Jump to content



Featured Articles

Check out the latest featured articles.

File Library

Check out the latest downloads available in the File Library.

New Article

Product Viscosity vs. Shear

Featured File

Vertical Tank Selection

1

Stabilization Column


11 replies to this topic
Share this topic:
| More

#1 chetanhm2

chetanhm2

    Gold Member

  • Members
  • 97 posts

Posted 12 August 2018 - 08:34 AM

Dear All,

 

I wan to ask you you that for Refinery CCR Stabilization column , is it possible to get 42 percent ethane volume basis in overhead liquid draw LPG and less butane say 9 percent in LPG ? There is vapour draw from top of the column which is recyleed to inlet of stabilizer in LPG absorber drum.

 

Regards,

Chetan



#2 PingPong

PingPong

    Gold Member

  • Members
  • 1,173 posts

Posted 12 August 2018 - 12:00 PM

Without detailed information such as PFD, heat and material balance, et cetera, it is for outsiders impossible to give useful advice.



#3 chetanhm2

chetanhm2

    Gold Member

  • Members
  • 97 posts

Posted 12 August 2018 - 06:29 PM

Dear Sir,

I can not share PFD. IT IS refinery CCR plant wherein reactor effluent is separated in stabilizer. STABILZER TOP contains LPG.LPG comp is mix of propane and butane as per design case and very less ethane say 9 peecent LIQ vol percent. BUT IN operating data, we r getting 42 percent vol of ethane liquid. Stabilizer top cobtains two streams one is liquid LPG and other gas stream which mainly contains methane abd ethane and propane. This stream is recycled to upstream of stabilizer in LPG drum. Vapour Outlet of this is sent to fuel gas header.

#4 Technical Bard

Technical Bard

    Gold Member

  • ChE Plus Subscriber
  • 332 posts

Posted 12 August 2018 - 10:39 PM

You need to build a simulation of the unit using the original design data, they try to tune the data to the plant data.  You may find that the operating mode if very different from the original design material balance.  

 

From that, you can try to determine why the performance is different.  It may be due to tray damage, over or under-reboiling, fouled exchangers, a very different feed composition.  Review the books my Kaes and Kister for more on simulating and troubleshooting columns.



#5 PingPong

PingPong

    Gold Member

  • Members
  • 1,173 posts

Posted 13 August 2018 - 04:19 AM

I can not share PFD.
A simple hand sketch with relevant info would be sufficient.

If you do not provide proper information you cannot expect proper advice.

 

Again and again people on this forum post short unclear questions, but nevertheless request top quality solutions.

Never expect a response that is longer than your question.

 

 

42 % ethane in stabilizer top liquid seems impossibly high. Maybe the lab analysis is wrong.

 

What is temperature and pressure in the Stabilizer Reflux Drum?
 

What is temperature and pressure in LPG Drum upstream the Stabilizer?



#6 chetanhm2

chetanhm2

    Gold Member

  • Members
  • 97 posts

Posted 13 August 2018 - 04:38 AM

Dear Sir,

 

I am using Aspen Refysys for simulating all these CCR downstream sections like Stabilization Column (overhead of column being liquid LPG  and vapour draw being rich in methane , ethane and propane ) , What I have as data input is detailed feed composition (heavy naphtha from NHT) and Lab data for products composition. So I did backblending of all products to arrive at reactor effluent composition. Now, After getting this reactor effluent composition at the reactor outlet (by calibration of reformer in hysys) , I am NOT getting more than 40 percent ethane in LPG liquid draw from column but getting only 20 percnet volume ethane in LPG  .  as per product data given by client there should be more than 40 percent volume of ethane in Stabilizer overhead liquid draw. and butane being only 9 percent .

I wan to ask you whether it is possible in plant as upstream unist like Net hydrogen removal happens at 02 deg where some ethane will also go with it and then some flow to fuel gas header upstream of stabilization ? So really is it possible ?



#7 chetanhm2

chetanhm2

    Gold Member

  • Members
  • 97 posts

Posted 13 August 2018 - 05:55 AM

Dear Sir,

 

Stabilizer top pressure is 14 kg/cm2 g and top condenser  temp is 35 degC and column top temp is 55 DegC .bottom pressure is 16.20 kg/cm2 g and bottom temp is 240 Deg C .Feed is 20 percent partial vapour. Stabilizer top has two outlets : one is Liquid LPG and other is vapour flow which is recycled to the upstream of column in LPG absorber drum  and outlet vapour of that drum goes to fule gas header and liquid outlet of this drum goes to stabilizer inlet as feed and so this drum will act as additional separation for lighters and improving separation.Bottom reboiler temp is 240 deg C and pressure is 17 kg/cm2 g and Before this stabilization system, whatever Hydrogen generated is sent to PSA for further purification dn typically , this hydrogen has 92 percent purity mol percent .This hydrogen is released by condensing inlet strem at -2 deg C and so all hydrogen almost will go to top as vapour as its BP is -50 deG and almost all ethane will aslo go as its BP is lower even at 27 kg/cm2 g operating pressure



#8 chetanhm2

chetanhm2

    Gold Member

  • Members
  • 97 posts

Posted 13 August 2018 - 06:07 AM

Dear Sir,

 

I wan to add one more thing . While doing Reformer Calibration in hysys, I could find 5 percent error in hydrogen balance closure whereas mass balance closure was 100 percent .

 

Can this lead to such erros?

 

Regards,

Chetan Chavan



#9 chetanhm2

chetanhm2

    Gold Member

  • Members
  • 97 posts

Posted 13 August 2018 - 06:08 AM

LPG drum pressure is 13 kg/cm2 g and temp is 30 deg C



#10 chetanhm2

chetanhm2

    Gold Member

  • Members
  • 97 posts

Posted 13 August 2018 - 06:31 AM

My client was saying that is the composition of LPG . but as per my knowledge it is not possible to get 42 liquid vol percent ethane as liquid as for that I needed to cool the top condenser temp to 5 deg C in hysys . So I think it can not be possible in real plant too. Request your advice.



#11 Technical Bard

Technical Bard

    Gold Member

  • ChE Plus Subscriber
  • 332 posts

Posted 13 August 2018 - 01:36 PM

It is quite common to end up with 5% error in mass balance from plant data.  Meters are usually +/- 1-2%, analytical data may be worse, and is often spot data, not averaged like flow measurements (which are near continuous and you can average over time).  Small errors in analytical data multiplied by small errors in large flowrates turn into big errors.

 

You need to adjust your input data based on the flow measurements and analysis you trust the most (final product, custody transfer meters, better analytical methods).   If the thermodynamics of pressure and temperature tell you it is impossible to get that much liquid ethane, then the plant data must be in error.



#12 chetanhm2

chetanhm2

    Gold Member

  • Members
  • 97 posts

Posted 14 August 2018 - 12:55 AM

Dear Sir,

 

But as per your experience, is it possible to get 42 liquid volume percent ethane in liquid LPG draw from stabilization tower given the temp and pressure conditions mentioned above. There is vapour draw at the top of the tower also which is recycled to upstream of stabilization tower






Similar Topics