The document summarizes Talha Mujeeb's 6-week internship at Engro Fertilizers. He was stationed at URUT 1 OPS, focusing on the air network. He gained insight into engineering and interest increased. The URUT section is the oldest and birthplace of Engro. It provides power, steam, firewater, cooling, and drinking water systems. Talha studied the instrument and plant air network in detail, looking at compressors, distribution, consumers, and handling emergencies. He assessed compressor C-702 which was facing high oil temperature issues and provided recommendations.

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Internship Report
Talha Mujeeb NUST SCME
During the 6 weeks of internship at Engro I was stationed at URUT 1 OPS
focusing on the utility section. Worked on the Air Network, gained a lot of insight
interest in engineering further increased. URUT is the oldest section of Engro and
is the birthplace of this Industrial giant. It was a pleasure to be a part of this
system.

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Talha Mujeeb  2
Internship Report
Talha Mujeeb NUST SCME
Preface:
As an engineering student it is extremely important to get a
feel of what goes on in the industry before you actually step
foot in it.
Engro fertilizers proved to be that training ground for me, a
place where I learnt a lot developed my interest about
engineering and more or less brushed up my concepts
regarding engineering and gained an insight of what goes on
in an industrial working environment.
This report carries the detail of all that I learned and gained
during this internship. Carries a brief detail of what goes on in
URUT-1 (my assigned unit). It focuses majorly on the
projects that I was assigned during this internship program
relating to the Instrument and Plant air network and C-702
reliability study. A detailed study regarding the subjects is
followed by analyzing the problems and ending with a list of
recommendations that could enhance the system’s performance.
Internship a
journey
Coming to Engro I
didn’t know what lie
ahead but this place
without a doubt gave
me a boost a direction
a goal. This is one of
the best Internship
program throughout
the country. Along
with the engagement
in the work
environment,
involvement in the
colony playing sports
or the time of 14th
August made this
experience one to
cherish for the days
coming by.
  

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Acknowledgement:
Without the help of Allah Almighty it is impossible to achieve anything. So I would like to thank
my lord for giving me a chance to prove myself in one of the very best company in the country.
Over in Engro I met a really supportive group of people who guided me through all my problems
and supported me whenever I needed their help. I would like to start with special thanks to my
mentor Zubair Khan who made my life at work easy by giving me a direction and providing me
timely assistance. I would also like to thank my GL Khawaja Bilal Mustafa, Zia Naqvi, Tahir
Hameed Farooq Laghari and specially TAM for their constant support. Without the guidance of
competent people getting know-how of the plant in a short period of time is no less than an
impossible job hence I would like to thank Najeebullah, Sajid Saeed, Abdul Haseeb, Javed
Soomro, Mohammad Younis and all the people from ops shift B at URUT 1.
Before coming to a closure my Parents deserve my gratitude for always being so supportive,
guiding, helping and supporting through all my endeavors.

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Tableof Contents
About The Company: ..................................................................................................................... 7
POWER:.......................................................................................................................................... 8
STEAM:........................................................................................................................................... 9
FIREWATER: .................................................................................................................................. 9
COOLING TOWER:...................................................................................................................... 10
Drinking Water System: ............................................................................................................... 11
INSTRUMENT AND PLANT AIR NETWORK:.......................................................................... 12
Abstract:.................................................................................................................................... 12
Compressor:.............................................................................................................................. 12
Plant Air: ................................................................................................................................... 12
Instrument Air:.......................................................................................................................... 13
INSTRUMENT AND PLANT AIR NETWORK PFD LINKING URUT 1 WITH AMMONIA 2
AND PLANT 2.............................................................................................................................. 13
Process flow description of Instrument and Plant Air Network:............................................. 16
Components taking part in Instrument and plant air circuit....................................................... 17
Positive Displacement Compressor.......................................................................................... 18
Centrifugal Compressors.......................................................................................................... 18
Differences between Centrifugal and P.d compressors............................................................ 19
Lubrication:............................................................................................................................... 19
Splash Lubrication: ................................................................................................................... 20
Pressure Lubrication:................................................................................................................ 20
Force Feed Lubrication:............................................................................................................. 20
Choke: ....................................................................................................................................... 20
Surge:......................................................................................................................................... 20
Turndown: ................................................................................................................................ 21
Design Point:............................................................................................................................. 21
C-702: ............................................................................................................................................ 22
Mode of Action:......................................................................................................................... 24

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Specifications:............................................................................................................................ 25
Alarm and tripping set points:.................................................................................................. 28
Lubrication System: .................................................................................................................. 31
Mode of action of lubrication oil:.............................................................................................. 31
Efficiency:.................................................................................................................................. 34
Issues Faced:.............................................................................................................................. 35
Current Situation:...................................................................................................................... 36
Possible Factors Causing High Oil Temperature:..................................................................... 36
Temporary Solutions:............................................................................................................... 36
Lapses at our end:..................................................................................................................... 37
What could be done: ................................................................................................................. 37
Heat Exchanger details: ............................................................................................................ 38
Viability Of Solutions:............................................................................................................... 39
Immediate Actions:................................................................................................................... 40
C-701 A/B:..................................................................................................................................... 41
Specifications:............................................................................................................................ 41
Working Principle:.................................................................................................................... 42
KGT-2501 ...................................................................................................................................... 43
Portable Compressors:.................................................................................................................. 44
MK-201/202:.................................................................................................................................. 44
K-421: ............................................................................................................................................ 45
Knockout Drum:........................................................................................................................... 45
D-711 Knockout Drum:............................................................................................................. 47
R-101:............................................................................................................................................. 48
Control valves and Instruments: .................................................................................................. 48
Control valves and instruments in the air circuit:.................................................................... 49
PIC-703:..................................................................................................................................... 49
PIC-704:..................................................................................................................................... 49

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HIC-201: .................................................................................................................................... 49
FI’s: ............................................................................................................................................ 50
FIL-711:...................................................................................................................................... 50
Dryers AD 712 A/B, AD 206 A/B:.............................................................................................. 50
AIR NETWORK CONSUMERS:................................................................................................... 53
Plant Air users’ schematic:........................................................................................................ 54
Instrument Air Consumers:...................................................................................................... 54
The list of Instrument Air Consumers:..................................................................................... 55
Instrument Air Calculation:...................................................................................................... 56
Air Balance:................................................................................................................................... 57
Max Generation Capacity: ........................................................................................................ 57
Best scenario air generation: ..................................................................................................... 59
Present Generation:................................................................................................................... 60
Handling Emergencies:................................................................................................................. 62
KGT Tripped:............................................................................................................................ 62
C-702 Tripped:........................................................................................................................... 62
PIC-704 Malfunctioning:........................................................................................................... 62
Plant 2 Process Air Failure:....................................................................................................... 63
Shutdown Jobs/Improvements:.................................................................................................... 63

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About The Company:
Engro comes in as a giant in the Pakistani Industry it is among the top employers of the
country having a business spread to 6 major industries, having its headquarters
established in Karachi.
Its major subsidiaries include Engro Fertilizers - which is one of the largest fertilizer
manufacturers of the world, Engro Foods which manufactures processes and markets
dairy products, frozen desserts and fruit drinks including the ice cream brand of
OMORÉ. Other major subsides include Sindh Engro Coal Mining Company, Engro
Powergen Limited and Engro Polymer & Chemicals Limited.
History and Overview EFERT:
The subsidiary that I was based in was Engro Fertilizers which is the birthplace of this
market giant.
It was 1957 when in search for oil by Pak Stanvac, an Esso/Mobil joint venture led to the
discovery of the Mari Gas field near Daharki Pakistan. Esso proposed the establishment
of a urea plant in that area which led to a fertilizer plant agreement signed in 1964. In
the subsequent year, Esso Pakistan Fertilizer Company Limited was incorporated, with
75% of the shares owned by Esso and 25% by the general public. The construction of a
urea plant commenced at Daharki in 1966 and production began in 1968. At US $43
million with an annual production capacity of 173,000 tons, it was the single largest
foreign investment by a multinational corporation in Pakistan at the time.
In 1978, it was decided to rename the company from Esso Fertilizer Company Limited
to Exxon Chemical Pakistan Limited. In 1991, Exxon decided to divest its fertilizer
business on a global basis. The employees of Exxon Chemical Pakistan Limited, in
partnership with leading international and local financial institutions, bought out
Exxon’s 75% equity. This was at the time and perhaps still is the most successful
employee buy-out in the corporate history of Pakistan. Engro Chemicals Pakistan was
formed and it passed from strength to strength over the years. The Company undertook
its largest urea expansion project in 2007. The state of the art plant enVen 3.0 stands tall
at 125 meters –dubbed the tallest structure in Pakistan. The total cost of this expansion
is approximately US$ 1.1 Billion, with the expanded facility making Engro one of the

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largest urea manufacturers in Pakistan, besides substantially cutting the cost of urea
imports to national exchequer.
This site has the largest single train urea production unit in the world.
POWER:
Power has been a major concern in Pakistan even more so in the past decade, electricity
is rare and if a plant is dependent upon the national grid for power supply the
management should be ready to gear up for large production losses.
Engro fertilizers plant in Daharki is self-sufficient in electricity with URUT housing 4
gas turbines generating and supplying electricity across the plant. Hence power
generation is a major characteristic of the URUT section. ILMS (Intelligent load
management system) controls the gas turbines electricity generation and supply.

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Following diagram illustrates the generation capacity of each of the following gas
turbines along with the reactors which manage load.
Along with the gas turbines the URUT section houses 4 generators that can be used in
critical situations hence all other units are dependent upon URUT 1 for power
generation.
STEAM:
Steam makes up an extremely component of any industry. Steam can be used for
cleaning, cooling, heating, running steam turbines and more so in ammonia synthesis
process it is used in the reformers along with that in the strippers as well making it very
important for the well-being and proper function of the plant. URUT 1 is the largest
exporter of steam across the plant and no wonder produces major chunk of steam
catering the plant requirements. We have on our plant 3 water tube boilers each having
a capacity of 20 tons. 4 HRSG’S using exhaust of the gas turbine to generate heat.
Details of steam generation:
SG-621 18 TPH
SG-631 18 TPH
SG-641 18 TPH
HRSG-651 24 TPH
HRSG-661 34 TPH
HRSG-691 36 TPH
HRSG-611 150 TPH
HRSG-611 is totally dedicated to cater the steam requirements of plant 2 while the
steam generated from other steam generators is circulated across plant 1.
FIREWATER:
Firewater can be termed as the water that is basically sored in order to be in an
emergency situation.

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 Outbreak of a fire.
 Ammonia leakage in the plant.
These two are the most common reasons for firewater being used in the plant. Salient
features of the firewater system as following:
 Make up done via canal water from offsite and underground raw water.
 Stored in firewater tank TK-701 having a capacity of 360,000 gallons.
 Pressure of the firewater maintained around 120-130 psi.
 Recirculation line is present to prevent overflow.
 4 pumps used all centrifugal, 3 motor driven and 1 diesel driven.
 Outlet flow maintained via P 723 A and 723 B each having a flow of 500 gpm.
 P 721 is auto cut in it has a flow rate of 1800 gpm. While P 722 is diesel powered
used in case of a very high demand.
 The lines containing firewater are red making firewater network easily
recognizable.
This is the only firewater system across a plant, and hence in case of an emergency
which in fact is very rare considering Engro’s safety protocols, all the firewater will be
provided from this very unit.
COOLING TOWER:
This is not unique to the URUT 1 section unlike the previous commodities but is a
pivotal part of the section. Cooling water is extremely necessary for plant’s health and
well the cooling tower fulfills this very need.
Cooling water Treatment:
Cooling water must be treated for any impurities which in coming times cause
hindrance in our various processes.
The canal water is treated in the offsite as well as in the filters leading up to the cooling
tower, removing SS (suspended solids) which can cause blockages in our lines.
While the raw water is treated with chemicals to reduce TDS (total dissolved salts)
which can react with the metallic layer of the tubes it is supposed to cool and can cause
scaling or corrosion.

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Salient features of the cooling water system.
 Induced cooling taking place, CT-401 capacity 360,000 gallons.
 Make up, raw water, canal water, firewater.
 Fil 401 used for filtration.
 4 fans D A (east to west) pitch angle (13-15) while current up
to 127 amps.
 3 Pumps 2 motor driven 1 turbine driven each having a flow capacity of 16000
gpm.
 P 421 A and P 421 B are online while P 421 C is auto cut in.
10,000 gpm Urea 1
32,000 gpm 2,000 gpm UTY 1
20,000gpm Urea 2
This is how the cooling water is distributed among the plant.
Drinking Water System:
The URUT plant also contains a drinking water tank TK-502 drinking water provision is
a secondary attribute of the URUT plant. The only treatment of the drinking water that
is done here is that of the chlorination of the drinking water. A water line coming from
outside the plant acts as the feed of this drinking water system. This water line is said to
be quite pure hence needs minimal treatment. 7 pumps are driving this drinking water.
MP 211 A-F are the pumps driving this water up to the tank each pump has a capacity
of 250 GPM and hence is pumping water from the water well offsite.
There are two motor driven pumps that supply water from TK-502 fulfilling plant’s and
colony’s requirements. MP 405 A/B both supply water at a flow rate of 400 GPM.

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Following was an overview of the major processes that are taking place at the URUT 1
utilities section, basically the ones which I have witnessed. Now coming over on to
another important process that is taking place at the utilities section which is of
supreme importance for me and actually is the project I was allotted for my internship
at Engro.
INSTRUMENT AND PLANT AIR NETWORK:
Abstract:
For a novice it may seem absurd that we are using air on a plant of such scale, but air is
a very important utility required for various reasons across the plant we shall cover
every single reason in this report. A full fledge air network is established at Engro
fertilizers plant.
Compressor:
A compressor is basically a device that compresses a gas as in squeezes the gas in a
tighter smaller place, hence automatically increasing the pressure and temperature of
the gas. Their action is similar to that of pumps the only difference being pumps deal
with fluids. Compressors are the sources of plant and instrument air networks hence
shall be covered in detail as we move forward.
Plant Air:
Plant Air is basically the air that is coming out of the compressor and it is not must that
the air is totally moisture or dirt free. This plant air basically serves various purposes,
basically this air helps forming a passivation layer, a passivation layer is basically a
layer that reacts with the metal surface and prevents corrosion or in fact rusting. Plant
air is also used to drive pneumatic controlled machines such as grinders and drillers.
This air can also be used in blowers. Plant air can also be referred to as process air; this
air even carries nitrogen which is further used in ammonia formation, aiding a major
characteristic of this plant. Plant air can also be utilized for cooling purposes, cleaning,
ventilation and purging. Plant air has to maintain a high pressure coming from the
outlet of the compressor; plant air maintains a high pressure. A pressure of around 120-
130 psi is ideal for plant air.

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Instrument Air:
Instrument air like plant air is also compressed air. But a major difference between plant
air and instrument lies in the fact that instrument air is totally free of any traces of dirt,
oil or any sort of moisture. Instrument air as the name suggest is used to operate
instruments. The instruments that this air operates are (CONTROL VALVES) control
valves are critical in controlling the process happening and maintaining a required flow
of various fluids and gases.
INSTRUMENT AND PLANT AIR NETWORK PFD LINKING URUT 1
WITH AMMONIA 2 AND PLANT 2
A brief description of the process flow shall be followed by detailed analysis of each
component of this circuit, detailed description of its consumers a proper air balance
highlighting a few frailties in this network and coming up with workable solutions.

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Process flow description of Instrumentand Plant Air Network:
 The URUT air circuit starts at C-702 compressor this compressor generates
around 2800 NMCH air working in normal conditions and can go up to 3200
NMCH, IGV controls the flow of air into the compressor the air is taken from the
atmosphere and compressed to 125 psi (8.7 kg/cm2). Air then passes through the
knockout drum D-702 where the moisture content is removed.
 The line then approaches two compressors namely C-701 A/B the only difference
being C-701 B is turbine driven while C-701 A is driven by a motor. They
generate around 800 NMCH air but in fact have a capacity of generating 1596
NMCH. They compress air up to 125 psi (8.7 kg/cm2), their discharge goes into
the line coming from C-702 but in case of a failure at C-702 a separate line is also
laid from these compressors approaching the knockout drum D-711.
 Part of air which is moisture free having passed from D-702 bypasses D-711 and
approaches directly towards the filter FIL-711.
 KGT 2501 is placed at Ammonia 2 it generates around 48,870 NMCH air of
which around 1800 NMCH is sent towards us though it can send around 2300
NMCH on an average day. The air from KGT is around 500 psi (35kg/cm2). This
air goes through the cooler E-711 than the storage tank R-101 which can store
about 20 min supply of air in case of an emergency situation. Finally that air is
brought up to control valve PIC-704V this works as a letdown valve bringing the
air pressure to 125psi (8.7 kg/cm2). This line joins with the line approaching from
the compressors present at URUT 1 and approaches towards D-711.
 On the other hand a steam turbine powered compressor K-421 present at plant 2
generates around 3500 NMCH air of which most of the air is sent towards
utilities 3 section while some of it can approach the base plant (URUT1) on a
good day up to 2000 NMCH air can be transferred from plant 2. The line passes
through HIC 201 control valve which works on minimum command, meeting at
the downstream of the line passing through PIC 704.
 All these lines combine and approach towards the knockout drum D-711 in
order to remove the moisture content. Approaching from D-711 is the plant air
some of the air approaches towards the filter FIL-711 while other goes into the
plant air header a control valve PIC-703 controls the flow at plant air header.
 In case of insufficient supply of air, portable compressors can be linked to the
plant air header so that air requirements can be fulfilled.

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 The filter removes all oil and dirt traces from the air, the outlet of the filter goes
into the dryers while some of it is sent towards Urea 2 where they have their own
dryers and can generate instrument air.
 The air than goes into the dryers D 712 A/B and hence the instrument air is
generated.
 Plant 2 also contains 2 compressors K 201/202 just like our C-702 compressor. The
air they generate along with the air coming from K-421 part of it is converted to
instrument air most of it is used at plant 2 while some of it feeds GT-604, GT-601,
HRSG-611 and HRSG 651. Ultimately meeting the instrument air header
Components taking part in Instrument and plant air circuit.
 C-702 (Reliability study).
 C 701 A/B Compressors.
 KGT 2501 Compressor.
 Portable Compressors.
 MK 201/202 Compressors.
 K-421 Compressor.
 D-711 and D-702 K.O drums.
 R-101.
 Control valves.
 Dryers AD 712 A/B, AD 206 A/B.
 FIL-711.
Before starting off and discussing each equipment in depth we must be knowing the
fact that most of the compressors are centrifugal (dynamic) compressors while C 701
A/B are the only positive displacement compressors present in this network.

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Positive Displacement Compressor.
A positive displacement compressor basically compresses the air via displacement. It is
usually driven by a piston giving a pulsating flow. It’s mode of action is relatively
simple it as mentioned before is driven by the action of a piston when the piston is
withdrawn the suction valve opens and the air is sucked in while when there is a
downward stroke the pressure inside increases opening the discharge valve hence
discharging flow.
Centrifugal Compressors.
Unlike positive displacement compressors, centrifugal compressors compress gas by
the action of an impeller. It can either be radial or axial compression. Radial refers to a
circular movement while axial is movement in a straight line. As the gas is done work
on in the compressor its velocity increases, than it enters the diffuser where its velocity
is decreased while the pressure is increased and then finally it enters the volute where
its velocity is further reduced.

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Differences between Centrifugal and P.d compressors.
Centrifugal Compressors Positive Displacement Compressors
 Maintain high flow and
comparatively low pressure.
 Maintain low flow and higher
pressure.
 Stages are increased to increase outlet
pressure.
 Cylinder Dia increased to increase
the flow.
 Temparature rise does not cause a
hefty damage.
 A rise in temperature can cause
damage.
 Surging (backflow due to high
pressure) is the problem related to it.
 Starvation occurs as in not enough
supply of oil to the compressor.
 It requires low maintainance  High maintainance is required.
 Relatively Cheaper.  Expensive.
 High efficiency.  Low efficiency.
We now must take into account a few very important details regarding the compressors
which would aid us aas we move further in this report.
Lubrication:
A compressor is a device that has to run 24/7 during this period of operation the
machine goes through a lot of wear and tear. When metallic seals and machinery
contact friction is caused excess heat is generated there is a good chance that some of
the equipment will get damaged. Keep in mind the compressor rotates at speeds of
1000’s of rpm and hence in no time your compressor can be totally dismantled.
Lubrication provides a layer that prevents friction alongside generates a cooling effect.
A high grade lubricating oil must be selected; a low quality oil could foul the check

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valves. There are 3 major types of lubrication regime that are followed in order to
lubricate the compressor.
Splash Lubrication:
Basically the phenomena that is takin place is a very simple one the oil via the action of
crankshaft and counter weights is splashed. Centrifugal force throws oil outward from
rotating crankshaft to an oil passage through which the bearings and and other part of
the compressor are lubricated.
Pressure Lubrication:
This type of lubrication is usually made use in centrifugal compressors the oil is first
filtered than sent towards a cooler after which the oil is again filtered to remove any
trace elements from it the cooled oiled is distributed into different channels so that it
lubricates different parts of the compressor. The oil pressure is constantly regulated and
monitored low pressure alarm and tripping mechanism is installed in a compressor to
safeguard it from any loss of lubrication which as mentioned before can be critical.
Force Feed Lubrication:
This type of lubrication regime is followed in a positive displacement compressor.
Force feed lubrication can be done by hand as there is a delivery tube fixed with a
plunger, it is put into the place which has to be lubricated the oil is sucked in via the
plunger lubricating the compressor parts. This is carried out manually or with he help
of a machine usually done when a machine is turned off.
Choke:
A compressor basically compresses a gas by limiting its space and ultimately increasing
its pressure. As the pressure decreases the flow delivered by a centrifugal compressor
increases. Suppose there is a compressor its pressure is being constantly decreased and
hence its flow rate is constantly increasing. With the passage of time the pressure
decreases quite a bit and the flowrate reaches a point at which it is similar to the rate of
sound, and a further decrease in pressure makes no difference. That’s what a choke is.
Baiscally choke is reffered to as the maximum flowrate a compressor can deliver.
Surge:
It would be fair enough to refer surge as being the direct opposite of a choke. As the
pressure is increased in a centrifugal compressor the flowrate decreases. The discharge

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pressure is increased to a limit that it is impossible for a compressor to deliver a proper
flow at the discharge. Hence due to this increased pressure a reversal of flow occurs as
it is extremely difficult for the compressor to keep up with the resistance this happens
to be a surge. The flow instead of moving out of the discharge travels back towards the
inlet. After the flow travels towards the inlet the pressure at the discharge decreases
hence as a result forward flow is ultimately resumed. If the conditions causing surge
persist, a surging cycle continues marked by a reverse and than a forward flow. This is
characterized by repeated slamming of the discharge check valve and an audible
whumping sound. Continuous operation in surge can cause high vibration and high
inter-stage air temperatures, resulting in compressor shutdown. Hence an anti surge
system is really important and we must make sure that the compressor is equipped
with such a system.
Turndown:
As we have came to know that pressure and flowrate are inversely propotional,
turndown can be reffered to as a state in which a centrifugal compressor maintains its
discharge pressure even at a low outlet flow. Inorder to establish or calculate the
turndown range we must keep on closing the throttling valve decreasing the flow until
a point where surge is reached. True turndown is the amount of flow (measured in % of
full flow) that the compressor can throttle back, while maintaining a constant discharge
pressure, until reaching the surge point.
Usable turndown is defined as true turndown minus a control margin. Typically, an
anti-surge control set point is established 5% above the minimum flow surge point. This
allows stable compressor operation during periods of large demand swings and
prevents surging.
Design Point:
Each compressor is designed to work on a certain set of conditions these conditions
correspond to a certain point in the compressor’s performance curve. Design point is
basically a point at which the compressor operates at it’s highest efficiency. A
compressor off it’s design point may not work efficiently.
Factors to take note off when considering design point.
 Inlet Temperature

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 Inlet Pressure
 Relative Humidity
 Input Speed
 Cooling Water Temperature
 Interstage Temperature
These conditions must be taken note off; the factors that cause totally adverse
conditions are of high inlet and inter stage temperatures, low inlet pressure, high
humidity, and low input speed. These factors tend to lower the pressure making
capabilities and decrease the usable operating range.
C-702:
C-702 is the most significant compressor and the generator of major chunk of air in the
Plant 1 air network. Its manufacturer is Turbo Air Compressors a company based in
Buffalo Newyork. It is actually called Cooper Turbo Compressor 3000.
Basically C-702 is a multi staged centrifugal compressor. It has 3 stages an impeller in
each stage, first stage has 40,000 rpm while the second and third stage have 60,000 rpm.
It is driven by an electric motor has a major gear and two pinion gears. It generates upto
3200 NMCH air, has two interstage coolers and one afterstage cooler, a lube oil cooling
system. It is controlled by an intelligent quad core system. IGV controls the inlet
air amount while BOV controls the pressure build up.
The intelligent core system that drives it is the quadcore microprocessor which
monitors each and every detail in the activity and performance of C-702 compressor.
The following diagram is self explanatory in explaining the design features of C-702
compressor.

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Mode of Action:
C-702 of capacity 3000NMCH air enters the system through the inlet filter/ silencer. It
travels through the intake pipe to the inlet valve. The inlet valve directs the flow of air
to the first stage. Air compressed by the first stage and directed to the first stage
intercooler. Air cooled in the intercooler and directed to the second stage where it
compressed further and directed to the second stage intercooler. Air cooled in the
second stage intercooler, and then directed to the third stage, where it compressed to
design pressure and discharged to the plant air system.The air enters the compressor
through the inlet connection, which proportioned to minimize shock or turbulence as
the air enters the impeller. The impeller imparts the velocity to the air and delivers it to
the diffuser where the flow decelerated and the velocity energy gradually converted to
pressure energy. The diffuser portion of the compressor has formed by the back flat
section of the inlet piece.The diffuser is a narrow passage channeling the air as it leaves
the impeller into the volute section of the scroll where the air is collected. A shaft seal
must be provided where the shaft passes through the scroll to prevent the air from
escaping out of the scroll. When the pressure ratio exceeds the limit of a single stage
compressor, a multistage must be used. This construction requires a return passage, the
air leaving each scroll and to deliver it to the inlet of each succeeding stage and keep in
mind that the impeller is the only means of adding energy to the air and all the work is
done in this element. The flow passages, as opposed to a reciprocating unit are open
throughout. There are no mechanical means of preventing back flow in the design of the
unit, and it can occur when the compressor is shut down unless a check valve is used
externally downstream of the compressor discharge.
Condensate drains are included as a part of each intercooler to remove condensate that
has resulted from cooling the compressed air. A bypass valve is used for unloaded
operation. A check valve is provided in the discharge line to prevent reverse flow of the
compressed air in the plant air system.
A block valve is used to isolate the compressor from the plant air system during
compressor shutdown.
Centrifugal air compressor performance can be represented by a characteristic curve of
discharge pressure versus flow. This is a continuously rising curve from right to left.

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Specifications:

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It is very important that the right type of lube oil is employed. Hence a few details on
the type of lube oil that must be used.

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The control system of C-702 compressor is state of the art and hence is keeping all the
critical problems regarding the compressor in sight, it has an alarm as well as a tripping
mechanism, at any stage where it is seen that the compressor is under a threat the
systems trips. Though in some instances there have been false alarms so inorder to
counter this problem 2 by 2 logic is used. 2 by 2 logic is actually a logic in which two
indicators are placed side by side and until both donot signal a thret the system keeps
on doing it’s work as usual.
Alarm and tripping set points:
As you can see for yourself each and every aspect is covered in th following table
making it a fool proof system hence enhancing it’s reliabilty manifold.

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Surging can prove to be a huge problem considering the efficiency of the compressor
and can have quite a few negative impacts on the compressor’s performance but C-702
has a proper anti surge system with a blow off valve preventing any such problem.
If basically demand flow is reduced to the point of surge the blow off valve will open to
maintain a minimum flow through the compressor resultantly preventing a surge. BOV
control is determined by comparing the operating point to a "pressure vs. amps" surge
control line. The slope and position of this line is determined at start-up and entered
into the PLC (minimum amps = surge slope * discharge pressure + current offset). The
compressor operates to the area to the right of the surge line. As flow is reduced the
operating point moves to the surge controlline.. At this point, a PI control loop begins to
regulate the opening of the BOV. This action prevents the compressor operating point
from crossing the line into the surge region.
The basic objective of the surge control is to keep the operating point to the right side of
the surge control line. In case of low load operation, sudden load rejection or sudden

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increase in the system pressure, the operating point moves towards left side. When the
operating point crosses the surge control line, the anti-surge control takes sudden action
and opens the MBOV accordingly
Surge Control Line Equation = Y = mx + C
Minimum Amperes = Surge Slope * Discharge Pressure + Current Offset
= 0.171 * PT-1 +12
Distance between surge limit line and surge control line is maintained at an optimum
value as large distance result in power wastage, and lesser distance provides lesser
margin for the anti-surge control system to prevent compressor from surging.

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Lubrication System:
Due to the high rpm rates of various mechanical parts of the compressors friction is
generated as well as that high amount of heat is generated. Hence lubrication is more or
less necessary because in no time the compressor can be damaged. Lube oil serves the
purpose of lubrication. The oil has to have a certain viscosity and so a cooler is placed to
maintain the oil’s temperature.
Mode of action of lubrication oil:
The main oil pump B pumps the oil from the reservoir 55 gallon in capacity, a check
valve prevents the backflow of oil. It than enters the lube oil cooler which cools the oil
and maintains a proper operating temperature of the oil, water from cooling towers
maintains the temperature within operating range. . It passes through the filter
removing all the impurities from the oil. The oil than passes through the pinion
bearings spray nozzle and the bull gear bearing making its route back to the main lube
oil reservoir. The importance of lubrication can be judged from the fact that an auxillary
pump runs and lubricates various parts of the compressor before startup.

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Attached with the heat exchanger is a thermostatic mixing valve which actually serves
as a temperature regulator basically what it does is that it bypaasses the oil through the
heat exchanger if the temperature is below a certain level while forces the other half of
the lube oil through the heat exchanger hence keeping the temperature down to a
certain degree.
Inorder for an equipment to keep performing the way it is supposed to proper
maintainance is necessary hence following are a few guidelines issued by the vendor of
C-702.
But before taking into account any maintainance record there is also an inspection that
must be carried out by the operations team on a daily basis.

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Now coming onto the more important part which happens to be the scheduled
maintainance the compressor.

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We must take note that after every 6 months a closure of 1-2 days for maintainance shall
be observed!
Efficiency:
Because of a lack in maintainance and along with it an unaddressed air leakage from
the compressor its efficiency is going down. The amount of power needed to generate
air is exponentially increasing as the graph illustrates.

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Issues Faced:
Though the compressor is state of the art few technical issues have came up over the
past years an overview of the issues faced is as following:
 14 September 2002: TE-5 (3rd Stage Suction) high temperature led to machine
tripping. Alarm setpoint of 130 degF to Trip setpoint of 140 degF reached in less
than 2 seconds. Before tripping, TE-5 reading was 101 – 102 degF. Cause of
tripping was SURGING due to incorrect parameters of SURGE CONTROLLER.
Thomas Richard (FSR) visited the site and corrected the parameters (changed the
BIAS setting from 8 to 12).
 Post 2002 : Ever since the adjustment in 2002, machine did not trip on TE 5,
however since last few years, tripping has occurred on TE-3 (2nd Stage Suction).
1st stage intercooler has been inspected a few times and bundles / fins were
found blocked and corroded. However, only cleaning was carried out.
 September 2012: Another tripping incident of TE-3, where the temperature from
alarm (54degC) rose to trip point (60 degC) in less than 2 seconds, led to an
investigation of the event. It was observed that as per practice, Ops team unloads
the machine in order to reduce the TE-3 temperature, however the machine flow
(calculated thru motor AMPS) comes very close to Surge line (and might even
surge if there are issues in inlet air parameters). It is suspected that the machine
surged and tripped. The reason is that due to poor condition / blockage in
interstage cooler, the flow rate is lesser than calculated thru motor AMPs. There
375
410
454
508
400
450
510
570
2040 2380 2700 3090
Ideal Real

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is no flowmeter on the machine, and the flow is calculated thru motor AMPs. In
the event that there is blockage in air supply / cooling, the calculated flow rate
thru AMPs will be higher than the actual flow rate. In such event, surging may
occur at perceived flowrates close to surge line. On 28 Sep, the machine was
unloaded slightly to flow rate of 2422 NMCH @ 1600 hours to reduce TE-3, this
flow is very close to the surge line.
Later these issues were sorted out and no further issues related to surging or high
interstage temperatures were reported. The tubes were replaced with W type bundles
and phenolic coating ensured such issues were prevented.
Current Situation:
In the recent there have been issues reported regarding the high lube oil temperature.
The lube oil trip is at 62.7 C while the alarm rings at 57.2 C. These days the temperature
remains fairly high reaching high 50s almost every other day.
In July 2015 the temperature rose upto 61.6 C this temperature could have initiate
tripping. But the cooler was backwashed by raising the tripping temperature to 85 C
this did prove as an appropriate action and the lube oil temperature came down to 55 C.
These days the temperature is hovering in the high fifties work is being done but
considering all the factors it is not a good sign.
Possible Factors Causing High Oil Temperature:
 Water flow to cooler insufficient.
 Coolant temperature too high.
 Oil cooler fouled.
 Thermal mixing valve faulty.
 Oil heater thermostat faulty.
 Faulty Gauges.
Temporary Solutions:
Though there have been efforts to cater this issue but whatever is being done is more or
less a temporary solution.
 Opening a spurger at the top of the lube oil cooler consequently decreasing the
temperature a few degree celcius. On an extremely hot day a water hose can also
be used to cool down the lube oil.

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 The faulty thermostatic valve is bypassed instead of correcting it.
 There is a consideration to raise the trip point to 70 C which would in some
instances prevent a trip but would double the rate of oil detereoration and also
would not result in proper lubrication of the system.
 A backwash was performed to remove fouling but that too is a temporary
solution considering that it would take no more than 3 months for fouling to
again decrease heat transfer rate.
Lapses at our end:
 Proper maintainance has not been ensured, specifications stated in the vendor’s
manual are not followed, to add to it no proper maintainance record has been
maintained.
 There has been air leakage from the second stage of the compressor, it has been
left un addressed, this results in high interstage temperatures as well as high
lube oil temperature.
 The lube oil used is T-46 while the vendor clearly stated that turbo oil shall be
used.
What could be done:
 A larger lube oil cooler can be installed.
 The pitch of the cooling tower fans can be increased inorder to increase cooling
water temperature.
 An autobackwash system can be installed which after every set period of time
backwashes the exchanger and the flow pases through a parallel exchanger.
 The problems in the system shall be immediately addressed with proper
maintainance procedure to be followed.
 To decrease any chance of fouling satellite dosing shall be performed with the
appropriate chemical.
 The tube bundle can be replaced with tubes of smaller diameter resultantly
increasing surface area and temperature difference.

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Heat Exchanger details:
Oil (Shell Side) Water (Tube Side)
Flow 34 GPM 34 GPM
Specfic Gravity .86 1.0
Viscosity cp@F 20 @ 127 .71 @ 96
Specific Heat .48 1.0
Temperaturein 134.5 93.0
Temperatureout 120.0 99.0
Passes 1 4
Pressure Drop 10 4
Fouling Resistance .0025 .0035
ThermalConductvity .078 .361
Heat Exchanged 101880 BTU/HR
Surface Area 56.9 SQ.FT/UNIT
Tubes 304 SS Tubes60 inchesin length
Following data is that in an ideal case. Though I suggested to the process department to
carry out flowmetering using an ultrasonic flow meter but it was deemed as not
possible because of the small size of the tubes.
To measure the extent of fouling a master gauge was also needed to measure the
pressure drop across the inlet and outlet of the water supply, but this was not granted
either hence fouling is a factor in the poor peroformance of the heat exchanger but the
extent to which it is present can be no more but a wild guess.
On ground calculations were based on the temperature difference that were considered
using a temperature gun while the quad system was used as refference.

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The quad system showed an outlet temperature of 54.4 C which is considered to be near
to the average range. This is because urea 1 is closed hence cooling water has a lower
temperature.
Readings using temperature gun.
Oil (Shell Side) Water (Tube Side)
T in F 142 90
T out F 122 102
Heat Transferred: 95060 BTU/HR
The value cannot be deemed as accurate because of the issues in the temperature gun
and keeping U constant in both the equations though fouling is a determining factor.
Viability Of Solutions:
 Installation of a larger lube oil cooler seems like the end of all problems. But a
larger lube oil cooler comes with a large price tag along with that a complete
overhauling of the lube oil system is required that would impact the company’s
production. Hence installing a larger heat exchanger can be put into
consideration but implemented only at a last resort situatuon.
 There are few complains relating to the high temperature of the incoming cooling
water. Increasing the pitch of the fans from 13-15 degrees may decrease the
temperature a good 1-2 C but would increase the tripping probability of the fans
causing a major hindrance in the plant’s performance.

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 There have been reports of fouling in the heat exchanger lately a previous
backwashing proved to be fruitful bringing the temperature down a good 5
degrees from where it stood. Installation of an Auto Backwash system can act as
good and permanent solution. We could either add a parallel heat exchanger or
bypass the heat exchanger during online backwashing. It can increase the
efficiency of the heat exchanger resultantly end this issue.
 There is no better solution than proper maintainance of the compressor. Properly
greasing various elements carrying proper inspection fixing the second stage air
leakage would cause the temperature of oil approaching the heat exchanger to
get lower as in the vendor specified units and decreasing the workload of the
cooler.
 Sattelite dosing could have been a viable solution but apparently because of the
small size of the heat exchanger and it being an offline job it is better to avoid it
as a solution and instead backwashing sounds like a better solution.
 Decreasing the tube size would increase the fouling tendency to a whole new
level with thinner tubes, hence it shall be avoided.
Immediate Actions:
 Ensure proper maintainance of the compressor because without proper
maintainance it is near impossible to keep the compressor up and running.
Following image shows the detereorating condition.
 Approach a vendor and start work on the auto backwash system installation so
that the fouling tendency can be reduced.

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 If following actions donot give the required results, than work on other
solutions.
C-701 A/B:
C-701 A and C-701 B have a totally same working principle the only difference being
the former is motor driven while the other one is driven by a steam turbine. They are
part of the old machinery present at the plant.
Specifications:
 Make: Ingersoll Rand
 Type: Reciprocating, two stages double acting
 Capacity: 1596 NMCH (980 SCFM) (at 100% load)
 Discharge pressure: 8.78~9.49 kg/cm2g (125~135 psig).
 Number of suction/ discharge valves : 6/6 for 1st stage
 Number of suction/ discharge valves : 4/4 for 2nd stage
 Number of Clearance valves : 4/4 for 1st & 2nd stage
 Max allowable discharge temperature : 176.5oC
 Driver : Motor/Steam Turbine

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Working Principle:
Only difference between C-701 B being that the driver is a turbine. So the air enters
from the atmosphere via an air filter. Both the turbines are double acting. Each
compressor is a two stage compressor with the piston being driven by a crank shaft.
Their capacity is 1596 NMCH but due to some implications, unavailability of
mechanical spare parts severe ambient temperatures they are made to run on half their
generation rate that is around 798 NMCH. The inlet are outlet valves are 6/6 for its first
stage while 4/4 for its second stage. So the air enters in the first stage and is compressed
by the action of the piston. The compressed gas than enters into the intercooler and
progresses towards the second stage. Flywheel is installed in order to provide inertia.
PSVs are installed after first and second stage. Set point given to the first PSV is of 2.6
kg/cm2 while that to the second PSV is of 10.55 kg/cm2. After the second stage the air is
sent to pulsation bottle because of the fact PD compressors generate a pulsating flow so

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in a pulsating bottle the pulse is removed and a smooth flow is attained which is than
cooled and sent towards the air network lines.
Few important details.
 The maximum allowable discharge temperature is 176.5 C a temperature above it
can seriously damage the compressor, hence a signal is generated in the control
room where the respective Boardman signals unloading of the compressor.
 AEG electric motor is the driver of C-701 A the motor is rated at 270 HP running
at 1400 RPM and having a gear ratio of 2.8:1.
 Elliot steam turbine drives the compressor C-701 B the turbine is rated at 240 HP
running at 3600 RPM also equipped with a Wood Ward governor requiring 12
kg/cm2 (175 psi) steam to run and function properly. Its gear ratio is 7:1.
 For cylinder lubrication force feed lubricator is used, on the other hand for the
lubrication of the crankshaft a pump is installed for instance a pump fails and the
pressure of oil goes below 0.84 kg/cm2 the compressor trips due to a signal
generated from the PLCO security system.
 Gearbox lubrication is carried out through shaft driven lube oil pump. For C-701
B’s case the bearings of the turbine are also lubricated by the same pump.
C-701 A/B have been a part of the base plant (where I am based) compressors
outside the base plant would not have such detailed information.
KGT-2501
KGT is a compressor based at ammonia 2 it is driven by a gas turbine as GT suggests.
Compared to any other compressor that I have seen or witnessed at the plant this
particular compressor has an extremely high generation capacity. KGT is a 4 stage
compressor there are two low pressure stages while two high pressure stages after each
stage there is a cooler and a knockout drum. Its generation capacity is around 1800
KSCFH when converted to NMCH rises up to 1800x27.5 48870 which is a mammoth
amount when other compressors are brought into consideration. KGT-2501 is basically
generating process air for the ammonia synthesis. The residual air is sent towards the
base plant as well as some of it is vented while some goes into the secondary reformer.

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Ammonia 2 is running at 130% load. Note 1% load requires 13 KSCFH (353 NMCH) air
hence the requirement of ammonia 2 is around (130x13) 1690 KSCFH around (45475
NMCH) the remaining air is around (48870-45475) 3400 NMCH of which around 40-
50% air is sent towards the base plant section. Which makes it around 1600-1700
NMCH. In earlier days around 2200-2300 NMCH air was received from ammonia 2 but
since the load has increased the delivery has decreased. The air is at 500 psi pressure
about 4 times more than what is required hence the air coming from ammonia 2 is
letdown at PIC 704 control valve making it a part of our air network. In case of an
emergency at URUT such as a compressor like C-702 has tripped KGT can increase the
supply up to 120-130 KSCFH around 3800-4000 NMCH resultantly fulfilling our
demands.
Portable Compressors:
These compressors were not the part of the air circuit since I have arrived at Engro
fertilizers but in case of an emergency they can be brought into use. Their generation
capacity is 700-745 NMCH air. These compressors can hooked up at plant air header
discharge or at the d/s of PIC 704 and PIC 703. A major drawback of using the portable
compressors is the fact that they cannot generate the same pressure as the other
compressors in the net. Hence these portable compressors are only used when C-702
has tripped or insufficient air is coming from ammonia 2.
MK-201/202:
MK-201/202 are basically two centrifugal instrument air compressors positioned at
plant 2 utilities 3. Both of them are driven by a motor and are kept there to provide
instrument and plant air to plant 2. Some of the air is sent towards the base plant,
instrument air that is towards the GT’s and HRSG’s. Both have the same working
principle and have a striking resemblance to C-702 present at the base plant. Each has a
capacity of generating 3300 NMCH air in the system. Most of the air requirements are
fulfilled by MK-201 and K-421 with MK-202 being on standby. They are both 3 stage
compressors the rated power of first stage is 40,000rpm while the second and third
stage has 60,000 rpm the gear ratio is 11.1 while the motor attached to them has a rated
speed of 3000 rpm. The instrument air that they generate ultimately combines with the
instrument air header at base plant.

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K-421:
K-421 is a centrifugal compressor present at ammonia 3; it is driven by a turbine and
has 4 stages. The compressor K-421 consists of two low pressure and two high pressure
stages. K-421 is basically placed to provide air to the ammonia synthesis reactor which,
we are dealing with its third stage discharge. The air it generates in the third stage
discharge is around 3075 NMCH. This air is then transported to three locations namely
utilities 3 ammonia 3 and base plant (URUT1) passing through the valve HIC 201
joining the base plant network at the downstream of the air coming from ammonia 2.
On an average day as much as 2000 NMCH air can be delivered towards the base plant.
These days due to the fact demands are not that high hence no air is being sent towards
the base plant.
Knockout Drum:
The instrument air or plant air has to be free from any moisture so that they could be
effective. A knockout drum is a vapor-liquid separator is a vertical vessel used in
several industrial applications to separate a vapor-liquid mixture. Gravity causes the
liquid to settle to the bottom of the vessel, where it is withdrawn.
In low gravity environments such as a space station, a common liquid
separator will not function because gravity is not usable as a separation
mechanism. In this case, centrifugal force needs to be utilized in a
spinning centrifugal separator to drive liquid towards the outer edge
of the chamber for removal. Gaseous components migrate towards the
center. But in our case ample gravity is available and a centrifugal
separator is not needed.
The gas outlet is usually covered by a spinning mesh screen or a grating which basically
serves to remove any sort of moisture from the exiting gas this mesh adds just like a
filter and traps the liquid particles. Any liquid that does approach the outlet strikes the
grating, is accelerated, and thrown away from the outlet. The vapor travels really fast
minimizes chances for entrainment. This can also be referred to as a flash drum or a
demister. Its feed can also be a liquid that can be totally flashed as it enters the flash
drum.

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There must be a liquid level sensor as well as that a drain to drain out the liquid that
has gathered in the drum. A higher level of liquid can hamper the efficiency of the K.O
drum to quite an extent.
Other Methodsto removethe liquid are asfollowing:
Liquid Absorption:
It is a technique in which basically a separate liquid engulfs a gas or a liquid separating
the two components.
Adsorption:
Adsorption is basically a technique in which cohesion occurs between the molecules
and the given surface it can either be chemical or physical. The dryers work on this
principle to separate the moisture content.
At least two identical packed beds are used in a fixed bed system one for adsorption
and the second for regeneration. A variety of adsorption systems have been developed
that permit both adsorption and regeneration to occur in the same unit.
Basically 2 adsorption regimes are followed.
Physical Adsorption:
Occurs when London-van der Walls forces bind the adsorbing molecule to the solid
substrate; these intermolecular forces are the same ones that bond molecules to the
surface of a liquid. It follows that heats of adsorption are comparable in magnitude to
latent heats 10~70 KJ/mole. Species that are physically adsorbed to a solid can be
released by applying heat (much the same as a liquid can be readily volatilized by
heating); the process is reversible. An increase in temperature causes a decrease in
adsorption efficiency and capacity. Almost all adsorption process pertinent to air
pollution control valve physical adsorption.
Chemical Adsorption:
Adsorption occurs when covalent or ionic bonds are formed between the adsorbing
molecules and the solid substrate. This bonding leads to a change in the chemical form

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of the adsorbed compounds, and is therefore not reversible. An example of a chemical
adsorption process is the formation of CO2 when O2 gas adsorbs to a carbon substrate.
The bonding forces for chemical adsorption are much greater than for physical
adsorption. Thus, more heat is liberated. For many applications, the adsorbent is
chemical impregnated with a substance that encourages chemical reactions with
particular adsorbate. With chemical adsorption, higher temperatures can improve
performance. Note that the heats of adsorption for oxygen and nitrogen are typically
small relative to those for the organics. It follows that the organics tend to be more
tightly bound than are the oxygen and nitrogen, and can therefore displace adsorbed
oxygen or nitrogen. This explains why VOCs (volatile organic compounds) are
effectively removed by activated carbon despite the relative abundance of oxygen and
nitrogen in typical carrier gases.
D-711 Knockout Drum:
If we scrutinize this network we will witness quite a few knockout drums. Each
compressor has one or more connected with them. Like D-702 is attached to the
discharge of C-702. D-711 is different as compared to the other knockout drums because
it acts as a common drum in which all the compressed air from plant 2 ammonia 2 and
base plant approaches. D-711 acts as a multipurpose device performing 3 functions in
tandem. First it acts as a pulsation dampener reducing or in fact eliminating the
pulsations caused by the various pressure variations in the air lines. Secondly it acts as a
reservoir for instrument system with storing 2 minutes worth supply of the air. Finally
there is also a trapping mechanism for the liquids or vapors hence the entrained vapors
are knocked down and flow through a sewer in to the trap, decreasing the water level
so that it can operate perfectly. A safety valve PSV-711 discharges air to atmosphere if
pressure increases to 10.55kg/cm2. A high-level switch installed at D-711.
The air from D-711 discharged into plant air and instrument air headers. Pressure in instrument
air header maintained by PIC-703 installed on plant air header. In case instrument air header
pressure drops to 8.08 kg/cm2, PIC-703V will be close to maintain pressure in the instrument
air header.
This acts as a focal point in the plant 1’s air network hence is really important and shall be taken
note of while working on the air network.

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R-101:
R-101 is a reactor vessel situated at Urea 1. The vessel has been there for a while and now is
basically not used in the urea synthesis process. Instead the vessel is used to store the supply of
air that is coming from the KGT compressor situated at ammonia 2. Due to its size the vessel
has a capacity of storing 20 minutes worth supply of the air in case of an emergency.
Control valves and Instruments:
Before starting off and discussing the control valves present in the system, we must be able to
understand that why do we require instrument air? And how is this commodity used? As
mentioned before we all are aware that the instrument air is used to drive the pneumatic
control valves. How it drives the control valves is as following. Basically two types of control
systems exist Electrical or pneumatic. Because our plant is a chemical plant hence there is
always a threat that an electric spark can generate a larger fire. A pneumatic system can be a
bit on the slower side but in fact is quite safe if we compare both the sides.
DCS I/P Regulato
r
Positione
r
Control Valve

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Following flowchart basically presents the way pneumatic control system works. The DCS
receives information from a measuring device; a controller at the board gives a set point. The
electric signal generated from the board has a rating of 4-20mA which is converted to a
pneumatic signal of 3-15 psi depending on the amount of pressure that has to be put on the
control valve. A diaphragm adjusts the flow; a constant 20 psi flow is entering the system
adjusted by the diaphragm. Two types of control valves exist, normally open and normally
closed hence either a high pressure air opens the control valve or it gets closed by the action of
air.
Because most of the valves are bleed through hence a constant supply of instrument air must
be maintained to keep the systemup and running.
Control valvesand instrumentsin the air circuit:
PIC-703:
PIC-703 is Located on plant air header; it closes if the system air pressure in D-711 drops below
8.08 kg/cm2, to maintain instrument air header pressure.
PIC-704:
PIC-704V Controls the air header pressure, at 8.58~8.79 kg/cm2, it is a letdown valve installed
on air import line from Ammonia-2 plant.
HIC-201:
HIC-201 is a control valve that is basically controlled by both sides as in plant 1 and plant 2; it
works on the lowest command rule as in would obey the lowest command of the two.

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FI’s:
Various FI’s are placed across the air network to measure the flow of the air at various points of
the network.
FIL-711:
The purpose of the pre-filter FIL - 711 is to remove oil mist and droplets from air before the air
reaches the Humidryer AD-712. Hence, it prevents any reduction in the moisture adsorption
capacity at the desiccant.
The filter unit comprises a welded steel chamber with inlet, outlet and drain connections and
integral legs. It is fitted with a filter pad composed of a highly resilient mineral fiber, treated
and prepared for removal of oil mist and droplets. The condensate thus removed collected and
drained off, once in every shift.
The separator operates at a temperature of 46 C and a pressure of 8.79kg/cm2 with a
maximum pressure drop of 0.35 kg/cm2 across the filters. The pre-filter operates on a
continuous 24 hours cycle. A bypass piping arrangement provided to facilitate cartridge
replacement without interrupting process airflow. Cartridge replacement carried out after
every six weeks. A safety valve PSV - 714 set at 11.25kg/cm2 provided to protect Filter-711.
Dryers AD 712 A/B, AD 206 A/B:
A compressed air dryer is a device for removing water vapor from compressed air.
Compressed air dryers are commonly found in a wide range of industrial and
commercial facilities.
The process of air compression concentrates atmospheric contaminants, including water
vapor. This raises the dew point of the compressed air relative to free atmospheric air
and leads to condensation within pipes as the compressed air cools downstream of the
compressor.
Excessive water in compressed air, in either the liquid or vapor phase, can cause a
variety of operational problems for users of compressed air. These include freezing of
outdoor air lines, corrosion in piping and equipment, malfunctioning of pneumatic
process control instruments, fouling of processes and products, and more.

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There are various types of compressed air dryers. Their performance characteristics are
typically defined by the dew point.
Regenerative desiccant dryers, often called "regens" or "twin tower" dryers
Refrigerated dryers
Deliquescent dryers
Membrane dryers
Water vapor is removed from compressed air to prevent condensation from occurring
and to prevent moisture from interfering in sensitive industrial processes.
The dryers present in the base plant work on the desiccant (regenerative principle).
Desiccant dryer:
The term "desiccant dryer" refers to a broad class of dryers. Other terms commonly
used are regenerative dryer and twin tower dryer, and to a lesser extent adsorption
dryer.
The compressed air is passed through a pressure vessel with two "towers" filled with a
media such as activated alumina, silica gel, molecular sieve or other desiccant material.
This desiccant material attracts the water from the compressed air via adsorption. As
the water clings to the desiccant, the desiccant "bed" becomes saturated. The dryer is
timed to switch towers based on a standard NEMA cycle, once this cycle completes
some compressed air from the system is used to "purge" the saturated desiccant bed by
simply blowing the water that has adhered to the desiccant off.
The duty of the desiccant is to bring the pressure dew point of the compressed air to a
level in which the water will no longer condense, or to remove as much water from the
compressed air as possible. A standard dew point that is expected by a regenerative
dryer is −40 °C (−40 °F); this means that when the air leaves the dryer there is as much
water in the air as if the air had been "cooled" to −40 °C (−40 °F). Required dew point is

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dependent on application and −70 °C is required in some applications. Many newer
dryers come equipped with dew dependent switching (DDS) which allows for the dryer
to detect dew point and shorten or lengthen the drying cycle to fulfill the required dew
point. Oftentimes this will save significant amounts of energy which is one of the
largest factors when determining the proper compressed air system.
Because AD-712 A-B are situated at the base plant hence would be discussed in detail.
Basically regeneration process consumes 4 hours. Hence 1 tower acts as a dryer for 4
hours and other regenerates and so this cycle continues.
The type DSR humidyer is a self-contained packaged air or gas-drying unit designed for
continuous 24 hour per day service. The humidryer incorporates twin vertical adsorber
towers to permit continuous operation, one adsorber being reactivated and cooled
whilst the other is on drying duty. The towers are connected by air operated 4-way
diversion valves, which automatically direct operation at regular intervals.
After its period of dryer duty, saturated bed is reactivated by the controlled application
of heat conveyed from and exchanger by a fix proportion of process flow. Reactivation
is carried out of full line pressure thus avoiding possible contamination of the process
fluid and elimination pressure buildup and blow down which are usually responsible
for premature desiccant break down. The required reactivation flow is maintained at a
constant level, regardless of fluctuation in the process throughput by means of an

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automatic control valve. The reactivation flow heated in an external exchanger and
passed the saturated bed where the previously adsorbed water vapor is released and
conveyed to the reactivation inter-cool in which it is condensed and ejected via a
separator and automatic discharge trap. The heating flow passes upwards through the
bed (countercurrent to the process stream). On completion of the heating period, the
heater is de-energized or bypass and the cold reactivation flow is directed in a
downward direction (co-current with the drying system) through the freshly
reactivated bed until complete cooling is affected.
When the reactivation heating and cooling periods are completed, the process flow
diversion valve automatically reverse to bring the freshly reactivated adsorber on
stream and initiate regeneration of the saturated bed.
The adsorber towers are charged with activated alumina. The desiccant is supported by
steel frame screens.
As the schematic shows air dryers play an extremely pivotal rule in the generation of
instrument air in fact a dryer convert’s plant air to instrument air.
AIR NETWORK CONSUMERS:
We shall first scrutinize the plant air users PLANT 1 shall be brought into
consideration as Plant 2 is out of my domain. What is the purpose of using plant air?

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Plant Air users’ schematic:
Hence as mentioned before plant air is used for passivation (forming an ore to prevent
corrosion) and for the operating pneumatic control machines. The following diagram
well and truly provides a good understanding of the plant air usage details as well as its
consumers.
Instrument Air Consumers:
If we compare plant air and instrument air we get this realization that instrument air is
more important considering the tasks it perform. Instrument air is used to operate the

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control valves without which you cannot maintain constant flow rates and keep your
reaction progressing the way you actually want it to.
The list of Instrument Air Consumers:
 GT-603/ HRSG-691
 GT-601/ HRSG-651
 PRC-2 A/B
 GT-602/ HRSG-661
 SG-621
 SG-631
 SG-641
 P-601’s
 PRC/ TRC-604
 C-702 control valves
 C-701 A/B loaders
 CT-401
 Firewater
 PRC-602 ABV
 Fuel letdown
 Workshop
 TIC 616
 Ammonia 2 control valves
 TK-101
 D-161/E-165
 E-161
 Ammonia Furnace
 P-102’s
 Air Mask
 E-162/163
 D-141 Area
 R-101 air mask
The list continues but basically all the pneumatic control valves are operated by
instrument air.

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Instrument Air Calculation:
Instrument air consumption shall be calculated during detail design to determine the
plant utility air requirement by pneumatic operated instrument as well as package
which require air for its utility such as purging or other purpose. Instrument air
consumption calculation will be the basis to size instrument air utility system which
consists of air compressor, air drier, and air receiver.
Actuated valve such as shutdown valve, blow down valve and control valve are
instruments which require instrument air for their operation. Instrument air
requirement of each instrument valves depends on its actuator size and its operation.
Shutdown valve and blowdown valve may be considered working intermittently, while
control valve working continuously. It should be noted that the instrument air required
by control valve during steady condition is much lesser than during its transient
condition.
To determine the instrument air consumption, some assumptions should be made
(please note that these assumptions are for example only, not as standard reference, and
may differ on each project)
Normal air consumption demand
Control Valve
From total number of control valve, 90% of control valve operates in stable condition
hence requires steady state air consumption only, while 10% could be in unstable
condition hence requires transient air consumption.
Shutdown valve / Blowdown valve
Shutdown valve and Blowdown valve only require instrument air when they are
operating which is predominantly during start up after shutdown, so it is considered
intermittent consumption and one can assume that only some number of valve are
working simultaneously. It could be assumed that 10% of the valve will operate
simultaneously for normal air demand calculation.
Peak air demand

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From total number of control valve, 70% of control valve operates in stable condition
hence requires steady state air consumption only, while 30% is in unstable condition
hence requires transient air consumption.
The next step is to gather data from vendor / manufacturer catalog which provides
information of instrument air consumption.
The following is data taken from catalog:
Control valve in stable condition 0.3 SCFM (0.5 NMCH)
Control valve in unstable condition 7 SCFM (11.9 NMCH)
For actuated valve, the instrument air consumption depends on size of actuator (swept
volume) which could be obtained from vendor catalog. The required opening or closing
time of the main valve will also influence the air consumption rate.
Hence using the following data we can easily calculate the amount of instrument air
needed.
Air Balance:
After all the details now it’s time to calculate the total amount of air that can be
generated at this plant and to calculate whether plant’s demands are fulfilled or not.
Current generation must also be kept account of.
Max Generation Capacity:
Following is a list of maximum generation capacity of each compressor without taking
account of any problem.
C-702: 3200 NMCH
C-701 A/B: 1596 NMCH
KGT-2501: 125 KSCFH (3400 NMCH)
Portable Compressors: 745 NMCH
MK-201/202: 3300 NMCH each.
K-421: 3075 NMCH third stage extraction.

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Maximum generation of each of the compressor is basically listed down but due to
some constrains most of them do not operate at their maximum generation capacity.
Specially because of some issues and unavailability of parts C-701 A/B operate at half
their capacity as a result the maximum air they can generate has gone down to
approximately 798 NMCH half of what they were supposed to produce.
Secondly there is a really high load on ammonia 2 plant and as mentioned before the
basic function of KGT is to provide process air for the ammonia process because of this
reason maximum 80-90 KSCFH (2500 NMCH) is its generation capacity.
Lastly as far as portable compressors are concerned their production capacity is not of
any good if the plant is running smoothly hence they are not used.
Plant 1 Air requirement.
5000 NMCH

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Best scenario air generation:
C-702 C-701A/B KGT-2501 Plant 2
8500 NMCH

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Present Generation:
C-702 C-701A/B KGT-2501 Plant 2
4900 NMCH
Maximum requirement of Plant 1 is 5000 NMCH, so the 4900 NMCH air that is
produced is enough to serve plant 1.
Plant 2

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6367 NMCH
TotalGeneration Capacity:
MK-201
MK-202 9675 NMCH
K-421
PresentGeneration:
MK-201
MK-202 6375 NMCH
K-421
MK-202 remainsdown asMK-201 and K-421fulfill the requirements.

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Hence totalrequirementofair is 5000 + 6367 = 11,367
Totalgeneration capacity withoutportablecompressors= 16175 NMCH
PresentGeneration= 11,275NMCH.
Hence there are sufficient sources of air generation and the air generated is fulfilling the
plant’s requirements.
Handling Emergencies:
Basically our goal is to maintain a certain pressure hence following are few cases that
can be considered as emergencies and ring alarm bells in the control room
 KGT Fails:
 C-702 fails
 PIC 704 malfunctioning:
 Plant 2 Process air failure:
The drop in instrument air pressure signals a failure. If the instrument air pressure
drops to 7.38 kg/cm2 low pressure alarm shall ring in plant 1 control rooms. PIC-703
will close if the pressure drops to 8.0 kg/cm2.
KGT Tripped:
If KGT trips; isolate the import coming from ammonia 2 by closing the valve PIC-704
because a pressure difference can lead the air towards ammonia 2. If the pressure drops
below 8.0 kg/cm2 close PIC-703. Generate air using C-702, 701 A/B and import air from
plant 2.
C-702 Tripped:
Incase C-702 trips isolate the line coming from C-702. Increase the import from KGT
and plant 2. Open up PIC-704 and finally cut plant air by closing PIC-703.
PIC-704 Malfunctioning:
Open the bypass with close eyes on air pressure so to avoid surging at C-702 and cut the
plant air by closing PIC-703.

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Plant 2 Process Air Failure:
Close the line of air coming from plant 2 a further pressure drop shall be confronted by
cutting of the plant air.
Shutdown Jobs/Improvements:
 PIC-703 Leak through.
 PIC-704 Leak through.
 C-702 Second Stage oil leakage.
 C-701 A/B overhauling.
The impacts these issues would have are as following:
Suppose there is a leakage or in fact one of the major compressor has tripped, in order
to maintain the instrument air pressure the first thing that should be done is to cut the
plant air header. Due to the leakage at PIC-703 this is more or less not possible and a
proper pressure if needed cannot be maintained.
PIC-704 acts as letdown valve for the high pressure air coming from the KGT
compressor, as it is leak through the desired pressure level cannot be maintained.
The second stage oil leakage at C-702 is adding to our worries. It is not only impacting
the efficiency of the compressor but is increasing the temperature of the lube oil, if this
issue is addressed properly most complications relating to C-702 would subside.
C-701 A/B need to be overhauled. Their overhauling would not only double their
generation capacity but would decrease the dependence of the base plant on ammonia 2
and plant 2.