Transcript Conductivity Theory

Conductivity Theory
Applied to Proper Hardware
Selection
Feb 2001
File Name: Conductivity.ppt
Conductivity Measurement
 Used to Measure and Control the Percent
Concentration of Acids, Bases and Salts in
Solution
 Measures Total Concentration
 Not Ion Specific
• May be Used to Determine the Dominant
Chemical
Feb 2001
File Name: Conductivity.ppt
Electrolytes
 Acids
• Substances which ionize in solution and produce hydrogen
ions, H+
• Hydrochloric Acid (HCl) dissociates into H+ + Cl-
 Bases
• Substances which ionize in solution and produce hydroxide
ions, OH• Sodium Hydroxide, NaOH, dissociates into Na+ + OH-
 Salts
• Substances which ionize in solution and produce neither
hydrogen or hydroxide ions
• Sodium Chloride, NaCl, dissociates into Na+ + ClFeb 2001
File Name: Conductivity.ppt
Typical Conductivity Values
10% NaOH
355,000
Sea Water
50,000
Mains Water Supply
50
Boiler Feed Water
1
Distilled Water
0.5
Ultra Pure Water
0.055
0
Feb 2001
1
100
File Name: Conductivity.ppt
10,000
1,000,000
Conductivity Measurement
 Units of Measurement
• U.S. Units = Micromhos/cm
• International Units = MicroSiemens/cm
• 1.0 S/cm = 1,000 mS/cm = 1,000,000 uS/cm
• umho/cm = uS/cm
 Conductivity is the Reciprocal of Resistance
• 1.0 MicroSiemen/cm = 1,000,000 Ohms/-cm
• 1,000,000 MicroSiemens/cm = 1.0 Ohm/-cm
Feb 2001
File Name: Conductivity.ppt
Conductivity Measurement
 High Purity Water Applications
• Power & Semiconductor Manufacturing
• Conductivity Measured as Resistivity in
MegOhms/cm
• Pure Water = 18.18 Meg Ohms/-cm = 0.055 uS/cm
 Water & Water Treatment Applications
• Industrial Boilers & Cooling Towers
• Conductivity Measured in Total Dissolved Solids
(TDS)
Feb 2001
File Name: Conductivity.ppt
Conductance of Common Acids, Bases and
Salts @ 25oC
MilliSiemens/cm
900
800
700
600
500
400
300
200
100
0
0
5
10 15 20 25 30
35 40 45 50 55 60 65
70 75 80 85 90 95 100
% by Weight
Feb 2001
Sodium Chloride
Potassium Chloride
Sodium Hydroxide
Hydrochloric
Sulfuric Acid
Nitric Acid
File Name: Conductivity.ppt
Conductivity Measurement
 Each Acid, Base and Salt has Its Own
Temperature Vs. Concentration Curve
 The Temperature Slope Varies for Different
Chemicals
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•
Feb 2001
Acids 1.0% - 1.6% /oC
Natural Waters 2.0%/oC
Bases > 1.8 - 2.2%/oC
High Purity Water 2.3% - 7.3%/ oC
File Name: Conductivity.ppt
Specific Conductivity of Sulfuric Acid
mS/cm
1500
1000
500
0
5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95
% Concentration
25C
Feb 2001
60C
File Name: Conductivity.ppt
5.0% Sulfuric Acid Solution
400.0
350.0
mS/cm
300.0
250.0
200.0
150.0
100.0
50.0
0.0
0
4
10
16
21
27
32
38
43
49
54
Degrees C
Feb 2001
File Name: Conductivity.ppt
60
66
71
77
82
88
93
93
Temperature Slope
Change in Temperature Slope/oC
8
7
6
5
4
3
2
1
0
0
10
20
25
30
40
50
75
Temperature
Ultra Pure Water
Feb 2001
Sodium Chloride
File Name: Conductivity.ppt
100
Conductivity Measurement
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Na+
Cl-
Apply an AC Voltage to Two Electrodes of
Exact Dimensions
Acids, Bases and Salts (NaCl) Dissolve
in Solution and Act as Current Carriers
The Current Flow is Directly Proportional
to the Total Dissolved Solids in Solution
The Physical Dimensions of a
Conductivity Electrode are Referred to as
the Cell Constant
Cell Constant is Length/Area Relationship

Cell Constant
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Feb 2001
Distance Between Plates = 1.0 cm
Area of Each Plate = 1.0 cm x 1.0 cm
Cell Constant = 1.0 cm-1
Used to Determine the Measuring Range
of the Analyzer
Acts as Multiplier
Used to Calibrate Analyzer
Determined Using NBS Standards
Can be NIST Traceable
File Name: Conductivity.ppt
Four Electrode Conductivity Cells
V
Feb 2001
 Measures Current and
Voltage Drop
 Current Increases with
an Increase in Voltage
Drop Across Electrodes
 Compensates for Minor
Coatings on
Conductivity Electrodes
 Used for Higher Range
Measurement
File Name: Conductivity.ppt
Inductive Conductivity


Also Known as Toroidal and
Electrodless
Principle of Measurement
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Advantage
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No Electrodes Exposed to the
Measured Solution
Not Affected by Coating
Disadvantage
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Feb 2001
Two Sealed Wire Wound Coils
Electrically Coupled by Solution
Conductivity
+- 10% Accuracy
High Range Measurement Only
> 100 uS/cm
File Name: Conductivity.ppt
Reverse Osmosis Unit
pH Transmitter
Feed Water
Acid Feed
Conductivity Transmitter
Feed
Water
Tank
RO Unit
Waste
Feb 2001
File Name: Conductivity.ppt
Demineralizer Unit
Caustic Regeneration
Acid Regeneration
Conductivity
Transmitter
Conductivity
Transmitter
Conductivity
Transmitter
Cation
Bed
Anion
Bed
Mixed
Bed
To Water Storage
Conductivity
Transmitter
Feb 2001
Conductivity
Transmitter
File Name: Conductivity.ppt
Power Utilities
Average Number of Analyzers for Each Demin Unit
Type
Conductivity
Concentration
pH
Total
Number
4
2
1
7
 Usually 2 per generation unit (make up & polisher) and
built in pairs
 Total X 4 = 28 Analyzers per Unit
 Two Units Built at a time = 56 Analyzers
Feb 2001
File Name: Conductivity.ppt
Power Utilities
Average Number of Analyzers Per Generating Unit
Analyzer Type
pH
Specific Conductivity
Cation Conductivity
Condensate Analyzer
Total
Number
5
6
11
1
23
Usually Units Built in Pairs = 46 Analyzers
Feb 2001
File Name: Conductivity.ppt
Boiler Blowdown and
Condensate Return Lines
Conductivity
Transmitter
Feed
Water
Tank
Condensate Return
Waste
Heat
Exchanger
Steam Header
Steam
Drum
Conductivity
Transmitter
Top Blowdown Line
Blowdown Valve
Mud
Drum
Flash
Tank
Manual Blowdown Valve
Do Not Automate !
Feb 2001
File Name: Conductivity.ppt
Clean in Place (CIP)
Conductivity
Transmitter
CIP Return Lines
Caustic
Conductivity
Transmitter
Water
Feb 2001
Caustic
Dilution
Tank
Solution
Recovery
File Name: Conductivity.ppt
Process
Vessels