume fraction gas component are always positive.  I think it is OK if you really prefer to convert the partial pressure in garage value from the mathematic point of view.  I mean it is the same thing if you want to tell people that this year is year -985 to year 3000 instead of year 2015.  Is it?