Cement Mill Control DB MS

BLUE CIRCLE TECHNICAL CENTRE

CEMENT MILL CONTROL DAVID BAIRD + MARK STOERKER

CEMENT MILL CONTROL AIMS OF THIS PRESENTATION… • To describe the various Control Loops available for automatically controlling Cement Mills.

• To identify the benefits to be gained. •To establish “ Where we are at present ”. •To ask the ?-”Where do we go from here ? ” •To help you to develop an Action Plan to improve mill control within HBM.

OPEN CIRCUIT CEMENT MILL CONTROL LOOPS

Open Circuit Mill Controls Clinker Gypsum Other

Mill outlet temperature Water injection

Feed TPH

Mill sonic

Chamber 1 exit temperature

Cement SSA m2/kg and temperature

CLOSED CIRCUIT CEMENT MILL CONTROL LOOPS

CLOSED CIRCUIT CEMENT MILL CONTROL LOOPS AUTOMATIC LOOPS…

• Constant Feed Rate-( tph ) •Ratio control of Feed Components-( % Clinker.Gypsum,MAC) •Total Feed Control (Rejects and fresh feed). •Sonic control (Folaphone)- Chamber 1 noise level. • Separator (H.E.S.) -airflow control. •Milling temperature control-( water injection % -C1+2) •Power -Mill Motor and Bucket Elevator KW.

ABERTHAW CM 10 - AUTO + MANUAL CONTROL LOOPS

MILL FAN DAMPER

LIMESTONE RATIO CONTROL

CEMENT MILL CONTROL LOOPS 1 CONSTANT FEEDRATE AND RATIO CONTROL OF FEED COMPONENTS • Accurate weight and Ratio control of the clinker /

gypsum / Limestone / MAC / Pozzolan is essential if we are to avoid….

•STEP changes/variability in cement quality. •STEP changes in mill performance / stability due to feed grindability changes.

Effect of Gypsum, Limestone + Pozzolan on Cement mill performance

● ● ● ● ● ●

1% SO3 = 1% Gypsum = 1% Gypsum = 1% Limestone = 1% Limestone = 1% Pozzolan =

+ 30 m2/kg Surface Area + 5% Production + 12 m2/kg Surface Area -2.5% B.C.I Grindability +2%Production at constant SSA. -0.4 to -0.67 % B.C.I.Grindability

CLINKER CHEMISTRY VARIATIONS-AFFECT ON MILL PERFORMANCE consumption and Chemistry for two closed circuit mills

Mills under Automatic Total Feed Control

C3S

No 2 Mill SRC

C3S

C2S

Nº1 Mill (OPC)

C2S Nº1 Mill (OPC)

L.S.F.

Nº2 Mill (SRC)

LSF Mill Only Kwh/t

+5% C2S =+ 1 kWh/tonne

LSF

32.5

33.0

33.5

BLUE CIRCLE TECHNICAL CENTRE

ESTIMATING THE COSTS OF POOR MILL CONTROL

S S A - m 2/kg

C em en t S S A V ariatio n s

460 420 380 340 300 T im e T a rg e t

Control +/- m2/kg

G o o d C o n tro l

Range

P o o r C o n tro l

kWh/tonne Avg. kWh/t

Poor

40

340 – 420 37.0 – 50.8

43.9

Good

10

340 – 360 37.0 – 40.3

38.6

Savings

5.3 kWh/t

Overgrinding - Power Penalty When we overgrind, we waste power in Chamber 1: 2

m / kg Max Chamber 1 Penalty Variability m2/ kg kWh/tonne kWh/tonne 0

340

9.0

0

+/- 10

350

9.4

0.4

+/- 40

380

10.6

1.6

CEMENT MILL CONTROL LOOPS SOUND CONTROL-CHAMBER 1 • Can act as protection against overfilling Chamber 1

by cutting feed if noise level drops due to other factors ie blockages within the mill or at the mill discharge. Feed cuts off at fixed sound level.

•A modification used at Aberthaw is to use Sonic to input to the Total Feed Control Loop. This forward feeds the effects of gradual build up in filling level.

2

Folaphone (Mill Sonic) Location 0.5 m from end of mill Chamber 1

Sensor 25 mm from shell

This bloody thing will never work!

Mill centerline or below

Direction of Mill Rigid stand

CEMENT MILL CONTROL LOOPS 3 MILLING TEMPERATURE CONTROL

•Essential for Cement quality control and to avoid Mill internal coating problems. •Control of Chamber 1 water injection should be based upon material temperature at Intermediate Diaphragm

•Mill outlet temperature control should be based upon the material temperature not gas temperature due to the effects of inleaking air.

CEMENT MILL CONTROL LOOPS 3 MILLING TEMPERATURE CONTROL (2)

•With a High Efficiency Separator-install a gas recycle system with 2 damper controls (fresh air and recycle) to control milling temperatures.

•Control of mill airflow is normally manual. Check mill

exit gas dew point temperature and increase mill airflow if high water injection is used.

•Mill outlet material temperature control should be typically 110 - 115 C to avoid Flash/False set .

Mill Temperature Control Water injection chambers 1and 2

Thermocouple in diaphragm

Thermocouple 90o C

Pickup transmitter

Inleak 15o C

Thermocouple 140o C

CEMENT MILL CONTROL LOOPS 4 TOTAL FEED CONTROL

•Essential for maintaining a constant mill filling level to achieve optimum grinding efficiency (optimum voids filling/powder loading-see C.T.C notes).

• The separator characteristics remain more constant

with constant feedrate thus avoid large variations in Cut size and Recirculating load.

•Typical relationship:-

.PLUS 1.4 tph Rejects = minus 0.6 tph Fresh

Feed Flow

Overfilled / Underfilled Mills OVERFILLED Poor Grinding Efficiency High Voidage Filling Noise Level Low Coating problems

UNDERFILLED Poor Grinding Efficiency Low Voidage Filling Noise Level High Risk of high wear and media/liner breakages

CLOSED CIRCUIT CEMENT MILL CONTROL SOME PROBLEM AREAS

POTENTIAL CONTROL PROBLEMS • Inaccurate weigh feeders. Rejects flow spiking. •Undersized Separators with non linear characteristics. •Undersized Separator fan. •Excessive inleaking air over mill (>30%) and Separator (>10%) dust filter plants.

•Undersized Bucket Elevator limiting circulating load. •Poor airslide design causing uneven feed+rejects flow.

• Hold up inside mill due to nibs/poor internals causing

surging.

POTENTIAL PROBLEM AREAS

Separator/Fan

Elevator/Airslides Mill Fan

Mill Dust filter

Main filter

Weigh feeders

Cement

To storage

Mill Internals

A VIEW INSIDE- WHAT CAN COMPLICATE AUTOMATIC CONTROL Chamber 2 Chamber 1

Material Surges Build up of Nibs at diaphragm

Material Surges

PROBLEM AREAS-MILL INTERNALS WORN LINERS

GAPS IN SECTIONS

WORN/BROKEN SLOTS ALLOW NIBS TO ENTER CHAMBER 2

THE FUTUREWHERE DO WE GO FROM HERE?

POSSIBLE OPTIONS FOR MILL CONTROL ● ● ● ● ●

ABB LINKMAN - NORTHFLEET MAGOTTEAUX “GO CONTROL”- COOKSTOWN POLYSIUS / FLS MILL EXPERT SYSTEMS ARTIFICIAL NEURAL NETWORK SYSTEMS,PANTEK ETC. - BOWMANVILLE ? IMPROVE ON LINE ANALYSIS-SSA/PSD - MALVERN , SO3, - ITECA, FLS LAB X 3000. 45 um ,ETC

WHAT NEW / OLD PROBLEM AREAS WILL WE FACE WITH THESE NEW SYSTEMS? ● ● ● ●

Level of reliability e.g. on line P.S.D. Analysers and Sampling systems. Needs a “Works Champion”. Needs commitment and capital to have the best chance of success. Expert system must be able to control process-e.g. avoid artificial limitations imposed by airslide/elevator/separator speed/mill internal limitations etc.

YOUR TASK DEVELOP AN ACTION PLAN TO IMPROVE AUTOMATIC CEMENT MILL CONTROL WITHIN H.B.M. BASE YOUR PLAN ON A CLOSED CIRCUIT MILLING SYSTEM.

HOW MUCH DOES THE LEVEL OF CONTROL AFFECT MILL PERFORMANCE?