Aux PRDS System

Auxiliary PRDS System

Auxiliary PRDS System:

Basic Layout

Technical Details

Protections & Provisions


Basic Layout

Technical Details


P & ID For Aux PRDS System

P & ID

Classification of System

The auxiliary PRDS system is basically divided into four

parts

– The inflow i.e the sources for steam to system

– HT PRDS i.e at higher temperature (15 Bar / 310 0C)

– LT PRDS i.e. at Lower temperature (15 Bar / 250 0C)

– The outflow i.e. the consumption ends

Layout for system

CRH

MS

BFP Interstage attemperation

Inflow HT PRDSUnitised

LT PRDSFor station

Deaerator initial heating

To CRH line for HP casing warmup

Mill inerting

APH soot blowing

Aux BoilerFuel oil atomising

Turbine Gland sealing

Supply to LT PRDS

CEP Attemp

VAM 1 & 2

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5 u

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s Road oil Tanker

SLOP Oil drain heater

HFO heater

Tank floor coil heater

Suction heater


Basic Layout

Technical Details


Acid Cleaning

• Purpose: Steam will be required initially during the acid cleaning of the unit

• Parameters:

– Acid cleaning : 15 T/Hr / 10 Bar / 300 0C / Intermittent

• Details:

– Cleaning of all the internals of boiler and piping for making it free of foreign

materials, grease, oil and dirt.

– For establishing a protective magnetite layer in the boiler internals

– Removal of thick debris and other foreign material which have been ingressed

during construction phase

Fuel oil coil heater and suction heaters

• Purpose: Steam will be required for heating of HFO for achieving the flow

• Tapping point: LT PRDS

• Parameters:

– Bottom heaters : 1.2 T/Hr / 14 Bar / 250 0C / Continuous

– Suction heaters : 3.1 T/Hr / 14 Bar / 250 0C / Intermittent

• Details:

– Oil is heated in the HFO tanks to achieve the flowability at heater inlet

– In second step the heating is done in the suction heaters

Fuel oil heater

• Purpose: Steam will be required for heating of HFO for achieving the flow


• Parameters:

– Fuel oil heaters : 11 T/Hr / 14 Bar / 250 0C / Intermittent

• Details:

– Oil is heated in the oil heater to achieve minimum viscosity for getting effectieve

and complete combustion in the boiler

Atomizing Steam

• Purpose: Steam will be required for atomising fuel oil

• Tapping point: HT PRDS

• Parameters:

– Atomising steam : 6.1 T/Hr / 14 Bar / 300 0C / Intermittent

• Details:

– The steam assists for effective atomisation as required in the application of low

NOX burner.

– This also ensures for a safe operation

Fuel oil unloading

• Purpose: Steam will be required for fuel oil unloading


• Parameters:

– Fuel oil unloading : 2.0 T/Hr / 14 Bar / 250 0C / Intermittent

• Details:

– The HFO before unloading needs to be heated up above the flow point

temperature

– The heating needs to be carried out in the truck tanker itself

Mill Inerting

• Purpose: Steam will be required for mill inerting


• Parameters:

– Mill inerting : 61 T/Hr / 14 Bar / 300 0C / Intermittent

• Details:

– During routine operation coal is transported to boiler with the help of hot air. The

coal and hot air mixture forms a fire hazardous situation.

– The steam in such condition is utilised as an inerting media

Deaerator initial heating & pegging

• Purpose: Steam will be required for deaerator initial heating and pegging


• Parameters:

– Deaerator initial heating : 11 T/Hr / 2 Bar / 300 0C / Intermittent

– Deaerator pegging at 5% MCR flow : 12 T/Hr / 2 Bar / 300 0C / Intermittent

– Deaerator heating during SG under recirculation : 28 T/Hr / 2 Bar / 300 0C / Intermittent

• Details:

– During cold startup the heat will be sourced thorough aux PRDS header.

– Once the CRH parameter is established the source will be switched over to CRH and will be

pegged upto 2.5 bar

– The changeover from CRH to normal source i.e. IPT extraction will be done at about 30% load

– During the turbine trip condition the deaerator will be pegged through CRH line upto 7.45 bar

Turbine Gland sealing

• Purpose: Steam will be required for turbine gland sealing system


• Parameters:

– Start up : 8 T/Hr / 13.7 Bar / 300 0C / Intermittent

– At 35% MCR : 1.89 T/Hr / 13.7 Bar / 300 0C / Intermittent

– At 60% MCR : 0.298 T/Hr / 13.7 Bar / 300 0C / Intermittent

• Details:

– During the normal operating conditions the HP-IP turbine will be self sealed and

the leak off will be utilised for sealing of LP turbine.

– During startup the sealing steam will be taken from Aux PRDS in order to

establish vacuum

Air Heater soot blower

• Purpose: Steam will be required for air pre heater soot blowing


• Parameters:

– APH soot blowing : 10 T/Hr / 14 Bar / 300 0C / Intermittent

• Details:

– During normal operation condition the soot blowing for APH alongwith furnace

and economiser will be done from the steam tapped from outlet of LTSH header.

– During startup i.e. during oil firing the APH soot blowing will be done by the

steam from Aux PRDS to avoid fire.

Turbine casing warm up

• Purpose: Steam will be required for turbine casing warm up


• Parameters:

– Turbine casing warm up : 12 T/Hr / 13.7 Bar / 300 0C / Intermittent

• Details:

– As per the OEM recommendation if the Inner metal temperature for first stage is

less than 150 0C then turbine pre warming needs to be conducted prior to turbine

startup. Normally the warming time will be approximately 4 to 5 hrs.

Vapour Absorption Machine

• Purpose: Steam will be required for turbine casing warm up


• Parameters:

– VAM : 1.8 T/Hr / 9 Bar / 176 0C / Continuous

• Details:

– There will be 2 AC plants each having 3 VAM (2W + 1S). For cooling unit control

room.

– In VAMthe refrigerant is seperated from the low concentration low temperature

absorbent in the generator by using steam. The tapping point for the same will

be between the interconnection of aux header for unit 1, 2 & 3,4.

Points to be highlighted

• The steam required for acid cleaning for Unit #1 will be taken from Aux boiler but

units followed will be tapped of from Unit # 1.

• During hot startup i.e. after black out the steam for gland sealing purpose will be

catered from MS line through PRDS in order to avoid startup of aux boiler.

• The Aux PRDS will be charged through MS once the MS parameter is achieved at 80

bar and 380 0C. The same will be changed from MS to CRH once the parameter is

achieved to 23.2 bar which is at about 35% TGMCR

• The source for deaerator pegging will be changed from Aux PRDS to CRH once CRH

pressure reaches 16 bar and 320 0C.


Basic Layout

Technical Details


Protection and Provisions

• The HT PRDS is provided with 3 safety valves having the total

blowdown capacity of 55 T/Hr

• Also thee is a provision for a stub thorugh which a new connection

can be stablished if required in future.

• The HT PRDS can be charged from Aux boiler through a motorise

valve. Whereas the LT PRDS can be charged through a manual

valve having a NRV in line.

• HT and LT PRDS are directly connected through a motorised valves

and no manual isolation valves are provided on either side.

Thank You

Documents

Aux PRDS System