Krebs - GMax Brochure

KREBS gMAX� CYCLONES –

For Finer Separations With Larger Diameter Cyclones

August 2000

Krebs Super Cyclones Page 1 of 7

Introduction

A significant challenge in many mineral and coal processing plants is to utilizethe installed cyclones to produce a fine separation at high feed densities. Thisrequires numerous small diameter cyclones operating at high pressure dropleading to higher operating and capital expenses. The new Krebs gMAX cycloneproduces a separation 35% finer than traditionally designed cyclones allowingthe use of larger diameter units and/or lower operating pressure drop.

The primary problem associated with operating small cyclones at high pressure drop ishigh cyclone and pump wear. This results in high manpower requirements formaintenance and often in poor cyclone performance. In large operations, the number ofrequired cyclones results in large floor space requirements and difficulty splitting theslurry equally between all of the cyclones. Larger diameter cyclones tend to mitigatethese problems but have not been capable of producing the fine separation required atmany operations.

Traditional Cyclone Design

The original cyclones offered prior to 1950 featured outer wall tangential feed entry and12-15 mm thick rubber liners. This design was not adequate for fine separations or forabrasive slurry applications. Krebs Engineers recognized the limitations of cycloneswith outer wall tangential feed entries in 1953 when the company patented a cyclonewith an involute feed entry. The patent was based on testwork that clearly showed theinvolute feed entry minimized turbulence in the inlet and this allowed the cyclone tomake slightly finer separations at higher capacities. Although reduced wear life was notpart of the patent, a cyclone with an involute entry provides longer wear life than acyclone with the standard outer wall tangential feed. Today, most cyclonemanufacturers have redesigned their cyclones to include some form of involute orcenterline tangential feed. Figure 1 illustrates the various types of cyclone feed entries.

Figure 1


Krebs Engineers recognized the limitations of cyclones with 12-15 mm thick rubberliners in grinding circuits and in 1990, introduced a whole new line of Super Cycloneswith 25 mm thick liners and other design feature to minimize wear. These cyclonesrange from 250 mm to 840 mm in diameter. Today nearly all cyclones 250 mm andlarger installed in mineral processing plants utilize thicker replaceable liners. Anexception is coal plants that use all ceramic liners in the cyclones.

In recent years, cyclone companies have introduced ramped or modified involute inletdesigns with claims of greatly improved cyclone performance. While someimprovements have been made in inlet head wear life, a ramped inlet design tends toresult in a lower capacity cyclone with no improvement in the cyclone separation. Thefull involute feed shown in Figure 2 with curved corners provides the best performancewhile not compromising on wear life. Figure 3 illustrates the performance differencesbetween an involute feed entry design and the relatively new ramped design. While theperformance is similar, the involute feed cyclone has significantly higher capacity.

Figure 2


Figure 3

Typically cyclones have used a cylinder section length equal to one cyclone diameter incombination with a 20-degree cone section. For finer separations the traditionalapproach was to add a second cylinder section. While the longer cylinder sectionprovided greater residence time and thus more capacity, it also reduced the tangentialvelocity. This results in minimal if any improvement in cyclone separation. The highercapacity with the longer cylinder section did allow cyclone manufacturers to providesmaller vortex finders, which does improve cyclone performance.

A better approach is to use a longer cone angle. Figure 4 illustrates the differencebetween 10 and 20 degree cones. The longer cone produced a finer and sharperseparation at a higher unit capacity. A number of cyclone manufacturers use longercones on 150 to 500 mm cyclones and in the past 3 years most new cyclones in thissize range have the longer cone sections. Side by side cyclone testwork in which onecyclone has a 10-degree cone versus the other cyclone with a 20-degree cone willgreatly favor the cyclone with the longer cone regardless of the inlet design.

Longer cone sections alone are not the answer. Maintaining the tangential velocity atits maximum is the key to optimal cyclone performance.

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Krebs 250 mm Cyclone with Involute Feed, 10.5 degree cone, 85 m3/h

D50c = 80, alpha = 4.2

Ramped 250 mm Cyclone, 10 degree cone, 72 m3/h

D50c = 84, alpha = 4.0

Comparison of Involute Feed and Ramped Feed Designs with 3096 sq mm Inlets and 100 mm Vortex Finders operating at 1.4 bar pressure drop

FEED CONDITIONS: 55-57% Solids, 65-70% +38 micron, ~35% +212 micron


Figure 4

gMAX Cyclone Design

Optimum cyclone performance relies on minimizing turbulence while maximizingtangential velocity. Minimizing turbulence reduces the amount of coarse materialmisplaced to the overflow and increases wear life. Maximizing tangential velocityresults in a finer separation and reduces the amount of misplaced fines in the underflow.The new gMAX cyclone focuses on these two important cyclone factors significantlyadvancing cyclone performance. To achieve the two design criteria, the gMAXincorporates performance enhancing improvements to the inlet head area, cylindersection, cone angles, and apex.

The Krebs involute feed has been redesigned to further minimize turbulence in the feedsection. Along with this updated inlet design, the gMAX also includes a longer vortexfinder design and an improved top cover plate. These improvements to the inlet headarea result in a reduction in turbulence which reduces the misplacement of coarsematerial to the overflow and results in a more efficient conversion of feed pressure tounit capacity.

The heart of the gMAX design is the optimization of the tangential velocity in criticalseparating zones of the cyclone. An intensive development program was undertaken tooptimize the length of the cylinder section and the cone sections to produce themaximum tangential velocity. It was discovered that each cyclone diameter has aunique combination of cylinder length and cone angles that maximizes the tangentialvelocity at a minimum overall cyclone length. The gMAX accomplishes this by using a

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Krebs 250 mm Cyclone, 10.5 degree cone, 85 m3/h

D50c = 80, alpha = 4.2

Krebs 250 mm Cyclone, 20 degree cone, 73 m3/h

D50c = 114, alpha = 3.7

Effect of Cone Angle on Cyclone Performance with 3096 sq mm Inlets and 100 mm Vortex Finders operating at 1.4 bar pressure drop



sharper upper cone to accelerate tangential velocity and then a gradual tapering lowercone to provide residence time for a finer separation. This results in a much betterperforming cyclone at an overall length similar to a standard cyclone.

Finally the apex angle and design also has a big effect on performance. The gMAXdesign incorporates an optimal apex angle in combination with a straight section tomaintain the finest possible separation with maximum dewatering.

This combination of the correct cylinder length with the right cone angles and apexdesign, along with the improved feed section is the basis of the new patented KrebsgMAX cyclone. Figures 5 and 6 illustrate the gMAX design.

Figure 6Figure 5

Figure 7 illustrates the performance differences between the Krebs gMAX cyclone,standard involute inlet cyclone with 10 and 20-degree cones, and ramped inlet cyclonewith a 10-degree cone. The gMAX cyclone results in a 35-40% finer separationcompared to the 20-degree cone and a 20-25% finer separation versus the 10-degreecone cyclones. The gMAX cyclone produces this finer D50 separation whilemaintaining a very sharp separation. A 35-40% improvement in separation is an entiremesh size and allows the use of a larger diameter cyclone at lower pressure drops.


Figure 7

Comparative Plant Performance

Figures 8 and 9 illustrate the large differences between the traditional cyclone designand the gMAX design. These results are from two different iron ore concentrators ontypical grinding circuit applications. Figure 8 is a comparison of 380-mm diametercyclones and Figure 9 is a comparison of 660 mm diameter cyclones. Theimprovements in the gMAX design apply uniformly to small and large diametercyclones.

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Krebs 250 mm Cyclone, 10.5 degree cone, 85 m3/h

D50c = 80, alpha = 4.2

Krebs 250 mm Cyclone, 20 degree cone, 73 m3/hD50c = 114, alpha = 3.7

Krebs 250 mm gMAX Cyclone, 77 m3/h

D50c = 59, alpha = 4.0

Ramped 250 mm Cyclone, 10 degree cone, 72 m3/hD50c = 84, alpha = 4.0

Comparison of Krebs gMAX Cyclone and traditional Cyclones with 3096 sq mm Inlets and 100 mm Vortex Finders operating at 1.4 bar pressure drop


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Krebs 380 mm gMAX Cyclone

D50 = 33 microns, Alpha = 3.5

Krebs 380 mm Standard Cyclone


Data for Standard and gMAX Krebs 380 mm Cyclones

FEED CONDITIONS: 40-44% Solids, 36-41% +25 Micron, 1.25 bar pressure drop North American Iron Ore Property


Figure 9

Conclusion

The gMAX cyclone solves the problems of producing fine separations at high densitiesin mineral and coal processing plants. It accomplishes this by uniquely combining thecorrect cylinder length with the right cone angles and apex design, along with animproved involute feed. These design enhancements minimize turbulence andmaximize tangential velocity in the separation zones.

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Krebs 660 mm gMAX Cyclone


Krebs 660 mm Standard Cyclone


Data for Standard and gMAX Krebs 660 mm Cyclones

FEED CONDITIONS: 58% Solids, 35% +150 Micron, 0.8 bar pressure drop South American Iron Ore Property

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