Ash Handling System

1. ASH HANDLING SYSTEM IN THERMAL
POWER PLANT – AN OVERVIEW

2. • CAPACITY OF THERMAL POWER
PLANTS IN INDIA
• AUG. 2008 - 77198 MW
• 2012 (ESTIMATED) -127768 MW
• ASH GENERATION - 130 Million Tons
(approx)
THERMAL POWER GENERATION
CAPACITY OF INDIA

3. CHALLENGES IN ASH DISPOSAL
• LAND AVAILABILITY
• POOR QUALITY OF COAL
LOW CALORIFIC VALUE
HIGH ASH CONTENT
• STRINGENT ENVIRONMENT NORMS
100% UTLISATION OF ASH IN 4 YRS
MONITORING GROUND WATER
CONTROL OF FUGITIVE DUST EMISSION
EFFLUENTS TO BE WITHIN PRESCRIBED LIMITS
POSSIBLE CLOSURE OF POWER PLANTS NOT ADHERING TO
ENVIRONMENT NORMS

4. FOR A TYPICAL 1000 MW FOR 25 YEARS - 800 ACRES
AS PER ASH UTILISATION GUIDELINES OF MOEF - 500 ACRES
FOR ADDITIONAL 50000 MW - 25000 ACRES
Land Requirement For Ash Dyke

5. ASH COMPOSITION
SILICA ( SiO2) – 61- 63 %
ALUMINA ( Al2O3)- 26 - 28%
IRON OXIDE( Fe2O3)- 4 – 5 %
TITANIA (TiO2) 1.75- 1.88 %
Phosphoric Anhydride(P2O5) 0.54-0.55 %
Lime (CaO) 0.77- 1.52 %
Magnesia (MgO) 0.46 – 1.12 %
Sulphuric Anhydride (SO3) 0.05 – 0.06 %
Sodium Oxide (Na2O) 0.08 %
Potasium Oxide (K2O) 0.32 – 1.22 %
ASH FUSION RANGE 1100 – 1400 DEG CENTIGRADE

6. PC FIRED BOILER
Bottom Ash
Hopper
Econ Ash Hopper
Flyash
To ESP
Air
Preheater

7. Typical Ash distribution for 2 pass boiler
ESP
Pulverized
Coal
Furnace
(1300 - 1500°C)
Electrostatic
Precipitator
Stage
A:
80
%
Stage
B:
17
%
80 %
Stage
C:
3
%
Fly ash
Air
preheater
APH
Economizer
Eco Ash APH Ash
Stack
Fineness
Bottom Ash
20 %

8. ASH PRODUCTION
• BOTTOM ASH - BOILER FURNACE
• COARSE ASH (grits)
- ECONOMISER
- AIR PRE-HEATER
• FLY ASH (dust)
- ELECTROSTATIC PRECIPITATORS
- DUCT HOPPERS (IF APPLICABLE)

9. ASH DISTRIBUTION
LOCATION % OF TOTAL ASH IN COAL
FIRED
FURNACE BOTTOM 15-20
ECONOMISER HOPPERS 5
AIR PRE-HEATER
HOPPERS
ELECTROSTATIC
PRECIPITATOR HOPPERS
75-80

10. ASH QUANTITIES
• ASH HANDLING SYSTEMS DESIGNED FOR
HANDLING ASH FROM WORST COAL AT BOILER
MCR CONDITION
• TYPICAL WORST COAL FIRED
– GCV : 3000 kcal/kg
– Ash content : 40%

11. CONVENTIONAL BOTTOM ASH
HANDLING SYSTEMS
• WET TYPE
• INTERMITTENT TYPES
– WATER-IMPOUNDED HOPPER WITH JET PUMPS (R/FII/TK/SIM/NEW STATIONS)
– OPEN-HEARTH HOPPER WITH TRENCH SLUICE/JET PUMPS (RIHAND)
• CONTINUOUS TYPES
– SCRAPER-CHAIN CONVEYOR WITH TRENCH SLUICE/CENTRIFUGAL PUMPS
(ALL OLD STATIONS)
– SCREW CONVEYOR WITH TRENCH SLUICE/CENTRIFUGAL PUMPS (V STG-I/KH
STG-I)

13. WATER - IMPOUNDED HOPPER
WITH JET PUMPS
• ONE REFRACTORY-LINED STORAGE HOPPER PER UNIT FOR
THE BOTTOM ASH
– SINGLE VEE (V) SHAPE (UPTO 110 MW TYPICALLY)
– BOX SHAPE (UPTO 60 MW TYPICALLY)
– DOUBLE VEE (W) SHAPE (ABOVE 110 MW-500 MW)
– TRIPLE VEE(VVV) SHAPE (ABOVE 500 MW)
• HOPPER SIZED FOR 5-6 HOURS OR 8 HOURS CAPACITY ON DRY
ASH BASIS DEPENDING ON ASH QUANTITY AND SPACE
AVAILABLE BELOW BOILER FURNACE
– TYPICALLY 180 CU.M. FOR 210 MW
– TYPICALLY 450 CU.M. FOR 500 MW
• HOPPER CONTINUOUSLY SUPPLIED WITH WATER FROM
DEDICATED PUMPS
– FOR COOLING THE REFRACTORY LINING
– FOR COOLING HOT BOTTOM ASH
– TO SHATTER CLINKERS

14. WIH WITH JET PUMPS
• OVERFLOW WATER RECYCLED IN ASH
HANDLING PLANT AFTER SETTLING OUT
THE CARRYOVER ASH .
• HOPPER EVACUATED ONCE IN 4 HOURS OR
8 HOURS USING JET PUMPS SUPPLIED
WITH HIGH PRESSURE WATER FROM
DEDICATED PUMPS. ASH SLUICED VIA
PIPELINES TO MAIN SLURRY PUMPHOUSE.

15. SCRAPER-CHAIN CONVEYOR
• ONE REFRACTORY-LINED TRANSITION HOPPER WITH
ISOLATION GATES PER UNIT FOR EMERGENCY STORAGE
OF ASH
• HOPPER SIZED FOR 3- 4 HOURS HOLDING CAPACITY
- TYPICALLY 150 CU.M. IN 210 MW
- TYPICALLY 300 CU.M. IN 500 MW
• WATER-FILLED TROUGH WITH SCRAPER BARS
ATTACHED TO PAIR OF MOVING ENDLESS CHAINS FOR
REMOVAL OF ASH CONTINUOUSLY
– 2 X 100% ( ONE WORKING + ONE STANDBY) , OR
– 2 X 50% (TWO WORKING + TWO STANDBY)
DEPENDING ON SUPPLIER’S CAPABILITY

16. SCRAPER CONVEYOR

17. SCC
• WATER SUPPLIED CONTINUOUSLY
- FOR SPRAY-QUENCHING OF ASH IN TRANSITION
HOPPER
– FOR COOLING OF ASH IN TROUGH
• OVERFLOW WATER FROM TROUGH
RECYCLED IN ASH HANDLING PLANT AFTER
SETTLING OUT CARRYOVER ASH

18. OPEN-HEARTH
• BOX -SHAPED REFRACTORY-LINED
STORAGE HOPPER , DIVIDED INTO
SEVERAL COMPARTMENTS
• WATER CONTINUOUSLY SPRAYED ON ASH
FOR QUENCHING
• COMPARTMENTS EMPTIED SEQUENTIALLY
• ASH EVACUATION FROM HOPPER ON
INTERMITTENT BASIS ( EG. ONCE A SHIFT)

19. OPEN-HEARTH
• ASH FLUSHED FROM COMPARTMENTS
USING HIGH PRESSURE WATER JETS
AND THE SLURRY SLUICED VIA
TRENCH TO DISPOSAL PUMPHOUSE
• ASH SLURRY CAN ALSO BE REMOVED
USING JET PUMPS/CENTRIFUGAL
PUMPS LOCATED BELOW FLOOR
LEVEL

20. SCREW CONVEYOR
• ONE TRANSITION HOPPER PER UNIT
• WATER SPRAYED ON BOTTOM ASH
FALLING THROUGH HOPPER FOR
QUENCHING
• ASH FALLS INTO TROUGH BELOW
HOPPER
• ONE SCREW CONVEYOR ,INCLINED
UPWARDS, PROVIDED IN TROUGH TO
REMOVE THE ASH CONTINUOUSLY

21. SCREW CONVEYOR
• DEWATERED ASH SLUICED VIA
TRENCH TO SLURRY DISPOSAL
PUMPHOUSE

22. BA HANDLING – COMPARISON
OF OPTIONS
JET
PUMP
Scraper
Conv
Open
Hearth
Screw
Conv
Experience
(India)
High + Med Less _ Less _
Power
cons.
High _ Med High _ Med
Water cons. High _ Med High _ Med
Capital
Cost
Less + High _ Less + Med
O&M cost Less + High _ Less + Med
O & M view High + Med Med Med

23. NEW TECHNOLOGIES FOR
BOTTOM ASH HANDLING
• DRY TYPE
-BELT CONVEYOR TYPE
-PNEUMATIC TYPE

24. BELT CONVEYOR TYPE
• REFRACTORY-LINED STEEL TRANSITION
HOPPER WITH DISCHARGE GATES BELOW
BOILER FOR EMERGENCY ASH STORAGE.
• AIR-TIGHT STEEL CASING BELOW HOPPER
FOR THE CONVEYOR.
• PANS ATTACHED TO ENDLESS CONVEYOR
BELT OF STEEL MESH RIDING ON IDLERS
FOR TRANSPORTING THE ASH.

25. BELT CONVEYOR TYPE
• AMBIENT AIR LEAKED INTO CASING FOR:
- COOLING THE HOT ASH
- COMBUSTION OF UNBURNT COAL
IN ASH
- TRANSFERRING THE HEAT EXTRACTED
FROM THE ASH TO THE BOILER
FURNACE.
• DRY, COOLED BOTTOM ASH DISCHARGED
FOR FURTHER PROCESSING AND
TRANSPORTATION.

26. BELT CONVEYOR TYPE
• DOWNSTREAM EQUIPMENT TO BE
PROVIDED SUITING FURTHER
USE/TRANSPORTATION OF THE DRY
ASH (CRUSHERS, BELT
CONVEYORS/PNEUMATIC
CONVEYORS, ETC.).

27. ECONOMISER ASH HANDLING
SYSTEMS
• WET TYPE
- FLUSHING BOX ,AND ,
- TRENCH SLUICE , OR
- TRANSFER TANK AND CENTRIFUGAL
PUMPS , OR
- COMBINED WITH BOTTOM ASH
- FEEDER EJECTOR , AND,
- TRENCH SLUICE
- TRANSFER TANK WITH JET PUMPS
• DRY TYPE
– VACUUM TYPE PNEUMATIC CONVEYING
– PRESSURE TYPE PNEUMATIC CONVEYING

28. ECO ASH SYSTEMS
• FLUSHING BOX BASED SYSTEMS
– CONTINUOUS ASH REMOVAL
– CAN BE COMBINED WITH CONTINUOUS -TYPE BOTTOM
ASH REMOVAL SYSTEMS( SSC , SCREW CONVEYOR) TO
OPTIMISE WATER AND POWER CONSUMPTION AND
LAYOUT
– PREFERRED AS HOT ASH IS CONTINUOUSLY COOLED AND
REMOVED
• FEEDER EJECTOR BASED SYSTEMS
– INTERMITTENT ASH REMOVAL
– CAN BE COMBINED WITH INTERMITTENT TYPE BOTTOM
ASH REMOVAL SYSTEMS (WIH) TO OPTIMISE WATER AND
POWER CONSUMPTION AND LAYOUT

29. FLUSHING BOX

30. ECO ASH HANDLING SYSTEMS
• PNEUMATIC SYSTEMS
– PERIODIC ASH REMOVAL USUALLY AS PART OF
CYCLE INVOLVING AIR PREHEATER AND ESP
DRY ASH REMOVAL SYSTEM
– SPECIAL CONSIDERATIONS FOR DESIGN OF
SYSTEM AS ASH PARTICLES ARE BIGGER AND
OF DIFFERENT SHAPE COMPARED TO ESP ASH.
– RELIABILITY OF ASH REMOVAL DEPENDS ON
ABILITY OF SEALING MATERIAL AT PIPING
JOINTS TO WITHSTAND THE HIGH ASH
TEMPERATURE (300-400 DEG. C) AND PIPING
LAYOUT WITH MINIMUM BENDS

31. AIR PREHEATER ASH REMOVAL
SYSTEMS
• SIMILAR TO ECONOMISER ASH
REMOVAL SYSTEMS.
• RELATIVELY EASIER DUE TO LOWER
ASH TEMPERATURE( 150-200 DEG. C)
• USUALLY COMBINED WITH ESP DRY
ASH REMOVAL SYSTEM

33. ESP ASH REMOVAL SYSTEMS
• WET TYPE
• DRY TYPE
• CONTINUOUS TYPE
• INTERMITTENT TYPE

34. ESP ASH REMOVAL SYSTEMS
• CONTINUOUS TYPE
- FLUSHING BOX AND TRENCH
SLUICE (WET SYSTEM)/WETTING
HEADS
- PNEUMATIC TYPE (DRY SYSTEM)
• INTERMITTENT TYPE
- FEEDER EJECTOR AND
TRENCH/PIPE SLUICE (WET
SYSTEM)

35. ESP ASH REMOVAL SYSTEM
(Fly Ash)
• TWO-STAGE SYSTEM
- PNEUMATIC CONVEYING FROM ESP
HOPPERS TO BUFFER HOPPERS /
WETTING HEADS/SLURRIYING UNITS
- PNEUMATIC TRANSPORTATION FROM
BUFFER HOPPERS TO STORAGE
SILOS/SLUICING VIA TRENCHES FROM
SLURRIYING UNITS TO SLURRY DISPOSAL
PUMP HOUSE

36. Vacuum conveying and pressure
transportation system

37. VACUUM CONVEYING SYSTEM
• MECHANICAL EXHAUSTERS (VACUUM
PUMPS) USED
• A ROW OF HOPPERS FROM FRONT OF ESP
TO REAR/ROW OF HOPPERS IN EACH FIELD
IN EACH ESP PASS CONNECTED TO ASH
CONVEYING LINE
• ASH REMOVED SEQUENTIALLY FROM ESP
HOPPERS IN EACH LINE AND CONVEYED TO
BUFFER HOPPER OR TO SLURRIYING UNIT.
• LIMITATIONS ON CAPACITY AND
CONVEYING DISTANCE - TYPICALLY 50-60
MTPH FOR 150 M

38. PRESSURE CONVEYING SYSTEM
• AIR COMPRESSORS (SCREW TYPE) USED
• PUMP TANK (BLOW TANK) BELOW EACH ESP
HOPPER FOR ASH REMOVAL IN BATCHES
• ASH CONVEYING LINE FOR EACH FIELD OF ESP
• ASH REMOVED SEQUENTIALLY FROM EACH FIELD
AND CONVEYED TO BUFFER HOPPERS
• ASH CAN BE CONVEYED TO A DISTANCE OF 1000
METER.

39. PRESSURE CONVEYING SYSTEM
(CONTD.)
LOW PRESSURE MEDIUM
PRESSURE
HIGH PRESSURE
MATERIAL
TRANSPORT MODE
SUSPENSION PARTLY IN
SUSPENSION,
PARTLY AS
MOVING BED
SLUG (DUNE OR
PLUGS FILLING
WHOLE PIPE
SECTION)
TYPICAL CONVEYING
AIR PRESSURE (BAR)
Up to 2 2-3 >3
TYPICAL ASH/AIR
RATIO BY WT.
<20 20-30 >50
TYPICAL CONVEYING
VELOCITIES(M/S)
15-20 10-15 5-8
TYPICAL AIR SOURCE BLOWER/COM-
PRESSOR
SINGLE-STAGE
SCREW
COMPRESSOR
TWO-STAGE
SCREW
COMPRESSOR

40. Ash Disposal System
• Conventional Lean Concentration
Slurry Disposal (LCSD) System
• High Concentration Slurry Disposal
( HCSD) System
• Dry Ash mound

41. Ash Disposal System
1. Conventional Lean Slurry Disposal System
• Bottom ash discharge rate based on Jet pump
capacity/SSC capacity
• The fly ash handling system shall be assumed to
operate continuously and the fly ash collection rates
shall be same as the rates considered for sizing
pneumatic conveying system, for the purpose of sizing of
the disposal system.
• The slurry line velocities shall not exceed 2.8m/sec.
• The ash concentration (W/W) shall be -
• For combined slurry disposal 28% max.
• For fly ash slurry disposal 30% max.
• For bottom ash slurry disposal 25% max.
• The value of `C’ factor( William-hazen eqn.) to be
considered for arriving at the pressure drop shall be 140.

42. High Concentration Slurry Disposal
( HCSD) System
• Design concentration for ash slurry pumping is
60% by weight.
• Range of concentration - 55% to 70%
• Ash pipe line velocity - 1.8 M/Sec. (max.)
• HCSD pump operating range - 10% to 100% of
rated flow.
• Shut-down Restart for pumping operation –
Minimum 12 hrs.
• The High Concentration ash slurry disposal pump
shall be positive displacement type.
• The high concentration slurry shall be disposed in
disposal area such that no significant free water is
released from the slurry.

43. What is ash dyke?
• Ash Dyke is a storage area to contain
huge quantity of ash generated in the
process of power generation.
• It’s a kind of tailing dam: made of earth or
ash.
• Ash is discharged into this ash dyke, in the
form of slurry through pipelines.
• This is also known as Wet Disposal
System.

44. PLAN OF ASH DYKES
(STARTER & RAISINGS)(WET
DISPOSAL)

45. TYPICAL SECTION THROUGH
U/S RAISED DYKE

47. Dry Ash Mound
• 24 hour storage of fly ash, shall be provided
in the storage silos in case dry ash disposal,
mound system is envisaged.
• Hydrobins for BA decantation
• Both FA and BA shall be transported by
conveyor system to the dry ash disposal
area.

48. Bottom Ash / Coarse Ash Removal System
.
OFT
CAT
Bottom Ash hopper
HBN-1
HBN-2
HBN-3
BAH Gates
CG
HE’s
OFP-1 & 2
HP Water
HP Water
LP Water
Economiser Hoppers
Flushing
LP Water
CG
Apparatus

49. Bottom Ash / Coarse Ash Removal System Contd..
.
Surge Tank
Settling Tank
Sludge Pumps
Hydro-bins
HP Water / LP Water / MS Water Pumps
To Hydro-bins
To Hydro-bins
From OFP/P’s

51. Ash Mound