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Operating Engineering - Second Class > Chapter 1 - Criteria for turbine application > Flashcards

Chapter 1 - Criteria for turbine application Flashcards

1
Q

What are the main types of steam turbines?

A
  • condensing turbines

- noncondensing turbines

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2
Q

What do steam turbines do?

A

Steam turbines are used in powerplant cycles to convert heat energy from steam generating equipment into mechanical work.

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3
Q

What are the industrial applications of a small single stage turbine?

A
  • pump drivers (up to 50MW)
  • Large compressors
  • Generation range (7.5-900KW)
  • 1000 to 6500 rev/min
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4
Q

What is regenerative cycle?

A

When a steam turbine bleeds (extracts) steam to heat feedwater

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5
Q

What is another term for regenerative cycle?

A

bleed turbine

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6
Q

Explain automatic extraction turbine.

A

When steam is extracted or bled from several points usually from one to eight points

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7
Q

Turbine cases are designed to handle to high pressures and temperature, while maintaining what?

A
  • resisting distortion
  • maintaining all clearances
  • correct alignment on rotating blading
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8
Q

Describe split casings

A
  • good for inspection upon removal, but no ideal for external flanges due to lack of temperature transfer and strength
  • higher chromium alloys are used in higher temp. applications (creep resistance)
  • surfaces steam tight, dowel pins and grooved slots
  • higher pressure/temp application require flange heating to evenly distribute heat in case of expansion
  • centerline support be designed to expand and contract evenly with the unit to maintain alignment
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9
Q

Describe double casing

A
  • used for very high pressure
  • highest pressure is injected to the inner casing, the inner casing exhausts out the end of the turbine into the outer casing
  • Exhausting the inner casing into the outer is done to reduce stress and promote even heating
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10
Q

Describe cylinder casing drains

A
  • used to remove remove water from turbine
  • water is bad for blades promotes corrosion and material loss
  • LP section designed usually to exhaust max at 14% wetness
  • drains are placed on the casing in critical places to remove condensate especially on LP
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11
Q

Name the 3 types of turbine rotors

A
  • solid forged rotor
  • disc rotor
  • welded rotor
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12
Q

Describe a solid forged rotor

A
  • Forged rotors of this type have wheels and shaft, which has been machined from one solid forging (one piece).
  • used in HP and IP sections
  • used based on your start-up procedure because it requires a long warm up
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13
Q

Describe a disc rotor

A
  • Also known as: “build-up rotors”
  • constructed of many separately forged discs or wheels
  • discs are slotted into the machined grooves along the motor
  • the outer rims of the wheels have machined grooves for blading
  • Used for LP cylinders
  • wheels or discs can come loose if improper warm-up/expansion occurs
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14
Q

Describe a weldor rotor

A
  • built up from discts and two shaft ends which are joined together by the welding in the inner circumference
  • discs must be very strong and small holes must be drilled in the discs to allow steam in for heating (expansion)
  • Grooves are machined on the outer edge of the discs to allow for blading
  • induction must be applied before welding on rotor (automatic argon arc welding)
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15
Q

Name the 3 types of blading

A
  • Reaction blading
  • impulse blading
  • combination of impulse and reaction
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16
Q

Describe reaction blading

A
  • pressure drops across both fixed and moving blades
  • tight clearances are required with this method to ensure no steam leaks by both rotating & stationary blading.
  • any steam that leaks by sections performs no work and causes loss of efficiency
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17
Q

Describe Impulse blading

A
  • machined from solid bars and are slotted into the discs and tangs are left at the tips for schrouding attachment
  • there is no pressure drop across moving blades in an impulse turbine
  • sealing is not as important as a reaction turbine, although proper sealing is required with this design between diaphragms to prevent leakage between stages
  • shrouding helps guide steam to incr. efficiency
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18
Q

What are the two main forces on blading?

A
  • bending force

- throwing out force

19
Q

Where are the greatest stresses in blading?

A
  • LP section because blades are the largest
  • double flow LP sections are designed and employed to cut forces in half versus a longer single flow design (you can get away with smaller blades this way)
20
Q

Describe blade shrouding

A
  • it is employed on the end of the blades and provides a right clearance to the casing
  • promotes steam through the blading to ensure efficiency and prevents steam leakage through stages
  • constructed of stainless steel which is strong and corrosion resistant
  • machined and welded if needed
21
Q

Describe diaphragms

A

Fixed blading of impulse turbine consists of nozzles mounted in diaphragms. constructed of two solid halve which fit into slotted grooves in the turbine casing

22
Q

Name 4 shaft sealing designs

A
  • stuffing box
  • carbon rings
  • labyrinth seals
  • water seals
23
Q

Describe carbon rings

A

spring backed carbon rings made of graphite and are self-lubricating

24
Q

Describe labyrinth seals

A
  • usually employed in large machines, where carbon rings cannot be used (exceeds carbon ring limits)
  • causes eddy currents in the steam passing through the seal reducing steam velocity and causing small pressure drops
  • steam leak off points are remove condensate and steam from the seals
25
Q

Describe water seals

A
  • used on the turbine ends for sealing from steam leakag
  • high purity water or condensate is injected into the seal
  • the seal centrifugal pump runner inside is fixed to the turbine shaft which makes the seal go positive and ensure steam sealing
  • no leakage
  • Not effective until running speed is achieved
  • quenching water fed to seal could cause shaft to crack
  • requires more adjusting than steam glands
26
Q

Name two types of bearings

A
  • ring oiled bearings

- pressure fed bearings

27
Q

Describe ring oiled bearings

A
  • ride freely on the journals revolving with them dipping into oil contained in the bearing housing
  • they carry oil to the top of the journal from the resevoir
  • rotation of the shaft forces the oil around the journal
  • this type may be fitted with a cooling jacket of auxillary cooling
28
Q

Describe pressure fed bearings

A
  • large turbines employ bambbitt-lined sleeve bearing
  • they are highly reliable and require minimal maintenance
  • have a very low coefficient of friction
    large steam turbine with these types of bearings are usually supported with two main bearings at each end
  • oil is pumped into the bearing housing by a circulating pump through oil groove. This forms an oil wedge in the journal, bearing and shaft float on the oil.
  • Cooling via a jacket or auxillary cooler usually required for this type of system
29
Q

Describe axial expansion

A

the expanding steam flow is parallel to the line of the shafts

30
Q

Describe radial expansion

A

(traverse) expansion at right angles to the shaft

31
Q

Describe Impulse turbines

A

have a small amount of thrust most still require a thrust bearing or thrust counteracting method

32
Q

Describe reaction turbines

A
  • have more thrust than impulse turbines
  • requires thrust bearings designing the turbines with double flow acting flow and other methods to help offset thrust by balancing forces through the turbine
33
Q

Name the 4 types of thrust bearings

A
  • ball bearings
  • tappered land bearings
  • Michelle bearings
  • kingsburry bearings
34
Q

Describe ball bearings

A

small turbines (impulse turbines) employ ball bearings “double row” or “deep groove” type bearings

35
Q

Describe tapered land bearings

A
  • large turbines
  • they build up an oil wedge from oil being forced through grooves in the bearing on the journal creating a separating film
36
Q

Describe kingsburry bearings

A
  • thrust bearings
  • consists of tilting pads which are free to rock
  • the oil wedge forms within the pockets of the bearing
  • require large amounts of oil and lot of heat to be carried away from the oil
37
Q

Describe dummy pistons

A
  • steam is fed from upstream in the turbine down a balance pipe and into a clearance pocket at the end of the rotor counteracting turbine thrust
  • calculation is done to find the amount of force you have to counteract the units of thrust
38
Q

Describe thrust adjusting gear

A
  • used to project axial seals and bearings it fits on like a piston cylinder which can be adjust on start-up to be pushed in the direction of the exhaust for max clearance between moving / stationary blades to avoid rubbing
  • in op. and temp. reached the thrust block is adjusted to tighten the tolerances (incr. efficiency)
39
Q

Name two types of nozzles

A
  • convergent nozzle

- convergent divergent nozzle

40
Q

Describe convergent nozzle

A
  • used for small pressure drops
  • as the pressure drop across the nozzle the velocity increases
  • Any extra NRG in this type of nozzle is given up in the form of eddy currents
41
Q

Describe convergent divergent nozzles

A
  • used for large pressure drops
  • the pressure at the narrowest part of the nozzle is at critical pressure
  • in the divergent section is where the pressure drop occurs and steam velocity incr, with next to no eddy currents
42
Q

What is Newtons second law and equation?

A

Change in momentum F=ma

43
Q

How do steam turbine produce mechanical energy?

A

steam turbine blades are used to direct steam onto turbine blades at the correct angle resulting in the efficient energy conversion

Operating Engineering - Second Class (1 decks)

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