Best_practice_guidance_paper_evaluation_ball_mill_grinding_plants_2016_02.pdf

HeidelbergCement Group Guidance Paper

Process Evaluation of Ball Mill Grinding Plants

Edition:

02

Valid as of:

2016-03-31

Process owner:

EG Grinding

Guidance Paper on Process Evaluation of Ball Mill Grinding Plants

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HeidelbergCement Group Guidance Paper Process Evaluation of Ball Mill Grinding Plants

Edition:

02

Valid as of:

2016-03-31

Contents 1

HEALTH AND SAFETY ........................................................................................................ 3

2

FUNDAMENTAL DATA ON THE TEST /TARGET ............................................................... 4

3

SCHEME OF A TYPICAL BALL MILL GRINDING PLANT................................................... 5

4

PLANT EXAMINATION – SITE INSPECTION ...................................................................... 6

5

RECORDING OF OPERATING DATA .................................................................................. 8 5.1

GENERAL OPERATING DATA ............................................................................................. 8

5.2

PRESSURE AND TEMPERATURE MEASUREMENTS .............................................................. 9

5.3

AIR/GAS QUANTITY MEASUREMENT .................................................................................. 9

5.4

TEMPERATURE OF THE MATERIAL ..................................................................................... 9

6

SAMPLING PROCEDURE .................................................................................................. 10 6.1

COMPLETE CIRCUIT SAMPLING ....................................................................................... 10

6.2

METER SAMPLING DURING INTERNAL BALL MILL INSPECTION ........................................... 13

7

ASSESSMENT OF PLANT DURING STOP CONDITION ................................................... 14

8

PROCESS EVALUATION ................................................................................................... 16 8.1

SEPARATOR ASSESSMENT ............................................................................................. 16

8.1.1 8.2

9

Separation curve: TROMP CURVE .......................................................................... 18

INTERNAL MILL INSPECTION............................................................................................ 25

8.2.1

Preparation of Grinding Diagram .............................................................................. 25

8.2.2

Determination of the Filling Degree .......................................................................... 26

8.2.3

Calculation of Grinding Media Quantity .................................................................... 28

8.2.4

Calculation of Power Consumption of Mill Tube ....................................................... 28

8.2.5

Determination of the Average Ball Diameter and Classifying Effect in Chamber 2 ... 29

ASSESSMENT OF MILL DRYING PLANTS ....................................................................... 30 9.1

BALANCE PREPARATION................................................................................................. 31

9.1.1

Air Quantity Balance ................................................................................................ 32

9.1.2

Heat balance ............................................................................................................ 34

10

LITERATURE, STANDARDS AND GUIDELINES .............................................................. 38

11

APPENDIX .......................................................................................................................... 38

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HeidelbergCement Group Guidance Paper Process Evaluation of Ball Mill Grinding Plants

Edition:

02

Valid as of:

2016-03-31

1 Health and Safety The auditing team (including all staff) should be familiar with normal cement manufacturing hazards and special risks in the cement, raw and coal grinding departments. All relevant local and Group safety guidelines and instructions should be followed. Each plant is different and there may be plant specific safety regulations. They should be requested before and to follow as well. Lockout procedures must be in place and rechecked before any equipment internal inspection. Individual risk assessments are necessary if existing plant procedures are not sufficient enough. Special attentions for all kind of ducts and roofs are needed for any kind of threat from falling coatings or objects. Some lockouts need special attention. In principle and as safe practice of good lockout procedure, the lockout should be checked and tested. For example the lockout of auxiliary drives should be checked before with the onsite switch AND in control room. The reason for such double testing is that the control room operator might have given for the test local control to the wrong motor. Then, the motor would not start by pressing the start button at the onsite switch wrongly assuming that the test was successful. All safety relevant issues should be followed up. But some locks need special attention (only as example):       

Mill main drive Mill auxiliary drive All connected fans (mill fan, separator fan….) Separator rotor drive Tightness and lock of hot gas flaps at raw mills Hot gas generators Feed and reject belts, screw conveyors….

In general all drives, which might have an impact on the specific working area during the audit has to be locked. For example a separator rotor drive might create huge hazard while entering the separator but no hazard while entering the mill. In case of any doubts please carry out a proper risk assessment of the situation. All measurement and sampling points should be safely accessible and all measurement and sampling procedures must be ensured for safe audits and inspection of plant.

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HeidelbergCement Group Guidance Paper Process Evaluation of Ball Mill Grinding Plants

Edition:

02

Valid as of:

2016-03-31

2 Fundamental Data on the Test /Target An examination for the assessment of a ball mill grinding plant should allow carrying out all measurements and samplings during a stable plant operating state. A reliable test requires a period of at least 8 hours. A grinding plant is to be examined, 

When the plant is new (to record the fundamental state) or a mill test has not been carried out at the plant so far,



If deviations from the expected grinding capacity occur,



As routine controls, approx. once a year to assess the actual state of the plant.

Target: the test is primarily to show the actual state of the plant operations and is part of current control. Furthermore, it helps to create the basis for optimization measures. The following overview shows the details with the procedure of a mill test. If possible, the test should be divided into the following periods:



Site inspection

At first, only a visual and audible control, partly as well by recording visible plant settings on site



Recording of the operating data

Includes:  Verification of the control room data  Assessment of the actual setting



Measurements at site

 Pressure  Temperature  Special features



Sampling

All around samples



Recording of the actual state

Equipment revision at plant stop

Important: the control room protocol during the test period should be used. Additionally, all relevant data is to be recorded in hourly intervals.

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HeidelbergCement Group Guidance Paper Process Evaluation of Ball Mill Grinding Plants

Edition:

02

Valid as of:

2016-03-31

3 Scheme of a Typical Ball Mill Grinding Plant       

Feeding station for components (with scales) Roller press (optional) Ball mill Static separator; preliminary separator (optional) Mill filter Dynamic separator with filter (or cyclones + filter) Auxiliary equipment for material transport

A device list of the plant equipment is generally to be prepared, which includes the relevant data (dimensions, parameters) of the installed equipment.

Picture 1: Scheme of a typical ball mill grinding plant with separator dedusting in filter

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HeidelbergCement Group Guidance Paper Process Evaluation of Ball Mill Grinding Plants

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02

Valid as of:

2016-03-31

Picture 2: Scheme of a typical grinding plant with separator dedusting in cyclones (+filter)

4 Plant Examination – Site Inspection Feeders area    

State of the weight equipment; when was the last calibration/control? Is a control necessary? Material flow conditions; homogeneous discharge without segregation; if not, which kind? Grinding aid addition; constant input; yes/no State of the conveying equipment

Roller press      

Regular running without unusual change of the grinding gap Unusual sound Unusual vibration Roller gap (right/left) Hydraulic pressure (right/left) Leakage, e.g. hydraulic cylinder

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HeidelbergCement Group Guidance Paper Process Evaluation of Ball Mill Grinding Plants

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02

Valid as of:

2016-03-31

Ball mill     

Audible control during running period over the mill length; protocol on unusual sound with meter number (chamber 1 and chamber 2) Visual control Dust emission or similar Material spillage at the inlet Control of well running valves at the mill outlet (discharge valve!) functioning

Static separator   

Position of the guide vanes Control of discharge valve on well running and functioning Leakages (dust/air)

Mill filter  

Leakage etc. (false air) Cleaning

Filter, fan  

Setting (inlet vane control system, damper or speed of rotation) Vibration

Dynamic separator     

Position and number of counter blades Position of the guide vanes Well running of discharge valves Sound/vibration Leakages

Separator/fan  

Setting (inlet vane control system, Flap) Vibration

Separator filter Best_practice_guidance_paper_evaluation_ball_mill_grinding_plants_2016_02.docx

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HeidelbergCement Group Guidance Paper Process Evaluation of Ball Mill Grinding Plants

 

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Valid as of:

2016-03-31

Leakage etc. (false air) Cleaning

Cyclones  

Well running of discharge valve Operation of discharge valve

Auxiliary equipment  

Bucket elevators Conveying equipment etc.  Control on obvious damage; audible control as well  Vibration etc.  Leakage

5 Recording of Operating Data 5.1

General Operating Data Power consumption of:     

Roller press Ball mill Separator (including fan) Mill filter fan Auxiliary equipment, with kWh meter (locally)

Speed of rotation Separator (min.-1 or %)  Rotor/ Counter blades  Mill filter fan  Speed of rotation (min.-1 or %)  Damper position/inlet vane control system 

Throughputs   

Feed components, continuously Grits, actual value Circulating load, actual value from the control room

In general: the control room protocol is to be considered during the test period! All relevant data is to be recorded in hourly intervals! Best_practice_guidance_paper_evaluation_ball_mill_grinding_plants_2016_02.docx

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HeidelbergCement Group Guidance Paper Process Evaluation of Ball Mill Grinding Plants

5.2

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2016-03-31

Pressure and Temperature Measurements Recording of the static pressure with a U-tube as well as of the gas temperature at the following spots:      

Before ball mill After ball mill/before static separator After static separator Between filter and fan After fan Dynamic separator; pressure difference of the fan

Further pressure and temperature curve   

5.3

Before separator filter/cyclone After separator filter/cyclone After separator filter fan.

Air/Gas Quantity Measurement Measurement of:   

5.4

Mill exhaust gas quantity (before or after fan) Separating air quantity (example: air separator) Potential cooling fresh air quantity (separator inlet)

Temperature of the Material Material temperature        

Feed material After mill Filter dust (mill filter) Separator feed material Separator grits Separator fine product Separator filter dust Finished material.

Important: It is necessary for all measurements (air quantities, pressure and temperature), that at least two measurements are carried out during constant running. If deviations occur, further measurements have to be carried out to receive a reliable result.

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HeidelbergCement Group Guidance Paper Process Evaluation of Ball Mill Grinding Plants

Edition:

02

Valid as of:

2016-03-31

6 Sampling Procedure 6.1

Complete Circuit Sampling In a test period of around 8 hours, at least two samplings should be carried out during constant operating state. Since the number of complete samples strengthens the reliability of the test, further samples can be taken. The additional staff, time and device expenditure for the sampling procedure and analysis should, however, be considered. The following Table 1 and Table 2 describe the sampling, location, quantity etc. and suggest analysis plan. If “individual sample” is stated, the sample is to be taken in short time intervals at the sampling location over the complete material flow width – in no case “sampling with the big bucket (put in and there we are!)”. In case of a large number of samples, please use a sample divider in the laboratory. For each sampling point it is important to consider the number of samples as representative for the sampled material flow! Appendix shows a table for recording of complete circuit sample results.

Picture 3: Ball mill circuit sampling points

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HeidelbergCement Group Guidance Paper Process Evaluation of Ball Mill Grinding Plants

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Table 1: Sampling Plan Sl. No.

Location

Type

Quantity

1.

Feed

Bulk sample during Main components test period  5-6 kg each

Frequency

Sampling

every 3 hours

Material flow over the complete width

every 3 hours

cakes vehicle

Others  2-3 kg each

-cakes-

Bulk sample during  4-6 kg each test period of each roll section  2 kg

3.

Mill discharge

Individual sample

 1-2 kg each

every 2 hours

Over complete material flow

4.

Static separator

Individual sample

 1 kg each

every 2 hours

Over complete material flow

5.

Cyclone separator Individual sample

 1 kg each

every 2 hours

Slot sampler

6.

Mill filter

Individual sample

 1 kg each

every 2 hours

In short time intervals

2.

Roller press

-Grits-

Discharging screw 7.1

Separator feed

Individual sample

 1-2 kg each

every 2 hours

Over complete material flow

7.2

Separator grits

Individual sample

 1 kg each

every 2 hours

Over complete material flow

7.3

Fine grains

separator Individual sample

 1 kg each

every 2 hours

Over complete material flow

8.

Separator filter

Individual sample

 1 kg each

every 2 hours

In short time intervals

Individual sample

 1 kg each

every 2 hours

Over complete material flow

Discharging screw 9.

Finished material

Important: Blending section of sufficient length!

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HeidelbergCement Group Guidance Paper Process Evaluation of Ball Mill Grinding Plants

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02

Valid as of:

2016-03-31

Table 2: Analysis Plan Sl. Location No.

Analysis

1.

Sieve analysis

Feed

Grind ability Mineralogy

***

**

**

Analyzing method

Evaluation

ISO 565

Particle size distribution

Zeisel

Grind ability in kWh/t

X-ray diffractometer RFA

(Main component) 2.

Roller press

Sieve analysis

***

ISO 565

Particle size distribution

Clarify cakes desagglomeration 3.

4.

5.

6.

7

Mill discharge

9.

****

ISO 565

Laser particle seizer

Laser particle seizer

Specific surface

Blaine

****

Static separator

Sieve analysis

-Grits-

Laser particle seizer

Cyclone separator

Sieve analysis

Mill filter

Separator feed  Feed material*  Separator grits*  Fine separator grains*

8.

Sieve analysis

Separator filter*

Finished material*

ISO 565

****

Particle size distribution

Laser particle seizer ISO 565

Laser particle seizer

Laser particle seizer

Specific surface

Blaine

Laser particle seizer

Laser particle seizer

Specific surface

Blaine

*

each : Sieve analysis

Particle size distribution

Particle size distribution

Particle size distribution

Particle size distribution ****

ISO 565

and

Laser particle seizer

Laser particle seizer

Specific surface

Blaine

separation curve calculation (Tromp curve)

Laser particle seizer

Laser particle seizer

Specific surface

Blaine

Laser particle seizer

Laser particle seizer

Specific surface

Blaine

Particle size distribution

Particle size distribution

*

Measurement of the complete particle size distribution

**

Only if required!

***

Sieve analysis suggestion (or similar diameters): 32/16/8/4/2/1/0.5/0.2/0.09 mm

****

Sieve analysis suggestion (or similar diameters): 2/1/0.5/0.2/0.09/0.045/0.032 mm

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HeidelbergCement Group Guidance Paper Process Evaluation of Ball Mill Grinding Plants

6.2

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Valid as of:

2016-03-31

Meter Sampling during Internal Ball Mill Inspection The grinding progress along the ball mill axis will be evaluated by meter samples. For this purpose, a material sample of 1 to 2 kg is taken in meter intervals, starting at the inlet (0 m). The sample is not to take directly at the surface, but from the level of the 3rd or 4th ball layer. After the partition wall, it is started again at 0 m. The last sample position is also directly before the outlet wall. Definition of the method Three samples are taken in each sampling meter: a. b. c.

on the mill center approx. 1 m right of the mill center approx. 1 m left of the mill center

To get a representative sample, some balls should be removed and the material taken from inside the ball charge.

Inlet

Outlet

Direction of rotation

1.0 m

Picture 4: Positions for meter sampling

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HeidelbergCement Group Guidance Paper Process Evaluation of Ball Mill Grinding Plants

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7 Assessment of Plant during Stop Condition Table 3: Inspection List Area

Plant assessment during stop condition

Roller press

    

Ball mill

Condition: Mill has to be shut down by emergency stop (incl. mill fan) – to prevent fine material losses!!

State of the roller surface Fractures, Wear Spilling Gap width between roller and side plate State of the internal primary seal: o Grease collar visible: good o No grease collar: plant maintenance  Zero gap

Internal inspection:    

Meter sampling along the total length of the mill (cf. 5.2) Filling volume determination Ball charge determination (cf. 7.2.1) Control mill internals: o Breakages / Wear o Inlet / outlet wall thickness Control of diaphragm on: o Slot width o Obstructions (clogging) of the slot wall o Material thickness o Adjustment of diaphragm control system (if adjustable)

 Evaluation of classifying effect  Balls sampling (cf. 7.2.3) Static air separator

Position of louvers or blades

Cyclone separator

Wear

Mill filter

 Condition of filter bags  Wear

Mill fan

 Wear of inlet vane control system

Separator fan

 Wear

Auxiliary equipment  Wear, holes, leakage e.g. bucket elevator

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HeidelbergCement Group Guidance Paper Process Evaluation of Ball Mill Grinding Plants

Area Dynamic separator

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02

Valid as of:

2016-03-31

Plant assessment during stop condition A) Turbo air separator  Wear of o Upper/internal fan blades o Distributor plate o Counter blades o Material feed cone o Grit cone/lining  Position and number of blades

B) Cyclone air separator  Wear of o External fan o Internal louver o Distributing plate o Counter blades /rotor Ref. to rotor: sealing between rotating and fixed part  Ascertain louver setting  Position and number of counter blades  Material deposit in cyclone inlet?  Separator lining

C) Cage separator  Wear on o Rotor o Guide vane o Distributing plate o Sealing of rotor between fixed and rotating part o Separator lining  Sealing of rotor: Adjustment of gap between fixed and rotating part

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HeidelbergCement Group Guidance Paper Process Evaluation of Ball Mill Grinding Plants

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8 Process Evaluation 8.1

Separator Assessment Definitions M A F G

= = = =

Fresh material Separator feed Separator fines Separator grits

[t/h] [t/h] [t/h] [t/h]

a f g

= = =

Passing of A Passing of F Passing of G

[%] [%] [%]

“Passing” means the weight share of a material as percentage, which particle size is smaller than or equal to the standard particle size; Passing (D) + residue (R) = 100%. ∆a ∆f ∆g

= = =

Weight share of a particle class of A Weight share of a particle class of F Weight share of a particle class of G

[%] [%] [%]

“Particle class” means the range between two particle sizes (xi); the sum of the weight shares of all particle classes of a material comes up to 100%. ∑a ∑f ∑g

= = =

Sum of all particle class results of A Sum of all particle class results of F Sum of all particle class results G

[%] [%] [%]

All weight share results over all particle classes are to summarize (Example: see bottom sum line in “Table 1”) For the calculation of the “Passing” (D) of a particle class must be applied: And

Dx=x(min)

=

0%

Dx=x(max)

=

100%

Additionally, these fundamental equations are applicable: A=F+G

(1)

A*a=F*f+G*g

(1.1)

A * a = F * f + G * g

(1.2)

The following sub items are classified in the system of naming below: Best_practice_guidance_paper_evaluation_ball_mill_grinding_plants_2016_02.docx

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HeidelbergCement Group Guidance Paper Process Evaluation of Ball Mill Grinding Plants

VF VG u  t dt

= = = = = =

Take out of fines Take out of grits Separator circulating factor Separation efficiency Separation degree Cut size

Edition:

02

Valid as of:

2016-03-31

[%] [%] [%] [%] [%] [µm]

Take out of fines and grits

𝑉𝐹 =

𝐹

𝑉𝐺 =

𝐺

𝐴

𝐴

=

Σ𝑎− Σ𝑔

=

Σ𝑓− Σ𝑎

(2)

Σ𝑓− Σ𝑔

(3)

Σ𝑓− Σ𝑔

𝑉𝐺 = 1 − 𝑉𝐹

(4)

with:

𝑉𝐹 𝑉𝐺

= =

Take out of fines Take out of grits

[-] [-]

Separator circulation factor and circulation load The circulation factor (u) defines the relation between feed and separator fines quantity:

𝑢=

𝐴 𝐹

=

1 𝑉𝐹

=

Σ𝑓− Σ𝑔

(5)

Σ𝑎− Σ𝑔

or related to particular particle class:

𝑢=

𝑓−𝑔

(5.1)

𝑎−𝑔

The circulation load (CL) defines the relation between rejects and separator fines quantity. It differs from circulation factor (u) by 1.

𝐶𝐿 =

𝐺 𝐹

= 𝑢−1=

Σ𝑓− Σ𝑎 Σ𝑓− Σ𝑔

or related to particular particle class: 𝐶𝐿

Best_practice_guidance_paper_evaluation_ball_mill_grinding_plants_2016_02.docx

=

𝑓−𝑎 𝑓−𝑔

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HeidelbergCement Group Guidance Paper Process Evaluation of Ball Mill Grinding Plants

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Separation efficiency Separation efficiency got as well different other names in literature. It is as well called: separator efficiency; recovery of fine particles; separation degree and some others. The separation efficiency () is related to a particular particle class. It means the share of the separator feed material below this particle class, which reaches the separator fine product. The result of the separation efficiency is changing with dedicated particle class.

𝜂=

𝐹∗𝑓 𝐴∗𝑎

𝜂 = 𝑉𝐹 ∗ 𝜂=

𝑓 𝑎∗𝑢

∗ 100 𝑓 𝑎

∗ 100

∗ 100

[%]

(6)

[%]

(6.1)

[%]

(6.2)

with: VF =  =

8.1.1

Take out of fines Separation efficiency

[-] [%]

Separation curve: TROMP CURVE Example calculation “Separation curve” The following particle size distribution has been considered:

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HeidelbergCement Group Guidance Paper Process Evaluation of Ball Mill Grinding Plants

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Table 4: Example of Particle Size Distribution Part.-Size [D%] Part.-Size [D%] [mm] Fines (f) Feed (a) Grits (g) [mm] Fines (f) Feed (a) Grits (g) 1.0 5.13 2.20 1.04 32.0 84.51 34.97 16.02 1.2 6.79 2.90 1.44 36.0 88.48 39.15 20.27 1.4 8.38 3.56 1.78 40.0 91.57 43.26 24.76 1.6 9.87 4.17 2.09 45.0 94.46 48.16 30.46 1.8 11.28 4.74 2.36 50.0 96.52 52.71 36.00 2.0 12.61 5.27 2.60 56.0 98.19 57.65 42.22 2.2 13.86 5.76 2.82 63.0 99.40 62.67 48.74 2.6 16.15 6.65 3.20 75.0 100.00 69.63 57.98 3.0 18.23 7.43 3.51 90.0 100.00 75.96 66.50 3.5 20.57 8.30 3.85 106.0 100.00 80.68 72.83 4.0 22.70 9.08 4.14 125.0 100.00 84.51 77.91 4.5 24.67 9.80 4.41 150.0 100.00 87.79 82.17 5.0 26.50 10.47 4.65 175.0 100.00 89.94 84.92 5.5 28.24 11.10 4.87 200.0 100.00 91.46 86.87 6.3 30.86 12.04 5.19 225.0 100.00 92.62 88.37 7.0 33.04 12.80 5.43 250.0 100.00 93.56 89.61 8.0 36.01 13.80 5.71 280.0 100.00 94.51 90.88 9.0 38.87 14.72 5.91 315.0 100.00 95.45 92.17 10.0 41.65 15.58 6.04 355.0 100.00 96.37 93.47 12.0 47.00 17.15 6.17 400.0 100.00 97.26 94.73 15.0 54.57 19.37 6.30 450.0 100.00 98.08 95.93 16.0 56.96 20.12 6.39 500.0 100.00 98.73 96.92 18.0 61.53 21.66 6.73 560.0 100.00 99.30 97.87 20.0 65.78 23.31 7.32 600.0 100.00 99.58 98.37 22.0 69.70 25.05 8.17 800.0 100.00 100.00 99.67 25.0 74.96 27.85 9.96 1000.0 100.00 100.00 99.97 28.0 79.50 30.83 12.28 Sum 3,468.54 2,429.68 2,019.97 VF =

0.283

VG =

0.717

For a reasonable evaluation of these results in process-technical respect, the model of the separation curve calculation according to the VDZ (Association of German Cement Producers) Guideline MT 28 was slightly modified. Each particle class is calculated with a failure ratio typical for the class (caused by analysis inaccuracy, rounding errors etc.). The subsequent calculation procedure then follows MT 28 again. On the right hand side of each formula is a numerical example shown, which is related to table 3 or 4. Procedure 1

Calculation of the material output (cf. 7.1.1) 2,429.68 − 2,019.97

𝑉𝐹 − 𝐹𝑖𝑛𝑒𝑠 (𝐹𝑜𝑟𝑚𝑢𝑙𝑎𝑟 2)

𝑉𝐹 =

𝑉𝐺 − 𝐺𝑟𝑖𝑡𝑠 (𝐹𝑜𝑟𝑚𝑢𝑙𝑎𝑟 3)

𝑉𝐺 = 1 − 𝑉𝐹 = 0.717

3,468.54 − 2,019.97

= 0.283

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HeidelbergCement Group Guidance Paper Process Evaluation of Ball Mill Grinding Plants

2

Edition:

02

Valid as of:

2016-03-31

Determination of the specific particle fraction failure S(X)

𝑆(𝑋) = 𝑎(𝑋) − [ 𝑉𝐹 ∗ 𝑓(𝑋) + 𝑉𝐺 ∗ 𝑔(𝑋) ] 𝑆(1) = 2.20 − [ 0.283 ∗ 5.13 + 0.717 ∗ 1.04 ] = 0.0009529 3

Correction of each particle fraction of the calculated failure S(X) according to the following formula:

∗ 𝑎(𝑋) = 𝑎(𝑋) − ∗ 𝑓(𝑋) = 𝑓(𝑋) + ∗ 𝑔(𝑋) = 𝑔(𝑋) +

4

(7)

𝑆(𝑋) 1 + 𝑉𝐹2

+ 𝑉𝐺2

𝑆(𝑋) ∗ 𝑉𝐹 1 + 𝑉𝐹2 + 𝑉𝐺2 𝑆(𝑋) ∗ 𝑉𝐺 1 + 𝑉𝐹2 + 𝑉𝐺2

∗ 𝑎(2) = 2,9 −

0.0009529 1 + 0.2712 + 0.7292

= 2.93

0.0009529 ∗ 0.271

∗ 𝑓(2) = 6,79 +

1 + 0.2712 + 0.7292

∗ 𝑔(2) = 1,44 +

1 + 0.2712 + 0.7292

0.0009529 ∗ 0.729

(8)

= 6.78

(9)

= 1.41

(10)

Supplementation of the table by the corrected mass distribution totals and the derived sizes derived according to MT 28

Calculation of the mass distribution of each particle class: ∗ ∗ ∗ ∆𝑔(1) = 𝑔(2) − 𝑔(1) ∗ ∗ ∗ ∆𝑔(2) = 𝑔(3) − 𝑔(2)

∗ ∆𝑔(1) = 1.41 − 1.04 = 0.372 ∗ ∆𝑔(2) = 1.74 − 1.41 = 0.329

(11)

fi * and ai* are to be calculated respectively. Following MT 28, the separator feed share should be calculated according to the following formula: ∗ ∆𝑎(𝑥)𝑀𝑇28 = ∆𝑓 ∗ ∗ 𝑉𝐹 + ∆𝑔∗ ∗ 𝑉𝐺 ∗ ∆𝑎(1)𝑀𝑇28 = 1.653 ∗ 0.283 + 0.372 ∗ 0.717 = 0.734

(12)

The rated value only slightly differs from the analytical one.

The separation degree () is calculated as follows:

𝜏(𝑥) =

∗ ∆𝑔(𝑥) ∗ 𝑉𝐺 ∗ 100 ∗ ∆𝑎(𝑥)𝑀𝑇28

𝜏(1) =

0.372 ∗ 0.717 ∗ 100 0.734

= 36.3

(13)

The following table shows the recalculated values:

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HeidelbergCement Group Guidance Paper Process Evaluation of Ball Mill Grinding Plants

Edition:

02

Valid as of:

2016-03-31

Table 5: Corrected particle distribution Particle [D%] Size [mm] Fines (f) Feed (a) Grits (g) 1.0 5.13 2.20 1.04 1.2 6.79 2.90 1.44 1.4 8.38 3.56 1.78 1.6 9.87 4.17 2.09 1.8 11.28 4.74 2.36 2.0 12.61 5.27 2.60 2.2 13.86 5.76 2.82 2.6 16.15 6.65 3.20 3.0 18.23 7.43 3.51 3.5 20.57 8.30 3.85 4.0 22.70 9.08 4.14 4.5 24.67 9.80 4.41 5.0 26.50 10.47 4.65 5.5 28.24 11.10 4.87 6.3 30.86 12.04 5.19 7.0 33.04 12.80 5.43 8.0 36.01 13.80 5.71 9.0 38.87 14.72 5.91 10.0 41.65 15.58 6.04 12.0 47.00 17.15 6.17 15.0 54.57 19.37 6.30 16.0 56.96 20.12 6.39 18.0 61.53 21.66 6.73 20.0 65.78 23.31 7.32 22.0 69.70 25.05 8.17 25.0 74.96 27.85 9.96 28.0 79.50 30.83 12.28 32.0 84.51 34.97 16.02 36.0 88.48 39.15 20.27 40.0 91.57 43.26 24.76 45.0 94.46 48.16 30.46 50.0 96.52 52.71 36.00 56.0 98.19 57.65 42.22 63.0 99.40 62.67 48.74 75.0 100.00 69.63 57.98 90.0 100.00 75.96 66.50 106.0 100.00 80.68 72.83 125.0 100.00 84.51 77.91 150.0 100.00 87.79 82.17 175.0 100.00 89.94 84.92 200.0 100.00 91.46 86.87 225.0 100.00 92.62 88.37 250.0 100.00 93.56 89.61 280.0 100.00 94.51 90.88 315.0 100.00 95.45 92.17 355.0 100.00 96.37 93.47 400.0 100.00 97.26 94.73 450.0 100.00 98.08 95.93 500.0 100.00 98.73 96.92 560.0 100.00 99.30 97.87 600.0 100.00 99.58 98.37 800.0 100.00 100.00 99.67 1000.0 100.00 100.00 99.97 Sum 3,468.54 2,429.68 2,019.97

Failure S(X) [%] 0.001 -0.054 -0.092 -0.119 -0.142 -0.161 -0.180 -0.215 -0.247 -0.282 -0.313 -0.341 -0.365 -0.387 -0.419 -0.445 -0.478 -0.507 -0.531 -0.565 -0.582 -0.580 -0.567 -0.547 -0.524 -0.488 -0.457 -0.427 -0.410 -0.404 -0.406 -0.410 -0.408 -0.395 -0.233 -0.011 0.164 0.355 0.580 0.756 0.882 0.964 1.016 1.049 1.063 1.060 1.037 0.995 0.934 0.830 0.753 0.235 0.019

Corrected fraction values a* f* g* ∆a* ∆f* [%] [%] [%] [%] [%] 2.20 5.129 1.040 0.734 1.653 2.93 6.78 1.41 0.683 1.579 3.61 8.36 1.74 0.631 1.492 4.24 9.85 2.03 0.584 1.404 4.83 11.26 2.29 0.541 1.322 5.37 12.58 2.53 0.503 1.245 5.87 13.82 2.74 0.908 2.291 6.78 16.11 3.10 0.802 2.067 7.58 18.18 3.40 0.892 2.338 8.47 20.52 3.72 0.802 2.125 9.28 22.64 4.00 0.735 1.961 10.01 24.60 4.26 0.685 1.834 10.70 26.44 4.49 0.643 1.734 11.34 28.17 4.70 0.959 2.617 12.30 30.79 5.01 0.778 2.171 13.08 32.96 5.23 1.026 2.967 14.10 35.93 5.49 0.940 2.854 15.04 38.78 5.68 0.870 2.770 15.91 41.55 5.80 1.593 5.349 17.51 46.90 5.91 2.230 7.567 19.74 54.47 6.04 0.746 2.393 20.48 56.86 6.13 1.539 4.565 22.02 61.43 6.48 1.629 4.254 23.65 65.68 7.07 1.731 3.927 25.38 69.61 7.94 2.781 5.270 28.16 74.88 9.74 2.959 4.544 31.12 79.42 12.07 4.115 5.014 35.23 84.44 15.83 4.172 3.967 39.41 88.40 20.08 4.102 3.098 43.51 91.50 24.58 4.903 2.890 48.41 94.39 30.28 4.553 2.061 52.97 96.45 35.82 4.935 1.668 57.90 98.12 42.04 5.021 1.207 62.92 99.33 48.57 6.853 0.633 69.77 99.96 57.87 6.194 0.039 75.97 100.00 66.49 4.606 0.031 80.57 100.03 72.90 3.712 0.034 84.29 100.06 78.07 3.141 0.040 87.43 100.10 82.43 2.039 0.031 89.47 100.13 85.26 1.444 0.022 90.91 100.16 87.26 1.107 0.015 92.02 100.17 88.80 0.907 0.009 92.93 100.18 90.06 0.925 0.006 93.85 100.19 91.35 0.932 0.003 94.78 100.19 92.65 0.927 -0.001 95.71 100.19 93.94 0.900 -0.004 96.61 100.18 95.20 0.842 -0.008 97.45 100.18 96.38 0.688 -0.011 98.14 100.17 97.34 0.640 -0.018 98.78 100.15 98.24 0.329 -0.014 99.11 100.13 98.70 0.743 -0.092 99.85 100.04 99.78 0.136 -0.038 99.99 100.00 99.98 0 0 2,429.68 3,468.54 2,019.97

Best_practice_guidance_paper_evaluation_ball_mill_grinding_plants_2016_02.docx

∆g* ∆a* MT28 [%] [%] 0.372 0.734 0.329 0.683 0.292 0.631 0.260 0.584 0.233 0.541 0.210 0.503 0.362 0.908 0.303 0.802 0.322 0.892 0.280 0.802 0.252 0.735 0.231 0.685 0.213 0.643 0.305 0.959 0.228 0.778 0.260 1.026 0.186 0.940 0.121 0.870 0.112 1.593 0.125 2.230 0.097 0.746 0.345 1.539 0.593 1.629 0.864 1.731 1.800 2.781 2.335 2.959 3.760 4.115 4.253 4.172 4.498 4.102 5.698 4.903 5.536 4.553 6.224 4.935 6.525 5.021 9.306 6.853 8.621 6.194 6.410 4.606 5.163 3.712 4.364 3.141 2.831 2.039 2.004 1.444 1.538 1.107 1.261 0.907 1.288 0.925 1.299 0.932 1.293 0.927 1.256 0.900 1.177 0.842 0.964 0.688 0.899 0.640 0.465 0.329 1.073 0.743 0.204 0.136 0 0

τ MT28 [%] 36.3 34.6 33.2 32.0 30.9 29.9 28.6 27.1 25.9 25.0 24.6 24.2 23.8 22.8 21.0 18.2 14.2 10.0 5.0 4.0 9.3 16.1 26.1 35.8 46.4 56.6 65.5 73.1 78.6 83.3 87.2 90.4 93.2 97.4 99.8 99.8 99.7 99.6 99.6 99.6 99.6 99.7 99.8 99.9 100.0 100.1 100.3 100.4 100.8 101.2 103.5 108.0 100.0

Page 21 of 52

HeidelbergCement Group Guidance Paper Process Evaluation of Ball Mill Grinding Plants

Edition:

02

Valid as of:

2016-03-31

Evaluation of the separation curve ( = Tromp curve ) The separating effect is generally characterized through the relation of two particle classes, which are classified with particular separation degrees. The dimension X35:X65 (particle size with a separation degree of 35% or 65%) or X25:X75 is frequently used as assessment criterion. During the process of cement separation, this is, however, not always possible to be put into practice, since an intersection with a X25 or X35 line is not available in every case (for example: by using separators of 1st generation).

The following features are used for the evaluation of the Tromp curve:

1.

Separator Bypass () The shortest distance () between separation curve and abscises (particle size) determines, which part of the total feed material enters the grits without separation.

The separator bypass () corresponds to the minimum of the curve, it is the lowest Tromp coefficient. The old generation of separators is characterized by a high bypass around 50%. With the same energy supply, a reduction of the  value does usually lead to an increase in throughput. The bypass level depends of the circulating factor, for low fineness cement (3.000 cm²/g acc. to Blaine) the bypass is low; it increases with the cement fineness. Separator bypass means the ratio between the quantity of a definite particle size (fines), which has reached the grits, and the quantity existing in the feed material. 2.

Cut point D50: It corresponds to 50% of the feed passing to the coarse stream. It is that size of grain which has equal probability of passing to either coarse or fine streams.

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HeidelbergCement Group Guidance Paper Process Evaluation of Ball Mill Grinding Plants

3.

Edition:

02

Valid as of:

2016-03-31

Imperfection I: It is calculated as follows

𝐼=

𝐷75 − 𝐷25 2𝐷50

If the separation is perfect, the Tromp curve is a step curve. In this case, D75 = D25 and I = 0 More I (Imperfection) is high, worse is the separator. 4.

Sharpness k: It is defined as ratio between the particle size at the separating degree of 75% and the particle size at the separating degree of 25%.

𝑘=

𝐷75 𝐷25

For an ideal separation k would be 1. Further information on separator assessment please find under: https://teamnet.grouphc.net/group/WOK/cemop/copgrinding/Pages/Documents_enUS.aspx Main category: Separator Guidance Paper for Separator Inspection and Optimization

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HeidelbergCement Group Guidance Paper Process Evaluation of Ball Mill Grinding Plants

Cement quality:

Edition:

02

Valid as of:

2016-03-31

CEM I 42,5 R (sp)

SEPARATION VALUES

TROMP CURVE VALUES

Circulating load:

3.54

Bypass :

Take out of fines VF:

28.3%

D25:

19 µm

Take out of grits VG:

17.7%

D50:

23 µm

Efficiency at 32 µm :

68.2%

D75:

33 µm

Efficiency at 45 µm :

55.4%

Imperfection:

0.3

Efficiency at 90 µm :

37.2%

Sharpness:

1.74

4% at 12 µm

TROMP- Curve 100% 95% 90% 85% 80%

D75 = 33 μm

75%

TROMP value T(x)

70% 65% 60% 55%

D50 = 23 μm

50% 45% 40% 35% 30%

D25 = 19 μm

25% 20% 15% 10% 5%

τ = 4%; X=12 μm

0% 1

10

100

Particle size [µm] Picture 5: Tromp Curve

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HeidelbergCement Group Guidance Paper Process Evaluation of Ball Mill Grinding Plants

8.2

Edition:

02

Valid as of:

2016-03-31

Internal Mill Inspection The analysis of the mill inspection refers to:     

8.2.1

Preparation of a grinding diagram over the grinding path length Determination of the filling degree Calculation of the grinding media quantity Calculation of the consumed power at the mill tube Determination of average ball diameter

Preparation of Grinding Diagram In the grinding diagram, the residue in [%] should be laid off as first ordinate and the grinding fineness (acc. to Blaine in cm2/g) as the second. The abscissa is the length of the grinding path. The residue values of various particle classes are laid off on the curve. Analysis and evaluation of meter samples General:

- Sieves analysis for both chamber** - In 2nd chamber also specific surface acc. Blaine from material < 0.5 mm

Evaluation:

In a diagram: residue (particle size) and Blaine (chamber 2 only) as function of mill length.

A good grinding is at steep sieve lines without big disturbances. The corn fraction of 2.3 mm shall be less than 5 % in front of the intermediate diaphragm. The corn fraction of 1 mm shall disappear in the second chamber within the first third of the chamber length. Just in front of the intermediate diaphragm or of the outlet diaphragm there can be strange results of the sieve curve. One or some curves may incline sharply instead of the expected further decline. This is because of air segregation of fine particles and off influence of the grinding performance.

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HeidelbergCement Group Guidance Paper Process Evaluation of Ball Mill Grinding Plants

Edition:

02

Valid as of:

2016-03-31

Picture 6: Ball Mill Grinding Diagram

8.2.2

Determination of the Filling Degree Following the example below, the filling ratio (f) can be graphically determined from the grinding level and the clear grinding chamber diameter. The concept of this example also supports the internal inspection of a ball mill and its result is to be considered in connection with the grinding diagram of the meter samples. As cutout of the form sheet, the following picture shows the graphical determination of the filling ratio. It is to be determined:  

Grinding level (h) Clear grinding chamber diameter (Dli).

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HeidelbergCement Group Guidance Paper

h/Dli

Process Evaluation of Ball Mill Grinding Plants

0,75 0,74 0,73 0,72 0,71 0,7 0,69 0,68 0,67 0,66 0,65 0,64 0,63 0,62 0,61 0,6

Edition:

02

Valid as of:

2016-03-31

y = -0,0086x + 0,9192

Dli

20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36

Filling ratio

Usual filling degree numbers:

f

%

25 – 28 %, optimized on power consumption. ~35 %, optimized on throughput.

Picture 7: graphical determination of the mill filling ratio

The filling degree f can be calculated correctly with the following formulas (MT22):

𝑓 = 𝑓 =

𝛼 180° 𝛼 180°

−

sin 2 𝛼

−

sin 𝛼 ∗ cos 𝛼

2𝜋

𝜋

For the range 065 <

ℎ 𝐷𝑙𝑖

with

cos 𝛼 = 2

ℎ 𝐷𝑙𝑖

− 1

< 0.75 resp. filling degree within 0.2 < f < 0.31, the following

formula can be used:

𝑓 = 1.0678 − 1.164

ℎ 𝐷𝑙𝑖

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HeidelbergCement Group Guidance Paper Process Evaluation of Ball Mill Grinding Plants

8.2.3

Edition:

02

Valid as of:

2016-03-31

Calculation of Grinding Media Quantity From the filling ratio calculated under 7.2.2 the weight of the grinding media filling (in t) can be derived: Grinding media quantity

𝐺 =

𝜋 4

∗ 𝐷𝑙𝑖2 ∗ 𝐿𝑙𝑖 ∗ 𝑓 ∗ 𝛾𝑀𝐾

[t]

Dli

=

Inside liner diameter of grinding chamber in m

Lli

=

effective length of the grinding chamber in m

f

=

grinding media filling degree

MK

=

bulk density grinding media in t/m3

reference value:

coarse ball charge (1st chamber): nd

fine ball charge (2 chamber):

approx. 4.4-4.5 t/m³ approx. 4.6-4.7 t/m³

The filling ratios determined by measuring the grinding level are to be reduced by 1 to 3 % depending on the material cover over the ball charge. OR the mill has to be emptied out to measure the degree of filling of the media.

8.2.4

Calculation of Power Consumption of Mill Tube Power consumption of mill tube Pw = G * 0.1026 * DLi ^ 1.014 * nR ^1.27 * f * (1.36 – 1.2 * f) G Dli nR f

= weight of grinding media = Inside liner diameter of grinding chamber = revolutions of the tube = grinding media filling degree

PZ

= Pw

A

= Total efficiency

1

A

[kW] [t] [m] [ rpm ] [ kW counter ]

The total efficiency  A = mech * el Following values can be used: For girth gear drive:  A = mech *  = 0.92 For central drive:  A = mech *  = 0.94 Best_practice_guidance_paper_evaluation_ball_mill_grinding_plants_2016_02.docx

Page 28 of 52

HeidelbergCement Group Guidance Paper Process Evaluation of Ball Mill Grinding Plants

8.2.5

Edition:

02

Valid as of:

2016-03-31

Determination of the Average Ball Diameter and Classifying Effect in Chamber 2 The first chamber of a ball mill is normally emptied every 1 to 2 years, the second chamber approximately every 3 to 5 years. The ball grading becomes obvious after balls sorting. Important: Balls and material are sampled together, at meter sampling.   

Ball sampling each meter in the same way as at material meter sampling. Balls and material will be taken at once. Dividing of balls and material can be done already in the mill or later, outside. The samples amount should approximately correspond to the volume of a 10-l bucket. Sampling device: robust shovel or similar

To evaluate the condition of the ball charge and define the ball charge with regard to grinding performance, the average ball diameter is to be determined and examined in connection with the results from the meter sampling. Per meter sample, only the number of balls and the total weight of the ball sample are to be determined. Out of this, the average ball diameter at the sampling point can be calculated when knowing the density of the ball material. Proceeding for evaluation: To be determined:

 total amount of balls per meter sample (number of balls)  total weight of the balls in meter sample (sample weight in t)

 material density () of the grinding media (usually 7.85 t/m3)

Given:

Calculation of the average ball diameter of a meter sample:

3

sample weight

Dm = 2 ∗ √ ∗ number of balls

1 ρ

∗

3 4∗π

[m]

The result should then be converted into mm.

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HeidelbergCement Group Guidance Paper Process Evaluation of Ball Mill Grinding Plants

Edition:

02

Valid as of:

2016-03-31

9 Assessment of Mill Drying Plants In addition to the procedures and methods described in items 1 to 7, the following issues must be examined, when evaluating combined drying and grinding units: 

Moisture of the material (complete sampling and analysis plan): o feed material o finished product



Gas/air quantity within the mill system



Temperature (moist and dry) of the mill exhaust air for calculation of the dew point



Gas/air temperatures in the mill system



With additional firing:



Gas analysis for determination of false air (at least 3 measurements / tests), when kiln exhaust air is used: o sampling before and after the mill

o o

o 

fuel consumption conveying and combustion air (can usually be neglected), fan adjustment

sampling after the separator and / or filter

Operating conditions (to be monitored every hour): o cooler fan outlet: position of the inlet vane control system or flap position or revolutions per minute o

clinker output (control room)

o

amount of cooling air (control room)

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HeidelbergCement Group Guidance Paper Process Evaluation of Ball Mill Grinding Plants

9.1

Edition:

02

Valid as of:

2016-03-31

Balance Preparation Air quantity balance

Air to mill Air from auxiliary burner (mostly to neglect)

Steam from material moisture

Mill system

Exhaust air from mill after filter

Quench / false air (mostly rest of balance)

Heat balance

Air to mill

Enthalpy power of exhaust air from mill

Air from auxiliary burner Radiation and convection losses Drive power heat conversion

Mill system Heating up of the raw meal

Quench / false air (mostly rest of balance) Enthalpy of steam

The false air volume flow is calculated on the basis of the air quantity balance or out of gas analyses, e.g. of the kiln exhaust gas.

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HeidelbergCement Group Guidance Paper Process Evaluation of Ball Mill Grinding Plants

9.1.1

Edition:

02

Valid as of:

2016-03-31

Air Quantity Balance Balance

𝑉̇ additional air (+𝑉̇ conveying air/combustion) + 𝑉̇ false air

+ 𝑉̇ steam = 𝑉̇ exhaust air

𝑉̇ additional air 𝑉̇ conveying air

Measured variables:

Operant:

[m3(s.c.)/h] [m3(s.c.)/h]

𝑉̇ exhaust air

[m3(s.c.)/h]

𝑚̇steam

[m3(s.c.)/h]

𝑉̇ false air

[m3(s.c.)/h]

Water amount to be vaporized 𝑓𝐴 − 𝑓𝑅

𝑚̇𝑤𝑎𝑡𝑒𝑟 = With:

100 − 𝑓𝐴

∗ 𝑀̇𝑚𝑒𝑎𝑙−𝑟𝑒𝑠𝑖𝑑.𝑚𝑜𝑖𝑠𝑡 =

𝑓𝐴 − 𝑓𝑅 100 − 𝑓𝑅

fA

initial moisture in %

F

residual moisture in %

𝑀̇meal-resid.moist 𝑀̇feed-wet

∗ 𝑀̇𝑓𝑒𝑒𝑑−𝑤𝑒𝑡

[kg/h]

meal incl. residual moisture in kg/h feed material with moisture in kg/h

Resulting steam volume

𝑉̇ steam = 𝑚̇water / 0.804 = 𝑅 ∗ With:

𝑚̇𝑤𝑎𝑡𝑒𝑟 ∗ 𝑇𝑁 𝑃𝑁 ∗ 100

[m3(s.c.)/h]

R

general gas constant: R = 461 J/kg K

TN

reference temperature 273 K

PN

1013 mbar

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HeidelbergCement Group Guidance Paper Process Evaluation of Ball Mill Grinding Plants

Edition:

02

Valid as of:

2016-03-31

Balance for false air calculation

𝑉̇ false air = 𝑉̇ exhaust air - 𝑉̇ additional air - 𝑉̇ steam (-𝑉̇ conveying air/combustion)

Example for false air determination via gas analysis Orsat analysis

CO2

O2

CO

N2

n

Before mill

(1)

30.75

4.15

-

65.1

1.315

After filter

(2)

21.50

9.10

-

69.4

1.974

Share of false air (in %) related to gas after mill:

VF [%] =

𝑛2 − 𝑛1 𝑛2

 100

Calculation: VF [%] = 33,4 % Gas amounts:

before mill:

75.500 m3(s.c., dry)/h

steam:

9.100 m3/h

after mill:

121.300 m3/h

From air quantity balance:

𝑉̇ false

= 121.300 – 75.500 – 9.100 = 36.700 m3(s.c.)/h

From gas analysis: Best_practice_guidance_paper_evaluation_ball_mill_grinding_plants_2016_02.docx

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HeidelbergCement Group Guidance Paper Process Evaluation of Ball Mill Grinding Plants

𝑉̇ false

= (121.300 – 9.100) ∗ = 37.475

Edition:

02

Valid as of:

2016-03-31

33,4 100

m3(s.c.)/h

The error is 2% related to the balance result. It can be explained by the measuring inaccuracy connected to the measuring method. The error in the Orsat analyses is up to 0,3 vol.-percent.

9.1.2

Heat balance Reference temperature should be 25°C, as the cp-diagrams (pictures 7 and 8) refer to this temperature.

Balance

𝑄̇input = 𝑄̇loss

𝑄̇input: 𝑄̇additional air + 𝑄̇additional firing + 𝑄̇combustion air + Pmech + 𝑄̇feed material + 𝑄̇fresh air + 𝑄̇false air 𝑄̇loss: 𝑄̇exhaust air + 𝑄̇water vaporizing + 𝑄̇finished product + 𝑄̇heat losses Input

𝑄̇additional air 𝑄̇additional firing 𝑄̇combustion air 𝑄̇fresh air 𝑄̇false air 𝑄̇feed material

=

[kJ/h]

=

𝑉̇ additional air * cp * (additional air - 25°C) 𝑚̇fuel * hu(fuel) 𝑉̇ combustion air * cp * (combustion air - 25°C) 𝑉̇ fresh air * cp * (fresh air - 25°C) 𝑉̇ false air * cp * (false air - 25°C)

=

𝑚̇feed material * cm * (feed material - 25°C)

[kJ/h]

Pmech

=

Pdrives *  * 3,600 s/h (0.9 <  < 0.96  efficiency)

[kJ/h]

with Pdrives

=

performance counter of the drives over test period

[kJ/h]

= =

0.92 for ball mill with girth gear drive 0.94 for ball mill with central drive

and

 

= = =

Best_practice_guidance_paper_evaluation_ball_mill_grinding_plants_2016_02.docx

[kJ/h] [kJ/h] [kJ/h] [kJ/h]

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HeidelbergCement Group Guidance Paper Process Evaluation of Ball Mill Grinding Plants

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02

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Loss

𝑄̇exhaust air 𝑄̇vaporizing water 𝑄̇finished product 𝑄̇losses

=

𝑉̇ exhaust air * cp * (exhaust air - 25°C) 𝑚̇water * 2,446 kJ/kg 𝑚̇finished product * cp * (finished product - 25°C)

=

balance deviation (accounts for appr. 5 % of thermal input)

= =

[kJ/h] [kJ/h] [kJ/h]

General issues to the theory of radiation and convection in ball mill systems The item „thermal losses” mainly includes losses due to radiation and convection, which relate to the whole system. A detailed calculation of the single losses is possible, but involves considerable effort and expenses, since the whole grinding system within the balance scope includes very different heat transfer mechanisms, which would have to be considered. Normally, a loss should be seen from the balance and only be checked in case of discrepancies. A rough check of the radiation and convection losses is possible on the basis of the following approximate values: 3,600 𝑠 𝑘𝐽 𝑄̇rad.-con. = total * Acomponent * (Tsurface – Tambient) * ℎ 1,000 𝐽

[kJ/h]

with total = rad + con rad =  *  *

𝑇𝑠𝑢𝑟𝑓𝑎𝑐𝑒 4 − 𝑇𝑎𝑚𝑏𝑖𝑒𝑛𝑡 4 𝑇𝑠𝑢𝑟𝑓𝑎𝑐𝑒 − 𝑇𝑎𝑚𝑏𝑖𝑒𝑛𝑡

with:

 = 5.67 * 10-8 W/(m2 * K4)

Emission factor

 ≈ 0.3 galvanized sheet metal

[W/(m2 K)]

 ≈ 0.4 iron with silver coating  ≈ 0.65 rusty surface (iron)  ≈ 0.9 heavily rusted iron, rust protection coating

The calculation of con is far more difficult. As, in this case, different heat transfer mechanisms overlap. Taking into account the following limits, the approximate values below can be used: Best_practice_guidance_paper_evaluation_ball_mill_grinding_plants_2016_02.docx

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HeidelbergCement Group Guidance Paper Process Evaluation of Ball Mill Grinding Plants

40°C

< mill tube

<

110°C

10°C

< ambience



30°C

2m

 Dmill tube



4m

15 min-1

 nmill



26 min-1

Edition:

02

Valid as of:

2016-03-31

As approximate value for the heat transfer coefficients at the rotating mill tube the following can be assumed:

con 

8 - 9 W/(m2 * K)

for 2 m  D  3 m

con 

9 - 10 W/(m2 * K)

for 3 m < D  4 m

Accuracy is about  15 %. To stationary components, which are not exposed to flows (tubes, housings etc.), the following considerably simplified relation applies, if the following boundary conditions are met: 20°C < surface < 70°C and 10°C < ambience  30°C con  1.6 (surface - ambience) 1/3 [W/(m2 * K)] Accuracy is about  10 %.

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HeidelbergCement Group Guidance Paper Process Evaluation of Ball Mill Grinding Plants

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The cp-values for air, furnace gas and raw meal can be taken from the corresponding sheets.

The specific thermal capacity of non-air is composed of:

with

cp(gas)

=

 xi * cp(i)

xi

=

share of component i in the total gas volume

cp(i)

=

specific thermal capacity of component xi

Units

V

=

[m3(s.c.)/h]

 m

=

[kg/h]

H

=

[kJ/h]

cp

=

[kJ/(kg * K)]

T

=

[K]



=

[W/(m2 * K)]

A

=

[m2]

hu

=

[kJ/kg]

P drives

=

[kW]

or

[m3(s.c., dry)/h]

or

[kJ/(m3 * K)]

(s.c. = at standard conditions)

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HeidelbergCement Group Guidance Paper Process Evaluation of Ball Mill Grinding Plants

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02

Valid as of:

2016-03-31

10 Literature, Standards and Guidelines [1]

Leaflet MT 22 „Rohrmühlen und Mahltechnik“ (= „Tube mills and grinding technology“); VDZ, 9/61; Düsseldorf

[2]

Leaflet MT 28 „Rohrmühlen und Mahltechnik“ (= „Tube mills and grinding technology“); VDZ, 2/65; Düsseldorf

[3]

Duda, H.W.: Cement-data-book; 3rd edition; 1985, Bauverlag Wiesbaden

[4]

Labahn, O., Kohlhaas, B.: „Ratgeber für Zementingenieure“ (= „Guidebook for cement engineers“), 6. edition, 1982, Bauverlag Wiesbaden

[5]

Guideline „Gasanalyse“ (= „Gas analysis“)

11 Appendix

1

Forms “Site inspection”

2

Forms “Control room data”

3

Form “Pressure and temperature curve”

4

Form “Material temperature curve”

5

Form “Mill inspection and observations”

6

Form “Mill internals 1st & 2nd chamber”

7

Form “All around samples”

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Page 1/3:

Edition:

02

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2016-03-31

Date:

Site inspection

Plant: Plant type: A

B

Time: Scales

discharge behavior

A:

of components

B: C: D:

homogeneous + segregated grinding aid where? distribution on material bed grinding aid flow

+/+/-

last control weighing

date

last calibration

date

condition

weight feeder

selection +, o, Roller press

zero gap

[mm]

grinding gap approx.

right

[mm]

left

hydraulic pressure

right

[Mpa]

left

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HeidelbergCement Group Guidance Paper Process Evaluation of Ball Mill Grinding Plants

vibration Ball mill

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02

Valid as of:

2016-03-31

yes/no

grinding sound chamber 1 mill sound along grinding path chamber 1 description with m grinding sound chamber 2 mill sound along grinding path chamber 2 description with m

= homogeneous; good o = medium; normal - = inhomogeneous; bad

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HeidelbergCement Group Guidance Paper Process Evaluation of Ball Mill Grinding Plants

Page 2/3:

Site inspection

Edition:

02

Valid as of:

2016-03-31

Date:

Plant: Plant type: A

B

Time: Ball mill

mill discharge

normal

well running of valves

bad

Material discharge at mill inlet dust discharge - where Static separator

setting of blades coarse – medium – fine

Cyclone(s)

Mill filter

Separator no. 1

discharge valve

normal

well running

bad

leakage

yes / no

discharge valve

normal

well running

bad

leakage

yes/no

fan setting inlet vane control system/valve

%

leakage

yes / no

discharge valves well running example: no. 1+, no. 2+, no. 3+

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discharge valves frequency

min ^-1

example: no. 1 (3), no. 2 (5) cooling air valves setting

%

separator settings main rotor

%/min ^-1

Counter blades

%/min ^-1

= homogeneous; good o = medium; normal - = inhomogeneous; bad

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Page 3/3:

Site inspection

Edition:

02

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2016-03-31

Date:

Plant: Plant type: A

B

Time: Separator no. 2

discharge valves well running example: no. 1+, no. 2+, no. 3+ discharge valves frequency

min ^-1

example: no. 1 (3), no. 2 (5) cooling air valves setting

%

separator settings

Separator filter

Auxiliary equipment

main rotor

%/min ^-1

Counter blades

%/min ^-1

fan setting inlet vane control system/valve

%

leakage

yes / no

unusual occurrences aggregate aggregate aggregate

= homogeneous; good o = medium; normal - = inhomogeneous; bad

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HeidelbergCement Group Guidance Paper Process Evaluation of Ball Mill Grinding Plants

Page 1/2: Recording of control room data

Edition:

02

Valid as of:

2016-03-31

Date:

Plant: Plant type: A

B

Time: components in t/h

A: B: C: D:

fresh material

t/h

fresh material

Counter

separator feed

t/h

grinding aid

l/min

material temperature discharge

°C

mill exhaust air temperature °C Separator no. 1 Type:

speed of rotation rotor

%/min^-1

counter blades

%/min^-1

fineness R (0.03)

%

specific surface

cm^2/g

(Blaine) separator fan setting

%/min^-1

filter fan setting

%/min^-1

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HeidelbergCement Group Guidance Paper Process Evaluation of Ball Mill Grinding Plants

Separator no. 2 Type:

Edition:

02

Valid as of:

2016-03-31

speed of rotation rotor

%/min^-1

counter blades

%/min^-1

fineness R (0.03)

%

specific surface

cm^2/g

(Blaine) separator fan setting

%/min^-1

filter fan setting

%/min^-1

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HeidelbergCement Group Guidance Paper Process Evaluation of Ball Mill Grinding Plants

Page 2/2: Recording of control room data

Edition:

02

Valid as of:

2016-03-31

Date:

Plant: Plant type: A

B

Time: Mill filter

fan setting

Power consumption

%/min ^-1

roller press indication

kW

kWh-meter

kWh

ball mill indication

kW

kWh-meter

kWh

separator drives indication

kW

kWh-meter

kWh

bucket elevator

kW

electric ear

%

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HeidelbergCement Group Guidance Paper Process Evaluation of Ball Mill Grinding Plants

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02

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2016-03-31

Date:

Pressure/temperature profile Plant: Plant type: Test periods:

A

Time: Static pressure

mbar

°C

B mbar

°C

before ball mill after ball mill before static separator (= after ball mill) before cyclone

Air/gas temperature

(= after static separator)

[°C]

before mill filter fan (= after filter) after mill filter fan separator 1 before fan after fan separator filter before filter after filter after fan

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HeidelbergCement Group Guidance Paper Process Evaluation of Ball Mill Grinding Plants

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02

Valid as of:

2016-03-31

Date:

Pressure/temperature profile Plant: Plant type: Test periods:

A

B

Time: feed component

A: B: C: D:

Material temperature [°C]

ball mill outlet: cyclone fines: (after static separator) mill filter temperature of filtered material: separator 1 fines: grits: separator filter temperature of filtered material: finished product:

A: clinker B: gypsum C: slag Best_practice_guidance_paper_evaluation_ball_mill_grinding_plants_2016_02.docx

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HeidelbergCement Group Guidance Paper Process Evaluation of Ball Mill Grinding Plants

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02

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2016-03-31

MILL INSPECTION AND OBSERVATIONS

Plant:

Date:

Mill:

Time:

Important:

Measurements and observations after mill crash stop

Material distribution (above or below ball charge)

(taken at three different locations)

in mm

Inlet

Middle

Outlet

1st chamber: 2nd chamber:

Material level measurements in mm

(h: taken from the material surface to the highest point on the midpoint of the mill shell liners) Inlet

Middle

Outlet

Mill inside liner diameter Dli

1st chamber:

Dli =

Lli =

Effective grinding length Lli

2nd chamber:

Dli =

Lli =

1st chamber: 2nd chamber:

in mm

Calculation of mill filling degree f 1st chamber: 2nd chamber:

h/Dli: h/Dli:

f: f:

Coarse particle in front of diaphragms 1st chamber: 2nd chamber:

Slotted plates

Yes, mm: Yes, mm:

No No

Openings free or clogged (clogging grade percentage %)

1st chamber: 2nd chamber:

Ball charge classification (2nd chamber)

O good O bad O No classification

Condition of mill shell liners 1st chamber: 2nd chamber:

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MILL INTERNALS Plant: Mill:

Date:

1st CHAMBER HEAD LINERS Lining Row 1 (outer) Row 2 Row 3 Row 4 (inner)

Nos. Plates

Orig. thickness Rem. thickness mm mm mm mm mm mm mm mm

Nos. Rings

Plates/Ring

Conditions:

SHELL LINERS 1st chamber Lining

Shape

Type

Lifter height (mm) o bolted o semi-bolted

Conditions:

GRINDING BALLS Conditions

Diaphragm Slotted plates Row 1 (outer) Row 2 Row 3 Row 4 (inner)

Nos. Plates

Orig. thickness Rem. thickness slots width mm mm mm mm mm mm mm mm mm mm mm mm

Conditions:

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2016-03-31

MILL INTERNALS Plant: Mill:

Date:

2nd CHAMBER Diaphragm Backside plates Row 1 (outer) Row 2 Row 3 Row 4 (inner)

Nos. Plates

Orig. thickness Rem. thickness mm mm mm mm mm mm mm mm

Conditions:

SHELL LINERS 2nd chamber Lining Nos. Rings

Plates/Ring

Shape

Type

Lifter height (mm) o bolted o semi-bolted

Conditions:

GRINDING BALLS Conditions

Outlet Diaphragm Slotted plates Row 1 (outer) Row 2 Row 3 Row 4 (inner)

Nos. Plates

Orig. thickness Rem. thickness slots width mm mm mm mm mm mm mm mm mm mm mm mm

Conditions:

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ALL AROUND SAMPLES

Plant: Mill:

Date: Time:

Cement quality:

Particle size: [mm]

0.2 R%

0.09 P%

R%

0.045 P%

R%

P%

0.032 R%

Blaine

P%

cm²/g

Separator Feed Separator rejects Separator fines Mill filter product Stat. Separator Finish product

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