ASH HANDLING SYSTEM
COLLECTION OF ASH FROM
SYSTEM
DISPOSAL OF ASH
COLLECTION OF ASH
BOTTOM ASH SYSTEM
FLY ASH SYSTEM
WET ASH SYSTEM
ASH SLURRY PIPE LINE SYSTEM
ASH UTILISATION
ASH HANDLING SYSTEM INCLUDES
• STAGE – I ASH HANDLING SYSTEM
» FLY BOTTOM ASH
» ASH
» ASH SLURRY PUMP HOUSE STG-I
• STAGE – II ASH HANDLING SYSTEM
» BOTTOM ASH
» FLY ASH
» ASH SLURRY PUMP HOUSE STG-II
• PIPELINES, BOOSTER PUMP HOUSE AND
ASH DYKE
ASH HANDLING SYSTEM
 BOTTOM ASH HANDLING SYSTEM (20%)
 FLY ASH HANDLING SYSTEM (80%)
ARRANGEMENT OF BOTTOM ASH
HOPPER
TROUGH SEAL
REFRACTORY
QUENCHING NOZZLE
V.C. GATE
L.P.WATER HEADER
VIEW GLASSINKER GRINDER CHUTE
CLINKER GRINDER
METOD OF ASH COLLECTION
FROM BOTTOM ASH HOPPER
SCRAPPER CONVEYOR
HYDROEJECTOR
HYDROEJECTOR
SCRAPPER CONVEYOR
SYSTEM DESCRIPTION
BOTTOM ASH GENERATED IS
EXTRACTED BY SCRAPPER CONVEYOR
AND GOES TO B.A. TRANSFER PIT
THROUGH CLINKER GRINDER. THE
SLURRY COLLECTED IN PIT IS
TRANSPORTED TO MAIN ASH SLURRY
PUMPS PIT BY B.A. TRANSFER PUMPS.
THREE METHOD OF ASH EVACUATION –
1. CONVENTIONAL FLUSHING SYSTEM
2. WET ASH SYSTEM
3. DRYASH SYSTEM
CONVENTIONAL FLUSHING
SYSTEM
CONVENTIONAL FLUSHING
SYSTEM
 ASH COLLECTION – DIRECT MIXING OF
ASH AND WATER
 CYCLE TIME – APPROX. 10 MIN.
 WATER CONSUMPTION – 2200 M3/Hr
WET ASH SYSTEM
ASH IS COLLECTED IN THE FORM OF
ASH SLURRY THROUGH WETTING HEAD
AND COLLECTING TANK AND GOES TO
THE SLURRY PUMP PIT.
TI e saI
laa[-na
vao@y
aUma
pmp
bafr
haÐpr
e ela
TI
P`aayamarI
klao@Tr
TOMk
saokNDrI
klao@Tr
TOMk
baoga
iflTr
eyar
vaaSar
vaoTIM
ga hoD
klao@T
r TOMk
saa[-
laonsa
r
ma
ao
Tr
21
NTPC
bafr haÐpr
BUFFER HOPPER
vaoTIMg
a hoD
WETTING
HEAD
klao@Tr
TOMk
COLLECTOR
TANK
eyar
vaaSar
AIR
WASHER
saa[-
laonsar
CYLINCER
P`aayamarI
klao@Tr
PRIMERY
COLLECTOR
saokN
DrIklao
@Tr
PRIME
RY
COLLE
CTOR
saIla
baa@s
a
Seal box
baoga
iflTr
TI e saI laa[-na
Vacuum header to v/pump
Vacuum from air washer to v /pump
19
To silo
Dry ash
To wet mode
T
o
d
r
y
m
o
d
e
Vacuum line
WET ASH SYSTEM
CONSTITUENTS OF THE SYSTEM :-
• WETTING HEAD
• AIR WASHER
• COLLECTING TANK
• PIPE LINES
• SEAL BOX
WET ASH SYSTEM
WET ASH SYSTEM
1. ASH COLLECTION – MIXING OF WATER AND ASH
BY SPRAY NOZZLES IN WETTING HEAD
2. IDLE CYCLE TIME – 5 MIN.
3. WATER CONSUMPTION - 100 M3/Hr. AT 35 MWC
4. MAIN PARTS-
a) COLLECTOR TANK – CAPACITY OF 12 Cu.M
b) WETTING HEAD – CAPACITY OF 54 T/Hr, 22 no.
OF SPRAY NOZZLE
c) AIR WASHER – 3 no. OF SPRAY NOZZLE FOR
CREATING FOG
DRY ASH SYSTEM
FROM ESP HOPPER ASH IS EVACUATED BY
VACUUM PUMP AND COLLECTED IN BUFFER
HOPPER, THEN IT IS TRANSPORTED VIA AIR
LOCK TANK TO SILO BY TRANSPORT AIR
FOR ASH UTILIZATION
DRY ASH SYSTEM
CONSTITUENTS OF THE SYSTEM :-
• PIPE LINES AND VALVES
• PRIMARY COLLECTOR TANK
• SECONDARY COLLECTOR TANK
• FILTER BAGS CHAMBER
• BUFFER HOPPER
• AIR LOCK TANKS
• 3 WAY VALVES
• ROTARY SEGREGATING VALVES
COMPRESSOR USED IN DRY FLY AND
WET MODE
INSTRUMENT AIR COMPRESSOR
TRANSPORT AIR COMPRESSOR
TRANSPORT AIR COMPRESSOR
PUMP
VACUUM PUMP
L.P.ASH WATER PUMP
H.P.ASH WATER PUMP
ASH SLURRY PUMP
DRAIN PUMP
SUMP PUMP
B.A.TRANSFER PUMP
H.M.D.C.
WASH PUMP
BLOWERS AND FAN
AREATION BLOWER
DUST EXTRACTOR/ DUST
SEPERATOR
DRY ASH SYSTEM
DRY ASH SYSTEM
1. IDLE CYCLE TIME – 10 MIN.
2. MAIN PARTS –
a) BUFFER HOPPER – CAPACITY OF 34.64
Cu.M
1. ASH COLLECTION – TRANSPORTATION OF ASH
IN DRY FORM TO SILO BY TAC
b) COLLECTORS – PRIMARY AND
SECONDARY COLLECTOR WITH CAPACITY OF
54 T/Hr EACH
c) ALT – CAPACITY OF 108 T/Hr
d) BAG FILTERS – 49 no. WITH PULSE
JETTING SYSTEM
– SCRAPPER CONVEYOR - 02 NOS ( 2 X 50%)
EACH UNIT
–CAPACITY – 15 T/HR
– CLINKER GRINDER-02 NOS (2 X 50% ) EACH
UNIT
STAGE-I FLY ASH SYSTEM
• 60 T/HR OF ASH IN EACH UNIT IS COLLECTED BY DRY FLY ASH
SYSTEM. NEW DRY FLY ASH SYSTEM IS PROVIDED ONLY IN UNIT
#2 AND UNIT #3 .
UNIT#1 HAS NO DRY ASH COLLECTING SYSTEM
• 56 ESP HOPPERS IN EACH UNIT
• 4 NOS OF COLLECTOR TANK
• 4 NOS OF AIR WASHER
• 4 NOS OF MECHANICAL EXHAUSTER
• 2 NOS OF I.A.C.
• DRY ASH IS COLLECTED AND SLURRY IS MADE BY WETTING
HEAD AND THROUGH TRENCH COLLECTED IN ASH PIT.
STAGE –II BOTTOM ASH SYSTEM
SYSTEM INCLUDES:
• SCRAPPER CONVEYOR – 02 NOS/UNIT (100%
EACH)
• CLINKER GRINDER – 02 NOS/UNIT (100% EACH)
• BA TRANSFER P/P – 02 NOS/UNIT (100% EACH)
• 05 SERIES FOR ASH DISPOSAL.
• ASH SLURRY PUMPS – 03 NOS / SERIES.
• SEAL WATER PUMPS FOR ASH SLURRY PUMP
GLAND SEALING.
• LP/HPASH WATER PUMPS.
STAGE –II DRY FLY ASH HANDLING
SYSTEM (500 MW)
• NO OF UNITS – 03 UNITS
• NO OF ESP PASSES – 04 / UNIT
• NO OF ESP HOPPERS – 24 / PASS
• TOTAL NO. OF ESP HOPPERS – 96
• NO OF VACUUM PUMP – 02/ PASS
STAGE # 1
200MW UNIT
Plant data for collection of ash-
Sr.no Description No. of
hopper per
boiler
Ash collection
rate per boiler
T/Hr
Holding
capacity storage
in Hrs. of max.
ash generation
1 Bottom ash hopper 1 12.85 4
2 Economizer hopper 4 3.22 8
3 Air heater hopper 4 3.22 8
4 ESP HOPPER
1 st row 8 39.61 12
2 nd row 8 9.002 12
3 rd row 8 1.39 12
4 th row 8 0.617 12
5 th row 8 0.335 12
6 th row 8 0.109 12
7 th row 8 0.061 12
5 Stack hopper 1 0.282 8
1) Bottom ash removal from each boiler unit = 15 T/Hr. continuously.
2) Fly ash removal from each boiler unit = 60 T/Hr. continuously
STAGE#2
500MWUNIT
Plantdatafor collectionofash-
Sr.no Description No. of
hopper per
boiler
Ashcollection
rateper boiler
T/Hr
Holding
capacitystorage
inHrs. ofmax.
ashgeneration
1 Bottomashhopper 1 32.8 Notmorethan2
Hrs.
2 Economizer hopper 4 8.19 8
3 Air Preheater hopper 4+4 2.8+5.31 8+8
4 ESPHOPPER
1strow 16 103 8
2ndrow 16 17.56 8
3rdrow 16 6.21 8
4throw 16 2.555 8
5throw 16 1.175 8
6throw 16 0.57 8
SILO
1. SILO CAPACITY - 400 MT EACH
2. SILO TRUCK LOADING -
a) WET ASH FOR ASH BRICK PLANTS
b) DRY ASH FOR CEMENT PLANTS
3. MAIN PARTS –
a) ROTORY FEEDER – CAPACITY OF 100 T/Hr
b) HMDC - CAPACITY OF 100 T/Hr, 16 no. OF
NOZZLES FOR 45 Cu.M/Hr OF WATER SPRAY
c) AERATION BLOWER- CAPACITY OF 76 Cu.M/Hr
AT 3 MWC
d) BAG FILTERS – 108 no. WITH PULSE JETTING
SYSTEM
SILO
ASP
5A 5B
ASP
4A
3A 3B
2A 2B
4B
1A 1B
Ash slurry
pit no. 1
Ash slurry
pit no. 2
SCHEMATIC FLOW DIAGRAM FROM STAGE#2 P/P HOUSE
ASP
5C
4C
3C
2C
1C
TO OLD DYKE
LP Water header for flushing.
450 NB pipe line
TO
BPH
From RWL-BPH
ASH UTILISATION
• Cement, Asbestos – Cement products &
Concrete manufacturing industries
• Land development
• Road embankments construction
• Ash Dyke Raising
• Building Products such as Bricks/ blocks/tiles,
• Reclamation of coal mine
• As a soil amender and source of micro –
nutrients in agriculture.
CONSTRAINTS
• CORROSION OF METAL PARTS DUE TO POOR QUALITY OF
COAL BURNED
• DIFFICULTY IN DETECTION OF SUCTION SPOT DURING
LOW VACCUM
• FREQUENT GLAND SEAL LEAKAGE AND BODY LEAKAGE
IN VACCUM PUMPS
• LESS AVAILABILITY OF TAC LINE DUE TO FREQUENT
COUPLING LEAKAGE AND DAMAGE OF RSV DISC
• FREQUENT DAMAGE OF BAG FILTERS
CONSTRAINTS
 BOTTOM PORTION OF PIPE GETS ERRODED OVER
THE PERIOD OF TIME.
 RATE OF EROSION DEPENDS ON MANY FACTORS
LIKE ASH- PARTICLE SIZE, CHEMICAL
COMPOSITION, LINE PRESSURE, SLURRY
CONCENTRATION, VELOCITY ETC.
 RATE OF EROSION OF ALL ASH LINES DIFFER DUE
TO CHANGE IN ASH SLURRY CONCENTRATION, IT
CARRIES.
• LESS UTILISATION OF ASH DUE TO LESSER ASH
TRUCKS AVAILABLITY
CONSTRAINTS
 BOTTOM PORTION OF PIPE GETS ERRODED OVER THE
PERIOD OF TIME.
 RATE OF EROSION DEPENDS ON MANY FACTORS LIKE ASH-
PARTICLE SIZE, CHEMICAL COMPOSITION, LINE PRESSURE,
SLURRY CONCENTRATION, VELOCITY ETC.
 RATE OF EROSION OF ALL ASH LINES DIFFER DUE TO
CHANGE IN ASH SLURRY CONCENTRATION, IT CARRIES.
• LESS UTILISATION OFASH DUE TO LESSER ASH TRUCKS
AVAILABLITY
ASH HANDLING PRESENTATION ON POWER PLANT

ASH HANDLING PRESENTATION ON POWER PLANT

  • 1.
    ASH HANDLING SYSTEM COLLECTIONOF ASH FROM SYSTEM DISPOSAL OF ASH
  • 2.
    COLLECTION OF ASH BOTTOMASH SYSTEM FLY ASH SYSTEM WET ASH SYSTEM ASH SLURRY PIPE LINE SYSTEM ASH UTILISATION
  • 3.
    ASH HANDLING SYSTEMINCLUDES • STAGE – I ASH HANDLING SYSTEM » FLY BOTTOM ASH » ASH » ASH SLURRY PUMP HOUSE STG-I • STAGE – II ASH HANDLING SYSTEM » BOTTOM ASH » FLY ASH » ASH SLURRY PUMP HOUSE STG-II • PIPELINES, BOOSTER PUMP HOUSE AND ASH DYKE
  • 4.
    ASH HANDLING SYSTEM BOTTOM ASH HANDLING SYSTEM (20%)  FLY ASH HANDLING SYSTEM (80%)
  • 5.
    ARRANGEMENT OF BOTTOMASH HOPPER TROUGH SEAL REFRACTORY QUENCHING NOZZLE V.C. GATE L.P.WATER HEADER VIEW GLASSINKER GRINDER CHUTE CLINKER GRINDER
  • 6.
    METOD OF ASHCOLLECTION FROM BOTTOM ASH HOPPER SCRAPPER CONVEYOR HYDROEJECTOR
  • 7.
  • 9.
  • 10.
    SYSTEM DESCRIPTION BOTTOM ASHGENERATED IS EXTRACTED BY SCRAPPER CONVEYOR AND GOES TO B.A. TRANSFER PIT THROUGH CLINKER GRINDER. THE SLURRY COLLECTED IN PIT IS TRANSPORTED TO MAIN ASH SLURRY PUMPS PIT BY B.A. TRANSFER PUMPS.
  • 11.
    THREE METHOD OFASH EVACUATION – 1. CONVENTIONAL FLUSHING SYSTEM 2. WET ASH SYSTEM 3. DRYASH SYSTEM
  • 12.
  • 13.
    CONVENTIONAL FLUSHING SYSTEM  ASHCOLLECTION – DIRECT MIXING OF ASH AND WATER  CYCLE TIME – APPROX. 10 MIN.  WATER CONSUMPTION – 2200 M3/Hr
  • 14.
    WET ASH SYSTEM ASHIS COLLECTED IN THE FORM OF ASH SLURRY THROUGH WETTING HEAD AND COLLECTING TANK AND GOES TO THE SLURRY PUMP PIT.
  • 15.
    TI e saI laa[-na vao@y aUma pmp bafr haÐpr eela TI P`aayamarI klao@Tr TOMk saokNDrI klao@Tr TOMk baoga iflTr eyar vaaSar vaoTIM ga hoD klao@T r TOMk saa[- laonsa r ma ao Tr 21
  • 16.
    NTPC bafr haÐpr BUFFER HOPPER vaoTIMg ahoD WETTING HEAD klao@Tr TOMk COLLECTOR TANK eyar vaaSar AIR WASHER saa[- laonsar CYLINCER P`aayamarI klao@Tr PRIMERY COLLECTOR saokN DrIklao @Tr PRIME RY COLLE CTOR saIla baa@s a Seal box baoga iflTr TI e saI laa[-na Vacuum header to v/pump Vacuum from air washer to v /pump 19 To silo Dry ash To wet mode T o d r y m o d e Vacuum line
  • 17.
    WET ASH SYSTEM CONSTITUENTSOF THE SYSTEM :- • WETTING HEAD • AIR WASHER • COLLECTING TANK • PIPE LINES • SEAL BOX
  • 18.
  • 19.
    WET ASH SYSTEM 1.ASH COLLECTION – MIXING OF WATER AND ASH BY SPRAY NOZZLES IN WETTING HEAD 2. IDLE CYCLE TIME – 5 MIN. 3. WATER CONSUMPTION - 100 M3/Hr. AT 35 MWC 4. MAIN PARTS- a) COLLECTOR TANK – CAPACITY OF 12 Cu.M b) WETTING HEAD – CAPACITY OF 54 T/Hr, 22 no. OF SPRAY NOZZLE c) AIR WASHER – 3 no. OF SPRAY NOZZLE FOR CREATING FOG
  • 20.
    DRY ASH SYSTEM FROMESP HOPPER ASH IS EVACUATED BY VACUUM PUMP AND COLLECTED IN BUFFER HOPPER, THEN IT IS TRANSPORTED VIA AIR LOCK TANK TO SILO BY TRANSPORT AIR FOR ASH UTILIZATION
  • 21.
    DRY ASH SYSTEM CONSTITUENTSOF THE SYSTEM :- • PIPE LINES AND VALVES • PRIMARY COLLECTOR TANK • SECONDARY COLLECTOR TANK • FILTER BAGS CHAMBER • BUFFER HOPPER • AIR LOCK TANKS • 3 WAY VALVES • ROTARY SEGREGATING VALVES
  • 22.
    COMPRESSOR USED INDRY FLY AND WET MODE INSTRUMENT AIR COMPRESSOR TRANSPORT AIR COMPRESSOR
  • 23.
  • 24.
    PUMP VACUUM PUMP L.P.ASH WATERPUMP H.P.ASH WATER PUMP ASH SLURRY PUMP DRAIN PUMP SUMP PUMP B.A.TRANSFER PUMP H.M.D.C. WASH PUMP
  • 25.
    BLOWERS AND FAN AREATIONBLOWER DUST EXTRACTOR/ DUST SEPERATOR
  • 26.
  • 27.
    DRY ASH SYSTEM 1.IDLE CYCLE TIME – 10 MIN. 2. MAIN PARTS – a) BUFFER HOPPER – CAPACITY OF 34.64 Cu.M 1. ASH COLLECTION – TRANSPORTATION OF ASH IN DRY FORM TO SILO BY TAC b) COLLECTORS – PRIMARY AND SECONDARY COLLECTOR WITH CAPACITY OF 54 T/Hr EACH c) ALT – CAPACITY OF 108 T/Hr d) BAG FILTERS – 49 no. WITH PULSE JETTING SYSTEM
  • 28.
    – SCRAPPER CONVEYOR- 02 NOS ( 2 X 50%) EACH UNIT –CAPACITY – 15 T/HR – CLINKER GRINDER-02 NOS (2 X 50% ) EACH UNIT
  • 29.
    STAGE-I FLY ASHSYSTEM • 60 T/HR OF ASH IN EACH UNIT IS COLLECTED BY DRY FLY ASH SYSTEM. NEW DRY FLY ASH SYSTEM IS PROVIDED ONLY IN UNIT #2 AND UNIT #3 . UNIT#1 HAS NO DRY ASH COLLECTING SYSTEM • 56 ESP HOPPERS IN EACH UNIT • 4 NOS OF COLLECTOR TANK • 4 NOS OF AIR WASHER • 4 NOS OF MECHANICAL EXHAUSTER • 2 NOS OF I.A.C. • DRY ASH IS COLLECTED AND SLURRY IS MADE BY WETTING HEAD AND THROUGH TRENCH COLLECTED IN ASH PIT.
  • 30.
    STAGE –II BOTTOMASH SYSTEM SYSTEM INCLUDES: • SCRAPPER CONVEYOR – 02 NOS/UNIT (100% EACH) • CLINKER GRINDER – 02 NOS/UNIT (100% EACH) • BA TRANSFER P/P – 02 NOS/UNIT (100% EACH) • 05 SERIES FOR ASH DISPOSAL. • ASH SLURRY PUMPS – 03 NOS / SERIES. • SEAL WATER PUMPS FOR ASH SLURRY PUMP GLAND SEALING. • LP/HPASH WATER PUMPS.
  • 31.
    STAGE –II DRYFLY ASH HANDLING SYSTEM (500 MW) • NO OF UNITS – 03 UNITS • NO OF ESP PASSES – 04 / UNIT • NO OF ESP HOPPERS – 24 / PASS • TOTAL NO. OF ESP HOPPERS – 96 • NO OF VACUUM PUMP – 02/ PASS
  • 32.
    STAGE # 1 200MWUNIT Plant data for collection of ash- Sr.no Description No. of hopper per boiler Ash collection rate per boiler T/Hr Holding capacity storage in Hrs. of max. ash generation 1 Bottom ash hopper 1 12.85 4 2 Economizer hopper 4 3.22 8 3 Air heater hopper 4 3.22 8 4 ESP HOPPER 1 st row 8 39.61 12 2 nd row 8 9.002 12 3 rd row 8 1.39 12 4 th row 8 0.617 12 5 th row 8 0.335 12 6 th row 8 0.109 12 7 th row 8 0.061 12 5 Stack hopper 1 0.282 8 1) Bottom ash removal from each boiler unit = 15 T/Hr. continuously. 2) Fly ash removal from each boiler unit = 60 T/Hr. continuously
  • 33.
    STAGE#2 500MWUNIT Plantdatafor collectionofash- Sr.no DescriptionNo. of hopper per boiler Ashcollection rateper boiler T/Hr Holding capacitystorage inHrs. ofmax. ashgeneration 1 Bottomashhopper 1 32.8 Notmorethan2 Hrs. 2 Economizer hopper 4 8.19 8 3 Air Preheater hopper 4+4 2.8+5.31 8+8 4 ESPHOPPER 1strow 16 103 8 2ndrow 16 17.56 8 3rdrow 16 6.21 8 4throw 16 2.555 8 5throw 16 1.175 8 6throw 16 0.57 8
  • 34.
    SILO 1. SILO CAPACITY- 400 MT EACH 2. SILO TRUCK LOADING - a) WET ASH FOR ASH BRICK PLANTS b) DRY ASH FOR CEMENT PLANTS 3. MAIN PARTS – a) ROTORY FEEDER – CAPACITY OF 100 T/Hr b) HMDC - CAPACITY OF 100 T/Hr, 16 no. OF NOZZLES FOR 45 Cu.M/Hr OF WATER SPRAY c) AERATION BLOWER- CAPACITY OF 76 Cu.M/Hr AT 3 MWC d) BAG FILTERS – 108 no. WITH PULSE JETTING SYSTEM
  • 35.
  • 36.
    ASP 5A 5B ASP 4A 3A 3B 2A2B 4B 1A 1B Ash slurry pit no. 1 Ash slurry pit no. 2 SCHEMATIC FLOW DIAGRAM FROM STAGE#2 P/P HOUSE ASP 5C 4C 3C 2C 1C TO OLD DYKE LP Water header for flushing. 450 NB pipe line TO BPH From RWL-BPH
  • 37.
    ASH UTILISATION • Cement,Asbestos – Cement products & Concrete manufacturing industries • Land development • Road embankments construction • Ash Dyke Raising • Building Products such as Bricks/ blocks/tiles, • Reclamation of coal mine • As a soil amender and source of micro – nutrients in agriculture.
  • 38.
    CONSTRAINTS • CORROSION OFMETAL PARTS DUE TO POOR QUALITY OF COAL BURNED • DIFFICULTY IN DETECTION OF SUCTION SPOT DURING LOW VACCUM • FREQUENT GLAND SEAL LEAKAGE AND BODY LEAKAGE IN VACCUM PUMPS • LESS AVAILABILITY OF TAC LINE DUE TO FREQUENT COUPLING LEAKAGE AND DAMAGE OF RSV DISC • FREQUENT DAMAGE OF BAG FILTERS
  • 39.
    CONSTRAINTS  BOTTOM PORTIONOF PIPE GETS ERRODED OVER THE PERIOD OF TIME.  RATE OF EROSION DEPENDS ON MANY FACTORS LIKE ASH- PARTICLE SIZE, CHEMICAL COMPOSITION, LINE PRESSURE, SLURRY CONCENTRATION, VELOCITY ETC.  RATE OF EROSION OF ALL ASH LINES DIFFER DUE TO CHANGE IN ASH SLURRY CONCENTRATION, IT CARRIES. • LESS UTILISATION OF ASH DUE TO LESSER ASH TRUCKS AVAILABLITY
  • 40.
    CONSTRAINTS  BOTTOM PORTIONOF PIPE GETS ERRODED OVER THE PERIOD OF TIME.  RATE OF EROSION DEPENDS ON MANY FACTORS LIKE ASH- PARTICLE SIZE, CHEMICAL COMPOSITION, LINE PRESSURE, SLURRY CONCENTRATION, VELOCITY ETC.  RATE OF EROSION OF ALL ASH LINES DIFFER DUE TO CHANGE IN ASH SLURRY CONCENTRATION, IT CARRIES. • LESS UTILISATION OFASH DUE TO LESSER ASH TRUCKS AVAILABLITY