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PE 4B > Unit 6 Water Treatment > Flashcards

Unit 6 Water Treatment Flashcards

1
Q

Impurities in a boiler can;

A

Result in lose of efficiency, and can create a dangerous situation that may result in catastrophic failure

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2
Q

Sludge

A

Produced elsewhere but carried along by flowing water, will deposit on the boiler heat transfer surfaces

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3
Q

Scale

A

Formation from salts, which have solubility in source water, but are totally insoluble under the conditions inside a boiler

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4
Q

Corrosion

A

Happens in the hottest areas of the boiler, includes water wall, screen tubes, and superheater tubes

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5
Q

Carryover

A

From impurities downstream of the boiler. Negatively affects the purity of the steam that contacts parts of the energy plant

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6
Q

Two methods of treating boiler water

A

External and internal water treatment

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7
Q

External water treatment

A

Takes place before the water enters the boiler

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8
Q

Internal water treatment

A

Adding specific chemicals to boiler water that target problematic impurities

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9
Q

Direct amine measurements can be made using a;

A

Gas chromatograph

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10
Q

Shock feeding only one type of biocide will result in;

A

Organisms becoming immune to it

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11
Q

Biological attack on cooling tower wood occurs when;

A

The cellulose deteriorates

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12
Q

Suspended solids

A

Substances that have not been dissolved, but are held or suspended in the water.

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13
Q

Examples of suspended solids;

A

Clay, sand, silica, organic materials

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14
Q

Particles smaller than ________ are considered to be dissolved solids

A

2um

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15
Q

Larger materials in water such as tree and branches are considered;

A

Not to be suspended solids, since they are easily dealt with using screens

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16
Q

If suspended solids are not removed;

A

They can form deposits within the boiler, which can reduce heat exchange, which in turn can lead to metal failure. Can also lead to erosion of metal surfaces or plug up equipment.

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17
Q

A higher concentration of suspended solids can lead to;

A

Foaming, which results in carryover or priming from the steam drum

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18
Q

Most common methods of reducing suspended solids externally;

A

Through gravity settling like clarifiers and pressure filtration

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19
Q

How to remove suspended solids internally;

A

Through boiler blowdown

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20
Q

Dissolved solids are usually:

A

Ionic compounds dissolved in water

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21
Q

Ionic compounds with calcium and magnesium cations are called

A

Calcium and magnesium salts

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22
Q

Brackish water

A

Water containing high dissolve salt concentrations

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23
Q

When conducting water hardness tests, calcium and magnesium appear as

A

Dissolved solids

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24
Q

Ppm is equivalent to

A

Mg/L for liquids

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25
Q

Bicarbonate of calcium and magnesium

A

Cause temporary hardness because they will precipitate out of the water at temperatures below the boiling point. these can be removed before they enter the boiler

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26
Q

Sulfates of calcium and magnesium cause;

A

Cause permanent hardness since they do not precipitate until the water boils at which point they form hard, dense scale on boiler surfaces

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27
Q

Technologies that remove silica

A

Lime softening, reverse osmosis and ion Exchange

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28
Q

Two ways sludge and scale reduce heat transfer

A

Scale insulates boiler surfaces, impeding heat transfer

Scale reduces the flow of boiler water

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29
Q

Sludge and scale build-up can lead to

A

Boiler overheating

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30
Q

3 ways foaming can occur in a boiler

A

Dissolved solids or by the presence of oils or suspended solids

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31
Q

Dissolved solids are most commonly removed externally using

A

Some sort of ion exchange such as lime softeners cation exchangers using zeolites, and anion exchangers and demineralizers

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32
Q

Dissolved gases

A

Gases that are in solution

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33
Q

Examples of dissolved gases

A

Nitrogen, ammonia, oxygen, and carbon dioxide

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34
Q

As the temperature increases, the solubility of gases in water tends to

A

Decrease, which results in the release of dissolved gases

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35
Q

2 dissolved gases of primary concern to power engineers

A

Oxygen and carbon dioxide, because of their ability to produce boiler corrosion

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36
Q

Dissolved oxygen in boiler water

A

Produces a form of ferrous metal corrosion due to improperly treated feed water.

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37
Q

While dissolved in boiler water, oxygen causes

A

A form of corrosion called pitting, which is localized and hard to spot

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38
Q

Oxygen removal is accomplished by a combination of

A

External and internal methods

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39
Q

Carbon dioxide, when dissolved in water forms

A

Carbonic acid

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40
Q

When condensate forms, the carbon dioxide dissolves, forming

A

Carbonic acid

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41
Q

Carbonic acid causes

A

Grooving on metal surfaces of condensate return lines

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42
Q

As more dissolved carbon dioxide is present,

A

The pH drops

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43
Q

Carbonic acid formation in condensate lines can be inhibited by adding

A

Neutralizing agents internally to the boiler or directly to the steam lines

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44
Q

The lower the pH value,

A

The more acidic the water is

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45
Q

A high pH value indicates

A

A basic or alkaline solution

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46
Q

Hard and softened water contains

A

Carbonate and bicarbonate salts of calcium, magnesium and sodium

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47
Q

A safe range of pH is

A

Between 8.5 and 12.7. Outside this range, corrosion can be significant

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48
Q

Magnetite

A

Prevents further oxidation of the boiler heat transfer surface. Therefore considered highly beneficial

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49
Q

Caustic embrittlement

A

May result from high pH levels. Very difficult to detect, due to its fine cracking. Caustic embrittlement commonly results in boiler metal failure

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50
Q

High pH boiler water may cause

A

Foaming in the boiler drum

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51
Q

Most boilers operate with a pH of about

A

9.5 to 10.5, balances corrosion and foaming

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52
Q

Sodium hydroxide, also known as caustic soda is commonly added to

A

Raise pH

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53
Q

To lower pH

A

The boiler is blown off or it’s continuous blowdown rate is increased

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54
Q

Three main steps Municipal potable water systems use to purify their water

A

Remove solids, remove pathogens, disinfect

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55
Q

When the temperature is low, water holds

A

Slightly more oxygen

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56
Q

Turbidity

A

Is a measure of water cloudiness

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57
Q

Municipal Water Treatment process

A

Clarification, filtration, disinfection

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58
Q

When boilers use Municipal Water as feedstock, it requires further processing. This will;

A

Reduce hardness, remove oxygen and other dissolved gases, adjust the pH

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59
Q

External treatment for dissolved oxygen will only lower the level to the range of

A

10 ppb

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60
Q

The first stage of water treatment is usually

A

The removal of suspended solids

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61
Q

Settling ponds

A

Slow or delay the velocity of water, this allows suspended solids to settle, by gravity, to the bottom

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62
Q

Clarifier vs settling pond

A

Clarifiers can finish in an hour or two, while settling ponds may take days. With clarifiers, the accumulations of solids are drained from the bottom

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63
Q

How a clarifier works

A

Water is introduced in the centre of the clarifier, and flows to the bottom middle section. As the water flows, the particles settle out, and are removed by a rake that moves the sludge to a central blow off point

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64
Q

Backwashing

A

Involves reversing the flow of water through the filter, thus freeing trapped solids. Backwash flow rate must be correct, otherwise it will be not be effective

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65
Q

Once the initial removal of suspended solids is done, the water usually

A

Passes through a filter to remove the last of the suspended particles

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66
Q

Four common types of filters

A

Pressure filters, filter Aid tubular filters, cartridge filters, activated carbon filters

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67
Q

Overtime, filters become plugged with suspended particles

A

And must be backwashed

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68
Q

Filter Aid tubular filter

A

Closed cylindrical housing that contains several screen type cylindrical tubes. Can be quite large and similar in concept to an air cleaning baghouse

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69
Q

Cartridge filters

A

Similar to an oil filter in an automotive engine. Outer shell can be either steel or plastic. Inner cylinder made of woven fibres

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70
Q

Activated carbon filter

A

Often used to remove taste or odours from water. Also used to remove chlorine, especially from Municipal Source water. Not very effective against dissolved solids

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71
Q

Chlorine must be removed to protect;

A

Reverse osmosis membranes and ion exchange material

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72
Q

Water is considered hard when it contains over;

A

Over 120 PPM (120mg/L) of calcium or magnesium ions

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73
Q

Scale could possibly lead to;

A

Deposit corrosion, and even cause metal failure

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74
Q

Calcium and magnesium ions are unaffected by;

A

Clarifiers or filters

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75
Q

Four methods to soften water

A

Lime soda systems, sodium zeolites, demineralizers, reverse osmosis

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76
Q

Lime soda softeners

A

Lime reacts with impurities that cause carbonate hardness. Soda ash reacts with impurities that cause non carbonate hardness. After these reactions, they become suspended solids, and are no longer dissolved solids. Now they can be removed using clarification, flocculation, or filtration.

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77
Q

Two categories of lime soda softeners

A

Hot ( 95-100°C )

Cold ( 25-30°C )

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78
Q

Lime soda hot process versus cold process

A

Hot process is more common because it is quicker, and the solids are easier to filter out. The hot process can remove silica, whereas the cold process cannot

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79
Q

Sodium zeolite system

A

Rely on the principles of ion exchange to soften water. They cost less than lime soda softeners, are easier to control, and the chemicals are safer for operators. Magnesium and calcium ions are replaced with ones that do not cause scale and are highly soluble. Can bring the hardness down to zero, while the sodium increases dramatically

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80
Q

When a sodium zeolite softener is removed from service the following procedure is followed;
4

A
  1. Backwashing
  2. Brining (regeneration)
  3. Slow rinse (displacement)
  4. Fast rinse
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81
Q

Sodium zeolite softener backwashing stage

A

Consists of flowing water backwards through the bed. This expands the volume of the bed by about 50%, and loosens dirt.

82
Q

Sodium zeolite softener brining stage

A

Salt brine is added to the vessel, while the resulting calcium and magnesium chloride salts are discharged to waste.

83
Q

Sodium zeolite softener slow rinse stage

A

Water flows downwards, and forces the remaining brine into areas it may not have penetrated earlier

84
Q

Sodium zeolite softener fast rinse stage

A

Water flow is almost doubled, and completely removes the brine from the zeolite bed. Used or spent brine is often flushed to the Sewer

85
Q

Demineralizer

A

Rely on ION Exchange. 2 exchange units are installed in series, cation exchanger and anion exchanger. Can remove most ions except for silica. Instead of using a brine solution, the Cation exchanger uses a diluted solution of sulphuric acid through the bed. The anion exchanger uses a dilute solution of caustic soda through the bed.

86
Q

Reverse osmosis

A

Uses a membrane technology, and not strictly a filtering process. Can remove up to 99% of dissolved solids, organic matter, and colloidal matter. Commonly used to desalinate seawater. Creates pure water, while concentrating the impurities.

87
Q

Daeration

A

The Daerator applies a pressure to the water, and heats it just below the saturation temperature. This frees the dissolved gases from the water, which are then vented from the daerator.

88
Q

Four important operating parameters to consider for efficient daerator operation

A

Temperature
Turbulence
Time
Surface area

89
Q

2 basic daerator configurations

A

Tray type: In what water is directed into a steam chamber, as the water heats up, it then Cascades down several trays. This increases the surface area of the water, which promotes greater water to steam contact.

Spray type: Inlet water is directed into a similar steam chamber, however, it is broken up into small particles with spray nozzles to promote water to steam contact.

90
Q

External vent condenser

A

When the vent condenser is mounted Outside The Daerator vessel.

91
Q

Sodium hydroxide solution is often used to

A

Raise the pH level within the boiler. The solution is fed either directly to the boiler drum, or to the feed water before it enters the drum

92
Q

Caustic embrittlement, also known as caustic;

A

Occurs when metal under stress is attacked by a concentrated caustic solution. Creates a corrosion pattern that runs around the circumference of the tube.

93
Q

How to prevent caustic embrittlement

A

Limit the boiler water sodium hydroxide concentration to the minimum required to achieve proper pH and alkalinity

94
Q

Caustic gouging

A

Another form of caustic embrittlement, also a result of concentrations of sodium hydroxide

95
Q

How to prevent caustic gouging

A

Maintain clean boiler metal surfaces, and monitor for the presence of excess sodium hydroxide.

96
Q

Foaming

A

The result of high concentrations of dissolved and suspended solids in boiler water. Foaming makes it difficult to determine water level, and also allows liquid water to lift over in the steam line, also known as carry over.

97
Q

Foaming is effectively controlled by

A

The use of continuous surface below down.

98
Q

Oxygen corrosion

A

Dissolved oxygen causes pitting in the boiler and condensate lines. It is highly localized, and can be difficult to spot.

99
Q

Preventing oxygen corrosion

A

By using oxygen scavengers, which combine with oxygen so that is it is no longer available to react with boiler metal.

100
Q

Two chemicals used as oxygen scavengers

A

Sodium sulfite and hydrazine. One disadvantage of sulfite is that it increases dissolved solids, which can lead to foaming.

101
Q

Hydrazine can cause

A

Cancer, so it must be handled very carefully according to its SDS.

102
Q

The most common used chemical to prevent corrosion caused by oxygen and carbon dioxide;

A

Amines

103
Q

Two main types of amines

A

Neutralizing and filming

104
Q

Neutralizing amines

A

They are volatile, the flash off and travel with the steam to the rest of the system. They are alkaline, they will neutralize any acids formed in the condensate.

105
Q

Filming amines

A

Not as soluble, and they’re usually injected into the steam header. When steam condenses, these chemicals will create a thin coat over the piping surfaces, protecting the surfaces from acidity and corrosion.

106
Q

Molybdate

A

Corrosion inhibitor which acts to protect the boiler against General corrosion and oxygen pitting. Common in hot water and low pressure steam boilers, and in closed-loop cooling systems.

107
Q

Concentration of molybdate is generally maintained at;

A

75 to 125 ppm, controlled by blowdowns

108
Q

Chemicals added so soft scale will form, rather than hard scale

A

Sodium phosphate

109
Q

Chelants

A

Commonly used in boiler water treatment programs to trap metallic ions, and make scales more soluble. The Trap and hold ions. However, they are more expensive and complicated to use. Chelants must be used carefully because they can cause large clumps of scale to be released.

110
Q

Common chelant used;

A

EDTA

111
Q

Organic compounds used to prevent sludge deposits

A

Starch, tannin, lignin, alginates. These coat the scale precipitates and prevent them from adhering to boiler internals

112
Q

The method used to supply the necessary chemicals to the boiler water is usually a

A

Small positive displacement motor driven metering pump

113
Q

Valve’s needed for the chemical feed line to the boiler

A

A shut off valve next to the boiler, a check valve between the chemical feed pump discharge isolation valve and the shut-off valve at the boiler

114
Q

Chemical feed pumps are;

A

High pressure, low capacity types with adjustable flow rates.

115
Q

Chemical feeders

A

Supply chemicals to the return line of a hot water circulating system, or directly into a boiler.

116
Q

Bypass chemical feeder

A

Feeds chemicals, supplied in liquid, briquette, or ball form into the feed water or circulating line

117
Q

The most important part of any treatment program

A

Make the dosing adjustments necessary for maintaining correct boiler water chemistry.

118
Q

Safety gear when testing boiler water

A

Heat resistant gloves, eye protection and protective coveralls

119
Q

Never take a sample from

A

A sight glass

120
Q

Sample cooler

A

Reduces the temperature of the sample to a standard temperature usually 24° Celsius. It then flows to a sample header.

121
Q

Testing area

A

An open area, so fumes do not accumulate. Should be equipped with a fume Hood, preferably. There should also be a supply of hot and cold water. Distilled water must also be available for final rinsing of any equipment.

122
Q

Titration

A

Allows precise determination of a reaction endpoint, and thus the amount of reactant in the sample. The main piece of equipment used is called a burette

123
Q

To conduct a hardness water test

A

Take a water sample, and then titrate to determine total hardness

124
Q

Low phosphate in boiler water May indicate

A

Hard water is entering the boiler

125
Q

Electronic pH meter

A

Automatically measures the temperature of the sample, and adjusts the reading accordingly. Probes need to be recalibrated from time to time, using calibration Solutions.

126
Q

Ph tests are commonly performed on

A

Condensate and boiler water

127
Q

Excessively High condensate pH indicates

A

An overfeeding of neutralizing amines

128
Q

Excessively low condensate pH indicates

A

An underfeed of neutralizing amines

129
Q

Excessively High boiler water PH

A

Increases the potential for caustic embrittlement , cracking and Gouging. Reduce the feed of caustic soda, and if necessary increase the rate of continuous blowdown

130
Q

Excessively low boiler water pH

A

Increases the likelihood of acidic corrosion. Increase the feed of sodium hydroxide to the boiler. If the total alkalinity is low, reduce continuous blowdown

131
Q

For boiler water, it is more important to know the _______ than to determine the pH

A

Hydroxyl alkalinity

132
Q

Total dissolved solids (TDS)

A

Measures all the salts in solution

133
Q

The dissolved solids can be determined using a;

A

Conductivity meter. The concentration of dissolved solids can be determined by multiplying the liquid water conductivity by a constant Factor. As the concentration of dissolved solids increase, so does the conductivity

134
Q

Manual conductivity measurement

A

Pour the water into the sample cup at the top of the metre, or submerge the top part of the metre directly into the water.

135
Q

Excessively High total dissolved solids

A

Results in forming, priming and carry over. Increase the rate of continuous blowdown.

136
Q

Excessively low total dissolved solids

A

Indicates excessive blow down or blow off. Reduce the amount of blow down and blow off

137
Q

Molybdate salts are often used as

A

Corrosion Inhibitors in closed-loop heating and cooling water systems.

138
Q

Alkalinity is a measure of a solution’s ability

A

To resist changes in PH

139
Q

Alkalinity test

A

Performed on both Source water and boiler water. Source water is tested to determine the efficacy of the feed water treatment program. Boiler water test allows the operator to make the necessary adjustments and total alkalinity are in the prescribed range

140
Q

Three types of alkalinity

A

Carbonate, bicarbonate, and hydroxyl

141
Q

Two types of alkalinity tests

A

Phenolphthalein alkalinity; tests for hydroxides and carbonates

Methyl alkalinity (total alkalinity); tests for hydroxide, carbonate and bicarbonate

142
Q

Excessively High total alkalinity

A

May result in foaming or carry over. Increase the rate of continuous blowdown and blowoff

143
Q

Excessively low total alkalinity

A

Indicates excessive continuous blowdown or bottom blow off. Decrease the rate of continuous blowdown and blow off

144
Q

Sodium sulfite

A

Eliminates the presence of dissolved oxygen. Usually added to the feed water system to protect the decorator, the feed water lines and pump, and the boiler

145
Q

Excessively high sodium sulfite

A

May cause sludge and scale formation. Reduce the rate of sulfite addition to the feed water

146
Q

Excessively low sodium sulfite

A

Will result in dissolved oxygen, pitting and corrosion. Increase the amount of sulfite fed to the feed water

147
Q

Phosphate residual range

A

20 to 60 ppm

148
Q

Excessively High phosphate

A

Will cause foaming and carry over. Reduce amount of phosphate fed to boiler or increase continuous blowdown and bottom blow off

149
Q

Excessively low phosphate

A

Will result in scale formation. Phosphate feed rate should be increased

150
Q

A small amount of carbon dioxide in contact with condensate can produce

A

Corrosive Solutions

151
Q

Oxygen enters the boiler make up water or condensate through

A

Contact with air

152
Q

When both carbon dioxide and oxygen corrosion occur in a system

A

The total combined corrosion rate is significantly higher

153
Q

4 main ways of Preventing condensate line corrosion

A

Mechanical inspection/maintenance

Installation of dealkalization equipment

Neutralizing amines

Filming amines

154
Q

Dealkalization Equipment

A

Used to treat the raw make up water, by reducing water alkalinity to zero. This will reduce the cost and complexity of condensate corrosion control.

155
Q

Condensate polishers

A

Mixed bed ion exchangers, designed to purify condensate. They are used when condensate may become contaminated, they filter out particulate and suspended matter, and perform ion exchange to remove hardness and chlorides

156
Q

Condensate polishers require

A

Regular back washing and regeneration

157
Q

Condensate polishing is essential for

A

High pressure boilers, where feed water Purity is critical

158
Q

For most purposes, most readings below ______ should be considered acceptable

A

0.5 ppm

159
Q

Direct amine measurements can be made using a;

A

Chromatograph

160
Q

Fluorometer

A

Device which measures and monitors the condensate amine concentration

161
Q

Corrosion coupons

A

An inexpensive and simple way to evaluate corrosion rates. Only useful at estimating average corrosion rates, they do not provide instantaneous readings of system corrosiveness

162
Q

Corrosion coupons are removed after

A

1 to 3 months

163
Q

Sources of impurities in cooling water

3

A

Avian waste
Contact with the atmosphere
Raw makeup water

164
Q

Water evaporates in cooling towers and leaves behind;

A

Dissolved solids

165
Q

Since the operating temperatures are much lower in cooling towers, _______

A

Scaling is not as severe as boilers

166
Q

Most cooling towers are open to atmosphere, so they are more susceptible to;

A

Airborne dust and debris, which can enter the water and eventually plug up the system

167
Q

Biological fouling of recirculating cooling towers

A

Caused by algae, fungi, avian waste, and bacterial growth.

168
Q

Biofilm or slime

A

Organic growths which can; reduce flow rates, release organic acids and waste products that can corrode metals, attack and Destroy wooden portions of a tower

169
Q

Legionella bacteria

A

Bacteria that causes a serious lung infection, or a less serious flu-like infection. There is no vaccine for it, so prevention is the only option

170
Q

Wood is composed of;

3

A

Cellulose, lignin, and natural extractives

171
Q

Biological attack on cooling tower would occurs when

A

The cellulose deteriorates

172
Q

The large white cloud seen above a power plant is often

A

Water vapour from cooling towers

173
Q

Cooling tower Crystal modifiers

A

Promote the formation of soft sludge. When these are used, the cooling water should appear turbid, which indicates that they are taking effect

174
Q

Cooling tower cycling control

A

Refers to the maintenance of the appropriate ratio of dissolved solids in the circulating water, to the dissolved solids in the makeup feed water

175
Q

Cooling towers that operate at higher cycles of concentration

A

Require less blowdown

176
Q

Two methods used for cycle control in cooling towers

A

Makeup proportional blowdown

Conductivity based blowdown

177
Q

Sacrificial anodes

A

Used for corrosion control in cooling water systems. Directs corrosion to sites where it can be tolerated or accepted

178
Q

Chemical inhibitors and three categories

A

The use of chemicals to form protective layers.

Cathodic, anodic, general

179
Q

Chromates

A

While effective at corrosion control, they cause unacceptable environmental damage when released through blow down or system drainage. Therefore, it is no longer used in systems from which water can escape

180
Q

Plugging or erosion of equipment

A

Screens and filters prevent the influx of solid matter and protect against plugging and erosion

181
Q

Deposition occurs when the flow is

A

Too slow

182
Q

Erosion occurs when the flow is

A

Too great

183
Q

Two methods to protect against biological fouling

A

Mechanical methods, such as trash bars and strainers. Chemical methods that kill the microorganisms

184
Q

Operators should be aware that biocides are

A

Poisonous

185
Q

Differential microbial analysis (DMA)

A

Test to detect various microorganisms, conducted in an off-site Laboratory

186
Q

Dip slides

A

Useful for determining Trends in bacterial activity. However, they do not provide precise measurements

187
Q

Chillers

A

Heat exchangers that cool fluids. The process fluid is continuously circulated in a closed loop. The chiller may use refrigerant or some other cold process fluid to chill the water

188
Q

Corrosion with Chillers

A

Corrosion rate is not as great, since they operate at much lower temperatures.

189
Q

Galvanic corrosion

A

Occurs when dissimilar metals, are in physical contact with each other, and exposed to a fluid. This transfers electrons and metal ions between the two metals. The metal that gives off ions will waste away and fail.

190
Q

Corrosion is likely to occur where ever

A

Deposits form

191
Q

2 closed system corrosion inhibitors

A

Sodium nitrate, and Molybdate

192
Q

Selective leaching, also called Dezincification

A

A form of corrosion in cooling systems. When this happens, one particular metal is preferentially attacked. It is usually zinc

193
Q

Freeze stats

A

Used in Chillers, so that if refrigerant temperature gets too low, the chiller trips off

194
Q

Sacrificial anodes can also be used to

A

Prevent galvanic corrosion

195
Q

Borescopes

A

Inspect the inside of tubes and shells during shutdowns for signs of corrosion or deposition

196
Q

Glycol

A

A colorless and odorless substance used mostly for manufacturing Plastics and antifreeze.

197
Q

Two main types of glycol

A

Ethylene and propylene

198
Q

Glycol reacts with oxygen to form

A

Organic acids that will increase corrosion, therefore they are equipped with Factory Blended corrosion inhibitors

199
Q

Glycol concentrations should never be less than

A

20%

200
Q

Glycol should not be used directly in a

A

Boiler or heater system

PE 4B (8 decks)

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