895 MW power station: MPC from 54.1 to 18.4, then rolled out on all three turbines
Varnish in the lubricating oil caused valve problems on all three turbines at a power station supplying 2.5 million homes. After offline filtration on the first gas turbine, the MPC value fell from 54.1 to 18.4, and the solution was rolled out on all three turbines.
MPC (varnish potential), gas turbine 1
A natural gas-fired combined cycle power station of 895 MW, enough for 2.5 million homes, had valve problems on both gas turbines and the steam turbine. Oil analyses pointed to varnish: degradation products in the oil that settle as deposits on valves and block filters. The station had standard filtration installed, but it did not solve the problem, and contractual supply commitments were at risk.
On the first gas turbine, Delta Xero cartridge filtration was connected to the lubrication system’s 14,000 litres of Shell Turbo 46, together with an inline particle counter so that oil quality could be followed continuously.
The MPC value, the recognised measure of varnish potential, fell from 54.1 to 18.4. The cleanliness code fell from ISO 22/16/11 to 14/13/10, and the number of particles above 4 µm from 34,448 to 151 per ml. On the second gas turbine the picture was the same: MPC from 49.5 to 15.3 and cleanliness code from ISO 23/20/11 to 14/13/09.
On the basis of those results, the station chose to roll the solution out on all three turbines.
The figures before and after
| Measurement | Before | After |
|---|---|---|
| MPC (varnish potential), gas turbine 1 | 54.1 | 18.4 |
| ISO 4406 cleanliness code, gas turbine 1 | 22/16/11 | 14/13/10 |
| Particles above 4 µm per ml, gas turbine 1 | 34,448 | 151 |
| MPC (varnish potential), gas turbine 2 | 49.5 | 15.3 |
| ISO 4406 cleanliness code, gas turbine 2 | 23/20/11 | 14/13/09 |
| Particles above 4 µm per ml, gas turbine 2 | 58,874 | 132 |
| Water content, gas turbine 1 | 18 ppm | 3 ppm |
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