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POWER EQUIPMENT INSTRUCTOR: ROBERT A. MCLAUGHLIN ZAILI THEO ZHAO PowerPoint PPT Presentation


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POWER EQUIPMENT INSTRUCTOR: ROBERT A. MCLAUGHLIN ZAILI THEO ZHAO. AUXILIARY TURBINES & CONTROLS. Learning Objectives. The various steam turbine types Steam turbine classifications Pressure drop and steam velocity change in turbine components.

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POWER EQUIPMENT INSTRUCTOR: ROBERT A. MCLAUGHLIN ZAILI THEO ZHAO

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Power equipment instructor robert a mclaughlin zaili theo zhao

POWER EQUIPMENT INSTRUCTOR: ROBERT A. MCLAUGHLIN ZAILI THEO ZHAO

AUXILIARY TURBINES & CONTROLS


Learning objectives

Learning Objectives

  • The various steam turbine types

  • Steam turbine classifications

  • Pressure drop and steam velocity change in turbine components.

  • Applications and limitations of auxiliary steam turbines

  • The methods of speed control and over speed protection

  • Gland seal assembly

  • The three factors that determine the effectiveness of a labyrinth seal assembly


Steam turbine classification by staging

Steam Turbine Classification by staging

  • There are two main categories of steam turbines based on the method of energy transformation taking place inside the turbine or how the steam is expanded.

  • The two methods are

    • Impulse and

    • Reaction.


Power equipment instructor robert a mclaughlin zaili theo zhao

  • High pressure impulse turbines are more commonly used in the U.S., whereas reaction turbines tend to be used more in Europe and Asia.

  • Impulse turbines:

    • tend to be smaller than reaction turbine of comparable power and

    • are more durable and

    • have longer time between overhaul than reaction turbines.

  • Reaction turbines have a slightly higher operating efficiency but are usually used in low pressure steam environments.


Steam turbine classification by staging1

Steam Turbine Classification by staging

  • Inflating a balloon and then releasing it to fly around the room uncontrolled, is an illustration of the reaction principle in action.

  • A water wheel is a good example of an impulse turbine.

    • However, it is also possible to create rotational force and power through the reaction principle.


1 simple impulse turbine delaval

1 Simple Impulse Turbine (Delaval)

  • It consists of a set of nozzles followed by a single set of rotating blades attached to a wheel or disk.

  • The nozzles

    • Convert thermal and pressure energy into velocity or kinetic energy

  • the moving blades

    • Capture some of this velocity

    • Turn it into rotational mechanical power.


Simple impulse turbine

Simple Impulse Turbine

  • There is only one pressure drop across the nozzle and essentially zero pressure drop across the moving blades.

  • The ideal ratio of the blade speed to the nozzle steam velocity to obtain maximum work from the stage is ½.

    • The blades would be moving approximately ½ the speed of the nozzle velocity.


Simple impulse turbine1

Simple Impulse Turbine

  • It is only found in small auxiliary turbines and has limited use.

  • It essentially consists of a casing top and bottom with bearing on each end to support a rotor assembly.

  • Disks or wheels are attached to the rotor shaft or are an integral part of the rotor as a casting.


Simple impulse turbine2

Simple Impulse Turbine

  • Attached to the disk are blades which convert the kinetic energy of the steam created in the nozzle into mechanical energy to drive any type of rotating equipment.

  • Applications of auxiliary turbines include:

    • Pump drives, forced draft fans, compressors,

    • feed pumps, generators and

    • just about anything that can be driven by an electric motor.


2 pressure compounded impulse rateau

2 Pressure Compounded Impulse (Rateau)

  • It consists of two or more simple impulse stages in series on one rotor.

  • The same basic rules apply for pressure drops and velocity changes as depicted in the illustration.

  • The ideal blade velocity is equal to ½ nozzle velocity


Pressure compounded impulse

Pressure Compounded Impulse

  • Rateau turbines are very common in large power generation turbines.

  • They are more efficient than Curtis or Delaval turbines and will extract thermal and pressure energy from the steam in small increments.

  • The use of this type of turbine for auxiliaries is usually limited to turbo-generator units, where more power is needed at greater efficiency.


3 velocity compounded impulse curtis

3 Velocity Compounded Impulse (Curtis)

  • It consists of a set of nozzles followed by two or more sets of moving blades attached to one wheel or disk.

  • There is also a set of redirectional fixed blades in between the rotating blades to direct the steam fro the first set of blades to the next.

  • There is still only one pressure drop and this occurs across the nozzles.


Velocity compounded impulse

Velocity Compounded Impulse

  • Theoretically there is no pressure drop across the moving or re-directional blades.

  • Velocity increases across the nozzle and decreases across the moving blades.

  • Pressure and velocity relationships for the velocity compounded impulse turbine are depicted in the illustration below.


Velocity compounded impulse1

Velocity Compounded Impulse

  • Curtis turbines are very common today in auxiliary steam turbines.

  • They are also used as astern elements in marine propulsion power plants as they will extract the maximum amount of energy from the steam in a single impulse stage.

  • They are also very rugged and durable but rather expensive to construct, therefore they are less common today in stationary power station turbines.

  • The ideal blade velocity is equal to 1/4 nozzle velocity


Reaction turbine stages parsons

Reaction turbine stages (parsons)

  • It consists of a set of fixed blades (nozzles) and a set of moving blades each of which is shaped like nozzles.

  • Therefore, there are two pressure drops per stage in a reaction turbine.

  • Approximately 50% of the momentum exchange takes place in the fixed assembly and 50% takes place in the rotating assembly.


Reaction turbine stages parsons1

Reaction turbine stages (parsons)

  • They are currently not used for auxiliary equipment and are not common in marine propulsion applications mainly because of their size, weight and shorter life expectancy.

  • However, some new reaction turbines are being built and used in the U.S. as demand for more efficient electric power generation increases.

  • Ideal blade velocity is equal to nozzle velocity


Condensing non condensing

Condensing & non-condensing

  • Condensing turbines are ones that exhaust at below 14.7 psia or sub atmospheric pressures.

    • Condensing turbines exhaust into a vacuum, which is mainly caused by the reduction in volume of steam as it turns back into water.

    • An air ejector or vacuum pump will begin the process and assist in maintaining the negative pressure by removing air and non-condensable gasses from inside the condenser.


Condensing turbine

CONDENSING TURBINE


Condensing non condensing1

Condensing & Non-condensing

  • Non-condensing turbines exhaust at or above 14.7psia.

  • Most auxiliary turbines exhaust at around 25-35 psig and are non-condensing units.


Classification by direction of steam flow

Classification by direction of steam flow

  • Radial, axial or tangential flow refers to the direction of steam flow in relationship to the axis of the rotor or shaft.

  • Radial flow turbines have steam flowing perpendicular to the shaft axis.


Classification by direction of steam flow1

Classification by direction of steam flow

  • Axial flow turbines have steam flowing parallel to the rotor axis.


Classification by direction of steam flow2

Classification by direction of steam flow

  • Tangential flow (Pelton) turbines have steam flowing at a tangent to the rotor.

  • The turbine blades act like buckets as picture, the water-jet gradually being diverted from its original direction.

  • Some kinetic energy is lost, but pressure is exerted in the peripheral direction of the wheel before being exhausted – at lower velocity – to the side.


Classification by direction of steam flow3

Classification by direction of steam flow

  • Turbines may also utilize dual or divided flow of the steam to help counteract axial thrust on the rotor.


Classification by number of casings

Classification by number of casings

  • Auxiliary turbines utilize one casing to extract the energy from the steam.

  • Larger more powerful turbines often utilize more than one casing to extract work from the steam.

  • When two or more casing are used to extract work, the configuration is call “compounding of casings”


Classification by steam admission control

Classification by steam admission control

  • Auxiliary turbines use throttling control valves and hand operated nozzle control valves to vary the speed and power of the turbine.

    • Nozzle control valves can be opened and closed by either bar lift devices, cam devices or manually.

  • Another form of control which is not common today is called by-pass control.

    • By-pass control, cam lift is used on the cruising turbine out side the classroom.


Auxiliary turbine usage

Auxiliary turbineusage

  • Auxiliary turbine usage is found on any rotating equipment.

  • Steam turbines have

    • Very high starting torque,

    • Good high speed control and also

    • Good variable speed capability.

  • Generally when steam is available, motors in excess of 50 hp can be replaced by steam turbines at a weight savings.

  • Steam turbines are very reliable,easy to maintain and easy to operate.

  • Reasons for using steam turbines instead of electric motors are as follows:

    • Power density or weight/hp advantages over 50 hp

    • High rotational speed requirements

    • Good control of variable speed devices


Turbine control safety devices

Turbine Control & Safety Devices

  • Auxiliary turbines driving pumps will use constant pressure governors

  • Turbines driving generators or compressors will use constant speed governors.


Constant speed governors

CONSTANT SPEED GOVERNORS


Speed limiting governor

Speed limiting governor

  • Speed limiting governors are used to prevent the turbine from going into an over-speed condition and are usually direct acting fly-ball type units.

  • The speed limiting governor takes over control of the steam admission valve when the rotor speed reaches about 107% of the rated speed of the turbine.


Over speed trip

Over speed trip

  • In the event that the primary governor and the speed limiting governor fails to control the speed of the rotor, the over-speed trip is designed to stop steam flow into the turbine and thus protect the unit from over-speed damage.

  • The over- speed trip is actuated by centrifugal force and consists of a spring loaded pin attached to the end of the rotor.


Over speed trip1

Over speed trip

  • At about 110-115% of the rated speed of the rotor the pin pops out and trips a mechanical device that completely shuts off the steam supply to the turbine steam chest.

  • The rotor speed will automatically slow down but in order to restart the turbine, the trip mechanism must be manually reset.


Turbine control safety devices1

Turbine Control & Safety Devices

  • Depending upon the size and cost of the turbine, other protective devices are used as follows:

    • Low Lube oil pressure trip

    • Relief valves and Sentinel valves

    • High back pressure trip

    • High vibration protection

    • High Exhaust Temperature protection

    • Hand trip


Shaft sealing labyrinth seals vs carbon seals

Shaft Sealing, Labyrinth Seals vs Carbon Seals

  •  All turbines must have some form of shaft seals to prevent steam from exiting the casing when the turbine is operating.

  • Mechanical labyrinth seals are common on most large steam turbines and carbon type seals are more common on small auxiliary turbines.


Shaft sealing labyrinth seals vs carbon seals1

Shaft Sealing, Labyrinth Seals vs Carbon Seals

  • Shaft seals

    • Keep steam inside the casing, air outside the casing,

    • Help maintain vacuum in condensing units and

    • Reduce the amount of oxygen entering the system.

  • Three factors that determine the effectiveness of a labyrinth seal as follows:

    • The number of teeth in the seal

    • The teeth length

    • The condition of the teeth or sharpness of the teeth


Shaft sealing labyrinth seals vs carbon seals2

Shaft Sealing, Labyrinth Seals vs Carbon Seals

  • Carbon packing

    • is not as effective as a labyrinth seal assembly but

    • it is cheaper and does have an application in small auxiliary turbines.


Thank you

THANK YOU


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