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Flashcards in Gas Turbines Deck (49)
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Describe a gas turbine

It is it in internal combustion constant flow engine designed to convert the energy of fuel into useful power


Describe the basic flow through a gas turbine

Gas flows through an axial compressor then into a combustion chamber then to a turbine for power and exhaust


What does efficiency depend on in a gas turbine

Efficiency depends primarily on the temperature to which the air can be raised. To maximize the efficiency you must operate gas turbines at maximum possible temperatures without harming the machine.


What is the purpose of an external combustion chamber?

The external combustion chamber allows the use of a wider range of fuels.


What is regeneration?

Regeneration is when some of the exhaust heat is used to heat the air in the compressor for combustion


What is cogeneration

It is when the exhaust heat is used to generate steam for power generation of other plant processes


Name the three shaft types

Single shaft, split shaft, twin spool shaft


Define a single shaft and the split shaft

Single shaft has one shaft connected directly to the compressor rotor.
Split shaft has two shafts one connected to the compressor and the gas generation turbine, while the other shaft is attached to the power turbine in the load or speed reducer


Describe a twin spool shaft

Twin spool shafts have one shaft running inside another there are two separate compressors and two separate turbines.


How much of the power that created is used for output and how much for gas generation to run the compressor

Approximately 65 to 75% of the power and is created is for gas generation


Describe an open cycle

The air is drawn in from the atmosphere and used in the turbine then return to the atmosphere after use. There is no provision to capture any of the wasted heat from the exhaust gases


Describe the semiclosed cycle

The semi-close cycle turbine has either a heat exchanger or regenerators attached to it in order to use the wasted exhaust heat


What is the biggest disadvantage of a gas turbine?

It's low thermal efficiency


Where does the waste heat go in regeneration?

It is added to the air after the compressor but before the combustion chamber. It adds approximately 3% increase in efficiency


What is one of the greatest advantages of the gas turbine?

It has a very high power to weight ratio. Compared to other engines the gas turbine is smaller and lighter for the same power output


What is the difference in start up between a steam turbine, and a gas turbine?

Gas turbines can be started very quickly with no harmful affects to the engine and can be shut down in a reasonably short time. This is the opposite for steam turbines


What are some disadvantages of gas turbines

Low thermal efficiency approximately 30 to 40%, high air intake. If they have a loss of air in the intake system surging can result


Where is the highest pressure in the gas turbine

In the diffuser. It must always be higher than in the combustion chamber, to keep the flame from coming back into the diffuser


What causes surge?

Restrictions at the inlet, if the pressure in the combustion chamber becomes higher than the diffuser


What is the purpose of the inlet guide vanes?

They straighten the airflow and direct it into the first stage of the compressor rotor


What are the two basic styles of compressors used for gas turbines?

Radial flow axial flow


Where is the air at the highest pressure on the gas turbine?

Directly after the diffuser before the combustion chamber


Which are more efficient axial or radial flow compressors?

Axial flow are more efficient


How many stages are typically in the axial turbine compressor section?

8 to 16 stages


What type of rotors are used on most present day high-speed turbines?

Disc type rotors


How are the blades usually fitted to the rotor?

They are fit by a bulb or Firtree type root The blades are locked in place by setscrews peening, lock wire, pins or keys


What is the purpose of variable pitch stater blades?

They help the turbine engine maintain maximum compressor efficiency over the operating speed of the engine


What controls the blades position on variable pitch stater blades

The fuel control system


What are the three zones of the combustion chamber?

Primary zone, intermediate zone, dilution zone


Describe what happens at each of the zones in the combustion chamber.

Primary zone- The first part of the chamber liner where fuel injection and ignition begins
Intermediate zone- where combustion continues and begins to mix with secondary air
Dilution zone- combustion is complete at this stage more secondary air is mixed with the burnt gases