8 replies to this topic

[walidd_23]

Hi everybody.

I am  designing a new deethanizer column wich it is fed by 3 stream, the coldest one enter on the top of  the tower as a reflux .

In commun columns, operating pressure is designed as the buble point (or dew point ) of condenser Temperatur  ( cooling medium),   and by this pressure we can calculate the other parameter ( reboiler temprature,stage number, feed position ect..).

In my case, how can I determine the optimum operating pressure,  feed position and theorical stage number?

Can I determined this optimum pressure by optimization (using optimizer) in HYSYS which I vary the pressure of the column untill to get the minimum reboiler duty and others duties that related in the process?

 

 

I hope that you can help me .

 

 

[PingPong]

Optimal column pressure depends on many things, such as:

- in what kind of unit is this deethanizer? Refinery? Ethylene Plant? Or what?

- what will be composition of distillate, and of column bottoms?

- what is destination (equipment type and pressure) of distillate?

- what cooling media are available (for condensor)?

- what heating media are available (for reboiler)?

- ..........

[Bobby Strain]

You need to determine what you are going to use for overhead condenser cooling before you do anything.

 

Bobby

[walidd_23]

Thank you for your respons,

1/ this deethanizer tower is included in gas processing plant.

2/ there is no condonser as I mentioned before the coldest feed enter in the top of tower as reflux. and the heating media for reboiler is hot oil.

3/ the attached filed represent the first schema of the process and I hope it  will clarify the problem better.

 

For  further clarification  don't hesitate

Attached Files

•  Gas Plant,Deethanizer,pressure optimization.pdf   29.91KB   256 downloads

[walidd_23]

Optimal column pressure depends on many things, such as:

- in what kind of unit is this deethanizer? Refinery? Ethylene Plant? Or what?

- what will be composition of distillate, and of column bottoms?

- what is destination (equipment type and pressure) of distillate?

- what cooling media are available (for condensor)?

- what heating media are available (for reboiler)?

- ..........

 

You need to determine what you are going to use for overhead condenser cooling before you do anything.

 

Bobby

Thank you for your respons,

1/ this deethanizer tower is included in gas processing plant.

2/ there is no condonser as I mentioned before the coldest feed enter in the top of tower as reflux. and the heating media for reboiler is hot oil.

3/ the attached filed represent the first schema of the process and I hope it  will clarify the problem better.

 

For  further clarification  don't hesitate

[Bobby Strain]

Well, you confused me with your terminology. Usually in the case of propane recovery from natural gas you want to operate the column at as high a pressure as you reasonably can to reduce the overall power required for gas recompression. If the pressure is too high, the K values approach 1. You can visit the Ortloff site and get some idea of the pressure range you can use.

 

Bobby

[RockDock]

what is your inlet composition, T, P and flow?

 

The pressure will be determined by the turbo expander pressure needed to cool the gas. This is a very common question. I just need to know the inlet conditions to help you.

[Neelakantan]

@walidd

 

other senior members are earnestly answering you; so let me go in tangent:

 

1) is this concept study ? or academic study? or live or potential project?

2) such a plant is normally designed (including hysys simulation) by a senior engineer with specific project objectives; what is your role and what is the objective of the project

3) the hysys schematic shows a TE with two reboosters; how their pressure levels are "optimized"

 

for a proper help and support, i would like to repeat:

1) make the post meaningful, with proper engineering information;

2) tell unambiguously, what is done, what is required to be done and what is the bottleneck/problem

3) be point clear about the objective of the question; after-all we are "professionals"!

 

regards

neelakantan

[paulhorth]

Walid,

 

Your flowsheet is a typical NGL recovery flowsheet, similar to several which I have designed. You need to understand that the column pressure is determined by the pressure drop across the expander, which in turn is determined by the temperature required at the expander outlet, to achieve the specified NGL recovery. You cannot optimise the column pressure independently of this central requirement.

 

The column is effectively an ethane stripping column.  You could route stream 16 directly to the top of the column and eliminate vessel V-103, instead using an enlarged diameter at the top of the column.

 

There are a couple of other problems with this flowsheet.

The dehydration is downstream of the large gas-gas exchanger E-100. This means that the colld gas leaving E-100 will be wet, so it will  form hydrates. In my flowsheets, Stream 8 is well below the hydrate point, so the dehydration should be upstream. Then, where is the liquid Stream 9 going? This stream will be wet so you can't route it to the deethaniser column, but it will contain methane and ethane as well as NGL.

 

Paul