4
Alfa – Laval
separator (I)
4.1 Function
? The purpose of the operation is either to
liberate a liquid from strange particles,or
to separate two intermixed liquids,
4.1 Definitions
? Throughput
– This means the quantity of liquid supplied per
unit time,The throughput is given in cu,m/h
or l/h.
? Reception ability
– This means the largest liquid quantity that the
bowl can treat per unit time,expressed in
cu.m/h or l/h,
4.1 Definitions
? Purification
– A liquid ? liquid separation in which the
machine is used for separating two intermixed
liquids,which are insoluble in each other and
have different specific gravities,Solids with
specific gravities higher than those of the
liquids can be separated off at the same time.
4.1 Definitions
? Clarification
– A liquid - sludge separation in which the
machine is used to separate particles,normally
solid ones,from a liquid having a lower
specific gravity than that of the particles.
4.1 Definitions
? Concentration
– A liquid ? liquid separation in which the
machine is used for separating two intermixed
liquids,which are insoluble in each other and
have different specific gravities,the heavier
liquid constituting the major part of the mixture,
– Solids with specific gravities higher than those
of the liquids can be separated off at the same
time,
4.1 Definitions
? Solids ejection
– Emptying of the bowl during operation
by uncovering and closing slots in the
bowl wall.
? Total ejection
– Total emptying of the bowl with the feed
(as a rule) turned off.
4.1 Definitions
? Partial ejection
– Total or partial emptying of the solids
space in the bowl but without emptying
the rest of the bowl,
– The feed need not be interrupted.
? Combined programme
– A combination of total and partial
ejections in succession.
4.1Factors influencing the
separation
? Difference in specific gravity
– The centrifugal force acts on all particles
proportionally to their specific gravity,
– This applies to solid Particles as well as to
fluid particles,
– The greater the difference in specific gravity,
the easier the separation,
4.1 Factors influencing the
separation
? Size and shape of particles
– The larger the particle,the quicker the sedimentation,
– The particles to be separated off must not be so small
that the mixture is close to colloidal state,
– The smooth and round particle is easier separated off
than the irregular one,
– Rough treatment,e,g,in pumps,can split the particles,
with reduced size and separating speed as a result.
4.1 Factors influencing the
separation
? Viscosity
– The more fluid a liquid is,the quicker is the
separating process and the better the
separation ― in other words,low viscosity
improves the separation result,
– The viscosity can in many cases be reduced by
heating,
4.1 Factors influencing the
separation
? Time in centrifugal field
– If the separation is not satisfactory,the
throughput must be reduced,
– Lower throughput gives,normally,a better
separation result,
4.1 Purification - Purifier bowl
? This bowl has two
outlets.
? The process liquid
flows through the
distributor to the
interspaces between
the bowl discs,where
the liquid phases are
separated from each
other by action of the
centrifugal force,
4.1 Purification- Purifier bowl
The heavy phase
and any solids move
along the underside
of the bowl discs
towards the
periphery of the
bowl,where the
solids settle on the
bowl wall.
Figure 4.1
Figure 4.1
4.1 Purification – Purifier bowl
? The heavy Phase proceeds
along the upper side of the
top disc towards the neck of
the bowl hood and
discharges over the gravity
disc – the outer way,
? The light Phase moves
along the upper side of the
bowl discs towards the bowl
center and discharges via
the hole in the top disc neck
– the inner way.
4.1 Clarifier - Clarifier bowl
? This bowl has one
outlet,
? The process liquid
flows through the
distributor to the
interspaces between
the bowl discs,
4.1 Clarifier - Clarifier bowl
? Through the action of the
centrifugal force the heavy
particles move along the
underside of the discs
towards the bowl Periphery,
where they settle on the bowl
Wall.
? The liquid proceeds towards
the bowl center and
discharges through the bowl
hood.
Figure 4.2
4.1 Clarifier
? The course of
separation can be
influenced e,g,by
changes in the
viscosity (rise in
separating
temperature) or in
the throughput.
4.1 Paring disc
? The paring disc has for its object to discharge the liquid
under pressure,
? The liquid rotates,driven by the rotating paring
chamber,in the form of a ring around the stationary
paring disc,
? This dips radially,to a greater or smaller depth,into the
rotating liquid ring,
which exerts a pressure
rising rapidly with
increasing diameter.
Figure 4.3
4.1 Paring disc
? The pressure produced by
the paring disc is
composed partly of the
―centrifugal pressure‖
prevailing at the periphery,
partly of the kinetic energy
of the rotating liquid ring
which is converted more or
less completely into
pressure energy.
4.1 Paring disc
? When the throughput
is small and there is
no backpressure in the
discharge line,the
inner diameter of the
liquid ring will
practically equal the
outer diameter of the
paring disc.
4.1 Paring disc
? If the liquid must overcome a
backpressure,such as a high
delivery head or pressure
absorbing apparatuses,the
diameter of the liquid ring in the
paring chamber will diminish
until the back pressure is
neutralized.
? Thus the paring disc will pump
out all liquid fed to the paring
chamber (not withstanding the
back pressure) up to the highest
pressure,the paring disc can
produce at this liquid quantity,
4.1 Liquid seal
? In a purifier bowl the so-called liquid seal
prevents the light phase from passing the
outer edge of the top disc,i,e,taking the
outer way,
? Thus the bowl must be filled with sealing
liquid before the
process liquid is
supplied,
4.1 Liquid seal
? The sealing liquid is subsequently forced
towards the bowl periphery so as to form a
liquid ring confined inwardly by the so-
called interface between the light phase and
the heavy one,
? The position of the interface will depend
partly on the ratio between the specific
gravities of the two liquid phases,partly on
the size of the diameters in the outer and the
inner outlet (D2 and D 1 respectively).
4.1 Liquid seal
? The sealing liquid,
– Must be insoluble in the light phase,
– May be soluble in the heavy phase,
– Must not be heavier than the heavy phase,
? Normally,the heavy phase is used as
sealing liquid.
4.1 Liquid seal
? Note:
– Provided the content of heavy phase in the
liquid mixture is sufficiently high (min,25%),
it may in some cases do to feed the process
liquid to the bowl,
– The liquid seal will then build up
automatically in some time.
4.1 Liquid seal
? If the specific gravity of the light phase is
S1 and the specific gravity of the heavy
phase is S2,the hydrostatic balance can
be expressed as follows:
2
1
2
3
2
2
2
3
2
1
DD
DD
S
S
?
??
4.1 Disposition of interface
? The purifier bowl is adjusted for separation of
liquid mixtures with various specific gravity
ratios by altering the diameter of the outlet for
the heavy phase (D2),
? The heavier or more viscous the light phase and
the larger the liquid feed,the smaller the
diameter should be,
? For this purpose a number of gravity discs with
various hole diameters is delivered with the
machine,
2
1
2
3
2
2
2
3
2
1
DD
DD
S
S
?
??
4.1 Disposition of interface
? Where to dispose the interface depends on which
phase should be delivered pure,and on the
proportions between the amounts of the two
phases as well.
? If the light phase is wanted more free from the
heavy one,the interface should be placed nearer
the bowl periphery; however not so far from the
bowl center that the liquid seal breaks (the
gravity disc is too large).
4.1 Disposition of interface
? If the heavy phase is wanted more free
from the light one,the interface should be
placed nearer the bowl centre,however not
inside the outer edge of the discs (gravity
disc too small),as this would prevent the
liquid flow,
4.1 Interface disposition
? The use of gravity disc has been explained in
chapters 4.1 and 5.3,
? Utilization of the equipment described below
allows quicker setting of the interface to the
correct position and reduces the number of
gravity disc exchanges,
? This is obtained by regulation of the backpressure
in the discharge pipe for the light phase (oil).
4.1 Interface disposition
? Equipment and
installation
– The equipment is
mounted on the
discharge pipe for
light phase or oil as
near the machine as
possible.
4.1 Interface disposition
?
Backpressure
is suitable,
The interface
between the
oil (the light
phase) and the
water is well
disposed.
4.1 Interface disposition
? Backpressure is too
high,The Interface is
disposed too near the
bowl periphery.
? The liquid seal is
broken and oil may
pass through the
water outlet.
4.1 Interface disposition
? Backpressure is too
low,
? The interface is
disposed too near the
bowl centre,
? Water may pass
through the oil outlet.
4.1 Interface disposition
? Setting back pressure
– Adjust the back pressure by increasing the
pressure slowly and stepwise while observing
the sight glass for heavy phase (water),
– As soon as light Phase appears in this sight
glass,stop the pressure rise,
– Then reduce the back pressure by 0.5 kg/sq,
cm,
4.1 Interface disposition
– If the liquid seal breaks because the back
pressure is too high,reduce the latter by l ? 2
kgs/sq,cm and throttle the feed of liquid to be
treated.
– Supply new sealing liquid of separating
temperature,
– Then slowly turn on the feed of liquid to be
treated and increase the back pressure to a
value of 0.5 kg/sq,cm below the seal breaking
pressure,
4.1 Interface disposition
? Changes of throughput,separating
temperature or density of the liquid to be
treated may necessitate a readjustment of
the back pressure,
4.1 Selection of gravity disc
? l,Gravity disc (D2) is
suitable.
– The interface (D3)
between the oil (the
light phase) and the
water (the heavy phase)
is well disposed.
4.1 Selection of gravity disc
? 2,Gravity disc is too
large,
– The interface is disposed
too near the bowl
periphery.
– The liquid seal is broken
and oil may pass through
the water outlet.
4.1 Selection of gravity disc
? 3,Gravity disc is too
small.
– The interface is disposed
too near the bowl centre,
– Water may pass through
the oil outlet.
? The hole pitch diameter
of the level ring is here
marked D1,
4.1 Total sludge discharge and
combined programme
Review the
working
principle
and
constructio
n of
separator
4.1 Total sludge discharge and
combined programme
4.1 sliding bowl bottom
? The sludge discharge
takes place through a
number of slots in the
bowl wall,
? Between discharges these
slots are closed by a large
valve slide,the sliding
bowl bottom,which
constitutes an inner,
sliding bottom in the
separating space,
4.1 sealing
? The sliding bowl bottom
is forced upward against
a seal ring by the liquid
pressure acting on its
underside,
? This pressure builds up
during the rotation
because of the
centrifugal force and
increases with the
distance from the axis of
rotation.
? separator
flash\Discharge4.swf
4.1 sealing
? The operating liquid
exert an upwards
pressure exceeding the
counting-acting
downward pressure from
the process liquid,
because the underside of
the sliding bowl bottom
has a larger pressure
surface (radius R1),than
its upper side (radius R2),
Figure 4.11
4.1 operating liquid make up
? Operating liquid is supplied
on the underside of the
bowl and evaporation or
leakage of operating liquid
is continuously made up for,
? This is done through a
paring disc device under the
bowl,which maintains a
constant horizontal
operating liquid level
(radius R3) under the bowl,
as its pumping effect
neutralize the static pressure
from the supply.
? separator
flash\Discharge4.swf
4.1 sludge discharge
? Operating liquid is now supplied through the outer wider
tube so that it flows over the lower edge of the paring
chamber (radius R4) and continues through a channel out to
the upper side of a sliding ring,the operating slide.
4.1 operating slide
? Between discharges,
the operating slide is
pressed upwards by
coil springs,
? It is now forced
downwards by the
liquid pressure,
thereby opening
discharge valves from
the space below the
sliding bowl bottom
so that the operating
liquid in this space
flows out,
4.1 sludge discharge
? When the pressure
exerted by the
operating liquid
against the underside
of the sliding bowl
bottom diminishes,
the latter is forced
downwards and
opens so that the
sludge is ejected
from the bowl
through the slots in
the bowl wall.
separator
flash\Discharge4.swf
4.1 nozzle (g)
? The operating liquid
on the upper side of
the operating slide
flows out through a
nozzle (g),
? This nozzle is always
open but so small that
the outflow is
negligible in view of
the rapid inflow
according to the
upper illustration,
4.1 sealing
? The coil springs again
force the operating slide
upwards,thus shutting
off the discharge valves
from the space below
the sliding bowl bottom,
? Operating liquid is
supplied through the
outer,wide tube but
only enough to flow to
the space below the
sliding bowl bottom and
force the latter upwards
so that the bowl is
closed.separator
flash\Discharge4.swf
4.1 sealing
? If too much liquid is
supplied,it will flow
into the channel to the
operating slide and the
bowl will open again.
4.1 Total sludge discharge and
combined programme
? The outer,wider inlet is
now closed while the
inner,narrower one is
open,
? The paring disc device
counter balances the
static pressure from the
operating liquid supply,
? The situation is identical
with that shown in the
first illustration of the
series but for the
difference that the sludge
discharge cycle is now
accomplished,separator
flash\Discharge4.swf
4.2 Operating liquid system
? The figure
shows four
examples of
operating
liquids supply.
? A = machine
with bowl for
total discharge;
manual control.
4.2 Operating liquid system
? B =
machine
with bowl
for total
discharge;
automatic
or manual
control.
4.2 Operating liquid system
? C = machine
with bowl for
partial
discharge
(with level
ring) or rapid
total discharge;
automatic
control.
4.2 Operating liquid system
? D = machine
with bowl
for
combined
programme
(combined
partial and
total
discharge);
automatic
control.
4.1 Operating liquid
? Pure,soft water can be used as operating liquid.
? Hard water involves the risk of lime deposits,which
may cause obstruction of the narrow channels in the
operating liquid system and thus interruption of the
service.
? The demands on the softness of the water increase with
higher operating temperature,since lime precipitation is
more liable to occur at higher temperatures.
? Addition of a dehardening agent or provision of a
dehardening filter in the operating liquid line will
prevent lime precipitation.
4.1 Operating liquid tank
? The operating liquid tank,which should be made
of copper or stainless steel and hold 50 ? l00 lit.
(11?22 hop,galls),must be placed so that the
liquid level will be lying within the height
measurement limits above the control valve
stated in the figure.
? In case the head room is too small,the tank may
be replaced by a reducing valve or the like.
? This may,however,be less reliable than the tank.
Besides,the tank system saves liquid during
operation,since the backpressure of the control
paring disc is balanced in an open system.
4.1 Bowl for total discharge
? When the machine is
equipped with bowl for
total discharge and the
discharge should be
controlled manually (by
means of control valve),
the operating liquid
system must be arranged
as shown in Fig.right.
? Pl—see figure 4.16;
? Liquid at pressure Pl
initiate all functions
according to the setting
of the control valve.
4.1 Bowl for total discharge
? For automatic
control,two
solenoid valves are
added to the system,
These solenoid
valves are provided
in the conduits to the
two inner
connections on the
control valve as
shown in Fig,right.
4.1 Bowl for total discharge
? As regards further
equipment see directions
for automatic control.
? If it is wanted to change
from automatic control to
manual control,simply
discharge the automatic
control device,whereupon
the sludge discharge can
be controlled in the usual
manner by means of the
control valve.
? Pl — see figure
4.1 Bowl for total discharge
? Liquid supplied through
conduit l close the bowl
when starting ? this pipe
must be shut off during
operation,Liquid supplied
through conduit 2 keeps
the bowl closed during
operation — the solenoid
valve must close when the
solenoid valve in conduit 3
opens,
4.1 Bowl for total discharge
? Liquid supplied through
conduit 3 opens and
closes the bowl during
operation — when the
solenoid valve closes,the
solenoid valve in conduit
2 must open.
4.1 Bowl (with level ring) for
partial discharge
? The discharge
mechanism of these
bowls is designed for
automatic control —
see directions for
automatic control,
The system is
arranged as shown in
Fig.right.
4.1 Bowl for rapid total
discharge
? In an emergency,for instance if
the automatic system fails,
manual control is possible — see
below.
? Pl,P2— see figure.
? Liquid at pressure Pl closes the
bowl when starting and keeps
the bowl closed during operation
all according to the setting of the
control valve.
? Liquid at pressure p2 opens and
closes the bowl at sludge
discharge.
4.1 Bowl for combined
programme
? The discharge
mechanism of this
bowl is designed for
automatic control with
possibility of setting to
various programmes of
total and partial
discharges – see
directions for
automatic control,
? The system is arranged
as shown In Fig,right,
4.1 Bowl for combined
programme
? In an emergency,for
instance if the automatic
control device fails,
manual control is
possible but will give
total discharges only.
? P l,P2,P3– see figure.
? Liquid at pressure Pl
closes the bowl when
starting and keeps the
bowl closed during
operation,all according
to the setting of the
control valve.
4.1 Bowl for combined
programme
? Liquid at pressure p2
opens the bowl for total
discharge.
? Liquid at pressure p3
opens the bowl for partial
discharge and closes the
bowl after partial and
total discharge,By
means of the pressure-
regulating valve the
liquid now quantity and
thus the degree of partial
discharge can be
regulated.
4.1 Manual control of
automatically operated liquid
? To allow manual control of the systems shown in Figs.
4.18 (C) and 4.19 (D) the solenoid valve in the conduit
for high-pressure liquid must be by-passed.
? Preferably,a manually controlled sludge discharge is
carried out as follows,shut off the feed of process liquid
and set the control valve to position 2 — open the valve
in the by-pass and close it again immediately after
accomplished discharge – set the control valve to position
3 and wait till the Indication shows that the bowl is closed
– set the control valve to position 4 and open for feed of
process liquid.
? Note,Manual control may necessitate a shortening of the
interval between discharges.
4.1 Fully automated system
? In connexion with the automatization of the operating
liquid system it is preferable and in some cases even
necessary to automatize also the other actions connected
with the sludge discharge (such as interruption of the feed
to the bowl before total discharge,flushing of the sludge
cover).
? If the automatic system is included in the delivery,the
installation and operation is carried out according to the
accompanying directions for the automatic control device,
otherwise consult an ALFA-LAVAL/DE LAVAL
representative on the choice of suitable equipment,
4.1 Alarm device
? Pressure drops in pipes from the machine during
operation may indicate a liquid loss,Such pressure drops
will occur if the bowl does not close,or if it closes only
partly,Whether the machine is automated or not,it is
suitable,with closed system,to provide a guard such as a
pressostat with alarm device in the pipe for treated liquid.
The device should have means for blocking the alarm
impulse from the pressostat when normal pressure drops
occur,for instance in connexion with normal sludge
discharge.
End of chapter 4
Alfa – Laval
separator (I)
4.1 Function
? The purpose of the operation is either to
liberate a liquid from strange particles,or
to separate two intermixed liquids,
4.1 Definitions
? Throughput
– This means the quantity of liquid supplied per
unit time,The throughput is given in cu,m/h
or l/h.
? Reception ability
– This means the largest liquid quantity that the
bowl can treat per unit time,expressed in
cu.m/h or l/h,
4.1 Definitions
? Purification
– A liquid ? liquid separation in which the
machine is used for separating two intermixed
liquids,which are insoluble in each other and
have different specific gravities,Solids with
specific gravities higher than those of the
liquids can be separated off at the same time.
4.1 Definitions
? Clarification
– A liquid - sludge separation in which the
machine is used to separate particles,normally
solid ones,from a liquid having a lower
specific gravity than that of the particles.
4.1 Definitions
? Concentration
– A liquid ? liquid separation in which the
machine is used for separating two intermixed
liquids,which are insoluble in each other and
have different specific gravities,the heavier
liquid constituting the major part of the mixture,
– Solids with specific gravities higher than those
of the liquids can be separated off at the same
time,
4.1 Definitions
? Solids ejection
– Emptying of the bowl during operation
by uncovering and closing slots in the
bowl wall.
? Total ejection
– Total emptying of the bowl with the feed
(as a rule) turned off.
4.1 Definitions
? Partial ejection
– Total or partial emptying of the solids
space in the bowl but without emptying
the rest of the bowl,
– The feed need not be interrupted.
? Combined programme
– A combination of total and partial
ejections in succession.
4.1Factors influencing the
separation
? Difference in specific gravity
– The centrifugal force acts on all particles
proportionally to their specific gravity,
– This applies to solid Particles as well as to
fluid particles,
– The greater the difference in specific gravity,
the easier the separation,
4.1 Factors influencing the
separation
? Size and shape of particles
– The larger the particle,the quicker the sedimentation,
– The particles to be separated off must not be so small
that the mixture is close to colloidal state,
– The smooth and round particle is easier separated off
than the irregular one,
– Rough treatment,e,g,in pumps,can split the particles,
with reduced size and separating speed as a result.
4.1 Factors influencing the
separation
? Viscosity
– The more fluid a liquid is,the quicker is the
separating process and the better the
separation ― in other words,low viscosity
improves the separation result,
– The viscosity can in many cases be reduced by
heating,
4.1 Factors influencing the
separation
? Time in centrifugal field
– If the separation is not satisfactory,the
throughput must be reduced,
– Lower throughput gives,normally,a better
separation result,
4.1 Purification - Purifier bowl
? This bowl has two
outlets.
? The process liquid
flows through the
distributor to the
interspaces between
the bowl discs,where
the liquid phases are
separated from each
other by action of the
centrifugal force,
4.1 Purification- Purifier bowl
The heavy phase
and any solids move
along the underside
of the bowl discs
towards the
periphery of the
bowl,where the
solids settle on the
bowl wall.
Figure 4.1
Figure 4.1
4.1 Purification – Purifier bowl
? The heavy Phase proceeds
along the upper side of the
top disc towards the neck of
the bowl hood and
discharges over the gravity
disc – the outer way,
? The light Phase moves
along the upper side of the
bowl discs towards the bowl
center and discharges via
the hole in the top disc neck
– the inner way.
4.1 Clarifier - Clarifier bowl
? This bowl has one
outlet,
? The process liquid
flows through the
distributor to the
interspaces between
the bowl discs,
4.1 Clarifier - Clarifier bowl
? Through the action of the
centrifugal force the heavy
particles move along the
underside of the discs
towards the bowl Periphery,
where they settle on the bowl
Wall.
? The liquid proceeds towards
the bowl center and
discharges through the bowl
hood.
Figure 4.2
4.1 Clarifier
? The course of
separation can be
influenced e,g,by
changes in the
viscosity (rise in
separating
temperature) or in
the throughput.
4.1 Paring disc
? The paring disc has for its object to discharge the liquid
under pressure,
? The liquid rotates,driven by the rotating paring
chamber,in the form of a ring around the stationary
paring disc,
? This dips radially,to a greater or smaller depth,into the
rotating liquid ring,
which exerts a pressure
rising rapidly with
increasing diameter.
Figure 4.3
4.1 Paring disc
? The pressure produced by
the paring disc is
composed partly of the
―centrifugal pressure‖
prevailing at the periphery,
partly of the kinetic energy
of the rotating liquid ring
which is converted more or
less completely into
pressure energy.
4.1 Paring disc
? When the throughput
is small and there is
no backpressure in the
discharge line,the
inner diameter of the
liquid ring will
practically equal the
outer diameter of the
paring disc.
4.1 Paring disc
? If the liquid must overcome a
backpressure,such as a high
delivery head or pressure
absorbing apparatuses,the
diameter of the liquid ring in the
paring chamber will diminish
until the back pressure is
neutralized.
? Thus the paring disc will pump
out all liquid fed to the paring
chamber (not withstanding the
back pressure) up to the highest
pressure,the paring disc can
produce at this liquid quantity,
4.1 Liquid seal
? In a purifier bowl the so-called liquid seal
prevents the light phase from passing the
outer edge of the top disc,i,e,taking the
outer way,
? Thus the bowl must be filled with sealing
liquid before the
process liquid is
supplied,
4.1 Liquid seal
? The sealing liquid is subsequently forced
towards the bowl periphery so as to form a
liquid ring confined inwardly by the so-
called interface between the light phase and
the heavy one,
? The position of the interface will depend
partly on the ratio between the specific
gravities of the two liquid phases,partly on
the size of the diameters in the outer and the
inner outlet (D2 and D 1 respectively).
4.1 Liquid seal
? The sealing liquid,
– Must be insoluble in the light phase,
– May be soluble in the heavy phase,
– Must not be heavier than the heavy phase,
? Normally,the heavy phase is used as
sealing liquid.
4.1 Liquid seal
? Note:
– Provided the content of heavy phase in the
liquid mixture is sufficiently high (min,25%),
it may in some cases do to feed the process
liquid to the bowl,
– The liquid seal will then build up
automatically in some time.
4.1 Liquid seal
? If the specific gravity of the light phase is
S1 and the specific gravity of the heavy
phase is S2,the hydrostatic balance can
be expressed as follows:
2
1
2
3
2
2
2
3
2
1
DD
DD
S
S
?
??
4.1 Disposition of interface
? The purifier bowl is adjusted for separation of
liquid mixtures with various specific gravity
ratios by altering the diameter of the outlet for
the heavy phase (D2),
? The heavier or more viscous the light phase and
the larger the liquid feed,the smaller the
diameter should be,
? For this purpose a number of gravity discs with
various hole diameters is delivered with the
machine,
2
1
2
3
2
2
2
3
2
1
DD
DD
S
S
?
??
4.1 Disposition of interface
? Where to dispose the interface depends on which
phase should be delivered pure,and on the
proportions between the amounts of the two
phases as well.
? If the light phase is wanted more free from the
heavy one,the interface should be placed nearer
the bowl periphery; however not so far from the
bowl center that the liquid seal breaks (the
gravity disc is too large).
4.1 Disposition of interface
? If the heavy phase is wanted more free
from the light one,the interface should be
placed nearer the bowl centre,however not
inside the outer edge of the discs (gravity
disc too small),as this would prevent the
liquid flow,
4.1 Interface disposition
? The use of gravity disc has been explained in
chapters 4.1 and 5.3,
? Utilization of the equipment described below
allows quicker setting of the interface to the
correct position and reduces the number of
gravity disc exchanges,
? This is obtained by regulation of the backpressure
in the discharge pipe for the light phase (oil).
4.1 Interface disposition
? Equipment and
installation
– The equipment is
mounted on the
discharge pipe for
light phase or oil as
near the machine as
possible.
4.1 Interface disposition
?
Backpressure
is suitable,
The interface
between the
oil (the light
phase) and the
water is well
disposed.
4.1 Interface disposition
? Backpressure is too
high,The Interface is
disposed too near the
bowl periphery.
? The liquid seal is
broken and oil may
pass through the
water outlet.
4.1 Interface disposition
? Backpressure is too
low,
? The interface is
disposed too near the
bowl centre,
? Water may pass
through the oil outlet.
4.1 Interface disposition
? Setting back pressure
– Adjust the back pressure by increasing the
pressure slowly and stepwise while observing
the sight glass for heavy phase (water),
– As soon as light Phase appears in this sight
glass,stop the pressure rise,
– Then reduce the back pressure by 0.5 kg/sq,
cm,
4.1 Interface disposition
– If the liquid seal breaks because the back
pressure is too high,reduce the latter by l ? 2
kgs/sq,cm and throttle the feed of liquid to be
treated.
– Supply new sealing liquid of separating
temperature,
– Then slowly turn on the feed of liquid to be
treated and increase the back pressure to a
value of 0.5 kg/sq,cm below the seal breaking
pressure,
4.1 Interface disposition
? Changes of throughput,separating
temperature or density of the liquid to be
treated may necessitate a readjustment of
the back pressure,
4.1 Selection of gravity disc
? l,Gravity disc (D2) is
suitable.
– The interface (D3)
between the oil (the
light phase) and the
water (the heavy phase)
is well disposed.
4.1 Selection of gravity disc
? 2,Gravity disc is too
large,
– The interface is disposed
too near the bowl
periphery.
– The liquid seal is broken
and oil may pass through
the water outlet.
4.1 Selection of gravity disc
? 3,Gravity disc is too
small.
– The interface is disposed
too near the bowl centre,
– Water may pass through
the oil outlet.
? The hole pitch diameter
of the level ring is here
marked D1,
4.1 Total sludge discharge and
combined programme
Review the
working
principle
and
constructio
n of
separator
4.1 Total sludge discharge and
combined programme
4.1 sliding bowl bottom
? The sludge discharge
takes place through a
number of slots in the
bowl wall,
? Between discharges these
slots are closed by a large
valve slide,the sliding
bowl bottom,which
constitutes an inner,
sliding bottom in the
separating space,
4.1 sealing
? The sliding bowl bottom
is forced upward against
a seal ring by the liquid
pressure acting on its
underside,
? This pressure builds up
during the rotation
because of the
centrifugal force and
increases with the
distance from the axis of
rotation.
? separator
flash\Discharge4.swf
4.1 sealing
? The operating liquid
exert an upwards
pressure exceeding the
counting-acting
downward pressure from
the process liquid,
because the underside of
the sliding bowl bottom
has a larger pressure
surface (radius R1),than
its upper side (radius R2),
Figure 4.11
4.1 operating liquid make up
? Operating liquid is supplied
on the underside of the
bowl and evaporation or
leakage of operating liquid
is continuously made up for,
? This is done through a
paring disc device under the
bowl,which maintains a
constant horizontal
operating liquid level
(radius R3) under the bowl,
as its pumping effect
neutralize the static pressure
from the supply.
? separator
flash\Discharge4.swf
4.1 sludge discharge
? Operating liquid is now supplied through the outer wider
tube so that it flows over the lower edge of the paring
chamber (radius R4) and continues through a channel out to
the upper side of a sliding ring,the operating slide.
4.1 operating slide
? Between discharges,
the operating slide is
pressed upwards by
coil springs,
? It is now forced
downwards by the
liquid pressure,
thereby opening
discharge valves from
the space below the
sliding bowl bottom
so that the operating
liquid in this space
flows out,
4.1 sludge discharge
? When the pressure
exerted by the
operating liquid
against the underside
of the sliding bowl
bottom diminishes,
the latter is forced
downwards and
opens so that the
sludge is ejected
from the bowl
through the slots in
the bowl wall.
separator
flash\Discharge4.swf
4.1 nozzle (g)
? The operating liquid
on the upper side of
the operating slide
flows out through a
nozzle (g),
? This nozzle is always
open but so small that
the outflow is
negligible in view of
the rapid inflow
according to the
upper illustration,
4.1 sealing
? The coil springs again
force the operating slide
upwards,thus shutting
off the discharge valves
from the space below
the sliding bowl bottom,
? Operating liquid is
supplied through the
outer,wide tube but
only enough to flow to
the space below the
sliding bowl bottom and
force the latter upwards
so that the bowl is
closed.separator
flash\Discharge4.swf
4.1 sealing
? If too much liquid is
supplied,it will flow
into the channel to the
operating slide and the
bowl will open again.
4.1 Total sludge discharge and
combined programme
? The outer,wider inlet is
now closed while the
inner,narrower one is
open,
? The paring disc device
counter balances the
static pressure from the
operating liquid supply,
? The situation is identical
with that shown in the
first illustration of the
series but for the
difference that the sludge
discharge cycle is now
accomplished,separator
flash\Discharge4.swf
4.2 Operating liquid system
? The figure
shows four
examples of
operating
liquids supply.
? A = machine
with bowl for
total discharge;
manual control.
4.2 Operating liquid system
? B =
machine
with bowl
for total
discharge;
automatic
or manual
control.
4.2 Operating liquid system
? C = machine
with bowl for
partial
discharge
(with level
ring) or rapid
total discharge;
automatic
control.
4.2 Operating liquid system
? D = machine
with bowl
for
combined
programme
(combined
partial and
total
discharge);
automatic
control.
4.1 Operating liquid
? Pure,soft water can be used as operating liquid.
? Hard water involves the risk of lime deposits,which
may cause obstruction of the narrow channels in the
operating liquid system and thus interruption of the
service.
? The demands on the softness of the water increase with
higher operating temperature,since lime precipitation is
more liable to occur at higher temperatures.
? Addition of a dehardening agent or provision of a
dehardening filter in the operating liquid line will
prevent lime precipitation.
4.1 Operating liquid tank
? The operating liquid tank,which should be made
of copper or stainless steel and hold 50 ? l00 lit.
(11?22 hop,galls),must be placed so that the
liquid level will be lying within the height
measurement limits above the control valve
stated in the figure.
? In case the head room is too small,the tank may
be replaced by a reducing valve or the like.
? This may,however,be less reliable than the tank.
Besides,the tank system saves liquid during
operation,since the backpressure of the control
paring disc is balanced in an open system.
4.1 Bowl for total discharge
? When the machine is
equipped with bowl for
total discharge and the
discharge should be
controlled manually (by
means of control valve),
the operating liquid
system must be arranged
as shown in Fig.right.
? Pl—see figure 4.16;
? Liquid at pressure Pl
initiate all functions
according to the setting
of the control valve.
4.1 Bowl for total discharge
? For automatic
control,two
solenoid valves are
added to the system,
These solenoid
valves are provided
in the conduits to the
two inner
connections on the
control valve as
shown in Fig,right.
4.1 Bowl for total discharge
? As regards further
equipment see directions
for automatic control.
? If it is wanted to change
from automatic control to
manual control,simply
discharge the automatic
control device,whereupon
the sludge discharge can
be controlled in the usual
manner by means of the
control valve.
? Pl — see figure
4.1 Bowl for total discharge
? Liquid supplied through
conduit l close the bowl
when starting ? this pipe
must be shut off during
operation,Liquid supplied
through conduit 2 keeps
the bowl closed during
operation — the solenoid
valve must close when the
solenoid valve in conduit 3
opens,
4.1 Bowl for total discharge
? Liquid supplied through
conduit 3 opens and
closes the bowl during
operation — when the
solenoid valve closes,the
solenoid valve in conduit
2 must open.
4.1 Bowl (with level ring) for
partial discharge
? The discharge
mechanism of these
bowls is designed for
automatic control —
see directions for
automatic control,
The system is
arranged as shown in
Fig.right.
4.1 Bowl for rapid total
discharge
? In an emergency,for instance if
the automatic system fails,
manual control is possible — see
below.
? Pl,P2— see figure.
? Liquid at pressure Pl closes the
bowl when starting and keeps
the bowl closed during operation
all according to the setting of the
control valve.
? Liquid at pressure p2 opens and
closes the bowl at sludge
discharge.
4.1 Bowl for combined
programme
? The discharge
mechanism of this
bowl is designed for
automatic control with
possibility of setting to
various programmes of
total and partial
discharges – see
directions for
automatic control,
? The system is arranged
as shown In Fig,right,
4.1 Bowl for combined
programme
? In an emergency,for
instance if the automatic
control device fails,
manual control is
possible but will give
total discharges only.
? P l,P2,P3– see figure.
? Liquid at pressure Pl
closes the bowl when
starting and keeps the
bowl closed during
operation,all according
to the setting of the
control valve.
4.1 Bowl for combined
programme
? Liquid at pressure p2
opens the bowl for total
discharge.
? Liquid at pressure p3
opens the bowl for partial
discharge and closes the
bowl after partial and
total discharge,By
means of the pressure-
regulating valve the
liquid now quantity and
thus the degree of partial
discharge can be
regulated.
4.1 Manual control of
automatically operated liquid
? To allow manual control of the systems shown in Figs.
4.18 (C) and 4.19 (D) the solenoid valve in the conduit
for high-pressure liquid must be by-passed.
? Preferably,a manually controlled sludge discharge is
carried out as follows,shut off the feed of process liquid
and set the control valve to position 2 — open the valve
in the by-pass and close it again immediately after
accomplished discharge – set the control valve to position
3 and wait till the Indication shows that the bowl is closed
– set the control valve to position 4 and open for feed of
process liquid.
? Note,Manual control may necessitate a shortening of the
interval between discharges.
4.1 Fully automated system
? In connexion with the automatization of the operating
liquid system it is preferable and in some cases even
necessary to automatize also the other actions connected
with the sludge discharge (such as interruption of the feed
to the bowl before total discharge,flushing of the sludge
cover).
? If the automatic system is included in the delivery,the
installation and operation is carried out according to the
accompanying directions for the automatic control device,
otherwise consult an ALFA-LAVAL/DE LAVAL
representative on the choice of suitable equipment,
4.1 Alarm device
? Pressure drops in pipes from the machine during
operation may indicate a liquid loss,Such pressure drops
will occur if the bowl does not close,or if it closes only
partly,Whether the machine is automated or not,it is
suitable,with closed system,to provide a guard such as a
pressostat with alarm device in the pipe for treated liquid.
The device should have means for blocking the alarm
impulse from the pressostat when normal pressure drops
occur,for instance in connexion with normal sludge
discharge.
End of chapter 4
