Document VGbnL4e5wjX49noYmaQVOn0yj
FILE NAME Colonial Sugar Refinery CSR
DATE 1950 DOC CSR023
DOCUMENT DESCRIPTION South African Department of Mines Report - Dust in Asbestos Mills
_'
UNIE VAN AFRIKA
mn
Do ve
bas,
Malpasoe ratete. +
Se
Mar!
Department of
Mines
DEPARTEMENT VAN MYNWESEMYNWESE
navorsingsafdeling
STOF IN ASBESMEULE
DUST IN ASBESTOS MILLS .
Die Staatsorukeis PRETORIS
1930
oo
The cobbing of asbestos rock must be done in the open
and in places where dust liberated from other operations does not blow
towards the persons engaged the work
eee vailiIntg wwainsdsnoftoerdsawleseopitnhgatofuutlloraddvialunttianggeduisstnoctreaatlewdayisn ttahekemniollf the pre-
oy
Mills should be so situated and designed that full advantage can be tzken of the prevailing winds for sweeping out or diluting dust created in the tzken
rms Fig 1 illustrates a shed which allows the winds to have relatively free
passage through the building and yet offers protection from the rains
an
blowing me It is perhaps hardly necessary to add that as far
Oe
should operate from the
as possible workmen
windward side that is in simple language they
nd
operate with the wi
on their backs so that dust made in
any operation should be blown away from them
|
entirely remove dust from the mill Winds however will not always be blowing and cannot be relied on to cannot ificiate ificiate
closures.andhoods locatebydmeans of ducts of the of connected The general method of dust control and removal described is by means
and hoods being
at source production enclosures
exhausting
^ ing
Tandumpjag from trucmkisght duse first of the more important dusty operations and
constitutes one of the
asion of dust control and elimination
comprehensive consider-
in the circuit
When
rock
is
tipped into
the
well be started from bins unless adequate
this
point
measures are taken dosis
displaced
newwith newwith
preventive petit
esposing them
cheavy
ne dles unhealthy and needless since it
concentrations SuSucchh exposure is
can easily be downcast through the bin
avoided by causing the air to
C
FIG.2 FIG.2 SHO
.
PLA
DUC DUC DUC
if A downward draft throug if air is not allowed to leak in
only be assured if the bin is de
doorrequiredis Atsome mille the mine car
chure which not intender
native
to shovel the
These
~
oy bin
7TS |] Duct
/qs y . _
t PLAN
FIG.2 METHOD OF EXTRACTING M DUST FRO ORE Deflection planes
downwardvelocityon The ofthethe
say 1,500 1,500
through exhausted through open area
the bin
or
ins wide
e
FRONT
DUCT OPENINGS OPENINGS OF
OPENINGS
if downward allowed leak
never theembpottioemd assured if the
through through
emptied
bearing bottom of thebin bin this
tom
y
the rom cksand inclined
inclined
asured mills the mine cars emptied forpurposes which which not intended
intended required required required shovel'the shovel'the rock
dudue e to the fact
work in this and place and curtains closing closing the closing
ate topheneingbsoxt,he box curtains closing the j If
of otrock
c ame,
cate
me ,0 ers
oan .
memes e
em
6 ee ee
removal removal Other tr s ao nsn fe s r 3 a illustrates a
hood suitable for dust removal at the point where a chute feeds on to a belt and Fig 3 b shows a hood arranged for collecting dust made during
the transfer of rock from one conveyor belt to another The ventilating
volume required at each of these points is 750 cu ft of air per minute It is common practice to bang leather or canvas strips over the openings to
cut down the air leakage but enough open area must be left for air to enter
otherwise the dust will not be carried away
A
Chute Hood
s
= rer
C Conveyor belt
FIG 3 ARRANGEMENT FOR COLLECTING DUST MADE AT DELIVERY POINT TO CONVEYOR BELT
ace
ee
oo
ONE CONVEYORCONVEYOR BELTBELT TO
Mahingvisa Mahingvisa that^"ral y operatiche bleaking production To overcome the dust problem crushing units usually have us be completely
houded as illustrated in Fig 4. The discharge from the crushers can
dealt with in a similar matiner to that indicated for conveyor hells on
gn, Se eee
ee ee elas enki tr eee ee: wee
FIG.4 ILLUSTRATION OF HOOD
FOR EXTRACTING DUST
FROM ROLLER CRUSHERS
{
Conveyor o.8
wy
: -
.
FOR_COL-
ISEMENT FOR_COL- FOR_COL-
G TRANSFER FROM
BELT TO
OHENR VEYOR
caking down lump rock to a finer size
hat indicated from conveyor conveyor belts sanied by the production of much dust
be be hing units usually have to completely
are
In either
through
dust
general
akinely
rotary
and the vibrating screen
case
crushed material is fed to the high end the rock pussing
chute end screenchute aatsbestoends Arrangements Arrangements for removing
at screens are shown in Figs 5 and 6
.
.
The outlets at the hopper and the screened should also be
fitted with hoods as previously illustrated The air volume for ventilation of screens is calculated on the basis of 75 cu ft of air per minute per square
foot of sectional area for rotary screens and screen box area for
vibrating screens
Mixing of the various grades of fibre is one of the dustiest operations in the mill To minimise the dust made by this operation it is preferable
Ar
e
MADE .
BUST
oe,
mee
Met
.
.
tit
SCRE N
Ri
ROTARYSCREN
Se
ROTARY ROTARY
et
FIGS
Me
shaped where where possible possible and
atmosphere atmosphere
mixing precautions done manually manually manually the g
turned
over
canopy
under canopy
bottom
edge
which
which
by means cone
handled handled forks made some
apex illustrated cone shaped canopy connected connected to the
ex is illustrated
connected made of some
ilustrated saholher saholher operation saholher saholher operation
where where workman workman
workman
fitting which The
Ar
AT ousr
-SECTIONA
gop
For
AEGEMNNT T
panpdaa3n7d5a375
panda375
intended air of
~ of used
Af
Velocity draw
function function intended
system function function although
intended preferable forced to draw to
a
ihe
>
ee
mes.
tm
ee
em
meme
+A
... ...
...
...
...
ee
LN
Sian
iintog
i
stucktruction
A common position of leak wherejointsjoints the pipes thes
paints become more serious the nearer they are to the intake to leaks
handiehandie .
.
;
f HAND
handie HAND -
HAND
gigion
DURING
Ling Ling q
DURING
| Ling
~
MADE
MADE
MADE
DUST
DUST
DUST
LIBRE
EXHAUSTING
EXHAUSTING
ASBESTOS
ASBESTOS
ASBESTOS
FOR
CANOPY
MIXING
MIXING
CANOPY
headi 7
.
canopy
FIG
mens
level
The purpose of an exhaust system is to bring dusts etc. into
to convey them to a suitable place for disposal This is
a hond an
creating an air movement in the
accomplished b
generated The air
vicinity of the source where the dust i
dispersing
into
the
movement air In
must
be
great
enough
to
keep
the
dust
fron
air velocity at the source is general most substances are controlled when th
roughly about 200 ft per minute The followin
LB
FRebte a
BEHe apEeay
PRESES
ag
fs
i. f
REHeaeet
Lawerri tess mens haods
te
7 . EXHAUSTING OF FIG.? CANOPY FOR
MIXING ASBESTOS FIGRE OUST MADE OURING HAND ,
SYTEM
1
EXTRACION
|
DUST
|
;
_
|
ILUSTRAING 210.6
00.9
L'AYOUT
5'012 emtra
F IG
Beginning with the remote end we have a diameter of 1 ins T
corresponds 5 in duct
to
an
area
of
38
5
sq
ins
It is joined before the paint A cs
having an area of 19.6 sq in
+ 19-6 58-1
in
The area at A is therefore US
sq
The diameter diameter at ,, will be therefore that whi
will give an area of 58-1 sq in which is to the nearest half inch !
Next we have branch a
branch of 5 in and adding this ares to the
area at a
SYTEM
EXTRACION rysah EXTRACTION
2Pers
DUST
oF
we te
4 ILUSTRANG
|4 Ay LAYOUT :
$
. .
FIG
vi we have a diameter of 7 ins This ins It is joined before the point A by 4. in The area at A is therefore 38 5 zjer at A will be therefore that which
which is to the nearest half inch 3 in and adding this area to the area at A
is also the area the fan inlet is +19.6 = 77-7 sq in Adding to this the
in and the 9 in branch 63-6 63-6 = 169-6 sq in whigicveh s a
in .
diameter
we
diameter
inch of 14 in Continuing to the last
9 in
A. - 169-6 + 63-6 233-s2q in The
which
of
this is done the diameters of every mains corres- Often 20 per cent
lower power consumption
excess area consumption
which
gives better
distribution
of flow
and
a branch enters
is added to that
main at
point
where
pooding to 1-2 greater than those calculated are obtained
entry of air as would be the case entering
pipe
entering which
from
a
branch
pipe
at
right
angles
to
the
header
of air
causes loss of momentum of the stream of air
causes turbulence
The suction at the fan is the sum of the suction
cumulative resistances of the
at the hoods and the
the boods and the fan
piping elbows and other units in series between
On straight piping it is found that a pipe 40 times
causes a resistance to flow or friction
as long as its diameter
existing in the pipe e.g. in
a
6
in
pressure diameter
equal
to
the
velocity
pressure
it at a velocity pressure of I in water
pipe with air travelling through
of straight pipe i.c. 40 times the gauge it is found that for every 20 1
water gauge
diameter the resistance will equal in
Elbows and bends also cause considerable loss in
and should be eliminated wherever
power due to friction
radius of
possible Elbows or bends with
a
approximately straight pipe with
11
times
their
diameter
have
a
friction
loss
equal
a to
a radius 11 times itsa length of 6 times its diameter a 6 in clbow with
The
use
of
baffles
diameter
for
is
equivalent
adding 3 ft of 6 sts pipe
regulating purposes is not recommended
if properly the It may be found that a
and
this is
usually found
to
designed be all
plant
is
not
working efficiently
in
place
due
to
partly
choked
pipes
or
a
"
hoods and silted
coverings
are
which are dirty Fans will stay cleaner for
up fan the blades of
is between them and the
a longer time if the dust trap or
cyclone tihne system to ascertain when pipingsources of dust Periodical inspection of
any cleaned tinhuamnby installation and in thipsicpionngneacntdionfaninspection shoulinspdection be
is essential
wing
type nuts should be provided and should be strong enough to stand frequent
last as long as the plant itself distortion so that the hoods or whatever is provided todiprevsentpmraenvetnltintghewdiutshtountuisance will
The midium of transport of dust in a local exhaust
settling
of dust
in
the
piping
system
is
usually
due
system is air
to insufficient
and
the
Most dusts are conveyed at relocities
velocity
exceeding 3,000 ft per minute
Dust traps which are
provided where
properly sealed against air leakage might be
is usually from very coarse and heavy dust is produced As this dust
otherwise the waste rock it can be allowed to fall into a tray of water
trap should be damped down and cleaned during an shift