Transcript Ing de Producto AIF Entrenamiento Básico
Ing de Producto AIF Entrenamiento Básico
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
De las tres categorías del costo la energía puede ser arriba del 90% en dias años de trabajo de un equipo
Consumo de Energía
Instalacion Mantenimiento
de hecho dentro de los primeros 12 meses, el costo de inversion es exedido por el costo del uso de la máquina
Inversión
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, 60 o 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 Ing de Producto AIF Entrenamiento Básico
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 $.09 X 8700 Hrs. =
$12,560
.93% Eff. Mtr. HP 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/in 2 ).
La temperatura se expresa en Fahrenheit (deg. F.) El volume se expresa en pies cúbicos (Ft 3 ) Volume Flow Rate is expressed in cubic feet / min (Ft 3 /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 temperatura
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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FAD l/s - cfm Acfm External leakage's Aíre libre entregado referido a las condiciones del sitio Im 3 /min - Icfm External leakage's Flujo Actual referido a las condiciones de entrada del compresor Scfm Nm 3 /min External leakage's Flujo de entrada Referido a las condiciones de entrada del elemento del compresor External leakage's Aíre libre entregado referido a las condiciones Normal o Standard air
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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 Ing de Producto AIF Entrenamiento Básico
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 Ing de Producto AIF Entrenamiento Básico
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 Ing de Producto AIF Entrenamiento Básico
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
Performance curves
DYNAMIC COMPRESSOR POSITIVE DISPLACEMENT COMPRESSOR CAPACITY
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P O W E R P R E S S U R E COMPRESSOR CHARACTERISTICS - DYNAMIC MACHINES SURGE LIMIT OIL FREE SCREW SURGE CONTROL
AT 25 DEG.C
1 BAR A
AT 40 DEG.C
0.97 BAR A 60 85 100 FLOW OIL FREE SCREW FLOW
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Inlet throttle valve
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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 = P 1 . V 1 . {( P 2 P 1 n-1 n ) -1 } n n-1 Inlet air temperature and weight flow (density) have no effect on power Where: P P 1 V 1 n P 2 /P 1 : : : : : Power Inlet pressure Inlet volume Adiabatic factor Pressure ratio Variables influencing power: P 1 = Inlet pressure V 1 P 2 /P 1 = = Volume flow (not mass!) Pressure ratio
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COMPRESSOR CHARACTERISTICS
Variables influencing dynamic compressor performance Where: POWER IS CALCULATED WITH FORMULA: H p m h is P = : : Head pressure Mass flow : Isentropic efficiency H p .
h is m There are three variables that affect the power: T : Inlet temperature m : Mass flow P 2 /P 1 : 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 P S 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 F 2 F 1 F 1 F 2 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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PISTON WEAR ITEMS A COMPARISON SCREW VEE BELTS (6) CRANKSHAFTS MAIN BEARINGS (4) 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 2 GEARS 6 BEARINGS 2 ROTORS 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 DELIVERY
V 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
MONDAY TUESDAY WEDNESDAY THURSDAY FRIDAY SATURDAY SUNDAY HOURS
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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
INTAKE 1 BAR A VACUUM PREVAILS: INTAKE 1/2 BAR A SCREW ELEMENT OUTLET 8 BAR A OUTLET 8 BAR A
PRESSURE RATIO=8 PRESSURE RATIO IS 16 WHICH IS MUCH HIGHER THAN THE BUILT IN PR.HENCE VERY INEEFECIENT AT PART LOADS
* 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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P R E S S U R E COMPRESSOR CONTROL - DYNAMIC MACHINES SURGE LIMIT SURGE CONTROL 60 85 100
DEMAND FALLS BELOW SURGE CONTROL
FLOW
DEMAND IS ABOVE SURGE CONTROL 2 SCENARIOS: CONTROL ABOVE SURGE CONTROL CONTROL BELOW SURGE CONTROL
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CONTROL SYSTEMS - DYNAMIC MACHINES
Inlet guide vanes
100 - 65% capacity control • Constant pressure within control range
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CONTROL SYSTEMS-DYNAMIC MACHINES CONTROL ABOVE SURGE CONTROL V1’ V1
VELOCITY CHANGE(V) =V1-V2
V2
NORMAL
V1 V2
VELOCITY CHANGE =V1’-V2 < V INLET GUIDE VANES
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 150 100 Plant demand 100 Inlet throttle valve at 100% pressure 90 80 Inlet guide vanes at 100% pressure Energy savings 70 60 70 80 90 100 110 Adjustable inlet guide vanes provide a pre whirl to the air or gas,smoothly controlling capacity without any turbulence unlike the throttle valve
9%energy savings at part load
Capacity %
CONTROL SYSTEMS-DYNAMIC MACHINES 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 SHAFT SIMPLE 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 V
SINGLE STAGE 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
X A
P
X
V
LESS EFFICIENT EITHER ABOVE (A) OR BELOW THE BIPR
V
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
aerodynamic efficiency total efficiency mechanical efficiency Efficiency versus number of stages [6-10.4 bar(e)] number of stages CURVE CORRESPONDS TO 7-8 BAR OPERATION
FACTORS DETERMINING AERODYNAMIC EFFECIENCY ARE SPECIFIC SPEEDS MACH NUMBERS REYNOLDS NUMBERS
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STAGING CRITERIA -TURBO MACHINES EFFECIENCY CONSIDERATIONS Specific Speed = rpm x (flow) ------------------ 1/2 3/4
(
Adiabatic Head)
na
0.23 - 0.24
SPECIFIC SPEED Operation above or below the optimum Specific Speed compromises on Aerodynamic Effeciency(n a) . Characteristically the optimum is achieved at 390 400m/s impeller tip speed with 45 deg. impellers
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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(n a).
The speed of sound being 332m/s,the critical Mach No.corresponds to about 400-410m/s
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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)
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THE RIGHT CHOICE
• • • • • •
COMPRESSOR TYPES WORKING PRINCIPLES CHARACTERISTICS CONTROL SYSTEMS STAGING
GENERAL INFORMATION
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• •
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 BEC 45,000 BEC 80,000 INTERCONNECTING AND INST. AIR PIPING AND VALVES MICRO INTAKE FILTER (2U) ISOLATED FOUNDATIONS (WITH CORK INLAY) INSTRUMENT AIR COMPRESSOR WITH DRYER EXPANSION JOINTS SILENCING CANOPY (OPTIONAL) OTHER ITEMS (WATER MANIFOLD,ETC) BEC 65,000 BEC 75,000 BEC 30,000 BEC 140,000 BEC 100,000 BEC 350,000 TOTAL INSTALLATION COST BEC 885,000 TOTAL INSTALLATION TIME 30 DAYS
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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
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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