In power generation occupancies, the arrangement, operation, and emergency planning procedures associated with the AC and DC lube oil pumps are key areas of focus as they relate to property loss prevention. In many other industries, shutting down the flow of combustible oil systems is a primary focus, often including automatic shutoffs (e.g. hydraulic oil systems, fuel oil systems, etc.). However, in the power generation industry, there is a balance that must be considered between shutting down lube oil systems to remove a potential source of fuel for a fire and safely running down the rotating equipment to avoid mechanical damage. The two FM Global Data Sheets (FMDS) that cover this topic are FMDS 13-17, Gas Turbines, and 7-79, Fire Protection for Gas Turbines and Electric Generators. Below is a simplified system per FMDS 13-17.
Since automatic shutoffs for lube oil systems are not an option, additional focus is placed on a well-drilled and robust emergency shutdown procedure in the event of a pressurized lube oil release. The key focus in these plans is having operators assess the extent of the release, determine if there is an additional fire hazard present, and (if appropriate) perform a safe and expedited shutdown of the units and oil systems involved. In the event of a three-dimensional spill, a pressurized spray fire, or an issue with the AC lube oil pumps, the DC pumps will continue to supply lube oil to the turbine generator unit for the duration of the rundown, which can range anywhere from 5 to 20 minutes or more for larger units.
A critical part of the shutdown procedure is ensuring that upon safe and expedited rundown of the turbine unit, to confirm that all lube oil systems are also subsequently shut down to avoid a potential for continued supply of combustible lube oil to a fire scenario. It is also critical that the DC lube oil systems are not shut off too early, as a lack of lubricating oil to the bearings can result in significant property damage and associated downtime as the unit is repaired or replaced. A balance must be struck between a safe rundown and shutting down of oil systems, achieved with extensive operator training and the development of a robust emergency shutdown plan.
The April 2019 edition of FMDS 13-17, Gas Turbines, has undergone an interim revision effective February 2023, which includes many clarifications as well as new guidance relating to the protection and safety features for gas turbines, particularly relating to lube oil systems. A couple of key changes are noted below:
- Added recommendations to provide independent backup power systems for lubrication pumps to prevent single-point failures and guidance on backup battery capacity to align with FMDS 13-3, Steam Turbines.
- Added a recommendation to provide an emergency operating procedure to manually rotate a hot rotor to prevent rotor bowing when no lube oil or turning gear is available.
- Added recommendations for AC or DC lube-oil pump powered by an internal combustion engine backup generator.
FMDS 7-79 also has some key guidance surrounding emergency response planning and lube oil system shutdown. A couple of key loss prevention items are noted below:
- Provide a system that will allow for an emergency trip of the turbine and for lubrication-oil systems to be shut down promptly and safely in emergency situations.
- Ensure equipment needed for emergency shutdown of the turbine, such as emergency turbine trip and controls for the AC and DC lube-oil pumps, is arranged for remote operation from the control room.
- Develop a documented emergency shutdown procedure to help limit the extent of property damage and downtime in case of fire.
- Establish a procedure, including shutdown of lubrication oil systems, if shutdown is necessary, for each of the following scenarios:
- A fire that is controlled by fixed fire protection systems and/or the emergency response team (such as a minor leak or insulation blanket fire). In this case, the unit will be tripped and the fuel will be shut off upon operation of the fire protection system. However, based on an assessment of the fire event, shutdown of lubrication-oil systems may not be necessary.A single point release of oil and subsequent fire that is not controlled by either fixed protection or the emergency response team, resulting in the need to shut down all equipment, including oil systems.
- Mechanical damage to turbine generator equipment severe enough to stop the rotating equipment with a subsequent fire.
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