hello guys now we will discuss
very important control system which is
known as empty search control system for
central visual compressors
centrifugal compressors are widely used
in industries especially
oiling gas sector fertilizer in
petrochemicals
the main purpose is to boost the gas
pressure
so talking about
something about centrifugal compressors
they are brightly used they have many
applications
the gas is accelerated upwards by
rotating impeller
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so it can be built for operation as low
as 350 millibars
operation as high as 550 car
size ranges from 300 pk to 50 000 pk
so this is the internal cross section of
a centrifugal compressor
and this is also a horizontal split
diagram of a centrifugal compressor
where
we see that the gas enters this is the
compression
compressor in that nozzle so the gas
enters
and tell it by impeller it goes further
and its pressure increases at each stage
and this is the final
outlet discharge compressor discharge
so it's also central compressors are
also high rpm machines
this is the horizontal split of a
centrifugal compressor
uh we will discuss the compressor system
of a typical oil and gas facility
suppose we have various belts
well from 1 to 30 where the gas
enters the main gas catering main system
this is known as gg and
scattering names so from ggm
which is also a ring drain type
the usual meant by playing type system
so from that common header gtm the gas
enters the structure
after a slow catcher the gas the liquid
is separated
by the action of gravity
so from here from slug catcher the gas
enters the inlet filters
its three trains are shown to go abc
these can be
greater than three up to five or up to
seven
so each train is usually a replica of
the other train
so the gas enters through to the inlet
gaskets to remove the
foreign particles so prior to entering
so at this point we have an inlet
scrubber
please remember that before every
compressor
we will install a scrubber stable
purpose is to remove the liquid droplets
from the gas
so because in a liquid wood damage
the compressor because compressor is
used for compressible fluids
air for gas not for the liquids
therefore we have to remove
the liquid from and clean the compressor
so for this we install the scrubber here
at this stage
then after the compression the gas
where the pressure of the gas increases
which temperature also increases
so in order to reduce the temperature we
install
after gas coolers
these are usually some fan coolers to
decrease the
temperature of the gas and then
the gas from each can enters a common
header and from that common header it
goes to the
normally dehydration plant where it is
dehydrated
and then it is assigned to the material
scale
for the sleep transfer
this can also be explained this is
explained easily here here the gas
center is at the
uh this is a two stage compression
system where the gas enters
uh the first stage of the knockout round
where the liquid is moved
and then the gas goes through the
compressor system from here
the gas there is a cooler installed here
at this
this point and then get the gas goes to
the
intermediate stubble from where the
liquid goes down
after cooling from the after this cooler
so the gas again goes to the second
stage compression
and from that compression it again goes
to the cooler and from that cooling
system the moisture is produced which is
removed by this
final scrubber
two-stage compression is basically used
for better volumetric efficiency
if we use one compressor for the same
compression ratio
there would be a great size of the
impeller
buyer as well as the compressor size so
for achieving the volumetric efficiency
we secure the compression ratio into two
two stages
so this is we will talk about this like
catcher the thumbnails the gas and
process like capsule where the liquid is
separated
and then it enters the inlet gas filters
and then it enters the
inlet manifold and it goes
to the scrubber vessel from where the
liquid is
separated and then after compression it
goes to the process gas coolers
hello guys now we will discuss
we will talk now about the compressor
system classifications
so this is a single case single section
a three-stage compressor single case
single section
three stage compression and this is a
single case
two section six stage compression
six straight eight stage represents each
entire
efficiency because for the hotter gas
you would need greater volume to
accommodate gas at such high temperature
this is a two case two section and six
stage compressor
and this is a serious network we have we
have two separate
uh cases and this is a parallel network
of two sentences here we have installed
the nr
non returned
speed there is a certain capacity below
which the operation is unstable
this breakdown point is called surge
so what is the term associated with the
low flow that for a certain rpm
the minimum flow point is search
searching for it is a phenomenon
resulting from the immobility of the
turbo compressor impeller
to produce the amount of energy that the
process system requires
we will further see how research
produces
it is a high speed phenomena no reverses
can occur in less than 150 milliseconds
pressure rapidly fluctuates noise is
generated
temperature increases it can be very
rapid
and mechanical dynasty the intensity of
search varies from application to
application
and it's proportional to the density of
the fluid so greater the density greater
than the
search numerator would be the damage
now we will see from the compressor
curve how the surface product
here we have the volume volumetric flow
along the x-axis and a compression ratio
along the y-axis and this is known as
the compressor characteristic curve
so this will be compressible for a
specific speed and
and this is a normal resistance being
felt by the compressor so for that flow
we have this much
resistance in the circuit
so for surge processing the flow
starts reducing so when the flow starts
reducing
the resistance held by the compressor
starts increasing
so here we see that q2 is less than q1
and compression ratio has increased
so this is an aggressive statistic curve
and where the
curves are shown for at various weights
this is the minimum speed
and this is the maximum speed and this
is the search limit
the minimum flow point where we want
the flow to the right side of this line
we don't want the flow
across this knob because this will lead
to the
damage and this flow it is the maximum
float
this is known as stonewall or soap
beyond this point the flow does not
remain stable in the compressor
and this is also a power limit imposed
on the overall power of the system
and this is the process limit that
this compression this pressure ratio
must not be exceeded so this is the safe
region
where we want our compressor to continue
so our main purpose would be to run the
compressor
in the system and to achieve this we use
the empty search control system
we further add margins for our stability
of the compressors before the red
margins
then we see that we have added margins
so we can say that the margin is 10
usually a ten percent standard margin is
used so we want the compressor to
operate
in this region this is further
a safer region
we will talk now about the compress now
we will see
how the search cycle develops
so this is the compressor and this is
the discharge pressure of the compressor
and this is the piping system where our
losses are the
losses in the parking system and this is
the
pressure of the vessel or under pressure
we can call it defending pressure
but there are multiple compressor planes
installed here
this is the prime mover at the
compressor
so pd is the compressor discharge
pressure
pv is the disc pressure and r losses
resistance losses over time
now suppose the pressure starts
build up resistance goes up compressor
writes like a
pd is equal to pv plus our losses
so here when the pressure would the
resistance would
starts increasing the pressure reaches
at the point a
where it again goes to the point b flow
is reversed
please note that the flow is reversed
here its direction
is reversed we know that for further
flow
pd should be greater than p
so our surface point ev becomes
greater than vt that's why the reverse
flow occurs
but this is a momentary condition result
of the
flow reversal is that pressure goes down
pressure goes down
less negative flow operating point goes
to the point c
uh in source cycle you see that the
pressure
the fluid starts the flow uh flows
or the flow of the gas is between
positive and negative that it
starts oscillating so here the point
goes to the point p
and then it again goes to the point c
and then it again reverse
stabilizes it goes to point d
so f one t when it reaches the point e
it again goes to the point k so this is
a typical
search cycle which is phased by the
compressor
and this is mainly due to the buildup of
the high pressure
at the other side so compressor
flow starts oscillating between these
values we will see further in the graph
for more elaboration
here are the typical timings from point
a to b
it is 20 to 50 milliseconds drop into
the
search and from point c to b it is
22 120 milliseconds jump out with the
search
so a b c d a 0.8
seconds so this is a cell cycle
uh time period
so here you see that the flow
rapid flow oscillations in search
condition there are never no
oscillations
trust reversals and potential damage to
the
metallurgy of the compressor
and this is the pressure here the flow
is greater and pressure is greater but
when the
pressure reduces the flow reverses and
then again
the pressure normalizes and then it
considers
so this is an oscillatory system
as a result the temperature of the
machine increases
so this since this is a very fast
phenomenon
it can be neglected by the operator so
there must be
a control system dedicated control
system uh
installed at the compressor which can
detect the search
and which should be such intelligent
that
and it should detect whether the surge
is coming or not and it should take
prior actions
to operate the compressor in the stable
zone
now we will see how
so this is a self cycle typical
compressor search language on
performance map this is also known as a
performance and let's learn on the
x-axis
and compression pressure video appears
along the y-axis
you see that the compressor flow starts
reducing reducing
and then this is the surge limit line
and close beyond the certain time where
the flow
becomes negative and then it recovers
so this cycle is a surf cycle
the compressor is operating at hundred
percent
and this is the time domain profile of
the search
we have discussed these that the flow
reverses in 20 to 50 milliseconds
circle at a rate of 0.3 seconds to 3
cycles per cycle
3 seconds per second compressive
vibrates
strong noise is produced which
temperature rises from using noise
conventional instruments or human
operators may fail
through that nice search so we need
a navigating control system to protect
the compressor from search
search consequences unstable flow and
pressure as we saw
standard and profile damage in sequence
with increasing
similarity to seals bearings in patterns
sharp
increased seal clearances and leakages
lower energy efficiency reduced
compressor life
use noted centrifugal compressions are
very costly machines
and now we discuss very important
factors leading to search
and the startup startup is usually a
point
where uh search can typically come
similarly at shutdown we can
search we can of course search at the
compressors
uh operation at the reduced router
when there is no flow condition that
then there is a danger and threat of
search
there are also operation to heavy
super with the trips suppose there is a
heavy flow going and the system
all of a sudden trips on certain port
and this condition is a very
dangerous condition and the search can
occur
but at this stage compressor shuts down
its pd decreases
and the edge can be greater so reverse
flow
is possible from header to discharge
question
so to duplicate other laws to the time
of the operator errors
process upsets no changes if there are
changes in the gas compositions
cooler problems filter or strain of
problems problem this is a
device which is installed in series
before the compressor uh to
remove the foreign particles so if the
strainer is choked
no flow condition can uh occur
or the private problems
surge is not limited to times of reduced
throughput
search can occur at full location
we will discuss in my master's thesis
i have simulated all the conditions like
startup
shutdown emergency shutdown
and all these factors i have simulated
and i will discuss the results
so our objectives would be with the
enter search control system
increase the reliability of machinery
and process we want the reliability of
the machine b
and the process so for this we need to
prevent
unnecessary process scripts and downtime
minimize the processedness sequences
prevent the search and search damage
simplify
and automate startup and setup
increase efficiency of machinery and
process operate at
lowest possible energy levels minimizing
anti-certainty cycle
of lower we know that recycling
is an energy wasting process so we want
such
intelligent system data where the cycle
should be minimum
and we also need to minimize that point
ignition
maximize throughput using all available
horsepower
and optimize load sharing of multiple
units
if there are compressors working in
parallel
so this is a search now we will discuss
possible causes of search possible for
this
as we already discussed some of them is
the high pressure builder md header
which is greater than the discharge of
the compressor
so if ph would be greater than pd the
flow would be reverse
and low suction pressure low suction
pressure will cause
decrease in the discharge pressure and
again if there is
pressure becomes lower than the higher
pressure surge can occur
at starter condition let's start above a
compressive stage there is lower
pressure at the discharge
and greater pressure so that condition
can cause
um search similarly emergency shutdown
of the unit
when the system emergency shutdown is a
shutdown which is due to any port
and at the emergency shutdown the speed
of the compressor
suddenly reduces so at that stage
the pd of the compressor will also
reduce and therefore
such the chances of the search engines
are very high
so search control strategies what are
the search control strategies
the simple strategy is the focus
strategy is to eliminate the search
is to rapidly reduce the pressure
builder by opening a blue
or recycled valve in the discharge
system to maintain minimum
flow we can blow up the
extra pressure buildup in the discharge
zone
if there is gas uh our process system
whichever process system is of gas
then it would be very costly to go off
so
the smart technique would be to get it
that put the gas back to the section of
the compressor
and recycle instead of wasting it
and gluing it
carried out through electronic 4 to 20
milliampere
operated control which is known as
anti-search controller
anti-search control system entry search
control system is designed to determine
the search condition in compressive
and to operate the anti-search
controller in efficient
and speedy manner to protect the
centrifugal compressor from the surf
in my thesis i simulated the compressor
in his version created
and implemented the efficient and
research control system
which consists of a very sophisticated
algorithm
which we will discuss further
this is the typical process diagram
at this section the gas goes to the
inlet scope and then
there are there is the orifice diameter
which measures the
flow of the gas
these instrumentation is installed to
make the compressor
map from where the system determines the
certain condition
and the output would be the uh output
would be four to twenty medium pair of
the empty search controller
so the gas goes to the compressor which
is given by the
domain and within this situation
and then the pressure increases in
temperature in phases the temperature is
then changed by this afternoon
and there is the non-return valve and
this is the discharge system
of head system and this is the use
cycling line
please uh i want to
repeat that another strategy is blowing
up
that if there is high pressure built up
in this system we can blow it off
but this will cause the waste of the
flow so the smart technique would be the
recycling of the process
so this is uh how empty search
controller this is the empty search
controller its input are
this differential pressure which gives
or
which gives us the flow suction pressure
suction temperature discharge pressure
and discharge temperature so five
sensors we have installed
five sensors
according to algorithm which will be
discussed further
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and then the rates and output um
4 to 20 million
so these are the formulas to build the
compressive map
this is the qr scale and
this is the calculations
but the resultant is
this is the suction pressure
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uh
in this algorithm this algorithm is
designed by the
uh triple c calculation compressor
temporal population
so in this algorithm uh the compressive
map is good using
these formulas
and this is the hr which is used
at a pressure compression ratio used at
aerotopic produced head so this is
included by
this partner rct power rc power
sigma minus 1.7 this sigma
rt is basically the temperature ratio
and rc
is basically your pressure
and this is how the compressive map is
and this algorithm
is this
of algorithm is controller i would like
to
explain another thing is that for this
control system they can also use a plc
but we normally use dedicated
controllers
so for one action we usually use a
controller
if there are multiple actions and
multiple loops then we'll use appears
furthermore in a controller
controller the time the response the
time response
uh is very fast as compared to the plc
where the time response is limited by
the
scan cycle so a dedicated controller for
this application is ideal
and as soon as it is a specific
application and if
it since this is a very speedy process
we need a very fast controller
for this therefore a dedicated
controller is
usually used for anti-search application
this is how the basic fantasy empty
search control system is demonstrated
here where we see tr scale and rc here
we have used the rc compression ratio
in algorithm is always used in
anti-search controller
uic protects the compressor against the
search by opening the recycling valve
opening of the recycling web lowers the
resistance when by decompressing
so if the this value is
different then the resistance is
decreased and the flow
increased because here the flow would be
restricting and the rest of the flow
will pass through this
so the flow will
we discussed that there are various
modes defined for the
compressive map we we normally use a 10
margin between the search limit which is
the actual kind of search
and this is the search component
normally there is 10
matching so when the operating time
crosses the
scl search control line the pa control
will open the respective so appeal
response is generated
pa response proportional and integral
will give adequate protection
protection per small disturbances so
clear control will include stable
control during slightly state recyclable
this will be steady state deciding
efficiency slow disturbances
but what if the
uh the search comes very fast when the
operating point moves quickly towards
the search control line the rate of
change can be used dynamically
increase the search control module this
allows the pid controller to react
earlier
smaller statistics search control
margins can be used without sacrificing
reliability
first this defense exactly
so if the
point search point comes very fast to
this point
we can use the rate of change the
derivative
this magnitude and give
this much uh high response to the
control board which is also known as the
cycle trick
the second grip response we will see
further
see so this is the search control line
and this is each cycle
and this is for the derivative this is
the proportional and integral action
and the circumference line is the
derivative
so this uh operating point when it
touches the rtl
there is a quick response so
for when it touches the search control
line the response is pi response
for since the operating point is coming
very fast
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and this magnitude is equal to the
derivative of this
rate of change therefore
the total response is the sum of this pi
response
plus this recycled resistance and
therefore the operating point returns
back to this search controller
so when the working hand comes back to
the search control line
the cycle click response diminishes
like an decay so this is an exponential
decay
response and the total response would be
the sum of this and this
so this is how the advanced empty source
controlled competition works
responsible soil energy savings due to
the smaller
serve margins need compressor has more
turned on before the cycle of blow up
search can be implemented for virtually
any disturbance
this line suddenly
so in this way this margin can be
reduced
but normally it is kept at 10 and
recycling trip line is kept at
5 with respect to the sales unit line
now we have seen that the total response
is the sum of pi response
and this derivative response so the
controller would be
p a plus b now we will see how the
controller
acts and produces gives this type of
response
so this is how this uh this is how the
search
map would be built in the computer this
is the reduced polypeptide and the
system usually
and this is your search limit line
this is the red region
below this line and ahead of this line
the upper side is blue again
now we define the parameter in the
controller which is the search parameter
which is the ratio of q r square s l
over q
of square operating the ratio of this
point against a certain argument
and to these operating points
you see that this is a ratio so if your
point
if the point is clear then this ratio
will be less than one
operating part is
this search parameter will be equal to
one
and and below on the left side
of this line the source parameter would
be greater than one
so this is how the controller
checks whether the operating point is on
the safe side
another parameter which is defined is
deviation which is equal to 1 minus ss
minus search match
the further such margin which can be
five to ten percent
the main purpose of the algorithm is to
determine the deviation parameter and
the key
for it for deviation we define it such
that
the deviation is equal to zero on our
desired line
and deviation is positive and the clean
zone for the
zone and deviation is negative on the
left side so we have
so this is another
a response and the cycle 39 degenerate
equal open distance and the total
response would be
ea control plus recycle protection
one may question that why not a pld
controller
is used so the answer to this question
is in a pid controller
the derivative
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application for flow application they
normally not use the derivative action
because
it produces something in the controller
in the controller
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so if we use a pid controller this will
cause
the derivative
so this is the main reason and this is
the main difference
between pid composer
led control action and pa plus