Loesche GmbH
Hansaallee 243
D-40549 Duesseldorf

 In the last few years Loesche has successfully developed a new so called LSKS classifier which is basically a cage wheel rotor classifier.

The author describes the appropriate modifications, which have been carried out on existing Loesche Vertical Roller Mills, have not only a strong infuence on the range of reduction of power consumption, and the reduction of process gas flow through the mill but also the increase of raw meal production.

This new classifier already proved LSKS its capability and by now every new  Loesche vertical roller mill, either for raw material grinding, clinker grinding as well as blast furnace slag grinding is equipped with the LSKS classifier.

Apart from various possibilities to increase the efficiency of a raw material grinding plant, this paper is mainly focused on classifier retrofits. Already a lot of LKS or LJKS classifier were replaced by the new LSKS cage wheel rotor classifier. Besides this replacement, Loesche found that the design of the Louvre Ring and Armour Ring (Nozzle Ring) is an important factor for the function of the classifier. Therefore the Louvre Ring and Armour Ring needs to be re-designed and replaced in most the cases.
 

• Classifier retrofit
• Installation of a new designed Louvre Ring with integrated Armour Ring

resulting in:
 

• saving of electrical power
• increasing the raw material production

The LSKS classifier is divided in the following assembly groups:
 
 

• Classifier Housing
• Rotor 
• Classifier drive 
• Guide vanes 

The LSKS High Efficiency Classifier is mounted on top of the mill housing. The classifier is supplied with walkways around the entire circumference of the classifier housing, as well as it’s variable speed drive and reducer.

Allowable space and location of the classifier is boardered b the feeding point (in usual case a Triple Gate Feeder) and the outlet duct for the material dis-charge.

Care must be taken to maintain at least 50° inclination for the outlet duct. Failure to do so will often result in build-ups of raw material in the duct and slug of material could fall back into the mill disturbing the mill operation.

The design of the classifier has to ensure to maintain an optimum velocity profile starting from the nozzle ring up into the guide vanes of the classifier

The upper housing of the classifier has a series of adjustable guide vanes, which are re-directing the dust/gas mixture from an upward flow into a tangential flow. The ribbed rotor revolves in the same direction as the tangential dust/gas flow. The guide vanes are pivoted so that their axial position may be changed. 

The angle of inclination determines the range of fineness influencing the slope of the grain size distribution on the Rosin Rammler Grain Size Distribution Chart. The adjustment of the guide vanes outwards (more tangential) and/or increasing the rotor speed results in a finer finished material, lowering the rotor speed and moving the guide vanes inward (more radial) in a coarser finished material.

The direction in which the rotor turns depends on the vortex of the louvre ring (located in the mill body). The directions of rotor rotation and the flow vortex developed by the Louvre Ring are the same.
 

Finished material passes through the ribbed rotor together with the carrier gas and leaves the classifier housing via the outlet duct. The carrier gases are cleaned by an electrostatic precipitator or bag house filter (in a 3-Fan
System pre-cleaning will take place in a cyclone battery) and finished material is collected and transported to a homogenizing silo.

The conical grit funnel creates an orderly circulation of coarse particles within the mill. On the one hand it separates the rising dust/gas mixture from the coarse particles flowing back on the inside of the grit funnel , and on the other hand it guides them into the middle of the grinding table where they are reground.

The new Louvre Ring with integrated Armour Ring is of the latest design and allows a remarkable reduction of the Differential Pressure across the Mill.
The Contour of the outer ring of the Louvre Ring is of conical design. The louvre blades are more inclined upright than that which is known from the existing design. Therefore the dust-laden gas gets a more optimized direction towards the static guide vanes of the classifier.
The Armour Ring which is positioned on top of the Louvre Ring is also of conical design. This will ensure that the coarse grits returning from the Mill Body and the Classifier are more directed towards to the grinding table. This will lead to a better grinding bed formation and a more efficient grinding of the raw material. The grinding bed will be more stabilized.

old design

It has been experienced that with the new design features for the Louvre Ring and Armour Ring the Mill Differential Pressure will be reduced by approx. 5 to 7 % compared to the old design.

Steeper Slope on Grain Size Distribution Chart
Reduced Power Consumption for Mill and Mill Fan due to:
 

• Increased Mill Production
• Reduced Gas Flow Through Mill
• Reduced Mill Differential Pressure
• Increased Production Rate of Mill due to less Internal Material Recirculation
• Downtime for Retrofit less than 10 Days
• Return of Investment less than two years

Expected on average for Cement Raw Material Mills
(subject to a grindability test)
 

LOESCHE MILL LM 48.4:
 

Description	LKS/LJKS	LSKS	Diff.
Mill Production rate [t/h]	325	365	+12%
Product fineness [%R; 0,032 mm]	32%	39%	+21%
Product fineness [%R; 0,09 mm]	12%	12%	0%
Product fineness [%R; 0,20 mm]	2,2%	1,2%	-33%
Gas flow at mill outlet [m³/h]	865.000	700.000	-19%
Power consumption
Mill Motor [kW@shaft]	3408	3053
Fan Motor [kW@shaft]	3282	2680
Mill Motor [kWh/t@shaft]	10,5	8,4	-19%
Fan Motor [kWh/t@shaft]	10,1	7,4	-27%

These data indicate that the LKS Classifier had 2.2% Residue on 0,20 mm compared to 1,2 % Residue 0n 0,20 mm for the High Efficiency Classifier. This even though the raw meal ground with the LKS classifier was finer on the 0,032 mm screen. The data further indicate that due to the steeper slope on the Rosin Rammler Size Distribution Chart the so called “over-grinding” has been reduced substantially especially in the range below the 0,09 mm screen.

It is significant to note that the coarser grind (range below 0,09 mm screen) has no negative influence on the kiln operation. Similar significant is the reduction of pressure drop across the louvre ring and classifier. This combined effect results in a differential pressure saving across the mill being approx. 10 % lower than before.

The data also indicated that the gas flow at the mill fan is 19 % lower after the modification resulting in a specific power consumption of 7.4 kWh/t compared to 10.1 kWh/t (27 % saving), and this with an increased mill production rate of  40 t/h (12%).
 

Particle Size

The particle size distribution of the raw meal before and after the LKS Classifier was replaced show a improvement in eliminating the coarse fraction in the raw meal
 

Louvre Ring with integrated Armour Ring.
The new Louvre Ring with integrated Armour Ring is of the latest design and made in welded construction. For Mill size above LM 38 we supply the louvre ring with integrated armour ring in polygon profile type (36 to 48 segments depending on the mill size). This allows partial replacement of individual segments if wear and tear occurs in certain areas. Each segment can be easily handled through the mill door and replacement of single segments is possible. For mills smaller than LM 38 the louvre ring and armour ring cannot be supplied in polygon profile (diameter does not allow). Therefore these segments will remain with the curved shape.

Louvre Ring and Armour Ring are fabricated (welded Construction) and made out of mild steel. In case that wear protection becomes necessary special wear protection can be provided. 
 

The assembly group "Classifier Housing cpl." mainly consist of the static parts of the classifier. These are the classifier lower housing, the classifier upper housing with the outlet duct, the frame between bottom and upper part and the grit funnel.

The inlet chute for the material to be ground is integrated into the classifier lower housing. The bottom of the chute and partially the sides, are lined with welded plates. The inspection cover in one of the sides of the chute makes it possible to inspect these parts. The classifier lower housing is joined by welding to the mill upper housing.

The frame is supported by the upper flange of the classifier lower housing. The frame serves to hold the guide bushes for the guide flap axles and for attaching the flange ring consisting of several components serving to close off the rotor and for stopping stray coarse particles. Tubular supports for the bottom bearing housing of the rotor bearing unit are also attached to the inside of the frame.
The classifier upper housing is supported by the upper flange of the frame. This serves on the one hand to redirect and guide the dust/gas mixture flow in the direction of the outlet duct, on the other hand it supports the bearing for the classifier rotor and the driving unit.

Guide plates in the outlet duct serve both for reducing the vortex in the gas flow from the rotor zone and for supporting the driving unit. An inspection cover in the classifier upper housing makes it possible to inspect and gain access to this area.

Seals between the detachable flange connections prevent atmospheric air from flowing into the classifier, which during operation is kept at underpressure internally.

The grit funnel is located below the rotor. This is attached to the classifier lower housing by tubular supports. In the upper part of the grit cone, brackets, in which the lower axles of the guide vanes are held, are welded on site.

Flat steel components within the grit cone below the rotor serve to reduce the rotary motion of the coarse particles and make them easier for them to return to the mill grinding table.
 

The assembly group "Rotor cpl." essentially consists of the rotor, the classifier ribs, the sub-assembly group "Bearing Cartridge cpl." and supports.

The bearing cartridge passes centrally through the classifier upper housing. The attachment flange is welded to the classifier upper housing using a curved flat piece of flat steel, after the rotor has been adjusted. The stiffening tubes serve to support the bearing unit in the area of the lower bearing. After rotor adjustment these are secured against loosening by spot welding in the area of the threaded stems. Additional sections of tube serve to protect them from wear.
The attachment screws in the flange connections between rotor and intermediate shaft and between the intermediate shaft and flange bush of the bearing unit have to be tightened with the torque given on the drawing.

The classifier ribs are pushed into the slots of the holder rings of the rotor and are secured against dropping out using bent clamping pieces. For avoiding impermissible imbalance the classifier ribs have to be weighed individually. Classifier ribs of equal mass are placed opposite to each other.

After the installation has been completed the rotor must be dynamically balanced. Due to the construction of the rotor it must only be run in the prescribed running direction. When the drive is switched off the rotor must be allowed to continue running freely until it has come to a full stop. A brake on the motor side should not be applied
The rotor shaft is held within the bearing unit in spherical roller bearings. The upper self-aligning thrust bearing accommodates the axial and radial forces, the lower self-aligning bearing only radial forces. The bearings are greased. The grease is supplied via two separate pipes.

The grease is supplied from below the bearing to the self-aligning thrust ball bearing corresponding to the natural transport direction of its rollers. The grease leaves via the upper rotary shaft seal and forms there a grease edge with prevents dust from entering into the bearing chamber. A disc of hard plastic closes the bearing chamber at the bottom and prevents to a high degree the grease from being pressed into the free space in the bearing cartridge.

The grease for the lower bearing is supplied via a tube which is located within the bearing cartridge. Here too a disc of hard plastic placed above the bearing prevents the grease from entering into the free space in the bearing cartridge. At the bottom the bearing is sealed from the dusty classifying chamber by a rotary shaft seal and a labyrinth.

This assembly group essentially consists of the lower and upper axles of the flaps, the guide bushes and the attachment and sealing material.

The upper axle of the flap is guided in a bush which is attached to the frame of the classifier casing using a welded-on plate. 

For preventing dust from entering the gap between the axle and bush and to compensating for production tolerances in this area of the frame, a sealing ring is pushed over the axle of the flap which is pressed against the lower plate of the frame by a helical spring.
 

This assembly group mainly comprises the components: motor, gearbox, couplings, coupling protection, supports, chopper disc and proximity switch.

The gearbox is mounted on a support which is centred on and attached to the bearing cartridge of the assembly group "Rotor cpl." After adjusting the gearbox in relation to the rotor shaft, the gearbox is dowelled to the support. An flexible coupling transfers the torque from the gearbox to the rotor shaft.

The electric motor is aligned during installation together with its support in relation to the shaft entering the gearbox. The support is then welded to the upper part of the classifier following the instructions on the drawing.

Another flexible coupling, enclosed by a coupling protection, connects motor and gearbox.

The rotation of the classifier is monitored using a chopper disc pushed onto the rotor shaft and a proximity switch which has to be adjusted on site.

The rotor speed is adjusted according to the fineness of the material to be classified. It is done continuously by adjusting the motor frequency using a frequency transformer and is possible during classifier operation.
 

This assembly group mainly encompasses the grease pump with storage container, a piston distributor, piping and couplings.

This unit serves to lubricate both bearings of the assembly group "Bearing Cartridge complete".

The grease pump is attached to the classifier upper housing using a mounting plate. The supplied grease is divided into two tubes by a piston.