Ash Handling Systems_ppt

ENERGY EFFICIENCY & ENERGY EFFICIENCY & TECHNOLOGIESTECHNOLOGIES

IN POWER PLANTSIN POWER PLANTS

ASH HANDLING SYSTEMASH HANDLING SYSTEM

28 28 –– 29 July, 200329 July, 2003

MACAWBER BEEKAY PVT. LTD.MACAWBER BEEKAY PVT. LTD.

INDIAN COALINDIAN COAL

• Generally high ash content.• Larger amounts of ash to

be handled.• Inconsistent Quality.

CHALLENGES OF ASH HANDLINGCHALLENGES OF ASH HANDLING

• Indian coal presents high ash content generally which tends to be inconsistent. Design of the system has to adequately cover anticipated variations and be capable of handling the worst scenario.

• System has to be environmentally friendly.• System has to be reliable with least

maintenance problems.• System has to be energy efficient.

TRADITIONAL TECHNOLOGYTRADITIONAL TECHNOLOGYTo dispose off large amount of ash efficientlyTo dispose off large amount of ash efficiently

(i) HYDRO-SLUICING:• Water impounded bottom ash hoppers with jet

pump systems followed by lean phase slurry pump system upto ash dyke.

• Dry type Bottom Ash Hopper with submerged scraper chain conveyor system followed by lean phase slurry pumps system upto ash dyke.

• Flushing Apparatus for Fly Ash

(ii) PNEUMATIC HANDLING:• Negative pressure type• Lean Phase

NEGATIVE PRESSURE (VACUUM) type operate essentially by Lean Phase fluidising method. There is a material handling valve below each hopper to segregate the hopper from transport line. The water operated hydrovector or mechanical vacuum pump mounted on the top of the silo exhaust air from the transport line and the resultant rise in vacuum operates high vacuum switch. Solenoid valve is energised and material handling and associated branch segregating valves are opened. Ash in the hoppers is fed into the vacuum lines and is conveyed to a fabric filter which separates the ash from the air. The ash is discharged into the storage silo and air is drawn through the vacuum pump via a line filter and exhausted to atmosphere. This system operates on the lean phase principle with a high air to ash ratio and high conveying velocities.

TRADITIONAL TECHNOLOGYTRADITIONAL TECHNOLOGY

LEAN PHASE SYSTEMS rely on fluidisation of the material in the air stream to achieve conveying of material. The material particles are carried by a high velocity air stream. The required velocity is dependent mainly upon the size and density of the material particles. In Lean Phase system, the velocity is in the range of 15 m/sec to 30 m/sec. and in Medium Phase, it is in the range of 10-20 m/sec. The material/air ratio in the lean phase is in the range of 10:1 and in medium phase, the range is 20:1.

TRADITIONAL TECHNOLOGYTRADITIONAL TECHNOLOGY

PRESENT TRENDS PRESENT TRENDS IN IN

FLY ASH REMOVAL FLY ASH REMOVAL IN IN

THERMAL POWER PLANTTHERMAL POWER PLANT


Dense Phase Pneumatic Pressure Conveying System

The Dense Phase Pneumatic Pressure Conveying Systems uses low volume, medium pressure air stream and relies on a continuously expanding volume of air pushing cohesive slugs of material along the pipe. This system uses a transfer vessel/pump tank to feed the material into the conveying line. It is a batch system with plugs of material separated by cushions of air. Average conveying velocities are low between 2 to 5 m/sec. The material air ratio is in the range of 20 - 100 to 1.


Dense Phase Pneumatic Pressure Conveying System

• Using positive pressure they generally utilise a blow tank to collect the material before being transferred into the pipeline in batches.

• With dense phase systems, a controlled use of both air pressure and volume pushes the batch of material from the blow tank and into the pipeline in a plug flow form.


Typical Operation Cycle

1System at rest

2Vessel filling

3Vessel full

4System conveying

LevelProbe Vent

Valve

Air supply

BlowValve


THE OPERATIONAL PRINCIPLETHE OPERATIONAL PRINCIPLEThe systems normally have dual operatability either through the timer or level probe which is installed in the collecting hopper.As soon as the ash level reaches a fixed level in the collecting hopper, the level probe senses its presence, it allows the system to initiate a conveying cycle. The inlet valve opens to allow the ash to gravitate into the conveying vessel, till it closes automatically. On closure of the valve, the conveying vessel gets pressurized and the material resistance helps pressure build up which conveys the material through pipe in the destination silo. When conveying is complete which is sensed by the control system, air supply to the system is stopped and system is ready for the next cycle.The total system is made automatic by use of level probes in destination silo(s) to control the transfer of material. Flexibility in the system allows to opt from single transfer of material from one point collection to single reception hopper or a multipoint collection. The system is flexible enough and programmable and automatically operated through a PLC based Central Control Panel.


INFLUENCE OF VELOCITY ON EROSIONINFLUENCE OF VELOCITY ON EROSION


INFLUENCE OF VELOCITY ON THE EROSIVE WEAR OF PIPE BENDSINFLUENCE OF VELOCITY ON THE EROSIVE WEAR OF PIPE BENDS


Relationship between Minimum Conveying Air Velocity and Phase Relationship between Minimum Conveying Air Velocity and Phase Density at which Product is conveyedDensity at which Product is conveyed


Dense phase conveying is considered to be dense phase if the product is predominantly conveyed in a non-suspension mode of flow.

One of the major causes of pneumatic conveying systems not achieving their specified duty is a change in the product specification or the problem of off-spec materials. To a large extent this is the responsibility of the user. There is no escape from the fact that changes in material characteristics which affect the flowability of the product will affect conveying performance. The most common deviations from specification are changes in the size distribution and moisture content of the material.

CONVEYING CAPABILITYCONVEYING CAPABILITY


i) Commercial utilisation of ash in :– Cement additives.– Brick plants.– Road making, etc.

ii) Saving of water – a precious commodity.iii) Energy Efficientiv) High reliabilityv) Long Plant Lifevi) Least maintenance vii) Environment concern:

– In a period, when environmental protection and awareness is a major industrial and social concern, Dense Phase pneumatic conveying, by totally enclosed handling system, is particularly amenable to the environment.

– All conventional problems of spillage, dust, contamination and storage are efficiently and successfully eradicated.

– Plant housekeeping is greatly improved.

ADVANTAGESADVANTAGES


The compressor works on load / no-load basis in a Dense Phase System. Dense Phase follows Batch Conveying System. Whenever conveying is in progress, there is a requirement of compressed air which is fed by conveying air compressor through air receiver. When there is no material available in the hopper and conveying does not take place, compressor switches over to no-load condition, thus saving power.

COMPRESSOR COMPRESSOR –– LOAD/UNLOAD BASISLOAD/UNLOAD BASIS


The Dense Phase Pneumatic Conveying system is flexible enough and compatible with all size and type of boilers.

– Whether Boiler is from 3 MW to 600 MW,– Water tube or Fire tube, – CFB, PFB, Stoker fired, – Coal, Coke, Lignite, Rice Husk, Bagasse,

Multi fuel or Co-generation type.

COMPATIBILITYCOMPATIBILITY


In the typical Thermal Power Plant, Dense Phase offers solutions for:

•Conveying of fly ash from Economiser, Air Heater and ESP collecting hoppers to intermediate silo(s) or directly to main silo.

•Conveying of bed ash from collecting hoppers to intermediate silo(s)/BA Silos.

•Conveying of ash from intermediate silo(s) to main silo installed outside the boundary of the plant for truck/bulker loading ensuring elimination of truck/bulker movement within the premises of power plant area.

•Long distance conveying of fly ash from the power plant silo(s) to the fly ash user premises, where the manufacturing facilities are installed, adjacent to that particular power plant.

•Fly ash recycling system for injection of fly ash into boiler furnace.•Handling the lime stone powder, sand dry gypsum, etc.•Handling of dry / wet coal and coal mill rejects.


Comparison of Dense Phase over Vacuum Extraction System

-Hopper heater required. - Fludising system required. - Failure due to above - Large Collection of ash can cause

boiler shut down. -Few hundred tonnes of ash may get

collected which can not be dumped on the floor. - Ash build up causes ESP electrode

shorting resulting in ESP failure and root being speeded against environmental moment.

Removal of ash as soon as collected - Hopper used for storage only during emergency as dense phase system disposes ash continuously.

Storage of ash in hopper for 8-12 hours causing bridging, ratholing, choking, compacting etc. ferms clinker (occidisation) sometimes which is virtually impossible to cover.

1

DENSE PHASEVACCUM/ LEANS. No.


Easier bends in Dense Phase System No limitation on lay out or number of bends since conveying achieved through pressure. No. of bends does not impact capacity –flexibility in layout.

Bends of 3D or less resulting drastic increase in bend failure rate imposing stringent limitations on plant lay out in order to reduce number of bends. -Each bend adds to equivalent length of pipe resulting in limitation on layout. -Additional equivalent length affects capacity of conveying.

4.

No. distance restriction in dense phase system silo can be conveniently located resulting in - Cleanner boiler areas. - Economic silo designs. - Silos can even be located outside plant area to avoid nuisance of truck movements in plant area which also is a security hazard.

Location of silos has to be very close to ESPs. Due to limitation of distance in vaccum system.

3.

Inflatable rubber to metal relating more reliable and less prone to leakage.

Intake valves have metal to metal seal which generally leaks.

2.



Ash is conveyed in batches as a long slug say of 40 mtrs at an average velocity of 7 m / Sec. Assuming number of cycles per shift typically as 240, any pipe section will be under effective use for 40/7 x 240 = 1371 secs or 23 minutes. Effective usage of pipe 7 to 14 times less resulting in much longer life.

Main Header is in use all the time during removal cycle typically 3 to 6 hours resulting in heavy pipe wear. Pipe in effective use 3 to 6 hours.

7.

In Dense Phase a number of pipes being there grouping can be done in such a way that only a few hoppers are affected increasing substantially reliability of the system.

Vaccum / lean phase generally has one or two main pipes to silo or extraction equipment. If any problem occurs it can lead to stoppage of system or even boiler shut down.

6.

Any leakage visually detectable for immediate correction maintaining high performance efficiency and capacity.

Any leakage in joint or due to loose bolts / gaskets is very difficult to locate / detect. -Leakage results in drop in -Performance and capacity thereby more evacuation, time and power consumption.

5.



Distance is not a limitation in a dense phase pneumatic conveying system single stage conveying possible in most case.

Due to inverse relation between distance and conveying capacity, in some cases two stage system is essential for longer distances.

10.

This does not apply to Dense Phase Pneumatic System since conveying medium is compressed air. Compressors can be installed in an enclosed room in a suitable far off location where proper ventilation and filtration can be done.

Conveying air move through the equipment generating vaccum. Due to high velocities lean air / ash separation’s is not efficient. Possibility of failure of cleaning devices like rupturing filter bag etc. resulting in passage of ash through vaccum generator. Maintenance problems of vaccum generator.

9.

In Dense Phase nominal quantities of air is used thus a small bag filter at the silo top cleans air to satisfy most stringent norms. Due to much lower velocities rate of wear of equivalent system is much lower.

Due to high velocities and lean phase ash / air separation is inefficient (2 to 4 stages of cleaning is normally required from pollution control point of view. )

High velocities result in high wear rates of associated equipment and system.

8.



No such problem due to inherent design.

Residual ash gets carried over in case of mechanical vaccum pump resulting in rapid wear. It may require sophisticated sensor for checking ash particles in the air stream.

13.

No such problem in Dense Phase due to inherent design.

Ash gets carried over from the system passing through water exhauster causing wear in its nozzles, throat etc. Water quantities being enormous gets recirculated eroding pumps, valves, nozzles of exhausts etc. resulting in higher maintenance cost. Due to the wear and tear of nozzles and loss of pressure of pumps system design capacity drops significantly.

12.

Water is required when disposing off slurry and not when collecting dry. Water pumps required for making slurry are of lower capacity and head thus saving power.

If high pressure water exhausts (hydro vector) is used. It requires large capacity / high pressure pumps, whether ash is being stored dry or disposed off as wet slurry.

11.



Low maintenance. Low maintenance cost Low power consumptionNeglible down time. System advantages.

Summary High Maintenance Prone. High maintenance costs. High power consumption High maintenance down time Prone to choking of hopper.

16.

Negligible wear rate due to very low conveying velocities.

Due to high pipe line velocity high wear and tear of pipelines. Wear rate increases with power of 2.65 on the ratio of increase in velocity normally 10-50 times.

15.

Dense Phase requires small compressor room and pump house.

Vaccum designed for wet disposal circulating water needs huge pump houses, storage sumps, settling tanks etc. – wasting valuable space – high civil costs.

14.


PROJECT DETAILSPROJECT DETAILS

PSEB, GGSSTPP, PSEB, GGSSTPP, RoparRopar

World’s single longest conveying distance of 1.6 kms for fly ash handling.Technology – Dense Phase Pneumatic conveying.Installed capacity – 6 x 40 tons per hourClient – PSEB, Ropar (Punjab)Units – 6x210 MWApplication – utilisation of ash by cement manufacturers namely ACC & GACL @ 2000 - 2500 tones per day.


PSEB, GGSSTPP, PSEB, GGSSTPP, RoparRoparThe system comprises of two stages -

PRIMARY : To collect fly ash as generated from ESP area Denseveyor Ash Vessels designed ad provided with a patented dome valve, and to transport fly ash in dense phase in the form of a slug at low velocities through Mild Steel pipe work to either of the two Intermediate Silos by means of Dump Valve type Diverter/Terminal Box. To cater for independent operation, the primary stage is provided with 6 Nos. air compressors to provide conveying air to the system, with 4 Nos. working and 2 Nos. standby. The fly ash is conveyed at the rate of about 30 TPH over a conveying distance of about 400 Meters.

A) Number of Conveying Line in each boiler : 2 Nos.B) Conveying rate of each line : 30 TPHC) Conveying Distance : 400 MetersD) No. of compressors for six boilers : 6 Nos. (4W+2S)E) Denseveyor ash vessel size provided below each ESP Hopper : 500 Litres

SECONDARY : To continuously transport their fly ash from intermediate storage silos through K-Pump to main storage silos. The K-Pump are continuous pumping system catering for high transfer rates over long distances. The K-Pump assembly also has Dome Valves. For the secondary system each of the intermediate silos is equipped with 4 sets of independent conveying air compressors with 2 working and 2 standby and system operates at a conveying rate of 40 TPH per stream over distance of about 1600 Meters.

A) Conveying rate of each line/K-Pump : 40 TPHB) Conveying Distance : 1550 MetersC) No. of compressors for both the silos : 8 Nos. (4 W + 4 S)


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Punjab State Electricity Board, Ropar

Punjab State Electricity Board, Ropar

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Ash Handling Systems_ppt