Vacuum filters

Vacuum filters

Vacuum filters Vacuum filtration is a well established technique used in industrial dewatering. Metso has successfully ­delivered and installed many hundreds of rotary ­vacuum filters covering a wide field of applications.

All rotary vacuum filters operate on a similar ­principle.

A pressure differential between the surface and inside of the drum (or disc) is applied by means of vacuum. This pressure differential causes transport of liquid through the filtration surface while the filter medium arrests solid particles and a cake is formed. As the drum rotates,

the cake rises above the slurry level in the filter tank and air is drawn through the cake, forcing out liquid.

The liquid (filtrate) exits the filter through the internal piping and the vacuum head.

giam 2 4 6

1

8 10

2 3

12 14 16 18

1. Top Feed Drum Filter 2. Drum Filter 3. Disc Filter 4. Belt Drum Filter

20 22

4

24 26 28 30 1

2

3

4

2

5 6 7 8 910

3

4 5 6 7 8 9100

2

3

4 5 6 7 8 91000

2

3

4 5 6 789

Comparison of suitable equipment for different particle size distribution and residual moisture.

Principal components of the drum filter model TF 1. Drum 2. Drum drive 3. Support Frame 4. Tank 5. Vacuum Head 6. Agitator

The range of rotary vacuum filters incorporates two basic design principles:

Pressure differential causes transport of liquid through the filtration surface while the filter medium arrests solid particles and a cake is formed.

High vacuum air flowrates The Metso filters are specially designed for high ­vacuum ­operation allowing very high air flowrates.

This results in: – higher capacities – lower cake moisture – extended application range Integrated components Modularized components and equipment results in: – flexibility in machine configuration – features may be added or altered to accommodate process changes – construction from proven, standard components – simplified maintenance and parts re- placement – lower equipment and operating costs

2 Vacuum filters

Options and accessories for TF and TFF filters Wire winding attachment For certain applications filter cloths are held onto the drum by means of wire. The wire winder automatically feeds cloth attachment wire onto the drum as part of the normal procedure of cloth replacement.

The device has a simple mechanical construction and includes drive motor and gearbox. – adjustable to suit all drum diameters and lenghts – feed wire drum may be placed in any location near the filter – adjustable wire tensioning brake on guide wheel – manual vari-speed drive as optional extra

1. Wire guide wheel 2. Guide trolley and main beam 3. Drive motor assembly 4. Idler sprocket assembly 5. Trolley drive chain 6. Feed wire drum and support trestle

Snap blow cake discharge system

A short duration pulse of compressed air injected into each filter sector immediately prior to the cake discharge point provides for: – positive discharge of thick or sticky cakes cleaning of filter cloth – short pulse inhibits blow back of filtrate into dry cake Position and duration of the air pulse is adjustable. Pulses may be either supplied on a continuous or intermittent basis as required.

Drum drive – thyristor controlled vari-speed drive – limit switch overload protection – continuous torque transmitter and overload protection.

1. Induction transmitter 2. Control box 3. Cog wheel on drum drive shaft 4. Sector at cake discharge point 5. Solenoid valve and air connection to vacuum valve

Construction materials Depending upon application drum filters are available in carbon steel and stainless steel.

Cake washing Spray bars may be fitted to wash the cake in the ­dewatering zone.

Typically, the wash liquor joins the primary filtrate; however separate discharge of liquor and primary filtrate is possible.

Cake washing For lower moisture cake requirements a sealed hood may be fitted to pass superheated steam through the cake in the dewatering zone.

Cake repulper Where the downstream process dictates, the drum ­filter may be fitted with water/liquor spray bars and cake repulping screw.

The screw is driven by a separate motor and gear ­reducer. The screw shaft is mounted in antifriction bearings and sealed using mechanical (standard) or ­hydraulics means.

Drum filter with repulper attachments.

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Standard features model TF Drum – – – – –

rugged all welded steel construction diameters from 1200 to 3620 mm “Snap in” replacable segment grids inspection/access manhole, drain and vacuum l­eakage “tell-tale” Selection of four drainage systems with capacities up to 350 m3/ min at max. 18 m/s flow velocity which minimizes internal pipe wear and reduces friction losses –­ two separate drainage pipes per drum sector, to p ­ revent liquid “puff” back when using snap-blow cake discharge.

Drum drive – standard 4-pole AC-motor, integral gear reducer and manual speed variator – standard drum speed range 0.2 to 1.0 rpm – rubber compression pad to absorb shock loads on start-up

Support frame – – – –

standard steel section all welded support frame one piece drum drive trestle bolted to the support frame two piece support facilitates vacuum head removal or inspection drum lifting bracket at valve end to facilitate simple vacuum head removal

High capacity drum filter. (Note the size of vacuum head)

Tank – steel all welded construction bolted to the support frame – independent from drum, drum drive, agitator and vacuum head

Central lubricator – automatic grease lubrication to vacuum head and bearings

Vacuum head – thick (30 mm) cast iron alloy or HD polyethylene wear ring and mating housing to allow for r­ emachining – three adjustable pressure springs for positive s­ ealing between head and wear ring – selection of heads to match each liquid drainage s­ ystem

Drum support shaft assembly – full length shaft to support drum, vacuum head and internal drainage tubes – “ringfeeder” tensioning element connection to drum heads – selection of three systems depending upon filter size, vacuum head and machine capacity

Agitator – – – – – –

TF 3042 Rotary Drum Filters during shop assembly

all welded “Y” blade construction for positive s­ tirring rotation eccentric to the drum shaft for full depth slurry stirring minimum clearance between drum and tank increasing drum clearance to allow for cake build- up easy access to vacuum head pivot support plate attachment allows mechanism to be swung out of the tank for maintenance and inspection – standard 4-pole AC-drive motor and gear r­ eduction box – drive motor, gear box and lower crank bearings are protected from spillages by removable inspection covers.

4 Vacuum filters

Belt drum filter model BTF Cake discharge systems Belt drum filters, model BTF, are identical in all respects to the TF range with one fundamental exception: cake discharge.

With the belt drum filter the cloth is ­removed from the drum after the dewatering zone and passes over the cake discharge system before w ­ ashing and return to the drum prior to the cake pickup zone. The three key system features of the belt drum filter are thus: • cake dishcarge • cloth washing • cloth tracking

In many applications the simple ‘break roller’ system, where the cloth is passed over a small diameter roller, is sufficient to effectively ‘break’ the cake away from the cloth for discharge.

Cloth washing system Cloth washing increases the capacity of the filter and extends the cloth service life by preventing blinding. After passing the cake discharge s­ ystem the cloth is washed over its full width by two high pressure sprays, one above and one below the cloth. Wash water is confined by a soft rubber curtain and collected for separate discharge through a launder.

Cloth tracking system Cloth tracking is achieved by means of a single hinged guide pulley m ­ ounted in spherical roller bearings after the cloth passes from the w ­ ashing system. The guide pulley is positioned by pneumatic diaphragm cylinders activated by optical or pneumatic sensors at each side of the cloth. Correct cloth tension is maintained by adjustable counterweights acting via levers to the cake discharge system.

The cloth tracking system – maintains cloth position within a few mm – eliminates need for special cloth edgings – provides self-adjusting cloth tensioning

1. Cake discharge system counter weight and lever arms 2. Pneumatic diaphragm cylinder 3. Cylinder tensioning spring 4. Optical or pneumatic cloth edge sensor 5. Guide pulley

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For more difficult cakes an ‘air-knife’ may be appropriate. The ‘air-knife’ consists essentially of two hardened steel (or other wear material) lips. The leading lip is proud of the following one and together they form a slot across the full cloth width. Compressed air from an air blower or high pressure fan is injected into the knife tube and exits from the slot onto the back of the cloth. This cake discharge system is very effective for thin and/ or sticky cakes.

A combination roller and ‘air-knife’ discharge system is also available for difficult applications. This type of discharge, in which the clearances between the ‘air-knife’ lips and the cloth is adjustable, avoids wear and replacement of the knife lips in abrasive duties. In addition there are often benefits in cloth cleaning by reduction in wash water consumption.

Top feed drum filters model TFF The top feed drum filter, model TFF, is especially s­ uited for dewatering slurries containing coarser solid fractions. The top feed principle promotes segregation of the coarser particles in the feed box forming a “precoat” which results in a high filtration rate cake.

Our capability to incorporate very high capacity ­vacuum heads and internal drum drainage systems into the TFF design results in high machine capacities and lower moisture cake.

Standard features include: – special seal between feed box and drum prevents leakage of feed and reduces mechanical wear of filter cloth – snap-blow cake discharge Optional features: – high pressure water, air or water/air mixture cloth cleaning between cake discharge and feed point.

System supply Typical vacuum filter system with filtrate pump and vacuum receiver.

2.

1. Vacuum receiver 2. Moisture trap (Normally used for aggresive filtrate only) 3. Vacuum pump 4. Liquid separator 5. Silencer

1.

6. Filtrate pump

5.

7. Floor drain For plants without a filtrate pump:

6.

8. Drain line from vacuum tank (barometric leg) 9. Water lock

7.

3.

4.

8.

9.

6 Vacuum filters

Dimensions for drum vacuum filters - Internal flow TF, BTF, TFF

Model A D TF/BTF/TFF

mm mm 1206 600 1200 1212 1200 1200 1218 1800 1200 1812 1200 1800 1818 1800 1800 1824 2400 1800 1830 3000 1800 2418 1800 2400 2424 2400 2400 2430 3000 2400 2436 3600 2400 2442 4200 2400 3030 3000 3000 3036 3600 3000 3042 4200 3000 3048 4800 3000 3054 5400 3000 3060 6000 3000 3636 3600 3600 3642 4200 3600 3648 4800 3600 3654 5400 3600 3660 6000 3600 3666 6600 3600

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L TF mm 1600 2200 2800 2500 3100 3700 4300 3260 3860 4460 5060 5660 4480 5080 5680 6280 6880 7480 5160 5760 6360 6960 7560 8160

W1 BTF mm 1600 1600 1600 2200 2200 2200 2200 2850 2850 2850 2850 2850 3630 3630 3630 3630 3630 3630 3910 3910 3910 3910 3910 3910

W2 W3 H TFF mm mm mm 2200 1600 1600 2200 1600 1600 2200 1600 1600 2700 2200 2300 2700 2200 2300 2700 2200 2300 2700 2200 2300 3500 2850 2865 3500 2850 2865 3500 2850 2865 3500 2850 2865 3500 2850 2865 4310 3630 3480 4310 3630 3480 4310 3630 3480 4310 3630 3480 4310 3630 3480 4310 3630 3480 4600 3910 4075 4600 3910 4075 4600 3910 4075 4600 3910 4075 4600 3910 4075 4600 3910 4075

Filter area m2 2.2 4.5 6.8 6.8 10.0 14.0 17.0 14.0 18.0 23.0 27.0 32.0 29.0 34.0 40.0 46.0 52.0 57.0 41.0 48.0 55.0 61.0 68.0 75.0

Weight excl.pulp TF ton 1.2 2.0 2.8 3.9 4.2 4.5 4.8 8.8 9.1 9.5 9.7 10.0 9.8 10.9 12.0 13.1 14.2 15.3 11.5 12.5 13.5 14.5 15.5 16.5

Weight excl.pulp BTF ton 1.3 2.1 2.9 4.5 4.8 5.2 5.6 9.7 10.0 10.4 10.6 10.9 10.3 11.5 12.7 13.9 15.1 16.3 13.0 14.0 15.0 16.0 17.0 18.0

Weight excl.pulp TFF ton 0.8 1.6 2.2 4.4 4.7 5.0 5.4 5.2 6.0 6.8 7.6 8.4 10.7 11.2 –­ – – – 9.0 9.5 – – – –

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Brochure No. 1583-03-11-MBL/Sala-English

© 2011 Metso Minerals

Printed in Sweden