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Prospects of Non-coking Beneficiation in India. Kalyan Sen, Emeritus Scientist, Bengal Engineering & Science University, Shibpur, Howrah. Institution of Engineers(India) International Coal Congress & Expo, Delhi,2006. INTRODUCTION. The choice of washers for effective cleaning of

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slide1

Prospects of Non-coking Beneficiation in India

Kalyan Sen,

Emeritus Scientist, Bengal Engineering & Science University, Shibpur, Howrah.

Institution of Engineers(India)

International Coal Congress & Expo, Delhi,2006

slide2

INTRODUCTION

The choice of washers for effective cleaning of

high ash Indian Coals primarily depends on the

Washability characteristics of the coal vis-a-vis

need of the industry.

The present scenario requires thermal power plant

feed to be prepared below 34% ash. The same for

Cement plants varies from 30 to 32% ash and for

Sponge iron industries below 28% ash.

Though there is no particle size restriction for

Pulverized coal fired plants, others prefer +6mm.

Moisture (total) in washed coal should be

restricted to 8 to 12%.

,

.

slide3

Coal quality requirements for Power plants

Sl.No. Characteristics Requirement

  • i. Total Moisture Content Max. 8 to 12%
  • ii. Volatile Matter, (air dry basis) Min. 19
  • percent by mass
  • Ash percent by mass Max. 34%
  • (annual average)
  • iv. Sulpur, percent by mass Max. 0.8
  • v. Chloride, percent by mass Max. 0.01
  • vi. Size, mm Max. 250
slide4

Coal quality requirements for cement industry

IS 12770: 1989

Sl.No. Characteristics Requirement

i. Total Moisture Content

(at 60% RH and 40 degree C)

Percent by Mass Max. 8

ii. Volatile Matter, (air dry basis)

percent by mass Min. 24

iii. Ash percent by mass

a) dry process Max. 27

b) wet process Max. 24

iv. Sulpur, percent by mass Max. 0.8

v. Chloride, percent by mass Max. 0.01

vi. Size, mm Max. 250

slide5

Coal Quality requirements for Sponge Iron

Sl.No. Characteristics Requirement

i. Total Moisture Content

(at 60% RH and 40 degree C)

Percent by Mass 6

ii. Grade & UHV kcal/kg B/C, 4940-6200

iii. Fixed Carbon above 42

iv. Volatile matter (air dry) above 30

v. Ash percentage by mass 22 - 25

vi. Initial deformation temp. > 1280 deg. C

Vii. Reactivity > 1.7 cc of CO per gm of ‘C’

viii. Size, mm -25 + 3

Source: OSI

slide6

Crushing coal before or after washing

Crushing raw coal to finer size before washing leads

to more energy requirement, products de-watering

and water effluent clarification problems than

crushing the washed coal to the size as per the

requirement of the consumers.

Washing, preferably at larger size i.e. at 100mm top

size seems to be beneficial considering the poor

liberation characteristics of Indian non-coking coals.

slide8

Figure 1: Liberation study of Talcher coal (Whole coal basis)

x100mm :100-3mm(93.7%, a 41.4%)

x25mm :25-3mm(84.3%, a 40.9%)

slide9

Choice of washers

Cement or sponge iron making warrants deep beneficiation of coal

to an ash range 24-27%.

Whereas dry or wet deshaling of coal may be acceptable

for achieving 34% ash for power plants.

Theoretical recovery of washed coal is calculated from

Washability data which are shown in Fig 1.

Practical yield of clean coal obtained from a coal of definite size

consist in dynamic conditions differs from the theoretical yield.

The magnitude of difference depends upon the efficiency of

separation of the washing unit.

slide13

Economical Aspect of washing process

A key element in process selection is maximum recovery of the

product from raw coal at lowest possible cost.

Selection of suitable circuit must be backed up by computer

simulated washability data for prediction of yield gain over other

circuits

.

Heavy medium washing plants cost more to build and operate, the

cleaning efficiency is comparatively more with more yield of

cleans.

HM circuit may yield sometimes 6-8% extra washed coal at

particular ash level when compared to the water only based

washing units like jig ,water only cyclones or hydro- separators.

slide14

Conclusion

Washability characteristics of the raw coal should be prime criteria

in selecting the washing circuit.

Considering the poor liberation characteristics Indian non-coking

coals should be washed, preferably, at larger size and after washing

cleans should be crushed as per requirement of the consumers.

Heavy medium baths/cyclones are the most efficient separator for

high ash Indian coals having high near-gravity material at

separation point and can be operated at wide range of gravity from

1.30 to 1.80 with minimum cleans misplacement.

Requirement of low ash coal (around 25 percent) for Cement and

Sponge Iron Industry can be met by Heavy medium separators.

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