12 replies to this topic

[rowanlim]

Good day! I'm currently doing preliminary sizing of air receivers for a new plant. I'm required to estimate total utility/instrument air consumption since the air will be provided from a common source. I understand the method to calculate but I seem to be missing some information, ie the typical air consumption figures for the users. I am referring to Shell Exploration's Air Systems for Offshore Installation but I couldn't find the figures for the following users:

i) packages (in continuous use)
ii) nitrogen generation package (in frequent use)

Is there any other reference I can use?

Thanks for your help!

[ankur2061]

rowanlim,

Have a look at the following link. If you use the "Search" feature of the forum you will find answers to a lot of queries since a lot of the posts on the forum are of a repetitive nature:

http://www.cheresour...h__1#entry20079


Regards,
Ankur.

[breizh]

Hi ,
for a nitrogen generator ( N2 # 97%) , I have a proposal where air consumption is 2.85 Nm3 air /Nm3 N2 , let say 3 .

hope this Helps .

Breizh

[rowanlim]

@Ankur: I did use the search function, I found the same thread you posted among others & I couldn't find the answer I needed. But after badgering a senior, I got more information & could estimate the service air consumption for the nitrogen generation package, turned out I didn't have enough information to find that value!

However another issue popped up: I now am trying to find a typical air consumption value for system packages, in a previous note, the value provided was 10 Sm3/h, however I couldn't find that value in the references mentioned in that note or any other reference that I have. How does one come up with 10 Sm3/h per system package? Any idea?

@breizh: I'm a bit confused, is Sm3/h different from Nm3/h?

[breizh]

@Ankur: I did use the search function, I found the same thread you posted among others & I couldn't find the answer I needed. But after badgering a senior, I got more information & could estimate the service air consumption for the nitrogen generation package, turned out I didn't have enough information to find that value!

However another issue popped up: I now am trying to find a typical air consumption value for system packages, in a previous note, the value provided was 10 Sm3/h, however I couldn't find that value in the references mentioned in that note or any other reference that I have. How does one come up with 10 Sm3/h per system package? Any idea?

@breizh: I'm a bit confused, is Sm3/h different from Nm3/h?

[breizh]

@Ankur: I did use the search function, I found the same thread you posted among others & I couldn't find the answer I needed. But after badgering a senior, I got more information & could estimate the service air consumption for the nitrogen generation package, turned out I didn't have enough information to find that value!

However another issue popped up: I now am trying to find a typical air consumption value for system packages, in a previous note, the value provided was 10 Sm3/h, however I couldn't find that value in the references mentioned in that note or any other reference that I have. How does one come up with 10 Sm3/h per system package? Any idea?

@breizh: I'm a bit confused, is Sm3/h different from Nm3/h?

S stands for standard condition ( to be defined , in US60F and 1atm)) and N for normal condition (0C and 1 atm).

For N2 Generator , I'm quite confident with my figures , I had several proposal but it depends of the quality of N2 .

[rowanlim]

Ooh okay thanks for the answer!

Well attached is a shot of the calculation I did to find out the service air consumed by the generator, assuming 95% membrane efficiency (I got this figure by reading several vendor documents & other sources on the web). I will insert this calculation in my report.

Attached Files

•  n2.JPG   30.95KB   65 downloads

Edited by rowanlim, 12 November 2010 - 02:48 AM.

[Zauberberg]

The figures given by Breizh for Nitrogen Membranes are more accurate ones - the ratio of Instrument Air feed vs Nitrogen product flows is somewhere between 2:1 and 4:1, in Nm3/hr, depending on membrane type and Nitrogen purity requirements. Significant amount of Nitrogen from the Feed Air stream ends up in the Membrane discharge (Reject) stream. If you need exact figures, you will have to get feedback from the Membrane vendor.

One internet source offers tabulated data for Air feed vs. Nitrogen flows at various recovery (Nitrogen purity) levels: http://www.igs-globa...eron/module.htm


As for the packaged units, it is virtually impossible to supply you with Air consumption/demand figure as it varies upon package size and, of course, the type of packaged unit. Again, contacting different vendors will put you on the right track. I'm sure they are willing to provide you with all the data you need - assuming that you are a serious potential customer of their products.

[rowanlim]

Thanks Zauberberg, I couldn't access that site (blocked by the company), I'll be sure to get it when I'm home

Yeah I realized that the air consumption is specific to the system package, which is why I'm wondering how the previous report used 10 sm3/h PER package, it wasn't logical & no references listed for that!

[rowanlim]

Greetings, I would like some advice on what would be a reasonable margin to accommodate drier regeneration losses: is 10% reasonable enough? This is the figure stated in Shell Engineering Reference Doc & I couldn't find other literature stating other figures.

Thank you!

[Zauberberg]

If you are referring to the PSA type of dryers, 10-15% air loss is reasonable figure.

[Zauberberg]

Just to add one more note: you'll see that some of the PSA dryers have an adjustable orifice in the Regeneration Air line. Position of this orifice is set by the manufacturer, based on their calculations and field trials, to ensure sufficient flow of dry air required for proper regeneration of the adsorbent. If, for any reason(s), one needs to change the flow this can be done by manipulating the orifice position. The correspond quantity of dry air losses will be changed in that case as well. The quoted figure (10-15%) basically should cover all the cases.

[rowanlim]

Thanks for your feedback, Zauberberg. I'll be using 10% margin for now, the result is slightly larger than anticipated, mainly because I don't have enough information (package air consumption, produced nitrogen flowrate etc), so my calculation was quite conservative. At least I've a better idea on how to estimate the utility/service air consumption!