Transcript Boiler Operation

INSTRUCTOR:
ROBERT A. MCLAUGHLIN
ZAILI THEO ZHAO
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AIR COMPRESSORS & AIR
HANDLING SYSTEMS
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POWER
EQUIPMENT
LEARNING OBJECTIVES
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Understanding of compressed air systems and air
compressor types.
Discuss compressed air uses, volume, pressure, and
temperature relationship.
Discuss safety issues and hazards associated wit
compressed air.
Discuss heat removal and moisture removal
requirements for compressed air systems.
Examine and determine classifications of air
compressors.
Define pressure ratings and capacity determination
on reciprocating compressors.
Examine the compressor unloader system and
determine why it is needed and how it functions.
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AIR COMPRESSOR SYSTEMS
Compressed air has several applications on ships
and in power plants.
 Operation of pneumatic tools
 Pneumatic control
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Automatic control of machinery
Diesel engine start and control
 Compressed air is stored energy or potential
energy
 We do work (add energy) on air during the
compression process and store it for future use.

 Air
compression takes place in one of two
ways:
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ADIABATIC PROCESS
It is a thermodynamic
process in which there is no
transfer of heat to or from
the system during the
process.
When compressed
adiabatically, all the work
done on the air goes to
increase its internal energy.
 The air temperature still
increases, but there is little
time for heat transfer to
occur.
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ADIABATIC PROCESS
compression is
very difficult to achieve
 One of the closest
mechanical devices
capable of approaching
this is the gas turbine.
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 Adiabatic
The gas turbine compression
phase involves a constant flow
process at a rapid speed and
thus approaches adiabatic
compression.
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ISOTHERMALLY PROCESS
remains
constant throughout the
compression process.
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 Temperature
To achieve an isothermal
compression you must have an
external cooling medium.
 As the compressor gets bigger,
more cooling becomes necessary
and it gets to the points where it
is no longer practical to strive
for a isothermal compression.
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ISOTHERMALLY PROCESS
Compression inherently produces a large amount
of heat .
 Look at the pressure, volume, and temperature
relationship given by Boyle’s, Charles’ and the
ideal gas laws.
P1V1T2= P2V2T1
 Isothermal
compression
 Isobaric process
 Isometric process
 Adiabatic compression
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P1V1
P2V2

T1
T2
T=C
P1V1 = P2V2
P=C
V1T2 = V2T1
V=C
P1T2 = P2T1
No heat transform
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BOYLES LAW CALCULATION
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Question: 4 ft3 of Nitrogen @ 100 Pisg. If we
allow the Nitrogen to expand to 6 ft3 , what is the
new gage pressure reading?
 Answer:
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Convert gauge to absolute pressure
100 psig + 14.7 = 114.7 psia
Use the equation P1V1 = P2V2
4 ft3 × 114.7 psia = 6 ft3 × P2
P2 = 4 ft3 × 114.7 psia / 6 ft3
P2 = 76.46 psia = 61.76 psig
61.76 psig is the new gage pressure reading
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PRACTICE PROCESS
practice, a combination
of both is used for most of
the applications we would use.
Air is compressed nearly adiabatic within any one
stage, and isothermally when considered from start
to finish.
 To receive benefits of both, most compressors have
more then one stage, and have cooling arrangements
after both.
 Pre-coolers are used before entering the compressors,
inter-coolers are used between stages and aftercoolers are found after all stages of compression.
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COMPRESSOR CLASSIFICATIONS
Compressors are classified according to:
 How much pressure is produced
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Low Pressure :
0 - 150 psi
 Medium Pressure: 151 - 1000psi
 High pressureOver 1000 psi
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 The
type of compressing element.
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Centrifugal
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Rotary
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Reciprocating
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CENTRIFUGAL OR
KINETIC COMPRESSORS
Used for capacities greater than 10,000 CFM and
100 psi to 150 psi (low to medium pressure)
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It is a dynamic compressor which depends on
transfer of energy from a rotating impeller to the
air.
It produce high-pressure discharge by converting angular
momentum imparted by the rotating impeller.
 In order to do this efficiently, centrifugal compressors rotate
at higher speeds than the other types of compressors.
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They are also designed for higher capacity because
flow through the compressor is continuous.
 Capacity or compressor output is often regulated by
controlling air flow into the inlet eye of the impeller
or fan
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ROTARYPOSITIVE DISPLACEMENT
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Capacities up to 10,000 CFM and pressures 0-150 psi
(low to medium pressure
 Air enters a sealed chamber where it is trapped
between two contra-rotating rotors.
 As the rotors intermesh, they reduce the volume of
trapped air and deliver it compressed to the proper
pressure level.
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RECIPROCATING
POSITIVE DISPLACEMENT

Capacities below 1000 CFM and pressures above 100
psi (medium to high psi)
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COMPRESSOR CLASSIFICATIONS
Number of stages
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Single stage
Several stages
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Stages are in series, with one stage discharging to the next stage
For medium and high pressures
Sources of power
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Electric motor driven
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Most common for power plant and shipboard applications
Steam turbine
Gas turbine
Drive connections
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Reciprocating applications
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V-belt drive very common for small low and medium pressure.
Rotary compressors
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Direct drive
Driven through solid couplings
Driven through flexible couplings
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RECIPROCATING COMPRESSORS
MAJOR COMPONENTS
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Trunk type
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Driven directly by connecting rods, connecting the crankshaft
and the piston through the piston wrist pin.
Differential or piggy back type.
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Flywheels
 Crankshaft
 Connecting rods
 Pistons
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They are trunk type pistons with two or more diameters fitted
in specially designed cylinders. Each diameter is designed to
deliver different pressures, and would be used in multiple stage
systems.
In multiple stage systems, the pistons of each stage will be
smaller as the pressure increases; the low pressure piston
will the larger than the high pressure system.
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RECIPROCATING COMPRESSORS
MAJOR COMPONENTS
Valves
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Compressor valves are made of special spring steel
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Opening and closing of the valves is caused by the difference in
pressure between the air in the cylinder and atmospheric air.
The pressure of the discharge valve causes it to open on the
upward stroke of the piston.
The suction valve opens as the piston strokes downward,
creating a vacuum in the cylinder.
Two common types
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Feather type - Made of spring steel, usually used in low
pressure systems
Disc type – usually used for high pressure applications.
Cylinders
Air cooled
 Water cooled
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COOLING SYSTEMS
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Two cooling mediums
 Air
 Water
Most compressors will have some sort of cooling.
 Between each stage – called interstage coolers
 After the last stage – called afterstage coolers
A typical water cooled two stage compressor might
have the cooling water entering the afterstage cooler,
then proceeding to the high pressure cylinder, to the
interstage cooler, and finally to the low pressure
cylinder.
 This is counter flow cooling.
Low pressure systems typically use air as cooling
means
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COOLING SYSTEMS
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Interstage cooling functions to:
 Remove moisture from the compressed air by
dropping the air below the dew point
corresponding to the pressure of the air at that
time
 Reduces the temperature in each cylinder
 Lower cylinder temperatures helps with cylinder
lubrication
 Increases the volumetric efficiency of each of the
stages.
Additional cooling is used to facilitate air drying for
air being used for control functions
 These air driers typically use refrigeration systems
to drop the compressed air below the dew point of
any moisture left in the air.
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Reciprocating Compressors
two stage and intercooler
Water cooled heat exchangers
are usually shell and tube type
heat exchangers.
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1 first stage
 2 intercooler
 3 second stage
 4 afterstage cooler
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COMPRESSOR P-V DIAGRAM
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Red line --- an isentropic
compression process (n=k)
Blue line --- a polytropic
compression process (1<n<k)
Green line --- an isothermal
compression process (n=1)
Yellow area represents the air
compressor work required during
compression process of an isothermal process
Because the area from each line to the left is the
required air compressor work, we can see that an
isothermal process requires loweer amount of energy
than polytropic process and isentropic process
respectively.
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LUBRICATING SYSTEMS
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Compressor lubrication systems for low, medium,
and high pressure systems are usually forced
systems, with an oil pump attached to the shaft.
 A complete system will have a filter, and an oil
cooler.
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COMPRESSED AIR STORAGE
For compressed air to be useful potential energy,
we must store it until it is needed.
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 Air
is stored in an accumulator or
receiver.
 Accumulators function to:
Act as a storage device when demand for air exceeds
compressor capacity.
 It helps eliminate pulsations in air supply systems.
 Allows the compressor to shut down or rest during
periods of light load.
 Acts as a place to remove moisture from the system
and also cools the air.
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Moisture comes in with air.
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CONTROL SYSTEMS
Control systems include:
 Control system modes of operation
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Start – stop operation
 Compressor is on or off based on receiver pressure.
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pressure gets to the set point, the compressor shuts off
pressure gets to the cut in set point, the compressor restart
The pressure is sensed via a pressure switch mounted on
the receiver.
 Constant speed control
 The compressor run constantly, but loads or unloads
based on the pressure in the receiver.
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Safety shutdown
Low oil pressure
 High air outlet temperature
 Low cooling water pressure
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UNLOADING SYSTEMS
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Unloading systems remove all but the friction
loads on the compressor
 The compressor motor is still turning, but is
not pumping air
 This is accomplished by holding the cylinder
suction valves open
 Unloaders automatic remove load during
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Start ups and shut downs
 When the air set pressure is met during constant
speed operation.
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There are several types of unloaders
Using oil pressure to hold open the suction valves
 Or using air pressure
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P
1/2
3/4
1
b
1/4
0
a
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MOISTURE REMOVAL
Most air systems will have an additional means
to remove moisture between the compressors and
the receiver.
 The State of Maine has two refrigeration/filter
units known as refigerfilters.
 They use a refrigeration process to lower the
temperature of the compressed air.
 When the temperature of the air is lowered,
the moisture in the air reaches the dew point,
and condenses.
 They also have filters to clean the air.
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HPAC
High pressure
air compressor
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AIR COMPRESSOR PISTONS
TRUNK TYPE & DIFFERENTIAL TYPE
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SHIP SERVICE LP AIR SYSTEM
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Question: If atmospheric pressure = 14.7 psia and we
pump up the flask to 100 psig, How much air can be
forced into an air flask?
Note: Use the equation P1V1 = P2V2
14.7 psia  V1  (100 14.7) psia  3gal
V1 
(100 14.7) psia
 3gal  23.4 gal
14.7 psia
V1  23.4 gal 231in3 / gal  5407in3
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Answer: 5407in3 air must be forced into the air flask.
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THANK YOU
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