4 replies to this topic

[Olaniyi]

Hi
Has anyone here ever done a PRO-II simulation for a N2 rejection unit from feed gas for NGL extraction?

Need some pointers.

Thanks
Ogeds

[Zauberberg]

What is the unit configuration (upstream/downstream of expander unit), and which technology is chosen for Nitrogen rejection?

Give us a flow scheme and basic process parameters, please.

[Olaniyi]

What is the unit configuration (upstream/downstream of expander unit), and which technology is chosen for Nitrogen rejection?

Give us a flow scheme and basic process parameters, please.

Hi Zauberberg
Apologies for the late response. The technology of choice is the triple column cycle i.e. prefractionator (to concentrate the N2) + double column cycle for the N2 rejection (see attached schematic)

Some process parameters below:
Feed composition: 9.8%N2, 89.8%C1, 0.4%C2
Feed conditions: Pressure 20-23barg, temp -102degC (feed is from overhead of NGL extraction plant)
Feed rate: 200kg/s

Final product: N2 to be rejected to atmosphere hence spec of ~99.9%
Sales gas C1: > 1% N2 to be compressed to 72bara pipeline pressure

Many thanks!
Ogeds

Attached Files

•  schematic.doc   51KB   77 downloads

[Zauberberg]

It looks like process scheme for Nitrogen rejection developed by Costain or Linde. What particular concerns you have when modeling this type of NRU?

I have been working on modeling Nitrogen rejection from liquid LNG, accomplished through a heat exchanger and a separation column. Since you must be having either design or operational data (or both), it should be relatively easy to configure the flowsheet. Can you be more specific on what is creating problems to you?

Best regards,

[Olaniyi]

It looks like process scheme for Nitrogen rejection developed by Costain or Linde. What particular concerns you have when modeling this type of NRU?

I have been working on modeling Nitrogen rejection from liquid LNG, accomplished through a heat exchanger and a separation column. Since you must be having either design or operational data (or both), it should be relatively easy to configure the flowsheet. Can you be more specific on what is creating problems to you?

Best regards,

Thanks Zauberberg,
I have set-up a configuration and I can't get it to converge.
My main challenges are:
(i) How to program the condenser and reboiler duty for the LP and HP columns, which have to be equal. I'm currently using a controller, but have problems converging when I try to equate them using either feed flow, duty or return temperature into the LP column.
(ii) I'm also not sure what the expected pressures and sometimes temperatures are in each of the columns
(iii) Seems by the time my N2 cools the overheads and the bottoms of the HP column the temp is already higher than the feed temp, but in all the flowschemes I've seen the N2 seems to play a part in cooling the feed as well.
(iv) In the prefractionation, I expect I need to have a condenser and a reboiler - wondering now if an interstage cooler is possible - how is this modelled in PRO-II. Also for the reboiler, I have a very little margin for even getting any reboiler heat somehow, thus ending up with approx thesame temp leaving and going back into the column


A lot of questions, sorry! Thanks for the help!
Ogeds