Chapter 71- Gas Turbines Flashcards
The three things a gas turbine is considered
*constant flow rotors engine * heat engine * prime mover
List two facts about early gas turbines
* handicapped by lack of metal that withstand high temps * air compressor and turbine had very love efficiency
____ of the power is used for the air compression on a gas turbine
2/3
Output power or ____ depends in _____
Power rating Mass of hot gas
Output increases in a gas turbine when using
Air of maximum density
An example of aero turbine
Jet engine
An open system gas turbine
Air drawn from atmosphere and returned
Air and hot gas are _____ from compressor to turbine
Ducted
Turbine has to be brought up to ___% speed before the fuel is turned on
20-30
The two types of gas turbine
Aero derivative Land based
A simple turbine system has no (3)
*heat exchanger *regenerator *intercooler
A single shaft gas turbine
Has only one shaft. Compressor and turbine are coupled together
What is the majority of gas turbines in industry
Simple Open single shaft
Five advantages of the gas turbine
*higher power to weight ratio *low installed coat *low maintenance and operating cost *minimum cooling water *rapid start up and loading
List four disadvantages of gas turbines
*low mechanical and thermal efficiency *high noise level *limited types of fuel *NOx emissions
Compared to a steam plant and gas turbine is
Smaller and lighter
Absence of reciprocating motion and min wear of moving parts results in
Low maintenance and operating cost
Gas turbines require Minimal cooling water and is ideal for
Areas where water is scarce
What type of fuel does a turbine use
Clean liquid or gaseous fuels
What’s the purpose of regenerators
Improve efficiency by recovering heat
Regenerators are more efficient with
Cold air
Heat recovered from exhaust gas
Reduces fuel quality
What are two main benefits from combining a gas turbine with a steam plant
*plant economy improves * reduction in boiler size
Gas turbines combined with steam plants are referred to as
Combine cycles
What are the two things that are important for an operator to understand about gas turbines
How the ambient temp and atmospheric pressure effects it
Atmospheric pressure affects _______ in a gas turbine
Internal combustion engine and boiler performance
Air temperature changes
Air density
Define manual start up
Operator starts all auxiliary systems and takes gas turbine to minimum governor setting
Define semi automatic start ups
Only auxiliary system and automatic control takes gas turbine to minimum governor setting
Define automatic starting methods
Operator pushes button
What should you do if the engine of a turbine doesn’t start up within 90 seconds
Abort start up
If 50% rpm is not reached in 60 seconds what should you do
Abort cranking
Large turbines are fitted with
Serval governors
The over speed trip device will
Cut off fuel immediately
Gas turbine load control depends upon
The load shaft speed
List the five gas turbine alarm singals
High vibration Generator stator high temp Ignition tripped High differential pressure air intake Low lub oil pressure
What do you do with high vibrations
Close fuel supply
No ignition will result in
Fire or explosion
High differential air pressure indicates
Dirty air inlet filters
Why is lubrication essential
Lube bearings Cooling of bearings
Define a major overhaul turbine maintenance
A total strip down and checking or replacing
Define short shutdown turbine maintenance
Clean and replace air inlet filters, wash compressor blading and replace bearings and coupling
Aging factor results in
.5% in power and efficiency loss for 1000 hours of services
Why do we cool the turbine blades?
So they don’t melt
HRSG
Heat recovery steam generator
Sag in a turbine shaft is called
Bowing
What is a regenerator
Takes heat from the exhaust to heat compressed air in the turbine
Define cogeneration
Takes hot exhaust gasses to boil water to produce steam Highest efficiency available
A major drawback of the gas turbine
Nox emissions are high Low mechanical efficiency
The compressor chamber of a gas turbine
Can be driven by the load turbine
Many typical steam plant auxiliaries are eliminated with a gas turbine due to its
SIMPLICITY
The temperature to which the air can be raised at the turbine inlet is
A indication of the units efficiency
DP
Differential Pressure
