6 replies to this topic

[DB Shah]

We are operating a fertilizer/petrochemical complex with a separate plant of Instrument air. The instrument air is distributed to various plants in the complex. Plants have individual air receiving vessel. In some of the plants NRV on Instrument air at battery limit is provided where as other plants do not have NRV at the battery limit. IS there any standard for provision of NRV? If I install NRV on the plants which do not have NRV presently will it effect adversely?

[ankur2061]

Divyang,

NRVs on instrument air lines are provided when you have multiple sources (air receivers) feeding to the same unit or plant. Multiple sources of instrument air may be due to a backup instrument air supply available based on the instrument air backup philosophy of the plant. NRVs are not required when a common source is feeding to all the plants or units. However, isolation valves should be provided at the individual plant / unit to isolate the air supply for any maintenance / shutdown.

Regards,
Ankur.

[DB Shah]

Dear Ankur,
Thanks a lot for the quick response. I was wondering for the reason of provision of NRV by some process licensor in battery limit of our plant. Maybe that is their standard or they wish to avoid back flow of IA to the complex from the Air receiver of that plant and hence save the plant from tripping. (Scenario - When there is major leak in the existing IA header. Also the NRV might give some buffer time for the perticular plant to take safe shut down.)


Regards
Divyang

[fallah]

Divyang,

Without more information, the only thing could be stated is:

Considering NRV at a plant battery limit may be for keeping IA pressure (of course for a limited time due to back flow leakage) at battery limits of the users included in the plant when the relevant compressor is tripped.

Fallah

[mishra.anand72@gmail.com]

I could not find any standard which states specifically for provision of NRV in instrument air line.

I don't think you are going to affect anything by providing NRV. But question is why you want to do it which has been tried to answer in other member's post.

[DB Shah]

Dear Anand Mishra
Yes, I agree with you and other members. NRV does not have specific purpose here. The issue was that one of our plant has NRV on IA at battery limit. While other plants do not have any. Now one of the engineer, based on existing NRV case has proposed to install on other plants also. This proposal is purely a duplication of one plant philosophy to other plants. The logic is - providing NRV will not add to hazards, and it will take care of any other scenario which we are not able to envisage presently.

Edited by DB Shah, 30 December 2011 - 10:37 AM.

[kkala]

For any non toxic fluid line (including instrument air line) we successively install: valve, NRV, 3/4" drain, spectacle blind, valve, at the (branch) pipe crossing battery limit of a unit to feed it. This concerns refineries and is included in written guidelines. I do not remember such a scheme in a fertilizer plant (1975-81), most probably there was not, but at that time instruments were much fewer.
In mentioned refineries at least some units have dedicated instrument air drums (downstream of the BL) to maintain air supply ~3 min after instrument air failure. This may be a good reason for installing NRV on instrument air line at the battery limit, though it is not certain that NRVs will stop back flow when needed (on demand).

Note: Due to mentioned drawback of NRVs, I assume there will be another NRV (of different type) just upstream the instrument air drum in the refineries.

Edited by kkala, 31 December 2011 - 11:21 PM.