Comparison between currently applied cement grinding technologies Hajo Reiners
Agenda
1. Cement Grinding with Loesche Vertical Roller Mills 2. Other Systems for Cement Grinding 3. Former Concerns regarding VRM Cement Qualities 4. The Proven Reality 5. Short Conclusion
2012
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Cement Grinding with Loesche VRM Mills Loesche cement mills worldwide
LOESCHE Ref. C/S Mills 11-2011 LM 63.3+3 LM 56.3+3 LM 56.2+2 LM 53.3+3 LM 46.2+2 LM 41.2+2 LM 35.2+2
Worldwide nearly 240 mills with the 2+2 / 3+3 system… About 170 of them are in operation 2012
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Cement Grinding with Loesche VRM Mills
kWh/t
Power consumption of ball mill system v/s LOESCHE VRM system (mill, classifier, fan) - OPC grinding
100 90 80 70 60 50 40 30 20 3000
Ball mill system
LOESCHE VRM system
3500
4000
4500
5000
cm²/g
2012
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Cement Grinding with Loesche VRM Mills Power consumption of ball mill system v/s LOESCHE VRM system (mill, classifier, fan) - slag (GBFS) grinding
160 Ball mill system
140
kWh/t
120 100 80 60
LOESCHE VRM system
40 20 3000
4000
5000
6000
cm²/g 2012
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Cement Grinding with Loesche VRM Mills Loesche cement mills worldwide
~ 60% of Mills for more than 1 product ~ 40% of Mills for more than 3 products 2012
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Agenda
1. Cement Grinding with Loesche Vertical Roller Mills 2. Other Systems for Cement Grinding 3. Former Concerns regarding VRM Cement Qualities 4. The Proven Reality 5. Short Conclusion
2012
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Other Systems for Cement Grinding Different Systems
2012
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Other systems for Cement Grinding Main Differences of grinding process parameters:
2012
Ball mill
Roller press
Vertical roller mill
Characteristics
(closed circuit)
Comminution by:
impact
pressure
pressure and shear forces
Retention time (min):
20 - 30
<0,1
<1
Comminutions before separation:
not countable
1
1-3
Circulation factor:
2-3
>10
6-10
Wear rate (g/t):
~ 50
5 - 10
3-6
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Agenda
1. Cement Grinding with Loesche Vertical Roller Mills 2. Other Systems for Cement Grinding 3. Former Concerns regarding VRM Cement Qualities 4. The Proven Reality 5. Short Conclusion
2012
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Former Concerns re. VRM Cement Qualities Compared to traditional Ball Mill systems
It was said that Cements produced in a VRM System have a… Higher Water Demand (Standard Consistency) Retarded Setting Time Lower Compressive Strength
due to… Steeper Particle Size Distribution (Slope n) Different Particle Shape Lower Gypsum Dehydration
2012
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Former Concerns re. VRM Cement Qualities Compared to traditional Ball Mill systems
Steeper Particle Size distribution?
Different Particle Shape?
Lower Gypsum Dehydration?
2012
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Agenda
1. Cement Grinding with Loesche Vertical Roller Mills 2. Other Systems for Cement Grinding 3. Former Concerns regarding VRM Cement Qualities 4. The Proven Reality 5. Short Conclusion
2012
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The Proven Reality
sum of residue Q (x) (w.-%)
Different Particle Size Distribution
slope n = tan α
position parameter d‘ particle size (µm)
VRM System (Slope n: 0,9 - 1,1)
Ball Mill System (Slope n: 0,8 - 1,05)
More fine material (Over Ground) in the cement produced by Ball Mill system due to high number of impacts and mill inefficiency 2012
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The Proven Reality Operational parameters…
Grinding Pressure Dam Ring Height Mill Airflow Classifier Rotor Speed Table Speed for very high Blaine cements
Dam Ring
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The Proven Reality
<== Shallow
Slope n
Steep ==>
Options to adjust the inclination “n” in the PSD Curve.
lower Grinding Pressure higher
lower Height of Dam Ring higher
higher Mill Air Flow lower
higher Classifier Speed lower
Simple adjustment options to achieve the desired product… 2012
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The Proven Reality Operational Results regarding Particle Size Distribution: Technical Properties Mill
VRM
BM
Separator
LSKS
O-SEPA
Density
g/cm³
3,164
3,152
Blaine
cm²/g
4258
4095
-
0,93
0,92
Position parameter, d'
µm
11,7
12,6
Water Demand (Standard consistency)
%
28
28,5
Slope, n
Same Slope n Same Water Demand A PSD as needed can be easily produced within a VRM System… 2012
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The Proven Reality Compared to traditional Ball Mill systems
Steeper Particle Size distribution?
Not True!
Different Particle Shape?
Lower Gypsum Dehydration?
2012
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The Proven Reality Different Particle Shape
More spherical shaped particles in cements produced with ball mill systems compared to
More shallow shaped particles in cements produced with VRM systems results in
Higher water demand for VRM systems
The particle circularity is determined with an L/Ø - ratio…
2012
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The Proven Reality Different Particle Shape
The maximum particle size in cements is usually between 45 and 55 μm depending upon the fineness of the final product and the slope n.
Fineness: about 4100 Blaine
95% of all cement particles are usually below 20 and 45 μm depending upon the fineness of the final product and the slope n. 52 μm
Particle size in cements all below 55 μm and 95% below 45 μm 2012
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The Proven Reality Different Particle Shape
Circularity of cement particles are similar for cements produced in a ball mill or VRM system.
Circularity
Clinker B 3000 cm²/g
VRM Roller press Ball mill
58 Particle size (µm)
The only notable differences appear at higher particle sizes >50 μm who have no influence on the strength development!
(VDZ 2007)
Similar particle shapes produced on VRM systems… 2012
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The Proven Reality Compared to traditional Ball Mill systems
Steeper Particle Size distribution?
Not True!
Different Particle Shape?
Not True!
Lower Gypsum Dehydration?
2012
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The Proven Reality Lower gypsum dehydration Ball mill (closed circuit)
Vertical roller mill
Retention time (min)
20 - 30
<1
Temperature (°C)
90 -140
80 -110
Characteristics
Gypsum Dehydration in Ball Mill Systems is different compared to VRM systems. This is due to Higher mill outlet temperature Longer residence time in mill system Different gas humidity (negative factor) resulting in
(Plaster)
(Gypsum)
(Anhydrite)
2012
Better drying of the gypsum, hence conversion into a higher content of reactive plaster, necessary as a setting regulator…
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The Proven Reality Simple Counter Measures in a VRM system
Increase mill exit temperature Increase gypsum content (0,5 – 1%) Add a small amount of plaster Add a small amount of natural Anhydrite Decrease humidity of mill gas flow resulting in
Same setting behaviour, i.e. same Setting Time and Compressive Strength Normal optimisation process by works quality department… 2012
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The Proven Reality Different Particle Shape
Technical Properties Mill
./.
VRM
BM
Separator
./.
LSKS
O-SEPA
Fineness acc. to Blaine
cm²/g
4258
4095
Standard consistency
%
28
28,5
Setting time, begin
min
130
125
Setting time, end
min
175
175
[2d]
MPa
29,8
29,9
[7d]
MPa
38,9
38,6
[28d]
MPa
57,1
54,1
Compressive strength (W/C 0,5)
Same Cement with the same characteristics… 2012
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The Proven Reality Compared to traditional Ball Mill systems
2012
Steeper Particle Size distribution?
Not True!
Different Particle Shape?
Not True!
Lower Gypsum Dehydration?
Partially correct, but simply adjustable! (Normal Optimisation!) Page 26 / 28
Agenda
1. Cement Grinding with Loesche Vertical Roller Mills 2. Other Systems for Cement Grinding 3. Former Concerns regarding VRM Cement Qualities 4. The Proven Reality 5. Short Conclusion
2012
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Short Conclusion With Loesche Vertical Roller Mills Cement can be produced with the same
Particle Size Distribution, Particle Shapes and Setting Behaviour
as Cements produced in ball mill systems! Therefore, cements produced with the Loesche Vertical Roller Mill will totally meet the required local market demands, regarding Water Demand, Setting Times and Compressive Strength. BUT much more Energy Efficient, Cost Effective and Flexible…
2012
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