Noise reduction in Queensland sugar mills


Macey, D.A.len,. Jr.;

Proceedings of the congress: 5th (v 3) 1604-1610

1974


Case
History
Number
1
Noise
Reduction
in
Queensland
Sugar
Mills*
Noise
levels
at
the
majority
of
operator
locations
in
Queensland
sugar
mills
are
5
to
10
dB(A)
higher
than
the
target
level
of
85
dB(A).
Noise
sources
include
a
broad
range
of
machinery
and
procedures.
The
progress
in
reducing
the
noise
of
locomotives,
shredders,
and
the
steam
system
is
described
by
D.
Macey.t**
The
milling
of
sugar
cane
is
a
process
that
most
people
un-
familiar
with
the
industry
would
probably
guess
to
be
quiet.
The
expression
of
juice
from
the
cane
involves
slow
crushing
between
large
rollers;
the
concentration
of
juice
is
simply
a
process
of
boiling
and
evaporation;
and
crystallization
involves
growing
crystals
in
a
supersaturated
solution.
Although
these
processes
are
quiet
in
themselves,
there
is
a
host
of
associated
plant
sources
and
equipment
producing
noise.
The
extent
of
the
problem
is
illustrated
in
Fig.
1,
which
shows
the
number
of
work
stations
with
various
noise
levels
found
in
surveys
of
six
sugar
mills.
Roving
personnel
were
not
included
in
the
survey.
It
can
be
seen
that
approximately
two-thirds
of
the
work
stations
had
a
noise
level
above
85
dB(A).
The
problem
of
occupational
noise
has
been
of
concern
to
the
Queensland
raw
sugar
industry
for
many
years.
The
first
sound
level
meter
used
by
the
industry
was
acquired
for
the
Sugar
Research
Institute
in
1965.
Since
that
time,
the
criteria
for
hearing
conservation
have
become
more
stringent
and
clearly
defined.
A
program
of
research
was
initiated
in
1971,
to
deter-
mine
the
extent
of
the
risk
to
sugar
mill
personnel
and
to
define
common
problem
areas
where
standard
methods
of
noise
control
could
be
specified.
Sources
of
Noise
The
first
step
in
the
program
was
to
identify
the
machines
and
processes
which
contributed
most
to
the
noise
exposure
of
factory
personnel.
The
milling
process
begins
when
cane
is
hauled
from
farms
to
the
factory
in
locomotives
and
trucks.
A
tipping
mechanism,
*Received
7
February
1977;
revised
6
January
1978
t141
North
Cray
Road,
Sidcup,
Kent,
England
*
*Work
on
this
paper
was
performed
while
the
author
was
an
employee
of
the
Sugar
Research
Institute,
Mackay,
Queensland,
Australia.
VolumelO/Numbier2
usually
with
a
hydraulic
drive,
dumps
cane
out
of
the
bins
and
onto
a
steel
slat
carrier.
The
carrier
feeds
cane
into
a
rotary
shredder,
which
delivers
the
shredded
cane
to
the
milling
train.
Juice
is
extracted
by
the
large,
slowly
rotating
mill
rolls
and
pumped
to
an
intermediate
storage
tank.
Most
mills
are
driven
by
steam
turbines
via
a
gear
reduction
of
approximately
1000:1.
The
factory
energy
requirements
are
met
by
a
boiler
fired
with
the
fibrous
residue
of
the
cane
(bagasse)
leaving
the
milling
train.
High-pressure
steam
drives
turbines
for
the
shredder,
mills,
and
the
alternators
that
meet
the
electrical
demands
of
the
factory.
The
turbine
exhaust
steam
is
used
for
boiling
and
evaporating
juice.
The
production
of
crystal
sugar
from
the
cane
juice
involves
heating,
clarification,
and
evaporation.
The
evaporation
begins
under
pressure
and
is
completed
under
vacuum
conditions.
Crystallization
then
progresses
in
large
cooling
tanks.
The
mix-
ture
of
crystals
and
molasses
is
separated
in
centrifugal
ma-
chines.
The
raw
sugar
is
conditioned
in
a
rotary
drier
and
conveyed
to
a
storage
bin.
Sources
of
noise
in
this
process
are
the
locomotives;
shred-
ders;
turbine
reduction
gearboxes;
boiler
fans;
steam
lines,
20
10
Iii
70
80
90
100
110
NOISE
LEVEL
dB(A)
Figure
1
—Distribution
of
noise
levels
measured
in
operator
locations
in
six
sugar
mills
67
0.
OF
OBSERVA
TI
ONS
TABLE
I
SUMMARY
OF
NOISE
TESTS*
Test
Cab
Lining
Exhaust
Silencer
Track
Speed
km/h
Engine
Speed
rpm
Load
Noise
Level
dB(A)
1
none
standard
0
1200
nil
90
2
none
standard
0
1600
nil
96
3
none
standard
25
1600
nil
98
4
none
standard
25
1600
full
99
5
4
m
2
standard
25
1600
nil
90
6
7
m
2
400
by
1200
0
1200
nil
80
7
7
m
2
400
by
1200
25
1600
nil
87
*Locomotive
No.
17,
Tully
Mill
vents,
and
control
valves;
centrifugals;
vacuum
pumps;
hydrau-
lic
pumps;
air
compressors;
and
alternators.
Solutions
to
noise
problems
due
to
gearboxes,
fans,
vacuum
pumps,
and
air
compressors
have
been
demonstrated
in
mills.
Standard
noise
control
procedures
were
used
(enclosure,
ab-
sorption,
and
so
on),
and
have
been
adequately
described
elsewhere.'
Other
problems
(hydraulic
pumps,
alternators)
are
best
overcome
by
the
manufacturer's
attention
to
design
and
installation.
This
article
is
a
description
of
efforts
at
reducing
the
noise
of
locomotives,
shredders,
and
the
steam
system.
Cane
Locomotives
Most
of
the
cane
is
transported
from
farms
to
mills
by
railroad
there
are
some
3000
km
of
600
mm
gauge
rail
line
in
Queensland
and
approximately
120
locomotives
in
operation.
A
typical
cane
locomotive
is
shown
in
Fig.
2.
It
is
obvious
that
noise
control
has
not
been
a
significant
consideration
in
the
design
of
cane
locomotives.
The
frame
is
rigid
(no
bogies),
the
engine
and
transmission
are
rigidly
mounted,
and
all
wheels
are
driven.
The
cabin
structure
is
welded
to
the
main
frame,
with
internal
surfaces
of
bare
steel.
The
exhaust
muffler
is
small
in
relation
to
the
exhaust
pipe
size,
and
the
exhaust
outlet
and
air
intake
are
located
near
the
front
windows.
The
noise
level
in
the
cabin
at
full
speed
and
load
is
typically
100
dB(A).
In
the
last
five
years
some
manufacturers
have
responded
to
the
sugar
mills'
demands
for
quieter
locomotives,
and
it
is
now
possible
to
purchase
a
locomotive
with
a
maximum
cabin
noise
level
of
75
dB(A).
Over
a
period
of
ten
to
fifteen
years,
as
old
locomotives
are
replaced,
the
noise
problem
will
disappear.
In
the
meantime,
methods
of
noise
reduction
are
required
for
existing
machines.
In
the
initial
measurements
of
locomotive
noise,
it
was
ob-
served
that
the
noise
level
outside
the
door,
at
arm's
length,
was
6
dB(A)
lower
than
inside
the
cabin.
The
character
of
the
noise
was
similar
to
that
of
the
exhaust.
Accordingly,
it
was
decided
to
investigate
the
effects
of
lining
the
cabin
with
a
sound-absorbing
material
and
fitting
an
improved
exhaust
silencer.
The
locomotive
chosen
for
tests
(Fig.
2)
was
one
of
the
most
common
types:
an
18
tonne
machine
with
a
six-cylinder
in-line
diesel
engine
developing
180
brake
horsepower.
The
operating
speed
was
approximately
25
km/h.
A
summary
of
the
tests
is
shown
in
Table
I.
Many
previous
noise
measurements
on
locomotives
under
operating
conditions
showed
that
the
noise
level
was
almost
independent
of
load.
This
observation
was
verified
in
these
tests;
the
noise
level
at
25
km/h
,
no
load,
was
98
dB(A),
and
at
the
same
speed
with
brakes
on,
the
noise
level
was
99
dB(A).
The
effect
of
engine
speed
was
more
significant.
An
increase
from
1200
to
1600
rpm
gave
an
increase
from
90
to
96
dB(A)
when
the
locomotive
was
stationary.
The
effect
of
lining
the
cabin
with
50
mm
Rockwool
(80
kg/m
3
)
was
significant.
Using
a
total
area
of
4
m
2
distributed
around
the
cabin
walls,
the
noise
level
at
25
km/h,
no
load,
was
reduced
from
98
dB(A)
to
90
dB(A).
A
simple
exhaust
silencer
(Fig.
3a)
was
designed
to
reduce
the
noise
below
90
dB(A).
The
length
and
diameter
(400
mm
and
1200
mm)
were
the
maximum
which
could
be
fitted
into
the
space
available.
A
straight-through
style
was
adopted
to
minimize
back
pressure
and
a
central
baffle
was
used.
The
space
between
the
central
pipe
and
the
outer
shell
was
filled
with
sound-absorbing
material:
25
mm
of
high-temperature
ceramic
wool
(Triton
Kaowool)
surrounding
the
pipe
and
the
remaining
space
filled
with
80
kg/m
3
Rockwool.
The
pipe
diameter
was
100
mm.
I
"
rp
(
-
Ng
.„
11
1
Figure
2
Typical
cane
locomotive
68
NOISE
CONTROL
ENGINEERING
/
March-April
1978
2x
65
mm
pipes,
150
centres
L
100
x
1800
r
CV
~I
I
2x
65mm
holes,
150
centres
I
100
x1800
U,
1;1
shell
diameter
330
mm
Figure
4
Reactive
locomotive
exhaust
silencers
110
100
90
ORIGINAL
dB
105
dB(A)
80
70
100
90
dB
80
SINGLE
BAFFLE
97
dB(A)
The
effect
of
this
muffler,
together
with
7
m
2
of
cabin
lining,
is
shown
in
Table
I
(observations
nos.
6
and
7).
Under
stationary
conditions,
with
an
engine
speed
of
1200
rpm,
the
noise was
reduced
from
90
to
80
dB(A).
At
25
km/h,
no
load,
the
noise
was
reduced
from
98
to
87
dB(A).
Although
the
400
by
1200
mm
silencer
could
be
fitted
to
the
engine,
it
was
found
to
be
too
large
to
allow
free
access
to
engine
parts
requiring
regular
maintenance,
such
as
the
air
and
oil
filters.
It
was
decided
to
make
a
comparative
study
of
several
silencers
of
the
same
style
but
decreasing
size
to
determine
the
smallest
size
consistent
with
a
reasonable
noise
reduction.
Four
new
silencers
were
constructed
and
tested
in
the
combi-
nations
shown
in
Fig.
3.
For
these
tests
the
locomotive
was
stationary
and
the
exhaust
line
was
directed
to
one
side,
perpen-
dicular
to
the
track,
so
that
the
outlet
was
4
m
from
the
engine.
The
noise
level
was
measured
300
mm
to
one
side
of
the
outlet.
The
noise
at
4
m
from
the
locomotive
on
the
other
side
was
monitored
to
ensure
that
the
noise
from
the
engine
itself
did
not
affect
the
measurement
at
the
exhaust
outlet.
The
exhaust
outlet
noise
at
1600
rpm
for
the
various
silencers
is
shown
in
Fig.
3.
Predictably,
the
largest
silencers
were
the
most
effective.
From
these
tests
it
was
concluded
that
the
minimum
diameter
and
length
would
be
300
mm
and
900
mm,
respectively.
A
specialist
in
engine
silencer
design
was
requested
to
specify
the
best
silencer
within
this
size
limitation,
with
a
100
mm
tailpipe
1800
mm
in
length.
The
two
arrangements
shown
in
Fig.
4
were
suggested.
No
sound-absorbing
material
was
used.
The
two
silencers
were
constructed
and
tested
on
a
second
locomotive,
similar
in
design
to
the
one
already
described.
At
300
mm,
the
outlet
noise
of
the
original
muffler
was
105
dB(A)
and
the
new
mufflers
97
dB(A)
and
99
dB(A).
The
three
spectra
are
shown
in
Fig.
5.
81dB(A)
GOO
mm
dia
x1200mm
-------
1111111111E1111111111F
(a)
85
dB(A)
300x900
(b)
DOUBLE
BAFFLE
99
dB(A)
104
dB(A)
200x
600
oswiesmsgra..._
(d)
100dB(A)
200,0200
(e)
99
dB(A)
200,0200
200x600
)
100
90
dB
80
70
93
dB(A)
300x600
(c)
70
111
dB(A)
100mm
EXHAUST
PIPE
3000mm
LONG
0
200
400
Hz
600
800
1000
(9)
Figure
5
Spectra
of
exhaust
outlet
noise,
measured
on
reactive
Figure
3
—Absorption
exhaust
silencers
tested
on
a
cane
locomotive
locomotive
silencers
Volume
10
/
Number
2
69
A
comparison
of
these
results
with
those
in
Table
I
is
not
completely
valid
since
two
different
engines
were
involved,
although
they
were
of
similar
size
and
power. Nevertheless,
the
use
of
sound-absorbing
material
appears
to
be
worthwhile.
These
investigations
showed
that
it
is
fairly
simple
to
modify
a
cane
locomotive
to
give
an
acceptable
cabin
noise
level.
From
the
results
in
Table
I,
it
is
apparent
that
a
sound-absorbing
cabin
lining
is
the
most
important
factor.
Shredders
Cane
arrives
at
the
mill
chopped
into
billets
approximately
250
mm
in
length.
Before
delivery
to
the
train,
a
shredding
process
is
necessary
to
facilitate
feeding
and
juice
extraction.
A
shredder
consists
of
a
horizontal,
rotating
shaft
on
which
swinging
hammers
are
mounted.
Billets
of
cane
fall
onto
the
rotor
and
are
forced
past
a
grid.
A
typical
shredder
layout
is
shown
in
Fig.
6.
Each
pivot
pin
holds
about
twenty
hammers,
giving
a
working
face
of
2130
mm.
The
hammer
tip
diameter
is
1800
mm
and
the
tip
speed
is
100
m/s.
The
rotor
is
driven
by
a
steam
turbine
developing
a
power
of
approximately
2000
kW.
Fig.
7
shows
a
recent
shredder
installation.
In
the
majority
of
sugar
mills
the
shredder
is
the
most
obvious
source
of
noise.
Its
position
at
the
front
entrance
to
the
mill
building
demands
that
people
walk
past
it
more
often
than
any
other
machine
in
the
plant.
The
noise
can
be
heard
throughout
the
entire
factory
and
is
a
source
of
great
annoyance.
The
noise
level
at
the
tip,
where several
operators
work,
is
95
to
100
dB(A).
Occasionally,
an
operator
must
venture
into the
shredder
pit
to
clean
up
the
mud
and
rubbish
which
falls
from
the
cane
carrier.
This
worker
would
spend
approximately
one
hour
per
shift
in
a
noise
level
of
110
dB(A).
0
SLAT
CONVEYOR
0
SHREDDER
DRAG
ELEVATOR
Figure
6
—Shredder
layout
Mechanisms
of
noise
generation.
The
action
of
a
shredder
has
been
studied
with
high-speed
photography
on
a
pilot
scale
machine.
Several
noise-generating
mechanisms
were
evident.
Impacts
occur
between
cane
billets
falling
into
the
entry
of
the
shredder
and
hammers
moving
at
100
m/s.
Approximately
400
billets
enter
the
shredder
per
second
at
a
crushing
rate
of
300
tonnes
per
hour.
There
is
a
free
path
for
airborne
noise
from
the
70
4
Figure
7
A
recent
shredder
installation
impacts,
going
up
the
head
box
and
down
the
carrier,
and
another
path
up
the
delivery
elevator.
The
impact
forces
on
the
hammers
could
be
transmitted
to
the
casing
via
the
bearings,
thus
resulting
in
casing
vibration.
Vibration
would
also
be
generated
by
cane
fragments
striking
the
inside
of
the
casing
around
the
entry
region
and
opposite
the
lower
edge
of
the
grid
section.
The
severity
of
this
effect
may
be
judged
by
the
fact
that
12
mm,
hard,
stainless
wear
plates
employed
in
these
areas
usually
do
not
last
one
season.
A
third
mechanism
by
which
noise
is
generated
is
the
fan
action
of
a
shredder.
The
machine
is
similar
in
principle
to
a
centrifugal
fan
1800
mm
in
diameter,
2130
mm
in
length,
at
a
speed
of
1200
rpm.
Failure
to
control
the
windage
results
in
a
fine
mist
of
cane
juice
distributed
throughout
the
mill
building.
Enclosure.
The
potential
for
noise
reduction
by
enclosure
is
limited
by
the
need
to
leave
openings
through
which
cane
can
enter
and
leave
the
machine.
A
reduction
of
a
few
decibels
is
achieved
by
covering
the
carrier
and
elevator
to
create
a
tunnel
effect.
Flexible
baffles
are
included
to
block
the
noise
path
as
much
as
possible
and
to
limit
windage.
In
principle,
it
would
be
possible
to
construct
a
special
building
around
the
carrier,
shredder,
and
elevator,
but
this
approach
is
unpopular
among
mill
engineers,
who
like
to
see
mechanical
problems
as
they
develop.
Casing
modification.
A
greater
degree
of
success
has
been
obtained
by
fitting
a
cover
of
3
mm
steel
on
the
shredder
casing,
with
a
50
mm
space
filled
with
dry
sand.
Noise
is
reduced
in
two
ways:
the
sand
damps
the
vibration
of
the
inner
casing,
and
the
outer
casing
acts
as
a
damped
barrier
to
noise
radiated
from
the
inner
casing.
Sand
is
probably
not
the
best
damping
material,
but
it
has
the
advantage
of
being
inexpensive
and
available;
in
an
emergency,
the'
casing
can
be
flame-cut
or
welded
upon.
A
noise
reduction
of
approximately
7
dB
was
obtained
in
one
installation
by
covering
the
carrier
and
elevator,
and
fitting
the
sand-filled
cover
to
the
casing.
NOISE
CONTROL
ENGINEERING
/
March-April
1978
NO1
MILL
23
0
3
21
0
0
190
0
0
17
0
0
0
0
0
15
13
11
AXIAh
0
0
9
0
7
9
11
13
15
17
19
SPIRAL
1
3
88
11
13
15
17
9
DIAMOND
M
0
0
7
PIVOT
PIN
0
NOTATION
AXIAL
102
dB(A)
SPIRAL
96
dB(A)
DIAMOND
98
dB(A)
Y
\ W
ATA
Hammer
configurations.
Because
the
hammers
in
a
shredder
are
fixed
in
straight
axial
rows
on
eight
pins,
all
cane
billets
that
fall
between
two
adjacent
rows
are
struck
simultaneously.
A
noise
reduction
could
therefore
be
expected
if
the
hammers
were
distributed
more
evenly
around
the
periphery
of
the
rotor.
The
extent
to
which
the
hammer
pattern
can
be
rearranged
is
limited
by
the
fact
that
no
more
than
twenty-four
pivot
pins
can
be
used,
since
the
mechanical
strength
of
the
rotor
discs
must
be
taken
into
consideration.
The
idea
was
tried
on
the
pilot
scale
shredder.
In
this
machine
the
rotor
length
was
restricted
to
five
hammers
instead
of
the
usual
twenty,
but
the
diameter
and
speed
were
the
same
as
for
a
full-size
shredder.
The
number
of
holes
in
the
discs
was
in-
creased
from
eight
to
twenty-four,
allowing
the
hammer
pat-
terns
shown
in
Fig.
8
to
be
tested.
The
noise
spectra
for
the
three
arrangements
are
shown
in
Fig.
9.
The
noise
level
for
the
standard
arrangement
was
102
dB(A),
the
diamond
pattern
98
dB(A),
and
the
spiral
pattern
96
dB(A).
There
was
no
significant
difference
between
the
fineness
of
shredding
in
the
standard
and
spiral
arrangements,
but
the
diamond
pattern
was
slightly
inferior
in
this
respect.
It
was
suspected
that
the
spiral
arrangement
would
tend
to
throw
cane
to
one
side
of
the
delivery
elevator,
but
this
was
not
observed
in
practice.
In
1975,
a
shredder
manufacturer
adopted
the
spiral
hammer
arrangement
for
a
new
installation
at
one
of
the
member
mills
of
the
Sugar
Research
Institute.
Fearing
possible
screwing
of
the
cane
to
one
side
of
the
shredder,
the
mill
personnel
did
not
continue
the
spiral
line
across
the
full
width,
but
used
four
smaller
spirals,
which
gave
a
double-herringbone
effect.
The
noise
level
at
initial
start-up,
3
m
from
the
turbine,
was
96
dB(A).
A
new
standard
shredder
at
another
mill
had
a
noise
level
of
116
dB(A)
at
the
same
distance.
Comparisons
among
different
installations
can
be
mislead-
ing.
It
would
have
been
interesting
to
measure
the
differences
among
the
double-herringbone,
single
spiral,
and
straight
axial
arrangements
on
the
one
machine,
but
unfortunately,
the
oppor-
tunity
never
arose.
The
changes
would
have
involved
a
great
deal
of
work,
when
other
operational
problems
existed;
the
mill
also
felt
a
natural
reluctance
to
experiment
with
a
system
which
was
working
satisfactorily.
Another
method
of
noise
reduction
relating
to
hammer
ar-
rangements
is
to
omit
every
second
hammer
on
each
pin.
The
hammers
and
gaps
are
staggered
on
adjacent
pins.
The
noise
reduction
is
approximately
3
dB(A).
Many
mills
adopt
this
approach,
although
the
shredding
effect
is
impaired
because
there
is
a
tendency
for
small
pieces
of
cane
to
escape
through
the
gaps.
More
than
two-thirds
of
the
thirty
sugar
mills
in
Queensland
have
installed
new
shredders
in
the
past
five
years.
Enough
noise
control
experience
has
been
gained
to
achieve
a
noise
level
of
90
dB(A)
at
the
tip.
To
reduce
noise
to
85
dB(A)
would
probably
require
a
change
in
the
basic,
traditional
arrangement
of
tip,
carrier,
shredder,
and
elevator,
to
control
more
effec-
tively
the
paths
of
propagation
down
the
carrier
and
up
the
elevator.
5
7
9
11
13
15
17
19
21
23
.4--
ROTATION
-
Figure
8
Standard
(axial)
and
noise-reducing
shredder
hammer
patterns
110
100
dB
90
80
100
90
dB
80
70
100
90
dB
80
70
200
400
Hz
600
800
1000
Figure
9
Spectra
of
shredder
noise
with
standard
and
modified
hammer
patterns
1
23
21
23
Volume
10
/
Number
2
71
Steam
Noise
In
most
mills
the
demands
for
high-pressure
and
low-pressure
steam
are
fairly
well
balanced
when
the
process
is
running
smoothly.
There
are
many
factors,
however,
which
can
upset
this
balance.
The
supply
of
cane
is
dependent
on
weather
condi-
tions,
and
mechanical
breakdowns
account
for
several
hours
of
stoppage
each
week.
The
mill
also
shuts
down
each
weekend.
When
turbines
stop,
the
process
steam
must
be
made
up
with
a
reducing
valve
from
the
high-pressure
system,
and
when
the
boiling
process
is
interrupted,
the
excess
process
steam
must
be
vented
to
atmosphere.
An
excess
of
bagasse
may
be
disposed
of
by
generating
extra
steam,
which
is
vented
from
high
pressure
to
atmosphere.
In
addition
to
these
factors
arising
from
an
unbal-
ance
in
the
system,
there
is
a
multitude
of
small
noise
sources:
condensate
traps
and
drains,
control
valves,
steam
leaks,
and
lines
with
excessive
velocity.
Low-pressure
vents.
Exhaust
valves
operate
to
maintain
the
pressure
of
process
steam
at
approximately
100
kPa.
Most
mills
use
at
least
one
450
mm
dead
weight
or
butterfly
valve
for
exhaust
blow-off,
with
a
capacity
of
70
000
kg/h.
At
3
m
from
the
outlet,
the
noise
level
is
115
to
120
dB(A).
A
series
of
absorption-type
silencers
have
been
designed
and
applied
to
exhaust
valves,
with
great
success.
A
typical
silencer,
to
suit
a
450
mm
butterfly
valve,
is
shown
in
Fig.
10.
It
was
not
possible
to
make
meaningful
measurements
of
the
outlet
noise
due
to
the
high
background
noise
level
of
92
dB(A).
The
exhaust
was
certainly
not
audible
at
30
m
a
distance
at
which
it
would
previously
have
been
very
difficult
to
conduct
a
conversation.
It
is
common
for
mills
to
construct
this
type
of
silencer
in
their
own
workshops,
to
specifications
supplied
by
the
Sugar
Re-
search
Institute.
Since
the
cane-crushing
season
occupies
only
six
months
of
the
year,
there
is
usually
time
in
the
off-season
for
this
kind
of
work.
The
materials
for
the
silencer
shown
in
Fig.
10
cost
approximately
one-tenth
the
cost
of
a
low-noise
valve
of
the
velocity-control
type,
to
suit
this
application.
The
useful
life
of
absorption-type
silencers
is
not
yet
known.
The
noise
from
the
silencer
described
is
beginning
to
become
audible,
after
four
years
of
service.
It
may
be
necessary
to
replace
the
insulation
every
five
years.
High-pressure
vents.
A
typical
high-pressure
dump
valve
is
a
150
mm
double-beat
globe
valve,
working
from
1700
kPa,
with
a
full-open
capacity
of
approximately
100
000
kg/h.
In
the
first
attempts
at
silencing
these
vents
the
type
of
silencer
discussed
above
was
used,
but
without
success.
The
noise
level
at
the
outlet
was
only
a
few
decibels
lower
than
at
the
unsilenced
stack.
One
possible
explanation
is
that
the
jet
of
steam
from
the
valve
did
not
expand
fully
and
did
not
give
uniform
flow
in
the
absorptive
section
of
the
silencer.
The
problem
was
overcome
by
expanding
the
steam
through
a
perforated
pipe
in
the
entry
to
the
silencer.
The
silencer
shown
in
Fig.
11
was
installed
on
a
100
mm
globe
valve
venting
from
760
4
Mow
1
,
44
Pow
pod
voted
MS
PIO.
MUM
et
IMO
t1M.•ti
1
/
1
1
Vlith
mircurniertneft
SO
mot.
.
14
1 1
G.
c
wh
/
0
14
*QM
M
.
FOrtetess
,
10
Was
ea
WO
watt
owl.
100
Ns
On1M
Nee
r
SImM
MS,
420
6mm
holes
100
72
NOISE
CONTROL
ENGINEERING
/
March-April
1978
1500
kPa.
The
noise
level
of
the
unsilenced
stack
is
unknown,
since
the
valve
was
a
new
installation.
However,
the
silencer
was
effective
enough
to
preclude
a
meaningful
noise
measure-
ment
in
the
background
noise
level
of
92
dB(A).
The
total
area
of
holes
in
the
diffuser
was
chosen
so
that
at
full
valve
opening,
the
pressure
ratio
across
the
valve
was
just
critical.
The
diffuser,
therefore,
had
no
effect
on
valve
capacity.
Napier's
formula
(neglecting
superheat)
was
used
for
flow
through
the
holes:
W
=
0.00526
p
a,
Acknowledgments
The
author
is
indebted
to
the
Sugar
Research
Institute
for
permission
to
publish
this
paper,
and
to
the
member
sugar
mills
of
the
institute,
whose
willingness
to
try
new
ideas
allowed
the
rapid
development
of
noise
reduction
methods
in
a
factory
environment.
Assistance
was
also
received
from
ICI
Australia
Engineering
Pty.
Ltd,
in
steam
vent
silencer
design
and
from
Dr.
R.
J.
Alfredson,
Monash
University,
in
locomotive
exhaust
silencer
design.
where
W
is
the
flow
per
hole
(kg/h),
p
is
absolute
upstream
pressure
(kPa),
a
is
the
hole
area
(mm
2
).
In
this
case
6
mm
diameter
holes
were
used,
so
W
=
0.00526
x
800
x
7r/4
x
6
2
=
119
kg/h
per
hole.
The
full-open
valve
capacity
was
50
000
kg/h;
therefore,
the
number
of
holes
required
was
50
000/119
=
420.
Pressure-reducing
valves.
Pressure-reducing
valves
are
used
to
maintain
process
steam
pressure
at
approximately
190
kPa
when
the
quantity
of
exhaust
steam
from
prime
movers
is
reduced.
The
valve
is
usually
identical
to
the
dump
valve
already
de-
scribed.
It
has
been
found
that
the
simple
perforated
diffuser
makes
a
significant
reduction
in
noise
when
fitted
on
the
downstream
side
of
the
valve.
The
noise
level
at
3
m
was
reduced
from
100
dB(A)
to
a
level
below
90
dB(A).
The
noise
reduction
is
satisfactory
over
the
full
range
of
valve
opening.
This
was
not
expected,
since
the
valve
pressure
ratio
must
increase
as
the
valve
opening
decreases.
Conclusions
Noise
control
methods have
been
found
for
most
of
the
major
problems
in
Queensland
sugar
mills.
Steam
noise
can
be
con-
trolled
with
absorption-type
silencers
on
vents
and
back-
pressure
devices
on
pressure-reducing
valves.
Locomotive
cabin
noise
can
be
reduced
to
an
acceptable
level
by
lining
the
cabin
with
sound-absorbing
material
and
fitting
an
effective
exhaust
silencer.
Cane
shredder
noise
has been reduced
to
90
dB(A)
at
points
where
operators
must
work
continuously.
Further
study
is
required
to
achieve
the
target
level
of
85
dB(A).
The
need
to
specify
noise
levels
on
new
equipment
has
been
recognized
and
the
benefits
can
be
seen
in
new,
quiet
locomo-
tives,
turbine
reduction
gearboxes,
air
compressors,
and
hy-
draulic
pumps.
The
use
of
earmuffs
is
increasing,
although
they
are
generally
unpopular
in
the
hot,
humid
environment
of
sugar
mills.
Reference
I.
D.
Macey
and
J.
R.
Allen,
"Noise
Control
in
Queensland
Sugar
Mills,"
presented
at
the
13th
Congress
of
the
International
Society
of
Sugar
Cane
Technologists
(Durban,
1974).
Volume
10
/
Number
2
73