Mechanical (Rotary) Common Questions -3

EPC-School 2012

M for Mechanical 

Topic - Turbine

1. Name at least three types of machines where steam turbines are used as drivers.

2. What are the advantages / disadvantages of steam turbine over a motor drive?

3. What is the primary difference between impulse and reaction stages of turbines?

4. What is a back pressure turbine?

5. What is a condensing turbine?

6. Name the device used to control the speed of a speed turbine? What are the types?

7. What is function of turning gear (barring gear)?

8. What is the cause of turbine deposits and what are its consequences?

9. Why any turbine is recommended to run at slow RPM (ratcheting or barring) during start up and shutdown?

10. Why must steam turbines be warmed up gradually?

11. What are the various safety devices installed on a turbine?

12. What are the different fuels used in gas turbine?

Answers to Above Questions-

1. Compressors, Pumps, Fans, Generator

2. Advantages: Steam turbines are more efficient. Transmission losses are lower in case of steam turbines as steam generated is directly used to drive the equipment. (instead of generating electricity from steam and transmitting it)

Steam turbines are more reliable

Steam turbines give better control over speed than motors

3. In an impulse stage the power is generated due to high velocity gas impinging on the rotating blade. Most of the pressure energy is converted into kinetic energy in a nozzle and velocity drop occurs across successive rotating blades only (no change in energy across static blades, only change of direction).

In a reaction stage the power is generated in the rotating blades as well by the reaction force on the rotating blade as the steam expands in the blades. Pressure drop occurs across both the rotating and the fixed blades. 

4. The turbine operates against a constant back-pressure, in these turbines the exhaust steam from the end of the stage is fed to a process header.

5. In condensing turbine a condenser in included in the thermal cycle which extracts the maximum thermal energy from the steam.

6. Governor – Types: Mechanical governor & Electronic governor.

7. Used for slow rolling of the turbine for preventing thermal bowing, warping while start – up and shut down.

8. Turbine deposits are mostly due to carry over of salts / particles in the steam. Deposits create unbalance and vibrations. Results in loss of power also.

9. To prevent thermal bowing, warping while start – up and shut down.

10. To enable uniform heating.

11. Safety valve, Vibration & temperature probes, over speed trip.

12. Naptha, Waste Fuel Gas, LPG.