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Fundamentos de Aire Comprimido
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Compressed Air Fundamentals
Life Cycle Cost of an air compressor
Why are we here?
Energy consumption
Installation
Maintenance
Investment
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Fundamentos del aíre comprimido
Ciclo del costo de la vida de un compresor

Consumo de Energía

Instalacion
Mantenimiento

Inversión

De las tres categorías del
costo la energía puede ser
arriba del 90% en dias años
de trabajo de un equipo
de hecho dentro de los
primeros 12 meses, el costo
de inversion es exedido por
el costo del uso de la
máquina
Comprar un compresor
representa el más bajo de
los tres costos
El consumo de energía es
por mucho el costo más
significante en la operación
de un equipo
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Fundamentos del aíre comprimido
Que es el Aire Comprimido?
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Fundamentos del aíre comprimido

Nosotros vivimos en el
fondo de un mar
llamado Atmosfera
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Fundamentos del aíre comprimido


El aíre es como un
sobre gaseoso que
rodea la tierra
ejerciendo una
presión en cada cosa
La presión actual
depende de la
localización con
respecto al mar.
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Fundamentos del aíre comprimido


Al nivel del mar la
presión atmosférica
es de 14.7 psiA
psiA: Libras por
pulgada cuadrada
(Absolutas)
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Fundamentos del aíre comprimido

a 500 pies bajo el nivel
del mar, la presión del
aire es 14.94 psiA
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Fundamentos del aíre comprimido


En la cima de una
montaña de 5000 pies,
la presión del aíre es
sólo de 12.2 psiA
La Montaña del Everest
esta a 29,000 pies
sobre el nivel del mar,
la presión sólo es de
4.56 psiA
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Fundamentos del aíre comprimido



Comprimir: Forzar a que entre
todo en un espacio más
pequeño
Aire: Es una mexcla incolora,
inolora, e insipida,
principalmente nitrogeno (78%)
y oxygeno (21%)
Cuando se Controla, el aire
comprimido puede ser usado
para ejecutar un trabajo
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Fundamentos del aíre comprimido
El aíre Comprimido guardado
es energía...



La energía contenida dentro de un
globo es igual a la energía que se
requirió para inflarla.
Si el volume de una cantidad dada
de aíre decrece, la presión se
incrementará
Con un compresor de
desplazamiento positivo, el aire
comprimido se obtiene forzando a
que este permanezca en un volume
más pequeño.
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Fundamentos del aíre comprimido
Porque la industria necesita
aíre comprimido?


Por la energía: El aíre comprimido es
un excelente medio para guardar y
transmitir energía para hacer
cualquier trabajo.
Por requerimientos de Procesos: El
aíre comprimido es una parte
activa de procesos (ejem. quimica,
farmaceutica, fermentación, etc.)
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Fundamentos del aíre comprimido
La energía del aíre

La energía del aíre
comprimido es usda para
impulsar equipos neumáticos
en la producción
 Ejemplos.--motores de aíre,
actuadores,
instrumentacion,
herramientas, etc.



Para enfriar componentes o
partes durante la fabricación
Para soplar basura
etc
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Fundamentos del aíre comprimido
Aire de Proceso

El aíre comprimido es una
parte integral de un proceso,
 Quimicos
 farmaceuticos
 Comidas y Bebidas
 Aeración y agitación
 Semiconductores y
Electronicos
 Aire de respiración medica
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Definiciones
Presión Absoluta
Es La Suma de la presión medida+la presión atmosférica
(100 psig + 14.2 psia = 114.2 psia “absolutos”)
Relación de Compresión
La relación de la presión absoluta de salida entre la
presión absoluta de entrada (100 psiG + 14.2 psiA) / 14.2 psiA =
8.04 ratios), ó simplemente son las veces las cuales se reduce el
volume de un gas a determinada presión a un volumen menor a
una presión mayor
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Definitions
Punto de Rocío
Es la temperatura de un gas a una presión dada, a la cual el
vapor de agua comienza a condensarse
Capacidad
Cantidad de un gas entregado, típicamente se refiere
a las condiciones de entrada, que son humedad, presión y
tempertura ejemplos: ACFM,ICFM, SCFM, Free air CFM, FAD
Aire Estandard (Ejemplo SCFM)
Un volume dado de aíre definido una especifica, o “estandard”
condicion. Los parametros comunmente aceptados en la
industria como estándar son: 14.7 psiA, 60o F, 0% RH
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Definiciones
Desplazamiento Positivo
Un volume de aíre es atrapado dentro de un espacio cerrdo. El
volume es reducido causando un aumento de presión (compresion)
Compresor Dinámico
El aumento de energía se obtiene convirtiendo la energía cinética
en energía de presión, aumentando primero la velocidad de las
partículas y después desacelarandolas
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Definiciones
Interenfriamiento
El enfriamiento de un gas entre etapas de compresión
1. Reduciendo la temperatura
2. Reduciendo el volume para la siguiente etapa
3. Licuando vapores condensables para reducir los HP
(Todo lo relacionado para reducir los HP)
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Formulas
Cambio de Presión vs Cambio de BHP (potencia)
Para compresores de Desplazamiento positivo: Un cambio de presión de 1
psig requiere un aumento de potencia del .5%.
Ejemplo: un compresor de 1000 CFM requiere 200 BHP para 100 psiG. El
mismo compresor, operando a la misma velocidad requerira (200 x 1.10) =
220 BHP para llegar a 120 psiG
Cálculo del costo de potencia--para un año de operación
BHP X .746 kW X
$
X Oper. Hrs = Oper. $
Mtr. Eff.
HP
kWh
Year
Year
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Formulas
Ejemplo - Para el compresor anterior el costo del incremento de
presión de 100 a 120 psiG. Es el siguiente:
20 BHP X .746 kW X
.93% Eff. Mtr.
HP
$.09
X 8700 Hrs. = $12,560
kWh
Year
Porque debo operar mi compresor a la más baja presión posible?
¡Sólo vea el ejemplo anterior!
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Formulas
Para cálculos de aíre comprimido se requieren fórmulas
termodinámicas.
En el sistema de mediciones Ingles, se utilizan las fórmulas siguientes
para cálculos termodinámicos




La presión se expresa en Libras por pulgadas Cuadrada (psi, or lb/in2).
La temperatura se expresa en Fahrenheit (deg. F.)
El volume se expresa en pies cúbicos (Ft3)
Volume Flow Rate is expressed in cubic feet / min (Ft3/min)
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Formulas
Relaciones de Presión


Todos los cálculos se basan en valores absolutos para Temp. Y Presión.
Presión Absoluta (psiA) = Presión en medida (psiG) + Presión
barométrica(ambiente).
 Ejemplo:
• 14.7 psiA Presión Barométrica
• 100 psiG Presión de descarga
14.7 + 100 = 114.7 psiA Presión absoluta de descarga.
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Formulas
Relación de Compresión
Relación de Compresión =Presión Absoluta de Descarga
Presión absoluta de entrada ó Medio Ambiente
Recuerdese: Presión absoluta de descarga = Presión de descarga medida + (Presión
barométrica ó ambiental (psiA)
Example:
• 14.7 psiA Presión de entrada
• 125 psiG Presión de descarga
• La Relación de Compresion es = (14.7 + 125) / 14.7
= 9.5
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Ratings
Flujo de volume
Del Ejemplo anterior:
Si un compresor de 100 CFM toma 100 CFM de aíre
del medio ambiente y lo comprime a 125 psiG. El aíre a
sido prensado 9.5 de su tamaño original, y ahora sólo
ocupa 10.52 pies cubicos en su estado comprimido.
Relación de Compresión = (14.7 + 125) / 14.7 = 9.5
100 pies Cúbicos / 9.5= 10.52 pies cúbicos
Si la Relación de Compresión del compresor = 9.5
este estará operando en el límite
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Formulas
La presión barométrica decrece incrementando la altitud y
viceversa.
Basandonos en una presión de descarga fija la relación de
compresión se incrementa si se aumenta la altitud.
– Ejemplo: si el mismo compresor se operara ahora a:
• 3,000 Pies Sobre el nivel del mar = 13.19 psiA Barometricos
• Manteniendo la presión de descarga a 125 psiG…
– Relación de compresión = (13.19 + 125) / 13.19 = 10.5 Se incrementa
• 100 Pies Cúbicos/10.5 = 9.52 pies cúbicos “Se Reduce aún
más la masa ó volume comparado con los 10.52 anteriores”
Si se sobrepasa la relación de compresión el volume es más
reducido, esto ocasionará mayor fuerza para tenderse a liberar
si el compresor no está diseñado para esta fuerza se producirá
calentamiento ó aumento de
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En la industria existen 4 diferentes capacidades para
CFM.
–
–
–
–
Aíre Libre entregado (FAD CFM)
Actual Pies Cúbicos por minuto (ACFM)
Entrada Pies Cúbicos por Minuto (ICFM)
Standard Pies Cúbicos por Minuto (SCFM)
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Acfm
FAD l/s - cfm
External leakage's
External leakage's
Aíre libre entregado referido a las
condiciones del sitio
Im3/min - Icfm
Flujo Actual referido a las condiciones de
entrada del compresor
Scfm
Nm3/min
External leakage's
External leakage's
Flujo de entrada Referido a las
condiciones de entrada del elemento del
compresor
Aíre libre entregado referido a las
condiciones Normal o Standard air
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The face of interaction
Fundamentos de Aire Comprimido
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THE RIGHT CHOICE
• COMPRESSOR TYPES
• WORKING PRINCIPLES
• CHARACTERISTICS
• CONTROL SYSTEMS
• STAGING
• GENERAL INFORMATION
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THE RIGHT CHOICE
• COMPRESSOR TYPES
• WORKING PRINCIPLES
• CHARACTERISTICS
• CONTROL SYSTEMS
• STAGING
• GENERAL INFORMATION
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The basic principals of air or gas compression
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Two Basic Principals of Air or Gas Compression
Compressors
Positive Displacement
Dynamic Compression
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THE RIGHT CHOICE
• COMPRESSOR TYPES
• WORKING PRINCIPLES
• CHARACTERISTICS
• CONTROL SYSTEMS
• STAGING
• GENERAL INFORMATION
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Two Basic Principals of Air or Gas Compression
Compressors
Positive Displacement
Dynamic Compression
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Positive
displacement
principle
Reducing the volume of
a gas increases its pressure
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Oil Free Rotary Screw Element Design
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The Positive Displacement
Principle As
Applies To Screw
The volume of the air or gas is progressively
reduced along the length of the screw,causing
a pressure increase.
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THE AC ASSYMETRIC PROFILE
•LOW ROTOR SPEEDS
-HIGH BEARING LIFE
-LESS WEAR AND TEAR
-LOW DYNAMIC AND MECHANICAL LOSS
•BETTER SEALING
-LOW VOLUMETRIC LOSSES-HIGH VOLUMETRIC
EFFECIENCY
•CONTACT POINT AT THE PITCH CIRCLE
-NO RELATIVE MOTION BETWEEN ROTORS
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A SCREW IS A POSITIVE
DISPLACEMENT MACHINE
AND HENCE
CAPACITY
SPEED
-The dynamic and mechanical losses
increase with the rotor tip speeds
-The volumetric losses decrease
-The total losses which are a sum of all losses are
minimum at 80 m/s for oil-free elements and
approximately 30m/s for lubricated elements
Since the total loss curve is almost flat between
60-120 m/s this range can be employed without
much compromise on effeciency
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Compressor Fundamentals
Two Basic Principals of Air or Gas Compression
Compressors
Positive Displacement
Dynamic Compression
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DYNAMIC COMPRESSOR
• Dynamic Principle
Velocity
(Kinetic Energy)
converted to pressure
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CENTRIFUGAL COMPRESSORS WORKING PRINCIPLE
RADIAL DIFFUSERS
PRESSURE CUTS
FLOW CUTS
VANES
INDUCER
PRESSURE INCREASE FOLLOWS THE PRINCIPLE OF BERNOULLI
2
P
V
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A CENTRIFUGAL IMPELLER
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Blade
TURBO WORKING PRINCIPLE
• Wheel turns
• Speed of the ball increases
• Speed suddenly reduced to
create pressure increase
DIFFUSER
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CENTRIFUGAL COMPRESSOR GENERAL ARRANGEMENT
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THE RIGHT CHOICE
• COMPRESSOR TYPES
• WORKING PRINCIPLES
• CHARACTERISTICS
• CONTROL SYSTEMS
• STAGING
• GENERAL INFORMATION
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GENESIS OF SCREW COMPRESSORS
•
IN THE 1930S COMPRESSED AIR AND GAS USERS HAD TWO MAIN OPTIONS RECIPS AND CENTRIFUGALS
•
RECIPS WERE POSITIVE DISPL. M/CS WHICH WERE :
–
THERMODYNAMICALLY STABLE AND POWER SAVING BUT
–
REQUIRED EXPENSIVE INSTALLATION AND FOUNDATIONS
–
WERE MAINTENANCE INTENSIVE - EXPENSE/DOWNTIME
–
CAPACITY FELL WITH USE
–
LIMITED USE WITH DIRTY GASES
•
CENTRIFUGALS WERE LESS MAINTENANCE INTENSIVE BUT
–
REQUIRED EXPENSIVE INSTALLATION AND FOUNDATIONS
–
WERE THERMODYNAMICALLY UNSTABLE
–
OPERATING BAND WAS LIMITED
–
SENSITIVE TO DUST AND UNSUITABLE FOR DIRTY GASES
–
CAPACITY FELL EVEN WITH A FEW MICRON DUST BUILDUP
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GENESIS OF SCREW COMPRESSORS II
PROFESSOR
LYSHOLM
OF THE
ROYAL
SWEDISH INSTITUTE
OF
SCIENCE
DOING
RESEARCH
ON COMPRESSORS SET ABOUT FINDING AN IDEAL SYSTEM ON THE FOLLOWING HYPOTHESIS
•
TO
OVERCOME WEAKNESSES
OF
THE
RECIPS HIS DREAM MACHINE HAD TO BE A ROTARY WITH NO
METAL CONTACT
•
TO OVERCOME DISADVANTAGES OF CENTRIFUGALS IT HAD TO BE A POSITIVE DISPLACEMENT MACHINE
THUS WAS BORN THE IDEA
OF THE
ROTARY
SCREW WHICH COMBINED THERMODYNAMIC AND
OPERATIONAL STABILITY AND LOW POWER CONSUMPTION
WITH UNPARALLELED RELIABIITY
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GENESIS OF SCREW COMPRESSORS III
•
ATLAS COPCO DREW ON THIS BASIC IDEA AND AFTER INTENSIVE RESEARCH COMMERCIALLY
INTRODUCED THE U SERIES IN
•
1957. MANY
OF THESE MACHINES ARE STILL OPERATING THE WORLD OVER
IN THE 1970S THE ATLAS COPCO RESEARCH CENTRE THE CERAC I NSTITUTE IN GENEVA DESIGNED AND
PATENTED A REVOLUTIONARY ASSYMETRIC SCREW PROFILE WHICH IS CURRENTLY USED IN THE G AND Z
SERIES MACHINES
•
IN THE WORLD TODAY 9 OUT OF 10 MACHINES PRODUCED AND SOLD IN THEIR RANGE ARE ROTARY SCREWS
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COMPRESSOR CHARACTERISTICS
PRESSURE
Performance
curves
DYNAMIC
COMPRESSOR
POSITIVE
DISPLACEMENT
COMPRESSOR
CAPACITY
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COMPRESSOR CHARACTERISTICS - DYNAMIC MACHINES
P
R
E
S
S
U
R
E
OIL FREE
SCREW
SURGE CONTROL
SURGE LIMIT
AT 25 DEG.C
1 BAR A
AT 40 DEG.C
0.97 BAR A
60
85
P
O
W
E
R
100
FLOW
OIL FREE
SCREW
FLOW
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Inlet throttle valve
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Pressure
DYNAMIC MACHINES- OPERATING BAND
Surge
Stonewall
Flow
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COMPRESSOR CHARACTERISTICS- DYNAMIC MACHINES
A DYNAMIC COMPRESSOR OPERATES IN A BAND
BETWEEN
SURGE
Breakdown of airflow due to high back pressure
(oscillation flow)
AND
STONE WALL (choke)
Maximum flow a compressor can handle at a given speed
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COMPRESSOR CHARACTERISTICS
Variables influencing compressor performance
• Positive displacement compressors
P = P1 . V1 . {(
P2
P1
n-1
n
) -1 }
n
n-1
Inlet air temperature and weight flow (density) have no effect on power
Where:
P
P1
V1
n
P2/P1
:
:
:
:
:
Power
Inlet pressure
Inlet volume
Adiabatic factor
Pressure ratio
Variables influencing power:
P1
V1
P2/P1
=
=
=
Inlet pressure
Volume flow (not mass!)
Pressure ratio
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COMPRESSOR CHARACTERISTICS
Variables influencing dynamic compressor performance
POWER IS CALCULATED WITH FORMULA:
Hp . m
P= h
is
Where:
Hp
m
his
:
:
:
Head pressure
Mass flow
Isentropic efficiency
There are three variables that affect
the power:
T
m
P2/P1
:
:
:
Inlet temperature
Mass flow
Pressure ratio
MASS FLOW IS HIGHER AT LOW TWMPERATURES AS WELL AS HIGH AMBIENT PRESSURES
HENCE HIGH POWER CONSUMPTIONS AT THESE CONDITIONS
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COMPRESSOR CHARACTERISTICS - DYNAMIC MACHINES
EFFECT OF SPEEDS
SINCE A DYNAMIC MACHINE DEVELOPS PRESSURES PROPORTIONAL TO THE
SQUARE OF THE VELOCITY REDUCTION
IT FOLLOWS THAT
IMPELLER SPEED REDUCTION CAUSES A PRESSURE REDUCTION ACCORDING TO
THE RELATIONSHIP
2
S
P
HENCE DUE TO FREQUENCY REDUCTION OF 3% THE OUTLET PRESSURE REDUCES BY
6%
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COMPRESSOR CHARACTERISTICS
THERMODYNAMIC INSTABILITY- DYNAMIC MACHINES
THERMODYNAMIC INSTABILITY CAN HENCE BE INTERPRETED AS :
•
PRESSURE AND VOLUME ARE INVERSELY RELATED.PRESSURE INCREASE LEADS TO
REDUCTION IN VOLUME CAPABILITY OF THE MACHINES.
•
LOWER AIR INLET TEMPERATURE RESULTS IN
- SAME VOLUME FLOW FOR HIGH POWER CONSUMPTION
- HIGHER MASS FLOW
- HIGHER PRESSURE CAPABILITY OF THE MACHINE
•
LOWER SPEEDS RESULT IN VERY LOW PRESSURES
•
THE MACHINE OPERATES WITHIN A NARROW BAND(BETWEEN SURGE AND STONEWALL)
•
THE SYSTEM IS PRONE TO SURGE DUE TO PRESSURE DROPS
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“BALANCED” OPPOSED PISTONS
FORCE BALANCE
F2
F1
F1
F2
1. HORIZONTAL FORCES F1 BALANCE OUT
2. UNBALANCED VERTICAL FORCES F2 ACTING ALONG WITH THE WEIGHT OF THE PISTON CAUSES
CYLINDER OVALITY
3. F2 FORCES ALSO CAUSE AN UNBALANCED COUPLE, NECESSITATING HEAVY FOUNDATIONS.
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PISTONWEAR
ITEMS - A COMPARISON
VEE BELTS (6)
2 GEARS
CRANKSHAFTS
6 BEARINGS
MAIN BEARINGS (4)
SCREW
2 ROTORS
BIG END BEARINGS (4)
CONNECTING RODS (4)
SMALL END BEARINGS (4)
CROSS HEADS (4)
WIPER RINGS (4 SETS)
PISTONS (4)
PISTON RINGS (16)
CYLINDERS (4)
40 VALVES (SUCTION/DELIVERY)
TOTAL 99 WEAR ITEMS
TOTAL 10 WEAR ITEMS
WEAR ALONG WITH OVALITY CAUSES A CAPACITY DERATION OF 5-6% PER YEAR,WITHOUT REDUCING THE
POWER CONSUMPTION
A HIGH NUMBER OF WEAR PARTS INCREASES DOWN TIME AND MANPOWER OUTLAYS
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P-V DIAGRAM - A COMPARISON
PISTON
SCREW
P
P
W
W
CV
DELIVERY
V
DELIVERY
V
CLEARANCE VOLUME CONTRIBUTES TO LOWER VOLUMETRIC EFFECIENCIES AND
HIGHER POWER CONSUMPTION
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PISTON COMPRESSORS
EFFECT OF VALVE FLUTTER ON P-V DIAGRAM
.
EFFECT OF VALVE
FLUTTER
P
w
V
VALVE FLUTTER CAUSES THE AREA OF THE P-V DIAGRAM TO INCREASE WHICH RESULTS IN HIGHER THAN
INDICATED POWER CONSUMPTION.
FLUTTER IS CAUSED BY WEAR ON THE VALVE PLATES CAUSING AIR TO LEAK IN SMALL CHANNELS.THE
PLATES BEGIN TO VIBRATE,SIMILAR TO A REED IN A FLUTE.FLUTTER OCCURS AFTER A SHORT SPAN OF
USAGE.
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PISTON COMPRESSORS
EFFECTS OF CYLINDER OVALITY
CYLINDER
PISTON
CYLINDER OVALITY PREVENTS RESUMPTION OF CAPACITY TO ORIGINAL LEVEL
EVEN WITH NEW RINGS LEADING TO CONTINUED AIR LEAKAGE
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SUITABILITY OF TURBO COMPRESSORS
•
CENTRIFUGAL COMPRESSORS ARE VERY SUITABLE FOR
•
HIGH VOLUME FLOWS ABOVE 6000 M3/HR
•
MASS RELATED PROCESSES LIKE AIR SEPARATION WHERE HIGH
POWER AT LOW TEMPERATURES IS COMPENSATED BY HIGH MASS FLOWS.
•
BASE LOAD OPERATION WHERE MACHINE RUNS AT FULL LOAD
•
PRESSURES UPTO 80 BAR
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THE RIGHT CHOICE
• COMPRESSOR TYPES
• WORKING PRINCIPLES
• CHARACTERISTICS
• CONTROL SYSTEMS
• STAGING
• GENERAL INFORMATION
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VERY FEW PROCESSES REQUIRE A CONTINOUS FLOW OF AIR,ALTHOUGH THE
DEGREE OF VARIATION CHANGES FROM PROCESS TO PROCESS.THE AIR DEMANDS
CAN CHANGE DUE TO DIVERSE CAUSES SUCH AS THE EXTENT OF UTILIZATION OF A
FACTORY,ACCORDINDG TO THE DAY OF THE WEEK OR THE TIME OF THE DAY.IT CAN
CHANGE DUE TO THE DEGREE OF MATURITY OF A PROCESS,SUCH AS IN
FERMENTATION OR OXIDATION PROCESSES.THE MANUFACTURING SET-UP MAY
EMPLOY VERY LARGE CONSUMERS OF AIR SUCH AS FORGING HAMMERS,PAINTING
BOOTHS,PNEUMATIC PRESSES,ETC.,WHICH RUN OFF AND ON.MASS DEPENDENT
PROCESS MAY REQUIRE A FIXED MASS OF AIR,BUT THE MASS FLOW THROUGH THE
COMPRESSORS CHANGE WITH THE AMBIENT TEMPERATURES.
OR SIMPLY
BECAUSE THE AIR DEMAND IS OVER ESTIMATED
The compresor therefore requires a control system to regulate the air
generation of the compressor in direct relation to the demand
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TYPICAL AIR DEMAND PATTERNS
AIR DEMAND
MONDAY
TUESDAY
WEDNESDAY
THURSDAY
FRIDAY
SATURDAY
SUNDAY
HOURS
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SCREW
SYSTEMS-MODULATION
IN ACONTROL
MODULATION
CONTROL A BUTTERFLY VALVECONTROL
REGULATES THE INTAKE
AT FULL LOAD THE BUTTERFLY VALVE IS OPEN
AND THERE IS FREE FLOW OF AIR.THE
MACHINE OPERATES AT THE BUILT-IN
PRESSURE RATIO
AT PART LOAD THERE IS A RESTRICTION IN AIR
FLOW LEADING TO A VACUUM . HOWEVER OUTLET
PRESSURE REMAINS THE SAME SINCE THIS IS
DETERMINED BY THE AIR NET PRESSURE
VACUUM PREVAILS:
INTAKE 1/2 BAR A
INTAKE 1 BAR A
SCREW
ELEMENT
OUTLET 8 BAR A
OUTLET 8 BAR A
PRESSURE RATIO IS 16 WHICH IS MUCH
HIGHER THAN THE BUILT IN PR.HENCE
VERY INEEFECIENT AT PART LOADS
PRESSURE RATIO=8
* FIGURES ARE USED FOR CONCEPT DEMONSTRATION ONLY
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SCREW CONTROL SYSTEMS
LOAD NO-LOAD REGULATION
IN A LOAD NO-LOAD CONTROL THE MACHINE RUNS AT EITHER AT FULL
LOAD OR UNLOADED
•IN THE LOADED CONDITION THE INLET VALVE IS COMPLETELY OPEN
AND HENCE THE MACHINE MAINTAINS ITS BUILT-IN PRESSURE RATIO
•IN THE UNLOADED CONDITION THE INLET VALVE IS COMPLETELY
CLOSED AND THE OUTLET IS ISOLATED FROM THE AIR NET.
POWER CONSUMPTION DROPS ALMOST PROPORTIONATELY DUE TO THE
MUCH REDUCED VOLUME FLOW AS WELL AS NO OPERATION ABOVE THE
BUILT-IN PRESSURE RATIO
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SCREW CONTROL SYSTEMS
VARIABLE SPEED CONTROL
IN A VARIABLE SPEED CONTROL,THE SPEED OF THE DRIVE MOTOR IS CONTINOUSLY VARIED TO
MATCH THE COMPRESSOR OUTPUT TO THE DEMAND.
A SIMPLE SCHEME IS SHOWN BELOW:
M
C
VSD
P/I
THE P/I (PRESSURE TO CURRENT
CONVERTOR)GENERATES A 4-20 MA
SIGNAL DEPENDING ON THE DOWNSTREAM
PRESSURE.PRESSURE INCREASE INDICATES
A DEMAND REDUCTION.THE VARIABLE
SPEED CONTROL (VSD) EMPLOYS THE CURRENT
SIGNAL AS THE INPUT,TO REDUCE THE
FREQUENCY TO THE DRIVE MOTOR(M).
SINCE THE DRIVE MOTOR SPEED IS
PROPORTIONAL TO THE SUPPLY FREQUENCY.THE MOTOR SLOWS DOWN.THE REDUCTION IN THE
FLOW,AS A RESULT,LEADS TO AN ALMOST PROPORTIONAL REDUCTION IN POWER CONSUMPTION.
VARIABLE SPEED CONTROLS CONSTITUTE THE MOST EFFICIENT METHOD TO CONTROL CAPACITY.
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SCREW CONTROL SYSTEMS
A COMPARISON
VARIABLE SPEED
CONTROL
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COMPRESSOR CONTROL - DYNAMIC MACHINES
P
R
E
S
S
U
R
E
SURGE LIMIT
60
SURGE CONTROL
85
DEMAND FALLS BELOW
SURGE CONTROL
100
FLOW
DEMAND IS ABOVE
SURGE CONTROL
2 SCENARIOS:
CONTROL ABOVE SURGE CONTROL
CONTROL BELOW SURGE CONTROL
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CONTROL SYSTEMS - DYNAMIC MACHINES
CONTROL ABOVE SURGE CONTROL
Inlet guide
Inlet Throttle Valve
vanes
Inlet Guide Vane
• Energy savings with
100 - 65% capacity
control
• Constant pressure
within control range
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CONTROL SYSTEMS-DYNAMIC MACHINES
CONTROL ABOVE SURGE CONTROL
V1’
V1
V2
V2
VELOCITY CHANGE(V) =V1-V2
VELOCITY CHANGE =V1’-V2 < V
NORMAL
INLET GUIDE VANES
V1
V2’
VELOCITY CHANGE =V1-V2’ < V
DIFFUSER GUIDE VANES
* ABOVE EXAMPLE IS FOR AXIAL FLOW MACHINES
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ZH-series
Efficient centrifugal compressors
Adjustable inlet guide vanes
provide a pre whirl to the air
or gas,smoothly controlling
capacity without any
turbulence unlike the
throttle valve
Pressure %
150
100
Plant demand
Inlet throttle valve
100 at 100% pressure
Inlet guide vanes
at 100% pressure
Power %
90
80
70
60
Energy savings
70
80
90 100 110
Capacity %
9%energy
savings at part load
CONTROL SYSTEMS-DYNAMIC MACHINES
Pressure
CONTROL BELOW SURGE LIMIT
AUTO DUAL AND MODULATED BLOW-OFF CONTROLS
Volume flow
RELOADING TIME IS LONG WITH
CONVENTIONAL RADIAL AND THRUST
BEARINGS OFTEN CALLING FOR HUGE
STORED CAPACITY TO PROTECT PROCESS
ENTAILS BLOW-OFF AT PARTIAL
LOADS THUS WASTING POWER
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BEARING CONFIGURATIONS
DYNAMIC MACHINES
JOURNAL
SIMPLE
SHAFT
TILTING PAD
TILTED PAD
DUE TO THE HIGH SPEEDS,DYNAMIC MACHINES EMPLOY SLEEVE BEARINGS,WHICH EMPLOY
AN OIL FILM TO SUPPORT THE SHAFT.THIS BEARING SYSTEM INTRODUCES RESTRICTIONS BECAUSE CHANGES
IN LOAD PATTERNS CAUSES THINNING OF THE FILM OR ‘FILM DISPERSION’.SUDDEN OR FREQUENT CHANGES
IN LOAD CONDITIONS HAVE TO BE CONTROLLED.
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THE FLEXIPAD BEARINGS
TILTING OR FLEXIPAD BEARINGS
WITH THRUST PADS IN BOTH
DIRECTIONS PROVIDE GOOD
DAMPING CHARACTERISTICS
WITH MANY BENEFITS
•IMPROVED MECHANICAL
SAFETY
•IMPROVED STABILITY WHEN
CROSSING CRITICAL SPEEDS
•BETTER TOLERANCES TO
IMPROVE EFFECIENCY
•FASTER TURN AROUND FOR
RELOADING
•ABILITY TO RUN UNLOADED
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THE RIGHT CHOICE
• COMPRESSOR TYPES
• WORKING PRINCIPLES
• CHARACTERISTICS
• CONTROL SYSTEMS
• STAGING
• GENERAL INFORMATION
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STAGING OF COMPRESSORS
A P-V DIAGRAM REPRESENTATION
.
P
P
W
W
V
SINGLE STAGE
V
2 STAGE
X - ENERGY SAVING
MULTI-STAGING SAVES ENERGY AND LIMITS OUTLET TEMPERATURES
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STAGING - SCREW MACHINES
EFFICIENT OPERATION AT THE
BUILT-IN PRESSURE RATIO (BIPR)
P
V
B
P
A
P
X
X
V
V
LESS EFFICIENT EITHER ABOVE (A) OR
BELOW THE BIPR
IF THE BUILT-IN PRESSURE RATIO IS 3 A 1-STAGE MACHINE OPERATES BEST AT A
PRESSURE RATIO OF 2.5-3.5 AND A 2-STAGE AT 6-10
X-EXCESS ENERGY
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STAGING CRITERIA - TURBO MACHINES
SAFETY CONSIDERATIONS
THE NO.OF STAGES IS DEDUCED AS FOLLOWS :
•
WITH 14 PH SS USED THE MAX. TIP SPEED IS 450 M/S.
•
WHEN USING 45 DEG.IMPELLERS THIS IS ATTAINED WITH A PR OF 2.1 PER STAGE.
•
HENCE A 2 STAGE MACHINE CAN ACHIEVE A MAX.WORKING PRESSURE OF 2.1 EXP 2 = 4.41 - 1
=3.41 KG/CM2 (G).
•
AND A 3 STAGE MACHINE CAN ACHIEVE A MAX.WORKING PRESSURE OF 2.1 EXP 3 = 9.26 - 1 =8.26
KG/CM2 (G).
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STAGING CRITERIA - TURBO MACHINES
EFFECIENCY CONSIDERATIONS
mechanical
efficiency
aerodynamic
efficiency
total efficiency
FACTORS DETERMINING
AERODYNAMIC EFFECIENCY ARE
SPECIFIC SPEEDS
MACH NUMBERS
REYNOLDS NUMBERS
Efficiency versus number of stages [6-10.4 bar(e)]
number of stages
CURVE CORRESPONDS TO 7-8 BAR OPERATION
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STAGING CRITERIA -TURBO MACHINES
EFFECIENCY CONSIDERATIONS
1/2
Specific Speed = rpm x (flow)
------------------- 3/4
(Adiabatic Head)
na
0.23 - 0.24
SPECIFIC SPEED
Operation above or below the optimum Specific Speed compromises on
Aerodynamic Effeciency(na). Characteristically the optimum is achieved at 390400m/s impeller tip speed with 45 deg. impellers
Ing de Producto AIF Entrenamiento Básico
STAGING CRITERIA-TURBO MACHINES
EFFECIENCY CONSIDERATIONS
Mach No. = Velocity of Flow/ Velocity of Sound
na
MACH NO.
Mc = 1.2
Operation above the “Critical Mach Number” results in a rapid decrease in the
Aerodynamic Effeciency(na).The speed of sound being 332m/s,the critical Mach
No.corresponds to about 400-410m/s
Ing de Producto AIF Entrenamiento Básico
THE RIGHT CHOICE
•
FOR RECIPROCATING COMPRESSORS THE STAGING RULES (THEORETICALLY) ARE MAINLY DETERMINED BY THE
OUTLET TEMPERATURE.THE LIMITING TEMPERATURE IS MUCH LOWER BECAUSE IN THESE MACHINES THERE ARE
MANY MOVING PARTS IN FRICTIONAL CONTACT WITH EACH OTHER.HIGH TEMPERATURE CAUSES DRAMATIC
INCREASES IN CONSUMPTION OF SPARE PARTS DUE TO LOWERED VISCOSITY AT THE PARTS INTERFACE.
•
DUE TO THIS REASON,THE STANDARD ‘ API 618’ LIMITS THE OPERATING TEMPERATURE TO 140 DEG.C. IF THIS IS TO BE
ACHIEVED,WORKING BACK FROM THE TEMPERATURE EQUATION,THE PRESSURE RATIO PER STAGE BECOMES:
•
P2/P1=(273+140/273+40)EXP (1.4/1.4-1)=2.63 AT AN INLET TEMPERATURE OF 40 DEG C. THEREFORE, IDEALLY A 2 STAGE
MACHINE SHOULD DELIVER 4.29 BAR(G)
Ing de Producto AIF Entrenamiento Básico
THE RIGHT CHOICE
• COMPRESSOR TYPES
• WORKING PRINCIPLES
• CHARACTERISTICS
• CONTROL SYSTEMS
• STAGING
• GENERAL INFORMATION
Ing de Producto AIF Entrenamiento Básico
UNLIKE THE ZH6 COMPETITORS GENERALLY FOLLOW A PREDICTABLE STRATEGY :
TURBO
COMPETITOR STRATEGY
CAPITAL COSTS ARE KEPT LOW :
•
THEY PROVIDE INCOMPLETE PACKAGES WHICH REQUIRE HEAVY SITE EXPENSES.
CUSTOMERS ARE NEVER INFORMED IN ADVANCE . COST BEC 1M PER M/C
•
THEY PROVIDE LOW PROFILE MACHINES AND CHEAP COMPONENTS
2 STAGE MACHINES INSTEAD OF 3 STAGE WITH HIGH SPEEDS
LOW VALUE HYDROSTATIC BEARINGS INSTEAD OF HYDRODYNAMIC BEARINGS
POOR QUALITY MICROPROCESSORS
THROTTLE VALVES INSTEAD OF INLET GUIDE VANES
LOW PROFILE CONTROL SYSTEMS
COPPER COOLERS INSTEAD OF CU-NI
MOTORS WITH HIGH SERVICE FACTORS
COST SAVINS OF BEC 1.5 M AT THE COST OF PERFORMANCE
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TURBO COMPETITOR STRATEGY
•
STAINLESS STEEL INTAKE PIPING
•
INTERCONNECTING AND INST. AIR PIPING AND VALVES
•
MICRO INTAKE FILTER (2U)
•
ISOLATED FOUNDATIONS (WITH CORK INLAY)
•
INSTRUMENT AIR COMPRESSOR WITH DRYER
BEC 75,000
•
EXPANSION JOINTS
BEC 30,000
•
SILENCING CANOPY (OPTIONAL)
BEC 140,000
•
OTHER ITEMS (WATER MANIFOLD,ETC)
BEC 100,000
TOTAL INSTALLATION COST
TOTAL INSTALLATION TIME
BEC 45,000
BEC 80,000
BEC 65,000
BEC 350,000
BEC 885,000
30 DAYS
Ing de Producto AIF Entrenamiento Básico
ZH-series
Efficient centrifugal compressors
NO MANUFACTURER EXCEPT ATLAS COPCO PROVIDES
READY TO RUN TURBO MACHINES
Complete
and ready
to use
• easy,
low cost
installation
• no special
foundation
• no anchor
bolts
• minimal
floor space
RADIAL MACHINES
API 617 VS API 672
FLEXIBLE SHAFT
API 672
BEARINGS
RIGID SHAFT
API 617
DUE TO DISPLACEMENT OF THE ENDS IN THE FLEXIBLE SHAFT DESIGNS,A GENEROUS CLEARANCE IS TO BE
MAINTAINED BETWEEN THE IMPELLER AND THE SHROUD,FOR SAFETY REASONS,CAUSING COMPROMISES ON
VOLUMETRIC EFFECIENCY. RIGID SHAFT DESIGNS CAN MAINTAIN MUCH CLOSER TOLERANCES AS IN API 617
TURBOS OR IN SCREW COMPRESSORS
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TURBO COMPETITOR STRATEGY
THEY UNDERSTATE RUNNING COSTS :
•
CAPACITIES ARE STATED IN INTAKE VOLUME WHICH IS OFTEN MUCH LOWER THAN FAD DUE TO
SYSTEM LOSSES
•
POWER IS ALWAYS SPECIFIED AT HIGHEST TEMPERATURES TO SHOW LOW POWER . FOR INSTANCE
AT 20 DEG C POWER IS 8.5%HIGHER THAN AT 40 DEG C
•
SPARE PART CONSUMPTION IS HIDDEN ALTHOUGH THIS IS GENERALLY
HIGHER THAN SCREW. GUARANTEES ARE ALWAYS VAGUE.
•
HIGH SPEEDS AT TIMES RESULT IN IMPELLER RUBS ,BLADE RESONANCE, EROSION AND SALT
DEPOSITIONS
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TURBO COMPETITOR STRATEGY
RUNNING AND MAINTENANCE : SOME FACTS TO CONSIDER :
•
UNLIKE THE ZH6 ALL IMPELLERS ARE CUSTOM MADE .HENCE NO STOCK CAN BE KEPT.
- IMPELLER FAILURE MEANS THIS HAS TO BE MANUFACTURED.
•
IMPELLERS NEED TO BE PERIODICALLY CLEANED AND BALANCED. FEW HIGH SPEED BALANCING
MACHINES ARE AVAILABLE.
•
OVERHAULS NEED TO BE DONE AT SITE MEANING PRODUCTION LOSS OR HIGH STANDBY
CAPACITY
•
AFTER A POWER FAILURE,MACHINE SHOULD BE PRELUBRICATED BEFORE START- UP.
•
LOADING UNLOADING CYCLES SHOULD BE LIMITED TO 1 IN 180 SECONDS.
•
PRESSURE DROPS IN FILTERS OR COOLERS CAN CAUSE SURGE IN THE MARGINAL DESIGNS OF
COMPETITION
Ing de Producto AIF Entrenamiento Básico
WE HAVE NO OPINION !
EACH COMPRESSOR TYPE HAS ITS OWN
CHARACTERISTICS AND IS BEST SUITED TO A
PARTICULAR APPLICATION.IT IS OUR RESPONSIBILITY
TO LOOK INTO THE APPLICATION AND SUGGEST THE
TECHNOLOGY WHICH SUITS HIM BEST.
WE HAVE THEM ALL
THE BEST COMPRESSOR FOR A SPECIFIC APPLICATION
Ing de Producto AIF Entrenamiento Básico