How Gas Turbines Work (Combustion Turbine Working Principle)

hi John here in this video we're going to take a look at a gas turbine also known as a combustion turbine I'll show you all of the main components that are

assembled to form a gas turbine I'll show you how it works and then I'll show you how a gas turbine looks when it's installed within a power plant before we

have a look at a real gas turbine in 3D let's take a look at this basic diagram if you've ever worked with combustion engines before you will have heard the

phrase suck squeeze bang blow or intake compression ignition exhaust with gas turbines it's very similar we have an

intake stage a compression stage a combustion stage and an exhaust stage the exhaust stage is also sometimes referred to as the expansion stage so we

have compression on the left and expansion on the right we also have the cold section of the turbine on the left that's everything colored in blue and

then we have a hot section which are the parts of the turbine that are colored yellow orange and red I'll tell you now briefly how a combustion turbine works because it's actually quite simple and

quick and easy to explain and then we'll look at some of the components in more detail when we take a look at the 3D model A combustion turbine ignites fuel

in order to heat up air air is a gas and that's why we call this type of turbine a gas turbine we're not calling it a gas turbine because we are using natural gas

to fire the turbine we're calling it a gas turbine because we're using a fuel it may be natural gas it may be a light fuel oil it may be coal dust it may be up to about 30 different types of fuel

and we're using that fuel the chemical energy from the fuel when we ignite it and burn it to heat up air like I say air is a gas so this is a gas turbine

the other type of turbine that you may have seen is a steam turbine steam turbines require steam to operate that's the working fluid gas turbines

require a gas it may be air but there are other gases that you can use as well it really depends upon the system one type of system is open and one type is

closed in this video we're looking at an open type system and that's the only type of system that we're going to discuss open type systems use air

ambient air from from the surrounding environment as the working fluid so what's happening we're drawing air in on the left through our air inlets we're

compressing the air we're increasing its pressure increasing its density and temperature as well then we're feeding that compressed air to the combustion

Zone where we ignite fuel to heat up the air and then this hot air this hot gas is discharged from the combustion Zone across a turbine and as it passes over

over the turbine blades the turbine blades are going to move and that's what's going to cause the shaft the central shaft to rotate the central

shaft is connected to the compressor all of the blades in the compression zone are referred to as the compressor each row of blades is referred to as a stage

so the compressor is connected to the turbine so that when the turbine rotates in the hot section of our combustion turbine the compressor and all of the

blades there will rotate as well this is going to cause more air to be drawn in and compressed and then fed to our combustion Zone and the process is

continuous this type of prime mover is referred to as an internal combustion engine the type of internal combustion engine that most people are aware of is probably the four-stroke engine or the

two-stroke engine these are the engines that you have cars and motorbikes etc those types of engines though are intermittent you you have combustion

periodically within the engine with a gas turbine you have constant combustion it's a steady flow internal combustion engine because it's a steady flow engine

it's actually quite efficient as well typical efficiencies for gas turbines are around 30 to 35% going all the way

up to 40% maybe slightly higher for Modern Gas turbines if we combine a gas turbine with a steam turbine we you can actually put that efficiency all the way

up to 55% maybe even 60% if we're using a very modern design and we have very modern Steam and gas turbines when we do that we actually call that type of plant

a combined cycle plant and I'm going to show you exactly how that type of plant Works towards the end of the video so we know now how a gas turbine works we draw

air in we compress it we ignite a fuel we heat up the air then we exhaust the air will discharge it from the combustion space across our turbine

blades our turbine blades move our main shaft rotates and the process then continues what's interesting about gas turbines is you can use them for many

different types of applications aircraft engines are essentially gas turbines they have a very high power to weight ratio and that's what makes them ideal

for usage in the airline industry where weight has to be reduced as much as possible in order that the aircraft can take off in the power generation industry we take a gas turbine and

modify it slightly so that instead of just discharging the hot air directly out to Atmosphere we can instead perhaps reclaim some of that heat to make our turbine more efficient and we can

connect the central shaft the single shaft of the turbine to a generator the generator rotor will rotate and we will generate electricity now there are

different types of gas turbine that are available to us heavy frame and arrow derivative are the two that you're likely to encounter but it's the heavy

frame design that allows us to reach megawatt capacities in excess of 250 megaw the arrow derivative design is

mostly used within the aircraft industry although it is used for power generation applications as well and it's essentially a streamlined version of the heavy frame design so heavy frame design

is used for large power generation requirements where we want a lot of electricity it's well suited to the power and energy Industries and then there is the aerod derivative design

which is like the Slimline version which we use in the aircraft industry and also for minor or smaller power generation applications if we take a look at this diagram here you can see that we've got

two main gas turbine designs aerody derivative and heavy frame the power output for the Aero derivative type gas turbines is in the range of about 30 to

60 megaw that's electrical power whereas the heavy frame design is within the 200 to 500 megawatt range in terms of efficiency they're quite similar Aero

derivatives have an efficiency of about 39 to 43% and the heavy frame design will be in the range of 37 to 40% actually think that's quite High I think it would be

more in the range typically of about 35 to 37% if if we were to combine those types of turbines with steam turbines and we get what's called a combined

cycle power plant then the efficiency increases as you can see to over 50% for both types of turbine that's a significant increase let's now take a

look at a real gas turbine and all of its components and then we'll take a look at a combined cycle power plant so here is our gas turbine this is

how it would look if you were looking at it in the field it normally would actually just sit within a box depending upon the size of the turbine the Box can be quite small or it may be quite large

and you can get in there and comfortably walk around may be air cooled it may be water cooled depends upon the design it

will have a control oil system installed nearby quite often the control oil system tank will be mounted directly underneath the turbine so

in this section here where my mouse is and then we'll have several pumps that we use in order that we can pump the control oil around the system and we'll

use it to actuate Valves and move actuation Pistons Etc the gas turbine itself is relatively simple in terms of

concept although there is a lot of engineering that goes into it we draw the air in on the left you can see where the air is being drawn in it's indic

ated in blue you can see our Central shaft as well it's this item here that's going to connect to our generator we

draw the air in it flows past a series of compressor blades and we're going to increase the pressure as the air moves

across each of these blades and remember that each row of blades is called a stage so every stage as we move from left to right we're going to increase

the air pressure and correspondingly the temperature as well for heavy frame gas turbine designs you'll be looking at

compression ratios of about 15 maybe up to 18 to1 so from here on the left over to here all the way on the right where

my mouse is where the air is discharged the compression ratio will be up to 18:1 with aerrow derivative engine it's actually higher it might be 30 to1 those

types of gas turbine are more focused on generating thrust compared to the heavy frame design where we're focused on generating electrical power or at least

that is our end goal aircrafts require thrust in order to stay up in the air power plants require as much power as possible in order to be profitable so we

take the air it's discharged through these two channels and then we reach our combustion Zone we're going to inject

fuel into this space the fuel's going to be injected here we ignite the fuel we get combustion we get heat and we use

the heat to heat up the air we go up to the top here you can also have a look from the top you can see the fuel lines coming along here mouses also along here

and along here and the two on the bottom and that fuel then is going to be sprayed and discharged into the combustion space initially we're going

to need to have a spark in order to ignite the fuel but once the gas turbine is up to speed typically Beyond 50% the temperature of the air is enough that we

can keep combustion constant and we don't need any external ignition source for example from a spark plug or similar the hot air that's being heated is then

going to be discharged through nozzles through these here the nozzles are stationary and we pass the hot air

across the blades of our turbine see here is one set here's the next set and here is the next set those

turbine blades will rotate the central shaft will rotate and we can connect the central shaft to the generator to generate

electricity when we discharge the hot air at this end here it may be 500 maybe 550 600° Celsius in extreme cases and

that's quite a lot of energy that we're going to discharge just potentially straight to Atmosphere out through this hole so rather than do that what we can

do instead is connect the gas turbine to a steam system this will increase the overall plant efficiency here is a combined cycle power plant we

call it a combined cycle power plant because gas turbines use What's called the braon cycle the braon cycle is a type of thermodynamic cycle the other

type of cycle that you'll see when looking at steam turbines is the Ranken cycle each of these Cycles is named after the person who invented them in

engineering you'll also see the auto thermodynamic cycle and the diesel thermodynamic cycle they're all just describing different types of

thermodynamic process because we're using a gas turbine that is housed within this box here and the steam

turbine it's housed over here within one type of power plant we're essentially using a braon cycle and the Ranken cycle together and that's why we call this

type of power plant a combined cycle power plant very briefly I'll explain you how it works we've got our gas

turbine here it connects on a shaft to a generator which is housed within this box and then we have three

phases of power which are coming out here they join to a Transformer and then we send that electrical power to our

consumers we draw air in through these lers here and the air will pass through a series of filters before it gets to

our gas turbine we filter the air because we don't want any foreign particles being sucked into the turbine because that might damage our compressor blades or our turbine blades so it's

important to filter the air it's also important to deise the air to make sure no water or moisture is sucked into the turbine those hot exhaust gases remember

they may be at 500° C or 550° C Etc will be discharged along here and into what's called a heat recovery steam generator

which is a type of boiler and as the exhaust gases move from left to right along here they transfer their heat to

water and then the water turns to steam at this point the hot gases the exhaust gases can be discharged through this

hole and to atmosphere the steam from the heat recovery steam generator is sent to the steam turbine and then the steam turbine rotor rotates and we

generate electricity through our generator here so one heat source which is used to operate both a gas turbine and a steam

turbine when we do that we have a combined cycle plant and we increase our efficiency for example from about 35% potentially all the way up to 50 55 and

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