Session 5 NPSH Made Simple (well, Simpler Anyway!)
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Pumps, Compressors and Seals
The most numerous types of fluid machineries are of the pump family (machines which add energy to the fluid), other important types are turbines (which extract energy from fluid). Both types are usually connected to a rotating shaft, hence also called turbomachineries. The prefix turbo- is a Latin word meaning ―spin’’ or ―whirl,’’ appropriate for rotating devices. The pump is the oldest fluid-energy-transfer device known. At least two designs date before Christ: (i) the undershot-bucket waterwheels, or norias, used in Asia and Africa (1000 B.C.) and (ii) Archimedes’ screw pump (250 B.C.), still being manufactured today to handle solid-liquid mixtures or to raise water from the hold of a ship. Paddlewheel turbines were used by the Romans in 70 B.C., and Babylonian windmills date back to 700 B.C. Since that time, many variations and applications of pumps have been developed. The power generating turbomachines (turbines) decrease the head or energy level of the working fluids passing through them and they are coupled to machines, such as electric generators, pumps, compressors etc.
Pumps, Compressors and Seals
The most numerous types of fluid machineries are of the pump family (machines which add energy to the fluid), other important types are turbines (which extract energy from fluid). Both types are usually connected to a rotating shaft, hence also called turbomachineries. The prefix turbo- is a Latin word meaning ―spin’’ or ―whirl,’’ appropriate for rotating devices. The pump is the oldest fluid-energy-transfer device known. At least two designs date before Christ: (i) the undershot-bucket waterwheels, or norias, used in Asia and Africa (1000 B.C.) and (ii) Archimedes’ screw pump (250 B.C.), still being manufactured today to handle solid-liquid mixtures or to raise water from the hold of a ship. Paddlewheel turbines were used by the Romans in 70 B.C., and Babylonian windmills date back to 700 B.C. Since that time, many variations and applications of pumps have been developed. The power generating turbomachines (turbines) decrease the head or energy level of the working fluids passing through them and they are coupled to machines, such as electric generators, pumps, compressors etc.
Chapter One Classification Of Pumps
What Is a Pump?
A pump is a machine or device for raising, transferring, or compressing fluids. Pumps represent the largest single use of power in the industry (31%) by motor-driven equipment. Process variables, including pressure and flow of gases and liquids, have long been regulated using mechanical clutches, throttles, and adjustable inlet guide vanes. Pumps often operate as a variable torque load, a load that increases as the speed increases. These mechanisms waste energy, require frequent maintenance, and provide inaccurate control.
Chapter One Classification Of Pumps
What Is a Pump?
A pump is a machine or device for raising, transferring, or compressing fluids. Pumps represent the largest single use of power in the industry (31%) by motor-driven equipment. Process variables, including pressure and flow of gases and liquids, have long been regulated using mechanical clutches, throttles, and adjustable inlet guide vanes. Pumps often operate as a variable torque load, a load that increases as the speed increases. These mechanisms waste energy, require frequent maintenance, and provide inaccurate control.
Chapter10. Compressors
Main Types of Compressors
The compressor is the heart of a mechanical refrigeration system.
There is the need for many types of compressors because of the variety of refrigerants and the capacity, location and application of the systems.
Generally, the compressor can be classified into two basic types: positive displacement and roto-dynamic.
Chapter10. Compressors
Main Types of Compressors
The compressor is the heart of a mechanical refrigeration system.
There is the need for many types of compressors because of the variety of refrigerants and the capacity, location and application of the systems.
Generally, the compressor can be classified into two basic types: positive displacement and roto-dynamic.
Guide To The Selection Of Rotodynamic Pumps
Purpose of this Guide to pump procurement
This Guide provides an introduction to the very complex subject of the selection of pumps. It is aimed at anyone who wishes to purchase or select a pump and, at the same time, wishes to save money on their energy bill. Almost invariably, this saving will be far more than the first cost of the pump. The reader may be the end user, a contractor, or a consultant. This Guide provides the reader with the basic principles of pump procurement, giving pointers to the pump type and performance they should consider. Pumps are divided into their main types, then their basic construction and performance are considered, their principal applications are described, the basic principles of pump selection are explained and, last but not least, target efficiencies are set to help minimize energy usage. The hope is that both pump users and the environment will benefit.
Guide To The Selection Of Rotodynamic Pumps
Purpose of this Guide to pump procurement
This Guide provides an introduction to the very complex subject of the selection of pumps. It is aimed at anyone who wishes to purchase or select a pump and, at the same time, wishes to save money on their energy bill. Almost invariably, this saving will be far more than the first cost of the pump. The reader may be the end user, a contractor, or a consultant. This Guide provides the reader with the basic principles of pump procurement, giving pointers to the pump type and performance they should consider. Pumps are divided into their main types, then their basic construction and performance are considered, their principal applications are described, the basic principles of pump selection are explained and, last but not least, target efficiencies are set to help minimize energy usage. The hope is that both pump users and the environment will benefit.
Centrifugal and Positive Displacement Pumps
Introduction
Centrifugal pumps basically consist of a stationary pump casing and an impeller mounted on a rotating shaft. The pump casing provides a pressure boundary for the pump and contains channels to properly direct the suction and discharge flow. The pump casing has suction and discharge penetrations for the main flow path of the pump and normally has small drain and vent fittings to remove gases trapped in the pump casing or to drain the pump casing for maintenance.
Figure 1 is a simplified diagram of a typical centrifugal pump that shows the relative locations of the pump suction, impeller, volute, and discharge. The pump casing guides the liquid from the suction connection to the center, or eye, of the impeller. The vanes of the rotating impeller impart a radial and rotary motion to the liquid, forcing it to the outer periphery of the pump casing where it is collected in the outer part of the pump casing called the volute. The volute is a region that expands in cross-sectional area as it wraps around the pump casing. The purpose of the volute is to collect the liquid discharged from the periphery of the impeller at high velocity and gradually cause a reduction in fluid velocity by increasing the flow area. This converts the velocity head to static pressure. The fluid is then discharged from the pump through the discharge connection.
Centrifugal and Positive Displacement Pumps
Introduction
Centrifugal pumps basically consist of a stationary pump casing and an impeller mounted on a rotating shaft. The pump casing provides a pressure boundary for the pump and contains channels to properly direct the suction and discharge flow. The pump casing has suction and discharge penetrations for the main flow path of the pump and normally has small drain and vent fittings to remove gases trapped in the pump casing or to drain the pump casing for maintenance.
Figure 1 is a simplified diagram of a typical centrifugal pump that shows the relative locations of the pump suction, impeller, volute, and discharge. The pump casing guides the liquid from the suction connection to the center, or eye, of the impeller. The vanes of the rotating impeller impart a radial and rotary motion to the liquid, forcing it to the outer periphery of the pump casing where it is collected in the outer part of the pump casing called the volute. The volute is a region that expands in cross-sectional area as it wraps around the pump casing. The purpose of the volute is to collect the liquid discharged from the periphery of the impeller at high velocity and gradually cause a reduction in fluid velocity by increasing the flow area. This converts the velocity head to static pressure. The fluid is then discharged from the pump through the discharge connection.
Centrifugal Pump Application and Optimization
Summary
Centrifugal pumps perform many important functions to control the built environment. The physics and basic mechanics of pumps have not changed substantially in the last century. However, the state of the art in the application of pumps has improved dramatically in recent years. Even so, pumps are still often not well applied, and become common targets in retrocommissioning projects where field assessment and testing can reveal significant energy savings potential from optimizing pump performance. Typically, retrocommissioning finds that pump flow rates do not match their design intent and that reducing flow rates to match load requirements or eliminating unnecessary pressure drops can save energy. As the example below illustrates, decisions made during the design phase have implications throughout the operating life of the building. Although fully optimizing any design will require some effort after installation, the prevalence and magnitude of the savings that are commonly found in retrocommissioning and ongoing commissioning begs the larger question: How much greater would the savings be if pumps were selected and applied optimally during the design phase?
Centrifugal Pump Application and Optimization
Summary
Centrifugal pumps perform many important functions to control the built environment. The physics and basic mechanics of pumps have not changed substantially in the last century. However, the state of the art in the application of pumps has improved dramatically in recent years. Even so, pumps are still often not well applied, and become common targets in retrocommissioning projects where field assessment and testing can reveal significant energy savings potential from optimizing pump performance. Typically, retrocommissioning finds that pump flow rates do not match their design intent and that reducing flow rates to match load requirements or eliminating unnecessary pressure drops can save energy. As the example below illustrates, decisions made during the design phase have implications throughout the operating life of the building. Although fully optimizing any design will require some effort after installation, the prevalence and magnitude of the savings that are commonly found in retrocommissioning and ongoing commissioning begs the larger question: How much greater would the savings be if pumps were selected and applied optimally during the design phase?
Centrifugal Pump Analysis
Introduction
Centrifugal pumps are used to increase pressure in a liquid for the purpose of transporting the liquid through piping and other devices for use in an industrial process. With the higher pressure, the liquid can be transported in short or long pipelines for delivery to an ultimate destination. Examples include water pipelines, refined petroleum and crude oil pipelines.
The pressure generated by the pump is gradually depleted as the liquid flows through the pipeline, due to friction in the pipe, as well as any elevation increase from the point of origin to the destination point. The liquid as it enters the pump has a certain amount of energy, due to its initial pressure (pressure energy), position (potential energy) and its velocity (kinetic energy). The potential energy depends on the location of the liquid from some datum, such as sea level. The kinetic energy is due to the motion of the liquid. The sum of three components is the total energy of the liquid. As the liquid comes out of the pump, energy is imparted by the rotating element (impeller) in the pump and the liquid pressure increases. The velocity of the liquid also changes from that at the pump inlet. In a centrifugal pump, the liquid is accelerated by centrifugal force during its passage through the rotating pump impeller and, finally at the exit, the kinetic energy is converted to pressure energy as it exits the pump volute into the discharge piping.
Centrifugal Pump Analysis
Introduction
Centrifugal pumps are used to increase pressure in a liquid for the purpose of transporting the liquid through piping and other devices for use in an industrial process. With the higher pressure, the liquid can be transported in short or long pipelines for delivery to an ultimate destination. Examples include water pipelines, refined petroleum and crude oil pipelines.
The pressure generated by the pump is gradually depleted as the liquid flows through the pipeline, due to friction in the pipe, as well as any elevation increase from the point of origin to the destination point. The liquid as it enters the pump has a certain amount of energy, due to its initial pressure (pressure energy), position (potential energy) and its velocity (kinetic energy). The potential energy depends on the location of the liquid from some datum, such as sea level. The kinetic energy is due to the motion of the liquid. The sum of three components is the total energy of the liquid. As the liquid comes out of the pump, energy is imparted by the rotating element (impeller) in the pump and the liquid pressure increases. The velocity of the liquid also changes from that at the pump inlet. In a centrifugal pump, the liquid is accelerated by centrifugal force during its passage through the rotating pump impeller and, finally at the exit, the kinetic energy is converted to pressure energy as it exits the pump volute into the discharge piping.
Chapter One Introduction To Reciprocating Compressors
Introduction
Compressors are used whenever it is necessary to flow gas from a low-pressure system to a higher-pressure system. Flash gas from low-pressure vessels used for multi-stage stabilization of liquids, oil treating, water treating, etc.; often exists at too low a pressure to flow into the gas sales pipeline. Sometimes this gas is used as fuel, and them the remainder is flared or vented. In many instances, it is economically attractive to compress this gas to a high enough pressure so it can be sold. Compression may also be required for environmental reasons. Flash gas that might otherwise be flared may be compressed for sales or gas produced with oil (associated gas) may be compressed for re-injection to avoid, flaring or to help maintain reservoir pressure. In some marginal gas fields, and in many larger gas fields that experience a decline in flowing pressure with time, it may be economical to allow the wells to flow at surface pressures below that required for gas sales. In such cases, a booster compressor (one where the ratio of discharge to suction pressure is low) may be installed. Booster compressors are also used on long pipelines to restore pressure drop lost to friction. The use of large compressors is probably more prevalent in oil field facilities than in gas field facilities. Oil wells often require low flowing surface pressures and the gas that flashes off the oil in the separator must be compressed. Often, natural gas is, injected into the tubing of the well to lighten the column of liquid and reduce downhole pressure. This "gas lift" gas is produced back with good fluids at low pressure. Compressors are used so the lift gas can be recirculated and
Chapter One Introduction To Reciprocating Compressors
Introduction
Compressors are used whenever it is necessary to flow gas from a low-pressure system to a higher-pressure system. Flash gas from low-pressure vessels used for multi-stage stabilization of liquids, oil treating, water treating, etc.; often exists at too low a pressure to flow into the gas sales pipeline. Sometimes this gas is used as fuel, and them the remainder is flared or vented. In many instances, it is economically attractive to compress this gas to a high enough pressure so it can be sold. Compression may also be required for environmental reasons. Flash gas that might otherwise be flared may be compressed for sales or gas produced with oil (associated gas) may be compressed for re-injection to avoid, flaring or to help maintain reservoir pressure. In some marginal gas fields, and in many larger gas fields that experience a decline in flowing pressure with time, it may be economical to allow the wells to flow at surface pressures below that required for gas sales. In such cases, a booster compressor (one where the ratio of discharge to suction pressure is low) may be installed. Booster compressors are also used on long pipelines to restore pressure drop lost to friction. The use of large compressors is probably more prevalent in oil field facilities than in gas field facilities. Oil wells often require low flowing surface pressures and the gas that flashes off the oil in the separator must be compressed. Often, natural gas is, injected into the tubing of the well to lighten the column of liquid and reduce downhole pressure. This "gas lift" gas is produced back with good fluids at low pressure. Compressors are used so the lift gas can be recirculated and
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