1. 1
CONTENTS
Page No.
1. History of IFFCO 2
2. Introduction 3
3. Introduction of centrifugal compressor 4
4. Part of centrifugal compressor 5
5. Working principle of centrifugal compressor 6
6. Types of centrifugal compressor 7
7. Some useful terms 8-11
8. Horizontally split type casing 12
9. Compressor cross sectional view 13
10. Barrel type casing 14
11. Journal bearings 15-17
12. Why centrifugal compressor 18
13. Co2 compressor flow diagram 19
14. Compressor rotor 20
15. Advantage & disadvantage 21
16. Conclusion 22
17. Reference 23
2. 2
HISTORY OF IFFCO
Indian Farmers Fertilizer Cooperative Limited, also known as IFFCO, is the world’s largest
fertilizer cooperative federation based in India which is registered as a Multistate Cooperative
Society. IFFCO has 40,000 member cooperatives.
History
During the 1960s the cooperative sector in India was responsible for the distribution of 70 per
cent of the fertilizers consumed in the country. This sector had adequate infrastructure to
distribute fertilizers but had no production facilities of its own and hence was dependent on
public/private sectors for supplies. To overcome this difficulty and to bridge the demand supply
gap in the country, a new cooperative society was conceived to specifically cater to the needs of
farmers. It was a unique venture in which the farmers of the country through their own
cooperative societies created this new institution to safeguard their interests.
The number of cooperative societies associated with IFFCO has risen from 57 in 1967 to more
than 39,800 at present. Indian Farmers Fertilizer Cooperative Limited (IFFCO) was registered on
November 3, 1967 as a Multi-unit Co-operative Society. On the enactment of the Multistate
Cooperative Societies act 1984 & 2002, the Society is deemed to be registered as a Multistate
Cooperative Society. The Society is primarily engaged in the production and distribution of
fertilizers. The bylaws of the Society provide a broad frame work for the activities of IFFCO as a
cooperative society.
Fig 1:
3. 3
INTRODUCTION
The Indian fertilizer industry has been supplying a substantial portion of growing demand of
fertilizer within the country India is the third largest producer of fertilizer in the world. There are
60 large size fertilizer plants in the country manufacturing a wide range of nitrogen; phosphate
and Complex fertilizer besides there are 81medium and small scale single super phosphate units.
IFFCO has emerged as a pioneer venture in the cooperative sector. It has witnessed meteoric rise
and has blossomed into the largest manufacturer and market of fertilizer in the country. The
success of IFFCO has encouraged the growth of the cooperative movement in India
.
Fig 2:
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Introduction of centrifugal compressor
Fig3: Centrifugal compressor
A machine which compresses the gases by centrifugal action with utilizing the rotating vanes or
impellers is called centrifugal compressor.
Centrifugal compressors, sometimes termed radial compressors, are a sub-class of dynamic
axisymmetric work-absorbing turbo machinery.
The idealized compressive dynamic turbo-machine achieves a pressure rise by adding kinetic
energy/velocity to a continuous flow of fluid through the rotor or impeller. This kinetic energy is
then converted to an increase in potential energy/static pressure by slowing the flow through a
diffuser. The pressure rise in impeller is in most cases almost equal to the rise in the diffuser
section
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Part of centrifugal compressor
1- Casing
2- Rotor (shaft, impeller, spacer, balance piston, coupling hub etc.)
3- Diffuser or diaphragm
4- Bearing housings with JB & Th.B.
5- Seals (stage, intermediate & end seals)
6- Coupling
Accessories of Centrifugal Compressors –
1- Inter-stage Coolers
2- Inter-stage Separators
Safety parts of Centrifugal Compressors –
1- Anti-surge control valve
2- Vibration probes
3- Axial shift protection
4- Thermo-couples
5- Thermometers
7. 7
Working principle of centrifugal compressor
Fig 4:
In centrifugal compressor, gas enters the impeller of the compressor in an axial direction
and exists in a radial direction in to diffuser. The gas initially enters at inducer or eye of the
impeller. When impeller rotates, its inducer rotates the gases. Due to this angular rotation & mass
of the gas, centrifugal force acts on the gas which leads the gas flow into the vanes of impeller
with high velocity. Pressure as well as velocity increases in the impeller. As impeller vane
design, gas passes through vanes and leaves radially from the impeller. The gas then goes in to a
diffuser, where kinetic energy is converted in to pressure energy. From the exit of diffuser, the
gas enters to scroll or volute or collector with decreased velocity and increased pressure. Thus
we get compressed
8. 8
Types of centrifugal compressor
1- As per casing design
(a) Horizontally split
(b) Barrel type or vertically split
2- As per stage
(a) Single stage
(b) Multi stage
3- As per gas handle
(a) Air centrifugal compressor
(b) CO2 centrifugal compressor
(c) Sync gas centrifugal compressor
Single stage centrifugal compressor –
Compression of gas in the centrifugal compressor through one go i.e. one suction and one
discharge is known as single stage centrifugal compressor. Single stage compressors are
suitable for low compression ratio say up to 4:1. In single stage there are one or more
than one impellers are used as per suitability.
Multi stage centrifugal compressor -
Compression of gas in the centrifugal compressor through more than one go is known as
multistage centrifugal compressor. Multi stage compressors are suitable for high
compression ratio. In multi stage centrifugal compressor there are more than one impeller
are used. In between every stage there is a cooler & separator is used. In our urea plants,
4 stage centrifugal compressors are used.
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Some useful terms
IBV –
IBV i.e. Inlet Butterfly Valve is used in suction line to control the gas flow.
IGV –
IGV i.e. Inlet Guide Vane is used in suction line to control the gas flow.
Separators –
After passing the gases through coolers, it get condensed. This condensate is harmful to the
compressor. So after every cooler, a separator is provided to separate this condensate.
Diaphragms –
The diaphragms make up the separating wall between each impeller. Each diaphragm
constitutes a diffuser, which converts kinetic energy of gas into pressure energy and leads it
to next impeller. The diaphragm is made of high strength cast steel.
Rotor –
Rotor consists of shaft with key, spacers, impellers, thrust collars, balancing drum etc. Before
being mounted on the shaft, each impeller are dynamically balanced and tested at a speed 15
% higher than the max. Continue speed.
Fig 5: Rotor
Critical Temperature of Gas –
Temperature at which the condensation of gas starts at a particular pressure is known as
critical temperature of the gas at this pressure. For example in urea plant, the critical
temperature of CO2 is 32 C at 78 kg/cm2 in 3rd stage.
Capacity of CC –
Volume of gas moving through the compressor per unit time is known as compressor
capacity. It is generally measured in NM3/hr. Speed control is the most easiest & economical
way to control the capacity.
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Impeller –
Impeller imparts energy to the fluid. Impeller is most critical part of centrifugal
compressor. Its size, shape and speed determine the compressor performance. There are two
types of impellers used in centrifugal compressor and these are closed impeller i.e. shrouded
impeller & semi-open impeller i.e. semi-shrouded type impellers.
Balance drum –
The centrifugal compressor is subjected to an axial thrust towards the suction end due to
the differential pressure acting on the hubs and covers of the impellers. With two stage opposite
suction a large amount of axial thrust is balanced. The balance drum reduces the net thrust
acting towards the suction. This is obtained by connecting the chambers , created by the balance
drum and relevant labyrinth seals , to the compressor suction by means of a thrust balancing pipe
so as to create a differential pressure across the balancing drum.
Journal Bearing –
The bearings which take the radial load of the rotor is known as journal bearings. There
are two journal bearings are provided (at both end of the shaft) for each shaft of compressor. The
shaft, where bearing comes in to contact is called journal bearing.
Thrust Bearing –
The bearings which take the axial load of the rotor is known as thrust bearing. There is
one thrust bearing is provided for each shaft of compressor. Thrust bearing provided at that end
the shaft so that buckling load could not act on the shaft.
11. 11
Critical Temperature of Gas –
Temperature at which the condensation of gas starts at a particular pressure is known as
critical temperature of the gas at this pressure. For example in urea plant, the critical temperature
of CO2 is 32 C at 78 kg/cm2 in 3rd stage.
Capacity of CC –
Volume of gas moving through the compressor per unit time is known as compressor capacity. It
is generally measured in NM3/hr. Speed control is the most easiest & economical way to control
the capacity.
Rotor –
Compressor rotor commonly consists of a solid center shaft. All the impeller, its keys and
spacers mounted on the shaft very slight clearance fit. CC rotors are normally built with a
balancing piston installed at discharge end to counter the axial force & relieve the thrust bearing
load.
Compression ratio –
The ratio of discharge pressure to suction pressure of a compressor or compression stage is
known as its compression ratio. The pressure ratio per stage in a centrifugal compressor can vary
from 1.5:1 to 5:1 in production unit.
12. 12
Surge control system –
To avoid the compressor run in the surge zone is a phenomenon in a centrifugal compressor
caused by drop in flow rate below a minimum level, at constant speed, corresponding to
compressors maximum discharge pressure. It occurs because of some kind of aerodynamic
instability.
Bearing lube oil system –
Due to high speed of compressor, forced feed lubrication are used for all the bearing lubrication.
For this purpose a system is used which is known as bearing lube oil system. It comprises
console oil tank, MOP, EOP, PCV, filters, coolers, throttle valves etc.
Condensate drain system –
After every compression & cooling some parts of gas get condensed. This condensate gas is
harmful to the centrifugal compressor. So this condensate needs to be separated from the gas. So
a condensate drain system is provided to separate the gas condensate. Condensate separators,
condensate drain valves etc. are used in this system.
Sealing system –
To prevent the leakage of the gas between impellers, stages and at the end of compressor a
system is used to know sealing system.
Degree of Reaction –
The ratio of pressure rise in the rotor blades to the pressure rise in the compressor stage in known
as degree of reaction
.
Rotor -
Compressor rotor commonly consists of a solid center shaft. All the impeller, its keys and
spacers mounted on the shaft very slight clearance fit. Centrifugal compressor rotor is normally
built with a balancing piston installed at discharge end to counter the axial force & relieve the
thrust bearing load.
Compression ratio –
The ratio of discharge pressure to suction pressure of a compressor or compression stage is
known as its compression ratio. The pressure ratio per stage in a centrifugal compressor can vary
from 1.5:1 to 5:1 in production units.
Choke –
When the compressed air system pressure decreases, centrifugal compressor delivers an
increased volume of air. As the system pressure continuous to decrease, the volume of air
delivered from the compressor continuous to increase until the air velocity somewhere in the
compressor reaches the speed of sound. At this point the flow is said to be CHOCKED because
further reduction in system pressure does not result in additional air volume delivered from the
compressor. CHOKE is the maximum flow that can be passed through the compressor
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Horizontally split type casing-
Horizontally split type casing of CC is shown in the fig. Its top & bottom half of casings are
bolted with each other. This type of compressor is used for low pressure. In our CO2
compressor, LP casing is horizontally split type casing.
A type of centrifugal pump in which the casing is split into two separate chambers, Its different
from an end suction pump or inline pump, in which the casing, the suction nozzle, and the
discharge nozzle are all included in a single chamber. When the casing is split along a vertical
plane in relation to the impeller, it’s known as a vertical split case pump; when it’s on a
horizontal plane, it’s known as a horizontal split case pump. This type of casing design is more
economical for higher flow applications, and the impeller can be supported by bearings on both
sides, an advantage for larger, higher flow pumps.
The pump has the suction and discharge connections in the lower half of the casing, opposed to
each other. The impeller is mounted on a shaft which is supported by bearings on both sides.
Fig 6: Horizontal split
14. 14
Compressor cross sectional view –
Fig 7: Compressor cross section
A cross sectional drawing of centrifugal is shown in the fig. It is a double & opposite suction
type compressor.
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Barrel type casing –
A cross sectional drawing of centrifugal is shown in the fig. It is a double & opposite suction
type compressor. As above fig. it is clear that,
Fig 8: Barrel type casing
Pressure rise in impeller = P2 – P1 Velocity rise in impeller = V2 – V1
Pressure rise in diffuser = P3 – P2 Velocity loss in diffuser = V2 – V3
16. 16
Journal Bearings -
The bearings which take the radial load of the rotor are known as journal bearings. There are two
journal bearings are provided (at both end of the shaft) for each shaft of CC. Generally lobe type
& tilting pad type journal bearings are used in CC.
Lobe type Journal Bearings -
Fig 9: Journal bearing
Two lobe, three lobe & four lobe journal bearings are generally used in CC. A four lobe
journal bearing is shown in the above figure. Here the lobe radius is larger than the shaft
radius by a specific amount. This difference in the radius of the shaft and the lobe, results in
the formation of a wedge gap in each arc.
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Tilting pad journal bearings
Fig10: Tilting pad journal bearings
In Tilting Pads Journal Bearings, pads are machined with a radius slightly greater than the
journal radius. The length to width ratio of the pads should be around 1. The pivoted points is
usually 60 to 65% of the pad length from the loading edge. In some machines centrally pivoted
pads are used.
Oil flow is not controlled to each pad. Usually a seal is provided on both side of bearing
& oil is fed into & out of the sealed space in such a manner as to ensure that it is always full. The
volume of oil flow must be sufficient to carry out heat generated in the bearing with reasonable
temperature rise.
18. 18
Thrust bearing –
The bearings which take the axial load of the rotor is known as thrust bearing. There is
one thrust bearing is provided for each shaft of compressor. Thrust bearing provided at that end
the shaft so that buckling load could not act on the shaft.
Fig 11:Thrust bearing
In the above fig. a KINGSBURY type thrust bearing is shown. It has three or more pads, which
enclosed in a housing. Each pad is an individual plate, which is free to pivot. The pivot line is
radial so that each pad can be inclined in a circumferential direction, which helps to make
tapered oil wedge.
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Why Centrifugal Compressor
Oil free air
High reliability
Lowest cost operation
Easy operation
Easy maintenance
Simple installation
High life expectancy
Less foundation, piping & Space cost
Best Specific Power Consumption & Efficiency
20. 20
Fig12: CO2 compressor flow diagram
CO2 flow diagram is shown in the above figure. The 2MCH is LP case & it has two stage with
opposite suction. It takes 1st suction from GB side and discharges at middle. Then gas goes to 2nd
suction at turbine side through 1st inter cooler and separator. From the middle of 2MCH gas
comes out and goes to 3rd suction at rear side of 2BCH through 2nd inter cooler and separator.
From the middle of 2BCH gas comes out and goes to 4th suction at middle of 2BCH through 3rd
inter cooler and separator & after 4th stage final discharge obtained from 2BCH at the GB side
end. 2BCH is barrel type HP compressor case which has two stages of unidirectional suction.
Here FRC-16V Anti-surge control valve
HIC-14V Vent between 2nd & 3rd stage
PRC-1V Vent in final discharge line (auto opens)
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Compressor Rotor –
The parts of CC which are rotate in their normal operation is known as rotor. The parts of CC
rotor are listed here under –
Fig 13: Compressor rotor
1- Shaft 4- Spacer 7- Coupling hub
2- Impeller 5- Thrust collar
22. 22
Decision to change the 01-K-1
To increase the flow from 30000 NM3/hr to 36000 NM3/hr which was required after CEP, there
are three ways to achieve as given below –
1- Replace all the internals, rotors, impellers etc. with latest modified.
2- By addition a small reciprocating compressor of 6000 NM3/hr. in parallel with existing.
3- By replacement of compressor with new modern compressor.
1st method was not applicable as per the manufacturer recommendations because in this
method, investment was more & benefits were less due to old design of casing. Therefore this
idea was dropped. 2nd method was applicable, but following advantage and disadvantages were
considered –
Advantages –
1- Primary investment is very low.
2- Independent machine having no direct effect on plant operation.
3- Erection and commissioning of new machine was possible with plant on stream.
4- Operational reliability of the old machine was well proven.
5- Old machine spares may use.
Disadvantage –
1- The efficiency of old compressor remains less about 58 %.
2- Parallel operation of reciprocating machine with centrifugal machine was suspected to pose
certain risk.
3- Frequent maintenance requirement and separate spares inventory had to be maintained.
4- Additional set up including piping, intercoolers, civil foundation was required resulting in
extra cost involved.
2nd method, replacement of new compressor was also applicable, but following
advantage and disadvantages were considered –
Advantages –
1- The efficiency of new compressor was very high as 70 % w.r.t. old compressor.
2- Its reliability is very high and maintenance cost is low because of new machine.
3- There is no problem to procure the spare because of new machine.
Disadvantage –
1- The cost of replacement of compressor was very high.
2- The scope of work was very high, as it needed to procure the whole new compressor.
3- There was risk of commissioning and start up problem, which could be serious nature.
Selected Option –
Option of new high capacity centrifugal compressor was selected because efficiency of new
compressor was very high as 70 % w.r.t. old compressor. The pay backs period was less than 4
year as energy saving point of view. Erection and commissioning period was no matter because
we have already taken annual s/d for minimum 20 days every year. During annual s/d 2008 the
whole compressor with its accessories were replaced.
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CONCLUSION
I have completed industrial training from the IFFCO UREA PLANT WORKSHOP PHULPUR
Allahabad. I have observed many shop in the workshop I mainly performed my training in the
centrifugal compressor.
In the IFFCO urea plant workshop all the SSE & J.E. and SUPERVISIORS of all the shops
helped me very much. Without his or her supervision I was not able to perform he training in the
workshop. I was very grateful to them.
We have learned so much in the workshop, DIFFERENT TYPE OF WORKSHOP
TECHNOLOGY, TESTING OF THE PARTS OF THE IFFCO AND THE PROPER
FUNCTIONING of the different part of urea plant as an UREA REACTOR, COMPRESSOR,
FILTERS, HEAT EXCHANGER, TOWERS, BLOWERS, and AGITATORS OF THE BODY
OF UERA PLANT.
