course 0101 combined cycle power plant fundamentals · the combined cycle power plant fundamentals...
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Copyright © 2017 by Technical Training Professionals
Course 0101
Combined Cycle Power Plant
Fundamentals
Fossil Training – 0101 – CC Power Plant Fundamentals
Copyright © 2017 by Technical Training Professionals
Copyright © 2017 by Technical Training Professionals
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Fossil Training – 0101 – CC Power Plant Fundamentals
Copyright © 2017 by Technical Training Professionals
Combined Cycle Power Plant Fundamentals Course
The combined cycle power plant fundamentals course will present the basic information
regarding the design and operation of the major components of a combined cycle power plant.
The course is divided into six sections, each covering a general topic, starting at the gas turbine
and building towards a complete plant. This course will provide the trainee with a solid
foundation of knowledge from which experience can be built upon.
0301 – Gas Turbines
0401 – Heat Recovery Steam Generators
0501 – Steam Turbines
0601 – Generators
0701 – Combined Cycle Plant Operation
1001 – Gas Turbine Routine Maintenance
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101_B5_Ch1 Combined Cycle Power Plant Overview
1. Introduction
a. Welcome to the Combined Cycle Power Plant Fundamentals overview video.
b. In this course, the trainee will learn about the basic fundamentals and equipment
operating principles to understand the concepts that allow these machines to
create electrical power.
c. At the end of the program, the trainee will comprehend the operation of the
combined cycle plant equipment and have the confidence to apply this
knowledge to their daily routines.
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2. Courses
a. The combined cycle power plant fundamentals course contains the following
sections:
• Section 0301, reviews the operating principles of each section of a typical
gas turbine
• Section 0401 explains the function of the heat recovery steam generator
• Section 0501 reviews the operation of a typical steam turbine
• Section 0601 reviews the design and operation of a generator
• Section 0701 reviews the layout and operation of a combined cycle power
plant, and
• Section 1001 covers routine maintenance of a gas turbine
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3. Combined Cycle
a. A combined cycle facility is an assembly of gas and steam turbines that work in
tandem from the same source of heat.
b. This heat is initially provided by the combustion of natural gas. The heat provided
by natural gas is converted directly into mechanical energy in the gas turbines
where it is used to turn an electric generator.
c. The waste heat from the gas turbine is used to create steam in the heat recovery
steam generator. The steam is then used to rotate the steam turbine.
d. By combining these multiple streams of work, the overall net efficiency of
producing electric power increases to as much as 60% as compared to a simple
cycle plant which may be typically around 30%.
e. If a plant does not utilize the heat recovery steam generators and steam turbines,
it is called simple cycle. In a simple cycle gas turbine, the exhaust heat of
combustion is generally released out the exhaust to the atmosphere.
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4. Gas Turbine
a. The first cycle of a combined cycle power plant is the gas turbine. Here outside
air is drawn into the gas turbine through the inlet air house. The air travels
through the compressor section of the gas turbine where its pressure and
temperature will rise.
b. This air is forced through the fuel combustion section where it mixes, ignites, and
expands hot gases through the turbine section.
5. Rotation
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a. The hot gases rapidly move and expand through the turbine blades toward the
heat recovery steam generator causing the rotor to spin at approximately 3600
rpm when the coupled generator is synchronized with the electrical grid.
b. As the gas turbine shaft rotates, it also rotates an electro magnet inside the
three-phase electrical generator where it induces electrical current into the
stationary phases of the generator. The electrical current flows from the
generator through three individual conductors called isophase conductors that
are connected to a step-up transformer.
6. Exhaust
a. Hot exhaust gas exiting the gas turbine is still very hot, typically at temperatures
approximately 1,150 degF.
b. Within the heat recovery steam generator, or HRSG, the hot gases flow over
finned boiler tubes. As hot gases travel over the finned tubes, the heat is
transferred to the water traveling on the inside of the tubes.
c. The heat energy gained by the water in the tubes eventually causes the creation
of high pressure steam.
d. Steam produced in the HRSG high pressure superheater joins with the steam
from other HRSGs if they are available and is piped to the steam turbine.
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7. Steam
a. The steam flows through the high pressure section of the steam turbine where its
thermal energy will be converted to mechanical energy. The steam at the HP
turbine exhaust will return to the HRSG for reheating and back to the IP turbine
section and the low pressure turbine.
b. The mechanical energy produced by the steam is converted to electrical power
by the coupled generator which will supply the local grid.
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Course 0301
Gas Turbine Fundamentals
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Fossil Training – 0301 – Gas Turbines
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Gas Turbine Fundamentals Course
Learning Objectives, Chapter:
1. Simple Cycle
In this course, we will review the operation of standalone gas turbine. The Brayton cycle
is explained and the advantages of a combined cycle power block are introduced.
2. Air Path
This chapter will review the operation of the axial flow compressor found on all gas
turbines. Although similar in construction each compressor is designed differently to
match the purpose of the specific gas turbine.
3. Hot Gas Path
This chapter will cover the design and operation of a typical gas turbine combustion
system that includes the combustors, control or power production, and combustion.
4. Turbine Section
This chapter covers the operation of the turbine section of the machine which converts
thermal energy into mechanical torque.
5. Auxiliary Equipment
This chapter reviews the gas turbine systems that make operation of the machine
possible. These systems include lubricating oil system, hydraulic oil system, lift oil
system, and other control type equipment.
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301_B5_Ch1 Simple Cycle
1. Gas Turbine
a. The gas turbine, also referred to as a combustion turbine, is an internal
combustion engine where a very lean mixture of fuel and air is burnt.
b. The resulting hot pressurized gas expands through a series of stationary and
moving blades in the turbine section, causing rotation of the shaft.
Classroom Discussion Point:
1. Gas turbines produce power at a relatively higher cost when compared to
other sources of power, but they can produce large amounts of power and
are only limited by the supply of fuel. A clear advantage over hydro-
electric plants is the high power production and availability; over coal
plants is the post combustion byproducts; and nuclear plants,
environmental concerns, regulation, and byproduct disposal.
2. Based on a 2014 FERC Form 1 report, Nuclear power plants produce
power at 2.68 cents per kilowatt-hour, Coal power plants at 3.9 cents per
kilowatt-hour, hydro-electric plants at 1.19 cents per kilowatt-hour, and
gas turbines at 4.26 cents per kilowatt-hour.
3. Some of the more desirable aspects of gas turbines is the relatively short
installation time and the footprint is generally smaller.
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2. Process
a. On a basic gas turbine, there are four processes that take place, compression in
the compressor, heat addition in the combustion chambers, expansion through
the turbine, and exhaust to atmosphere where heat is lost.
Reference Image:
See Reference 1 for an overview of a simple cycle gas turbine configuration.
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Reference 1 – Gas turbine simple cycle configuration
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3. Compression
a. The first process in the cycle is the drawing of air from the atmosphere through
an air filter and into the compressor.
b. As the air passes through the compressor, its pressure and temperature will rise.
c. The increase of the pressure is referred to as pressure ratio and varies by gas
turbine design. For example, if the pressure ratio is 10 to 1, then the air pressure
at the compressor exhaust is 10 times that of atmosphere, for this example, 147
psi absolute.
Classroom Discussion Point:
1. Higher compression results in more efficient compressor operation.
Manufacturers must balance the efficiency that can be reached with the
amount of power it will consume attempting to reach it since so much
power produced by the turbine is used to turn the compressor.
2. Air inlet houses condition the air for use in the compressor. See
Reference 2 for a cutaway of a typical air inlet house.
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Reference 2 – Gas turbine inlet house
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4. Turbine
a. As the gas passes through the turbine, its temperature and pressure drop. The
gas has given up heat energy and converted it to mechanical energy.
b. The gas is finally exhausted to the atmosphere. This is a simple cycle gas
turbine.
Classroom Discussion Point:
1. The hot exhaust gas is at high pressure at the inlet of the turbine section,
as opposed to air drawn through the compressor, as the gas expands, its
temperature and pressure will be reduced. This expansion occurs as the
gas passes through the turbine section, making it spin.
2. Turbine stage blade size increases toward the exhaust of the machine.
As the gas pressure is reduced by each stage of blades the increased
blade area continues to extract energy.
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5. Designs
a. Although compressors are designed differently to meet the purpose for the
turbine, they all perform the same function.
b. Here we can see the compressor of a 7FA gas turbine, here is a 501FD2, here is
an SGT-800, and here is an example of an aero-derivative LM6000 gas turbine.
Classroom Discussion Point:
1. Many new, modern large gas turbine designs include variable guide
vanes on several stages of compression. This multiple vane design is
borrowed from smaller aero-derivative machine designs.
2. Aero-derivative gas turbines will typically use multiple compressor
sections to achieve much higher pressure ratios. These compressor
sections will rotate at different speeds. In the following picture, the
exhaust gas drives two separate turbines, each connected to a
compressor.
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6. Ignition
a. The compressed air enters the combustion section where it is mixed with
incoming fuel.
b. At startup, a spark plug produces the initial ignition of the fuel and air mixture.
c. Due to the combustion, the temperature of the fuel-air mixture will be around
1800 degF; higher for larger machines.
d. The temperature of combustion will increase as the amount of fuel is increased to
accommodate the megawatt load increase.
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Classroom Discussion Point:
1. Spark plugs are relatively simple devices, utilizing a small transformer to
increase the voltage to a level which will cause a spark.
2. Turbines with multiple combustion chambers have the chambers
connected in such a way that only one sparkplug is required to ignite all of
the chambers. Any additional sparkplugs are for backup.
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7. Expansion
a. As the gas expands through the turbine, its temperature and pressure fall as it
converts heat energy into mechanical work before exhausting to the atmosphere
at low pressure and a temperature of around 1000 degF.
b. The turbine shaft is connected to a generator. The rotation of the generator
produces power.
Classroom Discussion Point:
Heat is energy; the high temperature of the exhaust will be dissipated into the
atmosphere in simple cycle configurations.
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8. Brayton Cycle
a. This simple cycle gas turbine operation is called the Brayton cycle and is
represented on a chart. The chart compares temperature to extraction or addition
of heat.
b. The chart depicts that from point A to point B, air drawn into the compressor will
experience an increase in temperature with no heat addition from an external
source.
c. At point B, fuel is added and combustion takes place, the temperature rises as
heat is added.
d. At point C, the hot gas enters the turbine and expands, converting the heat
energy into mechanical energy.
e. At point D, the gas exits the machine and out to the atmosphere, where the
remaining heat is lost. The cycle repeats as air at ambient temperature is drawn
into the compressor.
Classroom Discussion Point:
The Brayton cycle curve is typically used by engineers during the design phase
of a gas turbine. The data plot can be used to track the changes in gas turbine
performance and each section of the machine.
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9. Efficiency
a. The efficiency of a gas turbine’s Brayton cycle depends on the pressure ratio
achieved by the compressor.
b. On this chart, at a pressure ratio of 10 to 1, efficiency is around 50%.
c. On a typical gas turbine, the compressor requires 50 to 60 percent of the power
produced by the turbine.
d. Smaller gas turbines utilize a dual shaft arrangement, where the compressor is
driven by a separate turbine spinning at much higher speed, achieving higher
pressure ratio and efficiency.
Classroom Discussion Point:
Although aero-derivative gas turbines have higher compression ratios, the
volume of air they process is much lower than larger frame type gas turbines.
The efficiency of compression still applies to all gas turbines.
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10. Heat
a. Because the exhaust contains a lot of heat, a heat recovery steam generator is
installed to capture the energy. In the newest designs, the exhaust temperature
at the stack can be as low as 185 degF.
b. The heat recovery steam generator will produce steam at 100 to 1900 psi for use
in industrial purposes such as district heating or other heating requirements.
c. In a combined cycle facility, the steam is used to drive a steam turbine generator.
Classroom Discussion Point:
1. The combined cycle exhaust temperature is very important, too low may
cause damage to the HRSG rear tube metals, much higher than 170 to
185 degF means wasted energy.
2. The temperature spread from the inlet to the outlet of a HRSG requires
that construction materials be selected to withstand the temperatures
achieved in each section. High pressure superheater tubes will be made
from more exotic metals than LP economizer tubes.
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11. Combined
a. It is typical to use two gas turbines and heat recovery steam generators to
produce steam and drive a steam turbine which produces as much power as one
of the gas turbines.
b. The advantage of this arrangement is that the overall system efficiency is higher
since the heat in the gas turbine exhaust is not wasted.
c. Combined cycle plants will be covered in a separate training course.
Classroom Discussion Point:
1. Capturing the energy of the exhaust does not stop there, combined cycle
designs extract as much energy as possible while reducing wear and
tear, and operating costs.
2. The biggest draw-back of a combined cycle plant is the long startup time.
Even a hot start will take no less than 2 hours.
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12. Operation
a. Gas turbines used in simple cycle operations vary from smaller and rare 3
megawatt turbines up to larger and close to 100 megawatts.
b. The smaller turbines are typically used for black start capability, where their
output is enough to power the loads required to start a larger turbine.
c. These smaller gas turbines are usually aero-derivative type, meaning their
design is based on aircraft engines.
d. The larger gas turbines in simple cycle operations are used for peaking
capability. Due to their lower efficiency, they are only operated when the financial
return exceeds the cost of operation.
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Classroom Discussion Point:
1. Black start capability refers to a plant that can start power production
without backfeed from the grid. It is equipped with an independent power
source, typically diesel generators or a small gas turbine. These
generators can provide sufficient power to supply the start system for one
main gas turbine. Without black start capability, the plant will remain in a
shutdown condition.
2. An example of the power requirement is approximately 8 megawatts for a
solid state starting device such an SFC (static frequency controller) or LCI
(load commutated inverter).
3. Gas turbine generators are rated much higher than the gas turbine. This
is because gas turbine output varies with ambient temperatures; in cold
temperatures, gas turbines can produce much higher outputs than the
guaranteed rated output.
4. Aero-derivative gas turbines can be at full load within 10 to 15 minutes for
the most modern designs. Large gas turbines used in simple cycle (or
peaking) service will take around 30 to 45 minutes to reach full load.
Although slower, the larger gas turbines provide lower emissions at base
load compared to their aero-derivative counter parts. They also require
significantly less support equipment for operation (no water injection or
external cooling systems).
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Test
1) Combustion
A gas turbine is a machine that burns fuel and air to allow it to expand through
stationary and rotating blades to rotate a shaft.
A. True
B. False
2) Cycle
The basic thermodynamic cycle which describes the operation of a gas turbine is
which of the following?
A. Rankine cycle
B. Carnot cycle
C. Brayton cycle
D. Vapor-compression cycle
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3) Brayton
For which of the following reasons does the Brayton cycle indicate the
inefficiency of a simple cycle gas turbine?
A. The ratio of expansion through the turbine section is higher
B. The large difference in temperature between exhaust and inlet
C. The increase in mass through the turbine section
D. The rise in pressure at the compressor section is minimal
4) Power
Of all the power extracted from the fuel through the turbine section,
approximately 60% is used to turn the compressor.
A. True
B. False
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5) Exhaust
The high temperature of gas turbine exhaust gas can be used for which of the
following?
A. No use for it
B. Fuel heating
C. Steam production if equipped with a HRSG
6) Simple
Due to the efficiency of a simple cycle gas turbine, they are typically used for full
load, base-load operation.
A. True
B. False
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7) Stages
The number of stages of a compressor is the multiple for the increase in
pressure.
A. True
B. False
8) Compression
As air is compressed in the compressor section of a gas turbine, which of the
following parameters also increases?
A. Temperature
B. Gas cycle
C. Mass
D. Velocity
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Test Answers
1) True
2) C
3) B
4) True
5) C
6) False
7) False
8) A
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