coal washing - PowerPoint PPT Presentation

About This Presentation
Title:

coal washing

Description:

coal washing – PowerPoint PPT presentation

Number of Views:2922
Slides: 16
Provided by: murugianandam
Category:
Tags:

less

Transcript and Presenter's Notes

Title: coal washing


1
Coal Washing
2
Washing of Coal
  • Most of the coals when mined contain impurities
    associated with it. Impurities are removed by
    washing.
  • Fixed impurities
  • -Originate from the coal forming
    plants
  • - Can not be removed by washing
  • Free impurities
  • -Adhering to the surface
  • -Can be removed by washing of coal

3
Objectives of Coal Washing
  • To reduce its ash content
  • To reduce transportation and storage costs
  • To increase its heating value
  • To increase the fusion point of its ash by
    removing alkali chlorides
  • To reduce its clinkering tendency
  • To increase its efficiency in use
  • To reduce its sulphur and phosphorous contents

4
Coal Washing Processes
  • Some Types of Coal washing/cleaning plants
  • Dense Medium Separators
  • Jigs
  • Cyclone Washers
  • Froth Floatation

5
Dense Medium Washers
  • Properties of the Medium
  • The medium used to float the coal from its
    impurities must be of low viscosity
  • The medium must have also some stability so that
    it has effective uniform density
  • High specific gravity of the medium solid (the
    grains suspended in water) is also desirable to
    give effective medium densities upto or over 2.0
  • Mixture of sand and water can be used as washing
    medium

6
Dense Medium Washers
  • Many designs have been employed so not possible
    to generalize
  • Mainly there are two processes under this heading
  • Chance Process
  • (ii) Tromp Process

7
Chance Process
  • Washing medium is a mixture of sand and water
  • A deep bath of sand and water having intermediate
    specific gravity between clean coal and ash is
    used
  • Clean coal floats and dirt sinks and removed

8
Tromp Process
  • A shallow bath instead of deep bath of sand and
    water is used
  • Clean coal floats and dirt sinks which is removed
    by scraper conveyor
  • Requires much lesser volume of fluid
  • Requires lesser building height

9
Jig Washers
  • A coal bed is maintained on a perforated plate
  • Coal bed is subjected to action of upward and
    downward current of water
  • Clean coal being the lighter is concentrated at
    the top while the dirt sinks and removed from the
    bottom of the washer

10
Baum Jig
  • This is the most common type of Jig Washers
  • Baum Jig is U-shaped vessel divided into washing
    and air compartments
  • Compressed air is used to create the pulsating
    movement of water

11
Advantages of Jig Washers
  • Better separation efficiency for finer sizes of
    coal (25-200mm)

12
Cyclone Washer
  • The cyclone washer employs the same principle as
    cyclone dust collector except that the coal is
    fed in a STREAM OF WATER (or dense medium)
    instead in air
  • It is a settling chamber in which settling force
    is replaced by centrifugal force
  • The clean coal is obtained as an overflow from
    the cyclone
  • The underflow from the cyclone contains the
    heavier material or impurities

13
Advantages
  • Efficient for small sized coal
  • High flexibility of operation with respect to
    near gravity material, coal size and feed size
  • Disadvantages
  • Higher power consumption
  • Higher maintenance cost

Cyclone Washer
14
Froth Floatation process
  • Froth is made in a floatation cell by bubbling
    air through water in presence of frothing agents
  • Frothing agents used are normally cresol, pine
    oil or alcohols
  • When dirty coal powder is added to cell, the pure
    coal particles adhere to the bubbles of the froth
  • Dirt particles sink in the cell
  • The clean coal is recovered by filtration

15
Froth Floatation process
  • Advantages
  • It can produce ultra pure coal
  • It is suitable for fine coals
  • Disadvantages
  • High capital and running cost
  • Coal must be grinded to less than 0.5 mm
Write a Comment
User Comments (0)
About PowerShow.com