04 Milling

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1. Mill

1.1 Ball Mill General

a) Mill design General L/D ratio

• Raw mills: 1.5 < L/D < 3.2

• Finish / cement mills: 2.8 < L/D < 3.2

Length of first Compartments relative to total mill length

• Raw mills: First compartment length equals 35 – 45% of total mill effective length.

• Cement mill: First compartment length equals 30 – 35% of total mill effective length.

• When L/D>1.5, classifying liners might be used.

• The lower the L/D, the higher the circulating load needs to be (see below). b) Percent loading of mill

• % volume load =

(

)

2 2 r r h sin r r 360 2 π α α π ₋ ₋ where: - r is the radius - h is the free height - α= arccos r r h− - αin degrees π =3.14 0 10 20 30 40 50 0.5 0.6 0.7 0.8 0.9 % h/d % volume load Rules of thumb

• % vol. Load = 111.87 – 123.98 (h/d), 25 – 50%: error max 0.6%.

• It is estimated that material increases the actual ball filling ratio by about 2%.

• Another method (quick but not as accurate) consists in counting the number of visible shell liner plates (n) and to divide by the total number of shell liner plates per circumference (N): Angle

α

= n x 360 / N.

Values of angle h/d ratio in relation to the ball load (% filling degree)

Ball load (%) h/d n/N Ball load (%) h/d n/N

20 .7459 .667 31 .6516 21 .737 32 .6434 .590 22 .7281 .653 33 .6352 23 .7193 34 .627 .580 24 .7106 .639 35 .6189 25 .702 36 .6109 .569 26 .6926 .625 37 .6028 27 .685 38 .5948 .558 28 .6765 .611 39 .5868 29 .6682 40 .5789 .549 30 .6598 .601 41 .5709 42 .563 .539

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c) Mill Critical Speed 000000000000000000000000000000000000000000000000000000000000000000000000 Ž r m C P G • g r G r m C 2 2 ω ω = = where:

- G = Weight of grinding ball in kg

- ω = angular velocity of mill tube (rad/sec) - D = inside mill diameter (m)

- n = rev per minute - C = centrifugal power kg - D1 = inside mill diameter (ft)

• P=G*sin∂

(P is the resulting force of gravity)

• To maintain the ball in this position on the mill wall, it is necessary thatC≥P.

• Mill critical speed: n =_c

r 4 g 60 2 2 π =

D

3 .

42

(= 1 6 . 76

D ), with D in meters (D in feet)1

% Critical speed:

• Practically, mill speed between 68and 80% of critical speed.

• % critical speed is the mill actual speed in RPM divided by_nc. Example:

3.98 meter mill with rotational speed of 15.6 rpm then nc = 21.2, % critical speed = 73.6 %. d) Retention Time

Rules of thumb:

• Retention time: Open circuits:≥12 min Closed circuits:≥5 min

• The feed is pushing the material through the mill so that, If mill throughput increases: retention time decreases: 8 <

M C

< 12 where: C is the ball charge weight, M is the material weight Fluoresceine test:

• 2g/t of mill production. Prepare the fluoresceine with 800-ml alcohol and impregnate 2 kg of mill feed material (in a plastic bag).

• Put the material at mill inlet, start the time and sample every 30 s during 30 min. (others use salt). e) Mill Throughput

• Using elevator power and after calibrating we have:

•

(

)

H

kW

A

.

81 ,

9 .

3600

.

0

η

−

=

where: - A = Material flow (mtph)

- kW = Actual elevator power ( in kW)

- kW₀ = Elevator power empty

- η = Elevator efficiency

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f) Required air velocities for mill ventilation Rules of thumb

• Recommended 1.5 m/s above the ball charge: - inside the trunnion: 22-25 m/s.

- partitions: 8-14 m/s (<20 m/s).

- hood: <5 m/s to prevent dust from being sucked up (dust pick-up is proportional to speed^2). - dropout box: <2 m/s.

• 0.3-0.5 Nm3/kg ck 0.6-0.8 Nm3/kg raw mix

• Wet bulb temperature should be 30oC below the dry bulb temperature. g) Optimum filling ratio:

• U= (volume of powder in the mill)/ (volume of voids in the charge): between 60% and 110%, optimum around 90%.

• In practical terms, material level should equal ball level.

1.2 Ball Charge and Internals

a) Biggest Ball Bond Formula • 20 3

.

17 .

20

u i KMAX

D

W

K

d

Ψ

=

ρ

where:

- d_KMAX is the biggest ball diameter (mm) - d₂₀ is the sieve dimension (µ) with 20%

retained

- K is a constant (350 for a dry mill open or close circuit, 300 for wet)

- ρ is the specific mass of material (g/cm3) - W is the Bond work index (kWh/t)_i - D_u is the mill inside diameter (m)

- Ψ is the ratio between the actual / critical speed (%)

Quick evaluation • For clinker: 80

d

24 =

B

(Other formula exist that result in value differences of±5%)

- B = ball dimension (mm)

- d₈₀ is the sieve with 80% passing

Grinding Ball vs Clinker Size

.1 1 10 100 10 100 Clinker Size d80 O p ti mu m B a ll D ia me te r (m m ) Rowland Formula • _       Ψ = u i

D

W

K

d

B

281 .

3 .

.

100 .

.

4 .

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Material bulk density and Bond index i W kWh/st ρ (g/cm3) Clinker: 13.49 3.09 Limestone 10.18 2.68 Shale 16.40 2.58 Slag 15.76 2.93 Sand stone 11.53 2.68 Silica sand 16.46 2.65 Coal 11.37 1.63 Clay 7.10 2.23 Gypsum 8.16 2.69 Kiln feed 10.57 2.67 Bulk density g/l or kg/m3 lb/ft3 Sand Sand Iron Bauxite Brick Gypsum Fluid coke Limestone (crushed) Silica fume Bottom Ash Cement T I-II T 10 T III Clinker Clinker (underburnt) 1387 1679 2629 1980 1502 1677 926 1803 1024 1241 1234 1207 1054 1575 1400 86.6 104.9 164.2 123.6 93.8 104.7 57.8 112.6 63.9 77.5 77.1 75.4 65.8 98.4 87.4 Raw mix 1041 65.0

b) Grinding Balls Data Grinding Ball dimensions

Diameter

mm inch

Weight (g)

Surface

(cm2₎ Number of balls per_{metric tons} Weight of 1 m3 of_{balls (kg)} Specific surface_(m2_{/ mt)}

100.00 ± 4" 4,001.153 314.159 250 4560 7.854 90.00 ±3½" 2,916.841 254.469 343 4590 8.728 80.00 2,048.590 201.062 488 4620 9.812 77.00 ±3½" 1,826.658 186.265 548 10.207 70.00 1,372.396 153.938 729 4640 11.222 64.00 ±2½" 1,048.878 128.680 954 12.276 60.00 864.249 113.097 1,157 4660 13.085 50.00 ±2" 500.144 78.540 2,000 4708 15,708 40.00 256.074 50.265 3,905 4760 19.628 38.00 ±1½" 219.551 45.365 4,555 20.664 35.00 171.549 38.485 5,830 22.437 31.75 ±1¼" 128.061 31.669 7,809 24.730 30.00 108.031 28.274 9,257 4850 26.173 25.00 ±1" 62.518 19.635 15,996 4894 31.408 23.00 48.682 16.619 20,542 34.139 22.22 =7/8" 43.895 15.511 22,782 35.337 20.00 ±3/4" 32.009 12.566 31,242 4948 39.259 17.00 ±5.8" 19.658 9.079 50,870 4989 46.185

(Unit weight and specific surface of MAGOTTEAUX grinding media)

Quick calculation:

• Ball diameter (mm) = 3 _{250 P} ₍_{P = weight in g)}

• Specific surface of balls of diameter = m mt

d /

785 2

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Wear rates:

Ball diameter mm Wear GT ball

g/h.T Wear / Ball g/100h Wear∂ diam mm/100h 100 90 12.9 38.6 0.4 80 14.4 30.4 0.4 70 16.7 23.6 0.4 60 19.3 17.2 0.4 50 23.1 11.9 0.4 40 28.9 7.6 0.4 30 38 4.22 0.4 25 46.5 2.98 0.4 20 58.5 1.92 0.4 17 68.2 1.38 0.4

Bulk density for ball load

(coarse to medium ball size distribution):

• In first compartment; 4.3 –4.5 metric tonnes per tonne of balls (3.0 to 2.0 inch balls would be fine).

• In second compartment; 4.5 – 4.65 metric tonnes per tonne of balls (2.0 to 0.75 inch balls would be considered medium to fine).

• In single compartment: 4.5 – 4.55 metric tonnes per tonne of balls. c) Others internals

Partitions

• Total slot area: 10 to 20 cm2/tph production:

Slot Size Central Part Discharge Part

FM 7 mm±1 mm 9 mm±1 mm

RM 10 mm±1 mm 12 mm±1 mm

Liners

• Liners must be changed when 60% of their effective lifting height has worn away: - -8 to –10 % production

- reference points to measure lifting height are the lowest point on the liner to the highest release point (contact points between grinding ball and liner plate)

• American Lorrain pattern: diameter (ft)*2=# bolt holes/row, 18.8” center to center.

• DIN pattern: diameter (m)*10== # bolt holes/row, 31.4 cm center to center.

• Classifying liners if L/D>1.5 and volume load<35%.

• Without classifying liners, keep a maximum of 3-4 ball sizes.

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d) Mill Internal Inspection Sheet

Points to audit Ball Charge Remarks

Shell Liner Thickness Ball Coating Remarks Shell Liner Lifter Thickness Ball Classification Remarks Shell Liner Remarks Discharge Grate Slot Size-Average Inlet Head Liner Thickness Discharge Grate Slot Size-Maxim. Inlet Head Liner Remarks Discharge Grate Metal Thickness Inlet Opening Remarks Discharge Grate Percent Blinded

Height Liner, to Balls - Average Discharge Center Screen Percent Blinded Width Across Balls - Average Material Position in Mill

Calculated Percent Fill

1.3 Ball Charge Design (Finish Mill)

a) Recommended volume loading (see BP Ball Charge Management)

Recommended Volume Loading

1stCompartment 2ndCompartment 3rdCompartment

Minimum kWh/t1 26 – 28% 28 – 30% 28 – 30%

Maximum Production 32 – 34 % 34 – 36% 34 – 36%

(Ball level in the trunion should not be higher than 2 to 3 inches.) b) Polysius Design

• As a rule of thumb, it suits raw mills and especially monochambers very well, especially if no classifying liners are used.

• 13 . 0 6 . 9 D ln x e 6 . 9 D 013.x −     = ⇔ = − where: - D = Ø ball (cm)

- x = effective mill length (m)

• Process step-by-step, calculating each effective length starting from the input and with the largest ball: 1. Calculate effective lengths and the ball sizes you plan to use.

2. Double the first effective length which is both the first interval width and the first cumulative length. 3. Calculate each succeeding interval width by taking the effective length and substract the preceding

cumulative length and doubling it. Add this value to the previous cumulative length to get the new one. 4. If an interval overlaps with the partition divide the interval at the point of overlap. The excess is carried

over to the next compartment. At the end of the mill, the interval is truncated at the point of overlap. 5. Once the intervals have been adjusted for compartment lengths as described in step (4), divide the adjusted

interval by compartment length and multiply by 100. This is the percent weight for each size to be used in the compartment.

c) Slegten Model 1

The recommended volume loading for minimum kWh/t is based on an acceptable compromise with production. For minimum kWh/t the volume loading can be as low as 22%.

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First Compartment – Crushing

• Same number (n) of balls in each size range.80, 70 and 60 mm Ø and then add some 90 mm Ø to deal with oversize clinker. This equilibrium charge will not change as you add 90 mm Ø make-up balls to maintain volume load.

Ø Ball (mm) % of Weight (x) % of Weight Number/ 10 t of Charge

90 100-5x 20.0 670

80 2-4x 38.4 1820

70 1.6x 25.6 1820

60 x 16.0 1820

- x= is taken to be the number of balls in the last size.

• In recent years, Slegten has favored a 3-ball size distribution in first compartments over a 4- ball size as shown in table above.

Transition Zone

• This is at the beginning of the second compartment and basically its job is to clean up anything which penetrated the partition that is oversize for the second compartment charge to fracture.

• The design for this area is to use "n" balls of 50 and 40 mm.

Ø Ball (mm) Number/ 10 t of Charge

50 1820

40 1820

• The transition zone is made of the largest ball size used in this transition zone is sometimes identical to the smallest ball size used in the first compartment.

Second Compartment – Fine Grinding

• The envelope curve for the balls smaller than 40 mm follows the following formula:

• _D₌₃_.₃_e−010.x where:

- D = Ø ball (cm)

- x = distance from transition zone finish (m)

• The 30 mm balls start at the completion of the transition zone and the exponential curve follows. Rule of thumb:

• The smallest ball size should, as a minimum, be at least twice the width of the slots in the grates (ex.≥16 mm balls if slots are≤8 mm wide). For this reason, it is generally recommended to use ¾” (19 mm) balls as the smallest size in Finish mills. 5/8” balls are fine when the grates are new but often become problematic as the grate slots enlarge.

d) Example: Comparison Slegten/ Polysius

1stcompartment useful length = 3.81 m, 2ndcompartment useful length = 7.66 m

Using an average ball weight of 1.65 kg per ball and 3 ball sizes in the first compartment for the Slegten model.

Ball size and % compartment load Polysius design Slegten design

3 ½” 31.0% 32.1% 3” 31.2% 43.1% 1stcompartment 2 ½” 37.8% 24.8 % 2ndcompartment 2” 2.31% 7.67% 1 ½” 23.73% 2.94% Transition zone 1 ¼” 34.05% 10.08% 1” 2.57% 48.18% ¾” 37.34% 31.13% 5/8” - (Some)1

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A limited amount of 5/8” balls should theoretically be added but the designer decided to use ¾” as the smallest ball size.

e) Fineness in Finish Mills:

In the first compartment before intermediate diaphragm

• 95% passing of 2.365 mm (2360µor 8 mesh) for the material leaving the first compartment 33% of energy.

• Particle size distribution recommended on other sieves: - 86 – 92 % passing 1.0 mm (1000µm or 18 mesh) - 80 – 90 % passing 0.6 mm (595µm or 30 mesh) - 75 – 85 % passing 0.5 mm (500µm or 35 mesh) In the second compartment before discharge diaphragm

• 95% passing 0.5 mm (500µm or 35 mesh)

• 70- 80 % passing 0.2 mm (212µm or 70 mesh)

1.4 Grinding Laws

a) Absorbed Power of a Mill

• Only 5-10 % of the energy is used for grinding, 90% is wasted into heat, wear…

• With similar ball charge gradation and similar liners' lifting effect, the absorbed power is related to: - Tonnage of balls - Mill rpm - % volume load - Mill diameter Slegten formula • _j _Fr 27 . 1 cr K * K * V rpm * W P     = and *F *L* J*d 4 W =π _r2 where:

- P: the motor absorbed power (kW) - W : the weight of the load (T)

- F : internal diameter (inside liners) (m)_r

- J : the ratio between the apparent ball volume and the internal volume

- rpm: is mill speed (rpm) - d is the apparent density of load (t/m3)

#1 comp : d = 4.5

#2 comp : d = 4.65, if fine ball size distribution (say with average ball weight < 40 g) d = 4.6, if coarser ball size distribution (average ball weight > 40 g)

Average : d = 4.6

- _{Vcr is the critical speed inside liners=}

        r

F

3 .

42

, L : the useful length of mill (m) - K_j =1.36 −1.2J , K_Fr =C.F_r0.379

- K_Fr is the influence of the location of the center of gravity for the moving ball charge vs. the mill center (C is a constant depending on the material and the liners).

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• *F *d*C 4 * K * J * V rpm * L P _j _r2.379 27 . 1 cr π     = Simplified formula •

*

9 .

5

366 .

1 *

*

75

100 *

*

_j r cr

F

K

V

RPM

T

P

_     

=

Kj Function of Volume Load

Volume load _Kj 40% 30% 20% 0.9 1 1.1 Rules of Thumb

• One metric ton of balls increases the mill power draw by 10kW.

• Usually, 8 to 12 kWh/t is absorbed in the first compartment for clinker grinding. b) Grinding Laws

General Law: Charles

• dW =cx−ndx

- If W = Comminution work, x = Size of particles (initial, final)

Value of n

Energy Law Value of n: Applies well over range of:

Rittinger Kick Bond 2 1 1.5 10 – 1000µm

Normalized Blaine fineness equation

• Fineness equation, generally accepted within Lafarge Corp: n

Blaine

W

_     

=

2

1

1 2

- n = 1.4 for high efficiency separator (HES) circuit, n = 1.6 for Sturtevant separators, bearing in mind that 16’ and 18’ Sturtevant separators are more efficient than the larger 20’ and 22’ Sturtevant.

- W: communition work, W is proportional to production rates.

• Proposed by Polysius: C₂ =C₁*e0.43(Blaine1−Blaine2)/1000 where C₂ and C are production capacities₁

• Rene’s Study: +1% passing at 10µm: +10.8 SSB Rules of thumb

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2. Separator

2.1 Circulating Load

a) Junction with Three Streams

A

R F

• A, R, F are the feed, reject and fine of the separator

- a ,_i r ,_i f are the cumulated % passing at a defined sieve(i)._i - da, dr, df are the % retained corresponding to the sieve interval dx.

- A = R + F - A da = Rdr + Fdf

With:

da=a_i₊₁−a_i

,

dr df da df A R − − = , df dr da dr A F − − = b) Drawing • Plot

(

f_i −a

) (

vs f_i −r_i

)

If the mill circuit is steady, the graph has to be a straight line:

(

f −a

)

=α+β

(

f −r

)

- α should be close to 0

- β is the most probable value of A R

- The circulating load is defined as:

β β − = 1 F R c) CL calculation

• Using the least square line calculations, withα =0

d) Quick CL calculation

• With one set of results of sieving: r a a f F R − − = 2.2 Tromp Curve a) Tromp Curve

• On the Gausso-logarithmic paper, let's plot the probability for a given particle of a certain size entering the separator to go to the rejects

A * ) x ( da R * ) x ( dr = with:

∑

= = − − − = n 0 i 2 i i n 0 i i i i i ) r f ( ) r f )( a f ( A R

• The Tromp curve can be divided into two straight lines:

- The right one (higher sieves) has a slope which is representative of the separator efficiency (a perfect one would be vertical).

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b) Imperfection • 50 d * 2 25 d 75 d

I = − where:_- _{d25 is the size of the particle which has 25 % chance of going to rejects} - d50 is the size of the particle which has 50 % chance of going to rejects - d75 is the size of the particle which has 75 % chance of going to rejects I = 0.4 -0.5 for a high efficiency separator

0.6 - 0.7 for a Sturtevant

0.45 - 0.6 for a Raymond separator Imperfection vs Circulation Load

0 100 200 300 400 0.36 0.38 0.40 0.42 0.44 Circ. load (%) Imperfection c) Acuity Limit

• AL is the abscissa of the intersection of the two Tromp curve lines.

• It’s the size at which selection is initiated Rule of thumb

• Cement mill = Acuity limit: 20-30µm, Raw mill = Acuity limit: 30-60µm d) Bypass

Definition:

• By-pass is the ordinate of the intersection of the two Tromp curve lines.

• The bypass is the lowest percentage of feed that will go to the separator rejects. Bypass vs. feed rate – Sturtevant

• The following graph shows the Bypass of an 18’Sturtevant versus its feed rate.

50 100 150 200 250 300 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0 0 0 0 0 0 0 0 0 00 00 00 00 00 00 00 00 00 0 20 40 60 80 100 000000000000000000000000000000000000000000000000000000000000000000000000000000 000000000000000000000000000000000000000000000000000000000000000000000000000000 000000000000000000000000000000000000000000000000000000000000000000000000000000 000000000000000000000000000000000000000000000000000000000000000000000000000000 Feedrate to Separator (t/h) B y p ass (% )

Bypass vs. feed rate O’Sepa/Sturtevant

0000000000000000000000000000000000000000000000000000000000000000000000000 0000000000000000000000000000000000000000000000000000000000000000000000000 0000000000000000000000000000000000000000000000000000000000000000000000000 0000000000000000000000000000000000000000000000000000000000000000000000000 0000000000000000000000000000000000000000000000000000000000000000000000000 0000000000000000000000000000000000000000000000000000000000000000000000000 0000000000000000000000000000000000000000000000000000000000000000000000000 1.0 1.5 2.0 2.5 3.0 3.5 00 00 00 00 00 00 00 00 00 0 0 0 0 0 0 0 0 0 00 00 00 00 00 00 00 00 00 0 0 0 0 0 0 0 0 0

Qf/Qa (kg feed/m3 separator sweep)

0 10 20 30 40 50 60 70 80 O-Sepa Sturtevant B y p ass (%)

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QF/Qa vs. bypass

• IfQf is the separator feed rate (kg/h) and Qa the separator ventilation (m3/h),

• Qf/Qa is an important ratio for the separator efficiency. • Bypass =     ₋

+

Qa Qf f

e

1

- f1: coefficient for the separator 0 1 2 3 4

00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0 0 0 0 0 0 0 0 0 0 0 10 20 30 40 00000000000000000000000000000000000000000000000000000000000000000000000000 00000000000000000000000000000000000000000000000000000000000000000000000000 00000000000000000000000000000000000000000000000000000000000000000000000000 00000000000000000000000000000000000000000000000000000000000000000000000000 00000000000000000000000000000000000000000000000000000000000000000000000000 Qf/Qa (kg/m3) B y p ass (% )

e) Rosin Rammler Number

• The steeper the size distribution (RR# high) the more efficient the grinding and separating process.

• Raw mix RR# are usually lower

RRnumber vs. Feed to Air Ratio

1.0 1.5 2.0 2.5 3.0 3.5 4.0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1.00 1.05 1.10 1.15 1.20 000000000000000000000000000000000000000000000000000000000000000000000000000000000000 000000000000000000000000000000000000000000000000000000000000000000000000000000000000 000000000000000000000000000000000000000000000000000000000000000000000000000000000000 000000000000000000000000000000000000000000000000000000000000000000000000000000000000 000000000000000000000000000000000000000000000000000000000000000000000000000000000000 Qf/Qa (kg/m3) Ro s in -Ra mle r Nu mb e r (n ) Separation Performance

• Rate of recuperation in the fines of particles smaller than a given dimension. a f * A F r=

2.3 Indicators for Cement Milling and Typical Values IMLt > 37 (laser / sieve)

IMLm: in the 17 –19 range 100/c: 63 – 91 % range 100/c C1: 60 –85 % range 100/c C2: 80 –110 % range NRR fines: 1.1 – 1.4 for HES

0.85 – 1.0 for 1stgeneration separators (Sturtevant, Raymond) 1.2 for second generation separators

% recovery, 45µm: 55% for HES Acuity: 20 – 30µm Imperfection: 0.4 – 0.5 for HES

0.45 – 0.6 for Raymond separators 0.6 –0.7 for Sturtevant separators Bypass: 5 – 10% range for HES

Circulating load: 150 –200 % with HES HES Qf/Qa: 1.5 – 2.0 range

% Passing 45µm: 93% minimum (45µm = 325 mesh)

Cement Mill RR#

Open Circuit 0.75 – 0.85 Raymond Sturtevant 0.85 – 1.00 2ndgeneral HW 1.00 – 1.20 High Efficiency Separator 1.10 – 1.40

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2.4 Sturtevant/O'Sepa (Bath #B mill) Data before (22' Sturtevant)-after (O'Sepa)

T10 T1

Before After Before After

Prod(T/H) 81 93.3 71 79.4 kWh/t total 42.6 40.3 48.6 47.1 Mill+elev+sep 42.1 36 48.0 42.4 Mill 38.3 34.9 43.7 41.0 Blaine 380 358 380 361 45µ 89 91.6 90 94.7 Strength 3d (MPa) 24.3 24.8 25.2 24.7 7d (MPa) 28.4 28.9 29.7 29.2 28d (MPa) 34.5 34.4 35.2 35.2

Water dem (% for NC) 24.8 25.8 25.3 26.4

Flow@ 48%W/C 113 107 121 113

Gypsum dehydrant(%) 65% 25 65 25

Setting time VIS(min) 120 120 117 124

VFS(min) 218 225 218 231

Blaine vs 325 40.6 39.0

Circuit characteristics

Mill Separator

Diameter: 3.96 m O'Sepa N-2000

#1 comp length: 5.04 m eff Airflow design: 2000 m3/mi

#2 comp length: 9.72 m eff Pressure drop: 8"

Power Connect: 3581 kW Rotor speed: 100-230 rpm

Lining #1 comp: Lifting Feed capacity: 420 tph

Lining #2 comp: Classifying Power: 200 HP AC var. freq

Partition slots: 8mm-1

Discharge slots: 8mm+1

Ball charge (B mill)

Before After comp 3"1/2 20% 20% 3" 60% 60% 2"1/2 20% 20% Volume load 33% 33% comp 2"1/2 7% 3% 2" 4% 6% 1"1/2 8% 9% 1"1/4 9% 9% 1" 12% 22% 3/4" 60% 51% Volume load 34% 36% Power kw 3100 3260

Temp Press Flow Flow

ºC "WG m3/h Nm/h Mill sweep 78.3 -11 34101 25781 Separator Primary 15 0 66487 63024 Aux 1301 Secondary 15 0 24079 22825 Tertiary 15 0 13814 13095 TOTAL 100245 Outlet fan 61 0 143381 117156

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Separator sp = 174 RPM

Mill feed = 79.2 t/h

Mill #1 sound = 78.2 Mill #2 sound = 62.5

Mill out temp = 84 °C

Elevator = 34 kW

Mill = 3101 kW

Type 10 Tromp curve (A mill)

R/A) mean = 0.656 CL = 191% Acuity limit = 12 µm Bypass = 8 % Imperfection = 0.39 Rosin-Rammler(fine) = 1.15

2.5 Recommended Steps for Sizing a HES

a) Estimate new production rate

• Assume a specific power consumption for an optimized ball mill with HES (37 kWh/t TI @3700 Blaine)

• Back calculate the production rate based on the available motor power

• Use the standard Blaine adjustment formula (Prod1/Prod2 = [Blaine2/Blaine1]^1.4). b) Fix the Qf/Qa target with the circulating load

• Decreasing Qf/Qa (kg feed per Am3 of air) increases the separator efficiency but also increases the capital and the operating costs.

• The CTS process target is Qf/Qa = 1.6 @ CL (R/F) = 150%; Qa @ 65C; 3800 Blaine.

• The CTS upper limit is Qf/Qa = 2.0. Lower than this only marginally improve the separator Imperfection and Bypass of 2-5% and therefore has no effect on production or product quality

Other suppliers’ rules of thumb:

• Fuller typically sizes at a Qf/Qa = 2.0-2.5 @ CL = 180%.

• Christian Pfeiffer - Finish mill:

Qf/Qa = 1.8 @ CL = 200%; Qa @ 90C; 3500 Blaine; Qp/Qa (kg fines per m3 of air) 3000 Blaine 0.75-0.80 kg/Am3

4000 0.55-0.60

5000 < 0.50

- Raw mix:

Qf/Qa = 2.2 @ CL = 200%; Qa @ 90C; 12-14%R 90 µm., Qp/Qa: 0.55 kg/m3.

- Slag: Christian Pfeiffer sizes slightly larger for slag circuits due to lower density and higher CL, as does Polysius.

c) Fan and Bag House Sizing

• Use the new production rate (T/h), Qf/Qa (kg/ Am3) and circulating load (%) to specify the air flow.

• Most separators can operate at +/- 20% of nominal.

• Only a margin of 5 - 8% above the separator airflow is recommended for the BH.

• Margin of 5-10% is recommended on top of the BH for the fan.

• Correctly specifying the static pressure:

- Pressure drop can be estimated by the dP of the separator (8-12"), D/C (4-8"), ducting. (3-6") and if present, silencer (1-2").

- The recommendation is 26 in WG with a minimum of 24 in WG.

(19)

3. Heat and Water Balance

a) Water

Gypsum dehydration

• Water generated = 0.156977*M*K*D where:

- M = kg/h of SO3 source excluding clinker,

- K = % pure CaSO4(2H2O)

- D = % dehydration (from DSC) Spray cooling with water

• Water flow(kg/h) = Q*Cp*(Tf-Ti)/((100-Tw)+538.9*f) where:

- Tf and Ti are the temperatures of material or gas before and after cooling (in C) - Cp (kcal/kg) is the specific heat of material or gas and Q its flow rate (kg/h) - Tw is the water temperature (C) and f is the % water evaporated.

Rule of thumb

• Usually, water flow ranges from 0 to 3 % of the mill production b) Heat balance

Mill heat generation

• Kcal/h = kWh (power measured)*factor*860

- Factor = 0.75 for vertical mill and 0.9 for ball mill Furnace wall losses

• About 5kcal/kg fuel c) Mill heat balance sheet

Mill Product Rate (STPH)

Feed Temperature ___________ Percent H2O %

Mill Diameter_ Ft. Mill Length____ Ft. Mill Motor HP Mill Liner Thickness ________in Ball Charge % Separator Ventilator Volume ACFM Temperature F Pressure in.H2O

Mill Ventilator Volume ACFM

Temperature F Pressure in.H2O

Baghouse Ventilator Volume ACFM Temperature F Pressure in.H2O

Auxiliary Ventilator Volume ACFM Temperature F Pressure in.H2O

Percent H2O in Separator Rejects %

Product %

Mill Discharge % Percent Recirculating Load %

Percent Leakage Into Separator (CFM) % Maximum Separator Inlet Temperature F Ambient Temperature F

Percent Relative Humidity %

Plant Altitude FT

Fuel Type Heat

Value

Separator Rejects Temperature F Product Temperature F Baghouse Cloth Area FT2 Number of Compartments

(20)

4. Grinding Aid

Type of Products

• Surface active agents tend to saturate the free valence and inhibit the pack-set. Typical surface-active agents are:

- ligno-sulphonates - polyoils

- amines

- organic acids

• Polar compounds (water, ammonia) are known to have some action on such bonds through their polar moment. However, their practical use as surface agents is limited by their other impacts on the cement properties.

• Other agents, particularly coal dust, have been used in the past.

• Commercial products available as grinding aids are essentially (60-800 g/t ck): - Triethanolamine

- Polypropyleneglycols and polyethylene

• HEA2, DDA& and other products cause a definite reduction of pack-set but do not prevent agglomeration or lump-formation problems that are caused by:

- Alkalis (K₂SO₄) - Moisture

The effect of grinding aid on milling process:

- Enhances the flowability and prevents agglomeration

- Prevents coating on liners and grinding media- Decreases the "Blaine: Passing 325" ratio - Is lLowers effect on coarser product (below 320 m2/kg)

- Reduces contraction Example Bath

• HEA2 on the feeding belt, Range: 0.1-0.2 kg/t of kk

• Specific gravity: 1.195 kg/l, % active agent: 70%

• Price: 1.31 $/l, Cost: 195 . 1 * 7 . 0 15 . 0 * 1.31 = 0.234 $/t kk • At kWh/t cte, 200g/t of glycol: +80 SSB

• Production increase and pack set decrease. Mixed with water (3/1) and injected in #1 comp

HEA2 (Grace) HEA2/rm (Grace)

0.025% weight per weight of kk 2.02$/kg

6% production increase reduce cracks

0.078% weight per weight of kk 1.48$/kg

(21)

5. Sieve

Sieve Screen Micron Iso alter Screen Micron Iso alter

#400 37 38 #14 1400 #325 44 45 #12 1700 #270 53 53 #10 2000 2000 #230 63 63 #8 2360 #200 74 75 #7 2800 #170 88 90 #6 3350 #140 105 106 #5 4000 #120 125 125 #4 4750 #100 149 150 #3.5 5600 #80 177 180 1/4" 6350 6300 #70 210 212 5/16" 8000 8000 #60 250 250 3/8" 9510 9500 #50 297 300 7/16" 11200 11200 #45 354 355 1/2" 12700 12500 #40 420 425 5/8" 16000 16000 #35 500 500 3/4" 19000 19000 #30 595 600 7/8" 22600 22400 #25 707 710 1" 25400 25000 #20 850 1"1/4 32000 31500 #18 1000 1000 1"1/2 38100 38100 #16 1180 2" 50800 50000

04 Milling

Table of Contents

1. Mill

(

)

α

D

3

.

42

(

)

H

kW

kW

A

.

81

,

9

.

3600

.

η

−

=

.

.

17

.

20

D

W

K

d

d

Ψ

=

ρ

d

24

=

B

D

W

K

d

B

281

.

3

.

.

100

.

.

4

.

F

3

.

42

*

9

.

5

366

.

1

*

*

75

100

*

*

F

K

V

RPM

T