DGS for Recycle Gas Compressor

[norzul]

Hi,

Any experience to share on retrofiting of seal oil system to Dry Gas Seal (DGS) for the recycle gas compressor (200bar discharge) for the hydrocraker unit?

Thanks

norzul

 

[1969grad]

In the 1990s I worked with a gas transmission company that replaced their seal oil systems furnished on compressors installed in the 1970s with a DGS system. The DGS is better and everything went smooth. I suggest that you want tandem seals.

You will have to get a source for the seal gas which is generally from the discharge piping and install a filter and flow controls.

You will also want a separation gas between the bearings and the DGSs. The separation gas is generally IA at low pressure.

Finally, some compressor manufacturers will insist that you install a seal gas pressure boost system for when you start-up although in my opinion you do not normally need it.

 

[norzul]

1969grad,

Who is the manufacturer for the DGS? Compressor? and what is the discharge pressure of the compressor. If yu know what is the shaft diameter?

Are yu familiar with John Crane for the DGS?

Thanks

norzul

 

[LightBands]

Hi Norzul,

Retrofitting of seal oil system to dry gas seal requires a DGS seal with gas panel system to supply clean air or nitrogen.

Dry gas seals for a discharge pressure of 200 bar could be supplied by john crane or flowserve or burgmann.They can recommend a suitable solution based on your application requirement.Infact these manufacturers have in the past supplied seals to handle pressures more than 350 bar.

what is the shaft dia and who is the compressor manufacturer?

Ramesh babu

 

[cfin]

Norzul,

Key elements to any successful retrofit project are accurate collation of all relevant data and proper planning.
Retrofitting of DGS is always difficult and should not be considered lightly. If the seals are not supported by a suitable control system they will not function correctly and lead times on refurbs can be costly and time consuming.
On critical plant it is also advisable to have a rotordynamic study completed to ensure that critical frequencies of the rotor are not brought within the operating condition of the compressor as a result in changes to the damping charachteristics from the seals.
200 bar is a high pressure application, yes there are now numerous examples of DGS sealing to 350 bar but in the case of retrofits they are not so common.
First stage is to asses the suitability of the casing in question. DGS require more space than some wet seals which may mean that modifications to the casing are required, in addition suitable ports must be supplied to allow for seal gas and vents. A typical tandem seal with barrier seal outboard would require 4 suitable ports.
In addition a word of caution on Barrier seal gas supply, instrument air can be used however depending on the process/ seal gas used there will be some leakage through the 2nd stage of the DGS. This can lead to an explosive mixture in the secondary vent, a safer option is to use Nitrogen.
All that said the benifits of DGS retrofit are considerable and most would normally pay for themselves in less than 2 years and continue to show considerable efficiency improvement and reduced operating costs in subsequent years.
B rgds
cfin

 

[tgmcg]

One major oil company (#2) refuses to use DGS for high pressure H2 recycle application, as their proven MTBF is not adequate to achieve a 5 yr uninterrupted run with a sufficiently high level of confidence.