Course 0101 Combined Cycle Power Plant Fundamentals · The combined cycle power plant fundamentals course will present the basic information ... Based on a 2014 FERC Form 1 report,

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Course 0101

Combined Cycle Power Plant

Fundamentals

Fossil Training – 0101 – CC Power Plant Fundamentals



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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.

Page 7


Course 0301

Gas Turbine Fundamentals

Page 8

Fossil Training – 0301 – Gas Turbines


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.

Page 9



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.

Page 11


Reference 1 – Gas turbine simple cycle configuration

Page 12



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.


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.

Page 13


Reference 2 – Gas turbine inlet house

Page 14



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.


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.

Page 15



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.


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.

Page 16



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.

Page 17




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.

Page 18



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.


Heat is energy; the high temperature of the exhaust will be dissipated into the

atmosphere in simple cycle configurations.

Page 19



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.


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.

Page 20



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.


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.

Page 21



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.


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.

Page 22



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.


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.

Page 23



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.

Page 24




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).

Page 25



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

Page 26



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

Page 27



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

Page 28



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

Page 29



Test Answers

1) True

2) C

3) B

4) True

5) C

6) False

7) False

8) A

Page 30

Course 0101 Combined Cycle Power Plant Fundamentals · The combined cycle power plant fundamentals course will present the basic information ... Based on a 2014 FERC Form 1 report,

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