Instrument Air.ppt

INSTRUMENT & PLANT AIR SYSTEM

INSTRUMENT & PLANT AIR SYSTEM

Introduction To Unit Unit 910 is composed of the following systems: : Air Compressor Package Section : Air Dryer Package Section The Plant and Instrument Air System will produce 4168Nm3/h Instrument Air and 1400 Nm3/h (3020Nm3/h in the case of Diesel-Max Regeneration) Plant Air at max. demand rate. Plant and instrument air is supplied by two equal size centrifugal compressors (910-C1A/B), one operating and one spare as auto standby which cuts in at compressor downstream pressure of 8.5 Kg/cm2. Two dryer trains one in service and other as standby removes moisture, yields dry air with dew point at -20 OC. Instrument air receiver stores air with designed storage capacity of 5 minutes backup in case of instrument air failure.

INSTRUMENT & PLANT AIR SYSTEM

Specifications I.

1. 2. 3. 4. II.

1. 2. 3.

Compressor Type: Three stage centrifugal type Capacity / discharge pressure: 6000 Nm3/ hr, 8.7 Kg/cm 2 Make: Elliott (USA) Driver power: 1119 KW, 3000 RPM, 186 Amperes : 13 Ton / hr HP steam usage Air Dryers: Make: Delair Capacity: 4168 Nm3/hr with downstream pressure of 8.25 Kg/cm2 Type: Pressure swing with flow direction of bottom to top.

INSTRUMENT & PLANT AIR SYSTEM

Auxiliary Components a) b) c) d) e) f) g) h)

Suction filters Inlet valve / DCV Unloading valve / PCV 1st stage intercooler 2nd stage intercooler After cooler Lube oil system Seal air system

INSTRUMENT & PLANT AIR SYSTEM

Equipment Safety Tripping TAG NO. 1 910-PS-116B

SERVICE Turbine Low speed

2 910-PT-150 A/B Lube oil low pressure

UNITS RPM

ALA RM

TRI P

287 2000 0

Kg/cm2

1.7

1.6

3 910-VT-123 A/B HS pinion high vibration

um

22. 9

30.5

4 910-VT-122A/B

LS pinion high vibration

um

22. 9

30.5

5 910-TT-151 A/B

Lube oil high temperature

O

C

57

60

6 910-TT-111 A/B

Air 2nd interstage high temperature

O

C

57

59

7 910-TT-107 A/B

Air 1st interstage high temperature

O

C

62

65

8 910-TT-132 A

Motor stator high temperature

O

C

155

170

INSTRUMENT & PLANT AIR SYSTEM

Startup / Shut Down Modes & Load synchronization 1. 2. 3. 4. 5.

Inlet Valve Auto/Manual Unloading valve Auto/Manual Start / Stop Auto/Manual Load transfer Startup permissive

Following parameters are checked prior to auto startup. 



Lube oil Pressure: 15 seconds after the AOP starts, low oil pressure tripping enables. Compressor starts and auxiliary pump shut down. Lube oil temperature: If below 23 OC lube oil heater is switched on automatically.

INSTRUMENT & PLANT AIR SYSTEM

Operating Modes 1. 2. 3. 4.

Base mode Suction Throttle mode Intermittent mode Dual mode

Surge Control It is a performance characteristic of compressor and it arises when compressor cannot overcome the system resistance resulting in to and fro motion of compressed air. Surge is usually associated with excessive discharge pressure however excessive suction throttling can also cause surge.

INSTRUMENT & PLANT AIR SYSTEM

Dryer Train Moisture from inlet wet air is removed by silica based alumina ball bed through adsorption and process continues till equilibrium conditions of desiccant permits. Dry air of minimum dew point of -20 OC leaves dryer bed top and stored in instrument air receiver from where supplied to instrument air header. Instrument air header pressure maintained at 8.15 Kg/cm 2 through 910-PRC025 by cutting the flow to plant air header.

Components of Dryer Train    

Pre-filter After-filter Dryer Beds PLC Controller

INSTRUMENT & PLANT AIR SYSTEM

Dew point: It is the temperature at which first drop of liquid appears at given pressure. Dew point is dependent of mass of vapors present in stream of gas at keeping the pressure constant. This property is used to monitor the moisture contents present in instrument air or functional efficiency of dryers.

Adsorption & De-sorption Adsorption is a physical phenomenon in which moisture sticks to desiccant surface without bringing any chemical change to it. De-sorption is the phenomenon in which moisture leaves the desiccant surface through beating or purging out dry air.

INSTRUMENT & PLANT AIR SYSTEM

Service And Regeneration Cycle: Each train comprises of two beds, one in service and other on regeneration. Service and regeneration sequence is controlled by PLC based automatic timing sequence controller which diverts the air flow by changing the valve position. A stream of dried air from downstream of dryer bed is routed to the vessel on regeneration which regenerates the bed from top to bottom path. The cycle can be classified into following steps. • • • • • 

Drying Depressurization Regeneration Pressurize Parallel Drying Switch over