Instrument air system in power
plant is one of compressed air system. Instrument air system should be provided
for control and instrument equipment. The equipment of instrument air system in
power plant as follow:
- Compressors with oil free screw type and has sufficient capacity.
- After coolers and separators
- Pre filters
- Refrigeration type air dryers.
- Air receivers
- All piping, valves and supports in accordance with relevant sections of this specification.
- All instrumentation including fitting, valves and installation material
- Acoustic enclosure to house compressors and ancillary equipment
- All electrical equipment and wiring associated with the above equipment, including local compressors control and selector panel suitable for compressors.
Isolating valve (locked shut) and
check valve for connecting to an emergency air supply from the service air
system to instrument air system should be provided in the power plant.
From the outlet of each receiver,
a common header shall be equipped with the following connections but not
limited to:
- Isolating valve for Boiler
- Isolating valve for Turbine
- Isolating valve for CW pump house
- Isolating valve for Water Pretreatment Plant
- Isolating valve for Fuel Oil Storage area
- Isolating valve for WaterTreatment Plant
- Isolating valve for Chlorinationsystem
- Isolating valve for Spare connections
The instrument air requirements
for the turbine unit shall be taken from the appropriate connections provided
on the air receiver common header.
Pipe work shall be sized and
route to ensure minimum pressure losses throughout the system. All take off
connections from horizontal headers shall be from the top of the main. Cooling
water supply (if required) should be provided from closed cooling water system.
After Coolers and Separators
Each compressor shall he supplied
with an after cooler and moisture separator complete with all necessary
fittings, relief valves and automatic drainage facility.
Filters
In each of the three compressed
air discharge mains positioned after the moisture separators shall be provided
with a removable cartridge type filter. Each filter shall be capable of
removing oil, water, dirt and other extraneous material from the compressed
air.
Air Dryers
In each of the compressor
discharge main shall be provided refrigerant type air dryer after air
receivers. The air dryer should be supplied complete with refrigeration system,
self- regulating hot refrigerant gas by-pass valve, chiller section, separator automatic
condensate discharge trap and complete control system including moisture
indicator, power-on light and safety switch. The air dryers shall be completed
with by-pass piping and valves to facilitate servicing of each unit.
Air Receivers
The instrument air system can be
provided as vertical air receivers. The receivers should be of all welded
construction and shall conform to the requirements of ASME Section VIII
"Pressure Vessel" Division I. The receivers shall be supplied
complete with the outlet connections, manhole, drain connection, pressure
gauges, relief valves and instrument connections.
Compressors
Each compressor shall deliver oil
free air and shall be supplied with the following;
- Water cooled intercooler with safety valve and moisture separator
- Air intake filter and silencer to reduce noise
- Unloading mechanism and piping
- Relief valve
- All control (local control panel), electrical and protection equipment to ensure safe and reliable operation of the plant.
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