Environmental Stewardship – Lincoln Generating Facility

7EA lube-oil spill prevention logic mods

Owned by Lincoln GeneratingFacility LLC, Operated by NAES Corp

656-MW, gas-fired, simple-cycle facility located in Manhattan, IL.
Plant manager: Merle Churchill
Key project participants: Mark Lane, O&M supervisor Nicholas Agos, O&M tech IV, The entire plant staff

Challenge.

The triggering event occurred when the unit was on ratchet and there was need to circulate the oil while a kidney-loop oil filtration skid was connected and operating—meaning that the auxiliary and hydraulic oil pumps were in operation. A torque-converter hydraulic oil line failed mechanically and an oil spill commenced in the accessory compartment of the unit. The unit spilled more than 500 gallons of oil onto the compartment floor before the leak was discovered.

The OEM provided a low-lube oil-level alarm switch, but there was no logic to stop the lube-oil pumps. Unless an operator happens to enter the unit, an event like this will most likely go unnoticed until the low-lube-oil alarm comes in with a spill potential of about 500 gallons. Theoretically, a spill can continue until lube-oil pumps lose suction with a spill potential of more than 2000 gallons.  At thisvolume, oil could potentially end upon the ground.

Solution.

Plant personnel discussed the possibility of modifying the logic in the Mark V control system so that a low-lube-oil alarm would automatically select the unit off ratchet, thereby stopping the oil pumps to prevent excessive spillage. In addition, the discussion yielded a decision to raise the set point of the low-oil-level alarm switch so that only a small change in lube-oil level would annunciate the alarm much earlier than the current setting. The resulting spill would be decreased to less than 100 gallons rather than the more than 500 gallons spilled during the event profiled. The functional parameters for logic, named “Spill Prevention,” to be built into the DCS were as follows:

  • Upon the annunciation of a low lube-oil-level alarm, the unit would be selected OFF cool down/ratchet and stop the auxiliary lube-oil pump.
  • Spill Prevention could only be available to the operator during periods where oil starvation to the turbine bearings was not a concern—for example, an extended period of cool down/ratchet during lube-oil polishing operations.
  • Spill Prevention had to be manually selectable by the CRO.
  • Spill Prevention had to be fail safe in operation.
  • The changes could not interfere with any other logic residing in the Mark V controller, except for modifications to the cool-down logic to allow Spill Prevention to turn OFF cool down when enabled.

Design and implementation

A logic block was created giving theCRO enable/disable control of theSpill Prevention logic (L43SPV).Spill Prevention can only be enabled by the operator when the unit is in OFF mode (L43O). If any other mode is selected while Spill Prevention is enabled, the spill prevention logic automatically disables itself (Fig 8).

A logic block was modified to use the existing low-lube-oil alarm (L71QL) to activate a secondary coil (L43SPV1) and an alarm (L43SPV_ALM). The additional coils will only be active if Spill Prevention is enabled (Fig 9).

If the low-lube-oil alarm annunciates, the resulting signal would close a contact in the cool-down logic, energizing coil (L1Z), which shuts down the cool-down cycle and the auxiliary and hydraulic oil pumps (Fig 10).

A new set of “pushbuttons” were designed for the control room HMICimplicity screens to allow the operator to manually enable/disable Spill Prevention (Fig 11).

Results.

The low-lube-oil-level alarm switch was reset to 1 in. below the previous level in the reservoir without incident. After the modifications were made, numerous tests were run under a variety of control conditions. All testing proved that the low-lube oil-level alarm now automatically selects the unit OFF cool down when Spill Prevention is enabled. Oil spill potential is effectively reduced from more than 2000 gallons to less than100 gallons.