coal cleaning by dense medium processes h.j. ruff inpromin

7/25/2019 Coal Cleaning by Dense Medium Processes H.J. Ruff Inpromin

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COAL

CLEANING BY

DENSE MEDIUM

PROCESSES

with pa r t i c u l a r re fe rence to

the

new

Tr i -F lo development

H. J . R u f f - Direc to r

Inpromin - Southampton UK)

and

Genova ( I t a l y

Conference

I n t r oduc t i on

to

Coal Prepara t ion

Sweden 22 .2 .83 .

1. In t roduc t ion

~ INPROMIN

TFS-I-22

Dense medium separa t ion i s one of a

number

o f

t e chn iques

ava i l ab l e

fo r coa l

c lean ing . By way

of in t roduc ing t h i s

s ub je c t

it

i s perhaps use fu l to b r i e f l y d iscus s coa l

c l ean ing

in g e n e ra l

and

why coa l needs to be cleaned a t all

There a re

a

number

of reasons which

con t r i bu t e to t h i s

mechani sa t ion

of mining

the

mining

of poorer

seams

the need

fo r e f f i c i e n t

u t i l i s a t i o n

and

gre a t e r concern wi th the environment

In former t imes coa l

- l i ke

o the r minera ls

-

was mined

manual ly

and

se l e c t i ve l y

and

loaded

by

hand.

Not

su rp r i s i ng l y ,

the

coa l was gene ra l ly c lean

-

the re

was no

payment

fo r

d i r t

-

-

and

conta ined- f-e-

w-f-i-nes.

Prepara t ion cons is ted of hand pick ing and sc reen ing .

With mechani sa t ion a l l t h i s has changed a gre a t de a l . Today

coal

from

a

long

wal l face i s

l i k e l y to con ta in more

than 50

of m a te r i a l

sma l l e r

than 12 mm,

0.5 mm.

lTJd 15 to 2 0 ~ f i ne r than

Because machines

cannot

r e l i a b l y

d i f f e r e n t i a t e

between

coa l

and s tone - even with nucleonic senso rs , 4 0 5 0 ~ of

the

Run-of -

Mine

produced

by a

modern mechanised deep mine i s l i k e l y

to be

high ash r e fuse .

Whether the coa l i s

used

as chemica l feed s tock , fo r the

manufacture

of

coke

or

for hea t ing , modern processes demand

cons i s

t en t input to main ta in

e f f i c i e n t

ope ra t ion

and

minimum

po l l u t i on .

Coal Prepa ra t ion provides

the v i t a l

l i nk between produc t ion

and u s e ~


2/12

- 2 -

2.

Coal

Impurit ies and Methods of

Cleaning

Dirt associated with

the

coal varies widely. Some d i r t

is within the seam

from

the way t

was formed

or through

igneous

intrusions or t

may

come

from

the roof

above the

seam

or

the

f loor

oelow

or

ar ise

from

faul t ing.

Inherent di r t and organic sulphur

cannot -

be

removed by

conventional

preparation processes.

On

the other hand the

d i r t

from outside

the

seam proper and the

d i r t

ar is ing from

faul t ing and intrusions

can

be

removed more

or l ess

e f f e o ~ -

-

ively

with

proven technology.

The

impurit ies

may consis t of carbonaceous shales sand

stone clays pyri tes

etc .

They

are

heavier

than

olean

coal

and can therefore be tackled

by gravity

processes. Only

the f ines t

-

s izes are t reated

by other

methods in the main

by

froth

f lo ta t ion .

High

gradient magnetic separat ion

i s

one other

process

which

has at t racted

a good

deal

of in te res t these

l a s t

few

years

because i t a y prove a

good

low energy

al ternat ive

system

for

the

removal

of

both

ash

and

sulphur.

But

so

fa r

in sp i te

of much

in te res t

economic resul ts are not yet

cer tain nor

thought

to

be

imminent .

Gravity

processes

are

simple and can

prod

-

uce

a

good

separa t ion-a own

t o

remarkably

small- -

grain

s i z ~ ~ h r n y

-

consis t of

two

main groups. One i s

based

on

flowing

or

pulsat ing

water and

inc1udes

j igs shaking t a b ~ e s cones

and

sp i ra ls

and

wil l

be

described

in

a

l a t e r

p a p e r ~

The

second group

uses a

suspension of f ine sol ids in

water and i s cal led dense

or heavy

medium separat ion D M S

or H M S.

3. Principles of Dense Medium Separation

ow

ash

coal i s usually l igh ter than

1.40 kg/1

and

:

carbonaceous

shale

heavier

than

1.80

kg/1.

Middlings

contain more or less i m ~ u r i t i e s

and

consequently are of


3/12

In

order to opera te con t inuous ly and

e f f i c i e n t l y ,

Dense

Separa t ion

Systems a re r equ i r ed to

main ta in the

medium

the r i g h t cons i s t ency . and d e n s i t y

in

the face o f con tamin-

from

feed

and

breakage .

Ear ly sys tems

used media co n s i s t i n g

o f s o l u t i o n s o f s a l t

suspe ns i ons

of sand, ba ry te and

s h a l e .

Today,

f i n e l y

magne t i t e

i s

used

because

it

i s

recovered

very e a s i l y ,

i s

ecorwmic

in

use

and high sep

a r a t i n g

dens1 t i e s

can

be

e a s i l y .

Consumption

va r i e s with

the s i z e of the coa l t r e a t e d ,

of

p lan t and ope ra t ion

and

main tenance . In

a

modern

it might con t r ibu te 0 30 0.90 SEK/ton

of coa l

t r e a t e d ,

to 500 1500 g / t o n and the cos t o f

magne t i t e

600 SEK/ton.

A dense medium

plan t

c o n s i s t s of

four

main p a r t s as

3.1 Feed Prepa ra t ion

This

i s

des igned to minimise the f i n e s and contamin-

a t i o n (mainly c l ays

and

wate r )

e n t e r i n g

the dense medium

and thus

f a c i l i t a t e s

the

maintenance o f

s t eady o p e r a t i n g

cond i t ions .

3

;

2

Sep-a-rating

V e s

~ J

This may be s t a t i c or "dynamic" . In s t a t i c s e p a r a t o r s

the sur f ace of the pool i s l e v e l , medium

e n t e r s

the

pool

con t inuous ly

and,

toge the r with the

f l o a t i n g

coa l ,

over f lows

a t o

nP.

s

i de .

The heavy p a r t i c l e s s in k

and

a re

removed from

the

bot tom of

the

pool . hP.y s ink quick ly i they

a re

l a rge

and

heavy

and s lowly

i they

a re

smal l and /or near the

dens i ty of s e p a ra t i o n .

In order

to

acce l e r a t e

the

sepa ra t ion fo r f ine

and

d i f f i c u l t

near g ra v i t y p a r t i c l e s , dynamic

sys tems

were

in t roduced . Here medium and

feed

so l i d s e n t e r cyclones


4/12

4

4

Medium Reclaim and Cleaning Circu i t

After separa t ion

the

two o r th ree products

Clean

Ooal,

Middlings

and Shale leave the separa t ing v ~ s l w ~ t h vary

ing

amounts

o f

dense

medium.

In the

grea t major i ty o f

cases these produc ts

pass over

hor izon ta l v ib ra t ing sc reens . On the

f i r s t sec t i on o f

thes

sc reens the

f ree

medium i s drained from the products , and

immediately re turned to

the cor r ec t medium sump fo r r e

c i rcu l a t i on .

Fur ther down the sc reen the produc ts a re washed

by

cur ta ins of water in order to remove

the remaining

adhe r ing

medium

before f i n a l dewater ing.

The

underflow from t h i3

sec t ion of the sc reen i s the

d i l u t e

medium.

This

i s

passed

to

magnetic separa to rs which rec la im the

magnetic magnet i te a t high

densi ty

and r e j ec t the

bulk

o f

the

water and non-magnet ic f ines

and

s l imes

r s ~ l t i n g

from

imperfec t

feed

prepara t.ion

and mate r i a l

degradat ion .

The

recovered

magnet i te

i s

de-magnet ised

by

passing

th rough a

de-magnet is ing

c o i l

and

then

re turned to the sys tem fo r

re -use .

In t h i s connec t ion t should perhaps be r eca l l ed t ha t

eve n

with modern-

- -h

gtd

y ef-f ic ient

wet

d

r-um magne

ti-c:

-

separa tor s , the

consumption of magnet i te o f a

l a rge

c o a l

p lan t wil l

be

s ign i f i can t and proper mechanised systems

have

to

be

provided

for

the

easy

add i t ion

o f make

up

magnet i te .

3.4

Density Control

In modern coal prepara t ion p lan t s the densi ty i s

cont ro l led au tomat ica l ly . Densi ty

can

be measured with

dip

tubes ,

d i f f e r e n t i a l

pressure

pads

or nuclear dens i ty

gauges.

In recent

years

the

l a t t e r ones have become

accepted

widely with

appropr ia te

s t a tu to ry safeguards on

account of t h e i r r e l i a b i l i t y and sa fe ty .

The dens i ty

s igna l

obta ined can be used in a number o f


5/12

- 5 -

Often the c l ean i ng c i r c u i t i s a d jus t e d permanent ly to

c lean and r e t u rn s u f f i c i e n t high de ns i ty

medium

fo r

t he

we t t e s t

and

d i r t i

e

s t fe

e

d . The s igna l can then be used

to

a c t ua t e

a

s imple wate r

va lve

to

d i l u t e

t he

c i r c u l a t i n g

-

medium as r e qu i r e d .

In o the r

p l a n t s

the s igna l i s used

to vary

t he medium

passed

to

the c l ean i ng c i r c u i t ,

as

r e qu i r e d , so as to

mn-m-

i s e the loa

-d

o f

the magnet ic

separ-a

-t-o-

r .

A combina t ion

of these

two sys tems

i s

being

used a t

t he l a t e s t 100

t / h

T r i -F lo

p l a n t eng inee red by

Inpromin

fo r

a

Mining o m p a ~ y

in

Greece.

Some coa l pre pa ra t i on

p l a n t s have a se pa ra t e ove rdense

c

i r c u l a t i n g

c i r c

u i t

which

can prov ide

a va r i a b l e

bleed to

t he c o r r e c t

medium c i

r c u i t .

4. Types o f Den

s e

Medium P la n t

-

4.1

S t a t i c

S e pa ra to r s

The e a r l i e s t dense medium s e p a r a t o r s

c ons i s t e d o f

cones .

The feed en te red

the

su r f a c e

o f t he

pool

on

one s id e . Most

o f the medium was

i n t roduced

th rough organ pipes

o f

d i f f e r e n t l eng t hs a long

t he

v e r t i c a l a x i s o f the cone and

over f lowe aw:L

th

E e

f loat ing coa l p a r t i c l e s . The heavy

p a r t i c l e

s

sank to

the

bottom

and were removed by

irlift

o r

th r

oug h

lo

c

ked

c

hambers .

These were fol lowed by

ba ths

"

o f v a r

io

us

othe r

shapes which

mainly

d i f f e r e d in

the

way

s i n

ks

we

re

rem

o

ved

- .

usual ly

by

cha in

s c r a p e r s ,

e l e v a t o r s ,

r ubber be

lt

s ,

lifter

s o r wheels .

Today,

the maj

o r i t y of s t a t i c se pa ra t i ng ve s se l s a r e

r o

t a t i n g

drum s e pa ra t o r s with i n t e r n a l lifters or

s t a t i c

boxes with

r o t a t i n g pe r fo ra t e d wheel s fo r t he removal

o f

the s ink

s .

Tra

nspo r t of the

f l o a t p a r t i c l e s may be simply by t he

over f low o f the medium

or

it

may

be

a s s i s t e d

by

padd le s

or s i m i l a r dev ice s

Go

od

se par

a

t i on can be achieved wi th

s t a t i c

sys tems


6/12

- 6 -

4.2 Dynamic Separators

These were

in t roduced

by

the Dutch

St a t e

Mines fol lowed

l a t e r by the Dyna Whirpool DWP), Vorsyl

and

Tr i -F lo

separa tors .

In a l l

of these

the medium i s in t roduced t angen t i a l l y

in to

a cyl inder

and

separa t ion takes

place

under cen t r i fuga l

force . Dynamic

separa t ion

can be c l a s s i f i e d , depending upon

whether the raw coa l

i s fed i n to the

s ep a r a to r

with the

medium under

high

pressure or

s ep a r a t e ly

a t t m o s p h r i

pressure .

A pressur ised feed i s requi red with cyclones

and

the

Vorsyl separa tor

of the Br i t i sh Nat iona l Coal

Board.

t

i s

obtained

e i t h e r by

pass ing

the

coa l

with

the

medium

through

the pumps

or

by pumping the medium a lone

to

a

high

l eve l

head box.

In

tha t case

the coa l

can be

elevated to t h i s headbox by conveyor

and

from

the re fed

to the

separa tor via

a t a l l s tandp ipe . The

he ight requi red

i s_

typ ica l ly

about 9 x dia of the

cyclQne or about

4.5 to

7 m above the i n l e t

of

the sepa ra to r 2 .

By

con t ras t ,

the

i n t roduc t ion

of

the

coa l

feed

d i r e c t l y

in to the open

vor tex

of

the

WP and o f

the

Tr i -F lo

s ep a r a to r

requi res no ext ra pressure .

Using -

e i t h e r of these

sys tems

- -

al lows

plants

to

be kept lower

and

ye t pumping of coa l i s

avoided with savings both in

pump wear and

coa l degrada t ion .

Cyclones WP

and

Vorsyl separa to r s have been long

es tabl i shed in coa l prepa ra t ion p lan t s and f requen t ly

descr ibed in

the

l i t e r a t u r e .

On

the other hand the Tr i -F lo system has been

developed

much

more recent ly and so f a r ,

mainly for minera l

app l ica t ions . Nevertheless , the

opera t ing r e su l t s

from the

f i r s t

7

Tri -F l?

_mineral

i n s t a l l a t i o n s ,

and many

other t e s t s ,

have been so remarkable

and

a number of i t s f ea tu res so

spec ia l ly i n t e res t ing

for

coa l

app l i ca t ions ,

t h a t a

shor t

descr ip t ion here would seem

appropr ia te .


7/12

- 7 -

5.

The Tri -Flo

Separa tor

This device

d i f f e r s

from the other dyanmic

vesse l s

in tha t

t

combines 2 s tages

of separa t ion in

a

s ing le ves se l .

Two

s tag e wa s hing ca rt produce s ig n i f i can t improvements in recovery

( 3 ) a nd

can

a l

so produce

3

separa te

products

from

a

s ing le

co

mpa c t vesse l .

The

separa t o r has a cy l ind r ica l body as shown in the cu t -

away sec t ion of

Fig

.

3.

The vesse l is

divided by

a pa r t i t i on

wall in to

two

co n

sec

ut ive

chambers communicat ing

with each oth

th r

ough an ax ia l o r i f i c e each

chamber

being

equipped

with an

i nv o lu t e media i n l e t an d

s ink

discharge. The

feed

en t e r s the

f i r s t

c

hamber

o f th e

~ s s l where

a f i r s t

separa t ion

takes

pla ce ~ v n g a s ink l product .

The

f loa t

of

the f i r s t

s t age i s the feed of the seco nd

chamber

where a

second

separa

t i on , genera l ly a t

lower dens i ty

t akes p lace giv ing

a

s j

_nk 2 p r od uct ;

the f loa t

o f

the

second chamber i s

the

f in a l f loa t product .

Apart from - the fundamental novelty

inheren t

in

tf t

-i s

two

s tage des ign,

the oppor tuni ty was

a l so

taken for

improving

th e g eometry of the vesse l and p a r t i cu l a r ly

tha t

of

the

various

pa r t s .

As

a

re

s u l t in te rna l f r i c t i o n and

t he re fo re

v ea r a r d d

eg

r ad 8 t ion, were reduced and cap ac i t i e s increased

Fo r example, when Sacht leben Bergbau

G.m.b.H.

in t roduced

th

e i r

f i r s t

Tr i -F lo

separa tor a t t he i r Wolfach Plan t tha t

un i t r e pl aced a s ing le s tage separa tor

of

equal diameter .

Operat ing

the

new

two

s tag e s epara tor

over

the f i r s t four

mo

nth

s s howed

t

to be ca pable of handling approximately

30% mo

re

tonnag e with an in c rea s e of only

18%

in t o t a l medium

c i r cu l a t i on . Over

the

s ame period

the

losses were reduced

by 30% ,

co r re

spo nding

to

an increase

in

long

term recovery of

some

2 -

3%

compared

with the

previous

four months. ( 4 ) .

A s imi lar s tudy

on the po ten t i a l bene f i t s

poss ib le from

adding a seco nd re-wash s tage to well opera t ing cyclone coal

plan t s wa s publ i s hed

a t

the IX

In t e rna t iona l Coal Prepara t ion


8/12

8 -

6.

The Tri-F lo

Separa tor

and Coal

Prepara t ion

So

f a r , opera t ing exper ience has been with

high d e n s i t y

mineral p lan t s . Resul ts from these - inc luding the f i r s t

2-medium,

3-product plant and

from numerous

t e s t s , were

reported

in d e t a i l a t

the

XIV

In te rna t iona l

Mineral

Process ing Conference in

Toronto

in October

1982.

4

) .

These r e su l t s s h ~ w e d t ha t the

i n t eg ra l

second s t age

s ign i f i can t l y improved

long

term e f f i c i ency ,

p a r t i c u l a r l y

when

the

re-ed wa-s -v a r.

i ab l e , contained

l a rge a-

mounts of--el t he r

f l oa t

or s ink f r ac t i ons , or much

near g ra v i t y ma t e r i a l - -

t i s reasonable

to

expect s imi la r improvements a t lower

dens i t i e s and indeed the

f i r s t

low dens i ty 100

t / h

Tr i -F lo

coal

plant

i s due

to

s t a r t

up shor t ly in

u s t r i a ~

We sha l l

now examine

the var ious

fea tu res and

t he i r

po ten t i a l for improving

the

design

of

fu ture coa l

6.1

Higher

Long Term Eff ic iency

Some

~ i m e

ago

an

exerc ise

was car r ied out

the

Br i t i sh Nat ional

Coal

Board on

the

t echn ica l

and

economic

comparisons

between

Baum

j i g s

and

dense

medium cyclones . I t was found

t ha t even

with easy

coa ls the

overa l l

recovery w ~ almost

81

l ~ s s

~ i s

than with complete

dense medium t rea tment

and

t ha t

even 1

ex t ra recovery would pay

for the

d i f fe rence

in cos t between the

two

systems.

P r o f i t s

would

be higher still when sepa ra t iomwere

required

below

1.5

or

with

d i f f i c u l t

coals .

6

) .

The

evidence accumulated so fa r sugges ts t ha t

the

long term e f f e c t o f two

s tage

separa t ion should

help to

improve

these

r e su l t s

even more.

Exper ience

may

well

prove t ha t with a

2-Dtage

separa t ion the

need

for

expens ive homogenisation p lan t s may become

s ign i f i can t l y

l e s s press ing .


9/12

' ;) -

6

.2

Low

Level

Feed Entry

without

pumping of coal

This reduces

wear on the pumps and any degradat ion

of

the product ,

the

l a t t e r af fec t ing vend

and the load

on

the water c l a r i f i c a t i o n plant

.

In

a recent

paper

descr ib ing

the automation

of

a

pump

fe

d

cyclone i n s t a l l a t i o n

t r e a t i n g 0-38

mm coa l ,

the

feed

co

ntained 64.5 of +6.3 mm The products

contained

o

nly

50.4 and

50. O re spec t ive ly

. (

7 ) .

The a l t e

rna t ive

t o

pumping

the

cyclone feed means

a hi gh leve l grav i ty feed

with

a corresponding

inc rease

in

bui ld ing h

e i ght

and

cos t . The low l eve l grav i ty feed

o f the Tr

i -F lo se

para tor

make

s a lower

bui ld ing

and s h o r t e r

feed

conveyor

s

p o s s i l with

r esu l t ing saving

of space

and cos t - and redu c ed

environmental

impact .

6. 3

Hi g h S ink s

Capaci ty

due t o

the sec ond s inks

ou t le t

In creas ing

ly

high proport ions of waste have to be

re jected and con ventiemal s ingle s tage sepa ra to r s

have

to

be

down ra ted to s tay with in

t he i r

s inks ou t le t

ca

paci ty i n order to

avoid blockages

or contaminat ion

of

the clean coa l .

(

8 ) .

With the two s inks ou t l e t s

ava i l ab le here

the second

sca

venger s

tage

ensures

tha t

any

remaining

heavy

or near

gra

vi ty

heavy mat e r i a l

i s re jec ted

in the l i gh t ly loaded

second or

' 'cl

eane

r

s tag e .

6 .4 Th

i rd Product

Fac i l i ty

When th e s ys tem ope ra te s

with

a s ing le medium for

bo t h

the

f i r s t and

the second compartment the re wi l l

inheren t ly be a s l i gh t di f f e rence in q u a l i t y

between

Sinks 1 and

2. In

some cases

t h i s

is

i n s i g n i f i c a n t

a nd merely pr o

duces

a

sha rper two product separa t i

on

by

re -c leanin

g the f loa t

product

from

the

f i r s t compart

ment. In

tha t

ca s e

Sink

1

and Sink

2

are combined. In

o

ther

cases

the

s g ht ly lower ash

Sink

2 may

be

used

s

epara te

ly ,

perhaps in

a

l oca l f lu id i sed bed bo i l e r

ca

pable of

opera t ing

e f

f i c i e n t l y with a high ash

or


10/12

In a

third

case

t

may

be

desirable

to operate with

two more widely separated densi t ies . For example, one

may

wish to

produce a low ash,

low sulphur premium coal ,

a

second

qual i ty

fuel and

a clean

re jec t with the fac i l i ty

for to ta l ly separate

control of the

two cut points .

In

principle th is i s

s imi lar to

the

condit ions

under

which a

Tri-Flo

plarit

has been

operating

in

Northern

I t a ly

__s ince

1981.

That plalLt__Q

perates

a t ~

a t h e r

high dens i t i es ,

viz.

2.75

and 3.2

kg/ l ,_

producing

a

clean, low

densi ty

f loat , an

excel lent

metal lurgical

f luorspar

as the

i n t e r -

mediate product,

and

a

Sink

1

containing

over 9 0 ~ of the

available

lead

and intergrpwn heavies.

Operation i s

with

a

special ,

patented

c i r cu i t

with

two

separate ly

contro l led

densi t ies .

This was a par t icu lar ly in teres t ing development

which proved remarkably s i m p l ~

and steady to

operate , even

by

men without pr ior

experience

in process plant

operat ion.

This f ac i l i ty

could be useful

for

smaller

local cleaning

plants

where

two

separate

conventional

plant

in

se r ies

could

not be jus t i f i ed .

4 ) .

6.5 Fine Mediums

All dynamic

systems operat ing

with

high cent r i fugal

- t

Grces

r e q u i J . e a ~ i n e

m e d i u m

th-an s ta-

t ic

s-ystems- i n- o-rd-e-r

to prevent excessive segregation of coarse medium

towards

the

sink out le t .

This

i s par t icu lar ly important

with

a

cyclone

separator

and

with the small diameter

sinks

ou t le t

of

the Vorsyl

separator

and explains

why

these separate

a t

a higher densi ty

than

that

of

the feed medium. With the

paral le l sides of the DWP and of the Tri-Flo separator

and

tangential sinks out le t the radius

of

the

vessel

stays

constant and

i t

i s therefore inherent ly eas ier to

maintain the

required

accelera t ing

forces and

keep

the

density

gradient

more

nearly constant

over

the

fu l l

lengths

of the

separator .

9

. When

high acce lera t ing

forces are required

for

par t icu lar ly d i f f i cu l t

or

f ine


11/12

1 1 -

S i m1 1 a n l y i

t

s

n

ou l d ll e l e s s

of

a p r ob 1em ,t o

opera te a t the spec i a l l y low

dens i t i e s requi red

for

some

low

su lphur sepa ra t ions where media become

r eaJ i ly unsLable i.n conven t iona l vesse l s .

6.6 Larger Top Size

Tradi t i

o

nal Coal

Prepa ra t ion

Plants of ten

consis ted

of three

main s e c t i ons

to

t r ea t coarse coa l

small coal

and s l u r r i e s .

Now tha t little

coarse coal remains a f t e r

-

mechanised mining

many

new

p lan t s

are s imp l i f i ed by

e l imina t ing the

coarse

dense

medium sec t ion .

In

some

cases

the s ize range

t r e a t ed

in the dynamic sys tems

has been incceased t o 35/4 5

mm with

good

r esul ts

leaving

very little

ove rs i ze

to

be c rushed .

In

other

case

s j ig s are used for a high ash rougher sepa ra t i o n .

Dynamic dense media can then

be

u

se

d

e i t he r

to

re

wash the

high

ash j i g product a t lower dens i ty or

t o

re-wash the

j i g middl ings . -=-

In a l l these

cases

the

poss ib i l i t y of accep t ing

coarse r coal in

the

dynamic

sys tem i s use fu l

and

i s

becoming mo

re widely accepted .

With the Tri -F lo

se

pa ra to r the

coal

en te r s and

-

passes through both

s t ages

of the vesse l

ax i a l l y

r i d i ng on the

inner

fa ce of

the

r o t a t i ng

medium.

The wear and chance of

blockage

i s low and thus

s

hould

give

even

more

scope

if even l a rge r

top s i z e s

s h o

uld

become

i n t e r es t i ng .

The

r es t r i c t ion for the

s inks

removal are

a l so

r11inirnal,

with typ ica l

ou t l e t diameters

of 130

mm

. CorJ c ]us i o ns

Dense

medium

s widely

used

in coa l

prepa ra t ion p rac t i c e

and

provides

a f l ex ib le system

which can

be ea s i l y automated

t o a

djus t

to

cha

n

ges

in

feed

or markets

.

I t see ms . l j ke ly lh a t these

fea tures

wil l

be

importan t

c o e e be h e d a n d h a


12/12

REFERENCES:

1.

2.

4.

5.

6.

7.

8.

9.

HUCKO, MARONDE

M NG L RS

FERRARA, RUFF

DESSENIBUS

&others

ABBOTI &others

CAMMACK

Deputy Chief Coal

PreparatiOn-Engineer,

N.C.B.

TERRY

HILLMAN

KIRCHBERG,

SGHULZE

* Delhi =9th International Coal

Preparation Congress

The Application of HGMS n Coal Preparation

*

Delhi 1982. (F2)

The

Influence

of Cyclone Diameter on

Separating

Performance and Econany

* Delhi 1982. (B4)

Dynamic Dense Meditm Separation Processes .

Further developments with

particular

reference

to

the Tri-Flo Separator. ERZHETAlL

35

( 1982)

6 7 8

Plant

Operation of a new Heavy Media Dynamic

Concentrator

for Metallic

&nonHmetallic Ore

Processi.Dg .

XIV Intl.Min.Proc.Conf.,

Toronto

1982.

The Ecol'l01ii1cs of Secondary

Separation with

Recirculation

in Dense Medium

Processes .

*

Delhi 1982.

(G3)

Coal Beneficiation by Dense Medium Cleaning

Mackay

School o Mines_Symposium

Nevada 1978.

Automation

and

Control of Heavy Medium Cyclone

*

Delhi 1982.

(D2)

The Technology and Economics of large-capacity

Coal Preparation Plants .

Mine Quarry

Jan/Feb. 1983.

Study of the

Flow &

Separation Conditions in

a

Dyna

Whirlpool

Cylindrical

Cyclone

Report No. 156 - Freiberg,

DDR.

coal cleaning by dense medium processes h.j. ruff inpromin

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