ASH HANDLING SYSTEM IN THERMAL POWER PLANT – AN OVERVIEW

• 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

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

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

ASH COMPOSITIONSILICA ( 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

PC FIRED BOILER

Bottom AshBottom Ash HopperHopper

Econ Ash HopperEcon Ash Hopper

FlyashFlyashTo ESPTo ESP

Air Preheater

Typical Ash distribution for 2 pass boilerTypical Ash distribution for 2 pass boiler

ESP

PulverizedCoal

Furnace(1300 - 1500°C)

ElectrostaticPrecipitator

Sta

ge A

: 80

%

Sta

ge B

: 17

%80 %

Sta

ge C

: 3

%

Fly ash

Airpreheater

APH

Economizer

Eco Ash APH Ash

Stack

Fineness

Bottom Ash20 %

ASH PRODUCTION

• BOTTOM ASH - BOILER FURNACE

• COARSE ASH (grits)

- ECONOMISER

- AIR PRE-HEATER

• FLY ASH (dust)

- ELECTROSTATIC PRECIPITATORS

- DUCT HOPPERS (IF APPLICABLE)

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

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%

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)

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

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.

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

SCRAPER CONVEYOR

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

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)

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

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

SCREW CONVEYOR

• DEWATERED ASH SLUICED VIA TRENCH TO SLURRY DISPOSAL PUMPHOUSE

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

NEW TECHNOLOGIES FOR BOTTOM ASH HANDLING

• DRY TYPE

-BELT CONVEYOR TYPE

-PNEUMATIC TYPE

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.

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.

BELT CONVEYOR TYPE

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

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

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

FLUSHING BOX

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

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

ESP ASH REMOVAL SYSTEMS

• WET TYPE

• DRY TYPE

• CONTINUOUS TYPE

• INTERMITTENT TYPE

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)

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

Vacuum conveying and pressure transportation system

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

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.

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

Ash Disposal System

• Conventional Lean Concentration Slurry Disposal (LCSD) System

• High Concentration Slurry Disposal ( HCSD) System

• Dry Ash mound

Ash Disposal System1. 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.

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.

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.

PLAN OF ASH DYKES (STARTER & RAISINGS)(WET

DISPOSAL)

TYPICAL SECTION THROUGH U/S RAISED DYKE

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.

Bottom Ash / Coarse Ash Removal System

.

OFT

CAT

Bottom Ash hopper

HBN-1

HBN-2

HBN-3BAH Gates

CG

HE’s

OFP-1 & 2

HP Water

HP Water

LP Water

Economiser Hoppers

Flushing

LP Water

CG

Apparatus

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

Ash Mound