Gas Turbines Flashcards
What hazard exists when handling high temperature insulation?
Asbestos
High temperature insulation is often made of asbestos.
This should only be handled by trained personnel.
True or false: Gas turbines are constant flow internal combustion engines.
True
This is done to add heat to a gas which in then sent through a turbine to drive a turbine shaft.
What thing has the main effect on efficiency inside of a gas turbine?
The temperature to which the air can be raised.
To maximize efficiency, you must operate gas turbines at the maximum possible temperatures without harming the machine.
True or false: To maximize efficiency, you must operate gas turbines at the maximum possible temperatures without harming the machine.
True
The more the gases expand (due to temperature) the better the power and efficiency of the turbine.
What does the power rating of a gas turbine depend on?
The mass of hot gas flowing through the turbine blades per unit time
The more air passing by, the greater the power rating.
What effect does cold air have on the power rating of a gas turbine?
Cold air = power rating ↑
Cold air is more dense.
This has to due with the power rating being based off the mass of air passing by the turbine blades per unit of time ⟶ the denser the air (more mass per volume), the more air is passing by.
What is regeneration on a gas turbine?
When some of the exhaust heat is used to heat the air of combustion.
What is cogeneration of a gas turbine?
When exhaust heat is used to generate steam for power generation or other plant processes.
What is the advantage of an external combustion chamber on a gas turbine?
Allows for the use of a wider range of fuels.
Also makes it easier for the addition of regeneration and cogeneration.
What conditions would create the best efficiency for a gas turbine?
Cold intake air and a high turbine operating temperatures.
What are two air conditions improve a gas turbines efficiency?
- Dense air entering the compressor inlet
- High temperature air entering the turbine
This type of gas turbine shaft type has one shaft directly connected to the compressor rotor.
Single shaft type
These are very common and are good for single speed operation.
This type of gas turbine shaft arrangement is very common and good for single speed operation.
Single shaft type
What component needs to be added to a gas turbine single shaft arrangement in order for rotary output power to be harnessed?
A speed reducer
This type of gas turbine shaft type consists of two shafts, with one shaft connected to the compressor and the other connected to the gas generation turbine.
Split shaft type
True or false: Split shaft gas turbines are not suitable for variable speed operations.
False
True or false: Split shaft gas turbine speed can be reduced to improve fuel economy.
True
On a gas turbine running a split shaft arrangement, what direction would the output of the power turbine rotate in relation to the gas-generating turbine?
In the opposite direction.
This type of gas turbine shaft consists on one shaft running inside the other, with two separate compressors and two separate turbines.
Twin spool shaft type
The two sections are split into the high-pressue compressor and turbine and the low-pressure compressor and turbine.
What are the two sections of a gas turbine with a split shaft type?
- High-pressure (HP) compressor and HP turbine
- Low-pressure (LP) compressor and LP turbine
These can often be connected to a twin spool gas generation section with a split shaft type power section.
The gas generation section of a gas turbine brings in air from the 1.________ to mix with fuel in the 2.________ ________ to create hot expanding gases that can be harnessed.
- Compressor
- Combustion chamber
These are the two main sections of the gas generation section of a gas turbine.
What are the two main sections of the gas generation section of a gas turbine?
- Compressor(s)
- Combustion chamber(s)
The gas turbine brings in air from the compressor to mix with fuel in the combustion chamber to create hot expanding gases that can be harnessed.
What are the two main sections of a gas turbine?
- Gas generation section
- Power section
This section of a gas turbine brings air in from the compressor to mix with fuel in the combustion chamber to create hot expanding gases that can be harnessed.
Gas generation section
The two main parts of this section are the compressor(s) and the combustion chamber(s).
This section of a gas turbine has the job of harnessing energy from the hot gases as efficiently as possible without adversely affecting the operation of the gas generation section.
The power section
This section consists of the turbine wheel(s) and the speed reducter (if used).
Which section of a gas turbine delivers rotary motion that is usable to drive machinery?
The power section
What two things does the power section of a gas turbine consist of?
- Turbine wheel(s)
- Speed reducers (if used)
In a gas turbine with a single shaft arrangement, what is the main job of the turbine?
To drive the compressor for gas generation
Any remaining power can be supplied to the load.
On a gas turbine with a split shaft type, what is the gas generation turbine used for?
To drive the compressor
On a gas turbine with a split shaft type, what is the power turbine used for?
To drive the outside load
True or false: Gas turbines can be both internal combustion as well as external combustion engines.
True.
With this type of gas turbine cycle, any air drawn in from the atmosphere and used in the turbine is returned to the atmosphere after use.
Open cycle
This system is inefficient.
This cycle has no regenerators or heat exchangers in the system, and is typical of aircraft and standby gas turbines.
With this type of gas turbine cycle, either a heat exchanger or regenerators are attached in order to use the waste exhaust heat.
Semi-closed cycle
This cycle is much more efficient when compared to open cycle.
This is referring to thermal efficiency.
True or false: The most efficient gas turbine cycle is a closed cycle.
False
Semi-closed is the most efficient cycle.
A true closed-cycle gas turbine would have to reuse the gasses that pass through the engine, which is not possible.
What is the greatest disadvantage of a gas turbine?
Its poor thermal efficiency
Both the open and semi-closed cycle efficiency is referring to thermal efficiency.
This type of gas turbine cycle improves thermal efficiency of the gas turbine by using exhaust (waste) heat to assist in heating and expansion of the gases before the turbine.
Regeneration cycle
This is a semi-closed cycle.
On a regeneration cycle gas turbine, where is the waste heat from the exhaust added to the air?
After the compressor, but before the combustion chamber.
Cold air improves the efficiency of the compressor; adding the hot air before it would reduce the efficiency.
On a regeneration cycle gas turbine, why is the waste heat from the exhaust not added directly into the compressor air supply?
Compressors operate more efficiently with cold air.
Heating the air would reduce the density of it, reducing the amount of air that can be supplied to the combustion chamber.
On a gas turbine, what component gives the greatest single improvement in thermal efficiency?
A regenerator
It reduces the amount of fuel that must be burned to drive the same load.
What effect does a regenerator have on the fuel consumption of a gas turbine driving a load?
It reduces the amount of fuel that must be burned to drive the same load.
This increases the efficiency of the unit.
Why is it critical that regenerators on a gas turbine minimize the pressure drop within them?
If the regenerator increases back pressure in the turbine, the efficiency gains are lost.
This type of gas turbine cycle is comprised of one or more gas turbines exhausting into a heat recovery steam generator.
Cogeneration cycle
These are also known as combined steam-gas plants.
What is a combined steam gas plant?
Where a gas turbine exhausts into a heat recovery steam generator.
This improves the overall economy and capacity of the plant.
What does the temperature of the exhaust exiting a combined steam gas plant indicate?
The amount of energy captured from the fuel burned.
Hot gas = poor efficiency.
What is the greatest advantage of a gas turbine?
High power-to-weight ratio
Gas turbines are smaller and lighter for the same power output, when compared to other heat engines.
True or false: The initial capital cost of a gas turbine is higher per horsepower than a steam turbine plant.
False
It is lower.
The high horsepower per dollar installed cost is an advantage of a gas turbine.
Which type of turbine would require more support machinery: a steam turbine or a gas turbine?
A steam turbine
True or false: Gas turbines always require water cooling.
False
Think of jet engines ⟶ they are air cooled.
Most stationary gas turbines do take advantage of water cooling, but it is not required.
True or false: Gas turbines can be started very quickly with no harmful effects on the engine and can be shut down in a reasonably short amount of time.
True
This makes the gas turbine very practical for standby and emergency electrical generators.
What is the purpose for guide vanes on the air inlet of a gas turbine?
To help direct the air more efficiently into the compressor
The compressor of a gas turbine is constructed so that the area ________ as the air passe through each stage towards the rear of the compressor.
decreases
A convergent area
The compressor raises the air pressure and temperature in each succeeding stage.
In a gas turbine compressor, what happens to the air when it enters the rotating blades?
It is accelerated
The rotoring blades impart kinetic energy into the air, increase its velocity.
In a gas turbine compressor, what happens to the air when it enters the stationary blades?
Velcoity is converted to pressure
The air slows down, resulting in a change from kinetic energy into potential.
In a gas turbine compressor, the compression continues until the air enters the:
diffuser
This is the area within the gas turbine with the highest pressure.
What effect does the diffuser in a gas turbine have on the gas passing through it?
Velocity ↓ = Pressure ↑
The diffuser converts the velocity (kinetic) energy imparted into the air by the rotors blades into pressure (potential) energy.
Why is it important for the diffuser in a gas turbine to convert the velocity energy of the gas into pressure energy?
Without this change, the velocity of the gas would be too great for combustion to take place.
Where is a diffuser located in a gas turbine?
At the end of the compressor.
This is where the highest pressures are seen in a gas turbine.
Where are the highest pressures seen in a gas turbine?
In the diffuser.
This is located at the end of the compressor.
Why is it important for the pressure in a diffuser to be higher than the pressure in the combustion chamber?
To prevent surging or stalling
Once the air leaves the diffuser in a gas turbine, where does it go?
Into the combustion chamber
This is a divergent area.
What is the purpose of swirl vanes in a combustion chamber?
To create a region of low velocity recirculation in order for combustion to take place.
What would happen in a gas turbine if the combustion chamber pressure was higher than that of the diffuser?
Surging or stalling.
- Where is the fuel injected into on a gas turbine?
- How?
- Into the combustion chamber
- With the aid of fuel nozzles
What is used to ignite the fuel inside of a gas turbine?
Spark ignitors
There are usually two.
Once combustion takes place, the ignitors do not need to continually fire, as combustion is continuous.
In a gas turbine, why is the pressure during ignition lower than the pressure in the diffuser?
The buring gases are also accelerating toward the turbine wheel and exhaust
In a gas turbine, what effect do the nozzles in the turbine section have on:
1. Gas velocity?
2. Gas pressure?
- Velocity ↑
- Pressure ↓
Bernoulli’s Principle
These nozzles are housed in the stationary rings and consist of stationary reaction-type nozzles.
True or false: Stationary nozzles in gas turbines are impulse style nozzles.
False
They are reaction-type nozzles.
What constitutes a single stage in a gas turbine?
One set of stationary nozzles and the rotating turbine wheel
True or false: One set of stationary nozzles and the rotating turbine wheel constitutes one stage in a gas turbine.
True
What do the spaces between blades do in gas turbine?
Act as nozzles to direct the combustion gases uniformly and at the proper angle to the turbine blades.
In a gas turbine, approximately ____% of the power developed is used to drive the compressor and accessories.
75%
In a gas turbine, approximately ____% of the power developed is used to drive the load (driven machine).
25%
If the pressure in the combustion chamber of a gas turbine becomes higher than that in the diffuser, the gases back up and move into the compressor. What does this cause?
Stall or surging.
This condition can destroy the turbine in a matter of seconds.
True or false: In gas turbines, surging can be caused by restrictions in the inlet.
True
On a gas turbine, what are two things used to prevent surging?
- Adjustable inlet guide vanes.
- Bleed valves.
These devices help regulate airflow and pressure within the compressor.
These are used to maintain a safety margin between operating and stall conditions.
True or false: A gas turbine has an intake, compression, power, and exhaust stroke.
True
In a gas turbine, the event happen in different places, but at the same time.
True or false: The filtration systems used on gas turbines must have high flow with low restriction.
True
On gas turbine air filters, what type of filters are used in cold climates to reduce icing and hoarfrost build-up?
pulse-type filters
What type of filtration system may be used in high dust environments to clean the air for a gas turbine?
Self-cleaning pulse-type filters which sequenctially reverse the airflow in each section of the filter.
Why is it important that the airflow in a gas turbine air filtration system not restrict the airflow into the machine?
A restriction in the airflow can cause surging
This can result in a catastrophic failure of the turbine engine.
What are inlet guide vanes used for on gas turbines?
To straighten airflow and direct it to the first stage of the compressor.
The compressor section of a gas turbine is an axial flow compressor.
What effect does the inlet guide vanes on the compressor section of a gas turbine have?
They improve the efficiency of the compressor/turbine.
Positions of the blades for the most efficient airflow.
The function of this component of a gas turbine is to provide the turbine with pressurized air for combustion and cooling purposes.
The compressor
What are the two basic types of air compressors used in gas turbines?
- radial flow (centrifugal)
- axial flow
With this type of gas turbine compressor, the air enters parallel to the impellor shart and exits 90º to the shaft.
Radial flow (centrifugal) compressor
What are the three basic parts of a radial flow compressor in a gas turbine?
- impeller
- diffuser
- compressor manifold
Where does air enter into a radial flow compressor?
Into the inpeller eye (centre)
What component of a radial compressor in a gas turbine diverts the air into the combustion chambers?
The compressor manifold.
The manifold has very sharp corners, so several turning vanes are used to reduce turbulence and air pressure losses.
On a gas turbine with a radial compressor, what is used in a compressor manifold to reduce air pressure losses caused by the sharp elbows?
Several turning vanes.
In a gas compressor, which type of compressor is easily staged?
Axial flow compressors
Radial flow compressor can be staged, but it is more difficult.
This type of gas turbine compressor adds energy to the air by using centrifugal force to accelerate the air outward at high velcoity, which enters the diffuser where it is converted to low velocity high-pressure air.
radial flow (centrifugal) compressor
Which type of compressor is more efficient in a gas turbine: radial or axial flow?
Axial flow compressors
What are the two main components of an axial flow compressor?
- rotor with blades
- stator with blades
What forms a stage in an axial flow compressor?
Each consecutive set of rotor and stator blades.
How is air drawn into an axial compressor?
By the rotation of the rotor.
This draws air into the compressor in the same way that a fan works; by creating a low pressure area behind the blade, which is filled with my atmospheric pressure.
Which component of an axial compressor act like a diffuser?
The stationary blades
These slow the air down, converting the kinetic (velocity) energy into the potental (pressure) energy.
Which component of an axial compressor imparts velocity energy into the air?
The rotor blades.
They add energy to the air by accelerating it axially.
What are the two types of rotor assemblies found in the axial compressor sections in a gas turbine?
- drum type
- disc type
This type of axial compressor rotor assembly type has varying lengths of blades (long in the inlet section and short at the exit).
Drum type
What type of axial compressor rotor type is used only on lower speed compressors?
Drum type
This type of axial rotor type has a series of aluminum discs fitted to each other and shrunk on a steel shaft?
Disc-type rotors
Which type of aial compressor rotor makes it possible to have a parallel-sided case?
Disc-type rotors.
The rotor disc diameters increase in size, with small discs on teh inlet end and large discs on the outlet.
On some axial compressors, there is a tinkling sound heard when the comrpessor is turned over slowly. What causes this?
The rotor blades sit loose in the rotor
These tighten up by centifugal force when the compressor runs.
This component of an axial compressor delievers air to the next stage at a workable direction, velocity and pressure in order to obtain the maximum possible compressor blade efficiency.
The stator blades
These act like diffusers, reducing velocity and converting it into pressure.
True or false: Each space between a rotor blade and an adjacent blade in the stator acts as a diffuser.
True
Which control system controls the position of a variable pitch stator blade on an axial compressor in a gas turbine?
The fuel control system
What effect do variable pitch stator blades in the compressor have on a gas turbine?
Maintain maximum compressor efficiency over the operating speed of the engine.
True or false: In a gas turbine with an axial compressor, variable pitch stator blades can almost eliminate any compressor surge.
True
On a gas turbine, what is the combustor?
The outside housing of the combustion chamber.
On a gas turbine, what are the flame tubes?
The combustion chamber liner inside the housing.
What are the three zones of a combustion chamber in a gas turbine?
- Primary zone
- Intermediate zone
- Dilution zone
In a gas turbine combustion chamber, this is where fuel injection and ignition begins.
The primary zone
In a gas turbine combustion chamber, this is where combustion continues and begins to mix with secondary air.
The intermediate zone
In a gas turbine combustion chamber, this is where combustion should be complete, but secondary air is mixed with burnt gases.
The dilution zone
In a gas turbine, ________ air is air that enters the combustion liner (flame tube) to be mixed with fuel and burnt.
primary air
Secondary air has no part in the combustion process, and is rather used for cooling and dilution.
In a gas turbine, ________ air moves around the outside of the liner (flame tube) in a combustion chamber to control temeprature of the liner.
secondary air
This air has no part in the combustion process.
In a gas turbine combustion chamber, secondary air enters the liner through small holes in the ________ zone.
intermediate
In a gas turbine combustion chamber, in the ________ zone, secondary air becomes completely mixed with burned gases through larger holes in the liner.
dilution zone
In a gas turbine, what is the inlet of the combustion chamber connected to?
The diffuser
In a gas turbine, what is the discharge of the combustion chamber connected to?
The transition piece at the turbine.
This is where the hot gases are directed to the first set of turbine nozzles.
This component of a gas turbine has no moving components but is the hottest place in the turbine.
The combustion chamber
Which part of a gas turbine’s combustion chamber contains the fuel nozzle and ignitor?
The primary zone
This is the first part of the combustion chamber liner (flame tube).
This part of a gas turbine’s combustion chamber protects the injector and the flame from air currents that could cause flameout.
The primary zone.
This is also where the fuel nozzles and ignitor are housed.
This part of a gas turbine’s combustion chamber anchors the flame and provides sufficient air, time (due to its length), temperature and turbulence to complete the combustion of the fuel.
The primary zone
Continual combustion in a gas turbine works on the principle of:
flame propagation
Once the combustor is ignited, buring is continuous as long as there is an uninterrupted supply of fuel.
True or false: In a gas turbine, once the combustor is ignited, buring is continuous as long as there is an uninterrupted supply of fuel.
True
This works on the prinicple of flame propagation.
What is the two reasons for mixing secondary air with primary air in the intermeditate zone of a gas turbine’s combustion chamber?
- To reduce high-temperature gas pockets
- Keep the liner (flame tube) cool
Secondary air = cooling.
In this part of a gas turbine’s combustion chamber, secondary air is mixed after combustion to provide an outlet stream of hot gases at a temperature acceptable to the turbine.
The dilution zone
Secondary air = cooling
This component of a gas turbine connects the combustion chamber to the turbine and is a duct or passage long enough to make sure the hot air is thoroughly mixed, so there are no remaining hot gas pockets.
The transition piece
This type of gas turbine combustion chamber is most often used on engines with centrifugal compressors.
Can type chambers
With this type of gas turbine combustion chamber, each shell has a liner and a fuel nozzle.
Can type chambers
Which type of gas turbine combustion chamber can be used with axial flow compressors?
- Annular type chambers
- Can-annular type chambers
This type of gas turbine combustion chamber has one housing around the shaft and one undivided liner inside the housing, with the fuel nozzles evenly spaced out around the liner.
Annular type chambers
This type of chamber is very efficient and light, but cannot be repaired wihtout extensive engine disassembly.
True or false: Annular type combustion chambers are very efficient and light, but cannot be repaired without extensive engine disassembly.
True
This type of gas turbine combustion chamber is a combination of both the can and annular types.
The can-annular chamber
This style is used with axial flow compressors.
Which type of gas turbine combustion chamber can be used with a radial flow compressor?
Can type chamber
This type of gas turbine combustion chamber has individual cans (liners) mounted in an annular case, with each can being an individual combustion chamber with their own injectors interconnected by small passageways, sometimes called crossfire turbes, that enable the flame to pass to each can during start-up.
Can-annular chambers
What is the main advantage of can-annular combustion chambers?
Easily repairable
This is a rigid assembly with parts that can be replaced individually.
What is the purpose of crossfire tubes on a can-annular combustion chamber?
They allow for the flame to propagate to each can during start-up
Which type of combustion chamber has crossfire tubes?
The can-annular combustion chamber
These tubes allow for the flame to pass to each can during start-up.
What is the ignitor in a gas turbine?
A spark ignition system where high energy is discharged from a capacitor
These are only used during the start-up cycle.
What ignites the fuel in a gas turbine after the start-up?
Flame propagation.
The continuous flame ignites the incoming fuel.
True or false: On a gas turbine, can type combustion chambers require an ignitor in each can.
True
What is the purpose of spiral vanes in a combustion chamber?
To promote mixing of the air and fuel.
They swirl the primary air, creating turbulence
On gas turbines, what are atomizers and vapourizers?
A fuel nozzle/fuel injectors
This component of a gas turbine is used to spray the fuel in a fine mist into the combustion chamber.
Fuel nozzles
Also known as fuel injectors, atomizers, and vapourizers.
What are two basic methods for injecting liquid fuels into a combustion chamber in a gas turbine?
- An atomizer, which sprays a fine mist into the chamber
- Vapourize the fuel with heat before adding it to the combustion chamber*
The atomizer is the usual way to add fuel to the combustion chamber.
*This is done by metering the fuel into a tube surrounded by combution gases that vapourize the fuel, which is then discharged into the combustion chamber.
What are the two types of fuels used in gas turbines with separate combustion chambers?
- Liquid fuels (distillate such as kerosene)
- Gasesous fuels (natural gas, butane)
- Which type of natural gas fuel nozzle will be larger: a liquid fuel nozzle or a gasesous fuel nozzle?
- Why is this?
- A gasesous fuel nozzle
- This is because the fuel is already in vapour form.
Which type of fuels leave residue downstream of the combustion chamber on gas turbines?
Distillate fuels
These are fuels such as kerosene and heavy residual oils
What effect does unburned liquid fuel have on the blades of a gas turbine?
It pits and wears down the blades.
This happens when the liquid fuel is not completely atomized.
What effect is there when that atomizer of a gas turbine combustion chamber isn’t working correctly?
Unburned fuel travels to the turbine blades, where it pits and wears them down.
This is why gaseous fuels are preferred.
- Which type of fuel is preferred for gas turbines?
- Why is this?
- Gaseous fuels, such as natural gas and butane
- Unburnt liquid fuel damages the turbine blades
This happens when the atomizer is not working correctly.
What are the two main parts of the turbine assembly in a gas turbine?
- nozzles (stationary)
- turbine rotor (rotating turbine wheel)
This is very similar to a steam turbine, and the same principles of expansion through the blades apply (reaction-type blading).
A gas turbine usually has a lower ratio of blade length of wheel diameter than steam turbines. Why is this?
Rotational speed
This reduction in length makes the blades better able to withstand high rotational and surface speeds.
This component of a gas turbine harnesses the power of the hot expanding gases, and has to withstand the greatest stress from heating and loading.
The turbine assembly
True or false: Secondary air is often used for internal cooling of a gas turbine rotor.
True
On a gas turbine, what is a turbine rotor shield?
A protective component that serves to shield the turbine rotor from hot gases, thermal stresses, and erosion caused by the combustion process.
What type of nozzles are used in gas turbines?
Reaction-type blades fastened to a diaphragm.
This gas turbine component is located after the combustion chamber and just before the turbine blades.
The nozzles
These are reaction-type nozzles housed in a diaphragm.
How are nozzles cooled in the power section of a gas turbine?
Secondary air through the inside of the vanes
There are many small holes or slots on the leading and trailing edges where secondary air is forced through the blades for cooling.
True or false: In gas turbines, the diaphragms have an inner and outer shroud with the nozzle blades fixed between them.
True
These are reaction-type nozzles.
What are the three main components of a turbine rotor in a gas turbine?
- shaft
- discs
- blades
The rotor discs are welded or bolted to the low alloy steel shaft.
How are the rotor blades of a gas turbine cooled?
Internally, with secondary air.
This helps to reduce the thermal stresses placed on them.
How is cooling supplied to the rotor blades of a gas turbine?
By pushing the air under the rotor shield, which directs the gas to the holes in the rotor blades.
This thermal shield protects the shaft from direct gas exposure.
This can reduce the temperature of the turbine blades by as much as 300℃
What effect does cooling the nozzles and rotor blade assembly have on a gas turbine?
It allows for higher combution temperatures
This in turn makes higher power, more efficient, and a longer lasting turbine.
True or false: Can-annular combustion chambers have one igniter per individual can.
False
Because of the crossfire tubes, only one igniter is required.
True or false: Most issues caused in gas turbines is due to poor fuel.
True
This component of a gas turbine ensures that the engine speed and temperature are controlled within safe limits.
The governor
This controls the amount of fuel allowed into the combustion chamber
On a gas turbine, what does the governor control?
The fuel supply
This controls the amount of fuel allowed into the gas turbine.
Cooling the nozzles and rotor blade assembly on a gas turbine, results in higher combustion temperatures. What effect does this have on the efficeincy of the turbine?
Combustion temp ↑ = efficiency ↑
The hotter the temeprature in the combustion chamber, the better the efficiency of the turbine.
By cooling the nozzles and rotor blade assembly on a gas turbine, it allows for higher combution temperatures. What effect does this have on the power of the turbine?
Combustion temp ↑ = power ↑
The more energy added to the gases, the more expansion in the gases, which translates directly into more power.
True or false: In gas turbines, labyrinth seals are often assisted in sealing by jets of air routed from the compressor section.
True
True or false: Labyrinth sealing is also used to keep gases from leaking out of the casing and between stages.
True
- What components of a gas turbine have the most problems?
- Why is this?
- The hot section components
- The thermal shock resulting from extreme load fluctuations
The hot section components are the combustion chambers, transition piece liners, turbine nozzles and blades.
What are the four components in a gas turbine that make up the hot section components?
- combustion chambers
- transition piece liners
- turbine nozzles
- turbine blades
These parts experience the most thermal stress, resulting in more maintenence.
What is one of the most significant factors in determining the overall maintenance requirements of a gas turbine?
The frequency of starting and stopping the turbine
Start-up produce temperatures higher than noraml running conditions.
Why is it detremental to a gas turbine to have frequent start-ups?
Start-ups produce higher than normal temperatures, which result in abnormal thermal stresses.
What is the main disadvantage of using liquid fuels in a gas turbine?
They can cause erosion of the blades if the fuel is not fully vapourized.
Some of these fuels also leave deposits on the blades.
- What effect does dirty air/poorly filtered air have on a gas turbine?
- What effect does this have on the running characteristics?
- Contaminants will form on deposits on the compressor blades
- This reduces the efficiency of the turbine
What does buring natural gas or other clean gases have on the maintenance of a gas turbine?
Less maintenance
They do not leave deposits on the blades.
What are the two types of lubrication systems found in gas turbines?
- active lubrication system
- standby lubrication system
The standby lubrication system is used as a backup system.
Some large gas turbines have a gravity rundown tank. What is this used for?
In case of an emergency shutdown, oil drains from the tank to the bearings while the turbine is running down.
What effect does salt air from a seacoast have on gas turbine blades?
They corrode interal parts
What effect does sulphur from certain types of fuel have on the internal components of a gas turbine?
They corrode internal parts.
Poor fuel quality is a major cause of issues within gas turbines.
True or false: Gas turbines are self starting.
False
They require a starting motor to start.
This motor could be electric, diesel, or another gas turbine.
- How fast should a gas turbine be rotated before the fuel is supplied to the turbine?
- Why is this?
- 20% to 30% of maximum speed
- To ensure there is enough compression to ensure that the flame travels in the correct direction
What provides the cooling air for the blades and discs in a gas turbine?
Secondary air from the low pressure sections of the compressor
What is the purpose of the governor in a gas turbine?
To control turbine speed automatically under varying loads
This is done through automatic regualtion of fuel and compressor vanes.
How does a governor control the speed of a gas turbine?
Through regulation of the fuel supply and compressor vanes
What is the hottest location in a gas turbine?
The point where the heated air leaves the combustion chamber
True or false: The power a gas turbine develops can be determined by measuring the temperature before and after the turbine wheels.
True
This value gives an indication of the energy harnessed by the turbine.
What are the five main factors that determine the frequency of maintenance on a gas turbine?
- type of operation
- fuel type and quanity
- operational environment conditions
- design
- frequency of starting
What is the usual cause for power loss and high fuel consumption in a gas turbine?
dirt deposits on the compressor from airborne dust
Damaged turbine blading can also present as this issue.
If dirt deposits are suspected on the compressor section of a gas turbine, how would this be cleaned off?
Use the wash system first, and if that fails introduce a cleaning material into the compressor while its running.
The cleaning material is usually ground walnut shells.
What is the usual cause of low turbine inlet temepratures on a gas turbine?
Low fuel flow
This may indicate a defective fuel control system.
What are two common causes of vibration on a gas turbine?
- Out of balance conditions
- Excessive rubbing*
*This can be caused by rubbing between a large diameter rotor and seal or between blade tips and a shroud
What is the most common cause for a failure to start in a gas turbine?
Defective fuel control or ignition failure
How are nozzles cooled in the power section of a gas turbine?
Secondary air through the inside of the vanes
What would cause a very high abnormal frequency inside of a gas turbine?
Damaged compressor or turbine blades
This has a very small amplitude, but is very damaging to the unit.
This is usually caused by ingested foreign objects.
What three components should be examined if a gas turbine is is running abnormally hot?
- Combustion chambers
- Turbine inlet vanes
- Fuel nozzles
These high temperatures could be caused by clogged fuel nozzles or turbine bladding deterioration.
True or false: Before starting up a gas turbine, manually rotate the engine very slowly without fuel to check for excessive inteference and rubbing of air seals or blades.
True
Due to the high volume of air that passes through a gas turbine, contaminants gradually build up on the compressor blades. How is this dealt with?
By having a wash system
This removes build-up on the compressor blades.
How is a compressor on a gas turbine washed?
- A soak cleaning fluid is sprayed into the compressor
- Then a wash-of fluid
- Followed by an inhibiting fluid
What are two installation advantages of gas turbines?
- Light weight ⟶ requires no special foundation
- Low vibration ⟶ will not affect nearby machinery
On a gas turbine, a 1% loss in intake pressure results in a ____% loss in engine power.
2.5%
Why should exhaust ducting on a gas turbine avoid restrictions?
It adversely affects performance
Inlet restrictions are worse, as they can cause surge.
True or false: The combustion chamber of a gas turbine contains a liner, fuel injector, igniter, and an air swirler.
True
True or false: The turbine section nozzles and turbine blades are often cooled with air from the compressor section that is passed through holes in the blades.
True
True or false: Gas trubines often use labyrinth seals and air seals for their lubrication system.
True
True or false: The liner is the same thing as a flame tube in a gas turbine combustion chamber.
True
Which gas turbine cycle is used in stand-by power generation applications?
Open cycle
True or false: Serious gas turbine damage can result from continuous over-temeprature operation.
True
This is a reason why frequent start-ups are detrimental to the turbine.
This part of a gas turbine’s combustion chamber has holes or slots that allow for the entry of secondary air to mix in with the flow or the primary air.
The intermediate zone
