Operation & Maintainance Manual

8/3/2019 Operation & Maintainance Manual

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OPERATION,INSTALLATION AND MAINTENANCE MANUAL

AIA ENGINEERING PVT. LTD

HPMS SYSTEM

FOR

BOWL MILLS

OPERATION , INSTALLATION AND

MAINTENANCE MANUAL


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TABLE OF CONTENTS

HIGH PERFORMANCE MILLING SYSTEM

Description about system and parts

Installation procedure

Tools and tackle required for installation of HPMS system

Recommendation for mill operation

Precautions to be taken during normal shut down and start up of

mill

Preventive maintenance aspect / inspection procedure

Pre-requisites for HPMS system


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HIGH PERFORMANCE MILLING SYSTEM

HPMS SYSTEM FOR COAL MILLS AT THERMAL POWER PLANTS

HPMS system consists of a specially designed Airport Ring Assembly, a set of Inserted Rolls(having special carbide inserts with very high hardness embedded in soft ductile iron core) along

with a compatible design of Bull Ring Segments specially designed to combat the highly abrasive

Indian coal for long life and better grinding action.

AIRPORT RING ASSEMBLY

,

BHEL/AIAE specially designed to suit the site conditions. Its unique design reduces the turbulence

in the mill. The reduction in the turbulence and the reduction in the energy loss is utilised to save

auxiliary power consumption and increase the grinding efficiency of the mill. Unlike other rotating

vane wheels, the Airport Ring assembly is an integral component, which does not get damaged dueto normal foreign material entry into the mill. The Airport Ring Assembly is suitably hard faced to

combat erosion. The system eliminates the usage of wear parts like separator body liners, deflector

liners and intermediate liners and provides more working space for the maintenance crew to work

inside the mill.

INSERTED ROLLERS

The Inserted Rollers have special carbide inserts with very high hardness embedded in ductile iron

core. The core made of tough ductile iron is also capable of withstanding severe shocks without any

danger of failure due to breakage. A layer of ductile iron is always present between the hard inserts.

This forms small grooves between the inserts. As a result, there is literally a biting action on thecoal and this improves the grinding efficiency. The rollers are specially designed to minimise collar

formation. All these result in consistent grinding capacity of the mill and consistent P.F. fineness

throughout the life of the rolls.


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The selection of chemistry is such that bonding is perfect and the heat treatment responses of both

alloys are highly favourable.

BULL RING SEGMENTS

The Bull Ring Segments are of a compatible design with a hardness of about 64 RC in superior

high chromium metallurgy, specially developed to suit the Indian coal conditions.

The profile of BRS is so designed that it helps in reducing the wear on grinding rolls and hence

helps in maintaining nearly consistent capacity throughout the life of grinding elements.


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ADVATAGES OF HPMS SYSTEM

1. Consistency in Mill Performance

In conventional system, there is collar formation on the rolls and BRS. As a result, the gapbetween the rolls and segments increases and this results in high mill rejects limiting the mill

loading. Thus, the mill capacity in conventional system reduces as the grinding elements

wear.

In the HPMS system, there is less collar formation in the grinding elements due to special

desi n of Rolls and se ments. Hi h wear resistance of the Hi h Chrome Bull Rin

Segments and the inserts of the grinding rolls increase the wear life substantially. All these

result in longer life and consistent mill capacity. The specially designed Airport Ring

Assembly reduces the turbulence in the mill and helps in controlling the P.F. fineness at a

consistent level throughout the life of grinding elements.

The system as a whole ensures efficient control of mill rejects.

2. Reduction in Maintenance Cost

By eliminating the wear resistant liners such as Deflector Liners, Intermediate Liners and

Separator Body Liners, the requirement of spare parts is reduced considerably.

Due to high wear resistance of the grinding elements, the frequency of Ring Roll gapadjustment is also reduced in HPMS system. This, coupled with long life of grinding

elements and Airport Ring, reduces the mill outages and increases the mill availability thus

resulting in a considerable saving in the maintenance cost.


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3. Savings in Auxiliary Power Consumption

The Reduction in turbulence inside the mill and elimination of Deflector liners andIntermediate liners results in reduction in the system resistance and consequently reduction

in the energy loss. This reduction in the energy loss is realized as saving in Auxiliary power

consumption in terms of Mill Motor Power Consumption and/or P.A. Fan Power

Consumption,. Thus, the auxiliary energy consumption per ton of coal ground (Specific

Energy Consumption) is lesser than that in conventional mill.

4. Reduction in Combustible Loss

With the increased and consistent capacity of the mill, it is possible to generate full load with

lesser number of mills in operation compared to normal requirement for considerable perioddepending upon the total coal requirement. This results in reduction in total primary air

quantity. By increasing the Secondary Air correspondingly to maintain O2 levels, better

turbulence is achieved in the furnace resulting in better combustion. This consistent P.F

fineness from the mill leads to reduction in combustible loss in Fly Ash and Bottom Ash.


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TOOLS AND TACKLE REQUIRED FOR INSTALLATION OF HPMS

SYSTEM

Two sets of welding machine (preferably generator)

Two pairs of cutting sets.

One hand grinder.

Chain & pulley block.

EOT Hoist

Hammers of different sizes

Spanners of required sizes.

Welding electrodes oven for preheating.

Two sets of 12-volt hand lamp.


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INSTALLATION PROCEDUREMinimum one-week shutdown is required for HPMS installation.

Open all the three journal opening cover and remove all the three-roller journal assemblies.

If new sets of roller journal assemblies are available, then overhaul it before mill shutdown.

Otherwise parallel work can be carried out.

Remove the separator body liners assembly, worn-out BRS and bowl extension ring.

Plug the holes on the separator body with old bolts and weld the 10 mm hard-faced plate up

to the manhole door.

Grind all the available welding beads and projection on the bowl and apply a thin layer of hi

heat dum dum (faster foam sealer compound) on the bowl surface.

Install the High Chrome BRS on the bowl as per proper sequence and all the wedges should

be tightly fitted.

Install the new Bowl extension ring and bolt all the sectors of vane wheel at the outer

periphery of the bowl.

Align each sector of vane wheel on bowl and tack welds it to the bowl. After compete

alignment, tightened all the clamping bolts up to the required torque.

Stitch welds the vane wheel with the bowl for proper clamping of vane wheel.

Install one by one all the sector plate of body liners by maintaining the proper clearance

(spacer provided) and tack weld the same with the separator body.

Lock all the body liners with vane wheel outer ring, for preventing warpages during welding

and hard facing.

Weld the cap ring between the vane wheel inner ring and Bowl extension ring.Re-install all the three-roller journal assembies and close the journal opening cover.

Check the spring load of all the three assemblies and maintain it equal.

Do the Ring roll setting, maintain 1-1.5 mm gap between roller journal head and

springhead.

Close the manhole door.

Initially ensure that classifier vanes are 100 % open.

Take the mill into service and observe the performance.


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RECOMMENDATION FOR MILL OPERATION

For optimum performance of the mills equipped with HPMS system and to achieve the best

out of the HPMS System, the following operating guidelines are recommended: -

Important Parameters to be watched: -

The mill operating parameters like Mill outlet temperature, PA mass flow-rate, Temperature and

Pressure of PA inlet to the mill, Raw Coal Feed rate to the mill, Mill motor current, Bowl DP, etc.

are all important to be watched in service. In addition, a watch on the PF fineness and mill rejects

wou e p o now a ou e ea ness o m opera on.

Mill Outlet Temperature

It is preferable to maintain the mill outlet temperature at value as high as possible within the safe

operating limits as dictated by the constituents of coal. Usual range is between 650 C and 950 C.

Mills handing low volatile coals can be operated at higher temperatures whereas high volatile

coal demands lesser operating temperature. If the coal contains high volatile matter and also

high Sulphur content, then the mill outlet temperature can be as low as 650 C. It is advisable to

avoid mill outlet temperature above 100 C in order to avoid mill fires.

Primary Air Inlet Temperature and Quantity

It is preferable to close the Cold Air Damper and adjust the Hot Air Damper position so as tomaintain the Air Flow as per the recommendations. The Cold Air is to be admitted, only if the mill

outlet temperature goes above the safe working limits, or if the recommended airflow could not

be maintained with the hot air alone. It is preferred to maintain the P.A. Inlet temperature as high

as possible so as to maintain the outlet temperature within safe limits. This increases the heat

recovery from the flue gases, which would otherwise


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be wasted. It also helps in drying the coal and increasing the milling capacity. In addition, because

of higher inlet temperature the mill reject also reduces due to increase in the volume flow rate of

P.A. All these will help in performance improvement.

Raw Coal Feed

It is advisable to control the entry of foreign material in raw coal (like scrap iron, wood shoring,

rags, cotton waste, detonators and stones) as these can interrupt the coal flow, damage or jam the

equipment, or, may cause ignition of coal dust within the pulveriser. Interruption may also cause

total or partial flameout at the burners followed by possible re-ignition, which may result in

dangerous furnace puff or explosion. It is therefore essential to remove all foreign material fromthe raw coal before it is fed into the mill. (IS 3595 Code of Practice for Fire Safety of Pulverizer).

It is also preferable to control the raw coal feed size to the recommended value.

Frequency of Ring Roll Gap Adjustment

As the rollers and B.R. Segments wear, the gap between them increases. The mill rejects willincrease and the mill capacity will reduce. It is recommended to adjust the Ring Roll gap using the

journal stop bolts at this stage. Every adjustment of Ring Roll gap should be followed by

adjustment of gap between the journal head and the pressure spring seat. When no more

adjustment is possible with journal stop bolts, it is recommended to adjust the trunnion eccentricity

with the trunnion end cap. This will shift the grinding zone and the rejects will reduce. Generally

the rollers can be used up to the full thickness of the inserts. Apart from the ring-roll gap, there are

other reasons for excessive coal rejects from the mill.


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The most probable reasons for excessive coal spillage are: -

Overfeeding

Very low throat velocities

Jamming of the roller assembly

Insufficient spring compression.

Excessive P.F. Fineness setting of the classifier or choking in classifier

Overfeeding: -

Overfeeding occurs when the raw coal feed-rate is more than the mill capacity.

This can be because of-

Excessive feeder speed and mal-operation of the feeder (like inoperative hinge gate mechanism)

Mill Capacity reduction (due to high moisture in coal, low HGI and a high PF fineness)

Very low throat velocities: -

This can be because of-

Very low P.A. mass flow rate

Lower P.A. inlet temperature

Choking in the P.A. Inlet ductPhysical damage to the air port ring assembly like some missing or damaged vanes, damage to

the block off plate etc.


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Precautions to be taken during normal shut down and start up of mill: -

During normal shut down of a mill, stop the raw coal feeder; continue to admit primary air for

sufficient time till the mill is emptied of coal as dictated by the mill motor current. This will ensure

purging of the mill and P.F. ducts. Before starting the mill, first admit primary Air till the milling

circuit is purged and then start feeding raw coal initially at a fairly higher feed rate.

The above precautions will reduce the possibility of mill fires.


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PREVENTIVE MAINTENANCE ASPECT / INSPECTION PROCEDURE

INSERTED GRINDING ROLLS: -

The inserted grinding rolls should be inspected during preventative maintenance schedule for

free rotation and visual inspection of wear profile.

The wear on grinding rolls, need to be measured after every 1000 hrs and based on wear

rofile if re uired then roller forwardin would also be carried out.

Time to time, wear pattern would have to be compared for roller forwarding from position 1 to 4.

BULL RING SEGMENT: -

After every 1000 hrs, the wear depth on bullring segment should be measured along with

physical inspection of crack in BRS (if any) and level of tightening on bowl.

3.ROTATING AIR PORT MAINTENANCE/INSPECTION

The Rotating Air Port should be inspected during every planned maintenance period (or if

problems arise).

From the topside, the Rotating Air Port Assembly should be inspected for erosion or physical

damage due to foreign objects. The rotating components should be inspected for erosion ordamaged vanes. RotatingAir Port segments need to be replaced only if severe damage exists.

From below, the Rotating Air Port Assembly can be inspected by opening the pyrite chamber

access door and rotating the table. The lower portion of the rotating segments should be

inspected for damage caused by foreign objects.

Any portion of the Rotating Air Port Assembly can be repaired or maintained using standard

fabrication techniques and welding procedures.


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PREPREPREPRE----REQUISITES FOR HPMS INSTALLATIONREQUISITES FOR HPMS INSTALLATIONREQUISITES FOR HPMS INSTALLATIONREQUISITES FOR HPMS INSTALLATION

The condition of bowl to be reasonably good.Renew the worn out classifier blades and its operating mechanisms to be overhauled.

Journal assembly to be properly overhauled as per OEM standards.

New bowl extension ring to be arranged.

If necessary then mill bottom liners to be replaced before HPMS system installation.

Gearbox to be properly overhauled.

Classifier reject cone and inverted cone should be in good condition.

New sets of journal guard liners to suit the life of wearing elements.

10 mm MS plate with hard facing (bend to suit the separator body curvature) is to bearranged to protect the separator body up to the mill inspection door.

Minimum Man power required for installation: -

One mill right fitter

Two welders cum cutter,

Four skilled worker

One grinder


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SECTIONAL VIEW OF HPMS SYSTEM

Documents

Operation & Maintainance Manual