Instrument Air(IA) Flashcards
What’re the differences in Instrument Air & Service Air ?
Instrument Air- 125psig for pneumatic instrument operation & pneumatic actuators
Service Air- 125psig for pneumatic tools,resin transfer,refueling machine,& manual operation
Why is instrument air a safety related system ?
All AOVs will fail into there fail-safe position to safely shut plant down
What’re the capacity of the 3 compressors for the IA system ?
Three 100% capacity air compressors
When will LP Nitrogen automatically align to IA header ?
Will automatically align when IA header pressure goes down to 85psig
Where do the air compressors draw their air from ? What does it compress it down to ?
-Draws air from turbine building & compresses it down to 105-123psig
What size are the Inlet Air Filters for the compressors ?
Removes particles 3micron or larger 99.9% effective
What does the PT-4 pressure sensor represent ?
-Represents Inlet Filter cleanliness, calibrated to read 0psig for Atm. Press.
-Will sense lowering pressure(rising vacuum)
What does local controller PT-4 Inlet Vacuum information to do what ?
-Confirm drive motor is rotating in correct direction upon start
-Indicate condition of Inlet Air Filter
-Provide logic for positioning inlet valve during unloaded operation based on coolant injection temp &separator press.
What is the Air Inlet Control Valve opened & closed by ?
-Open & closed by a stepper motor, which is control by Intellysis Controller
What does the Intellysis Controller do ?
Regulated stepper motor to position Air Inlet Control Valve based on demand plant air system
During compressor startup why is the Air Inlet Control Valve closed ?
-Allows compressor to startup with minimum current
-Allows compressor to check for proper rotation by checking Inlet Vacuum is at 1psi within 2seconds
What will happen if Air Inlet Control Valve fails to open & close during startup?
This will cause an alarm
How does “loaded operation” work ?
-The Intellisys/stepper motor opens inlet valve & closes blowdown when plant pressure drops below Min. Setpoint of 109psig
-Then compressor will start to deliver air to plant system
How does “unloaded operation” work ?
-Plant air reaches Max. Press. of 119psig then Inlet valve will slightly close
-Blowdown will open
-Compressor will be at Min. Power
-Intellisys controller will maintain Inlet Valve open to maintain pressure
What pressure do the Compressors compress to ? What’re the compressors driven by ?
-They compress press. between 105-123psig
-Driven by 480VAC motor driven
Where do the compressors discharge to ?
-They discharge into separator tank
What’re the compressors alarms when discharge temp is to high ?
-If discharge of compressor reaches a temperature watching it’ll be on Compressor Display Panel
-If compressor continues to operate until it reach alarm setpoint, it’ll trip due to alarm
What is used to prevent water vapor from condensing in Air Receiver ?
Injecting coolant at high temp which will keep discharge above dew point
What does the Thermostatic Control Valve do for the IA Compressor at Coolant Cooler discharge ?
Controls how much COOLANT flows through or bypasses Coolant Cooler
What cools the Air Compressor Cooler during normal operation ? What is used a backup cooling source ?
-Turbine Cooling Water
-Domestic Water is aligned when TC isn’t available
What is the Separator Tank used for ?
-Removes Coolant from compressed air to provide clean air for system
-While maintaining Coolant for Compressor package
How does the coalescing separator element work that’s installed at airside discharge of Separator Tank ?
-Two filters remove compressed air oil
-Droplets collected on first filter fall to Separator Tank sump
-Droplets on second filter are drawn to After cooler (<3ppm oil)
What is the Air Aftercooler used for ?
-Prevents damage to excessive temps, condenses moisture
What is the Air Aftercooler cooled by?
-Cooled by Turbine Cooling Water normal operation
-Domestic water is used at backup cooling water
In unloaded operation what is the position of the Air Inlet Control Valve? Why is it in that position ?
Air Inlet Valve is minimally opened to maintain Separator Tank Sump pressure
During unloaded operation of compressor where is the Separator Tank vented to ?
Vented through a blowdown solenoid operated valve to suction side of Airend
During unloaded operation what does Minimum Pressure Check valve do ?
-It maintains 60psig in Separator Tank for motive force of coolant flow through system
-Prevents back flow of air into the compressor package
Where does the Separator Tank Sump drains the coolant to ?
Flow from bottom of sump to Coolant Cooler & three-way TCV
When does the Coolant stop solenoid valve open/close ?
It opens & closes when the compressor starts
What do the Instrument Air Receivers provide on a compressor trip ?
Provides 30seconds of storage capacity on compressor trip & providing pressure dampening of system
What is the check valve at the discharge of the Air Receivers used for ?
Prevents failure upstream of check valve from allowing downstream header to discharge through failure & depressurize system
Why must you not open Pre-Filter isolation valve so quickly when playing filter in operation ?
May cause damage to Air Dryer Desiccant if the Chambers aren’t at system pressure
When will Air Dryer chambers be automatically switched ?
Will automatically switch by moisture detector in middle of chamber
How many chambers are in service ?
Usually one chamber in service
How long are drying cycles per chamber?
between 2min 45sec & 3min 15sec per chamber
When one chamber is in service what is the second chamber doing ?
-Pressurized in standby
-Used for regeneration cycle for removal of previously absorbed moisture
How many air dryers are there? How many chambers per air dryer ?
-Two air dryers in parallel
-Two chambers per air dryer
What happens inside the Air Dryer during Drying Cycle ?
-Alternately cycles air through ONE of the TWO desiccant filled chambers, then sends dry air to IA header
-Adsorption through exothermic process later contributed regeneration
What happens during Regeneration Cycle for Air Dryer chambers ?
1.)The chamber not in service will be isolated & depressurized
2.)Portion of the in service discharge chamber will be directed backward through Regenerating Chamber and purged to atmosphere
3.)After Regeneration Cycle controller places chamber in Standby
What does Blue & Pink mean for the Air Dryer Moisture Indicator ? Where does the Moisture Indicator get it’s sample from ?
Blue -DRY
Pink-WET
Local Moisture Indicator receives a sampling line at discharge of dryer
What needs to be done for Air Dryers if there is a High Humidity alarm on control panel ? What kind of alarm will control room get ?
Descant must be replaced & the control room will receive a trouble alarm to have AO switch Air Dryers
