9 replies to this topic

[EngrHamza]

Hello guys, I hope you all are fine and doing great.

 

I need some guidance regarding modelling packed bed distillation column in Aspen Hysys. For instance I am consider only one packed bed column. 

 

Its a propane recovery unit. The propane is recovered from LPG. In whole unit, there are two packed bed distillation column. I know the height of bed in both column as well as type and size of random ceramic rashing rings. The HETP used is 0.4 m for random packing. The reflux drum pressure and bottom pressure is known. The feed temperature is know only. The composition of LPG is know. Currently, de-ethanizer is packed column with reflux reflux mode. It is equipped with stab in reboiler. 

 

How can I know the feed location ? I can convert bed height into no of trays, but how I can locate feed stage ? I have all temperature of column which are bottom temperature, top temperature of stream entering to condenser and as well as reflux temperature. 

[Pilesar]

I think you are asking 'how do I find the best feed location for a new column design?' I suggest trying different feed locations to see which one meets the product specs while requiring the least amount of energy. Consider also whether you want to adjust your feed condition as it has an effect on performance. Packed beds should not be too short or too tall so the best feed location may not be the theoretical optimum.

[Bobby Strain]

Is this an existing column? Enlighten us about the LPG composition and column pressure.

 

edit:

I just noted that you are a student. So, do as Pilesar suggests. Are you modelling a depropanizer, following the deethanizer?

 

 

Bobby

Edited by Bobby Strain, 31 August 2023 - 12:18 PM.

[EngrHamza]

 

I think you are asking 'how do I find the best feed location for a new column design?' I suggest trying different feed locations to see which one meets the product specs while requiring the least amount of energy. Consider also whether you want to adjust your feed condition as it has an effect on performance. Packed beds should not be too short or too tall so the best feed location may not be the theoretical optimum.

 

Now I am asking about existing column. The column already exist and is in service and it's de-ethanizer. How can I verify or evaluate feed stage ? 

[EngrHamza]

Is this an existing column? Enlighten us about the LPG composition and column pressure.

 

Bobby

Yes it's an existing column and it's name is de-ethanizer. It bascially separates methane and ethane from propane and butane. The composition is given below;

 

C1 = 2.1 %

C2 = 18.9 %

C3 = 42.9 %

n-C4 = 14.2 %

i-C4 = 19.2 %

n-C5 = 0.2 %

i-C5 = 1.9 %

H2 = 0.6 %

 

All is in mole percent.

 

The operating parameter is; 

 

Feed pressure = 3700 kPa

Column Top pressure = 400 psig

Column Bottom Pressure = 405 to 407 psig

 

Note: It's full/total reflux column. 

[EngrHamza]

 

I think you are asking 'how do I find the best feed location for a new column design?' I suggest trying different feed locations to see which one meets the product specs while requiring the least amount of energy. Consider also whether you want to adjust your feed condition as it has an effect on performance. Packed beds should not be too short or too tall so the best feed location may not be the theoretical optimum.

 

I really don't know feed location even though I see it physically feed inlet nozzle. But I didn't seen internal section as it's in service.

[EngrHamza]

Is this an existing column? Enlighten us about the LPG composition and column pressure.

 

Bobby

For simulation I am using Peng Robinson. Did this property package gives nearer results as compared with practical results ? 

[Bobby Strain]

So, maybe you are not a student? And it is not total reflux, but taking overhead product as vapor. You can readily estimate the feed location. If the column is operating, match the operation with you simulation.

 

Bobby

Edited by Bobby Strain, 31 August 2023 - 12:24 PM.

[Pilesar]

The feed will be between packed beds. Often each bed in a column has the same height. If you are in the plant, there should be mechanical drawings of the column available if you know where to look or who to ask.

[breizh]

Hi,

Probably good to review the PId of the column and /or as built drawing of this particular column.

BTW you should check for the specification sheet of the packing material and vendors' bids. 

Additional document:

You may want to consider this link to support your work:

https://escholarship...96n0xv#page-489

 

Breizh