Summer Internship Report
Project topic: - “HOW TO IMPROVE COMPRESSOR EFFICIENCY”
ACKNOWLEDGEMENT
I would take this opportunity to thank Mr. Atul Sharma(Mech.HOD), Shree
Cement Ltd., my project guide for his valuable guidance, suggestions and
encouragement. I am very grateful to Mr. Nitesh Sharma(Mech.) of Shree
Cement Ltd., for their kind help and essential information provided to me as per
my requirements.
I thank all the CCR and compressor house staff and the rest of Shree cement
community for their valuable information and assistance provided to me.

Finally, I would like to thank Mr. G. Tripathi (HR department, Shree cement
Ltd) for providing me this opportunity to work as a summer internship in Shree
cement Ltd.
Shree Cement Limited is the one of largest cement producing company of
North India. It is located in central Rajasthan, catering to the entire Rajasthan
market with the most economic logistics cost.
Shree Cement, Beawar

Shree Cements Ltd.
Shree Cement Ltd. is an energy conscious & environment friendly
business organization. The company is managed by qualified
professionals with broad vision who are committed to maintain high
standards of quality & leadership to serve the customers to their
fullest satisfaction. The board consists of eminent persons with
considerable professional expertise in industry and field such as
banking, law, marketing & finance.
Presently Shree Cements has ten units. Two units are at Beawer
(incorporated in 1979 and1997) and rest units are at Ras (Started in
2005).
STAGES OF CEMENT PRODUCTION
There are seven stages of cement production at a cement plant:
1. Procurement of raw materials
2. Raw Milling - preparation of raw materials for the pyroprocessing
system
3. Pyroprocessing - pyroprocessing raw materials to form cement
clinker
4. Cooling of cement clinker
5. Storage of cement clinker
6. Finish Milling
7. Packing and loading

1. Raw Material Acquisition
Most of the Raw material is sourced through Shree Cements own
mines which it has leased.
2. Raw Milling
Raw milling involves mixing the extracted raw materials to obtain the
correct chemical configuration, and grinding them to achieve the
proper particle-size to ensure optimal fuel efficiency in the cement
kiln and strength in the final concrete product. Three types of
processes may be used: the dry process, the wet process, or the
semidry process. If the dry process is used, the raw materials are
dried using impact dryers, drum dryers, paddle-equipped rapid
dryers, air separators, or autogenous mills, before grinding, or in the
grinding process itself. In the wet process, water is added during
grinding. In the semidry process the materials are formed into pellets
with the addition of water in a pelletizing device.
3. Pyroprocessing
In pyroprocessing, the raw mix is heated to produce cement clinkers.
Clinkers are hard, gray, spherical nodules with diameters ranging
from 0.32 - 5.0 cm (1/8 - 2") created from the chemical reactions
between the raw materials. The pyroprocessing system involves
three steps: drying or preheating, calcining (a heating process in
which calcium oxide is formed), and burning (sintering). The
pyroprocessing takes place in the burning/kiln department. The raw
mix is supplied to the system as a slurry (wet process), powder (dry
process), or as moist pellets (semidry process). All systems use a
rotary kiln and contain the burning stage and all or part of the

calcining stage. For the wet and dry processes, all pyroprocessing
operations take place in the rotary kiln, while drying and preheating
and some of the calcinations are performed outside the kiln on
moving grates supplied with hot kiln gases.
4. Clinker Cooling
The clinker cooling operation recovers up to 30% of kiln system heat,
preserves the ideal product qualities, and enables the cooled clinker
to be manoeuvred by conveyors. The most common types of clinker
coolers are reciprocating grate, planetary, and rotary. Air sent
through the clinker to cool it is directed to the rotary kiln where it
nourishes fuel combustion. The fairly coarse dust collected from
clinker coolers is comprised of cement minerals and is restored to
the operation.
5. Clinker Storage
Although clinker storage capacity is based on the state of the market,
a plant can normally store 5 - 25% of its annual clinker production
capacity. Equipment such as conveyors and bucket elevators is used
to transfer the clinkers from coolers to storage areas and to the
finish mill. Gravity drops and transfer points typically are vented to
dust collectors.
6. Finish Milling
During the final stage of cement production known as finish milling,
the clinker is ground with other materials (which impart special
characteristics to the finished product) into a fine powder. Up to 5%

gypsum and/or natural anhydrite are added to regulate the setting
time of the cement. Other chemicals, such as those which regulate
flow ability or air entrainment, may also be added. Many plants use a
roll crusher to achieve a preliminary size reduction of the clinker and
gypsum. These materials are then sent through ball or tube mills
(rotating, horizontal steel cylinders containing steel alloy balls) which
perform the remaining grinding. The grinding process occurs in a
closed system with an air separator that divides the cement particles
according to size. Material that has not been completely ground is
sent through the system again.
7. Packing and Loading
Once the production of cement is complete, the finished product is
transferred using bucket elevators and conveyors to large, storage
silos in the shipping department. Most of the cement at Shree
Cements is transported in by truck fleets in multiwalled paper bags.
Once the cement leaves the plant, distribution terminals are used as
an intermediary holding location prior to customer distribution.

Cement manufacturing from the quarrying of limestone to the
bagging of cement.
POWER GENERATION
SHREE POWER
Shree Cements are self sufficient in electricity as they have their own
45MW power generation plant. It has 2 x 18 MW and 1 x 6 MW units
and one 2.5 MW unit. It also has a line from State Electricity
Department in case of emergency. Shree Power has resulted in
making Shree Cements self sufficient in its Power needs and also lets
it produce electricity at lower costs which in turn translates into
better bottom line.
Basically fossil fuel power plant is an energy conversion center that
combusts fossil fuels to produce electricity, designed on a large scale
for continuous operation. The chemical energy stored in fossil fuels
which in this case is pet coke, a waste from petroleum refineries, is
convered successively into thermal energy, mechanical energy, and
finally electrical energy for continuous use and distribution across
Shree Cements. Different processes related to Shree Power are:

1. Fuel transport and delivery
Pet Coke is delivered by Reliance Refineries through mass transport
systems. Earlier the fuel was aquired free of cost but now Reliance
charges Rs3200/Metric Ton of Pet Coke.
2. Fuel processing
Pet Coke is prepared for use by crushing the rough coke to pieces of
desired size. The coke is transported from the storage yard to in-
plant storage silos by rubberized conveyer belts. Coke from the silo is
fed into a coal pulverize (coal mill). It is introduced into the top of the
pulverize which grinds the coke to a powder the consistency of face
powder and blows powder mixed with air into the furnace.
3. Feed water heating
The water used in the steam boiler is a means of transferring heat
energy from the burning fuel to the mechanical energy of the
spinning turbine. Because the metallic materials it contacts are
subject to corrosion at high temperatures and pressures, the water is
highly purified before use. A system of water softeners and ion
exchange demineralizers produces water so pure that it
coincidentally becomes an electrical insulator. The feed water cycle
begins with condensate water being pumped out of the condenser
after travelling through the steam turbines. The water flows through
a series of intermediate feed water heaters, heated up at each point
with steam extracted from an appropriate duct on the turbines and
gaining temperature at each stage. Typically, the condensate along

with the makeup water then flows though a de aerator, which
removes dissolved air from the water, further purifying and reducing
its corrosivity.
4. Boiler operation
The boiler is a rectangular furnace. Its walls are made of a web of
high pressure steel tubes. Fuel is blown into the furnace from fuel
nozzles at the corners and it rapidly combusts, forming a large
fireball at the center. This heats the water that circulates through the
boiler tubes. The water circulation rate in the boiler is three to four
times the throughput, and is typically driven by pumps. As the water
in the boiler circulates, it absorbs heat and changes into steam at
700 °F (370 °C) and 3200 psi (22.1 MPa), which is separated from the
water inside a drum at the top of the furnace. The saturated steam is
introduced into superheat pendant tubes hanging in the hottest part
of the combustion gasses as they exit the furnace. Here the steam is
superheated to 1000 °F (540 °C) to prepare it for the turbine.
5. Steam turbine generator
The turbine generator consists of a steam turbine connected to a
generator on a common shaft. As steam moves through the system
and drops in pressure, it expands in volume, moving blades in
turbine to extract the energy. In operation, the superheated steam
from the boiler passes through feeder pipes down to the high
pressure turbine, where it falls in pressure to 600 psi (4 MPa) and
600 °F (315 °C), exits through cold reheat lines and passes back up

into the boiler where the steam is reheated in special reheat
pendant tubes back to 1000 °F (540 °C).
The generator contains a stationary stator and a spinning rotor, each
containing heavy copper conductor— no permanent magnets here.
The electricity produces flows to a distribution yard, where
transformers step the voltage up to requirements as needed for
transmission to its destination.
6. Steam condensing
The exhaust steam from the turbines contacts condenser tube
bundles which have cooling water circulating through them.
Typically, the cooling water causes the steam to condense at a
temperature of about 90–100 °F (32–38 °C) and that creates an
absolute pressure in the condenser of about 1.5–2.0 in Hg (5–7 kPa),
which is a vacuum of about 28 in Hg (95 kPa) below atmospheric
pressure. The condenser in effect creates the low pressure required
to increase the efficiency of the turbines. From the bottom of the
condenser, powerful pumps recycle the condensed steam back to
the feedwater heaters for reuse.
7. Stack gas path and cleanup
As the combustion gas exits the boiler it is routed through a rotating
flat basket of metal mesh which picks up heat and returns it to
incoming fresh air as the basket rotates, This is called the air
preheater. The gas exiting the boiler is laden with fly ash, which are
tiny spherical ash particles. The fly ash is removed by fabric bag
filters or electrostatic precipitators. Shree Power has also installed

two RO (Reverse Osmoises) units to conserve water because of the
scarcity of water in the region.
Pet Coke Fired Thermal Power Plant
MINING
The raw materials used in cement manufacturing are extracted from
the earth through mining and quarrying and can be divided into the
following groups: lime (calcareous), silica (siliceous), alumina
(argillaceous), and iron (ferriferous). Since a form of calcium
carbonate, usually limestone is the predominant raw material, Shree
Cement plants are situated near a limestone quarry fields. This is
because the plant must minimize the transportation cost since one
third of the limestone is converted to CO2 during the pyroprocessing
and is subsequently lost. Quarry operations consist of drilling,
blasting, excavating, handling, loading, hauling, crushing, screening,
stockpiling, and storing.

Shree Cements has leased two mines one at Beawer and other at Ras
with reserves that will last for a long time. The Raas mines give a
limestone of very good quality which is easier to process and gives
better overall quality of cement which is comparable with the best.
Information Technology
Shree Cements has developed an in house ERP system which has
integrated various departments with the InfoTech Department. The
system runs on Microsoft Windows platforms with IBM servers and
Oracle is used as a database.
In the future Shree Cements is looking for implementing ERP from a
worldwide vendor which will give it more flexibility and compatibility
with the outside environment. Because at present all departments
use similar platforms Shree Cements will not find shifting to ERP as
difficult as in case of standalone departmental systems. Shree
Cements is looking at SAP and ORACLE as probable ERP system
vendors. They expect that ERP from these vendors would need to be
customized to 50-60% in order to meet Shree Cements
requirements.
Introduction to compressor and its use in cement
plant.

Air compressor is a device that is used to increase the pressure of air (air at a
high pressure than atmospheric pressure). We classify the compressor as
1:- Positive-displacement compressor: - This type of compressors increases
the pressure of air by decreasing its volume. Under this type of compressors
we have
1)-Reciprocating compressors
2)-Rotary compressors
2:-Non-Positive displacement or Dynamic compressor: -This type of
compressors increases the pressure of a air by first increasing its speed and
then it stops it to increase its pressure. Under this type we have
1)-Centrifugal compressors
2)-Axial compressors
In our company we are using reciprocating and rotary compressors,
therefore we are discussing only about them.
Reciprocating compressor: - In reciprocating compressors we use pistons
driven by crankshaft to compress air. There are two types of reciprocating
compressors we use.
1) Single-acting: - When compressor uses only its circular plane surface of
piston to compress air. The compressor is called single acting
compressor.
2) Double acting: - When compressor uses both of its circular plane surfaces
of piston to compress air than compressor is called double acting
compressor.
To understand the difference physically we can look at the diagrams given
below.

Fig. 1 Single acting compressor mechanism
Fig. 2 Double acting compressor mechanism
Except these two types there is another type of reciprocating
compressor called Diaphragm compressor in which we use a flexible
membrane to compress air. But this type of compressor is used in compression
of toxic airs and we are using compressed air in our plant. Hence, we are not
discussing about them.
Now, we discuss about Rotary screw compressors we are using.
Rotary screw compressor: - This compressor use two meshed rotating positive
displacement helical screws to force the air in to smaller spaces. The
compression process in rotary screw compressor occurs in three dimensions
therefore it is difficult to show it in two dimensions. However we can look at its

common terminologies and also we can look at how a screw compressor looks
practically in diagram and picture given below.
Fig. 3 Common terminologies
Fig. 4 Practical look of screws inside the compressor

Fig.5 Pictures of screws and its compressing action.
• Compressed Air Demand in Shree Cement Ltd.
a) Low Pressure with high volume- For material conveying like
1.Filler transport for Cement Mill by FK Pump .
2.Coal Transport by FK Pump for Calciner firing
3.For burner pipe in Unit II
4.Bulker Unloading at cement mill(Fly Ash)

b) Normal Pressure compressed air
1.For instrumentation
2.For bag filter
3.For blasters and other pneumatic operated equipments
• Advantages of piston type compressor
1. Piston type compressors are available in wide range of capacity and
pressure
2. Very high air pressure (250 bar) and air volume flow rate is possible
with multi-staging.
3. Better mechanical balancing is possible by multistage compressor by
proper cylinder arrangement.
4. High overall efficiency compared to other compressor
• Disadvantages of piston type compressor
1. Reciprocating piston compressors generate inertia forces that shake
the machine. Therefore , a rigid frame, fixed to solid foundation is often
required
2. Reciprocating piston machines deliver a pulsating flow of air. Properly
sized pulsation damping chambers or receiver tanks are required.
3. They are suited for small volumes of air at high pressures.
Now, we will discuss about the function and thermodynamics of
reciprocating and rotary screw compressor. The thermodynamic cycle (P-V
diagram of compression cycle) occurring in reciprocating compressor is shown
schematically in its indicator diagram below. Area under this P-V curve will
provide us the net work input required. In this diagram we can clearly see that
minimum work input is required when the compression process is isothermal
and maximum when compression process is adiabatic. However both of them
are not possible in real life. Actual real life process is polytropic in nature.

Fig. 6 Compressor indicator diagram
For the reciprocating compressor compression occurs in following
steps.
Step 1:- As the compressor starts, piston starts from its TDS (top dead centre)
and starts sucking atmospheric air through suction valves.
Step 2:- Piston moves up to BDS (bottom dead centre) and now the piston is
full with air at atmospheric pressure.
Step 3:- Now the piston starts moving towards TDS and compresses the air in
the cylinder. Compression process may be adiabatic, isothermal or polytropic.
All of them are shown on the indicator diagram.
Step 4:- As the air volume is reduced its pressure increases and when the air
reaches up to the required pressure delivery valves opens and compressed air
is delivered.
In the indicator diagram P1=P4 is the intake pressure of air which is
normally equals to atmospheric pressure and V1 is the total volume of the
cylinder. P3=P2 is the supplied air pressure, V2 is the reduced volume of air in
the piston and V3 is clearance volume. Clearance is provided to avoid the
hitting of cylinder by the piston in the case of compressor we call it as Bumping
Clearance. After delivery process a little volume of compressed air is left in the

clearance volume. This air will expand as the piston moves towards BDS. Now,
the suction starts when this expanding air reaches the pressure equals to
atmospheric pressure or intake pressure. Therefore FAD (Free Air Delivery) of
the compressor per cycle is given by
FAD/Cycle= V1-V4
To look clearly at the terminologies look at the diagram shown below.
Fig. 6 Piston cylinder terminologies, suction and compression stroke
In the part B of above diagram you can see the air trapped in clearance
volume expanding.
Volumetric efficiency is defined as
The indicated work done per cycle for the polytropic exponent is given by

For we will get the work done when compression process is
adiabatic and for we will get work done for polytropic process.
When the process is isothermal ( ) work done is given by the equation
`
For the calculation of indicated, adiabatic and isothermal power we multiply
this work done by the frequency of the crankshaft. Power is defined by the
type of compression process. For example if the compression is adiabatic the
power we get is called adiabatic power. Similarly we can get indicative and
isothermal power. Now, we define the types of efficiencies commonly used.
1)-Adiabatic efficiency is defined as ratio of adiabatic power and actual power.
2)-Isothermal efficiency is defined as the ratio of isothermal power to the
actual power required
3)-Mechanical efficiency is defined as ratio of actual power to shaft power
4)-Indicative efficiency is defined as the ratio of indicative power (Power
required in actual polytropic process) to the actual power consumed.
Now, the things which have a physical significance are the volumetric
efficiency, indicative efficiency and FAD. Therefore we will calculate them using
our formulas.
Above calculations are only for a single stage compressor. We also
have 2-stage compressors in our compressor house units. In a multistage

compressor pressure is increased using same cycle but in a number of stages.
We have 2 stage compressors therefore we will discuss about them. First we
increase the pressure of air up to intermediate pressure in one cycle and then
than in another cycle we increase the pressure up to desired pressure. We can
look at the block diagram to get a physical look at the double stage
compressor. This staging of compressor affects its efficiency in a way. We will
discuss this later in this report.
In the case of screw compressor thermodynamics is not so complicated.
Indicator diagram of a screw compressor is given below.
Fig.7 Indicator diagram of screw compressor
At the beginning of the process the suction pressure fills the flute spaces as
the rotors unmesh. Air continues to fill, until the trailing lob crosses the inlet
port. At this point air is trapped in the flute space. This volume of air is defined
as inlet volume. On the underside of the rotary screw compressor, rotors begin
to mesh this meshing causes the compression of air. To get physical look at the
Fig.5 and Fig.4 . Air starts to discharge from the discharge port when air
reaches the desired pressure. The final volume of air after compression is
called discharge volume. Theoretically the volumetric efficiency of a screw

compressor is 100% because there is no clearance but there is no air tight seal
between rotors and the housing. This causes leakage between flutes and
lowers the volumetric efficiency. Leakage is a function of compressor tip speed
and pressure difference, and decrease the inlet volume up to 90% from 100%.
In screw compressor there are two important terminologies called volume
ratio and pressure ratio. We define the volume ratio by the equation
In the similar way we define the pressure ratio. Both of them are related
to each other by the equation
A compressor with fixed volume ratio will develop the same internal
pressure, regardless of the line pressure. Compressors that have an axial port
have a fixed volume ratio. Other compressors have changeable volume ratio by
removing a slide valve (that contain radial discharge port), and replacing it with
a slide valve that has a different sized radial port. Others can vary the volume
ratio while the compressor is in operation. Volume ratio can be changed by
changing the size or location of the discharge port. A smaller discharge port
will increase the volume ratio by holding the air inside for a longer time than
larger discharge port. Longer the air is held inside, more rotation will be there
and air is released at higher pressure.
Fig.8 Axial port and different volume ratio radial discharge port
Till now we have discussed about the single stage compressors. We
are using Double-Stage compressors in our plant. Therefore, we should know

about multistage compressors and how it consumes less energy than a single
stage compressor.
Block diagram of a Double-stage compressor
In a Double-Stage compressor we compress the air up to
intermediate pressure and then in the second stage up to final pressure
required. We use heat exchanger in between two stages to reduce the volume
of the air. This reduction in volume minimize the input work require. To see
this effect we can look at the indicator diagram given below.
Fig.9 Double stage compressor indicator diagram compared with single
stage.
In this diagram 3 bars is intermediate pressure and 8 bars is final pressure
and shaded area is the work saved by the heat exchanger. As the no of stages

increased, work done saved will be more. Indicator diagram of a multistage
compressor compared with a single stage compressor is given below.
Fig.10 Indicator diagram of a multistage compressor
Factors affecting efficiency: - Now we will discuss about the factors that
affects the efficiency of a compressor. There are two types of factors that
affect the efficiency of compressor.
External factors: - These factors are
1)-Intake air: - For getting the high efficiency out of compressor intake air
should be cool and clean as possible. Air temperature is very critical in
compressor efficiency. Every 3 degree decrease in intake air temperature can
increase the compressor efficiency by 1%. Contaminated air contains dust
particles these particles can erode the compressor parts and also the
equipments using the compressed air. These particles are solid in nature
therefore their volume is not reduced with the air compression and their
concentration increases with air compression. Therefore, they also reduce the
volumetric efficiency of compressor effectively.
2)-Cooling water: - It is used in heat exchangers and cooling jackets of piston.
Water used for cooling purpose should be as clean as possible. If the water is
not clean enough it can erode heat exchanger and hardness of water can cause
calcium carbonate precipitation on heat exchanger tubes.
Internal factors: -These are

1)-Suction filter: -Suction filter should be clean and effective. Otherwise it will
cause pressure drop in the line or it may pass small dust particles. This can
erode compressor parts and can increase the required power.
2)-Suction and delivery valves: -Suction valves should be able to provide
sufficient area for the passage air. Small area decreases the FAD of the
compressor. It should be cleaned properly and regularly. Rust and other
deposition on it can cause drag to the intake air which lead to increase in load
on compressor. In compressor suction valves are spring operated. The actual
opening area is not same as expected. Losses occur due to this bounce in the
valve is called valve losses.
Fig.11 Valve losses
There valve plates should be strong enough to bear the vibration occurring
during suction and high pressure of compressed air. Since the temperature of
air increases very high after compression its material should be temperature
resistance. Valves should be leakage free. They should be corrosion resistance
and design should be such that they should provide minimum drag to the air
and keep the flow laminar. Leakage in valves can cause pressure loss and
reduce FAD.
3)-Piston rings: -Piston rings should be leakage free. Leakage in piston rings can
cause pressure losses. There should be minimum friction losses between
cylinder and piston rings.
4)-Inter-coolers and after-coolers: -Effectiveness of the heat exchangers should
be high. High effectiveness lead to minimum water flow rate required and

hence, minimum pumping power will be there. Pressure drop should be
minimum across the inter-coolers and after-coolers. Tubes should be smooth
for minimum drag force to air and thickness should be minimum to get
maximum effectiveness possible. Tube material should have high thermal
conductivity. According to energy efficiency standards a decrease in
temperature of 5 degrees in inlet of 2nd
stage can increase the efficiency by 2%.
This shows the importance of intercooler.
5)-Air line filter (oil separators): -These filters are necessary for lubricating
compressors as oil in the compressed air combine with the dust particles and
water to form amalgam which is a thick viscous matter and can stuck up in
airline and pneumatic system and instrumentation.
6)-Air dryer: -After compression the concentration of water vapour increases.
This raises due point of the compressed air relative to the atmosphere and
leads to condensation within the pipes as the compressed air cools
downstream of the compressor.
Excessive water in compressed air can cause
1-corrosion
2-fouling of process and products
3-freezing of outdoor air lines
7)-Internal compression ratio in screw compressor: -To get the maximum
efficiency out of screw compressor the internal compression ratio of the
compressor should match with the system compression ratio. Otherwise, over
compression or under compression occur. The effect of both of them can be
seen in diagram given below.

Fig.12 Over compression and under compression P-V diagram
In over-compression air is compressed more than the system requirement and
then expands down to system pressure after discharge. Extra work is required
to compress the air up to internal discharge pressure than the system
pressure. Under-compression occurs when the internal discharge pressure of
compressor is lower than the system pressure. This causes the air to flow back
in to the flute and more work is required to compress the same air twice.
“Over compression is less efficient than the under-compression because in
over-compression extra work is done on the entire air stream wile in under-
compression extra work is done only on the air which backflows in to the
flutes.”
8)-Oil system in screw compressor: -Oil lubricates, seal and absorbs the heat of
compression during the compression process. Hence it improves the efficiency
as compared to non-lubricated compressors. Oil comes directly in contact with
air. This makes oil selection an important issue.
9)-Intermediate pressure: -By calculations it can be shown that for minimum
work input intermediate pressure should be square root of the product of
intake pressure and discharge pressure. For this report we are omitting these
theoretical calculations.

10)-Supply pipeline: -There should be no sudden bends in the distribution
system. Sudden change in cross section area of pipeline should be avoided. All
bends should be circular in nature and radius should be as large as possible.
Also area of the pipeline should be sufficient for a given flow rate so that no
pressure drop occurs. According to industrial standards maximum pressure
drop that is allowed from the production point to usage point is 0.5kg/cm2.
Above mentioned specifications for the pipeline can be easily seen from
the Darcy-Weisbach equation given below.
Using this head loss we can calculate pressure drop. Friction factor in the
above equation is called Darcy friction factor. This friction factor is calculated
using Moody chart. For the case of Butterfly valves and bends in the path.
Head loss is calculated differently. For the case of bends and valves we use
h=K*(v^2/2g)
K=f*(L/D)
In case of valves and bends “f” is for the fully turbulent flow. Therefore we
combine it with length and diameter. Value of “K” is experimental.
11)-Compressor RPM: -Compressor rpm is important factor for the
improvement in efficiency. “Lower the rpm of compressor higher will be the
efficiency of compressor”. Therefore, compressor speed plays an important
role in optimizing the efficiency.
12)-Output pressure: -Output pressure should be optimized according to need.
The energy requirement rises as square reciprocating function of the final
pressure i.e. more energy is required in increasing the pressure from 7 bar to 8
bar than 6 bar to 7 bar.

13)-Altitude (Elevation): -Altitude has a direct impact on the efficiency of the
compressor. Higher the altitude lower will be the efficiency of the compressor.
A table is given below data given by Confederation of Indian Industries.
Fig.13 Compressor efficiency at various altitudes
Above are the man important factors that affect the efficiency of
compressor in industry. Now we will discuss about our present system in Shree
Cement Plant in Beawar.
Types of compressed air bands and there uses in our unit
We have two types of bands in our compressor house units that are
1)-Low pressure band -up to 2.5 kg
-In material conveying equipments (pneumatically operated). In these
types of equipments we have F. K pumps.
2)-Medium pressure band -up to 7kg

-90% to 80% is used in pollution control devices. In pollution control
devices we have bag filters.
-Instrumentation devices operated by pneumatic system. In these devices
we have
1- Solenoid valve.
2- Pneumatic cylinders.
3- Actuators.
4- Girth gear spray system for kiln and cement mill.
The Specifications of the compressors in our compressor house units is given
below in the table.
Now for our calculation purpose we will calculate the FAD, Volumetric
efficiency, Isothermal Efficiency and Adiabatic efficiency of compressor no 9.
Since the compressor no 9, 10, 12 are of same type and specification
theoretically calculated
Above is a indicator diagram of 2 stage compressor

P1, V1-Pressure and volume at point 1
P2, V2-Pressure and volume at point 2
P3, V3- Pressure and volume at point 3
P4, V4-Pressure and volume at point 4
P1||, V1||-Pressure and volume at point 1||
P2||, V2||-Pressure and volume at point 2||
P3||, V3||-Pressure and volume at point 3||
P4||, V4||-Pressure and volume at point 4||
Now,
RPM of the compressor is =736
Experimental value of FAD is=32 m^3/min
Running KW of compressor=168
L.P cylinder bore=47 cm
H.P cylinder bore=28 cm
Bumping clearance=1.8 mm
V1=Cylinder volume of Low Pressure side, P1=Atmospheric pressure
V3=Clearance volume of Low Pressure side
V1||=Cylinder volume of High Pressure side, P1||=Intermediate pressure
V3||=Clearance volume of High Pressure side
Assuming all the compression and expansion process as polytropic in nature,
n=1
P1=P4=1.033kg/cm^2, V1=35025.27cm^3
 V2=(P1*(V1^n)/P2)^(1/n)

After putting these values we get V2=22049.8 cm^3
Similarly we calculate
V4=(P3*(V3^n)/P4)^(1/n)= 496.2605cm^3
Using the same technique we calculated the V2||, V4|| for high pressure
side,
we have
V1||=12430.88 cm^3, V3||=110.88 cm^3
P1||=P4||=1.8 kg/cm^2, P2||=P3||=6kg/cm^2
We get
V2||=4557.95kg/cm^3
V4||=302.4026cm^3
Work done is calculated of each cycle using the formula
Work done for the Low pressure and high pressure cycles are
W1-L.P-indi=2.075296 KJ
W2-L.P-indi=2.910698 KJ
Since our compressor is double acting compressor we have our total work
done require is
W-ind=2*(W1-L.P-indi+ W2-L.P-indi) =9.972 KJ/cycle
=>Total indicative power required is
P-indi= (W-indi)*(736/60) =122.323 KW
Our compressor is double acting therefore

FAD= 2*(V1-V4)*736= 50.82671 m^3/min
Theoretically expected FAD=2*(V1-V3)*736=51.09733 m^3/min
For adiabatic compression process work input we put n=1.4 and recalculate
the quantities
V2, V4, V2||, V4|| and they came out
V2=23556.77 cm^3, V4=464.513 cm^3, V2||=5260.39 cm^3, V4||
=262.022 cm^3
Adiabatic work input required will be
W-adi=10.59213 KJ/cycle
Adiabatic power will be
P-adi=W-adi*736/60=129.9302 KW
For isothermal compression work calculation we have n=1and area under
P-V curve is given by
Again we calculate V2, V4, V2||, V4|| and they came out
V2=20100.61 cm^3, V4=464.5139 cm^3, V2||=3729.264 cm^3
V4||=369.6 cm^3
Isothermal work required will be
W-iso= 9.1836 KJ/cycle
P-iso=W-iso*736/60=112.6235 KW
Now,
Theoretically expected Volumetric efficiency is= (50.82671/51.09733)*100
=99.47%

Actual Volumetric efficiency= (32/51.09733)*100=62.62%
Adiabatic efficiency= (129.9302/168)*100=77.3393%
Isothermal efficiency= (112.6532/168)*100=67.05545%
• Compressed Air Demand in Shree Cement Ltd.
a) Low Pressure with high volume- For material conveying like
1.Filler transport for Cement Mill by FK Pump .
2.Coal Transport by FK Pump for Calciner firing
3.For burner pipe in Unit II
4.Bulker Unloading at cement mill(Fly Ash)
b) Normal Pressure compressed air
1.For instrumentation
2.For bag filter
3.For blasters and other pneumatic operated equipments
Compare various types of compressors

So centrifugal compressor is better than the reciprocating compressor
Suggestions for improvement
For improvement in compressor we have taken in to account all the
factors that affect compressor efficiency. Considering those factors I have tried
my best to study the products available in market and also I have tried to
optimize the system as much as possible.
1-Hard water treatment: -Water available in our plant is extremely hard. Due
to high hardness there is scale deposition on heat exchanger tubes of our
compressor units. This scale deposition reduces the heat transfer rate
significantly and also scale deposition make the water supply pipeline rough.
Hence, it increases the required pumping power also.
The most common way to soften water is through an ion exchange water
softener. This system works by exchanging positively charged hardness
minerals (calcium and magnesium) with positively charged softness minerals
(sodium or potassium) on a resin surface that is regenerated. This exchange of
minerals softens the water and can extend the life of plumbing systems since
there is reduced clogging in the pipes.

There are currently three basic types of ion transfer softeners. The first is an
automatic softener. This type of softener is connected to a clock timer which at
certain time intervals begins the regeneration process by flushing out the hard
ions stuck to the resin and replacing them with the soft ions. This then allows
for a continuous exchange of hard and soft ions throughout the day. The
second type of softener is the demand initiated regeneration (DIR). With this
system, regeneration occurs only when soft water has run out. Since this
system adjusts to the amount of water used as opposed to the automatic type,
it uses less salt and water and is more efficient. The final softener is a portable
exchange. Here a tank is rented to the homeowner and has a regenerated
resin. When the resin can no longer exchange ions, the tank is returned to the
company and regenerated there .
2-PEEK (Poly Ether Ketone) valve plates(reticular valve plates): -The purpose
of the valves in a reciprocating compressor is to let air in and out of the
cylinder during the compression process. The key to long valve life is to have
positive action of the sealing components with minimum resistance.
Compressor valves serves as check valves for the inlet and discharge passages
of the cylinder and will open and close once for every revolution of the
crankshaft. If the compressor is running at 500 rpm for 24 hours a day, the
valves will open and close 720,000 times every day. With high temperature
PEEK polymer plates installed both seat wear and valve noise is reduced.
(Lower valve plate weight results in reduced valve plate momentum hence less
wear.) .It withstands impacts better than steel and does not damage the
compressor if the sealing element breaks.

Material: 3cr13, PEEK, 45#steel.
Function: Used in compressor air valve, play a sealing role in compressor air
valve. PEEK is the special high temperature thermoplastic polymer, as it a high
temperature, corrosion resistance, chemical resistance, abrasion resistance,
and other characteristics, has become a leading many high-tech field of key
materials.
First, the main properties
Melting point: 334o
C
Tensile strength: 97.38MPa
Bending strength: 134MPa
Second, the main properties
1: - Heat resistance, long-term continuous use temperature of the evaluation
method, the UL temperature index valve of 250℃
2: - Chemical resistance, PEEK only dissolved in concentrated sulphuric acid,
a good chemical resistance.
Energy Saving in Compressed air system.
Benefits of managed system
• Electricity savings: 20 –
50%
• Maintenance reduced,
downtime decreased,
production increased and
product quality improved

Installing VFD for saving electrical energy .
i. Variable frequency drive (VFD) can be installed with the compressor to
follow load with high accuracy, achieving the highest part load efficiency
available VFD compressors are most appropriate in systems in which the
compressor runs for long periods at partial load as the present case in
the plant.
ii. By providing VFD in compressor control we can vary the Compressor
RPM depending on requirement. This completely avoids unloading and
saves unload power consumption.
Saving calculation of VFD
The most important thing is that the power wasted in unloading will be saved.
An average of 17% power will be saved.
Cost of installation of VFD for 75kW motor is approx. 2.25 lakhs
Cost of installation of VFD for 200kW motor is approx. 6 lakhs.
• Amount saved/year for comp 7 = 9.73kW*330days*16hrs*3.5 Rs/kWh =
Rs 1,72,788/-
Payback period = LESS THEN 2 YEAR.
At compressor no 8 , VFD installed but still not in working condition
Compressor 7 is similar to comp 8 so here VFD can be installed
Amount saved/year for comp 9 = 34kW*330days*16hrs*3.5 Rs/kWh = Rs
6,28,320/-
Payback period = LESS THEN 1 YEAR.

The benefits of this technology include:
1. Reducing power cost.
2. Reducing power surges (from starting AC motors)
3. and delivering a more constant pressure.
4. VFDs reduce thermal and mechanical stresses on motors and belts.
5. VFDs provide the most energy efficient means of capacity control.
6. VFDs have the lowest starting current of any starter type.
7. VFD installation is as simple as connecting the power supply to the VFD.
8. VFDs provide high power factor, eliminating the need for external
power factor correction capacitors.
9. Your equipment will last longer and will have less downtime due to
maintenance when it’s controlled by VFDs ensuring optimal motor
application speed.
Compressor controls
Air compressors become inefficient when they are operated at significantly
below their rated CFM output. To avoid running extra air compressors when
they are not needed, a controller can be installed to automatically turn
compressors on and off, based on demand. Also, if the pressure of the
compressed air system is kept as low as possible, efficiency improves and air
leaks are reduced.

Energy savings by using a high-efficiency motor
A high-efficiency motor (HEM) uses low-loss materials to
reduce core, and copper, losses. Design changes, better materials,
and manufacturing improvements, reduce motor losses, making
premium, or energy-efficient, motors, more efficient than standard
motors are. Reduced losses mean that an energy-efficient motor
produces a given amount of work with less energy input than that
required by a standard motor
Several leading electric-motor manufacturers, mainly in USA
and Europe, have developed product lines of energy-efficient
electric motors that are 2–8% more efficient than the standard
motors are Electric motors cannot convert into mechanical
energy completely, the electrical energy they take. The ratio of the
mechanical power supplied by the motor to the electrical power
used during operation is the motor’s efficiency. High-efficiency
motors cost less to operate than do their standard counterparts.
Motor efficiencies range from about 70 to over 96% at full-load
rated power

Air Intake
• The effect of intake air on compressor performance should not be
underestimated.
• Intake air that is contaminated or hot can impair compressor
performance and result in excess energy and maintenance costs. If
moisture, dust, or other contaminants are present in the intake air.
These contaminants can build up on the internal components of the
compressor.
• The compressor generates heat due to its continuous operation. This
heat gets dissipated to compressor chamber and leads to hot air intake.
This results in lower volumetric efficiency and higher power
consumption. As a general rule, “Every 40C rise in inlet air temperature
results in a higher energy consumption by 1 percent to achieve
equivalent output”. Hence cool air intake improves the energy efficiency
of a compressor.
• When an intake air filter is located at the compressor, the ambient
temperature should be kept to a minimum, to prevent reduction in mass
flow. This can be accomplished by locating the inlet pipe outside the
room or building. When the intake air filter is located outside the
building, and particularly on a roof, ambient considerations may be
taken into account.
For reducing ambient air temperature
• Install Ventilation and centralization cooling System at both Compressor
Houses
• Remove Halogen bulbs from compressor house in unit 2
• For circulation of fresh air inside the houses and fresh cool air is
available for suction for compressors

inter/after cooler
As the air is compressed, the temperature of the air increases. Therefore
the air needs to be cooled. This is done by using a cooler. It is a type of
heat exchanger. There are two types of coolers commonly employed viz.
air cooled and water cooled. In the air cooled type, ambient air is used
to cool the high temperature compressed air, whereas in the water
cooled type, water is used as cooling medium. These are counter flow
type coolers where the cooling medium flows in the direction opposite
to the compressed air. During cooling, the water vapor present will
condense which can be drained away later.
 Shell and Tube Heat Exchanger with Helical Baffles (STHXHB).
1. 1.It has been observed that shell-and-tube heat exchangers with
segmental baffles STHXHB have higher total heat transfer rates
and lower pressure drops when compared to STHX for the same
flow rate and inlet condition. STHXHB with helix angle 40 Deg.
shows best performance.
2. 2.Use of helical baffles in a heat exchanger reduces the shell side
pressure drop, size weight fouling etc., as compared to segmental
baffles.
3. 3.The temperature of inlet air at 2nd
stage and final discharge
outlet will be lowered to greater extent and this will definitely
increase the efficiency of the compressors. Which will result in
power saving.

Using nano fiuid as coolant liquid instant of water

Nanofluids are a new class of fluids engineered by dispersing
nanometer-sized materials (nanoparticles, nanofibers,
nanotubes, nanowires, nanorods, nanosheet, or droplets)
in base fluids. In other words, nanofluids are nanoscale
colloidal suspensions containing condensed nanomaterials.
They are two-phase systems with one phase (solid phase)
in another (liquid phase). Nanofluids have been found to
possess enhanced thermophysical properties such as thermal
conductivity, thermal diffusivity, viscosity, and convective
heat transfer coefficients compared to those of base fluids like
oil or water.
Nano fluid Advantages
Improved heat transfer Suspending nanoparticles in a base fluid, can improve
heat-transferring rate, the main reasons behind this thermal conductivity
improvement are
1. The large surface area of Nano particles that allows more heat transfer;
particles finer than 20nm carry 20% of their atoms on their surface,
making them instantaneously available for thermal interaction
2. The suspended nanoparticles that increase the effective (or apparent)
thermal conductivity of the fluid. This can be approximately15–70%
thermal conductivity increment can be achieved depending on the
volume fraction of nanoparticle
3. The mobility of the tiny sized particles that bring sab out micro
convection of fluids and hence increases the rate of heat transfer
through improving its convection factor
4. The intensified interaction and collision among particles (Brownian
motion), fluid and the flow passage surface
5. The intensified mixing fluctuation and turbulence of the fluid and
_flattened temperature gradient across the fluid due to the dispersion of
nano particles
The benefit of enhanced thermal conductivity of Nano fluids can be also
captured by reducing the pumping power of the air in compressor system .

Leaks in Compressed Air System:
Leaks can be a significant source of wasted energy in an industrial compressed
air system, sometimes wasting 20 to 30 percent of a compressor’s output. In
addition to being a source of wasted energy, leaks can also contribute to other
operating losses. Leaks cause a drop in system pressure, which can make air
tools function less efficiently, adversely affecting production. In addition, by
forcing the equipment to run longer, leaks shorten the life of almost all system
equipment (including the compressor package itself).
Increased running time can also lead to additional maintenance requirements
and increased unscheduled downtime. Finally, leaks can lead to adding
unnecessary compressor capacity. While leakage can come from any part of
the system, the most common problem areas are:
• Couplings, hoses, tubes, and fittings
• Pressure regulators
• Open condensate traps and shut-off valves

• Pipe joints, disconnects, and thread sealants.
Estimation of leakages:-
For compressors like that in Shree Power having load/unload controls, there is
an easy way to estimate the amount of leakage in the system. This method
involves starting the compressor when there are no demands on the system
(when all the air-operated, end-use equipment is turned off). A number of
measurements are taken to determine the average time it takes to load and
unload the compressor. The compressor will load and unload because the air
leaks will cause the compressor to cycle on and off as the pressure drops from
air escaping through the leaks. Total leakage (percentage) can be calculated as
follows:
Leakage (%) = [(T x 100)/(T+t)]
where: T = on-load time (minutes)
t = off-load time (minutes)
It is recommended that regular estimation of such leaks be undertaken at
Shree cement
Leak Detection
Since air leaks are almost impossible to see, other methods must be used to
locate them. The best way to detect leaks is to use an ultrasonic acoustic
detector, which can recognize the high-frequency hissing sounds associated
with air leaks. These portable units consist of directional microphones,
amplifiers, and audio filters, and usually have either visual indicators or
earphones to detect leaks.

Ultrasonic Leak Detection:
Ultrasonic leak detection is probably the most versatile form of leak detection.
Because of its capabilities, it is readily adapted to a variety of leak detection
situations. The principle behind ultrasonic leak detection is simple. In a
pressure or vacuum leak, the leak flows from a high-pressure laminar flow to a
low-pressure turbulence. The turbulence generates a white noise which
contains a broad spectrum of sound ranging from audible to inaudible
frequencies. An ultrasonic sensor focuses in on the ultrasonic elements in the
noise. Because ultrasound is a short wave signal, the sound level will be
loudest at the leak site. Ultrasonic detectors are generally unaffected by
background noises in the audible range because these signals are filtered out.
Ultrasonic detectors can find mid to large-sized leaks. The advantages of
ultrasonic leak detection include versatility, speed, ease of use, the ability to
perform tests while equipment is running, and the ability to find a wide variety
of leaks. They require a minimum of training, and operators often become
competent after 15 minutes of training.
Because of its nature, ultrasound is directional in transmission. For this reason,
the signal is loudest at its source. By generally scanning around a test area, it is

possible to very quickly hone it on a leak site and pin point its location. For this
reason, ultrasonic leak detection is not only fast, it is also very accurate.
How to Fix Leaks
Leaks occur most often at joints and connections. Stopping leaks can be as
simple as tightening a connection or as complex as replacing faulty equipment,
such as couplings, fittings, pipe sections, hoses, joints, drains, and traps. In
many cases, leaks are caused by failing to clean the threads or by bad or
improperly applied thread sealant. Select high quality fittings, disconnects,
hose, tubing, and install them properly with appropriate thread sealant.
Pressure Settings
For the same capacity, a compressor consumes more power at higher
pressures. Subsequently, compressors should not be operated above their
optimum operating pressures as this not only wastes energy, but also leads to
excessive wear, leading to further energy wastage. The volumetric efficiency of
a compressor is also less at higher delivery pressures.
Reducing delivery pressure
The possibility of lowering and optimizing the delivery pressure settings should
be explored by a careful study of pressure requirements. The operating of a
compressed air system gently affects the cost of compressed air. Operating a
compressor at 120 PSIG instead of 100 PSIG, for instance, requires 10 per cent
more energy as well as increasing the leakage rate. Therefore, every effort
should be made to reduce the system and compressor pressure to the lowest
possible setting.
Compressor modulation by optimum pressure settings
Very often in an industry, different types, capacities and makes of compressors
are connected to a common distribution network. In such situations, proper
selection of a right combination of compressors and optimal modulation of
different compressors can conserve energy. For example, where more than

one compressor feeds a common header, compressors have to be operated in
such a way that the cost of compressed air generation is minimal.
Segregating high/low pressure requirements
If the low-pressure air requirement is considerable, it is advisable to generate
low pressure and high-pressure air separately and feed to the respective
sections instead of reducing the pressure through pressure reducing valves,
which invariably waste energy.
Design for minimum pressure drop in the distribution line
Pressure drop is a term used to characterize the reduction in air pressure from
the compressor discharge to the actual point-of-use. Pressure drop occurs as
the compressed air travels through the treatment and distribution system.
A properly designed system should have a pressure loss of much less than
10per cent of the compressor’s discharge pressure, measured from the
receiver tank output to the point-of-use. The longer and smaller diameter the
pipe is, the higher the friction loss.
Pressure drops are caused by corrosion and the system components
themselves are important issues. Excess pressure drop due to inadequate pipe
sizing, choked filter elements, improperly sized couplings and hoses represent
energy wastage.
Pipe Nominal Bore(mm) Pressure drop(bar) per
100 meters
Equivalent power
losses(kW)
40
50
65
80
100
1.80
0.65
.22
.04
.02
9.5
3.4
1.2
0.2
0.1
Typical pressure drop in compressed air line for different pipe size
(Confederation of Indian Industries)
Controlled usage Since the compressed air system is already available, plant
engineers may be tempted to use compressed air to provide air for low-

pressure applications such as agitation, pneumatic conveying or combustion
air. Using a blower that is designed for lower pressure operation will cost only
a fraction of compressed air generation energy and cost. Note: in some
companies, staff uses compressed air to clean their clothes. Apart from the
energy wastage, this is a very dangerous practice.
Compressor controls
Air compressors become inefficient when they are operated at significantly
below their rated CFM output. To avoid running extra air compressors when
they are not needed, a controller can be installed to automatically turn
compressors on and off, based on demand. Also, if the pressure of the
compressed air system is kept as low as possible, efficiency improves and air
leaks are reduced.
Maintenance Practices
Good and proper maintenance practices will dramatically improve the
performance efficiency of a compressor system. Here are a few tips for
efficient operation and maintenance of industrial compressed air systems:
Lubrication: Compressor oil pressure should be visually checked daily, and the
oil filter changed monthly.
Air Filters: The inlet air filter can easily become clogged, particularly in dusty
environments. Filters should be checked and replaced regularly.
Condensate Traps: Many systems have condensate traps to gather flush
condensate from the system. Manual traps should be periodically opened and
re-closed to drain any accumulated fluid and automatic traps should be
checked to verify they are not leaking compressed air.
Air Dryers: Drying air is energy-intensive. For refrigerated dryers, inspect and
replace pre-filters regularly as these dryers often have small internal passages
that can become plugged with contaminants.

Centrifugal air compressor
•Replacement of multiple reciprocating compressors with one centrifugal air
compressor
• 4 # 1000 CFM Base Load & 1 # 1000 CFM trimming reciprocating air
compressors.
• Power consumption - 700 KW for 3500cfm @ 100psig
• Investment - Rs.90 to 100 lacks.
• Centrifugal air compressor - 560 kw
• Savings - 140x8000x4.5 = Rs 50,40,000/yr
• Payback period less than 2 years
• Replacement of multiple screw air compressors with one centrifugal air
compressor
• 2 #’s 900 cfm & 1 # 700 cfm Oil free screw air compressors.
• Power consumption - 500 kw for 2500cfm @ 100psig
• Investment - Rs.90 to 100 lakhs.
• Centrifugal air compressor - 400 kw
• Savings = Rs 44,00,000/yr
• Payback period less than 2 years.
Thank You