Model Answers of Fractionation

Distillation & Fractionation Model Answers ________________________________________________________________________

Question No.1: MULTIPLE CHOICES: Place the letter of the statement that best completes the sentence in space provided. 1. Hydrocarbon molecules are made up of: ---------A. hydrogen and oxygen atoms B. carbon and nitrogen atoms C. hydrogen and carbon atoms D. none of the above

2. Most products produced in a refinery or petrochemical plant pass through: ---------A. several different distillation columns B. only one distillation column C. sieve-deck trays

3. A product formed in the distillation process will contain hydrocarbons with: ---------A. very different boiling points or boiling point ranges B. similar boiling points or boiling point ranges

4. The purpose of the distillation process is to:

----------

A. removes water and sediment from hydrocarbons B. chemically crack or reform hydrocarbon molecules C. separates a mixture of hydrocarbons into relatively pure tractions

5. When a mixture of hydrocarbons is heated, which fractions are the last to vaporize? ---------A. Heavy components B. Light components C. Medium-sized components D. Depends on the particular mixture

6. One way to separate a mixture of hydrocarbons is to: ---------A. partially vaporizes them and then condenses the vapors back to liquid B. completely vaporizes them and then condenses the vapors back to liquid. C. places the mixture under a complete vacuum D. keeps the vapor pressure of the hydrocarbons below 14.7 psi ______________________________________________________________________________________

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7. What kind of heat is removed when a vapor is condensed to liquid? --------A. Sensible heat B. Thermal heat C. Latent heat D. Atomic heat

8. When the vapor pressure of a liquid equals the pressure against that liquid, it: ---------A. condenses. B. boils. C. does not change its state.

9. Heavy hydrocarbons have:

-----------

A. low vapor pressures and low boiling points B. high vapor pressures and high boiling points C. high vapor pressures and low boiling points D. low vapor pressures and high boiling points

10. Which hydrocarbon mixture is more difficult to separate? ----------A. A mixture with very narrow boiling point differences B. A mixture with wide boiling point differences

11. When the pressure against a liquid is increased, the liquid boils at: ----------A. a lower temperature B. the same temperature C. a higher temperature D. None of the above. It depends on the composition of the liquid.

12. Why is steam sometimes added to a distillation column? ----------A. Steam strips out light components by reducing the hydrocarbon partial pressure B. Steam strips out heavy components by increasing the hydrocarbon partial pressure

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13. Reflux is the:

-----------

A. liquid that enters a distillation column as feed B. vapor that boils light components out of the downward flowing liquid in a distillation column C. cool liquid that flows down a column and removes heat from hot, rising vapors

14. What happens when the reflux rate is increased?

----------

A. More heat is removed from the tower B. Less heat is removed from the tower C. More heat is added to the tower D. Less heat is added to the tower

15. Hot vapors bubble through the liquid:

----------

A. on each tray in a distillation column B. in the downcomers C. only in the bottom of a column D. only in the top of a column

16. A heavier fraction will develop on a tray when:

----------

A. the tray temperature is decreased B. the feed rate is increased C. the tray temperature is increased D. a bubble cap is removed from the tray

17. The liquid on the bottom trays of a distillation column is: ---------A. lighter than the liquid on the top trays B. heavier than the liquid on the top trays C. the same composition as the liquid on the top trays

18. Material balance means that:

----------

A. whatever material enters the tower as feed must leave the tower as products. B. half of the feed leaves from the top of the tower while the other half leaves from the bottom. C. light and heavy fractions will always balance each other out

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19. A vacuum distillation column operates at a very low pressure in order to: ---------A. decrease the amount of heat that is needed to distill hydrocarbons B. minimize the amount of vapors that are formed C. reduce stress damage

20. For good fractionation to occur there must be:

----------

A. good vapor-liquid contact on each tray B. a temperature difference (or gradient) between trays in the tower C a two-way flow of fluids inside the column D. All of the above

21. Which of the following is a heat exchanger?

----------

A. Kettle-type reboiler B. Thermosyphon-type reboiler C. Condenser D. All of the above

22. A product with an initial boiling point (IBP) specification of 100-105°F tests at 95°F. This product: ----------A. contains material that is too light B. does not contain enough light material C. contains material that is too heavy

23. A product with an end boiling point (EP) specification of 150-155°? tests at 158°F. This product: ----------A. contains material that is too light B. contains material that is too heavy C. does not contain enough heavy material

24. A product with a flash point specification of 100-105°P tests at 95°F. This product: ----------A. contains material that is too heavy B. contains material that is too light C. is too dense

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25. A product with a low API gravity is relatively:

----------

A. light B. heavy C. pure D. Depends on the product being tested

26. When the heat balance in a distillation column is adjusted: ----------A. product composition changes B. more of one product and less of another will be produced C. both A and B

27. Cut point changes can be made in a distillation column by: ----------A. changing the reboiler temperature B. changing the reflux rate C. changing the furnace temperature D. changing any of the above variables

28. If the reflux rate in distillation column is increased and other tower operating conditions are kept constant, which of the following occurs? -----------A. Heavier overhead, bottom, and side draw products are produced B. Lighter overhead, bottom, and side draw products are produced C. The amount of top product produced increases D. None of the above

29. If we increase the reboiler temperature for a depropanizer and keep other tower operating conditions constant, which of the following occurs? -----------A. Heavier overhead and bottom products are produced. B. Lighter overhead and bottom products are produced. C. The amount of bottom product produced increases. D. None of the above

30. Opening a stripper draw makes this product and the products below this tray: ----------A. heavier B. lighter C. vaporize D. condense ______________________________________________________________________________________

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31. How can you change the composition of one side draw product without affecting the composition of products below this tray? -----------A. Close a stripper draw B. Open a stripper draw C. Close one stripper draw and open another

32. The four main process variables are:

------------

A. pressure, temperature, liquid level, and flow B. viscosity, density, temperature, and pressure C. liquid level, temperature, viscosity, and pressure

33. A control loop is:

------------

A. a combination of instruments that works together to keep a process variable at a desired value B. a series of controllers that keeps a distillation column producing products that are on-specification C. a group of valves that keeps process variables at setpoint D. a device that records and indicates the condition of a process variable

34. What does this symbol stand for? ----------------

PRC

--------------- ------------

35. Can instruments automatically correct all process upsets? -----------A. Yes B. No

36. Light hydrocarbons have:

-------------

A. low vapor pressures and low boiling points B. low vapor pressures and high boiling points C. high vapor pressures and high boiling points D. high vapor pressures and low boiling points

37. A liquid will not boil until its:

------------

A. vapor pressure is double the pressure against the liquid B. vapor pressure equals the pressure against the liquid C. molecules move faster than the gas molecules above it D. latent heat is converted to sensible heat ______________________________________________________________________________________

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38. A distillation column that operates at or slightly above 14.7 psi is called: ----------A. a vacuum tower B. a pressure tower C. a stripping column D. an atmospheric tower

39. In order to make useful products, hydrocarbons must be separated into: -----------A. Completely pure fractions B. relatively pure fractions C. a mixture of fractions D. Doesn't really matter

40. When the reflux rate is decreased:

------------

A. more heat is removed from the tower. B. less heat is removed from the tower. C. more heat is added to the tower. D. less heat is added to the tower.

41. What happens on each tray in a distillation column? ---------A. Cool vapors bubble through a warmer liquid on the tray B. Hot vapors bubble through a cooler liquid on the tray C. The liquid does not come in contact with vapors on the tray

42. A lighter fraction will develop on a tray when:

------------

A. the tray temperature is increased B. the feed rate is increased C. the tray temperature is decreased D. a bubble cap is removed from a tray

43. The liquid on the top trays of a distillation column is: -------A. lighter than the liquid on the bottom trays B. heavier than the liquid on the bottom trays C. the same composition as the liquid on the bottom trays

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44. When heat is added to a mixture of hydrocarbons, which fractions are the first to vaporize? ---------A. Heavy components B. Light components C. Medium-sized components D. Depends on the particular mixture

45. What kind of heat is added to vaporize a substance already at boiling temperature? ----------A. Sensible heat B. Latent heat C. Thermal heat D. Atomic heat

46. Which hydrocarbon mixture is easier to separate? ---------A. A mixture with very narrow boiling point differences B. A mixture with wide boiling point differences

47. When the heat balance in a distillation column is adjusted: ----------A. product composition changes B. more of one product and less of another will be produced. C. Both A and B

48. If the reflux rate in crude distillation column is decreased and other tower operating conditions are held constant, which of the following occurs? ----------A. Heavier overhead, bottom, and side draw products are produced B. Lighter overhead, bottom, and side draw products are produced C. The amount of top product produced decreases D. None of the above

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49. If the reboiler temperature for a depropanizer is decreased and other tower operating conditions are kept constant, which of the following occurs? -----------A. Heavier overhead and bottom products are produced B. Lighter overhead and bottom products are produced C. The amount of bottom product produced decreases D. None of the above

50. Closing a stripper draw makes this product and the products below this tray: -----------A. vaporize B. condense C. heavier D. lighter

52. A product with an initial boiling point (IBP) specification of 100-105°F tests at 110°F. This product: -----------A. contains material that is too light B. does not contain enough heavy material C. does not contain enough light material

53. A product with an end boiling point (EP) specification of 150-155°? tests at 140°F. This product: -----------A. contains material that is too heavy. B. does not contain enough heavy material. C. does not contain enough light material.

54. A product with a flash point specification of 110-115°F tests at 125°F. This product: -----------A. contains material that is too light B. does not contain enough light material C. does not contain enough heavy material

55. Which of the following process upsets can instruments correct automatically? -----------A. Pump failure B. Stuck valve C. Feed composition change D. Leak in condenser ______________________________________________________________________________________

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56. A product with a high API gravity is relatively:

------------

A. light B. heavy C- pure D. Depends on the product being tested

57. The four main process variables are pressure, temperature: -----------A. liquid level, and viscosity B. density, and viscosity C. liquid level, and flow D. flow, and density

58. What does this symbol stand for? ---------------

----------------

FRC

----------------

59. The molecules that form crude oil are called:

------------

A. hydrocarbons B. carbonates C. petroleum D. water, salt, and sediment

60. What atoms make up hydrocarbons? (Pick two) --------- & -------A. Water B.Carbon C. thane D. Hydrogen

61. When we heat a mixture of hydrocarbons, the first molecules to boil and vaporize are: -----------A. the heavy, or large, hydrocarbons B. the light, or small, hydrocarbons C. the medium-sized hydrocarbons D. none of the above. They all start boiling at the same temperature

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62. What happens when a mixture of hydrocarbons is distilled? ----------A. The hydrocarbons are physically separated B. They are chemically changed

63. Most of the products produced in a refinery or petrochemical plant pass through: ----------A. several distillation processes B. atom splitters C. vacuum towers D. all of the above

64. Why can we separate hydrocarbon mixtures by heating them and then condensing the vapors? ----------A. Different hydrocarbons have different boiling points B. Different hydrocarbons have the same boiling point C. Heat causes hydrocarbon molecules to break in half D. Latent heat equalizes the vapor pressure of hydrocarbons

65. During the distillation process, heat put into the tower: -----A. is consumed by the hydrocarbons B. is always less than heat taken out C. is taken out as latent heat of condensation and as sensible heat in the products themselves

66.

Choose two molecules:

characteristics

of

light

hydrocarbon ------- & -------

A. High boiling temperatures B. Low boiling temperatures C. High vapor pressures D. Low vapor pressures

67. Distillation of hydrocarbons is easiest components have boiling points that are:

when the -----------

A. dose together B. far apart C. neither of these. Boiling points do not affect distillation

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68. What happens to the boiling point of a liquid when pressure against that liquid is increased? ----------A. The boiling point temperature is increased B. The boiling point temperature is decreased C. The boiling point does not change unless the vapor pressure of that liquid changes D. It depends whether the liquid is water or a mixture of hydrocarbons

69. The temperature on each tray in the tower is controlled by: -----------A. the downward flow of reflux and upward flow of vapors B. the downward flow of vapors and upward flow of reflux C. the composition of the feed D. none of the above

70. Inside the distillation column:

------------

A. vapors by-pass the liquid through downcomers B. vapors bubble through the liquid on the tray C. vapor-liquid contact occurs in the chamber space between the trays D. liquid flows down the tower through bubble caps

71. What happens on each tray as a result of vapor-liquid contact? ----------A. Light materials in the liquid tend to condense, and heavy materials in the vapor tend to vaporize B. Light materials in the liquid tend to vaporize, and heavy materials in the vapor tend to condense

72. The vaporization-condensation cycle eventually produces: -----------A. a different fraction on each tray B. the same fraction on each tray C. a heavy product at the top of the column and a light product at the bottom

73. As vapors rise up the column, they become progressively: -----------A. heavier B. lighter ______________________________________________________________________________________

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74. Liquid moving down the column becomes:

------------

A. heavier B. lighter

75. In a crude distillation column, products drawn from the side of the tower pass through a: -----------A. condenser B. reboiler C. stripping column

76. The temperature in a distillation column decreases from: -----------A. bottom to top B. top to bottom

77. The heaviest fraction will be formed on the tray with the: -----------A. lowest temperature B. highest temperature

78. An atmospheric tower is a distillation column that operates: -----------A. at or slightly above 14.7 psi B. below 14.7 psi

79. In order to maintain a vacuum in a distillation column: ------A. steam must be injected into the tower B. all noncondensibles vapors must be continually removed from the tower C. only the heavy hydrocarbon molecules must be removed D. none of the above functions must be performed

80. Which type of tower is generally used to distill reduced crude? ----------A. Atmospheric tower B. Vacuum tower

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81. Good fractionation requires:

------------

A. a tower with a large number of trays B. a multiple feed-port tower C. multi-pass downcomers D. good vapor-liquid contact on each tray

82. "Entrainment" occurs when:

------------

A. vapor rates are too low B. not enough heat is put into the tower C. small drops of liquid suspended in vapor are carried up from one tray to the next

83. Which of the following can generate the most heat to vaporize feed? -----------A. Condenser B. Heat exchanger C. Furnace

84. A heat exchanger is a device in which:

------------

A. heat is transferred from one fluid to another B. burners heat feed using radiant and convection heat C. vapors bubble through liquid to increase surface area D. products drawn from the side of a tower are further distilled

85. A product with an IBP specification of between 115-120° F tests at 110° F. This product contains too much: -----------A. light material B. heavy material C. medium weight material D. None of the above

86. A product with a flash point specification of between 95100° F tests at 105° F. This product does not contain enough: -----------A. light material B. heavy material C. medium weight material D. None of the above

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87. A product with a high API gravity is relatively:

------------

A. light B. heavy C. Cannot be determined with the above information

88. Cut point changes can be made in a distillation column by: ------------A. changing the reflux rate B. changing the feed temperature C. changing the reboiler temperature D. changing any of the above

89. What happens when the heat balance inside a distillation column is adjusted? -----------A. Product composition changes B. More of one product and less of another will be made C. Both A and B are correct

90. If we increase the reflux rate in a crude distillation unit and hold other operating conditions constant, which of the following will occur? -----------A. Lighter overhead, bottom, and side draw products B. Heavier overhead and side draw products C. Heavier bottom product D. More overhead product

91. If we increase the feed temperature in a crude distillation unit and hold other tower variables constant, which of the following will occur? ----------A. Heavier overhead, bottom, and side draw products B. Less bottom product C. More overhead product D. All of the above

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92. Opening a stripper draw makes this product and products below this tray: ----------A. heavier B. lighter C. Does not affect the stripper draw product

93. The products made in a distillation column:

------------

A. should just meet product specifications B. should exceed product specifications C. do not always have to meet product specifications

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