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Centrifugal·, C m ressors

. HOWELL TRAINING

Program developed for API by:

Programer:

Editors:

Production Editor:

Artists:

Content Specialist for API:

Validation provided through the cooperation of:

Howell Training Company 5201 Langfield Road Houston, Texas 77040-6694

Igor Guro

Marc Shaberman David Sprey

Daniel Follette

Robert Culp Dave Evans David A. Tschirhart

B. Turner Imperial Oil Enterprises, ltd.

Coastal States Gas Producing Company Corpus Christi, Texas

Imperial Oil Enterprises, Ltd. Sarnia, Ontario . ·

Total Leonard, Inc. Alma, Michigan

Union Oil Company of California Chicago Refinery

Special Acknowledgement

For the general encouragement and support given the PROFIT programed learning series by the API Executive Committee on-Training and Development: J.P. Malott, Continental Oil Company, Chairman; H.D. Aggers, Thums Long Beach Company, Chairman,· Committee on Vocational Training; Howard Swaim, Continental Oil Company, Chairman, API Sub-Committee on Programed Learning, and members of the subcommittee.

This text has been validated on behalf of the Production Department, American Petroleum Institute by the Subcommittee on Programed Learning of the Committee on Vocational Training and approved by the Executive Committee on Training.

PILOT_tp ~ROfiT © Howell Corporation, Training Division 1973

Fifth Reprint January 1'988

This program may not be reproduced in whole or in part without express permission of Howell Training Company. All translation

rights are reserved by the publisher.

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CENTRIIIFUGAL COMPRESSORS

Section One

Potential and Kinetic EnErgy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Pressure and Velocity-Two Forms of Gas Energy . . . . . . . . . . . . . . . . 2

Laws of Motion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Dynamic Compressors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Centrifugal Compressors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Axial Compressors ...................................... 14

Review ..................................................... 16

Ratio of Compression . . . ..................................... 17

Capacity of Compressor:::s ..................................... 18

Review ............. -· ...................................... 19

. Foot-Pounds and Horsepower ................................. 20

Head of Compression .......... .- .............................. 20

RPM and Horsepower . _ ...................................... 22

Review ............. -· ...................................... 23

R, RPM and BHP ..... -· ...................................... 24 Surging ............. _ ...................................... 25

Operating Charac~eristics ...................................... 27

Interpretation of Cum rves .................................. 28

Effects of External Syste rn on a Compressor ..................... 28

Review ...... · .... -· ......... ~ ; ............................. 30

Performance Features . . ..................................... 31

Section Two

Construction of Com pre ssors ................................. 32

Construction Detai Is . . . . ..................................... 35

Impellers . . . . . . . . . ..................................... 35

Diaphragms . . . . . . . ................ · ..................... 36

Guide Vanes . . . . . . ..................................... 39

Review ................................. · ............... 41

Shaft Seals . . . . . . . ..................................... 42

Contact Shaft Seals ..................................... 48

Bearings . . . . . . . . . . ..................................... 53

Balancing Drums . . ..................................... 56

The Oil-Circulation System ..... _ .......................... 59

Review· ................................................ 61

Cooling .... -. . . . . . . .... -................................. 61

Drivers .............................. · .................. 63

Safety Devices .......................................... 64

Vents and Bypasses ..................................... 67

Operation of Compresso" rs .................................... 69

Operation in Series and Parallel ........................... 69

Startup and Shutdo~wn: Presta.rt ........................... 71

Startup and Shutdo""Wn: Startup ............................ 72

Startup and Shutdo""Wn: Normal Shutdown ................... 7 4

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CENTRIFUGAL COMPRESSORS

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In the petroleum industry, gas is com­pressed for transportation to consuming markets and for refining processes. This program is about the construction and operation of compressors.

Unit 3 of Compressors teaches the oper­ating principles of centrifugal and axial compressors and the .construction and operation of centrifugal compressors.

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INSTRUCTIONS

This is a programed learning course.

Programed learning gives information in a series of steps called frames. Each frame gives some information and asks you to make use of it.

Here is how it works. · First, cover the response column at the right with a mask.

Read this frame and use the information it gives to fill in the blank.

A micrometer is an instrument designed to measure in thousandths of an inch.

A micrometer is a good tool for measuring very ___ _ differences in size.

Move the mask down to uncover the word at the right of the frame. If you have filled the blank with that word or a word that means the same, you are ready to go ahead to the next frame.

The drawing of a micrometer provides information that will help you .fill in the next blanks.

OBJECT TO BE MEASURED

Seven major parts are shown in the drawing, but only the and the contact the object . to be measured.

small

anvil, spindle

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The next frame calls for a choice. Circle or underline the ap­propriate word.

Of the two parts that contact the object, only the (anvil/ spindle) moves.

A program is a series of frames that work like the ones you have just done.

Read the frame.

Use the information to fill in the blanks or make a choice.

Move the mask down and check the response column.

Go on to the next frame.

Remember to cover the response column with a mask before you begin each page.

Notice that the left-hand pages from here on are printed upside down. The program is designed so that you will go through all the right-hand pages first, and then turn the book upside down and go through the other pages.

spindle

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.r--~~~~--------------.----:""'-------------:-...,...--~---.....,.....-__,. _______ ....,.._ ___

CENTRIFUGAL COMPRESSORS

Section One

POTENTIAL AND KINETIC ENERGY

Exhibits for this program are placed in the center of the book so that they may be removed easily for reference. Please remove them now so that you will have them available when needed.

1. To do work, some form of energy is needed. An electric motor needs energy.

2. Under certain conditions, matter can do work. A wound-,up clock spring ( can do work I cannot do work).

3. A moving hammer, due to its motion, ( can I cannot ) do work.

4. Both the moving hammer and the wound-up spring possess some kind of that enables them to do work.

5. The hammer is moving and the spring is not.

The energy of a moving hammer and the energy of a wound-up spring is (the same I a different) kind of energy.

6. A moving hammer and flowing water possess kinetic energy.

Kinetic energy is the energy that a body possesses due to its ( motion I molecular arrangement ) ..

7. A wound spring and still water behind a dam have potential energy.

Potential energy is the energy that a body possesses due to its position or arrangement.

8. When a spring is wound,--------- is done on it.

9. Because of the work that was done on it, the wound-up spring possesses potential

10. Suppose a ball of iron is lifted 20 feet off the ground.

Work was done in lifting the iron ball. The ball, due to its position, possesses energy.

11. The ball is allowed to drop. As the ball drops, it acquires energy, due to its motion.

12. When the ball hits the ground, it does------

1

electric

can do work

can

energy

a different

motion

molecular

work

energy

potential

kinetic

work

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13. Something possessing kinetic energy can do ____ _ when it is slowed down or stopped.

14. Work is done in lifting the ball. Due to the work done on it, the ball acquires energy.

15. The potential energy of the ball is turned into ____ _ energy as the ball drops.

16. The kinetic energy in turn can be converted into ---'------as the ball is stopped.

17. Energy cannot be created or destroyed, but it can be converted from one to another.

18. Potential energy can be converted into-----­energy or work.

19. Kinetic energy can be converted into -----­energy.

20. As work is done on an object, some kind of ----­is added to it.

PRESSURE AND VELOCITY-TWO FORMS OF GAS ENERGY

21. When an ·amount of gas is compressed into a smaller volume, the pressure of the gas ( increases I stays the same).

22. To compress the gas, some ------ has to be done to it.

23. Compressed gas in a static state exerts its energy in the form of pressure in all directions.

When a gas is flowing, some of its energy in the form of pressure is converted to energy in the form of motion in (a single direction I all directions).

2

work

potential

kinetic

work

form, or type

kinetic

potential

energy

increases

work

a single direction

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...

24. A compressed gas possesses potential energy due to the ------it exerts.

25.· A flowing gas possesses kinetic energy due to its ------, in one direction.

26. Gas in a static state has all of its energy in the form of ------only.

27. Velocity is the speed of flow. The higher the speed of flow, the higher the------

28. If the gas is allowed to flow, some of its pressure is converted into------

29. The total energy of a flowing gas is a function of its velocity, plus its-----'----

30. If no work is done and no energy is lost, the total energy of a gas during flow (changes I remains constant).

31. When the total energy stays the same, and energy in the form of velocity increases, energy in the form of pressure must ( increase I decrease).

32. If the flowing gas is slowed down so that its velocity is decreased, then its pressure must _____ _

33. -Anything possessing potential energy must have had some ______ done on it at some previous time.

34. A gas with pressure has had------ done on it

35. By doing work on so~ething, one ( can I cannot ) increase its total energy.

36. A compressor does work on a gas and thus adds or in-. creases the total · of the gas.

LAWS OF MOTION

37. When a car accelerates quickly from rest, the driver is thrown (forward I backward ).

38. When the brakes are applied as the car is moving, the driver is thrown (forward l backward ).

39. If the wheels of a moving car are turned, but there is no traction, as on ice, the car tends to ( turn I continue in a straight line).

_ 40. A body at rest tends to remain at------

41. A body in motion tends to continue in------

3

pressure

motion, or flow

pressure

velocity

velocity

pressure

remains constant

decrease

increase

·work

work

can

energy

backward

forward

continue in a straight line

rest

·motion

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42. When a body is in motion and there is no outside force acting on it, it tends to continue in a ( straight line I curved line).

43. When a driver turns his car, the car ( opposes I does not oppose) the change of direction.

44. A body at rest remains at rest unless it is acted upon by some outside------

45. If a gas in a pipe is not flowing, the gas tends to ( remain static I flow ) .

DYNAMIC COMPRESSORS

46. A dynamic compressor adds energy to gas in the same manner that an electric fan does.

The rotating blades of the fan force air to------

47.· Air that is at rest tends to remain at------

48. As the fan blades start turning, they push on the air.

-

The stationary air------ the push of the blades.

4

straigh-t line

opposes

force

remain static

move, or flow

rest

resists

49. As the air resists the blades, the molecules of the air are brought ( closer together I further apart ). ·

50. When the air molecules are compressed, th.e volume of the air (decreases I i-ncreases).

·51. As the volume of the air decreases, its pressure

52. The blades of the fan overcome the resistance of the air and thrust the air forward.

The faster the blades turn, the ( faster I slower ) the air is pushed.

53. The fan, by doing work on the air, actually increases the -------'--and velocity of the air.

54. When velocity and pressure are added to a gas, its total energy------·

55. A dynamic compressor increases total gas energy by adding and to the gas.

56. The total energy of a gas leaving a compressor is ( less than I greater than ) the total energy of the gas entering the compressor.

57. The energy that a gas gains in a compressor is due to the done on it.

Centrifugal Compressors

58 .. Any bodyset in motion tends to continue in motion.

If· there is no gravity pull, nor any obstacle. to deflect it, any body in motion travels in a ( straight I curved ) line.

59. Suppose a ball attached to a string is set in motion. Assume that there is no gravity and that the string has no effect on the ball.

BALL. STRING

The ball moves in a (circle I straight line).

5

closer together

decreases

increases

faster

pressure

increases

pressure, velocity

greater than

work

straight

straight line

60. Suppose the string is fastened to a fixed pivot point and then the ball is set in motion.

' FIXED PIVOT POINT

At first, the ball moves in the direction of motion I toward the pivot).

· 61. When the string becomes taut, it deflects the ball.

Because of the deflection, the ball actually travels in a(an)-----------

6

in the direction of motion

arc, or circle

62. Assuming it has enough energy, the ball continues to move in a series of arcs.

At each Instant of its travel, the physical tendency of the ball is to travel in a line.

63. But instead, the ball travels in a circle because it is held or deflected by the------

64. The string actually applies centripetal ( pulling-in­toward-the-center ) force, causing the path of the ball to _____ _

65. If the string breaks, the ball flies out in a ( larger circle I straight line).

66. Any object traveling in a circle is kept in that path of travel by ( centripetal/ centrifugal ) force.

67. If the centripetal force is eliminated, the object then moves in a line.

68. The force pulling an object in a circular path toward the center is force.

69. The centrifugal tendency of the object is its tendency to pull away from the of rotation, or to pull

· against the centripetal force.

70. The centrifugal tendency acts in ( the same direction as I the direction opposite tp) the centripetal force.

7

straight

string

change, or curve

straight line

centripetal

straight

centripetal

center

the direction opposite to

i "

71. The centrifugal tendency is actually not a force but is the result of the tendency of the object to move in a ------ line while being pulled toward a center of rotation by force.

72. A ball bearing is placed close to the center of a disc that has blades.

BALL BEARING BLADES

As the disc begins to move, one of the blades forces the ball bearing to------

73. The ball bearing tends to travel in a ( straight I curved ) path.

74. The drawing shows the actual path of the ball bearing as the disc rotates.

Centripetal ( pulling-in-toward-the-center ) force ( is I is not) acting on the bearing.

75. Because of the lack of centripetal force, the bearing is forced ( toward I away from ) the center of the disc.

8

straight centripetal

move

straight

is not

away from

_ ___.. .•.

76. As the disc rotates, the ball bearing ( is I is not ) in contact with the vane.

77. This disc is rotating.

For each rotation, point ( A I B ) has the largest distance to cover.

78. When the disc is rotating, point ( A I B ) moves faster.

79. Anything that is being carried along by the rotation of the disc has a greater velocity when it is near ( the center I the outer rim ) of the disc. ·

80. If anything being carried along by the rotation of the disc also travels outward from the center to the outer rim, it gains------

81. This is a compressor impeller.

BLADES

PLATES

An impeller is made of two plates separated by

9

is

A

A

the outer rim

velocity

blades

82. Suppose the impeller begins to rotate.

As the impeller rotates, the blades force the air in the impeller to-------'---

83. Air molecules tend to travel in a------ line.

84. Because there is no centripetal force, the rotation forces the air molecules outward from the of the impeller.

85. As the air molecules move outward, they gain-----

86. The air also tends to oppose the push of the blades, so the pressure of the air is------

87. The impeller adds both ______ and __ _:. _ _:._ to the air.

88. The tendency of air or gas to move outward from the center of a rotating impeller is the centrifugal tendency.

A compressor that uses centrifugal tendency to impart pressure and velocity to a gas is a compressor.

89. The part of the centrifugal compressor that moves the gas is the impeller. ·

EYE

GAS IN

As the impeller rotates, it . moves the gas toward the ------rim of the impeller.

10

move

straight

center, or eye

velocity, or speed

increased

pressure, velocity

centrifugal

outer

90. As the .gas moves toward the outer rim of the impeller, its velocity------

91. This increase in velocity away from the eye creates a low­pressure area at the (eye I outer rim).

92. This low-pressure area at the eye causes a suction which (allows I does not allow) more gas to enter.

93. The impeller does work. on the gas. The work is converted into the that the gas gains.

94. The energy that the gas gains is in the form of both -----------and ______ __

95. When the gas is at the tips of the impeller blades, it is at ( maximum I minimum ) velocity.

96. As the gas leaves the impeller, it is thrust into a passage­way called the diffuser.

When the gas enters the diffuser, the impeller ( is I is not) acting directly on the gas.

I

11

increases

eye

allows

energy

pressure, velocity

maximum

is not