analysis of failure in boiler industry

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 A case study 

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INTRODUCTIONy Apart from main equipments boiler consists

of some auxiliary equipment .

yEquipments for fuel supply , air supply , ashremoval are pulverizing mills , conveyors,induction fans,etc .

yPulverization mill is one which convert rawlignite to fine powder

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IMPORTANCE OF PULVERIZING

MILL

yPulverization is done in order to

improve the utilization of the fuelefficiently 

yreducing the unburnt fuel in the

boilers

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PULVERISING MILL

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Construction Details of Pulverizing

Millsy The mill consists of a hollow shaft on which discs with

suspended hammers are provided

y T

he hammers are made of high wear resisting materialsuch as 13% of manganese steel.

y The side walls of housing are provided access forreplacing the worn out hammer and holders

y The mill rotor is mounted on the double row self adjusting roller bearings

y Each mill is provided with emergency button nearby for stopping the mill in case of emergency.

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IDENTIFIED FAILURESy Hammer throw off.

yBearing Failure.

yRotor shaft failure.

y Wear plate failure.

yShield plate failure.

yOver loading of mills.y Knocking of bearings.

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SUGGESTIONSy Magnetic separators must be installed at intake side of the

mill to avoid the entry of foreign particles into the mills.This reduces the problem of hammer throw off.

y The conveyor belt speed must be reduced from 9.3m/sec toan optimum speed of 4.2m/sec in order to separate foreignmaterials from lignite. Because slower speed increases thecontact of lignite with magnetic separator.

y  Width of the belt over the conveyor should be increasedfrom 900mm to 15600mm as increased width of the beltensures greater contact of lignite with magnetic separator.

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y Inspection of bearings must be done at regular intervals toavoid bearing knocking at free and coupling end of themill. Also proper lubrication must be done to avoid

damages due to friction.y The cooling water line must be coated with paint to avoid

the corrosion of the pipe lines. Also the replacement of cooling pipe lines at regular intervals of time must becarried out.

y The shaft material must be surface hardened to increasethe fatigue strength. This must be done to avoid the fatiguefailure.

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y The shaft key material must be replaced with C55Mn75 whose tensile strength is 700-850

N/[m.sup.2], where as the existing one is made of C50 and its tensile strength is 650 N/[mm.sup.2].

y Preventive maintenance schedule is to bemodified and its frequency must be increased.

y T

he hollow shaft must be replaced with splinedshaft to avoid shaft puncture.

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Severity Ranking.

EFFECT RANKING

y Hazardous with & without warming 10,9y   Very high 8y High 7y Moderate 6y

Low 5,4y Minor 3y   Very minor 2y None 1

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Occurrence Ranking.

EFFECT RANKING

y  Very high: Persistent Failures 10,9

y High: Frequent failures 8,7

y Moderate: Occasional Failures 6,5,4

y Low: Relatively few failures 3,2

y Remote: Failure is unlikely 1

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Detection Ranking.EFFECT RANKING

y   Almost impossible 10y   Very remote 9y Remote 8y   Very low 7y Low 6y M

oderate 5y Moderately high 4y High 3y  Very High 2y  Very High 1

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y Author:Danalakshmi, C. Sowmya; Mohankumar,G.Article

yT ype:Report

y Geographic Code:1USA 

y Date:Jul 1, 2009

y Words:2780

y Publication:International Journal of AppliedEngineering Research I

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yThank you