8 replies to this topic

[Aranga]

Hai all,

 

    We are having 2 De-ethaniser columns in our plants. One in ERU, another is in PRU. But their design is different. I want to Know, why they are different eventhough doing the same function?

 

   ERU column is wider at the Top section. PRU De-ethaniser column is wider at the bottom section (Doing same function but operating conditions are different). Why is that so?

 

Thanks.

[Pilesar]

You have two questions. I will rephrase them to what I understand you to ask and then reply.

 

Question One "Why are there different refrigerants?" Check the operating pressures of the two DeC2 columns. The condensing temperature is different for the different pressures so you are using different levels of refrigeration.

 

Question Two "Why are the columns not the same diameter from top to bottom?" The expected internal traffic is used in designing the column diameters. The columns would likely operate fine if they had the wide diameter at both the top and bottom. But since the traffic was expected to be significantly lower in one section, the diameter of the shell in that section was reduced to save capital cost.

 

If you have access to a steady-state process simulator, these columns are pretty easy to model. Building and reviewing a model may give you a better feel for what is happening inside the columns.

[Aranga]

Hi Pliesar,

 

 

     I am not confused about overhead system of the columns, and refrigeration used for the condensers. The two columns are doing the same function. Seperating out C2s (at the top) and C3s (at the bottom). But handling different volume, with different Pressure & Temperature. It is a bit surprising to me The entirely opposite (one column looks as inverted shape of the other)  design of the columns. (might reasoned by, something essentially Technical) 

 

 

 

I dont have process simulator facility. But I can understand your Answer. The key point behind the column design might be " capital & operating costs".

 

Moreover what I think, Composition of the feed matters.

 

Thanks for your reply.

[gegio1960]

aranga,

if ERU and PRU means Ethane Recovery Unit and Propane Recovery Unit the two columns are not making the same service.

You're right saying "composition of the feed matters". For a better understanding, you should provide them and also the operating conditions and the specifications required to the products.

regards

[Aranga]

Hi,

 

Pls view the attached file.

 

Thanks.

Attached Files

•  forum.xlsx   40.73KB   62 downloads

[gegio1960]

aranga,

you can easily find the answer to your question by looking at the two compositions:

- in ERU you have about 80% of the feed as light components: so you have a bigger diameter for the top section;

- in PRU you have about 99% of the feed as heavy components: so you have a bigger diameter for the bottom section.

good luck

[meetyourmaker]

Flooding velocity determines the column diameter in a particular section so if the vapor traffic in a particular section of the column is higher, it must have higher diameter. In your case the ERU deethanizer has high concentration of lighter products so vapor traffic in top section of the column will be more hence it will have higher diameter. Exactly the opposite is true for the PRU DeC2 column. You can alwas simulate the colums in any process simulator to get a better understanding of this.

[ncarrascob]

you should to check the ORTLOF papers to understand a bit more.

Apart from capital cost considerations, maybe the reason could be that they are designed to operate in different mode (ethane recovery or propane) 

It is correct to say that both columns can do the same job, but is essential to recognize that: (Imagine that only one column works), then, for a desired NLG/LPG % of recovery, the process will consume more energy with one than with the other <this because of design>. where each of one is more efficient in the operation mode for which was designed. that also briefly explains why the different operational conditions.

 

take a look at.

Attached Files

•  NLG-LPG RECOVERY.pdf   222.99KB   37 downloads

[Aranga]

Neil 20,

 

   Our columns are not designed to operate with different modes as like in LNG plants. Our plants are downstream units of RFCC in Refinery.(Recovering C2s, C3s, C4s from RFCC off gas).

 

  But your Answer helped me to have better understanding. Thanks for your knowledge share.

 

Thankyou.