process control of lurm mill

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LUCEEN POWDER TECHNOLOGY

PROCESS CONTROL OF LURM MILLS

1.0 PREFACE

This document is intended used only as a guideline for descriing asic conce!t of

the !rocess control of the LURM "ertical roller mill es!ecially for the limestone

grinding system# The !articular !rocess control system should e designed according

to the indi"idual condition#

$ safe and economic o!eration is not only de!endent on the condition of the mill itself

as %ell as of !eri!heral e&ui!ment such as feeding system' system fan' ag filter' hot

gas generator' !roduct con"eying system and ductings in mechanical res!ect utalso the condition of the !rocess control measures in electrical res!ect#

2.0 MILL PERFORMANCE INDEXES

2.1 Mill Feeding Rate

The mill through!ut should e controlled constantly in continuous %ith suitale

incremental mass rate until reach a ma(imum rate for asoring the ma(imum mill

motor horse!o%er ut o!erating in a safe and reliale long)term condition and

!roducing the &ualified !roduct according to the &uality control standard of the!roduct#

The mill feed mass rate is measured y a measuring scre% or a elt)%eighing feeder

under the feeding ho!!er and controlled y the mill differential !ressure#

The ma(imum lum! si*e of the feed shall e maintained according to the outside

diameter of the grinding rollers' the gri!!ing angle of the material ground and the

thic+ness of the grinding ed#

The segregation of the fed material during the dosing !rocess should e asolutely

minimi*ed for +ee!ing the e"en feed lum! si*e distriution for ma(imi*ing the mill

through!ut and minimi*ing anormal mill "iration#

Furthermore foreign matter such as iron and metal !ieces should e se!arated

efore entering the mill !ro!er for a"oiding damage of the grinding elements#

In case of too lo% or interru!ted feed mass flo%' the grinding rollers shall e lifted if

necessary#

2.2 Fineness of Finish Pod!"t

The fineness of the finish !roduct' re!resenting not only the s!ecific surface area ut

also the re&uired !article si*e distriution' is mainly decided y,

-rinding !ressure


LUZIM POWDER ENGINEERING CO., LTD

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Nov 12, 2004Frank Lu


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-as flo%

Classifier s!eed

In general the finer !roduct %ith the higher s!ecific surface area is otained y,

.igher grinding !ressure

Lo%er gas flo%

.igher classifier s!eed

Normally the fineness of the !roduct is controlled y the classifier s!eed only %hile

the mill o!erates at the o!timum grinding !ressure and the o!timum gas flo% rate'

%hich %ere otained during the commissioning and should e +e!t constant during

normal o!eration#

In the mean%hile' the circulating load %ithin the mill influences the !article si*e

distriution# Increasing circulating load %ithin the mill y ad/usting the follo%ing!arameters generates the narro%er !article si*e distriution,

.igher classifier s!eed

Lo%er grinding !ressure on the material ed

.igher gas flo% rate through the mill

In other %ords' if %e inter!ret from the stand!oint of the internal circulation load

%ithin the mill' %e could oser"e that,

The higher grinding !ressure results to a lo%er circulation load and %ider !article

si*e distriution# Lo%er grinding !ressure results to a higher circulation load andnarro%er !article si*e distriution#

Moreo"er if the gas flo% rate through the mill is increased' thus leads to a higher

circulation load and !ro"o+es a shar!er slo!e in the RRS0 chart# On the

contrarily if the gas flo% rate through the mill is decreased' thus leads to a lo%er

circulation load and !ro"o+es a flatter slo!e in the RRS0 chart#

1ith the same reason' if the classifier s!eed is faster' naturally increase to a

higher circulation load thus may !ro"o+es a higher 0laine "alue as %ell# On the

contrarily if the classifier s!eed is slo%er' naturally decrease to a lo%er

circulation load thus may !ro"o+es at lo%er 0laine "alue#

2.# Moist!e Content Of Pod!"t

There is no need for installing an e(tra hot gas source %hile the moisture content of

the feed material is elo% around 23 ecause the heat generated during grinding

shall dry the material to an acce!ted le"el# If the moisture of the material e(ceeds a

certain "alue' then the mill inlet tem!erature should e ad/usted y the other heat

in!ut from a hot gas generator or other heat source according to the moisture content

of the feed material#

The moisture content of !roduct is mainly influenced y the follo%ing !arameters,



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-as tem!erature at mill outlet

-as tem!erature at mill inlet

-as flo% rate and tem!erature from recycling

.eat in!ut from hot gas generator#

In order to !re"ent from clogging of the ag filter' the o!erating tem!erature of the

mill e(haust gas should e aout 45 ℃ ao"e the de% !oint#

2.$ S%e"ifi" Po&e Cons!'%tion

The !o%er consum!tion of the grinding system is the +ey issue of the !roduction cost

of the grinding !lant# The main contriution of the !o%er consum!tion consisting of,

Mill

Classifier

System fan $u(iliary e&ui!ment such as feeding and con"eying system#

The o!timum "alue of the s!ecific !o%er consum!tion shall e otained through

o!timi*ation of the control !arameters of the grinding system including,

Mill gas flo% rate

Mill differential !ressure

Mill inlet gas !ressure

-rinding !ressure

Classifier s!eed -rinding ed thic+ness

Mill "iration le"el

#.0 MILL CON(ROL PARAME(ERS

#.1 )as (e'%eat!e At Mill Inlet

Unless s!ecial design is made' the tem!erature should not e(ceed 655℃ for

!rotecting main gearo( and grinding rollers from o"erheating# Other%ise a s!ecial

construction shall e made y a heat resistance design for the mill#

#.2 )as (e'%eat!e At Mill O!tlet

The gas tem!erature at mill outlet is a measurement of the drying !rocess

accom!lished in the mill# The mill outlet tem!erature can e ele"ated y increasing

the recycling gas or su!!lementary hot gas and also can e cooled do%n y o!ening

the tem!ering air# Normally the mill should e sto!!ed automatically at 245℃ for

!re"enting the earing and sealing of the grinding rollers from o"erheating# S!ecial

cooling system %ith heat resistant sealing shall e ado!ted should the tem!erature is

higher than the ao"e)mentioned "alue#

#.# Mill )as Flo& Rate



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The gas flo% can e measured ehind the ag filter and controlled at constant "alue

y ad/usting the o!ening of the gas dam!er and7or the rotating s!eed of the system

fan during commissioning#

The gas flo% should e al%ays +e!t constant and inde!endent of the fluctuations in

!ressure and tem!erature of the system# The gas flo% through the grinding system is

a comination of,

Fresh air

.ot gas

False air

E"a!orated %ater

Recycling gas

Inade&uate gas flo% through the mill causes a decrease of the mill ca!acity ando!erating disturances# .o%e"er e(cessi"e gas flo% causes higher %ear %ithin the

mill resulting uneconomical maintenance %or+ and !o%er consum!tion#

#.$ Mill Diffeential Pess!e

The mill differential !ressure measured as a difference et%een the static !ressure at

mill inlet and mill outlet re!resenting a loading condition of the mill#

The differential !ressure of the mill de!ends on the follo%ing !arameters,

Feed mass rate

-as flo% rate -rinding !ressure

Classifier s!eed

Usually only the mill feed mass flo% rate has a decisi"e influence on the differential

!ressure %hile gas flo% rate' grinding !ressure and classifier s!eed are maintained

at the similar condition according to the !re)ad/ustments during !re"ious o!eration

unless the characteristics of the ra% material such as the grindaility of the material

has een changed#

1hen the differential !ressure is too high' %hich indicates the mill is in o"erloading#

The mill is su/ect to se"er "iration and higher re/ect amount resulting an

uneconomical o!eration#

On the contrarily' %hen the differential !ressure is too lo% %hich indicates the mill is

in !artial loading and is o!erated in also an uneconomical condition# 1hen the

differential !ressure is reduced to the certain limit "alue such as 853 ) 953' the feed

%ill e sto!!ed# The mill shall e started again %hile the normal "alue is restored#

#.* )inding Pess!e

The grinding !ressure e(erted y the grinding rollers against the "ertical is a decisi"e

factor for the efficiency of the communition !rocess#



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.o%e"er too high !ressure causes higher anormal %ear on the grinding elements'

rough mill o!eration and higher !o%er consum!tion#

.o%e"er too lo% grinding !ressure reduces the mill ca!acity and changes in the

fineness of the !roduct resulting an uneconomical o!eration#

The relationshi! et%een the grinding !ressure and the corres!onding nitrogen

!ressure in the accumulator' re!resenting the s!ring constant of the hydraulic

system' %ill e ad/usted during commissioning# 1hile the !ressure of the hydraulic

system dro!s elo% a certain limit the mill %ill sto!# $s the rule of thum' the filling

!ressure of hydraulic accumulator should e recommended as follo%s,

The ma(imum filling !ressure of hydraulic accumulator : ;53 of the minimum

o!erating hydraulic !ressure

The minimum filling !ressure of hydraulic accumulator : 483 of the ma(imumo!erating hydraulic !ressure

#.+ Mill Inlet Pess!e

The mill inlet !ressure should e maintained at constant "alue# The static !ressure

measured at the mill inlet gas duct is influenced y the gas flo% entering into the mill

y mean of,

Recycling gas dam!er

.ot gas generator

Fresh air inlet dam!er Too high negati"e !ressure efore the mill increases the energy consum!tion of the

mill system fan#

.o%e"er too lo% negati"e inlet !ressure influences the steady gas flo% %ithin the

system and leads the grinding system into disturances#

#., Mill -iation

The mill "iration le"el' usually measured at the in!ut shaft of the gearo(' is a!!lied

for !rotecting the +ey mechanical com!onents from damage# The o!timum condition

of the mill shall e achie"ed y otaining the ma(imum mill through!ut in accordance

%ith the &ualified !roduct standard ut in an acce!tale "ertical mill "iration le"el#

The mill motor should e sto!!ed %hile the mill occurs e(cessi"e "iration for

securing the long)term safety of the e&ui!ment#

#./ )inding ed (hi"ness

The grinding ed thic+ness' defined as the minimum ga! et%een the grinding rollers

and the grinding tale during the o!eration' is ad/ustale y the height of the dam

ring the grinding !ressure and mill circulation load during commissioning#

The thic+er grinding ed gi"es narro%er !article distriution ut results %ith higher

!o%er consum!tion and softer o!eration#



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Ne"ertheless the thinner grinding ed gi"es %ider !article distriution ut %ith lo%er

!o%er consum!tion and rougher o!eration#

The o!timum grinding ed thic+ness shall e decided during commissioning#

$.0 PROCESS CON(ROL LOOP

-enerally s!ea+ing' the grinding system can e installed %ith the follo%ing PI<

control loo!,

For cooling !rocess' the fresh air dam!er or the amount of the %ater and

grinding aid solution controls mill outlet gas tem!erature#

For heating !rocess' the urner of the hot gas generator or the amount of steam

"a!or controls mill outlet gas tem!erature#

The rotating s!eed or the gas dam!er of the system fan controls gas flo% ratethrough the mill#

The recycling gas dam!er controls mill inlet !ressure#

The mill differential !ressure or the +ilo%atts of the mill motor controls feed mass

flo% rate#



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process control of lurm mill

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