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POWER PLANT OPERATIONS
FUNDAMENTAL
Noor Azman Muhammad
Table of Contents 1. Basic Electricity ............................................................................................ 0
1.1. Electron Theory ...................................................................................... 0
1.2. Magnetism and Electromagnetism Explained ........................................ 1
1.3. Introduction to Alternating Current (AC) ................................................ 0
1.4. AC Induction Motors .............................................................................. 0
1.5. AC Generators ....................................................................................... 1
1.6. Transformer Basic Operation and Theory .............................................. 2
2. Power Plant Basics ....................................................................................... 0
2.1. Energy Conversion .................................................................................... 1
2.2. Steam Turbine Basics ............................................................................. 2
2.3. Combustion System Component Overview ............................................. 3
2.4. Internal Combustion System Component Overview ............................... 5
2.5. Boiler Water and Steam Cycle Overview ................................................ 0
2.6. Generator Overview ............................................................................... 1
3. Plant Instrumentation and Control Theory ................................................... 1
3.1. Instrumentation and Control Overview .................................................. 2
3.2. Temperature Instruments ...................................................................... 0
3.3. Pressure Measuring Devices .................................................................. 0
3.4. Level Measuring Devices ........................................................................ 3
3.5. Flow Measuring Devices ........................................................................ 0
3.6. Introduction to Automated Control ........................................................ 0
4. Intro to Plant Equipment .............................................................................. 0
4.1. Introduction to Pumps ........................................................................... 0
4.2. Introduction to Valves and Their Components ....................................... 1
4.3. Heat Exchanger Theory .......................................................................... 3
4.4. Introduction to Hydraulics ..................................................................... 1
5. Plant Drawings ............................................................................................ 2
5.1. P&ID Basics ............................................................................................ 2
5.2. Reading a P&ID ...................................................................................... 0
6. Plant Systems ............................................................................................... 0
6.1. Introduction to Combustion Air and Flue Gas Systems ........................... 0
6.2. Introduction to the Circulating Water System ........................................ 0
6.3. Introduction to the Condensate System ................................................. 0
6.4. Introduction to the Feedwater System ................................................... 0
7. Turbines ....................................................................................................... 0
7.1. Steam Turbine Design ............................................................................ 0
7.2. Steam Turbine Valves and Controls........................................................ 2
7.3. Steam Turbine Auxiliaries ...................................................................... 0
8. Internal combustion Engines ........................................................................ 1
8.1. Combustion Turbine Fundamentals ....................................................... 1
8.2. Introduction to Gas Turbines ................................................................. 2
8.3. Gas Turbines major components............................................................ 3
8.4. Introduction to Internal Combustion Engine ........... Error! Bookmark not
defined.
9. Boilers & Boiler Fuel Systems ....................................................................... 0
9.1. Coal Handling System ............................................................................ 0
9.2. Boiler Fuel System .................................................................................. 0
10. Power Generation ..................................................................................... 0
10.1. Generator and Auxiliary Systems’ Functions ....................................... 0
10.2. Generator and Auxiliary Systems’ Flow Paths and Major Components
1
10.3. Environmental Protection ................................................................... 1
10.4. Flue Gas Desulfurization System ......................................................... 1
11. Electrical Systems and Equipment ............................................................. 0
11.1. Protection Relays ................................................................................ 0
11.2. Generator, Transformer and Motor Protection ................................... 0
11.3. Grounding and Bonding ...................................................................... 2
11.4. Main Transformers ............................................................................. 2
11.5. Fuses and Circuit Breakers .................................................................. 1
12. Steam Tables ............................................................................................ 0
12.1. Understanding the Basic Properties of Water and Steam ................... 0
13. Basic Water Chemistry and Treatment ..................................................... 0
13.1. Corrosion Control in a Power Plant ..................................................... 1
13.2. Corrosion Control in a Power Plant ..................................................... 2
1. Basic Electricity So what is electricity and where does it come from? In its simplest terms, electricity is the movement of charge, which is considered by convention to be, from positive to negative. No matter how the charge is created, chemically (like in batteries), the movement of the discharge is electricity.
1.1. Electron Theory
There is an equal number of electrons and protons in an atom. Hence, atom is in general electrically neutral. As the protons in the central nucleus are positive in charge and electrons orbiting the nucleus, are negative in charge, there will be an attraction force acts between the electrons and protons. In an atom various electrons arrange themselves in different orbiting shells situated at different distances from the nucleus.
The force is more active to the electrons nearer to the nucleus, than to the electrons situated at outer shell of the atom. One or more of these loosely bonded electrons may be detached from the atom. The atoms with
lack of electrons are called ions. Due to lack of electrons, compared to number of protons, the said ion becomes positively charged. Hence, this ion is referred as positive ion and because of positive electrical charge; this ion can attract other electrons from outside.
The electrons which move from atom to atom in random manner are called free electrons. When a voltage is applied across a conductor, due to presence of electric field, the free electrons start drifting to a particular direction according the direction of voltage and electric field. This phenomenon causes current in the conductor.
The movement of electrons, means movement of negative charge and rate of this charge transfer with respect to time is known as current.
Conventional Flow of Current Vs Electrons
Flow
In the early days, it was thought that the current is, flow of positive charge and hence current always comes out from the positive terminal of the battery, passing through the external circuit and enters in the negative terminal of the battery. This is called conventional flow of current.
The true electron flow
The actual cause of current in a conductor is due to movement of free electrons and electrons have negative change. Due to negative charge, electrons move from the negative terminal to the positive terminal of the battery through the external circuit. So the conventional flow of current is always in the opposite direction of electrons flow. The true electron flow is used only when it is necessary to explain certain effects (as in semiconductor devices such as diodes and transistors).
Conductors, Insulators and Semiconductors
Materials can be classified as conductors, insulators, and semiconductors according
the ability of the material to allow the flow of electricity. All materials have a measurable property called electrical conductivity that indicates the ability of the material to either allow or impede the flow of electrons. Materials that easily conduct electricity have a high conductivity.
Conductor
A conductor is a material that readily allows the flow of electricity. Metal wires are usually good conductors, though some metals are better conductors than others. Copper, aluminium, silver and gold are examples of good conductors. Compared to non-conductors, these materials have a high electrical conductivity.
Insulator
An insulator is a material that is a poor conductor. We say that an insulator tends to prevent the flow of electricity. Rubber, wood, ceramics and air are examples of good insulators. Compared to conductors, these materials have a low electrical conductivity. If a positively charged region is separated from a negatively charged region by a conductor, then electrical current will flow
between the regions. If instead the positively charge region is separated from a negatively charged region by an insulator, little or no electrical current will flow.
Semiconductor
A semiconductor is a material that has an intermediate tendency to allow the flow of electrons, i.e. it is somewhere between an insulator and a conductor. The conductivity of semiconductor materials can be changed by the presence of an electrical field, exposure to light, or the application of mechanical pressure or heat. The ability to change the apparent electrical conductivity by introducing these stimuli allows semiconductors to be used as the building blocks of semiconductor devices. Semiconductor devices are like switches that allow electricity to flow. Sometimes that switching is controlled intentionally to control the flow of electricity, for examples in LEDs (light emitting diodes) and transistors. Other times the switching of the flow of electricity is passive and controlled by the environment, for example in photovoltaic solar cells or semiconductor sensors.
Transistors
Transistors are semiconductor devices that can be used to switch or amplify electrical currents. Digital logic and computing devices
like microprocessors, communication chips, and signal processing chips can have hundreds, thousands, millions or billions of transistors.
1.2. Magnetism and Electromagnetism
Magnetism is one aspect of the combined electromagnetic force. It refers to physical phenomena arising from the force caused by magnets, objects that produce fields that attract or repel other objects.
The motion of electrically charged particles gives rise to magnetism. The force acting on an electrically charged particle in a magnetic field depends on the magnitude of the charge, the velocity of the particle, and the strength of the magnetic field.
Magnet has a north pole and a south pole. Opposite poles attract each other (north and south) and similar poles repel each other (north-north or south-south)
There are several different types of magnets.
Permanent magnets are magnets that permanently retain their magnetic field. This
is different from a temporary magnet, which usually only has a magnetic field when it is placed in a bigger, stronger magnetic field, or when electric current flows through it Another type of temporary magnet, called an electromagnet, uses electricity to create a magnet.
Electromagnetism
When a wire is moved in a magnetic field, the field induces a current in the wire. Conversely, a magnetic field is produced by an electric charge in motion. This is the Faraday’s Law of Induction, which is the basis for electromagnets, electric motors and generators. A charge moving in a straight line, as through a straight wire, generates a magnetic field that spirals around the wire. When that wire is formed into a loop, the field becomes a doughnut shape, or a torus.
The applications of electromagnets are nearly countless. Faraday’s Law of Induction forms the basis for many aspects of our modern society including not only electric motors and generators, but electromagnets of all sizes.
1.3. Introduction to Alternating Current
Alternating current (AC), is an electric current in which the flow of electric charge periodically reverses direction, whereas in direct current (DC, also dc), the flow of electric charge is only in one direction
AC is the form in which electric power is delivered to businesses and residences. The usual waveform of alternating current in most electric power circuits is a sine wave.
Electric power is distributed as alternating current because AC voltage may be increased or decreased with a transformer. This allows the power to be transmitted through power lines efficiently at high voltage, which reduces the power lost as heat due to resistance of the wire, and transformed to a lower, safer, voltage for use. Use of a higher voltage leads to significantly more efficient transmission of power.
Power transmitted at a higher voltage requires less loss-producing current than for the same power at a lower voltage. Power is often transmitted at hundreds of kilovolts,
and transformed to 100–240 volts for domestic use.
High voltage transmission lines deliver power from electric generation plants over long distances using alternating current.
Three-phase electrical generation is very common. The simplest way is to use three separate coils in the generator stator, physically offset by an angle of 120° (one-third of a complete 360° phase) to each other. Three current waveforms are produced that are equal in magnitude and 120° out of phase to each other. If coils are added opposite to these (60° spacing), they generate the same phases with reverse polarity and so can be simply wired together.
In three phase circuit, connections can be given in two types:
Star connection
Delta connection
1.4. AC Induction Motors
One of the most common electrical motor used in most applications is induction motor. This motor is also called as asynchronous motor because it runs at a speed less than its synchronous speed. Here we need to define what synchronous speed is. Synchronous speed is the speed of rotation of the magnetic field in a rotary machine and it depends upon the frequency and number poles of the machine.
An induction motor always runs at a speed less than synchronous speed because the rotating magnetic field which is produced in the stator will generate flux in the rotor which will make the rotor to rotate, but due to the lagging of flux current in the rotor with flux current in the stator, the rotor will never reach to its rotating magnetic field speed i.e. the synchronous speed.
Working Principle of Induction Motor
We need to give double excitation to make a machine to rotate. For example a DC motor, need one supply to the stator and another to the rotor through brush arrangement. But in induction motor require only one supply.
Actually the supply is given to the stator winding, flux will generate in the coil due to flow of current in the coil. Now the rotor winding is arranged in such a way that it becomes short circuited in the rotor itself. The flux from the stator will cut the coil in the rotor and since the rotor coils are short circuited, according to Faraday's law of electromagnetic induction, current will start flowing in the coil of the rotor. When the current will flow, another flux will get generated in the rotor. Now there will be two flux, one is stator flux and another is rotor flux and the rotor flux will be lagging wth regard to the stator flux. Due to this, the rotor will feel a torque which will make the rotor to rotate in the direction of rotating magnetic flux. So the speed of the rotor will be depending upon the ac supply and the speed can be controlled by varying the input supply. This is the working principle of an induction motor of either type single and three phase.
1.5. AC Generators
The turning of a coil in a magnetic field produces motional emfs in both sides of the
coil which add. Since the component of the velocity perpendicular to the magnetic field changes sinusoidal with the rotation, the generated voltage is sinusoidal or AC. This process can be described in terms of Faraday's law when you see that the rotation of the coil continually changes the magnetic flux through the coil and therefore generates a voltage.
1.6. Transformer Basic Operation and
Theory
Electrical power transformer is a static device which transforms electrical energy from one circuit to another without any direct electrical connection and with the help of mutual induction between two windings. It transforms power from one circuit to another without changing its frequency but may be in different voltage level.
Working Principle of Transformer
The working principle of transformer is very simple. It depends upon Faraday's law of electromagnetic induction. Actually, mutual induction between two or more winding is
responsible for transformation action in an electrical transformer.
The alternating current through the winding produces a continually changing flux or alternating flux that surrounds the winding. If any other winding is brought nearer to the previous one, obviously some portion of this flux will link with the second. As this flux is continually changing in its amplitude and direction, there must be a change in flux linkage in the second winding or coil. According to Faraday's law of electromagnetic induction, there must be an EMF induced in the second. If the circuit of the later winding is closed, there must be a current flowing through it. This is the most basic of working principle of transformer.
The three main parts of a transformer are,
Primary Winding of Transformer
Which produces magnetic flux when it is connected to electrical source.
Magnetic Core of Transformer-
The magnetic flux produced by the primary winding, that will pass through this low reluctance path linked with secondary
winding and create a closed magnetic circuit.
Secondary Winding of Transformer-
The flux, produced by primary winding, passes through the core, will link with the secondary winding. This winding also wounds on the same core and gives the desired output of the transformer.
2. Power Plant Basics Energy comes in various forms but electrical energy is the most convenient form of energy since it can be transported with ease, generated in a number of different ways, and can be converted into mechanical work or heat energy as and when required.
The Power Plant
Power or energy is generated in a power plant which is the place where power is generated .Energy cannot be created or destroyed but merely changed from one form to the other. More correctly, a power plant can be said to be a place where electrical energy is obtained by converting some other form of energy. The type of energy converted depends on what type of power plant.
Types of Power Plants
There are several different types of power plants used across the world
Thermal Power Plants
These power plants convert heat energy into electrical energy. The working fluid of these plants is mostly steam and they work on the Rankine cycle. A steam power plant consists of a boiler which is used to generate the steam from water, a prime mover like a steam turbine to convert the enthalpy of the steam into rotary motion of the turbine which is linked to the alternator to produce electricity. The steam is again condensed in the condenser and fed to the boiler again.
Hydro Power Plants
These plants use the kinetic energy of flowing water to rotate the turbine blades, hence converting kinetic energy into electrical energy. These types of power plants are very good for peak loads. Their main disadvantage lies in the fact that their location depends on a number of factors which are beyond the control of human beings such as the hydrological cycle of the region and so forth. If there is shortage of water it could lead to shut down of these plants.
Apart from these main two types there are plants which use nuclear energy, solar energy and even wind energy to generate power.
3. Energy Conversion Energy transformation or energy conversion is the process of changing one form of energy to another form of energy. In physics, the term energy describes the capacity to produce certain changes within any system, without regard to limitations in transformation imposed. Changes in total energy of systems can only be accomplished by adding or removing energy from them, as energy is a quantity which is conserved (unchanging), as stated by the first law of thermodynamics. Mass-energy equivalence, which rose up from special relativity, states that changes in the energy of systems will also coincide with changes (often small in practice) in the system's mass, and the mass of a system is a measure of its energy content.
Energy in many of its forms may be used in natural processes, or to provide some service to society such as heating,
refrigeration, light, or performing mechanical work to operate machines. For example, an internal combustion engine converts the potential chemical energy in gasoline and oxygen into thermal energy which, by causing pressure and performing work on the pistons, is transformed into the mechanical energy that accelerates the vehicle (increasing its kinetic energy).
3.1. Steam Turbine Basics
A steam turbine is powered by the energy in hot, gaseous steam and works like a cross between a wind turbine and a water turbine. Steam turbines use high-pressure steam to turn electricity generators at incredibly high speeds. A typical power plant steam turbine rotates at 1800–3600 rpm. Which needs to use a gearbox to drive a generator quickly enough to make electricity.
Just like in a steam engine, the steam expands and cools as it flows past a steam turbine's blades, giving up as much as possible of the energy it originally contained. The flow of the steam turns the blades continually:
Electrical energy generation using steam turbines involves three energy conversions, extracting thermal energy from the fuel and using it to raise steam, converting the thermal energy of the steam into kinetic energy in the turbine and using a rotary generator to convert the turbine's mechanical energy into electrical energy.
3.2. Combustion System Component
Overview
Combustion is a chemical process in which a substance reacts rapidly with oxygen and gives off heat. The original substance is called the fuel, and the source of oxygen is called the oxidizer. The fuel can be a solid, liquid, or gas, although for airplane propulsion the fuel is usually a liquid. The oxidizer, likewise, could be a solid, liquid, or gas, but is usually a gas (air) for airplanes. For model rockets, a solid fuel and oxidizer is used.
During combustion, new chemical substances are created from the fuel and the oxidizer. These substances are called exhaust. Most of the exhaust comes from chemical combinations of the fuel and
oxygen. When a hydrogen-carbon-based fuel (like gasoline) burns, the exhaust includes water (hydrogen + oxygen) and carbon dioxide (carbon + oxygen). But the exhaust can also include chemical combinations from the oxidizer alone. If the gasoline is burned in air, which contains 21% oxygen and 78% nitrogen, the exhaust can also include nitrous oxides (NOX, nitrogen + oxygen). The temperature of the exhaust is high because of the heat that is transferred to the exhaust during combustion. Because of the high temperatures, exhaust usually occurs as a gas, but there can be liquid or solid exhaust products as well. Soot, for example, is a form of solid exhaust that occurs in some combustion processes.
During the combustion process, as the fuel and oxidizer are turned into exhaust products, heat is generated. Interestingly, some source of heat is also necessary to start combustion. Gasoline and air are both present in your automobile fuel tank; but combustion does not occur because there is no source of heat. Since heat is both required to start combustion and is itself a product of combustion, we can see why
combustion takes place very rapidly. Also, once combustion gets started, we don't have to provide the heat source because the heat of combustion will keep things going. We don't have to keep lighting a campfire, it just keep burning.
For combustion to occur three things must be present: a fuel to be burned, a source of oxygen, and a source of heat. As a result of combustion, exhausts are created and heat is released. You can control or stop the combustion process by controlling the amount of the fuel available, the amount of oxygen available, or the source of heat.
3.3. Internal Combustion System
Component Overview
An internal combustion engine is a heat engine where the combustion of a fuel occurs with air in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal combustion engine the expansion of the high-temperature and high-pressure gases produced by combustion apply direct force to some component of the engine. The force is applied typically to pistons, turbine blades, rotor or a nozzle.
This force moves the component over a distance, transforming chemical energy into useful mechanical energy.
The term internal combustion engine usually refers to an engine in which combustion is intermittent, such as the more familiar four-stroke and two-stroke piston engines. A second class of internal combustion engines use continuous combustion: gas turbines, jet engines and rocket engines, which are internal combustion engines on the same principle as previously described
Internal combustion engines are quite different from external combustion engines, such as steam engines, in which the energy is delivered to a working fluid not consisting of, mixed with, or contaminated by combustion products. Working fluids can be air, hot water, pressurized water or steam in a boiler.
Internal combustion engines are usually powered by energy-dense fuels such as petrol or diesel, liquids derived from fossil fuels. While there are many stationary applications, most Internal combustion engines are used in mobile applications such as cars, aircraft, and boats.
3.4. Boiler Water and Steam Cycle
Overview
Boiler or more specifically steam boiler is an essential part of thermal power plant.
Definition of Boiler
Steam boiler or simply a boiler is basically a closed vessel into which water is heated until the water is converted into steam at required pressure.
Working Principle of Boiler
The basic working principle of boiler is simple and easy to understand. The boiler is essentially a closed vessel inside which water is stored. Fuel (generally coal) is bunt in a furnace and hot gasses are produced. These hot gasses come in contact with water vessel where the heat of these hot gases transfer to the water and consequently steam is produced in the boiler. Then this steam is piped to the steam turbine of thermal power plant. There are many different types of boiler utilized for different.
Types of Boiler
There are mainly two types of boiler
1. Water tube boiler
2. Fire tube boiler.
Fire Tube Boiler
As it indicated from the name, the fire tube boiler consists of numbers of tubes through which hot gasses are passed. These hot gas tubes are immersed into water, in a closed vessel. Actually in fire tube boiler one closed vessel or shell contains water, through which hot tubes are passed. These fire tubes or hot gas tubes heated up the water and convert the water into steam and the steam remains in same vessel. As the water and steam both are in same vessel a fire tube boiler cannot produce steam at very high pressure.
Water Tube Boiler
A water tube boiler is such kind of boiler where the water is heated inside tubes and the hot gasses are passed through tubes which are surrounded by water.
3.5. Generator Overview
An electric generator is a device that converts mechanical energy obtained from an external source into electrical energy as the output.
Generator uses the mechanical energy supplied to it to force the movement of electric charges present in the wire of its windings through an external electric circuit. This flow of electric charges constitutes the output electric current supplied by the generator. This mechanism can be understood by considering the generator as a water pump, which causes the flow of water but does not actually ‘create’ the water flowing through it.
The modern-day generator works on the principle of electromagnetic induction the flow of electric charges could be induced by moving an electrical conductor, such as a wire that contains electric charges, in a magnetic field. This movement creates a voltage difference between the two ends of the wire or electrical conductor, which in turn causes the electric charges to flow, thus generating electric current.
There are two types of generators, one is ac
generator and other is dc generator.
DC Generator
A dc generator converts mechanical energy into direct current electricity.
A DC generator has the following parts
1. Yoke
2. Pole of generator
3. Field winding
4. Armature of DC generator
5. Brushes of generator
6. Bearing
AC Generator
The working principle of an alternator or AC generator is similar to the basic working principle of a DC generator.
Alternating voltage may be generated by rotating a coil in the magnetic field or by rotating a magnetic field within a stationary coil. The value of the voltage generated depends on-
1. The number of turns in the coil.
2. Strength of the field.
3. The speed at which the coil or magnetic field rotates.
4. Plant Instrumentation and
Control Theory Instrumentation is defined as the art and science of measurement and control of process variables within a production area. The process variables used in industries are Level, Pressure, Temperature, Humidity, Flow, pH, Force, Speed etc. Control engineering or control systems engineering is the engineering discipline that applies control theory to design systems with desired behaviours.
The practice uses sensors to measure the output performance of the device being controlled and those measurements can be used to give feedback to the input actuators that can make corrections toward desired performance. When a device is designed to perform without the need of human inputs for correction it is called automatic control.
Control systems engineering activities focus on implementation of control systems mainly derived by mathematical modelling of systems of a diverse range.
4.1. Instrumentation and Control Overview
Instrumentation is often used to measure and control process variables within a laboratory or manufacturing area,
The ability to make precise, verifiable and reproducible measurements of the natural world, at levels that were not previously observable, using scientific instrumentation.
The control of processes is one of the main branches of applied instrumentation. Instruments are often part of a control system in refineries, factories, and vehicles. Instruments attached to a control system may provide signals used to operate a variety of other devices, and to support either remote or automated control capabilities. These are often referred to as final control elements when controlled remotely or by a control system.
4.2. Temperature Instruments
Temperature is one of the most widely measured parameters in a power plant. No matter the type of plant, accurate and reliable temperature measurement is essential for operational excellence.
Incorrect measurement because of electrical effects, nonlinearity or instability can result in damage to major equipment. Using advanced diagnostics, modern temperature instrumentation can inform a plant's maintenance department that a problem exists, where it is and what to do about it long before anyone in operations even suspects that an issue exists.
Devices for measuring temperature include:
• Thermocouples.
• Thermistors.
• Resistance temperature detector (RTD)
• Pyrometer.
• Infrared.
• Thermometers
4.3. Pressure Measuring Devices
A pressure gauge is a common component in operations from various industries across
the world. But not every gauge is created equally or made for every situation.
Gauges with bourdon tubes are the most common pressure measuring devices used today. They combine a high grade of measuring technology, simple operation, ruggedness and flexibility with the advantages of industrial and cost-effective production. Needing no external power supply, bourdon tube gauges are the best choice for most applications.
Applications for gauges with a bourdon tube range from highly automated chemical processes, such as, refineries and petrochemical processing, to hydraulic and pneumatic installations. These types of gauges can also be found at all critical process monitoring and safety points in today’s energy industries, from exploration wells and petrochemical plants, to power stations and wastewater operations.
A pressure measurement can further be described by the type of measurement being performed. The three methods for measuring pressure are absolute, gauge, and differential.
Absolute Pressure
The absolute measurement method is relative to 0 Pa, the static pressure in a vacuum. The pressure being measured is acted upon by atmospheric pressure in addition to the pressure of interest. Therefore, absolute pressure measurement includes the effects of atmospheric pressure. This type of measurement is well-suited for atmospheric pressures such as those used in altimeters or vacuum pressures. Often, the abbreviations Paa (Pascal’s absolute) or psia (pounds per square inch absolute) are used to describe absolute pressure.
Gauge Pressure
Gauge pressure is measured relative to ambient atmospheric pressure. This means that both the reference and the pressure of interest are acted upon by atmospheric pressures. Therefore, gauge pressure measurement excludes the effects of atmospheric pressure. These types of measurements include tire pressure and blood pressure measurements. Similar to absolute pressure, the abbreviations Pag
(Pascal’s gauge) or psig (pounds per square inch gauge) are used to describe gauge pressure.
Differential Pressure
Differential pressure is similar to gauge pressure; however, the reference is another pressure point in the system rather than the ambient atmospheric pressure. You can use this method to maintain relative pressure between two vessels such as a compressor tank and an associated feed line. Also, the abbreviations Pad (Pascal’s differential) or PSID (pounds per square inch differential) are used to describe differential pressure.
4.4. Level Measuring Devices
Level measurement devices can detect, indicate, and/or help control liquid or solid levels. Level measurement sensors fall into two main types. Point level measurement sensors are used to mark a single discrete liquid height–a preset level condition. Generally, this type of sensor functions as a high alarm, signaling an overfill condition, or as a marker for a low alarm condition. Continuous level sensors are more sophisticated and can provide level
monitoring of an entire system. They measure fluid level within a range, rather than at a one point, producing an analog output that directly correlates to the level in the vessel. To create a level management system, the output signal is linked to a process control loop and to a visual indicator.
Level measurement devices can be used for continuous monitoring of fluid level, or for point-level monitoring. In point-level monitoring they are used to determine if the fluid level has exceeded a high point, which could cause a spill, or gone below a low point, which could mean the system is close to running on empty.
4.5. Flow Measuring Devices
Flow measurement is the quantification of bulk fluid movement. Flow can be measured in a variety of ways. Positive-displacement flow meters accumulate a fixed volume of fluid and then count the number of times the volume is filled to measure flow. Other flow measurement methods rely on forces produced by the flowing stream as it overcomes a known constriction, to indirectly calculate flow. Flow may be measured by measuring the velocity of fluid over a known area.
The most common principals for fluid flow metering are:
• Differential Pressure Flowmeters
• Velocity Flowmeters
• Positive Displacement Flowmeters
• Mass Flowmeters
• Open Channel Flowmeters
4.6. Introduction to Automated Control
Automation or automatic control, is the use of various control systems for operating equipment such as machinery, processes in factories, boilers, ships, aircraft and other
applications with minimal or reduced human intervention. Some processes have been completely automated.
The biggest benefit of automation is that it saves labour; however, it is also used to save energy and materials and to improve quality, accuracy and precision.
Automation has been achieved by various means including mechanical, hydraulic, pneumatic, electrical, electronic devices and computers, usually in combination. Complicated systems, such as modern factories, airplanes and ships typically use all these combined techniques
Distributed Control System (DCS)
A distributed control system (DCS) is a control system for a process or plant, wherein control elements are distributed throughout the system. This is in contrast to non-distributed systems, which use a single controller at a central location. In a DCS, a hierarchy of controllers is connected by communications networks for command and monitoring.
Distributed control systems (DCSs) are dedicated systems used to control processes that are continuous or batch-oriented, such as oil refining, petrochemicals, power generation, fertilizers
DCSs are connected to sensors and actuators and use setpoint control to control the flow of material through the plant. The most common example is a setpoint control loop consisting of a pressure sensor, controller, and control valve. Pressure or flow measurements are transmitted to the controller, usually through the aid of a signal conditioning input/output (I/O) device. When the measured variable reaches a certain point, the controller instructs a valve or actuation device to open or close until the fluidic flow process reaches the desired setpoint. Large power plant have many thousands of I/O points and employ very large DCSs. Processes are not limited to fluidic flow through pipes, however, and can also include things like variable speed drives and motor control centers, .
DCSs are usually designed with redundant processors to enhance the reliability of the control system. Most systems come with
displays and configuration software that enable the end-user to configure the control system without the need for performing low-level programming, allowing the user also to better focus on the application rather than the equipment. However, considerable system knowledge and skill is required to properly deploy the hardware, software, and applications. Many plants have dedicated personnel who focus on these tasks, augmented by vendor support that may include maintenance support contracts.
DCSs may employ one or more workstations and can be configured at the workstation or by an off-line personal computer. Local communication is handled by a control network with transmission over twisted -pair, coaxial, or fiber-optic cable. A server and/or applications processor may be included in the system for extra computational, data collection, and reporting capability.
Automatic Generation Control
In an electric power system, automatic generation control (AGC) is a system for adjusting the power output of multiple generators at different power plants, in
response to changes in the load. Since a power grid requires that generation and load closely balance moment by moment, frequent adjustments to the output of generators are necessary. The balance can be judged by measuring the system frequency; if it is increasing, more power is being generated than used, and all the machines in the system are accelerating. If the system frequency is decreasing, more load is on the system than the instantaneous generation can provide, and all generators are slowing down.
5. Intro to Plant Equipment 5.1. Introduction to Pumps
What is a pump?
A pump is a device that moves fluids. Pumps are selected for processes not only to raise and transfer fluids, but also to meet some other criteria. This other criteria may be constant flow rate or constant pressure.
Pumps are in general classified as
1. Positive Displacement pumps
The centrifugal pump produce a head and a flow by increasing the velocity of the liquid through the machine with the help of the rotating vane impeller. Centrifugal pumps include radial, axial and mixed flow units.
2. Positive Displacement Pumps
A positive displacement pump operates by alternating filling a cavity and then displacing a given volume of liquid. A positive displacement pump delivers a constant volume of liquid for each cycle independent of discharge pressure or head
5.2. Introduction to Valves and Their
Components
Valves are mechanical devices that controls
the flow and pressure within a system or
process. They are essential components of a
piping system that conveys liquids, gases.
Some valves are self-operated while others
manually or with an actuator or pneumatic
or hydraulic is operated.
Functions from Valves are:
• Stopping and starting flow
• Reduce or increase a flow
• Controlling the direction of flow
• Regulating a flow or process pressure
• Relieve a pipe system of a certain
pressure
Regardless of type, all valves have the
following basic parts:
• the body,
• bonnet,
• trim (internal elements)
A typically Trim design includes a disk,
seat, stem, and sleeves needed to guide
the stem.
• Valve Disk and Seat
• Valve Stem
• actuator, and packing.:
Classification of Valves
1. Linear Motion Valves.
Gate, globe, diaphragm, and lift Check
Valves, moves in a straight line to allow,
stop, or throttle the flow.
2. Rotary Motion Valves. When the valve-
closure member travels along an angular
or circular path, as in butterfly, ball, plug,
eccentric- and Swing Check Valves,
3. Quarter Turn Valves. Some rotary motion
valves require approximately a quarter
turn, 0 through 90°, motion of the stem to
go to fully open from a fully closed
position or vice versa.
5.3. Heat Exchanger Theory
The general function of a heat exchanger is to transfer heat from one fluid to another. The basic component of a heat exchanger can be viewed as a tube with one fluid running through it and another fluid flowing by on the outside. There are thus three heat transfer operations that need to be described:
1. Convective heat transfer from fluid to the inner wall of the tube,
2. Conductive heat transfer through the tube wall, and
3. Convective heat transfer from the outer tube wall to the outside fluid.
Heat exchangers are typically classified according to flow arrangement and type of construction. The simplest heat exchanger is one for which the hot and cold fluids move in the same or opposite directions in a concentric tube (or double-pipe) construction. In the parallel-flow arrangement the hot and cold fluids enter at the same end, flow in the same direction, and leave at the same end. In the counter flow arrangement the fluids enter at opposite
ends, flow in opposite directions, and leave at opposite ends.
Shell and Tube Heat Exchanger
A shell and tube heat exchanger is a class of heat exchanger designs. It is the most common type of heat exchanger in oil refineries and other large chemical processes, and is suited for higher-pressure applications. As its name implies, this type of heat exchanger consists of a shell (a large pressure vessel) with a bundle of tubes inside it. One fluid runs through the tubes, and another fluid flows over the tubes (through the shell) to transfer heat between the two fluids. The set of tubes is called a tube bundle, and may be composed of several types of tubes: plain, longitudinally finned, etc.
Plate Heat Exchanger
Plate heat exchanger is a type of heat exchanger that uses metal plates to transfer heat between two fluids. This has a major advantage over a conventional heat exchanger in that the fluids are exposed to a much larger surface area because the fluids spread out over the plates. This facilitates the transfer of heat, and greatly increases the speed of the temperature change.
5.4. Introduction to Hydraulics
A hydraulic drive system is a drive or transmission system that uses pressurized hydraulic fluid to power hydraulic system. The term hydrostatic refers to the transfer of energy from flow and pressure, not from the kinetic energy of the flow.
A hydraulic drive system consists of three parts:
1. The generator (e.g. a hydraulic pump), driven by an electric motor
2. Valves, filters, piping etc. (to guide and control the system);
3. Actuator (e.g. a hydraulic motor or hydraulic cylinder) to drive the valves/machines.
Hydraulic valves
These valves can control the direction of the flow of fluid and act as a control unit for a system. Classification based on function:
• Pressure control valves (PC Valves)
• Flow control valves (FC Valves)
• Direction control valves (DC Valves)
Classification based on method of activation:
• Directly operated valve
• Pilot operated valve
• Manually operated valve
• Electrically actuated valve
• Open control valve
• Servo controlled valves
6. Plant Drawings Process and Instrumentation Diagrams use special shapes to represent different types of equipment, valves, instruments and pipelines.
6.1. P&ID Basics
Process and Instrumentation Drawing or P&ID is also known as the mechanical flow diagram and piping and instrumentation diagram. A P&ID is a complex representation of the various units found in a plant. It is used by people in a variety of crafts. The primary users of the document after plant startup are process technicians and instrument and electrical, mechanical, safety, and engineering personnel.
Process and Instrument diagrams provide information needed by engineers to begin planning for the construction of the plant. P&ID shows how industrial process
equipment is interconnected by a system of pipelines. P&ID schematics also show the instruments and valves that monitor and control the flow of materials through the pipelines.
The Advantages of Process and Instrument
Diagram
• Gives everyone a clear understanding of the instrument process
• Represents the sequence of all relevant operations occurring during a process
• Help to identify the scope of the process and analysis
• Presenting events which occur to the materials
• Incorporates specifications, standards and details that go into the design
• Facilitate teamwork and communication
• Shows graphically the arrangement of major equipment, process lines and main control loops
6.2. Reading a P&ID
To better understand the process and instrumentation diagram, you need to understand the symbols used in the piping and instrumentation diagram.
Letter and number combinations appear inside each graphical element and letter combinations are defined by the ISA
standard. Numbers are user assigned and schemes vary. While some companies use sequential numbering, others tie the instrument number to the process line number, and still others adopt unique and sometimes unusual numbering systems. The first letter defines the measured or initiating variables such as Analysis (A), Flow (F), Temperature (T), etc. with succeeding letters defining readout, passive, or output functions such as Indicator (I), Recorder (R), Transmitter (T), etc
7. Plant Systems 7.1. Introduction to Combustion Air and
Flue Gas Systems
All fossil fuel burning appliances need ample air intake and draft to complete the combustion process in a safe and efficient manner. Homes have furnaces and water heaters all requiring ample amounts of combustion air. Whether one or multiple, including gas boilers, the same rules apply.
The combustion triangle containing the three elements required for combustion to take place. These elements are: fuel, heat (ignition) and air.
Combustion Air
(1) Air that is supplied to combustion appliances to be used in the combustion of fuels and the process of venting combustion gases. Inadequate combustion air can lead to dangerous problems.
(2) The duct work installed to bring fresh, outside air to the furnace and/or hot water heater. Normally 2 separate supplies of air
are brought in: one high (for ventilation) and one low (for combustion).
Flue gas System
Flue gas is the gas exiting to the atmosphere via a flue, which is a pipe or channel for conveying exhaust gases from a fireplace, furnace, boiler or steam generator. Quite often, the flue gas refers to the combustion exhaust gas produced at power plants. Its composition depends on what is being burned, but it will usually consist of mostly nitrogen (typically more than two-thirds) derived from the combustion of air, carbon dioxide (CO2), and water vapor as well as excess oxygen (also derived from the combustion air). It further contains a small percentage of a number of pollutants, such as particulate matter (like soot), carbon monoxide, nitrogen oxides, and sulfur oxides
7.2. Introduction to the Circulating Water
System
All thermal power plants, be they coal fired or nuclear, use the modified Rankine steam cycle. The steam exiting from the steam turbine condenses in a condenser and then is reused in the steam cycle. Almost all thermal power plants use a surface condenser for cooling the steam. The only
exception is in a geothermal plant where a direct contact condenser is used.
In a surface condenser, the steam flows over a tube bundle. The condenser cooling water flows through the inside of these tubes. In a large power plant, the condenser will have about 15,000 tubes. The heat transfer takes place through the surface of these tubes.
In a direct contact condenser, cooling water mixes with the steam. The evaporation of the water cools and condenses the steam.
The circulating water system consists of an intake canal, the pumps, piping, cooling towers and an outfall system.
There are two different systems based on how the water is sourced and recycled.
Open Cooling system.
In an open circulating water system, water from a large water body like the sea, or a river or a lake is pumped to the condenser and is returned back to the same source. Since the sea is a free and large open source of water, we see many power plants located on the seacoast.
Closed Cooling System.
The second is the closed cooling system where Circulating water is in a closed circuit. The Circulating water removes the heat from the condenser and flows to cooling towers. In the cooling towers an airflow, natural or forced, cools the water and the water returns to the condenser. Power plants located away from large sources of water utilise this type. The large concrete hyperbolic towers that you see near thermal power plants are used for cooling the circulating water.
7.3. Introduction to the Condensate
System
The condensate system cools the exhaust steam from the turbine which is then collected in the condenser hot well to be used again as feed water. The lower the pressure and temperature that can be achieved in the condenser, the greater the overall efficiency of the plant.
Steam condensing
The condenser condenses the steam from the exhaust of the turbine into liquid to allow
it to be pumped. If the condenser can be made cooler, the pressure of the exhaust steam is reduced and efficiency of the cycle increases.
The surface condenser is a shell and tube heat exchanger in which cooling water is circulated through the tubes. The exhaust steam from the low pressure turbine enters the shell where it is cooled and converted to condensate (water) by flowing over the tubes.
For best efficiency, the temperature in the condenser must be kept as low as practical in order to achieve the lowest possible pressure in the condensing steam. Since the condenser temperature can almost always be kept significantly below 100 °C where the vapour pressure of water is much less than atmospheric pressure, the condenser generally works under vacuum. Thus leaks of non-condensible air into the closed loop must be prevented.
Typically the cooling water causes the steam to condense at a temperature of about 25 °C and that creates an absolute pressure in the condenser of about 2–7 kPa (0.59–2.07 inHg), i.e. a vacuum of about −95 kPa (−28
inHg) relative to atmospheric pressure. The large decrease in volume that occurs when water vapor condenses to liquid creates the low vacuum that helps pull steam through and increase the efficiency of the turbines.
The condenser generally uses either circulating cooling water from a cooling tower to reject waste heat to the atmosphere, or once-through water from a river, lake or ocean.
The heat absorbed by the circulating cooling water in the condenser tubes must also be removed to maintain the ability of the water to cool as it circulates. This is done by pumping the warm water from the condenser through either natural draft, forced draft or induced draft cooling towers
Another form of condensing system is the air-cooled condenser. The process is similar to that of a radiator and fan. Exhaust heat from the low pressure section of a steam turbine runs through the condensing tubes, the tubes are usually finned and ambient air is pushed through the fins with the help of a large fan. The steam condenses to water to be reused in the water-steam cycle. Air-cooled condensers typically operate at a
higher temperature than water-cooled versions.
From the bottom of the condenser, powerful condensate pumps recycle the condensed steam (water) back to the water/steam cycle.
7.4. Introduction to the Feedwater System
The boiler feedwater used in the steam boiler is a means of transferring heat energy from the burning fuel to the mechanical energy of the spinning steam turbine. The total feed water consists of recirculated condensate water and purified makeup water. Because the metallic materials it contacts are subject to corrosion at high temperatures and pressures, the makeup water is highly purified before use. A system of water softeners and ion exchange demineralizers produces water so pure that it coincidentally becomes an electrical insulator, with conductivity in the range of 0.3–1.0 microsiemens per centimeter.
The feed water cycle begins with condensate water being pumped out of the condenser after traveling through the steam turbines.
The water is pressurized in two stages, and flows through a series of six or seven intermediate feed water heaters, heated up at each point with steam extracted from an appropriate duct on the turbines and gaining temperature at each stage. Typically, in the
middle of this series of feedwater heaters, and before the second stage of pressurization, the condensate plus the makeup water flows through a deaerator that removes dissolved air from the water, further purifying and reducing its corrosiveness. The water may be dosed following this point with hydrazine, a chemical that removes the remaining oxygen in the water to below 5 parts per billion (ppb.)
8. Turbines What is a turbine?
A turbine is a machine designed to capture some of the energy from a moving fluid (a liquid or a gas) The key parts of a turbine are a set of blades that catch the moving fluid, a shaft or axle that rotates as the blades move, and some sort of machine that's driven by the axle. In a modern wind turbine, there are typically three propeller-like blades attached to an axle that powers an electricity generator. In an ancient waterwheel, there are wooden slats that turn as the water flows under or over them, turning the axle to which the wheel is attached and usually powering some kind of milling machine.
Impulse turbine
In an impulse turbine, a fast-moving fluid is fired through a narrow nozzle at the turbine blades to make them spin around. The blades of an impulse turbine are usually bucket-shaped so they catch the fluid and direct it off at an angle or sometimes even back the way it came (because that gives the
most efficient transfer of energy from the fluid to the turbine)
Reaction turbine
In a reaction turbine, the blades sit in a much larger volume of fluid and turn around as the fluid flows past them. A reaction turbine doesn't change the direction of the fluid flow as drastically as an impulse turbine: it simply spins as the fluid pushes through and past its blades. Wind turbines are perhaps the most familiar examples of reaction turbines.
8.1. Steam Turbine Design
A steam turbine is powered by the energy in hot, gaseous steam and works like a cross between a wind turbine and a water turbine. .Steam turbines use high-pressure steam to turn electricity generators at incredibly high speeds, so they rotate much faster than either wind or water turbines. (A typical power plant steam turbine rotates at 1800–3600 rpm) which needs to use a gearbox to drive a generator quickly enough to make electricity.) Just like in a steam engine, the steam expands and cools as it flows past a steam turbine's blades, giving up as much as possible of the energy it originally contained.
All steam turbines can be classified into two categories; extraction (condensing) steam
turbine and non-condensing steam turbine also known as back pressure steam turbines.
The extraction turbine
The extraction turbine contains two outlets .The first outlet extracts the steam with intermediate pressure for the feeding of the heating process while the second outlet extracts the remaining steam with low-pressure steam for the condensation. The extraction of heat from the first outlet can be stopped to generate more output. Steam control valves at this outlet make this steam very flexible and allow adjusting the output as per demand. The steam from the second outlet goes to the condensation chamber where cooling water brings the temperature of the steam down. The condensed water then goes back to the boiler for the regeneration of the electricity of power, therefore, it is also known as the regenerative steam turbine
Back Process Steam Turbine
The non-condensing steam turbine uses high-pressure steam for the rotation of blades. This steam then leaves the turbine
at the atmospheric pressure or lower pressure. The pressure of outlet steam depends on in the load, therefore, this turbine is also known as the back-pressure steam turbine. This low-pressure steam uses for processing and no steam is used for condensation.
8.2. Steam Turbine Valves and Controls
Steam turbine governing is the procedure of controlling the flow rate of steam to a steam turbine so as to maintain its speed of rotation as constant. The variation in load during the operation of a steam turbine can have a significant impact on its performance.
Steam Turbine Governing is the procedure of monitoring and controlling the flow rate of steam into the turbine with the objective of maintaining its speed of rotation as constant. The flow rate of steam is monitored and controlled by interposing valves between the boiler and the turbine.
Throttle governing
Throttle governing the pressure of steam is reduced at the turbine entry thereby
decreasing the availability of energy. In this method steam is passed through a restricted passage thereby reducing its pressure across the governing valve. The flow rate is controlled using a partially opened steam control valve. The reduction in pressure leads to a throttling process in which the enthalpy of steam remains constant.
Nozzle governing
In nozzle governing the flow rate of steam is regulated by opening and shutting of sets of nozzles rather than regulating its pressure. In this method groups of two, three or more nozzles form a set and each set is controlled by a separate valve. The actuation of individual valve closes the corresponding set of nozzle thereby controlling the flow rate.
Emergency Governing
Emergency governors come into action under the following condition.
• When the speed of shaft increases beyond 110%.
• Balancing of the turbine is disturbed.
• Failure of the lubrication system.
• Vacuum in the condenser is quite less or supply of coolant to the condenser is inadequate.
8.3. Steam Turbine Auxiliaries
Some of the main auxiliaries of associated
with steam turbine are
Lube-oil System
1. Pumps
The lubricating oil system has three separate
pumps which supply the bearings and
hydraulic system with oil.
• Lube oil Jacking pump – this is used when
the turbine is being rotated by the turning
gear.
• Emergency Lube oil Pump – this cuts in if
the turbine trips through loss of power.
• Main lube oil pump – this pump draws the
oil from a lube oil tank and supplies the
turbine bearings and governor. This is
normally a centrifugal pump driven by the
turbine or generator shaft.
2. L.O. Filters
Some systems have duplex filters on the
suction and discharge pipework of the
pumps, but at a minimum a set on the
discharge. These remove any debris picked
up by the oil before the oil is fed to the
bearings.
3. L.O. Coolers
The oil lubricates the bearings absorbing the
heat from friction. This heat is dissipated by
the coolers. These are usually tube coolers,
water being the medium used to cool the oil.
4. L.O. Centrifuge
The centrifuge is usually positioned above
the lube oil tank and runs continually whilst
the turbine is operating, only coming off line
for cleaning. It draws the lube oil from the
lube oil tank removing any water and
particles by centrifugal force before
discharging the clean oil back to the tank.
5. Turbine Governor
9. Internal combustion Engines 9.1. Combustion Turbine Fundamentals
Combustion Turbines are an essential component in power production. A combustion turbine is a simple, but yet a complex machine. It is simple in terms of its theory of operation. It is complex in terms its size, its risk to mis-operation, and the need to provide complex support and/or protection schemes. Combustion Turbines are used in various applications including, simple cycle peaking plants, or combined cycle operations.
Internal-combustion engine, one in which combustion of the fuel takes place in a confined space, producing expanding gases that are used directly to provide mechanical power. Such engines are classified as reciprocating or rotary, spark ignition or compression ignition, and two-stroke or four-stroke; the most familiar combination, used from automobiles to lawn mowers, is the reciprocating, spark-ignited, four-stroke gasoline engine. Other types of internal-combustion engines include the reaction
engine (see jet propulsion, rocket), and the gas turbine. Engines are rated by their maximum horsepower, which is usually reached a little below the speed at which undue mechanical stresses are developed.
9.2. Introduction to Gas Turbines
A gas turbine, also called a combustion turbine, is a type of internal combustion engine.
The basic operation of the gas turbine is similar to that of the steam power plant except that air is used instead of water. Fresh atmospheric air flows through a compressor that brings it to higher pressure. Energy is then added by spraying fuel into the air and igniting it so the combustion generates a high-temperature flow. This high-temperature high-pressure gas enters a turbine, where it expands down to the exhaust pressure, producing a shaft work output in the process. The turbine shaft work is used to drive the compressor and other devices such as an electric generator that may be coupled to the shaft. The energy that is not used for shaft work comes out in the
exhaust gases, so these have either a high temperature or a high velocity. The purpose of the gas turbine determines the design so that the most desirable energy form is maximized.
Gas turbines are used to power aircraft, trains, ships, electrical generators, and tanks
9.3. Gas Turbines major components
Major components of a gas turbine
Compressor — the compressor is made up of stages. Each stage consists of rotating blades and stationary stators or vanes. As the air moves through the compressor, its pressure and temperature increase. The power to drive the compressor comes from the turbine (see below), as shaft torque and speed.
Combustor or combustion chamber — Fuel is burned continuously after initially being ignited during the engine start.
Turbine — the turbine is a series of bladed discs that act like a windmill, extracting energy from the hot gases leaving the combustor. Some of this energy is used to drive the compressor.
10. Boilers & Boiler Fuel
Systems A boiler is a closed vessel in which water or other fluid is heated. The fluid does not necessarily boil. The heated or vaporized fluid exits the boiler for use in various processes or applications.
Industrial Boilers by Fuel Type
Many classify, or talk about, boilers according to the fuel they burn. The possibilities are quite diverse.
Coal: Most industrial boilers burn pulverized coal.
Biomass encompasses all types of burnable plant material, such as wood
Gas fired boilers burn natural gas, which can be a mix of methane, ethane, propane, butane, or pentane.
Oil: Boilers that burn gasoline, diesel, or other petroleum-based fluids are classified as oil-fired boilers
.
10.1. Coal Handling System
In a coal based thermal power plant, the initial process in the power generation is “Coal Handling”.
The huge amount of coal is usually supplied through water ways. The coal is delivered to the storage yard. The coal is taken from the unloading site to dead storage by belt conveyors. The belt deliver the coal to 0m level to the pent house and further moves to transfer point.
The transfer points are used to transfer coal to the next belt. The belt elevates the coal to breaker house. It consists of a rotary machine, which rotates the coal and separates the light dust from it through the action of gravity and transfer this dust to reject bin house through belt.
The belt further elevates the coal to another transfer point and it reaches the crusher through belt. In the crusher a high-speed 3-phase induction motor is used to crush the coal to a size of 50mm so as to be suitable for milling system. Coal rises from crusher house and reaches the dead storage by passing through transfer point.
10.2. Boiler Fuel System
In order for a boiler to convert water to steam, a fuel source must release its energy in the form of combustion in the boiler furnace. Fuel systems play a critical role in the performance of a boiler. The most commonly used fuels in power boilers are natural gas, fuel oil, coal, and wood (biomass). Each of these fuels have different physical properties that require delivery systems that are unique to that fuel. Fuel systems should be properly operated and maintained to run efficiently
11. Power Generation Electricity generation is the process of generating electric power from other sources of primary energy. The other processes, electricity transmission, distribution, and electrical power storage and recovery using pumped-storage methods are normally carried out by the electric power industry. Electricity is most often generated at a power station by electromechanical generators, primarily driven by heat engines fuelled by chemical combustion or nuclear
11.1. Generator and Auxiliary Systems’
Functions
Auxiliary system equipment is critical to ensure efficient, reliable and safe operation of the generator. Time and wear of auxiliary system components have direct impact on generator availability
Generator Auxiliaries
All large generators require auxiliary systems to handle such things as lubricating oil for the rotor bearings, hydrogen cooling apparatus, sealing oil, demineralized water for stator winding cooling and excitation systems for field-current application.
Seal & Lube Oil System
A typical lube oil system provides oil for both the turbine and generator bearings while also serving as a source of seal oil to the generator seals.
Hydrogen Cooling System
Generators operate with hydrogen rather than air as the internal medium because hydrogen has less drag for a given thermal convection capability.
Stator Winding Cooling Water System
The stator cooling water system is used to remove heat from generator armature bars.
Exciter Systems
A number of different types of excitation systems are used on large synchronous
machines. Within the three main categories, rotating, static and brushless,
Monitoring/Sensor Systems
• Generator Fan Differential Pressure Gages and Transmitters.
• Vibration Monitoring Systems
• Generator Condition (Core) Monitors detect overheating
• Gas Purity Analyzers
• Dew Point Analyzers
• Temperature Sensors
• Gas Dryers
11.2. Generator and Auxiliary Systems’ Flow
Paths and Major Components
An AC generator in its most basic form, has these components:
• Rotor - an armature wound with wire coils
• Slip Rings - part of the rotor / armature, connected to the wire coils
• Brushes - part of the frame, ride in contact with the slip rings
• Field (stator) - magnetic field for the rotor / armature. This can be either a permanent magnet or an electromagnet.
The rotating armature spins the wire coils through the field. The changing (alternating) field seen by the wires induces a corresponding alternating current that is picked up by the brushes from the slip rings.
When an electromagnet is used for the field, the alternator's output can be regulated by simply changing the field current. A feedback system monitors output voltage and controls the field coil to regulate the output to the correct voltage.
There are variants on this setup where the rotor and stator reverse roles. For example, an automotive alternator supplies DC current to the rotor through slip rings. The rotor makes a rotating magnetic field which induces current in the fixed stator coils, which in turn makes the AC output. In a car system this this is then rectified into DC by a set of diodes, for an AC system the current is taken as-is.
The "rotating bridge" (brushless) style of AC generator couples AC to the rotor through a rotary transformer to power the rotating field. This AC is then rectified into DC right on the rotor by a bridge diode set, which then energizes the rotor coils. The energized
rotor makes a rotating field which is then picked up the the stator coils as AC.
11.3. Environmental Protection
The Clean Power Plan will reduce carbon pollution from power plants, the nation’s largest source, while maintaining energy reliability and affordability.
11.4. Flue Gas Desulfurization System
Flue-gas desulfurization (FGD) is a set of technologies used to remove sulfur dioxide (SO2) from exhaust flue gases of fossil-fuel power plants, and from the emissions of other sulfur oxide emitting processes.
Methods
As stringent environmental regulations regarding SO2 emissions have been enacted in many countries, SO2 is now being removed from flue gases by a variety of methods. Below are common methods used:
• Wet scrubbing using a slurry of alkaline sorbent, usually limestone or lime, or seawater to scrub gases;
• Spray-dry scrubbing using similar sorbent slurries;
• Wet sulfuric acid process recovering sulfur in the form of commercial quality sulfuric acid;
• SNOX Flue gas desulphurisation removes sulfur dioxide, nitrogen oxides and particulates from flue gases;
• Dry sorbent injection systems.
For a typical coal-fired power station, flue-gas desulfurization (FGD) may remove 90 percent or more of the SO2 in the flue gases.
12. Electrical Systems and
Equipment An electric power system is a network of electrical components used to supply, transfer and use electric power. An example of an electric power system is the network that supplies a region's homes and industry with power—for sizeable regions, this power system is known as the grid and can be broadly divided into the generators that supply the power, the transmission system that carries the power from the generating centres to the load centres and the distribution system that feeds the power to nearby homes and industries. Smaller power systems are also found in industry, hospitals, commercial buildings and homes. The majority of these systems rely upon three-phase AC power—the standard for large-scale power transmission and distribution across the modern world.
12.1. Protection Relays
The objective of power system protection is to isolate a faulty section of electrical power system from rest of the live system so that the rest portion can function satisfactorily without any severer damage due to fault current.
Actually circuit breaker isolates the faulty system from rest of the healthy system and this circuit breakers automatically open during fault condition due to its trip signal comes from protection relay. The main philosophy about protection is that no protection of power system can prevent the flow of fault current through the system, it only can prevent the continuation of flowing of fault current by quickly disconnect the short circuit path from the system. For satisfying this quick disconnection the protection relays should have following functional requirements.
12.2. Generator, Transformer and Motor
Protection
A generator is subjected to electrical traces imposed on the insulation of the machine,
mechanical forces acting on the various parts of the machine, and temperature rises. These are the main factors which make protection necessary for the generator or alternator. Even when properly used, a machine in its perfect running condition does not only maintain its specified rated performance for many years, but it does also repeatedly withstand certain excess of over load.Hence, preventive measures must be taken against overloads and abnormal conditions of the machine so that it can serve safely. Despite of sound, efficient design, construction, operation, and preventive means of protection, the risk of that fault cannot be completely eliminated from any machine.The devices used in generator protection, ensure the fault, made dead as quickly as possible.
The various forms of protection applied to the generator can be categorized into two manners,
1. Protective relays to detect faults occurring outside the generator.
2. Protective relays to detect faults occurring inside the generator.
12.3. Grounding and Bonding
Earthing and Grounding are actually different terms for expressing the same concept. Ground or earth in a mains electrical wiring system is a conductor that provides a low impedance path to the earth to prevent hazardous voltages from appearing on equipment.
Bonding is simply the act of joining two electrical conductors together. These may be two wires, a wire and a pipe, or these may be two Equipments.
Earthing means connecting the dead part (it means the part which does not carries current under normal condition) to the earth for example electrical equipment’s frames, enclosures, supports etc. The purpose of earthing is to minimize risk of receiving an electric shock if touching metal parts when a fault is present. Generally green wire is used .
12.4. Main Transformers
Generation Transformer is employed in power plant for stepping up the voltage for transmitting the power to the grid. Electrical power is generated in the power plant at
lower voltages (typically generation voltage will be between 11kV to 33kV). In order to transmit the power to long distances voltage has to step up to reduce the losses. Rating of the generation transformers will be almost equal to the rating of the generator (500MW generating unit will have generating transformer rating about 588MVA). Connection between the generator transformer and power plant generator will be through isolated Phase Bus Duct (IPBD).
Unit auxiliary Transformer (UAT):
Power plant is provided with Unit Auxiliary Transformers (UAT) connected to the generator terminals through Isolated Phase Bus Duct (IPBD). Unit Auxiliary Transformers provides electrical power to power plant distribution buses by stepping down the voltage from 11kV to 6.6kV
Station Service Transformer
Station Transformers are employed for supplying power to plant auxiliary loads during the event of starting of the plant or when generating unit is not generating power. Station Transformers are connected to the swichyard bus. LV side of the station transformer is connected to the auxiliary load buses.Station transformer is normally rated for supplying power to the auxiliary loads. On-load tap changing mechanism is provided to regulate the terminal voltage of the transformer.
Auxiliary Transformers
These transformers are employed in the power plants for delivering power to low voltage loads (voltage below 1kV). These
transformers connects between HV distribution buses and LV distribution buses of the plant. Their rating will be around 1 to 5MVA. Natural oil cooling or air cooled transformers are used.
12.5. Fuses and Circuit Breakers
A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by overcurrent or overload or short circuit. Its basic function is to interrupt current flow after protective relays detect a fault. Unlike a fuse, which operates once and then must be replaced, a circuit breaker can be reset (either manually or automatically) to resume normal operation. Circuit breakers are made in varying sizes, from small devices that protect an individual household appliance up to large switchgear designed to protect high voltage circuits
A fuse interrupts an excessive current so that further damage by overheating or fire is prevented. Wiring regulations often define a maximum fuse current rating for particular circuits. Overcurrent protection devices are essential in electrical systems to limit threats
to human life and property damage. The time and current operating characteristics of fuses are chosen to provide adequate protection without needless interruption. Slow blow fuses are designed to allow harmless short term currents over their rating while still interrupting a sustained overload. Fuses are manufactured in a wide range of current and voltage ratings to protect wiring systems and electrical equipment.
13. Steam Tables A complete set of steam tables is available, consisting of the five regions from sub-saturated water through to superheated steam.
Sub Saturated Water Region
Saturated Water Line
Wet Steam Region
Dry Saturated Steam Line
Superheated Steam Region
13.1. Understanding the Basic Properties of
Water and Steam
While the properties of water at atmospheric pressure are commonly known, water under different pressures will exhibit different properties. When water is boiled at pressures higher than atmospheric, the same events occur as described above with two exceptions. First, the boiling temperature will be higher than 100°C. Second, less latent heat is required to be added to change the water completely into steam. If water were to be boiled at a pressure lower than atmospheric pressure,
then we would find that the boiling temperature would be less than 100°C and a larger amount of latent heat would be required to change the water completely into steam.
When water is below the boiling point, the addition of heat is seen as sensible heat. This water is said to be a subcooled liquid when water is below the boiling point, the addition of heat is seen as sensible heat. This water is said to be a subcooled liquid. When enough sensible heat is added so that the temperature of the water approaches saturation temperature but no steam has yet been formed, the water is said to be a saturated liquid. When enough sensible heat is added so that the temperature of the water approaches saturation temperature but no steam has yet been formed, the water is said to be a saturated liquid.
As the water is transformed from a saturated liquid to saturated steam, boiling is occurring. As latent heat is added, the temperature of the water remains the same but the saturated liquid is being changed into a saturated vapor. During this period the water is referred to as a liquid/vapor mixture.
When enough latent heat is added so that all of the liquid is converted into vapor, the water becomes a saturated vapor. Note that the saturated vapor is 100% vapor and exists at the same temperature as the saturated liquid. Above the saturated steam point, vapor exists at a temperature higher than saturation temperature. This is the superheated vapor region.
Once the boiling point is reached, the water’s temperature ceases to rise and stays the same until all the water is vaporized. The water goes from a liquid state to a vapour state it receives energy in the form of “latent heat of vaporization”. As long as there’s some liquid water left, the steam’s temperature is the same as the liquid water’s. Steam is then called saturated steam.
When all the water is vaporized, any subsequent addition of heat raises the steam’s temperature. Steam heated beyond the saturated steam level is called superheated steam.
14. Basic Water Chemistry
and Treatment Services for power plant and boiler water chemistry
The water-steam circuit boilers are very fickle systems. The most commonly faced problems are caused by corrosion, sedimentation and other challenges typical for water chemistry. This can be the result of, for instance, sub-standard quality of return condensate, incorrect chemical program, insufficient sampling and supervision, or simply poor processing.
Examples of power plant chemistry services
solving immediate water chemistry problems
assessing water-steam circuits
determining the power plant’s own control system
Demineralization Plant
The function of demineralization plant is to remove dissolved salt by ion exchange method (chemical method) and there by producing pure feed water for boiler.
14.1. Corrosion Control in a Power Plant
Power plants have to increase efficiencies, lower costs and reduce the amount of time offline for maintenance, corrosion prevention techniques will help lengthen the life of various components and increase safety. While many thermal power plants share the same types of corrosion issues, some require different preventive approaches
Common Types of Corrosion
Oxide corrosion: An electrochemical process that occurs when metal is exposed to water and changes in composition.
Galvanic corrosion: A process that occurs when two dissimilar metals contact each other; the resulting electrical reaction leads to and accelerates corrosion.
Erosion: The result of an aggressive chemical environment combined with high fluid surface velocities that
ultimately wear away a surface’s protective scale or coating.
14.2. Corrosion Control in a Power Plant
Generators: Maintain low humidity levels of 35 percent or lower using a closed-loop system.
Pipes: Install insulation with a jacket or protective coating, replace pipes with more resistant materials or improve the piping design so it has better flow geometries.
Water chemistry changes: When chemicals or organic agents in the water (e.g., anaerobic bacteria) lead to corrosion, a water-conditioning agent may be helpful. Replacing steel components with composite lines may also be effective, particularly in nuclear plants.
Turbines: Seal openings as tightly as possible.
Controlling water and steam: Use drains or vacuums to prevent water pooling.
Dehumidifiers are good for air that passes through a turbine, drying pockets of water and reducing relative humidity (rH) levels.
Oil-fired boilers: Use an open system and a dehumidifier to dry the air to 20 percent rH after shutting down a boiler.
Protective coatings: Use protective coatings on components exposed to water, the outside environment, or in areas that may experience condensation or moisture. Protective coatings or surfaces are also helpful for preventing erosion-related wear.
Cooling stacks: Install a windshield or protective liner to prevent chemical attacks and thermal shock.
Inspections: Regularly inspect and test components that are at risk for corrosion, even if they have protective surfaces. Such components include turbines, ducts, pipes, welded areas, areas with demineralize water and scrubber modules.
Water is essential to running a power plant. At the same time, water can cause vital
components to fail when the materials oxidize. By preventing and controlling erosion at a plant, you’ll reduce maintenance costs and downtime, improve performance and increase worker safety.
