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In our wet gas centrifugal Compressor (capacity-130TPH), dry gas seal system (nitrogen) is given as primary, secondary and separation gas. The N2 header pressure is 7.5 kg/cm2g. Is any back-up facility (N2 bottles, booster etc.) required for safe and smooth operation of WGC in case of header pressure low or failure of supply?
26/10/2011 A: G KAMALAKANNAN, Foster Wheeler India Ltd, siddhukamal@yahoo.co.in
Nitrogen volume bottles are not necessary if the refinery is having back-up liquid nitrogen storage.
Please check the following:
a) Flow rate required for dry gas seal system of WGC
b) In the event of nitrogen plant trip, please study the reasons and back-up available in the nitrogen unit:
- Standby air compressor is generally turbine driven or connected to an alternate emergency power
- Quantity of liquid nitrogen available and time upto which this can be used to avoid reduction in
nitrogen header pressure.
- Liquid nitrogen vaporiser system and its response time for avoiding the dip in nitrogen header
pressure in refinery.
After ensuring the above, you may decide to go for back-up bottles of nitrogen. Using nitrogen bottles will also have some time delay. Change-over from normal nitrogen supply to bottles is normally done manually and it is very difficult to have automated system for this operation. Also, you can consult with compressor vendor to find out the bearable time for non-availability of nitrogen in DGS.
18/04/2011 A: Hubert Mueller, Bayernoil, guhumueller@web.de
As backup we used a bundle of nitrogen bottles (120nm³). This should allow a safe shutdown if the primary nitrogen source should not be available for a longer period. But you need to check the bundle pressure continuous or in a short frequency in order to have the backup available in an emergency case.