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DEWATERING

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PREPARED BY: MD.ALAM (492/08) * The separation of solids from fluids (dewatering) is one of the important subjects in the field of mineral dressing Water purification ... – PowerPoint PPT presentation

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Title: DEWATERING


1
DEWATERING
  • PREPARED BY
  • MD.ALAM (492/08)

2
INTRODUCTION
  • The separation of solids from fluids
    (dewatering) is one of the important subjects in
    the field of mineral dressing
  • Water purification
  • In mining and smelting operations

3
WHAT IS DEWATERING?
  • A simple answer would be the process of removing
    water from sludge (suspension of solid matter in
    liquid).
  • Dewatering is the process of natural, chemical,
    or mechanical removal of water from sludge,
    thereby reducing it to a damp solid with the
    lowest level of moisture attainable .

4
  • Mechanical separation of solids from liquids is
    accomplished by one of two general procedures
  • Thickening.
  • filtration.
  • (Ultimate moisture removal is obtained by
    drying.)
  • Separation of solids from gases
  • settling.
  • Filtration.

5
THICKENING
  • A suspension of solids in a liquid is allowed to
    settle until a clear liquid layer tops a mud
    layer.
  • A volume reduction of approximately 30 80 can
    be reached with sludge thickening before a
    further treatment.

6
IMPORTANT TERMS
  • Flocculation it is a process of contact and
    adhesion whereby the particles of a dispersion
    form large size clusters.
  • Floccules or flocs these are rounded aggregates
    of solid particles.
  • Pulp any soft or soggy(soft and watery) mass.
  • Slime any thick viscous matter.
  • Flocculant Particles finer than 0.1 µm (10-7m)
    in water remain continuously in motion due to
    electrostatic charge (often negative) which
    causes them to repel each other

7
THICKENING
  •  At smaller wastewater treatment plants, where
    the sludge is driven off regularly,
  • thickening usually takes place directly in the
    sludge storage tank. The sludge is compressed at
    the tank bottom only by the force of gravity,
    while above the sludge a cloudy water layer is
    formed, which is taken off and led back into the
    inlet.

8
STEPS IN PROCESS OF THICKENING
  • Flocculation of the minute solid particles so as
    to form aggregates or flocs of many particles.
  • Sedimentation of the liquid-laden flocs,leaving
    clear liquid.
  • Compaction of the sedimented flocs.
  • Elimination of the clear fluid and of the
    thickened mud.

9
PROCESSES INVOLVED IN DEWATERING FLOCCULATED PULP
  • Free settling of flocs.
  • Hindered settling of flocs.
  • Exudation of water from the settled flocs,under
    the influence of pulp pressure.
  • Exudation of water from the settled and naturally
    exuded flocs by application of outside pressure
    or suction.

10
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11
SLIME SETTLING ZONE IN DORR THICKENER.
12
DORR THICKNER
  • Although less expensive per square foot of
    settling area they are
  • Less effective and more difficult to operate.
  • More power consumption.

13
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14
WORKING
  • The revolutionary EIMCO E-CAT
    Clarifier-Thickener combines optimized
    flocculation, high-rate clarification and
    high-density thickening in a single compact unit.
    It streamlines liquid-solid separation flowsheets
    by optimizing chemical settling aids and
    providing a dedicated escape route for displaced
    free liquid. Even more impressive, the E-CAT
    Clarifier Thickener system accomplishes all of
    this with no moving parts. 

15
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16
FEATURES AND BENEFITS
  • No moving parts - Lower capital cost - Lower
    energy consumption - Less maintenance
  • Smaller surface area than conventional
    thickeners - Lower capital cost - Smaller
    footprint
  • Self diluting feed - Optimal flocculant
    utilization - No external dilution pumps required
  • Good overflow clarity - Effluent re-use
  • Dense underflow - Lower energy requirement for
    drying - Less ponding area required - Reduced
    handling volume

17
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18
FILTRATION
  • Filtration is that separation of finely divided
    solid particles from a fluid which is
    accomplished by driving the pulp to a membrane or
    septum, porous to the fluid but impervious to the
    solid, through which the fluid passes, and by the
    removal of the solid cake from the septum.

19
MECHANISM OF FILTRATION
  • The simplest type of filter consists of a tube of
    small bore through which the fluid is sucked
    while the solid particles accumulate at the
    entrance. As the device is operated, solids at
    first pass through the tube, but they quickly
    arch or bridge across the opening, allowing only
    clear liquid to pass

20
RATE OF FILTRATION
  • The filtering area.
  • The difference in pressure between two sides of
    the filter.
  • The average cross section of the pores within the
    filter cake.
  • The number of pores per unit area of the septum.
  • The thickness of the filter cake.

21
TYPES OF FILTERS
  • Pressure type pressure is applied to push the
    liquid through the filter bed.
  • (for hydrometallurgical work in which interest
    centers on the filtrate, as in cyanidation.)
  • eg. Hardinge filter thickener.
  • Suction type suction is applied to pull the
    liquid through the filter bed.
  • (used in chemical laboratories, for mineral
    dressing in which interest centers on the cake.)
  • eg. Genter thickener.

22
PRESSURE AND SUCTION FILTERS
  • Adv
  • higher fluid capacity per square foot of
    filtering surface,
  • better control of cake formation,
  • possibility of better washing of cake.
  • Disadv
  • A great disadvantage is that they are
    intermittent (stopping and starting at regular
    intervals) instead of continuous.

23
BENEFITS FROM DEWATERING
  • A good reason would be cost savings and
    environmental awareness .
  • Lower Transport and Disposal costs .
  • Dewatered solids are cheaper and easier to
    incinerate.
  • Ease of handling with dewatered solids.
  • Less offensive smells.
  • Reduced volume in landfills .
  • Reduced leachate production in landfills .
  • Lower amount and cost for bulking agents for
    composting

24
CONCLUSION
  • Keeping in mind the optimum sludge removal and
    dewatering technique a site and sludge specific
    evaluation process should be performed with the
    objective of developing the safest, most
    economical, and environmentally responsible
    approach that meets or exceeds the objectives and
    expectations of the client.

25
THANK YOU
26
REFERENCES
  • PRINCIPLES OF MINERAL DRESSING
  • BYA.M. GAUDIN.
  • www.FLSmidthMinerals.com
  • www.lenntech.com
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