Gas turbine power plant

Combustion and Power

Generation Dr. O.P. TIWARI

H.O.D, Mechanical

Engg.

S.R.I.M.T

S.R.I.M.T

DEPARTMENT OF MECHANICAL ENGG. S.R.I.M.T,Lko DEPARTMENT OF MECHANICAL ENGG. S.R.I.M.T, Lko

Power Plant Engineering

Classification of Power Plants

Steam (Thermal) Power Plant

Hydro Electric Power plant

Nuclear power Plant

Gas Turbine Power Plant

Diesel Power Plant

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DEPARTMENT OF MECHANICAL ENGG. S.R.I.M.T,Lko

Gas Power Plant • A gas power plant uses gas turbine as the prime mover for generating electricity.

• It uses natural gas or kerosene or benzene as fuel.

• Gas plant can produce only limited amount of the electricity.

•Efficiency of the plant is only 35%

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Layout of the Gas turbine Power plant

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Types of Gas Turbine Plants

• Simple Cycle – Operate When Demand is High – Peak Demand

– Operate for Short / Variable Times

– Designed for Quick Start-Up

– Not designed to be Efficient but Reliable

• Not Cost Effective to Build for Efficiency

• Combined Cycle – Operate for Peak and Economic Dispatch

– Designed for Quick Start-Up

– Designed to Efficient, Cost-Effective Operation

– Typically Has Ability to Operate in SC Mode

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Gas Turbine Basic Components

Compressor

Compressor

Turbine

Section

Power

Turbine

Section

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http://emcon-systems.com/images/GE.LM2500.Gas.Turbine.jpg

Basic Components S.R.I.M.T


Basic Components • Compressor

– Draws in air & compresses it

• Combustion Chamber – Fuel pumped in and ignited to burn with

compressed air

• Turbine – Hot gases converted to work

– Can drive compressor & external load

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compressed air



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compressed air



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Compressor

• Compressor types

1.Radial/centrifugal flow compressor

2.Axial flow compressor

3.Supplies high pressure air for combustion

process

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Compressor • Radial/centrifugal flow

– Adv: simple design,

good for low

compression ratios

(5:1)

– Disadv: Difficult to

stage, less efficient

• Axial flow

– Good for high

compression ratios

(20:1)

– Most commonly used

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Compressor

• Controlling Load on Compressor

– To ensure maximum efficiency and allow for

flexibility, compressor can be split into HP &

LP sections

– Vane control: inlet vanes/nozzle angles can

be varied to control air flow

• Compressor Stall

– Interruption of air flow due to turbulence

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Use of Compressed Air

• Primary Air (30%)

– Passes directly to combustor for combustion process

• Secondary Air (65%)

– Passes through holes in perforated inner shell & mixes with combustion gases

• Film Cooling Air (5%)

– Insulates/cools turbine blades

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Blade Cooling

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Gas Turbine Combustion

F/A – 0.01

Combustion efficiency : 98%

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Combustion Chambers

• Where air & fuel are mixed, ignited, and burned

• Spark plugs used to ignite fuel

• Types

– Can: for small, centrifugal compressors

– Annular: for larger, axial compressors (LM 2500)

– Can-annular: rarely used

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GAS TURBINES

• Invented in 1930 by Frank Whittle

• Patented in 1934

• First used for aircraft propulsion in 1942 on Me262 by

Germans during second world war

• Currently most of the aircrafts and ships use GT engines

• Used for power generation

• Manufacturers: General Electric, Pratt &Whitney,

SNECMA, Rolls Royce, Honeywell, Siemens –

Westinghouse, Alstom

• Indian take: Kaveri Engine by GTRE (DRDO)

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Turbines

• Consists of one or more stages

designed to develop rotational energy

• Uses sets of nozzles & blades

• Single shaft

– Power coupling on same shaft as turbine

– Same shaft drives rotor of compressor

and power components

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Turbines • Split Shaft

– Gas generator turbine drives compressor

– Power turbine separate from gas generator

turbine

– Power turbine driven by exhaust from gas

generator turbine

– Power turbine drives power coupling

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Dual Shaft, Split Shaft

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Gas Turbine Systems

• Air System

– Air intakes are located high up & multiple filters

– Exhaust discharged out stacks

• Fuel System

– Uses either DFM or JP-5

• Lubrication System

– Supply bearings and gears with oil

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Brayton Cycle(working cycle)

1-2: Compression

2-3: Combustion

3-4: Expansion through Turbine

and Exhaust Nozzle

4-1: Atmospheric Pressure)

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s

T

1

42'

3

24'

3'

3''

v

P

1 4

2 3

Closed Brayton

cycle (cont.)

QH

QL

s=const

QH

QL

p=const

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Efficiency of a Brayton cycle

1st law for this cycle: W Q QH L

energy conversion efficiency is:

useful work

heat input

W

Q

Q Q

QH

H L

H

1 1

4 1

3 2

Q

Q

mC T T

mC T T

L

H

P

P

1

1

1

1 4 1

2 3 2

T T T

T T T

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Efficiency of a Brayton cycle (cont.)

for an isentropic process:

P P V Vk

1 2 2 1

T

T

P

P

P

P

T

T

k

k

k

k2

1

12

1

3

4

3

4

1

in case of an ideal gas:

T

T

T

T

3

2

4

1

1 11

2

1

2

1

T

T

P

P

k

k

PV P V T T1 1 2 2 1 2

Pv constk

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So…

Efficiency of a Brayton cycle (cont.)

isentropic

pressure

ratio

1

1

2 1

1

P Pk

k

0

10

20

30

40

50

60

0 5 10 15

Pressure ratio

Ther

mal

effici

ency

%

Example

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PRINCIPLE OF OPERATION

• Intake – Slow down incoming air

– Remove distortions

• Compressor – Dynamically Compress air

• Combustor – Heat addition through

chemical reaction

• Turbine – Run the compressor

• Nozzle/ Free Turbine – Generation of thrust

power/shaft power

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The energy contained in a flowing ideal

gas is the sum of enthalpy and kinetic

energy.

Pressurized gas can store or release

energy. As it expands the pressure is

converted to kinetic energy.

Principles of

Operation • Open Cycle Also referred to as simple cycle)

Link to picture

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heat

exchanger

Closed Brayton cycle

2

1 4

turbine compressor Wnet

QH

QL

heat

exchanger

3

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Thermodynamic Fundamentals • Pressure Ratio &

CT Components

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COGENERATION

• Decentralized combined heat and power production-cogeneration is

a very flexible and efficient way of utilizing fuels.

• Cogeneration based on biomass is environmentally friendly, and all

kinds of biomass resources can be used. • Cogeneration plants can be used in all situations where a given heat

demands exists.

• COGENERATION TECHNOLOGIES

• Gas Engines.

• Gas Turbines.

• The Stirling Engine.

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Brayton cycle

with regeneration

turbine

exhaust

compressor

air

intake combustion

chamber

fuel

Wnet

regenerator

x

1

2

3

y

regenerator

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Modified Brayton cycle

turbines

exhaust

compressors

combustion

chamber

regenerator 9

8

1

5

6 7

10

fuel

air

intake

2 3

intercooler

4

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Modified Brayton cycle

• multi-stage compression with intercooling

• multi-stage expansion with reheat

s

T

3

8

4

7

1

6

5

2

9

10

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AUXILIARY SYSTEMS • Auxiliary systems are the backbone of the gas turbine plant. Without

auxiliary system, the very existence of the gas turbine is impossible.

1.STARTING SYSTEMS : Two separate systems-starting and

ignition are required to ensure a gas turbine engine will start satisfactorily.

• Types of Starter :-The following are the various types of gas turbine

starter.

• (a) Electrical :-(i) A.C. and (ii) D.C.

• A.C. cranking motors are usually 3 phase induction types rated to

operate on the available voltage and frequency.

• D.C. starter motor takes the source of electrical energy from a bank of

batteries of sufficient capacity to handle the starting load. Engaging or

disengaging clutch is used.

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• (b) Pneumatic or Air Starter :-Air starting is used mostly as it

is light, simple and economical to operate. As air starter motor has a

turbine rotor that transmits power through a reduction gear and clutch to

the starter output shaft that is connected to the engine.

• (c) Combustion Starter. It is in every respect a small gas turbine.

It is a completely integrated system which incorporates a planetary

reduction gear drive with over-running clutch.

• (d) Hydraulic Starting Motor. It consists of a hydraulic starter motor

for main engine, an accumulator, a hydraulic pump motor for auxiliary

power unit (A.P.U.).

• 2 .IGNITION SYSTEMS :-Ignition system is utilized to initiate spark

during the starting. Once it starts, the combustion is continuous and the working of

ignition system is cut-off automatically .

• The following are the types of ignition system.

1. Capacitor discharge system.

(a) High tension system and (b) Low tension system.

2. Induction system.

3. A. C. power circuits.

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LUBRICATION SYSTEM

• Elements of Lubrication System:-The

following are the elements of lubrication system of a gas turbine

• 1. Oil tank,

• 2. Oil pump

• 3. Filter and strainer,

• 4. Relief valve,

• 5. Oil cooler,

• 6. Oil and pipe line,

• 7. Magnetic drain plug,

• 8. By-pass, valve, and

• 9. Warning devices.

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Fig:-Lubrication System for gas turbine

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CONTROL OF GAS TURBINES • The purpose of gas turbine controls is to meet the specific control requirements

of users and safe operation of the turbine. There are basically two types of

controls. They are as follows:- • (A) Prime control and

• (B) Protection control

1.PRIME CONTROL

• The objective of the prime control is to ensure the proper application of the

turbine power to the load.

• The users of the gas turbines have specific control requirements according the

use of gas turbines . The requirements might be to control:

• (1) The frequency of an a.c. generator,

• (2) The speed of a boat or ship,

• (3) The speed of an aircraft,

• (4) The capacity or head of a pump or compressor,

• (5) The road speed of a vehicle.

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Fig-prime control (hydro-mechanical)

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2.PROTECTIVE CONTROLS:- The objective of

the protective control is to ensure adequate protection for the

turbine in preventing its operation under adverse conditions.

Basically, the protective control is of two types:-

• 1. Shutdown control and

• 2. Modulating control

• 1. Shut Down Control

The shut down type control detects a condition which can cause a serious

malfunction and actuate the shut-off valve to stop the turbine following are the

various types of shut down controls.

• (a) Turbine over temperature,

• (b) Turbine over speed,

• (c) Low lube oil pressure,

• (d) High lube oil temperature, and

• (e) excess vibration.

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• (2) Modulating Controls • The purpose of modulating control is to sense an impending malfunction or

a condition, which could adversely affect turbine life and make some

modification to the operating condition of the turbine in order to alleviate

the undesired conditions.

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Engine Power Transfer

• Turbojet • Thrust provided by reaction against expansion of

exhaust gases

• Turbofan • Thrust provided by reaction against expansion of

large volumes of air

• Marine systems • Thrust provided by turbine

• SCRAMjet/RAMjet

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Combustion Turbine Fuels

• Conventional Fuels

– Natural Gas

– Liquid Fuel Oil

• Nonconventional Fuels

– Crude Oil

– Refinery Gas

– Propane

• Synthetic Fuels

– Chemical Process

– Physical Process

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Emission in Gas Turbines

•Lower emission compared to all conventional methods (except nuclear)

•Regulations require further reduction in emission levels

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What is the CCGT?

A combined cycle gas turbine power plant,

frequently identified by CCGT shortcut, is

essentially an electrical power plant in

which a gas turbine and a steam turbine

are used in combination to achieve

greater efficiency than would be possible

independently.

The gas turbine drives an electrical

generator. The gas turbine exhaust is then

used to produce steam in a heat

exchanger (steam generator) to supply a

steam turbine whose output provides the

means to generate more electricity.

However the Steam Turbine is not

necessarily, in that case the plant produce

electricity and industrial steam which can

be used for heating or industrial

purpose.

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49 Picture courtesy of Nooter/Eriksen

How does a Combined Cycle Plant Work?

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Combining the Brayton and Rankine Cycles • Gas Turbine Exhaust used as the heat source for the Steam

Turbine cycle

• Utilizes the major efficiency loss from the Brayton cycle

• Advantages:

– Relatively short cycle to design, construct & commission

– Higher overall efficiency

– Good cycling capabilities

– Fast starting and loading

– Lower installed costs

– No issues with ash disposal or coal storage

• Disadvantages

– High fuel costs

– Uncertain long term fuel source

– Output dependent on ambient temperature

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Combined Cycles Today • Plant Efficiency ~ 58-60 percent

– Biggest losses are mechanical input to the compressor and heat in the

exhaust

• Steam Turbine output

– Typically 50% of the gas turbine output

– More with duct-firing

• Net Plant Output (Using Frame size gas turbines)

– up to 750 MW for 3 on 1 configuration

– Up to 520 MW for 2 on 1 configuration

• Construction time about 24 months

• Engineering time 80k to 130k labor hours

• Engineering duration about 12 months

• Capital Cost ($900-$1100/kW)

• Two (2) versus Three (3) Pressure Designs

– Larger capacity units utilize the additional drums to gain efficiency at

the expense of higher capital costs

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Combined Cycle Efficiency • Simple cycle efficiency (max ~ 44%*)

• Combined cycle efficiency (max ~58-60%*)

• Correlating Efficiency to Heat Rate (British Units) = 3412/(Heat Rate) --> 3412/ = Heat Rate*

– Simple cycle – 3412/.44 = 7,757 Btu/Kwh*

– Combined cycle – 3412/.58 = 5,884 Btu/Kwh*

• Correlating Efficiency to Heat Rate (SI Units) = 3600/(Heat Rate) --> 3600/ = Heat Rate*

– Simple cycle – 3600/.44 = 8,182 KJ/Kwh*

– Combined cycle – 3600/.58 = 6,207 KJ/Kwh*

• Practical Values – HHV basis, net output basis

– Simple cycle 7FA (new and clean) 10,860 Btu/Kwh (11,457 KJ/Kwh)

– Combined cycle 2x1 7FA (new and clean) 6,218 Btu/Kwh (6,560 KJ/Kwh)

*Gross LHV basis

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Gas Turbine Generator Performance

Factors that Influence Performance

– Fuel Type, Composition, and Heating Value

– Load (Base, Peak, or Part)

– Compressor Inlet Temperature

– Atmospheric Pressure

– Inlet Pressure Drop

• Varies significantly with types of air cleaning/cooling

– Exhaust Pressure Drop

• Affected by addition of HRSG, SCR, CO catalysts

– Steam or Water Injection Rate

• Used for either power augmentation or NOx control

– Relative Humidity

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Advantages and Disadvantages

• Lower emission levels

• Great power-to-weight

ratio compared to

reciprocating engines.

• Smaller than their

reciprocating

counterparts of the

same power.

• Expensive:

– high speeds and high operating

temperatures

– designing and manufacturing

gas turbines is a tough problem

from both the engineering and

materials standpoint

• Tend to use more fuel when

they are idling

• They prefer a constant rather

than a fluctuating load.

That makes gas turbines great for things like transcontinental jet aircraft and

power plants, but explains why we don't have one under the hood of our car.

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Needs for Future Gas Turbines

• Power Generation – Fuel Economy

– Low Emissions

– Alternative fuels

• Military Aircrafts – High Thrust

– Low Weight

• Commercial Aircrafts – Low emissions

– High Thrust

– Low Weight

– Fuel Economy

Half the size and twice the thrust

Double the size of the Aircraft and double the distance traveled with 50% NOx

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Ongoing Research

• Effect of inlet disturbances

• Combustion in recirculating flows

• Spray Combustion

–Needs and Challenges

–Controlled atomization

–Emissions in spray combustion

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THANK YOU

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