VP_10 - Ball Cement Mill Monitoring, Inspection & Evaluation

Valid Practice #10

Valid Practice

for the

Production Process

#10 BALL Cement Mill

Monitoring, Inspection & Evaluation

Athens, December 2007

Ball Cement Mill

Monitoring, Inspection & Evaluation31.Safety GUIDELINES for BALL CEMENT Mill InsPection

62.Ball Cement Mill Monitoring

62.1.Flow sheet

72.2.Performance

112.2.1.Material Sampling

112.2.2.Gas measurement

112.2.3.Radiation & Convection

122.2.4.Heat Balance

142.2.5.Process flow sheet

153.Ball Cement Mill Inspection

153.1.Circuit efficiency

173.2.Separator efficiency

233.3.Grinding efficiency

243.3.1.Guideline for Crash Stop

293.3.2.Guideline for Empty Grinding Stop

314.Ball Cement Mill Evaluation

324.1.Relative mill speed calculation

334.2.Axial sampling

354.3.Ball charge calculation

374.4.Ball charge Management

374.4.1.Recommended Ball Charge Sorting Frequency

374.4.2.Ball Mill Loading

384.4.3.Ball charge record keeping

394.4.4.Ball sorting

404.5.Conclusions

Introduction

The purpose of the respective Valid Practice is to outline the parameters that should be included in a Ball Cement Mill Evaluation as well as the appraisal of the findings in order to identify the bottlenecks and suggest the necessary actions that would result in the Ball Cement Mill Optimization.1. Safety GUIDELINES for BALL CEMENT Mill InsPectionInitially, it should be noted that each Plant is responsible for the implementation of the own safety procedures and the following are suggestive general guidelines that could be included.SAFETY FIRST

The workers should be trained for the job, work always in pairs and should be equipped with the following safety equipment (Personal Protection Equipment, PPE):

Uniform Safety Boots Fireproof/heatproof Gloves Helmet Mask Safety glasses Body belt with rope Portable scaffolding with barriers Fork lift vehicle

Guideline for safe entry

Danger of unwanted mill start-up during the mill inspection. The power of the main motor should be cut off from the main power supply and the fuses should be removed. Danger of unwanted material entry to the mill interior during the mill stoppage. The power of the main raw material belt conveyors should be cut off from the main power supply and the fuses should be removed. Also the respective pipes should be blocked mechanically from the dampers or using steel sheets. Given the dusty environment inside the mill, anyone entering the mill must be wearing a face shield and goggles.

Danger of severe burning in case hot gases enter the mill. The safety damper at the hot gases duct should be closed, its power should be cut off from the main power supply and the fuses should be removed. Also the damper should be blocked mechanically. Prior to dismantling any doors and guards, make sure that the following equipment has been stopped and interlocked to prevent starting:

Mill main motor

Mill and separator fan

All feeding equipment Water spraying and grinding aid addition

Heat generator

The power supply for the above mentioned equipment must be effectively locked by means of padlocks in the MCC (motor control center) room to prevent accidental starting of the motors. The supervisors in charge of the inspection team undertaking work inside the mill must keep the key for the lock. The padlocks must remain fitted until all personnel have left the mill and all doors and guards have been remounted.

Apart from the respective Plants safety procedure, everybody should keep in mind:

Ensure Safe Isolation:

Mill drive, auxiliary drive, feed belts, etc

Physical barrier (locked closed/de-activated)

Comply with local Permit to Work procedure

Ensure Safe Access:

Consider fall hazard (e.g. access door on top of mill)

Confined space someone outside mill

Maintain ventilation to cool air space

In case of a ball mill inspection there is danger of speeding balls from the pavement due to contact with the fork lift wheels. The pavement should be properly cleaned. Mill door opening Danger of load displacement during the mill door opening. Ensure that the ball charge is leveled horizontally using the auxiliary mill drive, the mill door is at the correct location for opening and finally before opening the door ensure that the mill is not linked to the auxiliary drive. Danger of mill door falling in case of hoist malfunction. After lifting the mill door it should be placed on the mill shell.

Danger due to high dust concentration as well as high level of hot material. After opening the door the leveling of the ball charge as well as the level of hot material is checked with a flash light.

Case 1: Ball Mill entry through the top of the mill

Scaffolding and protective barrier placement: Danger of fall during getting in or out of the mill. Ensure that the scaffolding and the protective barriers are safely placed at the top of the mil shell and that they are firmly attached at least to two different points.

Ladder placement: Danger of fall during getting in or out of the mill. Ensure that the ladder is safely placed at the top of the ball charge and that it is tightly connected to the mill shell or the protective barriers. Case 2: Ball Mill entry through the side of the mill

Installation of false-door: Danger of ball charge falling. A false-door (temporary for easy in/out) is installed and the loading displacement is taken into consideration. False door removal: Danger of load displacement during the mill door opening. Ensure that the mill door is at the correct location and remove the false-door.During Inspection

Danger of faint. In case somebody faints, he should be wearing the body-belt in order to facilitate easier taking out.

2. Ball Cement Mill Monitoring2.1. Flow sheet

2.2. Performance

Monitoring the Cement Mill (CM) performance is considered the most critical aspect of a CM evaluation. The performance monitoring procedure for each cement type produced should include:

i. Checking the weigh feeders on regular basis.

ii. Operating the mill at the recommended fineness (Blaine) target set by quality control.

iii. Collecting representative spot sample of each raw material used (~30 Kg) after any change at the feeding of raw materials. All samples should be safely kept for further analysis (Moisture, XRF, wet chemical analyses & LOI).

iv. Collecting samples of the cement produced, as well as from certain locations of the grinding circuit (mill outlet, filter outlet, separator inlet, separator rejects and separator fines). All samples should be safely kept for further analysis (Moisture, fineness (Blaine & sieves), XRF/wet chemical analysis, LOI, strength analysis, Water Demand, Setting time (early & late), and Granulometry (laser) analysis)

v. Perform gas measurements (flows & temperatures). Repeat the measurements after every permanent change at the process parameters.

vi. Perform temperature measurements at the mill shell in order to calculate the heat loss due to radiation & convection. In case there is necessity to implement heat balance with boundaries that include the separator, include the separator to the shell temperature measurements for losses calculation.

vii. Record the operating parameters.

viii. Record the specific electrical energy consumption.

The following table is submitted as template in case of a mill inspection, while part of it could be also used in daily operation logging, for the recording of the CM operating parameters, specific electrical energy consumption data, gas measurements data as well as quality parameters.Technical Details

Plant.

Mill

Mill Supplier

Mill Type

Operating hours since installation

Operating hours since last ball charge refill

Operating hours since last inspection

Operating ParameterUnit

Cement Type

Datedd/mm/yy

Timehh:mm

Production rate (wet)t / h

Composition (wet)

Clinkert / h

Natural Gypsumt / h

Limestonet / h

Pozzolanat / h

Othert / h

Water content%

Water injectionlt / min

Grinding aidg/t

Iron Sulfate Heptahydrate (FeSO4.7H2O)g/t

Production rate (dry)t / h

Composition (dry)

Clinker%

Natural Gypsum%

Limestone%

Pozzolana%

Other%

Grinding aid%

Iron Sulfate Heptahydrate (FeSO4.7H2O)%

Temperature

Mill inlet temperatureC

Mill outlet temperatureC

Mill filter outlet temperature C

Pressure

Mill inlet pressurembar

Mill outlet pressurembar

Mill delta Pmbar

Mill filter delta Pmbar

Separator filter delta Pmbar

Gas Measurement

Flow at mill filter stack (wet)Nm3/h

Flow after mill (wet)Nm3/h

Flow at separator filter stack (wet)Nm3/h

Flow after separator (wet)Nm3/h

Flow fresh air (wet)Nm3/h

Flow hot gas (wet)Nm3/h

Operational Parameters

Folafon%

Separator speed%

Mill fan speed%

Separator fan speed%

Recirculation elevator%

Mill fan damper%

Recirculation damper%

Fresh air damper%

Energy Consumption

Mill motorKW

Mill separatorKW

Mill fanKW

Separator fankW

Mill bucket elevatorKW

Specific Electrical Energy Consumption (SEEC)

Mill motorkWh / t

Mill classifierkWh / t

Mill fankWh / t

Separator fankWh / t

Mill bucket elevatorkWh / t

Mill motor, separator, mill fan & separator fankWh / t

TotalkWh / t

Quality ParametersUnit

Gypsum moisture%

Limestone moisture%

Pozzolana moisture%

Other moisture%

Blaine

Mill outletcm / gr

CM Filter outletcm / gr

Separator Filter outletcm / gr

Separator inletcm / gr

Separator rejectscm / gr

Separator finescm / gr

Final productcm / gr

Corrected Final product Blaine (w/o effect of additives)cm / gr

Fineness (Residue at 90m)%

Fineness (Residue at 45m)%

Water Demand (WD)%

Setting Time (initial)min

Setting Time (Final)min

Strength (N/mm)1day

2days

7days

28days

LOI%

IR%

SO3%

Free CaO%

SiO2%

Al2O3%

Fe2O3%

CaO%

MgO%

K2O%

Na2O%

Granulometry Analysis, Sieve

Cumulative Passing, %

1%

1,5%

2%

3%

4%

6%

8%

12%

16%

24%

32%

48%

64%

96%

128%

192%

Rosin - Rammler

Slope, n#

d m

Production between 3 - 32 m%

Tromp curve

Separator efficiency as recovery of fines, Uf%

Circulation load based on laser#

d50%

d75%

Kappa (k), slope of the curve in the interval 50%-75%#

Cut size, particle size corresponding to the Tromp value 50%%

By-pass, Tromp value at the lowest point of curve%

Separator efficiency as reduction in power consumption, Vs (32 m sieve)

Circulation load#

As reduction in power consumption, Vs%

Apart from the above, on monthly basis the following tables should be completed: regarding operation:

Mills Stoppages

Available hoursh

Actual operating hoursh

Duration of Annual Maintenanceh

Duration of Strategic stoppages (for example Saturation etc.)h

Duration of stoppages because of Other external reasons (for example Power failure etc.)h

Downtime

Downtime because of Operational reasonsh

Downtime because of Mechanical reasonsh

Downtime because of Electrical reasonsh

Downtime because of Planned maintenance(excluding annual maintenance)h

Total Downtimeh

Grinding media consumption (including refilling and new load)

5 year historyg/tCement produced

1 year historyg/tCement produced

regarding quality:

Quality ParametersUnitMONTHLY AVERAGE

CEMENT TYPE

Composition (dry)

Clinker%

Natural Gypsum%

Limestone%

Pozzolana%

Other%

Grinding aid%

Iron Sulfate Heptahydrate (FeSO4.7H2O)%

Blaine

Fineness (Residue at 90m)%

Fineness (Residue at 45m)%

Water Demand (WD)%

Setting Time (initial)min

Setting Time (Final)min

Strength (N/mm)1day

2days

7days

28days

LOI%

IR%

SO3%

Free CaO%

SiO2%

Al2O3%

Fe2O3%

CaO%

MgO%

K2O%

Na2O%

regarding ball charge management:

Ball charge

1st compartment2nd compartment

Amountt

Specific weightt/m3

Composition

90mm

80mm

70mm

60mm

50mm

40mm

30mm

20mm

Ball charge compensation

Last date

Amountt

regarding maintenance cost:

The maintenance cost (including spare parts and man-hours cost) should be calculated and attributed per mill.

The logging of the parameters as well as the data warehouse management should be automated and implemented in the Plant everyday procedures.

2.2.1. Material Sampling

As far as the sampling procedure is concerned it is vital to know the Sampling Points before sampling is needed. The samples are being collected only be those assigned by plant personnel in order to know the locations (e.g. product, circuit samples).

Before starting the sampling procedure the access for sufficient size (and sampler) should be verified. There safety for access (heights, steps, guard rails, etc) should be assessed whereas the exposure risk to pressure/suction, heat, dust, etc should be checked.

Finally, all participants should have suitable equipment (PPE, containers, sample devices, etc) and be aware of moving parts (e.g. rotary valves, screw conveyors). Note that when in Doubt ASK!

2.2.2. Gas measurement

In order to calculate the flows at the grinding circuit, the temperature and the pressure has to be measured. Temperature is being measured using thermocouples while the pressure (differential and static) is being measured using Pitot tube. The flows should be depicted at the relevant process flowchart.

2.2.3. Radiation & Convection

In order to evaluate the heat transfer, the heat losses which are being attributed to radiation and convection has to be verified. In order to calculate the heat loss, the temperature at the surface of interest is being measured and following the heat loss is being calculated.

2.2.4. Heat Balance

A heat balance is being conducted in order to evaluate the heat transfer and calculate the dew point. The mill should operate under steady conditions throughout the test. The following steps are being followed:

Define system boundaries to evaluate heat inputs and outputs.

Define test duration.

Define mill operating conditions.

Define type of measurements to be carried out (e.g. temperature, air flows, etc).

Define parameters to be measured.

Define position and frequency of measurements.

Define inputs from panel to be recorded.

Define material sampling methodology.

Prior to testing, make sure that everyone involved has fully understood the test procedure (what, when and how). Prepare logsheets.

Make sure that the electronic data recording systems are operating.

Calibrate and check the proper operation of all instruments (portable and stationary).

Reference Temperature: i.e. 20 C.

The dew point can be calculated using either the wet bulb temperature method or gas measurement and applying the respective chart from the bibliography (i.e. FLS manual).

A typical is example is presented hereafter:

2.2.5. Process flow sheet

It is suggested to present the process data in flowcharts per CM and per cement type in order to have better control compared to the every day operation, as following:

Based on the above information, it is possible to provide a clear picture of the CM performance and evaluate it compared to the typical values in terms of: Throughput and Specific Electrical Energy Consumption (SEEC). The production rate and the SEEC per cement type produced compared to the design values and the typical references (benchmarks, other mills).

Cement quality. The contribution of the additives at the Blaine value, the relationship between the separator and the mill fan speed and the Rosin-Rammler (RR) slope as well as the effect to the water demand and the strength profile.

Mass & Energy (heat) Balance. Based on the results, the weighing feeder accuracy as well as the heat demand and the amount and location of false air. Utilization & reliability. Even though, utilization is subject to the sales demand (quantity) and scheme (peak and saturation), reliability is judged by the reliability (run) factor which should lie above 90%. Ball charge (composition) and wear profile (g/t).

It should be noted that even though the monthly performance (utilization, reliability, wear) is judged based on average values, the monitoring of the hourly performance (throughput, SEEC) as well as any additional measurements and evaluation should be done during stable conditions.3. Ball Cement Mill Inspection3.1. Circuit efficiency

The evaluation of the circuit efficiency involves sampling at specific locations of the circuit. In particular, the necessary samples include:

1. Mill outlet

2. CM filter outlet

3. Separator inlet

4. Separator rejects

5. Separator fines

6. Separator filter outlet

7. Final product

The above locations should be sampled under stable operating conditions and at least three times per location. Also is should be noted that ideally all sampling of the above locations should be done at the same time.

Based on the sieve and Blaine values of the mill outlet and the filter outlet we calculate the percentage of the separator feed that comes from the mill outlet. Also, using the same principle we can calculate the amount of the separator filter returns to the final product.

Based on the sieve and Blaine values of the mill outlet and the filter outlet we calculate the percentage of the separator feed that comes from the mill outlet. Also, using a mass balance we can calculate the amount of the separator filter returns to the final product.

As far as the circulation loading is concerned, it is a function of:

Product fineness.

Chamber I ability to prepare the feed for chamber II.

In-mill fineness (mill exit Blaine) and hence the degree of particle agglomeration and coating.

Separator loading and hence separation efficiency.

Grinding efficiency.

Each mill has its optimum circulation loading which is determined from operation at different total feed set-points and will be higher for large diameter mill, large separator and use of additive.

3.2. Separator efficiency

Major part of the cement mill evaluation regarding a ball mill circuit is the evaluation of the separator efficiency.Based on sieves analysis:

Separator efficiency as recovery of fines

Separator efficiency measured as Recovery of fines is calculated according to the expression:

Uf=100*(100-Rf)/(100-Rm)/C [%]

The method can be used for comparison between separators operating at the same circulation factor.

Separator efficiency as reduction in power consumption

The separator efficiency as reduction in power consumption (Vs) is calculated according to the expression:

Typical values for efficiency, Vs, relating to residues in the interval 32m-45m:

1st generation separators:

CV, Heyd, Sturtevant

Vs:=25%-40%

2nd generation separators:

REC, Wedag, ZUB

Vs:=40%-60%

3rd generation separators:

Sepax, O-Sepa, Sepol

Vs:=75%-85%

Based on CILAS (laser) analysis of the above samples the Rosin Rammler Curve as well as, the Tromp Curve are constructed:

The Rosin Rammler Curve is the logarithmic chart of the particle size distribution where the critical parameters are:

Slope (usually varying from 0.8-1.2; increases with the technology applied)

Limiting grain size / characteristic diameter, d [m] for the RR value of 36.8% (typically 10-30m)

Fraction of material between 3mm and 32mm

Rosin Rammler

The Tromp curve values are calculated according to the expression:

T=100*(C-1)/C*Rg/Rm

where, for the interval representing the particle size:

Rg is the percentage of return material

Rm is the percentage of material leaving the mill

The Tromp curve resulting from the Tromp curve values shows for each individual particle size of the separator feed the percentage which gets into the fine fraction.

Tromp Curve

The main parameters of the Tromp Curve, are depicted hereafter:

i. Cut size:

ii. Kappa (Imperfection) slope:

iii. By-pass:

The above are being compared to the reference values:

Reference Values

Product Blainecm2/g3.800

Mill Outlet Blainecm2/g