Horizontal_Vertical Mill Comparison-2

Horizontal & Vertical Mills Comparisons & Lab Testing Methods

The Netzsch Disc Mill

Operation Mode Normally one or two passes depending on the product

Applications

Inks; paints; pigments; textile dyes; magnetic coatings; paper coatings; agriculture chemicals; ores; minerals; technical ceramics and utility ceramics; pharmaceutical; cosmetics; food; bio technology

Development of Wet Grinding Machines

1896

Netzsch has been making fine grinding mills for over 100 years 1958

1963

1974

1985

1995

1974

1991

2000

Horizontal & Vertical Disc Mills Netzsch makes both Netzsch also make Pin type Mills Have different advantages for Inks, Paints, Etc coolable grinding chamber

Separation system

Agitator shaft

Horizontal & Vertical Mills Energy Efficiency - kWh/t • What determines Energy Efficiency? • Energy Efficiency is determined by ore characteristics, media size/type and classification efficiency, when energy input and other operating parameters (density, etc) are held constant • Decreased media size improves energy efficiency (many studies-200+, eg: McIvor, 1997, Weller,1999, Jankovic, 2002, Nesset, 2006) and type/quality (Kwade, 1996, Curry, Clermont, 2005, Yang, 2006) • Improved classification efficiency (sharper cut) improves energy efficiency (many studies, eg: McIvor, 1988, Morrell,2008) • Power measurement and sample segregation in lab mills need to be carefully measured and/or controlled, or lab results will be misleading compared to full scale operation

Horizontal & Vertical Mills Energy Efficiency - kWh/t • Disc vs Pins – Same Energy Efficiency for same conditions – Pins have increased power draw per set, and increased wear/decrease life – Disc have more wear surface Signature Plot 1000.0 P98 - Pin

Specific Energy (kWh/t)

P80 - Pin

P98 - Disk

P80 - Disk 100.0

10.0 1.0

10.0

100.0 Size (um)

1000.0

Horizontal & Vertical Mills Energy Efficiency - kWh/t • Horizontal vs Vertical – Same Energy Efficiency for same conditions – Beware size segregation – if mill load sized, PSD larger – But operating differences affect performance at full scale continuous operation Signature Plot P80 1000

Specific Energy (kWh/t)

Vertical Test

100

Horizontal Test

10

Vertical Lab Test Size Segration

Vertical Lab Test Result when all mill load is sized

1 1

10

100

Particle Size (micron) Vertical Test Vertical Test 4

Horizontal Test Pow er (Horizontal Test)

Vertical Test 2 Pow er (Vertical Test)

Horizontal & Vertical Mills Lab Testing Methods • Batch Lab Test – sub-sampling from top or part of charge measures finer result than bulk mill load – need to empty mill and size complete charge, at each sampling time. – Generally not practical. • Continuous Throughput Testing – Sample segregation still an issue – need to ensure there is no retention of coarse in the mill • Recommend passing minimum of THREE times the volume of solids through the mill, compared to Mill volume – to ensure steady state discharge of feed sample • Can be tested by making large feed sample and pump through mill at testing feed rate, with no media, but stirrer running – calculate the volume of feed required to achieve mill discharge at original feed PSD. • Isamill testing is conducted with 25L of slurry – 6-8L of solids – being passed through a mill with 2L of net volume (3.5L1.5L media) – Volume of solids is THREE times mill volume.

Horizontal & Vertical Mills Energy Efficiency - kWh/t • Isamill Maxmises Energy Efficiency by – Finer Media Sizing – Energy efficient media types – Improved classification, sharper product size distribution, due to plug flow through 8 chambers and patented product separator Media Size Tests

Weller, Gao - 1999

Horizontal & Vertical Mills Energy Efficiency - kWh/t • Isamill Maxmises Energy Efficiency by – Finer Media Sizing – Energy efficient media types – Improved classification, sharper product size distribution, due to plug flow through 8 chambers and patented product separator KOC RoC Regrind Test - MT1 Media - Open Circuit

Sharp Classification Reduce Top Size, With Minimal Fines Production

100

Cumulative % Passing

80

Narrowing Size Distribution with increased IsaMilling 60 Feed 20 kWh/t

40

36.7 kWh/t 57.4 kWh/t 20

79.1 kWh/t

Minimal over-grinding 0 0.1

1

10 Size (um)

100

1000

IsaMill Horizontal Layout - Benefits •

Shell on wheels. Easy maintenance. Single component lifts.

•

Wide operating range. Continuous turn-down.

•

Low breakaway torque.

•

•

Restart after crash stop is no problem. No need to dump media on a mill stop like some vertical mills.

Relatively equal media distribution along the length of the shaft.

•

Suitable for coarse and high SG products which tend to sedimentation.

Best access to all wear parts. Relatively low lifting weights as single components can be removed.

•

Horizontal configuration enables large scale designs – up to 3.0 MW.

•

M10,000

M3000

M1000

Limitations of Vertical Mills •

High risk of sedimentation and fine-coarse particle separation in the mill, especially at low flow rates.

•

Media distribution unequal due to unbalanced drag and gravity forces.

•

Maximum breakaway torque due to high media compression at the bottom. Hard to restart under load.

•

Limited shaft speed. Vortex generated. Vortexing at high density - lowers grinding volume. – Vortex changes repose angle as density changes – mill can go from low fill and low power draw to slurry being spun out from the top of mill and high power draw as density is lowered.

•

Heavy components to lift. Exchange of wear parts preferably in the workshop.

•

Limited in mill capacity/motor size.

•

Media floats at high density

•

Needs cyclones and density control.

•

Screen discharge : – Short circuit of feed for top fed. – Media block feed pipe for bottom fed. – Screens blocks with media.

IsaMill Product Separator •

Patented product separator keeps media inside grinding chamber allowing only product and consumed media to exit.

•

Invention of product separator eliminates screens from ultra-fine grinding - delivers process with robustness required by mining industry.

Typical Fine Screen on Vertical Mill

Patented IsaMill Product Separator

IsaMill Internals • 8 grinding chambers in series – no short circuiting • Product separator retains media without fine screens GRINDING DISCS

PRODUCT SEPARATOR

IsaMill Product Separator

• Advantages – No screen to block. – Centrifugal forces higher than a cyclone – 60G. – Retains media and classifies product. – Sharp cut, fine P98. – Minimal over-grinding. – Media does not blind the screens since worn media simply discharges from mill when fine enough. – Media does not wear out the screens, as media not push against screens.

Stirred Mill - lab vs full scale - Century Lab. v. Continuous SMDs 100

Cumulative Percent Passing (%

90

Plant P98 38 um

Lab SMD

80 70

Lab 98 19.5 um Continuous SMD

60

Same P80 8um

50 40 30 20 10 0 0.01

0.1

1

10

100

1000

Size (µm)

Numbers provided by Laurie Reemeyer, Concentrator Manager, Century The difference in P98 may not be important in flotation, where coarse particles still float, but is crucial in leaching since the coarse particles may not leach.

Impact of Product Separator on Size Distribution

MRM plant IsaMills: Lab. v. Continuous SMDs 100

P80 9.5

Lab SMD

Cumulative Percent Passing (%

90 80 70

P98 19.5

Continuous SMD

MRM IsaMill Discharge

Century plant

60

P80 8

50

P98 38 Century Lab scale

40 30 20

P80 8

10 0 0.01

P98 19.5 0.1

1

10 Size (µm)

100

1000

End