mill performance

7/31/2019 Mill Performance

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May 24, 2012 PMI Revision 00 1

MILLPERFORMANCE


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Must be able topulverize consistentlythe design quantity of

coal suitable forcombustion.Able to dry wet coal upto the design wetness

even at full outputcondition.Able to maintain the

products within thedesired grading

The Pulverizers are the HEART of a

Pulverized Coal Fueled Boiler!


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PULVERIZER DESIGN CRITERIA

PULVERIZERS SIZE & TYPE ARESELECTED TO PROVIDE A GRINDING

CAPACITY BASED ON COAL

CHARACTERISTICS

MARGINS IN CAPACITY ARE BASED ON

EXPECTED WEAR LIFE AND RANGE OF

COAL TO BE FIRED

OPERATING CAPACITY AFFECTED BYCOAL MOISTURE, INLET AIR

TEMPERATURE AND AIR FLOWS.


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MILL PERFORMANCE INDICATORS

MILL OUTLET TEMPERATURE

MILL OUT PUT MT/H

MILL FINENESS FRACTIONS

MILL AIR FLOW

MILL PRESSURE DROP (D.P)

MILL REJECT RATE

MILL MOTOR AMPERES

WEAR PART LIFE


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CAUSE OF MILL PERFORMANCE

DETORIARATION QUALITY OF COAL (MOISTUR, HGI ETC.)

UN BALANCED FLOW IN COAL PIPES.

SETTLEMENT OF COAL IN COAL PIPES.

POOR COAL FINENESS

LOW PA TEMPERATURE

FOREIGN MATERIAL INGRESS.

LOSS THROUGH REJECTION

WEAR PART LIFE


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MILL PERFORMANCE - IDENTIFICATION

METHODS NO LOAD RUN

CLEAN AIR FLOW TEST

DIRTY PITOT TUBE TEST

MILL FINENESS SAMPLING

TRENDING OF COAL PIPE METAL

TEMPERATURE


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OBJECTIVE OF TESTING

CLEAN AIR BALANCING BETWEEN

BURNERS

DIRTY AIR BALANCING BETWEENBURNERS

FUEL BALANCING BETWEEN BURNERS

FINENESS TESTING OF PF BETWEENBURNERS

SETTLEMENT OF COAL PARTICLE IN

COAL PIPE.


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CLEAN AIR FLOW TESTS STEPS INVOLVED ARE DETAILED IN THETEST PROCEDURE

STANDARD L TYPE PITOT IS USED.

CLEAN AIR FLOW BALANCE IS COMPUTED

BETWEEN COAL PIPES

DEVIATION OF +\- 2% INDICATES A

SATISFACTORY FLOW BALANCE ANDFURTHER TRENDING IS REQUIRED.


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10/21


Acceptance range

Clean air flow distribution to be with in +/-2.5%.

Dirty air flow distribution to be with in +/- 5.0%.

PF distribution to be with in +/-10%.

Guarantees to be established for end mills with

unequal length in fuel piping


11/21


Fuel lines balanced to each burner by Clean Air test 2%

or better.


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COAL FINENESS

ANALYSIS

FINENESS SAMPLE ANALYSIS NEEDS

TO BE CARRIED OUT IMMEDIATELY TO

AVOID COAGULATION IN CASE OF HIGH

MOISTURE COALS

MINIMUM FOUR STANDARD MESH

SCREENS TO BE USED

TVA DEVELOPED SOFTWARE ENABLESREVIEW OF MILLS PERFORMANCE DATA

TO FOCUS ON VARIOUS TRENDS


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Accurate weighing and sieving of the samples through 4 sieves is also important. Why four sieves?

Because, with the desired near zero on 50 mesh sieve, at least three points are needed on the

Rosin-Rammler Chart to plot the fineness Results. Four sieves of 50, 100, 150 and 200 mesh are

recommended for fineness sampling. 70 % in 200mesh


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WHY IS MILL PERFORMANCE

TESTING IMPORTANT? UNIT CAPABILITY GOVERENED BY MILLPERFORMANCE

BOILER AND COMBUSTION SYSTEM

PERFORMACE AFFECTED BY QUALITY OF PFCOAL AND ITS DISTRIBUTIION

RELIABLE FEEDBACK SHOULD FOCUS ON

TIMELY MILL OVERHAUL VERY EFECTIVE CROSS CHECK OF THE

STATION INSTRUMENTS FEEDBACK


17/21


USE OF METAL TEMPERATURE IN FUEL

PIPE TO MONITOR CHOCKING FUEL PIPING METAL TEMPERATURE IS BEINGMONITORED IN FARAKA TO MONITOR FUEL PIPE

CHOCKING.

RECENT STUDIES SHOWED THAT LOWER THAN MILLOUT LET TEMPERATURE IS NOT NECESSARILY AN

INDICATION OF PIPE CHOCKING.

DIFFERENCE OF 7 TO 8 C WAS OBSERVED BETWEEN

COAL AIR TEMPERATURE METAL TEMPERATURE FOR

A PIPE WHICH WAS CLEAR.


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Pulverizer Troubleshooting-Matrix

LACK OF CAPACITYOR HIGH POWER

CONSUMPTION

HIGH MOISTURE

LOW GCV

INCREASED RAW

COAL SIZE.

GRINDING TOO FINE

EXCESSIVE BED

DEPTH

INSTRUMENT ERROR


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EXCESSIVE MILL

REJECTS

CHANGE IN COAL

GRINDABILITY, SULFUR &

ASH.

IMPROPER COAL/AIRRATIO

THROAT GAP WEAR.


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LOW COAL \AIR

TEMPERATURE

HIGH MOISTURE

LOW PA INLET

TEMPERATURE

PASSING OF COLD AIR. LOW A.H INLET

TEMPERATURE


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mill performance

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