4b power engineering Flashcards
example of a prime mover
steam turbine
advantages of a steam turbine over a diesel engine
smaller foundation, lighter, less expensive greater thermal efficiency easily coupled with electrical generator no lubrication- oil free exhaust more reliable, reduced vibrations lower maintenance costs
5 steps in starting up a typical steam engine
Ensure no tools are left in the way of moving parts
open drain cocks on steam chest and cylinders
open separator drain and empty of water
once water stops flowing, open stop valve slightly until steam flows freely through the drains
Slowly open steam valve. to prevent water hammer
Steam flow is regulated to control engine speed by
throttle valve
A steam turbine’s exhaust can supply a process with steam because
it is free of oil
2 types of steam turbines
Reaction and Impulse
The stationary passage of reaction turbines is the
fixed blade
Larger high output machines use a shaft seal known as
labyrinth glands
6 steps in shutting down a large condensing turbine
regulate steam supply as load is reduced
start auxiliary oil pump
when stop order is received, the stop valve may be closed gradually
watch that bearings are getting proper oil supply
shut off steam supply and water to the glands
when machine has stopped, shut off water supply to the oil coolers and stop the aux oil pump
In order to move the throttling valve in a large steam turbine, a governing system uses a
pilot valve
Dirty air filters on a gas turbine could lead to what
high differential air intake
cooling tower design in which the fan is least likely to ice up is
dry cooling tower
What is a diesel engines camshaft driven by
gears from the crankshaft
in a venture type cooling tower, how is airflow created
by spray nozzles
A gas turbine
heats compressed air
crossflow mechanical draft cooling tower
has a low pressure drop
Rate of heat transfer in a cooling tower depends on
Exposure area of water surface in contact with the air
Residence time
Relative velocity of air and water during contact
temp differential of inlet water temp and relative humidity of the air
Advantages of steam engine include
It is possible to change direction without gears
How high might compression ration in a diesel engine be
25:1
A very accurate method of checking flanges for offset and axial misalignment which can be used on any flanges is the
dial indicator
A stuffing box
stops air leaking into the casing, and is filled with packing
Valves on a reciprocating compressor are opened by
Pressure differential
What is the purpose of bleeding hot air from the compressor of a gas turbine and reintroducing it to the compressor inlet
anti icing
large internal combustion engines achieve cooling by use of
water jackets
The reciprocating motion of a steam engine is converted to rotory motion
via the valve gear
How are microbiological organisms most effectively killed in cooling tower
by temporarily raising the concentration of the chemical to a high level
Packing rings
are pressed into packing glands to provide a seal
packing glands
provide a seal around piston rod and valve rod
Governor
controls engine speed by regulating steam flow to the engine as load on the engine changes
If the steam pressure drops in the stationary blades of a turbine, it is classified as an
impulse turbine
Rotor passages of a steam turbine consists of blades or buckets which are attached to
the turbine rotors
With some governors, the oil pump is driven from the
turbine shaft
The purpose of the hand speed changer is to
allow the operating speed to be varied
To avoid excessive speeds in turbines, when load is suddenly reduced, they are fitted with
overspeed trips
Cooling towers are divided into 2 classes.
Mechanical and Natural draft
sub classes of natural draft cooling towers are
atmospheric towers and chimney towers
3 tasks to be performed monthly in an atmospheric tower
clean scale, dirt, algae from louvers, piping and nozzles
clean water basin and check for leaks
clean the suction screen and check the float control valve
water distributors purpose and construction
fiberglass, wooden or stainless steel piping and spray nozzles spray water into the top section of the tower.
side louvers
wooden or fiberglass panels direct air flow into the towers
side sheeting
cement board or fiberglass panels enclosing the cooling tower
fill or packing
wood or plastic slats which fill the tower below the water inlet sprays and ensure that the water surface area is large providing good contact with air
Mist eliminators
wood or plastic slats located above the inlet water sprays to remove water carried along with the air flow
water basin
concrete containment located at the bottom of the cooling tower to collect the cooled water falling from the fill
fans
stainless steel or plastic fans located at the top of the cooling tower to draw air through the tower opposite to the water flow.
The cause of corrosion in a cooling tower
low pH (below7.5) and dissolved oxygen which is high because water is constantly circulated through the tower
wood delignification is caused by
attack of chlorine and alkaline solutions and biological attack of wood cellulose
hot air from the gas turbine combustor is expanded through
the turbine blading
In a simple gas turbine, air is first drawn into the compressor and compressed air is discharged into
the combustor
Prior to fuel being admitted, an auxiliary starting motor is used to bring a gas turbine up to a speed of
20-30% of operating speed
Typically it takes how long to start up a steam turbine
8-12 hours
The 4 strokes referred to in a four stroke cycle engine are
intake, compression, power, exhaust
what keeps the oil in the crankcase out of the cylinder walls
piston rings
How is the crankshaft and bearings of a 2 stroke cycle engine are lubricated
oil and gas are mixed together and drawn through the crankcase
what is the pressure and temperature of a typical compression ignition engine
2800-4200kPa and 540-650 C
removal of exhaust gases from the engine cylinder before the compression stroke is called
scavenging
What is the ideal cooling water temperature in a large industrial diesel engine
50-65 C
when a pump is located above the source of supply, the vertical distance from the surface of the supply to the pump center line is called
Static suction lift
static suction head is
when a pump is below the source of supply the vertical distance from the surface of the supply to the pump center line
the distance measured from the pump center line to the surface of the liquid in the discharge tank or to the free end of the discharge line
discharge head
vertical distance, measured in meters or feet of water, between the level in the suction tank of a pump to the level in the discharge line.
Total static head
the sum of friction, velocity and pressure head expressed in meters or feet of water head
Dynamic head
The force required to put the water in motion
Velocity head
the sum of static and dynamic head
Total head
The additional pressure required to overcome the pressure inside a closed discharge tank such as a boiler
Pressure or equivalent head
Describe how the power requirement of a centrifugal pump is affected by throttling in on the pump discharge valve
the power requirements of the pump are reduced because the pump is transferring less water and therefore doing less work
Directing the flow from one centrifugal pump impeller to the inlet of another is referred to as
staging
a positive displacement pump should always be equipped with a relief valve that is located
on the discharge of the pump before the isolation valve
