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Millwright Level 3 > Air Dryers > Flashcards

Air Dryers Flashcards

1
Q

What is the purpose of an air dryer?

A

Remove moisture from the air.

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2
Q

What are some variables that determine how much moisture air holds?

A

Temperature

Pressure

Nearby bodies of water

Wind conditions

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3
Q

As air warms up the amount of water in the form of vapour ________?

A

Increases

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4
Q

What is needed to dry materials other than warm air?

A

Flow,

Warm air will just become saturated and not able to dry anything

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5
Q

Relative humidity is low after it comes out of the compressor. What happens when it come into the after cooler?

A

Relative humidity increases

Dropping back down as it leaves the air dryer

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6
Q

What is relative humidity?

A

A comparison of the amount of water a sample of air holds to the amount it could hold if saturated

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7
Q

If the atmospheric relative humidity rises What also rises?

A

The amount of water the air must remove from the system

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8
Q

What is the dew point?

A

Further cooling after 100% relative humidity results in condensation of water vapour.

Dew point is temperature to which a gas must be reduced before the water vapour it Carries begins to condense

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9
Q

What is the function of an air dryer?

A

To reduce the dew point of the air

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10
Q

As compressors reduce the volume of gas, the pressure and temperature rise. The increase in temperature tends to reduce the amount of moisture the air can carry but the increase in temperature does what?

A

The opposite

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11
Q

Why are slugs (large quantity of liquid) bad?

A

Because liquid is not compressible could damage compressors or any tool that compresses the gas

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12
Q

Why are low points in air systems important?

A

To catch the water and get drained out of the system

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13
Q

In cold environments what can happen to moisture in air lines?

A

Can freeze and block lines completely

Called a frost plug

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14
Q

Why is excess moisture in air systems bad for air spraying?

A

Wet air can result in poor adhesion of the product being applied to the surface being coated

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15
Q

What are the types of air and gas dryers

A

Adsorption dryers
Absorption dryers
Refrigerant dryers
Mechanical dryers

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16
Q

What is the difference between adsorption dryers and absorption dryers

A

Absorption dryers use a chemical bond between the drying agent and the gas stream being dried

Adsorption dryer - the moisture is absorbed by the absorption material and forms a solution

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17
Q

Absorption is not always _______ as it is with with adsorption dryers

A

Reversible

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18
Q

Adsorption dryers is the?

A

Adhesion of molecules in a thin layer on a surface. Adsorption dryer uses the attraction of certain compounds to water.

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19
Q

Alumina is used in adsorption dryer to?

A

Attract water vapour

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20
Q

Why are two towers needed in adsorption dryers?

A

One tower is in service while the other is regenerating (drying medium)

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21
Q

Regeneration means?

A

Process of removing accumulation of moisture from the dryer bed

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22
Q

How much percent or dry air is used to regenerate a dryer bed??

A

10 to 15 percent

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23
Q

To reduce wear on moving parts what do some types of adsorption dryers do?

A

Measure the dew point of the air leaving the system: this prevents the air dryer from switching prematurely

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24
Q

What system can reach the lowest dew points

A

Adsorption

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25
Q

What are the four common desiccants

A

Activated alumina
Granular silica gel
Bead type modified silica gel
Molecular sieves

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26
Q

Activated alumina is?

A

Porous aluminum oxide and is inert

Suitable for us with a variety of gas streams and processes

Spherical shape most common

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27
Q

Granular silica gel

A

Acts as a filter by restricting the size of particles able to pass through the bed

Available in Rod or sphere particles

Applications are:
Hydrocarbons
Nitrogen
Hydrogen
Hydrogen sulfide
Carbon dioxide

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28
Q

Sizing of adsorption dryers is important because:

A

Correct velocities so that air passing through the desiccants spends adequate time in contact with it to ensure proper moisture removal

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29
Q

Because desiccant wears down over time it is recommend to have _______

A

A down stream filter

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30
Q

Why would a pre filter be important on a desiccant filter he important

A

To ensure the desiccant does not become loaded with oil or any other contamination

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31
Q

Flow from the regeneration is usually reversed through the bed. Why?

A

Flow is generally reversed through the bed

Reverse flow can break up or reduce compaction of the bed

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32
Q

Heated regeneration cycles use

A

A hot flow of gas through the bed to pick up and remove accumulated moisture

33
Q

15 % of dry air is re routed in a

A

Heatless dryer

34
Q

What is the negative aspect of a heatless dryer?

A

The oversized compression equipment required to meet the regeneration cycle plus the process requirements.

Cycle time is greatly reduced to only 2-5 minute but dew point could reach as low as -70c 158f

35
Q

What is the heat source for a heated dryer?

A

External heater

36
Q

Quality pre filters must be installed to prevent?

A

Oil or any other contamination from getting to the desiccant

Proper filter maintenance is very important

37
Q

what dryer uses chemical bond between drying agent and the gas stream? adsorption or absorption

A

Absorption

38
Q

what are the two types of absorption dryers

A

Chemical and liquid dehydration

39
Q

does a chemical dryer have a regeneration cycle?

A

no the Deliquescents slowly dissolve or melt away. bed must be replenished periodically,

40
Q

what are the most common types of deliquesants

A

various salts or a type of urea. most popular is calcium chloride

41
Q

flow through the chemical dryer is usually upward moisture that has been absorbed forms a ______ that drops to the bottom of the tank where it can be drained

A

Brine

42
Q

what is the typically dew point reached with a chemical dryer?

A

10C from that of the incoming gas If plant temps drop below 5 degrees vessel must be heated

43
Q

Heating the chemical dryer vessel can have a negative affect because?

A

performs best in a cool environment

44
Q

carryover of brine or salt dust has _______results?

A

corrosive

45
Q

chemical dryers are not the best system if constant dry air required because?

A

dryer must be shut down to replace the deliquescent

46
Q

Which dryer uses an absorbing agent such as ethylene glycol to remove moisture?

A

Liquid dehydration

47
Q

how does the liquid dehydration dryer work?

A

air traveling upward through the spray is scrubbed by the glycol which absorbs the moisture from the air.

48
Q

how does the wet glycol get the moisture removed from it?

A

gets passed through a still heated between 190C and 205C the moisture is evaporated and vented out

49
Q

Efficiency of liquid dehydration is affected by:

A

glycol temperatures
concentration
amount of interaction between glycol and gas to be dried

50
Q

What type of air dryer uses a drum composed of corrugated fibres?

A

Rotary drum

51
Q

Glycol returning from the still is % pure

A

98 percent 2 % of the gas will still have water in it

52
Q

dew point in liquid dryers can be lowered up to _______ to 60 degrees from that of the upstream gas

A

40

53
Q

what dryer is considered the least expensive of dew point reduction? why?

A

refrigeration dryer because there are no absorbtion materials that require maintenance or replacement

54
Q

Refrigeration dryers are made up of a _______ and a refrigeration cycle

A

heat exchanger

55
Q

can latent heat be recorded with a thermometer? why or why not

A

no any heat in a liquid past its boiling point will not change instead the state of the matter will change. ice to water or water to steam

56
Q

what is sensible heat

A

heat that can be read with a thermometer> sensible heat can be read until it reaches its boiling point.

57
Q

incoming air is first ________ before it passing through the refrigerant

A

pre cooled in the air to air heat exchanger

58
Q

after passing through the refrigerant heat exchanger the condensate is separated from the air and drained by the water separator before leaving the exchanger the air does what?

A

the cold dry air passes through the air to air heat exchanger to get warmed back up.

59
Q

Refrigerant dryers are only capable of lowering the dew point what degree? why

A

2-3 degrees because water freezes at 0 if the machine was set to low the water would freeze in the dryer

60
Q

How do mechanical dryers work?

A

They only used mechanical, physical means to cause the moisture to fall out the air stream.
-liquid separators
-centrifugal separators
-demister pads
-over-compression
- coalescing filters

61
Q

what is the least complicated of all dryers?

A

liquid dryer the reduction of velocity afforded by the the size of the dryer allows contaminants such as sand, oil, or other liquids to drop to the bottom of the vessel

62
Q

Liquid separators are often found where? why?

A

used for liquid removal upstream of a large gas compressor because of the amount of liquid that that frequently accompanies gas as it is being extracted from the ground

63
Q

Where can you find Centrifugal compressors?

A

often found downstream of compressor aftercoolers or where ever excess moisture needs to be removed

64
Q

How do the drains work on centrifugal separators work

A

float auto drain system

65
Q

What is a Demister Pad?

A

drying devises that use a fine wire mesh screen or pad. the gas passes through the screens trapping the liquid mist

66
Q

what is the only mechanical drying that can actually lower the dew point?

A

Over compression

67
Q

What type of air dryer uses a drum composed of corrugated fibres?

A

Rotary drum

68
Q

What is a health hazzard associated with Oil Carry over

A

Oil will stay in the air unless it goes through a coalescing filter and can cause harm if breathed in

69
Q

Coalescing filters are a very effective means of mechanical dryers removing oil and water. what size micron can it catch?

A

.01 micron (.00001”)

70
Q

What temperature of gas holds more liquid? warm or cool

A

warm gas can hold more moisture

71
Q

Why is it important to monitor Regeneration gas temps

A

Because if the gas temps are to low regeneration may not be competed in the set time period. High temps may cause air to move through the bed to quickly lowing efficiency.

72
Q

What is pressure Drop?

A

the difference between the incoming pressure and outlet pressure.

73
Q

what can it mean if you have unusually high pressure drop in your system

A

filter over loading or compacted desiccant bed

74
Q

If you have unusually low pressure drop in the system it could mean

A

switching valve may be stuck open or filter has a hole in it or it is bypassing

75
Q

What happens if you have to much flow through the dryer?

A

rapid decay of the desiccant, compaction of the bed, more dusting, inadequate contact time with the gas to be sufficiently dried

76
Q

what is the best way to test if an air dryer is operating properly?

A

by measuring the dew point with a dew point hygrometer

77
Q

when dew point begins to rise it is a sign?

A

the system is not functioning properly

78
Q
A

Millwright Level 3 (15 decks)

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