Vertical Roller Mill

VERTICAL ROLLER MILLS

© Confederation of Indian Industry

Vertical Roller Mills (VRM)  An

advancement over ball ball mill



Roller Roll er mill – Grind Grinding ing by Compress Compression ion



Rollers / Balls on ring



Presently for Raw meal, Coal & Cement



More Energy efficient © Confederation of Indian Industry

1

VRM - Features  VRM

Drive - 40% of ball mill



Dry moisture up to 15 %



More compact & Less space



Fan Power consumption - High



Separator - Integral Part of Mill © Confederation of Indian Industry

Features of VRM  Energy 

Efficient Grinding System

Mill drive – 40% less consumption

 Most

suited for drying – upto 15%

moisture  More

compact & occupies less space

 More

amenable for Controls © Confederation of Indian Industry

2

Comparison of Ball Mill & VRM Ball Mill

Moisture (%) Mill Drive (units/ton) Fan + separator Total

VRM

3.0

7.0

3.0

7.0

14.0

14.0

6.5

6.5

1.9

5.0

7.5

7.5

15.9

19.0

14.0

14.0

Ideal choice for high moisture material © Confederation of Indian Industry

ENERGY SAVING IN VRMs 

Fine tuning of louvres



Mechanical Recirculation system



High efficiency classifier



High Level Control system


3

Install Variable Area Louvre Ring  Air

flow inside VRM not uniform

 Material

leaves in a definite pattern

around table  Max.

material behind and in front of each

roller


Install Variable Area Louvre Ring 

Uniform area louvre ring 

Uniform gas system



Uneven bed of material



Gas prefers path of least resistance



Higher gas flow rates essential


4

Install Variable Area Louvre Ring  Variable 

area louvre ring

Larger area at points of larger concentration



Gas flow directed to material



Potential open area higher



Lower Pr.Drop and lower gas flow



Reduced fan power consumption



Presently fixed area louvre ring



Pr.Drop across mill – 870MM WG



Flow thro mill – 3,40,000 M3 / HR



Mill output – 155 TPH



Recommended to install variable area louvre © Confederation of Indian Industry

5


Pr. Drop across mill – 820 MM WG



Flow thro mill – 3,10,000 M3/HR



Mill output – 155 TPH

 Annual

savings – Rs 9.2 Lakhs


R e j e c t s

Area – 1.132 m2

G a s R e j e c t s

D

C

B

A A

B

C D

Velocity – 83 MPS

E

F

F E

E F

D

F

C

r e l l o R 1

E D C B A

4 Roller

B A A 2 Roller

A

B C D

r e l l o R 3

B C

E F F

D o r o t M

E

Mill Door

E F

F

E

B D C B A A


C

R e j e c t s

D G a s R e j e c t s

6

Fan Power Consumption in VRM 

High in comparison to Ball Mill



Major Reason  Higher 

pressure drop

400 – 900 mm WG

 Higher

air flow rates


Pressure drop in a VRM 

Ranges from 400 - 900 mm Wg



Pressure drop 

75% - Mill louvre



25% - Housing & classifier


7

Why High Pressure Drop ? 

High louvre velocity : 55 – 85 m/sec



Why high louvre velocity ? 

Lift particles of higher sizes 



Grinding table to separator

Reduction of louvre velocity 

Reduction of mill - ∆P



Higher quantity of rejects at mill bottom


Mechanical Recirculation System 

Rejects handled mechanically



Recirculated back to mill through BE



Tremendous reduction in pressure drop & energy consumption


8

Mechanical Recirculation ESP

VRM VRM Fan


Louvre velocity vs. Mill power Louvre velocity (m / sec) 75

50

35

Mill ∆P (mm Wg)

900

630

450

Reject rate (% of fled)

0

5 – 15% 150%

Fan Power (units / ton)

6.9

5.5

4.7

Mill power (units / ton)

6.5

6.6

7.2

Total power

13.4

12.1

12.1*

* Includes power for mechanical recirculation © Confederation of Indian Industry

9

Louvre velocity – How much reduction possible ?  Air   



flow through mill depends on

Louvre velocity Drying requirement Separator requirement

Reduction of louvre velocity to lower levels  

Large material handling equipment Large mill housing  

Leads to pre-separation Less stability & Table vibration

Optimum louvre velocities with mechanical recirculation : 45 – 55 m/sec © Confederation of Indian Industry

Reduce Recirculation Air in VRM Recirculation High

air – 60 kM3/Hr

recirculation air

High

velocity At louvres

High

∆P

High

power consumption


10

Reduce Recirculation Air in VRM

Trial

taken

Recirculation RPM

reduced by 20 kM3/HR

of class red.

Same

residue maintenance


Reduce Recirculation Air in VRM R/M

Fan power consumption reduced by 150 kW

Savings -

Rs 30 Lakhs


11

Separators for VRM’s 

I stage

-

Static separator



II stage

-

Dynamic conventional separator



III stage

-

High efficiency separator


High Efficiency Separators  Air

requirement lower



High eff. - 0.6 – 0.8 kg matl / kg of air



Conv.

- 0.4 – 0.5 kg matl. / kg of air



Better separation efficiency



Lower “∆P” across mill



Higher output & lower specific energy consumption © Confederation of Indian Industry

12

High efficiency Separator

Old Separator

Features of high efficiency Separator 

Minimum pre-separation in mill housing



Maximum separation in the separator



Coarse return drops exactly in the centre of the table


13

Features of high efficiency Separator 

Benefits 

Increase in output – 10 to 30%



Reduction in specific energy – 

 Very

1.5 to 3.5 units/ton

attractive financially


Replacement with High Efficiency Separator (Raw Mill) Before Capacity

After

250 TPH 290 TPH

Residue (90 µ)

11.5%

13.2%

Mill power (units / ton)

4.7

4.1

Fan power (units / ton)

8.5

6.2

13.3

10.3

Total Power


14

Effect of Roller to Table Dia


Effect of Roller to Table Dia

For the LM 38.4 the ratio between diameter for roller and table is 0.45, for the Ube LM 45.4 the ratio is 0.5, whereas for the LM 56.4 the ratio is 0.40.


15

Effect of Roller to Table Dia LM 38.4

LM 45.4(Ube)

LM 56.4

Diameter of Grinding Table

3.80 m

4.50 m

5.60 m

Diameter of Rollers

1.70 m

2.24 m

2.24 m

Width of Rollers

0.67 m

0.85 m

0.85 m

Kwh/ts, Mill

6.31

5.99

7.00

Kwh/ts, Fan

6.23

5.51

7.00

12/0.8

11/0.8

11/0.9

Dust Load (g/cum)

610

630

595

Delta P, Mill

83

56

87

3-5

2-4

5-8

Residue (90/212 microns)

Vibration of Mill


Effect of Operating Pressure Ube LM 40.4

Grinding Pressure

650

662

675

687

700

Capacity

290

295

300

305

310

Kwh/ts, Mill

9.0

9.0

9.0

9.0

9.0

Vibration

4-5

4-5

4-5

4-5

4- 4.5

Delta P of Mill

54

53.5

53

52.5

52

kN/m2


16

Effect of Operating Pressure



10 % increase in Grinding pressure 

Capacity increase by 7%



Mill drive SEC no change



Fan power 0.5 kWh / MT reduction © Confederation of Indian Industry

Influence of Feed Size for an LM 40.4 Raw Mill Max 90 mm Max 30 mm Capacity

240

262

Kwh/ts, Mill

8.05

7.41

Delta P, Mill

76

73

5-7

4-6

Vibration


17

High Level Control System for Mills 

Conventional – Open loop controls



I Generation  “∆P”



vs Feed controls

Latest control system 

Min. 3 to 5% improvement – Production & Energy



More stable operation of VRM © Confederation of Indian Industry

High Level Control System for Mills 

Latest control system  “Feed”

– Based on ∆P, Load & Recirculation (B.E)

 “Mill 



flow” kept constant

Mill Load, ∆P, Recirculation load 

Fineness predicted



Separator speed varied

Prediction mechanism varied depending on actual fineness © Confederation of Indian Industry

18

To Sum-Up  VRM

– Developing into an excellent

choice 



Raw mill, Coal, Cement & Slag

Further improvement opportunities 

Mechanical recirculation



High efficiency separators



High level control system © Confederation of Indian Industry


19

Vertical Roller Mill

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