POWER EQUIPMENT INSTRUCTOR: ROBERT A. MCLAUGHLIN ZAILI THEO ZHAO

1. POWER EQUIPMENT INSTRUCTOR: ROBERT A. MCLAUGHLIN ZAILI THEO ZHAO AUXILIARY TURBINES & CONTROLS

2. 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

3. 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.

4. 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.

5. 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.

6. 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.

7. 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.

8. 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.

9. 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.

10. 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

11. 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.

12. 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.

13. 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.

14. 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

15. 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.

16. 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

17. 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.

18. CONDENSING TURBINE

19. 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.

20. 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.

21. Classification by direction of steam flow • Axial flow turbines have steam flowing parallel to the rotor axis.

22. 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.

23. 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.

24. 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”

25. 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.

26. 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

27. Turbine Control & Safety Devices • Auxiliary turbines driving pumps will use constant pressure governors • Turbines driving generators or compressors will use constant speed governors.

28. CONSTANT SPEED GOVERNORS

29. 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.

30. 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.

31. 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.

32. 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

33. 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.

34. 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

35. 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.

37. THANK YOU