Best of the Best 2016 : BRANDYWINE

BOB 2016 buttonReadiness plan assures reliable transfer from gas to oil

Switching from natural gas to fuel oil during times of seasonal or contractual need brings with it a special set of risks. Plant Manager Mark Briggs and his O&M team at the NAES-operated Brandywine Cogen LP developed maintenance procedures to assure a reliable supply of liquid fuel to the 7EA-powered combined cycle during the critical winter run season. The plant, located in Brandywine, Md, near Washington, DC, is owned by KMC Thermo LLC.

One of the challenges to reliable fuel transfer is heat—in the combustion compartment from casing leakage, in the purge air, etc. These and other heat sources raise the temperature of oil as it is fed to the combustion system.

Plant personnel knew it was not possible to eliminate all sources of heat, but were able to mitigate its impact and keep dispatches reliable. They developed two preventive-maintenance (PM) procedures—one for the spring, one for the fall—to meet expectations.

The fall PM is particularly important. Maintenance Manager Chris Nevitt and David Trask, maintenance technician, came up with the following plan:

      • Replace the duplex filters and clean strainer screens on the fuel-oil transfer skid.

      • Replace the Moog filters on the bypass valve and 10-port actuator.

      • Flush the tubes that run from the 10-port isolation valve to the fuel-oil check valves.

      • Replace flex hoses.

      • Replace check valves in the purge-air, water-injection, and primary and secondary fuel circuits.

In the spring, plant personnel rebuild the fuel-oil check valves, verify the integrity of tubing insulation, and look for leaks in the combustion air circuit, repairing any found. Tubing is not flushed in the spring unless operating data show an uptick in pressure during the winter run season. Fuel-transfer exercises are conducted weekly during the spring and summer.

Additional steps:

      • Protected fuel-oil tubing and flex hoses against excessive heat inside the combustion compartment by wrapping them with insulation (Fig 1).

      • Repositioned secondary fuel-oil check valves to minimize the risk of coking, which can inhibit proper valve operation. Fig 2 shows fuel now is supplied above the horizontal centerline of the secondary inlet. With fuel entering at this location, and purge air flowing horizontally, no fuel oil remains inside the check-valve ball area to be cooked by the hot purge air. While it is not possible to install secondary check valves in the most favorable positions on all cans, critical to success is positioning the secondary inlets above the centerlines so oil drains down rather than puddling.

      • Replaced the OEM-supplied fuel-oil check valves with ones from a third-party provider to mitigate coking. They feature a Teflon-coated ball cage less prone to sticking from heat and coking.

Brandywine Figs 1,2

Another enhancement: Installation of screens at the primary check valves to catch liberated coke particles before they clog an injector orifice. When a screen clogs, you still see higher-than-normal pressures for that can, but replacing a clogged check valve is much easier, and less costly, than removing the primary fuel-oil tubes. When O&M personnel see higher pressures, they replace the check valve, flush the system and look for root causes of heat interference.

Clean-up. Solvent M-Pyrol® was selected as an aggressive carbon cleaner that doesn’t harm metal or leave a residue. It is corrosive, but works well if you keep it away from rubber, avoid skin contact to the degree possible, and replace the 55-gal drum every other season.

Conventional oven cleaner also does a quick, thorough job of cleaning metal check-valve components—provide you keep it contained and rinse the residue off your parts immediately.

Coking debris settles in the ribs of flexible hoses, so the flushing solution described in the sidebar doesn’t remove all of it. Nevitt and his staff send the hoses to a contractor for thorough cleaning.

Results. A 100% reliable fuel-transfer process is a lofty goal. Brandywine has had consistent success with the approach described by keeping the process simple and adapting it to the exigencies at hand. It has saved numerous man-hours and expense by avoiding unplanned outages and has extended the service life of the plant’s combustion systems. Applying this regimen of preventive measures also spares personnel the tedium of more noxious tasks—such as disassembling the primary fuel-oil cans to remove and clean the oil tubes.

Fuel-oil flushing procedBrandywine sidebar Figure

1. Disconnect selected can tubing from 10-port isolation tee.

2. Connect pump discharge tubing.

3. Disconnect selected can tubing from check valve at can in combustion compartment.

4. Connect flush tubing at check valve to discharge into “Empty” drum (see diagram).

5. Connect air supply to pump discharge tubing.

6. Blow out can tubing with 30-psig air for 30 seconds.

7. Disconnect air and connect tubing to pump discharge.

8. Line up valves to pump M-Pyrol® through selected tube and recirculate to the “M-Pyrol” drum.

9. Recirculate the cleaning solution for 30 minutes.

10. Shut off pump to allow M-Pyrol to soak in tube for another 30 minutes.

11. Recirculate M-Pyrol for an additional 30 minutes.

12. Disconnect M-Pyrol pump suction tube and vent to atmosphere.

13. Allow pump to continue running, to drain tubing of M-Pyrol.

14. Attach pump discharge tube to plant air and blow remaining M-Pyrol into its drum.

15. Disconnect plant air and connect pump discharge tube to pump.

16. Connect clean fuel-oil drum to pump suction tube.

17. Line up valves to pump clean fuel oil through selected tube and recirculate to the “Fuel oil” drum.

18. Flush with clean fuel oil for 30 minutes.

19. Flushing complete, reconnect all fittings.

20. Clean tubing for the remaining cans in the same manner.

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