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STEAM AND WATER ANALYSIS SYSTEM (SWAS)
SUBMITTED BYPRIYANK MODI
DEPTT. C&I BLA POWER PVT
LTD.
STEAM AND WATER ANALYSIS SYSTEM (SWAS)
SUBMITTED BYPRIYANK MODI
DEPTT. C&I BLA POWER PVT
LTD.
ContentsWhy Required SWASSampling Conditioning/ Wet PanelSchematic Diagram of Sample Inlet Important Equipments of Sample SystemSample Analysis
pH AnalyzerConductivity AnalyzerSilica AnalyzerDO AnalyzerPhosphate Analyzer
DO’S & DON’TSCONCLUSION
What is the need for boiler water treatment?
Inhibit corrosion
Prevent freezing of the water in the system
Increase the boiling point of the water in the system
Inhibit the growth of mould and bacteria
Allow improved leak detection
What Happen if You don’t have SWAS
50% of forced power plant shutdowns can be attributed to impurities and other cycle chemistry problems.
A well designed SWAS package directly attacks these problems.
People with good knowledge, experience and expertise prefer on-line monitoring of all the necessary parameters involved in plant cycle chemistry.
You will always find a properly maintained SWAS in all power plants that are running at 95+ PLF / PAF
Why Required In any power plant running on steam, the purity of boiler
feed water and steam is absolutely crucial; especially to steam turbine, steam boiler, super heater, condenser and other steam equipment. To prevent damage of steam turbine, steam boiler and other apparatus due to scaling and corrosion, on line steam and water analysis of critical parameters such as pH, Conductivity, Dissolved Oxygen, Silica, Sodium, Phosphate etc. is a must. The steam can be as hot as 560ºC.The pressures can be as high as 250 bar. To keep the power plant up and running, with minimum erosion and corrosion of steam turbine, steam boiler and condenser.
To protect these equipments SWAS works in to stages:-1. Sample Conditioning2. Sample Analysis
1. Sampling Conditioning or Wet Panel
The Sample is First cooled in Sample Coolers, depressurized in pressure regulators and then fed to various analyzers while keeping the flow characteristics constant by means of a Back Pressure Regulating Device. There are a lots of safety equipment provided in wet panels, so that the operators feel safe while working with these systems.
The Sample is First cooled in Sample Coolers, depressurized in pressure regulators and then fed to various analyzers while keeping the flow characteristics constant by means of a Back Pressure Regulating Device. There are a lots of safety equipment provided in wet panels, so that the operators feel safe while working with these systems.
Schematic Diagram of Sample Inlet
SAME OF THE IMPORTANT COMPONENTS OF SAMPLING SYSTEMS (WET RACK)
1. SAMPLE COOLER Sample Coolers are COIL-IN-SHELL type CONTRA-FLOW
heat exchangers.
Coil Materials are available such as Stainless Steel AISI 316,Monel 400 & Inconel 625 and so on.
2. High Pressure Regulator
Piston Type High Pressure Regulators. These are used in primary conditioning where sample pressures are higher than 100 Kg/cm2.
As these are piston type Pressure Regulators , there is no fear of diaphragm rupture etc.
3. Back Pressure Regulator Back Pressure Regulator (BRP) to avoid low flow (or
fluctuating flow) conditions to analyzers in the event grab sample valve operation. In the absence of such a device ,the sample would flow to grab sample line when the grab sample valve is opened. This can create low flow alarm conditions in sample going to analyzers.
A pressure Regulator and Back Pressure Regulator combination provides very stable pressure & flow conditions, thereby ensuring reliable, efficient and accurate analysis.
4. Sight glass
Sample flow Indicator (sight Glass) to view the sample flow inside the sample line.
A rotating wheel indicates presence of cooling water. The sight glass is made of high grade stainless steel.
5. Sample Filter
The Filter which is required to ensure particle -free sample. Any particle of size up to 40 microns size can be filtered
out.
Forged stainless steel body and hexagonal cap help easy cleaning of filter element.
6. Pressure Relief Valve
Pressure relief Valve comes fitted with Sample Cooler.
Pressure Relief Valve is important as it protects the Sample Cooler in case the coil fails.
This is also important for human safety as pressurized cooler may burst due to full sample pressure under coil failure conditions.
7. Hi-Temp Isolation Valve
This valve is an easy to operate & can be used for most high pressure and temperature applications.
Its unique plug/seat geometry and stuffing box design allow these valves to operate for extended period of time without gland leakage and passing.
8. Cation Column The Duplex type Cation Conductivity Column is a field
proven design.
The Cation Conductivity measurements are considered to be more reliable than ordinary conductivity measurements
This ensures Elimination Of Masking Effect of desired chemicals used in treating the water.
This provides a more realistic picture of dissolved impurities in sample
ANALYSERS INSTALLED FOR :
Area Analyzers
Feed waterDO2 (ppb), pH, Conductivity (Mho),
SiO2, Cation Conductivity (Mho),
Blow Down Conductivity (Mho), pH, SiO2 (ppb),
PO4 (ppm)
Saturated steamConductivity (Mho), pH, Cation
Conductivity (Mho), Silica
Superheated SteamCation Conductivity (Mho), pH,
Conductivity (Mho), SiO2 (ppb)
Condensate WaterpH, Conductivity (Mho), SiO2 (ppb),
Cation Conductivity (Mho)
DeaeratorDO2, Conductivity (Mho), pH, Cation
Conductivity (Mho), Dissolved Solid
General Specification of Analyzers
SNO. Descriptions Model No. Range AccuracySample Flow
rate
1 pH Transmitters SMART Pro 8966 P 0 - 14 pH +/- 0.01 pH 10~15 LPH
2 Conductivity Transmitter SMART Pro 8967 P 0-100 μS/cm +/- 0.01% 10~15 LPH
3Dissolved Oxygen
AnalyzerPolymetron 9100 0-150 ppb O2 +/- 0.5 ppb 10~15 LPH
4 Silica Analyser Polymetron 9210 0-2000 ppb +/- 2 ppb 1~5 LPH
5 Phosphate Analyzer Polymetron 9211 0-10 ppm 0.2 ppm 3 - 5 LPH
6 Total Dissolved Solids SMART Pro 8969 P 0-10 ppm 0.2 ppm 3 - 5 LPH
pH Analyzer
pH is a measure of the acidity and alkalinity properties of a water solution, which are determined by the concentration of hydrogen ions (H+) present in the solution.
pH is defined as pH=-log10 ［ H+ ］
Why pH Measurement Required
The steam which goes to the turbine has to be ultra pure. The pH value of the feed water gives direct indication of alkalinity or acidity of the water.
The ultra pure water has pH value of 7.
In a steam circuit, to keep the pH value of feed water at slight alkaline levels.
It helps in preventing the corrosion of pipe work and other equipment.
pH Analyzers are recommended at following location in a steam circuit : high pressure heaters, DM Makeup, CEP discharge
Specifications
Supply
Type 2 wire
Supply voltage 12-36VDC
Load Resistance 600Ω @24VDC
Accuracy
Display pH 0.01pH
Display mV 1mV
Display Temperature 0.5% FSD
Output Current 0.1mA
Outputs
Current 4-20mA HART©
Display 2 Line 10 Character per line LCD
Inputs
Primary Sensors pH
Secondary sensors PT100/PT1000
Data Input 3 Button Keypad
THE MEASUREMENT OF pH (Glass electrode method ) pH measurement is based on
i) pH sensitive electrode (usually glass), ii) a reference electrode, iii) a temperature element
pH sensitive glass develops a potential (voltage) proportional to the pH of the solution.
The reference electrode is designed to maintain a constant potential at any given temperature.
The difference in the potentials of the pH and reference electrodes provides a mill volt signal proportional to pH.
Most pH sensors are designed to produce a 0 mV signal at 7.0 pH, with a (theoretically ideal) slope (sensitivity) of -59.16 mV / pH at 25°C.
REFERENCE ELECTRODES
The reference electrode consists of a silver wire(Ag) coated with silver chloride (AgCl ) in a fill solution of potassium chloride(KCL) .
The purpose of the potassium chloride (KCL) is to maintain a reproducible concentration of silver ions(Ag+ ) in the fill solution
“Dual point calibration”
1. The flow chart for “Dual point calibration” is shown considering two buffer solutions of pH 4 and pH 9.
2. Dip the sensor in the buffer solution with pH 4.
3. Press Enter when message “ready” appears on screen.
4. Dip the sensor in the buffer solution with pH 9.
5. Press enter when message “ready” appears on screen.
6. %slope, Zero Offset are shown. Enter the date.
7. These parameters can be seen in future in menu
“Single point calibration”
1. The flow chart also shows “Single point calibration” method, also called as standardization.
2. In this method the pH value of the solution is measured with the standard pH instrument
3. The sensor is dipped in this solution, and earlier measured pH value is fed during calibration
How to clean the electrode
The pH electrode is an electro-chemical sensor. When the pH electrode is used, the junction and glass membrane contaminates because of process fluid. This in turn increases the sensor response time.
Salt deposits
Immerse the electrode in tap water for 10 to 15 minutes. The salt dissolves in water. Rinse the electrode with distilled water.
Oil/Grease film
Use mild detergent and water to gently wash the electrode bulb.Rinse the electrode tip with distilled water.
Protein deposits
Dip the electrode in a solution prepared as 1% pepsin solution in 0.1M of HCL for 10 min. Rinse the electrode with distilled water.
Clogged reference junction
Heat diluted KCL solution to 60 to 80 deg C. Place the sensing part of the electrode into the heated solution for about 10 min. Allow the electrode to cool in unheated KCL solution.
6.6 Do’s and Don’ts for pH (Glass) electrodes
1. Remove the special transportation seal, Before putting the electrode in process line,
2. Clean the pH electrode under low pressure tap water or any suggested cleaning solution. 3. Do not touch the diaphragm or tip of the electrode during cleaning.
4. Gently tap dry the tip of the electrode using a clean and soft tissue paper.
5. Do not rub the tissue paper on the electrode as it may generate static charges.
6. Calibrate the transmitter with pH electrode as a system. If you change/replace transmitter and/or electrode it is necessary to recalibrate as a system.
7. Keep the electrode wet when not in use.
8. Dip the electrode in 3M KCL solution (or any storage solution as recommended by manufacturer).
Error During Sensor Calibration
Error Message
Action
Zero errorThis shows that sensor “zero point” isshifted by more than 1pH units from the idealvalue.
Use the procedures to clean and rehydrate thebulb. Check again. If the same message repeatsthen replace the sensor.
Remedy
Slope errorThis shows that sensor “slope” is outof the normal acceptable slope range 70% to110%.
Use the procedures to clean and rehydrate thebulb. Check again. If the same message repeatsthen replace the sensor
Remedy
How to rehydrate the bulb?
1.Immerse the electrode in pH 4 buffer solution
for 10 to 30 minutes.
2. Rinse the electrode with distilled water.
3. Check the response of the electrode.
CONDUCTIVITY ANALYZER
Conductivity is the ability of a solution, a metal or a gas - in brief all materials - to pass an electric current. In solutions the current is carried by cation and anions whereas in metals it is carried by electrons.
How well a solution conducts electricity depends on a number of factors
• Concentration• Mobility of ions• Valence of ions• Temperature
ConductivityElectricity is the flow of electrons. This indicates that ions in solution will conduct electricity. Conductivity is the ability of a solution to pass current. The conductivity reading of a sample will change with temperature.
κ = G • Kκ = conductivity (S/cm)G = conductance (S), where G =
1/RK = cell constant (cm-1)
ConductanceConductance (G) is defined as the reciprocal of the electrical resistance (R) of a solution between two electrodes.
G = 1/R (S)The conductivity meter in fact measures the conductance, and displays the reading converted into conductivity.
Cell constantThis is the ratio of the distance (d) between the electrodes to the area(a) of the electrodes.K = d/aK = cell constant (cm-1)a = effective area of the electrodes (cm2)d = distance between the electrodes (cm)
(SmartPro 8967P)
2-wire, working voltage of 24VDC ( 17.5-36 VDC)Transmitter draws current of 4-20mA from supplyADC digitizes the analog voltage, suppresses the noiseMicrocontroller processes the data, displays the results
on LCD display and generates retransmission current output with HART© protocol
Microcontroller accepts the inputs from keyboard during programming and calibration
Sensor Wiring
The Cable of the conductivity sensor consist of a screw cap at one end.
The Four wires on other side are to be terminated at the transmitters
CONDUCTIVITY SENSOR
2- pole conductivity sensors are ideal for pure & ultra pure water applications.
FM 8310/8311/8312 SPECIFICATION
SENSORS FM 8310 / FM 8311 / FM 8312
TYPE 2 Pole cell
CELL CONSTANT K=0.1
CONDUCTIVITY RANGE Up to 20 uS/cm
ELECTRODE CONNECTION ¾ “ NPT(M) or 1.5" TC
TEMPERATURE RATING T max = 80ºC
PRESSURE RATING 6 bar
ELECTRODE MATERIAL SS 316
TEMPERATURE SENSOR Built in Pt 100
CABLEIntegrated 7.5m, 6-wire doubled shielded, open ended
Conductivity Solution
Conductivity is typically measured in aqueous solutions of electrolytes.
Electrolytes are substances containing ions, i.e. solutions of ionic salts or of compounds that ionize in solution.
The ions formed in solution are responsible for carrying the electric current.
Electrolytes include acids, bases and salts and can be either strong or weak.
How to clean the electrode
Make sure that conductivity sensor is clean, dry and no deposition is observed.
Clean the sensor in case of deposition, clean the electrode with Iso Propyl Alcohol (IPA) before using.
If required keep the electrode in IPA overnight
It recommended to clean the electrode before each calibration.
Conductivity values at 25°C
Pure water 0.055 μS/cm Deionised water 1 μS/cm Rainwater 50 μS/cm Drinking water 500 μS/cm Industrial wastewater 5 mS/cm Seawater 50 mS/cm 1 mol/l NaCl 85 mS/cm 1 mol/l HCl 332 mS/cm
Why Conductivity Measured
Conductivity is an important parameter for detecting any contamination of steam in the boiler circuit.
Conductivity of pure water is almost zero (1-2 μ Siemens)
Ingress of any kind of dissolved impurity will raise conductivity instantly.
Thus conductivity is an important parameter for the detection of leakages.
Parameters to be Maintained
1) Boiler drum water i) before Cation conductivity between 10 to 30
μS/cm
ii)after Cation conductivity between 5 to15 μS/cm
2) Extraction pump discharge i) after Cation conductivity between 0.1 to0.3
μS/cm with an alarm value of 0.5 μS/cm
3) Economizer inlet after Cation conductivity between 0.1 to0.3 μS/cm
4) Hotwell conductivity between 2 to 4 μS/cm
5) Make-up treated water outlet conductivity between 0.02 to0.1 μS/cm with alarm level at 0.2 μS/cm and trip at 0.4 μS/cm
Indications of the Problem
If the conductivity at the make-up treated water outlet goes
a) >0.1 μS/cm stream in service is exhausting needs to be taken out of service with the
other mixed-bed stream brought into service
In the case of the hot well, if the conductivity reading is i) < 2 μS/cm LP dosing failureii) > 4 μS/cm over-dosing of LP dosing or
condenser tube leakage
At the economizer inlet if the conductivity increases Cation column exhausting .
Conductivity decreasing before the cation column
Probable reasons Boiler water tube leakage Boiler blowdown is in progress Boiler drain valves or blow down valves passing Instrument reading wrongly due to fault or loss of sample
flow
The corrective action
Confirm tube leak and dose caustic soda through HP dosing system and maintain conductivity
Check drain valves and blowdown valves for any leak and attend
Check for free flow of sample or rectify instrument if needed
Conductivity increasing before the Cation column
Probable reasons
Condenser tube leakage Boiler HP dosing is in progress Instrument reading wrongly due to fault or loss of sample
flow
The corrective action
Confirm condenser tube leak and take action to maintain conductivity till shutting down unit
Check for free flow of sample or rectify instrument if needed
Conductivity decreasing after the Cation column
Probable reasons
Boiler water tube leakage Boiler blowdown is in progress Boiler drain valves or blowdown valves passing
The corrective action
Confirm tube leak, check conductivity before cation column and dose caustic soda through HP dosing system and maintain conductivity
Check drain valves and blow down valves for any leak and attend
Conductivity increasing after the Cation column
Probable reasons Condenser tube leakage Cation column getting exhausted / exhausted Contamination of make-up water from the water treatment
plant Instrument reading wrongly due to fault or loss of sample flow
The corrective action Confirm condenser tube leak and take action to maintain
conductivity till shutting down unit Inform chemist regarding increase in conductivity after
checking other possible causes Ensure mixed bed and final treated water outlet conductivity Check for free flow of sample or rectify instrument if needed
Total Dissolved Solids
Total Dissolved Solids (TDS) are the total amount of mobile charged ions, including minerals, salts or metals dissolved in a given volume of water.Unit :- mg per unit volume of water (mg/L) or PPM
In general, the total dissolved solids concentration is the sum of the cation (positively charged) and anions (negatively charged) ions in the water
Parts per Million (ppm) is the weight-to-weight ratio of any ion to water
Where Do Dissolved Solids Come From?
Dissolved solids come from
1)Organic sources :- leaves, silt, plankton, and industrial waste and sewage
2)Inorganic sources :- Rocks and Air that may contain calcium bicarbonate, nitrogen, iron phosphorous, sulfur, and other minerals
3)Note:- The efficacy of water purifications systems in removing total dissolved solids will be reduced over time,It is highly recommended to monitor the quality of a filter or membrane and replace them when required.
Deciding on the required boiler water TDS
The actual dissolved solids concentration at which foaming may start will vary from boiler to boiler.
Conventional shell boilers are normally operated with the TDS in the range of 2 000 ppm for very small boilers, and up to 3 500 ppm for larger boilers.
Calculating the blowdown rateThe following information is required:
1) Boiler water TDS (PPM)2) Feed water TDS (PPM)3) The quantity of steam which the boiler generates, usually measured in kg / h
Boiler water TDS measurement :-conductivity (µS / cm) x 0.7 = TDS in parts per million (at 25°C).
F=Feed water TDS (ppm)S=Steam generation rate (kg / h)B=Required boiler water TDS (ppm)
Closed loop electronic control systems
These systems measure the boiler water conductivity, compare it with a set point, and open a blowdown control valve if the TDS level is too high.
The actual selection will be dependent upon such factors as boiler type, boiler pressure, and the quantity of water to be blown down
The measured value is compared to a set point programmed into the controller by the user
The labour-saving advantages of automation.Closer control of boiler TDS levels.Potential savings from a blowdown heat recovery system
(where installed).
Manual Blowdown Closed loop electronic TDS control
TDST ANALYZER
2-wire, working voltage of 24VDC ( 17.5-36 VDC)Transmitter draws current of 4-20mA from supplyADC digitizes the analog voltage, suppresses the noiseMicrocontroller processes the data, displays the results on
LCD display and generates retransmission current output with HART© protocol
Microcontroller accepts the inputs from keyboard during programming and calibration
Power Supply & Sensor Wiring
Sensor Configuaration
Cable Terminations
Calibration & CommissioningPower On the TransmitterCalibrate the Temperature sensor with standard Thermometer
in Water at Ambient Temperature.Calibrate the sensor with the help of Standard Conductivity
Solution.Dip The sensor in known conductivity solutionSolution temperature is Shown 25 Deg CEnter The Cell ConstantEnter the conductivity of the SolutionDisplays Actual Measured Value of SolutionCheck & Set Transmitter Range as required by the ProcessMount the sensor carefully in Process PipeSet the Flow through the chamber or tank as per requirement.
store electrode after use
Silica Analyzer
The Presence of silica in the steam and water circuits of a power generation plant is associated with a number of problems both in the Super Heater and Turbine sections.
The solubility of silica in steam increases with pressure. Hence there are chances of silica carryover. The Presence of Silica in the steam can lead to deposition in Superheated tubes and on Turbine Blades which may lead to loss of efficiency and Turbine blade Failure.
Silica in the steam cycle can result in deposition of a “glass” layer on surfaces, resulting in a loss of thermal process efficiency.
Deposition of silica on the turbine blades can result in the turbine becoming imbalanced, reducing efficiency and, in extreme cases, causing extensive damage to the turbine.
Analyzer Panels Front & Rear View
Operation Diagram
Working principal1. The 9210 can analyze up to six different samples.
2. Adjustment of the flow is carried out with the help of a needle valve (2)
3. At the beginning of the analysis, the sample is introduced into the measuring cell (4) with the use of a solenoid valve (5).
4. The reagents R1M and R1A are first added using two of the reagent pumps (9).
5. The silica contained in the sample then reacts with the molybdate and forms the silicomolybdic complex.
6. The reaction will take up to 5 minutes. Oxalic acid is then added using a reagent pump (9) to avoid phosphate interference and to intensify the color.
7. The silicomolybdic complex is reduced to a blue molybdenum complex by means of ferrous ions
8. A photometric measurement is carried out at the end of the reaction.
SpecificationsSample
Number of channels 1 - 6
Measurement cycle < 10 min / channel
Sample pressure 0.2 to 6 bar (3 to 87 psi)
Temperature 5 - 50°C (41 - 122°F)
Sample flow Minimum 5L / hour Maximum 30L / hour
Analysis
Value measured Dissolved SiO2
Cycle time Approximately 10 minutes per channel
Measurement range 0 - 1000 ppb
Repeatability ± 2% or ± 0.5 ppb
Detection limit 0.5 ppb
Maintenance
Calibration Chemical zero, slope with calibration solution
Reagent consumption Approximately 1L per month and per reagent
Calibration solution consumption
Approximately 200 ml / calibration
Reagent preparation
Reagent 1M - Molybdate (2 liters)
Label Composition Concentration
R1M Sodium dihydrate molybdate Na2MoO4.2H2O >99
55 g/L
Reagent 2 - Oxalic acid (2 liters)
Label Composition Concentration
R2 Oxalic Acid 40 g/L
Reagent 1A - Nitric acid (2 liters)
Label Composition Concentration
R1A Nitric Acid, HNO3 (65% ) 150 mL/L, 15% V/V
Reagent 3 - Reducing reagent (2 liters)
Label Composition Concentration
R3 1. Ammonium-iron(II) sulfate hexa hydrate (NH4)2Fe(SO4)2, 6H2O 2. Sulfuric acid (H2SO4) (95-97%)
20 g/L
12.5 mL/L
Calibration solution :-
+ DILUTE 100 TIMES
2 liters of calibration solution When
DM Silica =0
CONCENTRATED SOLUTION (Use of Titrisol® (Merck) cartridge )
DM water (1 Lit)
2139 mg/lit of SiO2
10 mL per liter to give a concentration of 21.39 mg/liter SiO2
Connecting the canisters
Each reagent tubing is labeled individually and delivered already connected to the analyzer. They are fed through, and attached to, caps that attach to the reagent canisters
Connect each cap to its canister: • Tube R1M to reagent canister labelled R1M: Sodium molybdate • Tube R1A on reagent canister labelled R1A: Nitric acid • Tube R2 on reagent canister labelled R2: Oxalic acid • Tube R3 on reagent canister labelled R3: Sulfuric acid and ferrous ammonium sulfate
Calibration
Calibrations allow the adjustment of: • ZERO of the system
• SLOPE of the system • Both ZERO and SLOPE of the system
1.ZERO calibration is performed chemically by the analyzer. In order to avoid the use of water free of SiO2, the analyzer carries out a measurement without a colorimetric reaction .
2.Slope of the system is then calibrated with a standard solution of known concentration of SiO2.
Maintenance menu overview
Monitoring Silica for Demineralization
Demineralization is an effective means of removing dissolved solids such as silica through the use of anion or mixed bed ion exchangers. Silica has a very low ionic strength and it is one of the first ions to break through when the bed is reaching exhaustion
For proper working of Turbines, Continuous Monitoring of Silica is highly recommended.
In Steam circuit where Silica Analysis is required are :-
1. Low Level Silica Measurement :- HP & LP Turbines, Drum (Saturated) Steam, CEP Discharge, DM Make up Water
2. High Level Silica Measurement:- Drum Water
Dissolved oxygen The DO determination measures the amount of dissolved (or
free) oxygen present in water or wastewater At elevated temperature dissolved oxygen causes corrosion which
may cause puncture and failure of piping and components respectively.
Dissolved oxygen also promotes electrolytic action between dissimilar metals causing corrosion and leakage at joints and gaskets.
Mechanical Dearation and chemicals scavengers additives are used top remove the DO.
DO monitoring is imperative in power stations using neutral or combined operating conditions (pH 7.0-7.5 or 8.0-8.5)
In steam Circuit where DO monitoring is required are Deaerator Inlet and Outlet (Feed water, Condenser & Deaerator Outlet) .
Working principle
The measurement of dissolved oxygen is based on the well known Clark cell principle.
An oxygen-permeable membrane isolates the electrodes from the sample water, thus obviating the need for sample conditioning
A gold working electrode (cathode) reduces the dissolved oxygen to hydroxyl ions:
O2 + 2H2O + 4e- ® 4OHA
A large silver counter electrode (anode) provides the oxidation reaction which occurs on its surface:
4Ag+ + 4Br - ® 4AgBr + 4e-
The reduction of oxygen is the current limiting reaction, thus making the cell current linearly proportional to the dissolved oxygen concentration
Electrochemical reactions and diffusion rates are temperature-sensitive
Main characteristicsRange 0-2 ppmCalibration in the airTemperature compensationProgrammable alarm levels, outputs on relays4-20 mA, 0-20 mA analogue outputs (standard) and
RS485 (option)Wall- , panel- and tubing mounting
Technical characteristicsSAMPLE
Number of channels 1
Temperature 0-45 °C (32-113 °F)
Working pressure Atmospheric pressure
Flow rate 4...10 l/h
MATERIALS
Working electrode Cathode: gold
Counter-electrode Anode: silver
Membrane holder Noryl
Membrane PFA
Probe with optional immersion Stainless steel 316L
OPERATING CONDITIONS
Ambient temperature -20...+60 °C
Relative humidity 10...90 %
Power supply voltage fluctuation ± 10 %
Description of the analyzer
Hydraulic mounting
Detailed cable connections
The standard length of the cable is 10 m
Zero Calibration
Make sure the water used for the chemical zero is really oxygen-free (< 1 ppb).
Press ENTER, the "CAL" message flashes and indicates the instrument is in calibrating mode.
Wait for the current stabilization (approximately 10 min.) and press OK to validate the calibration.
The oxygen concentration value flashes during 3 seconds. The instrument displays zero.
SLOPE Calibration
Humidify the wadding of the calibration cap and take off the probe from the sample
Position the cap on the electrode and press ENTER. The probe should be positioned vertically with the membrane downwards The flashing "cal" message indicates that the instrument is in calibration
mode. Wait for the current stabilization (approximately 10 min.) and press
OK to validate the calibration. The oxygen concentration value flashes during 3 seconds.
Dismounting the membrane1. A. Unscrew cap and gasket.2. B. Unscrew nut.3. C. Remove electrode without scratching the cathode.4. D. Empty the electrolyte left in the probe.5. E. Unscrew the worn membrane.
Mounting the new membrane
1. F. Screw the new membrane on the body till the dead stop.2. G. Replenish the probe body with 5 ml of electrolyte. Check there
is no impurity or bubble in the electrolyte.3. H. Preposition the electrode without forcing. It should take its
place by simple gravity.4. I. Screw the probe nut till the electrode meets a resistance.5. J. Put back the cap and gasket, screw the cap to ensure water
tightness.
Oxygen electrode rejuvenation procedure
A dark Ag Br coating may cover part of the silver anode.This coating does not affect the measurement until more than 90% of
the surface is contaminatedWhen changing the electrolyte and membrane, visually check the silver
anode If more than 2/3 of the surface is covered then an electrode
rejuvenation according the following procedure is needed :-
1. Soak the anode in 10 % ammonia for about 1 hour then rinse it with demineralised water and wipe it with a soft cloth.
2. If the ammonia cleaning is not sufficient, rejuvenation of the silver electrode has to be done by repolishing softly (coating is a only few microns thick) the areas covered with silver bromide with soft abrasive (N° 400 to 600)
3. After polishing, rinse the anode with demineralised water and wipe it with a soft cloth.
4. The cleaned electrode performs immediately as well as a new electrode.
Functional troubleshootingCauses Solutions
1. An electrolyte leak (through the membrane). The current is too high because of an excessive penetration of oxygen
Change the membrane
2. An important pollution of the electrolyte due to an incorrect adjustment of the filling Screw
Change the electrolyte. Check there is a gasket and the screwing. Check the Teflon band is correctly positioned
3. The membrane holder is incorrectly screwed. Risk of electrolyte pollution
Change the electrolyte and tighten correctly the membrane holder
4. Mud or particles on the golden cathode
Clean the cathode with an absorbent soft tissue and rinse the membrane
5. The probe current is null There is no electrolyte in the probe (leak).
6. The probe current is negative •Connation problem to the anode circuit (loose contact).• Ag Br deposit on the anode
PHOSPHATE analyzerThis treatment is used to precipitate the hardness
constituents of water and provide alkaline pH control, which will reduce boiler corrosion.
Maintains the sodium-to- phosphate molar ratio – (2.1 to 2.9)
This ratio must be maintained to prevent formation of phosphoric acid (ratio below 2.1) or free sodium hydroxide (ratio above 2.9)
The use of phosphate analyzer is to provide a safe alkaline environment in the boiler.
Phosphate water boiler treatment serves 2 basic purposes:
I) Phosphate controls the ph in the range that is least corrosive to carbon steel
II) The event of a condenser leakage or other process upset, phosphate or the alkalinity produced by it, reacts with Ca, Mg, Si and other minerals to produce soft sludge that can be blown down
Working principal
Working OperationWorking Operation
The 9211 can analyze up to six different samples
Adjustment of the flow is carried out with the help of a needle valve (2).
At the beginning of the analysis, the sample is introduced into the measurement cell (4) with the help of a solenoid valve (5).
The 9211 can analyze up to six different samples
Adjustment of the flow is carried out with the help of a needle valve (2).
At the beginning of the analysis, the sample is introduced into the measurement cell (4) with the help of a solenoid valve (5).
Two different methods are available
1) For standard measurement range 0-50ppm PO4 ( "Molybdate-Vanadate yellow“ )
When the sodium molybdate and the ammonium meta-vanadate are added using the pump (10)
They react with the orthophosphate to form a yellow-coloured phospho-vanado-molybdate compound in an acid medium.
+ Reactions with orthophosphate
This method, known as the "Molybdate-Vanadate yellow“ method, provides measurements across a wide range of values (0.5 to 50 ppm), with equivalent accuracy to that of the "Molybdate blue“ method.
(sodium molybdate)(pump 10)
(ammonium meta-vanadate)
a yellow-coloured phospho-vanado-molybdate
Limited to a range of 0 and 5 ppm PO4: "Blue method"
Sodium molybdate, added with the pump (10), reacts with the orthophosphate to form a yellow-coloured phosphomolybdate compound.
Previously, for total acidity reasons, the reducing reagent is added using the pump (9). Thus, any phosphomolybdate compound formed is immediately reduced to molybdenum blue.
The formation of this molybdenum blue compound is highly dependent upon the pH of the solution and upon the type and amount of reducing agent.
It is therefore critical to carefully follow the reagent preparation instructions. The "blue method" will be selected specially when local susceptibility restrict the use of vanadate from the "yellow method".
Please note that "blue method" restrict measurement range (0-5 mg/L PO4 only) and temperature ranges of samples and room (0 - 35°C).
+ +
(sodium molybdate) (pump 10)
Orthophosphate
Phosphomolybdate compund (yellow)
Reducing Agent (pump 9)
Molybdenum (Blue)
Technical specifications
SAMPLE
Number of channels 1 – 6
Measurement cycle < 10 min / channel
Sample pressure 0.2 to 6 bar (3 to 87 psi)
Temperature «Yellow» method: 5 - 50 °C (41 - 122°F)«Blue» method: 5 - 35 °C (41 - 95 °F)
Sample flow 15 to 20 L / hour during sampling, ie, 3 to 5 L/hr, on average, per sample.
MAINTENANCE
Calibration Chemical zero, slope with calibration solution
Maintenance No particular maintenance is necessary. Cleaning can be done with a soft non-aggressive cloth.
MAINS POWER SUPPLY
Mains • 100- 240 VAC 50 - 60 Hz.• Automatic switching.• Max. consumption: 80 VA.
Presentation of the analyzer
Direct sample connections
Reagent preparationVanadate method - 0 to 50 ppm
To make 2 litres of the reagent:• Sodium Molybdate dihydrate 180 g• Ammonium Metavanadate 9 g• H2SO4 500 mL
ANSA method - 0 to 5 ppmReagent 1 = Molybdate reagentTo make 2 litres of the Molybdate reagent:
• Sodium Molybdate dihydrate 90 g• Concentrated sulfuric acid 500 mL
Reagent 2 = Reducing agentTo make 2 litres of ANSA reducing agent:• 1-Amino-2-naphtol-4-sulphonic acid 2 g• Sodium meta-bisulphite 140 g• Sodium sulphite 84 g
Analyzer programming
Menu
Calibration
Calibration
PROGRAMMINGEXECUTION PRIMARYEXECUTION MANUALPARAMETERSHISTORIC
EXECUTION MANUAL
EXECUTION ZEROEXECUTION SLOPEEXECUTION ZERO+SLOPE
PROGRAMMING
OFFSET INTERVAL : xxx hAUTOMAT SLOPE CAL. : YES / NOCAL. SOL : xxx,x ppbAUTOMAT CAL: NO
Parameters analyzing
Water Treatment Technologies for Thermal Power Plants have been examined and improved as a countermeasure against damage due to factors such as corrosion and scale deposition.
As shown in figure abnormalities in water quality can be a precursor of problems and therefore serious problems can be prevented by analyzing the data and taking necessary measures.
SWAS Do’s And Don’ts
Do’sAlways keep the coolants flowing, even if sample is stopped.Check the wiring for the possible loose connections.Always flush all the Sample / Coolant lines before starting operation.Ensure that sufficient differential pressure exists in coolant inlet and
outlet header (Typical Minimum 2.5 Kg/sq cm)Check for leaks in both sample and coolant lines.Check whether the connections to valves / pressure regulator / Flow
indicators etc are in right direction.Always switch Off the mains power supply while carrying out any
maintenance on the system
Don’tsDon’t disturb the settings of Pressure regulator, temperature switch,
pressure switch and safety valve without consulting service Engineer.Don’t stop the coolant supply, before isolating the sample supply.Don’t carry any maintenance function without isolating the sample
supply
