1. Measurements used for assessing feed water and boiler water quality and their effect on boiler efficiency and lifetime Dr. Dusan Kordik, Office of Standardization Metrology and Testing, Slovak Republic, Bratislava, Slovakia E-mail: dd.kordik@gmail.com

2. Concept of water treatment Steam generator and heating systems : Factors influencing heating system operation: Correct selection of construction materials in steam circuit Treatment of made-up water Optimized chemical treatment Design, quality of construction and operation process Feed water = condensate flux in the system +made-up water to compensate losses Refluxed condensate: Heat power plant – over 70 % Power stations with condensing steam turbine- over 97% Made-up water pretreatment Physical (sedimentation, filtration, steam degassing) Chemical (demineralization, alkalization, degassing

3. Objectives of chemical control of the water/steam circuit The objectives of chemical control are to minimize: corrosion damage and deposition on the internal surfaces of water/steam circuit as far as is economically prudent: The basic principles involved in minimizing corrosion and deposition are: a)minimization of the ingress of impurities into the water/steam circuit. b)Redox potential control to stabilize oxide films and to minimize transport of metal oxides (control of oxygen). c)pH control of the to counter corrosion effects, to stabilize oxide films and to minimize transport of metal oxides. Control of the corrosion and deposition processes areas: Feed-water and condensate system Boiler Turbine and steam circuits Ref: Chemical guidelines for water/steam cycle of fossil fired units, Union of the Electricity Industry - EURELECTRIC, 2000

4. EN 12952 - Water tube boilers and auxiliary installation ParameterUnit Feed water with concentration of salts Demineralised and Injection Water Pressure MPa0.05 – 2.00.05 – 4.04.0 - 10Full range H + conductivity μS cm -1 ---< 0.2 pH at 25 °C ★ > 9.2 Concentration of Ca + Mg mmol L -1 <0.02<0.01<0.005 Concentration of of Na + K mg L -1 ---< 0.010 Concentration of Fe mg L -1 < 0.05< 0.03< 0.02< 0.020 Concentration of Cu mg L -1 < 0.02< 0.01< 0.003 Concentration of SiO 2 mg L -1 ---< 0.020 Concentration of O 2 mg L -1 < 0.02 < 0.1 Conc. of oil and grease mg L -1 < 1.0< 0.5 Organic comp. TOC mg L -1 < 0.5< 0.2 ★ ) Note: for Cu alloys pH should be limited to 8.7 – 9.2 EN 12952-12: Requirements for boiler feed water and boiler water quality

5. ParameterUnit Pressure [MPa] 0.15 – 2.52.5 – 6.56.5 – 8.0 Conductivity (25 °C) μS/cm 7000 (6000 a )2700 (2000 a )500 Salinity mmol/L 60183 Alkalinity (evident) mmol/L 2 - 101 - 50.1 – 1.0 Soluble P 2 O 5 mg/L 10 - 305 - 122 - 10 SiO 2 mg/L 7040 (20 b ) Notes: a) For neutralized samples, b) for power plant steam generators CSN 07 7401: Water and steam for heating and power plants – pressure < 8 MPa

6. Methods to asses the feed water parameters ISO Water Quality standardsCodeMethod Range of application Measure 1 Determination of the sum of calcium and magnesium. EDTA titrimetric method. ISO 6059, ISO 7980 titration AAS extend of decarbonization 2 Determination of iron. Spectrometric method using 1,10 Phenantroline ISO 6332spectrometry(0.1 - 5.0) mg/Lresiduals after coagulation 3 Determination of alkalinity. Part 1: Determination of total and composite alkalinity EN ISO 9963-1titration(0.4 - 20) mmol/Llevel of alkalinity 4 Determination of Cobalt, Nickel, Copper, Zinc, Cadmium and Lead. Flame AAS method. ISO 8288AASdissolution of metals, corrosion 5 Determination of Phosphorus. Part 1: Ammonium molybdate spectrometric method. ISO 6878-1spectrometry residuals of hardness removal and passivation 6 Determination of Sodium and Potassium. Part 1: Determination of Sodium by AAS. ISO 9964-1AAS(5 -50) mg/Lalkalization 7 Determination of Sodium and Potassium. Part 2: Determination of Potassium by AAS. ISO 9964-2AASalkalization 8 Determination of pH. ISO 10523pH-metry2.0 - 12.0corrosion 9 Determination of dissolved oxygen. Electrochemical probe method. ISO 5814ISE(1-100)% of satur.corrosion 10 Determination of electrical conductivity ISO 7888condutometry Ionized inorganic and organic compounds (cations + anions) 11 Guidelines for the determination of total organic carbon (TOC) and dissolved organic carbon (DOC) ISO 8245

7. Quantities of water quality Electrolytic conductivity : Symbol κ Conductivity of 1m 3 (water) between two parallel electrodes of 1 m 2 area, distant 1m one from the other. SI unit = S m -1, in analysis of water mS m -1, μS cm -1 (1 μS cm -1 = 0.1 mS m -1 ) Measuring instrument: conductivity meter, calibrated with solution of KCL + electrolytic cell Parameter of quality: approximate measure of electrolyte in water, highly temperature dependent: 1°C ≈ pH pH = -log a (H 3 O + ) or activity a (H 3 O + ) = 10 -pH e.g. pH 9 activity (conc.) of H + = 10 -9 mol/kg SI unit: non-dimensional parameter Measuring instrument: pH-Meter – voltage between measuring electrode (e.g. glass) and reference electrode Parameter of quality: acidity rate of water influencing reactions between ions in water, stability or aggression of water (corrosion, incrusts deposits etc.) Calcium and magnesium content Symbol: ρ – mass concentration, c – molar concentration Total Ca and Mg concentration – form of carbonates ≈ hardness of water (historic name) SI unit: mg / L -1, mmol / L -1 Measuring instrument: burette for titration method, AAS – spectroscopic method Parameter of quality: stability of water – equilibria of H 2 CO 3, HCO 3 -, CO 3 2-, Ca 2+, H +, OH -, aggression, corrosion, incrusts and sediment deposits Iron Symbol: ρ – mass concentration, c – molar concentration Fe concentration : total concentration Fe II + Fe III in water, total concentration of soluble Fe II + Fe III in water, conc. of soluble Fe II in water Measuring instrument: VIS spectrometer + color of sample with chemical agent – measurement at 510 nm wavelength Parameter of quality: immunity, corrosion or passivation of material (e.g.Fe 3 O 4 )

8. Quantities of water quality Alkalinity Alkalinity– capability of water media to react wit H + ions- depends upon final pH value (ACN 4.5 ) - total alkalinity = c(OH - ) + c(HCO 3 - ) + 2(CO 3 2- ) – c(H + ) + c(A - ) (ACN 8.3 ) - composite alkalinity= c(OH - ) + c(H 2 CO 3 ) + (CO 3 2- ) – c(H + ) + c(A - ) (ACN 10.6 ) – caustic alkalinity= c(OH - ) - c(HCO 3 - ) - 2c(H 2 CO 3 ) – c(H + ) + + c(A - ) Symbol: ANC, BNC ρ – mass concentration, c – molar concentration SI unit: mg / L -1, mmol / L -1 Measuring instrument: burette for titration method Parameter of quality: pH value in alkaline region, passivation of the boiler, tubes and pipelines material Copper, Cobalt, Nickel, Zinc, Cadmium and Lead Cu, Co, Ni, Zn, Cd, Pb – concentration in 3 different ranges A: mg/L, B: μg/L, C: μg/L Measuring instrument: flame AAS spectrometry Co (240.7 nm), Ni (232.0 nm), Cu (324.7 nm), Zn (213.8 nm), Cd (228.8), Pb (283.3 nm, 217.0 nm) Parameter of quality: measure of copper and copper alloys corrosion or passivation - with phosphate = solids e.g. Cu 3 (PO 4 ) 2, Cu 2 (PO 4 ) OH, Cu 3 (PO 4 ) (OH) 3 – anticorrosive layers in Cu tubes – solubility depends upon pH value Dissolved oxygen Symbol: ρ – mass concentration, c – molar concentration Measuring instrument: potentiometer with O 2 electrode Parameter of quality: concentration of oxygen in combination with pH, protective magnetite layer formation, reduction of Fe content in water

9. Chemical systems for conditioning feed-water systems Chemical systems for conditioning feed-water fall into two groups: Reducing (ammonia or an amine with hydrazine) (AVT) - All Volatile Treatment, in which: protection steel is based on low solubility of iron oxides at elevated pH Oxidizing (oxygen with a low concentration of ammonia) (OT) treatment, in which: very low anion concentrations (low acid conductivity), protection of steel - based on low solubility of iron oxides at elevated oxidation-reduction potential. Limited concentration range vs. experience indicates: two protection mechanisms act simultaneously no distinguished border lines between these types of conditioning. continuum of suitable operation conditions in a broad range with high pH and low oxygen concentration at one end, and low pH and high oxygen concentration at the other. achievable purity of feed-water determines the degree of freedom available to operators within this range Ref: Chemical guidelines for water/steam cycle of fossil fired units, Union of the Electricity Industry - EURELECTRIC, 2000

10. Chemical systems for conditioning feed- water for boilers Two general classes of boilers in use: A) Once through boilers in which water is evaporated to a high steam content. not tolerant of nonvolatile dosing chemicals and operate without further dosing downward the feedwater chemical dosing. B)Drum boilers in which steam separation takes place in an unheated vessel. boiling occurs in tubes water from the drum is re-circulated, preventing dryout at the boiling surfaces. boilers may be tolerant of addition of low levels of non-volatile alkalis to prevent any risk of acidic corrosion. Note: During initial operation or post chemical cleaning, the boiler steel reacts with the water and steam forming a protective film of iron oxides. The rate of reaction decreases with time as the thickness of the protective oxide film increases. Ref: Chemical guidelines for water/steam cycle of fossil fired units, Union of the Electricity Industry - EURELECTRIC, 2000

11. Chemical systems for conditioning feed-water for turbine, superheater and reheater Steam purity - high - actual quality is determined by: concentration and solubility of salts in steam ( function of pressure, temperature and other chemicals) droplets of boiler water carried over from water contaminated feed-water injection into steam Acidic and alkaline contaminants - important : NaOH, hydrogen sulphates and chlorides at certain concentrations present a stress corrosion cracking risk to steels, particularly with austenitic structures. Salts deposited in steam pipework -on-load can result in the development of concentrated solutions - off-load following condensation of residual steam - significant for reheaters and feedheaters. Organic impurities decomposition products (organic and carbonate anions) - may damage turbine. Low volatility contaminants - turbine early condensation zone is particularly sensitive to surfaces and in the very first droplets of condensate to form an aggressive environment. Silica - the most soluble at high pressure steam of the common boiler water contaminants - supersaturated during expansion in the turbine – resulting in deposition on the blades causing loss of turbine efficiency.

12. Water/Steam Quality Monitoring ParameterConductivity H + conductivity pH O 2 concentr. Na concentr. Phosphate Redox potential 1Make-up water YES 2Condensate YES 3After treatment condensate YES 4Degassing input water YES 5Feed water YES 6Blow-down YES 7Steam YES Basic parameter monitoring in the operating water-steam cycle Ref.: Pavel Hübner, Water treatment in heat-power engineering, VSCHT Prague, 2010 (cz), ISBN 978-80-7080-746-0 Basic quantities of quality: H + conductivity - defines ion impurities concentration Na concentration – defines alkalinity and conductivity pH measurement – monitoring important for solid alkalization agents and for presence of Cu alloy materials RedOx potential – hydrazine alkalization agent monitoring

13. Guidelines for continuous operation and for plant start-up The guidelines recommend conditions for both continuous operation and for plant start-up. Target range - no action required; this range covers the practicable values which plant managers will normally achieve without excessive cost. Action level 1 (AL 1) - minor disturbance requiring investigation, diagnosis and optimization. Action level 2 (AL 2) - serious disturbance in chemical control requiring diagnosis and action to eliminate the cause. Action level 3 (AL 3) - very serious disturbance requiring substantial operator intervention, such as load reduction, or plant shut-down.

14. Definitions and characteristic of Action Levels Action level Characterization Risk Action during operation (specific actions on condensate) Target Normal stable operation, where everything is under control The maintenance of chemical control through the monitoring of key parameters should be continued. AL 1 Periodic or minor disturbances in chemical control. Long term damage and reduction in remaining life of power cycle components. Monitoring of the circuit chemistry should be extended to diagnostic components to identify the source of the problem. Strategic considerations should be made to avoid similar occurrences in the future. AL 2 Serious loss of chemical control. Serious damage to components due to deposition and corrosion. Significant reduction in the component life Immediate action should be taken to find and eliminate the cause within hours and/or actions should be taken to minimize the damage (e.g. decrease load). AL 3 Chemistry out of control. Component failure.The unit should be shut down within 1 hour using the normal shut down procedure if one of the key parameters deteriorate to action level 3. If one of the diagnostic parameters deteriorates to this action level, reduce load to prevent immediate damage and to gain time to restore chemical control. Ref: Chemical guidelines for water/steam cycle of fossil fired units, Union of the Electricity Industry - EURELECTRIC, 2000

15. Key parameters for control of water/steam cycle CircuitSampling pointConditioningKey parameter Drum BoilerBoiler Water-AVTConductivity after cation exchange Drum BoilerBoiler WaterNaOHConductivity after cation exchange Specific conductivity or pH Drum BoilerBoiler WaterPhosphateStrong mineral acids and pH Drum BoilerFeed-waterAVTpH Once through boilerFeed-waterAllConductivity after cation exchange AllSteamAllConductivity after cation exchange and sodium Ref: Chemical guidelines for water/steam cycle of fossil fired units, Union of the Electricity Industry - EURELECTRIC, 2000

16. pH and oxygen values in feed water Ref: Chemical guidelines for water/steam cycle of fossil fired units, Union of the Electricity Industry - EURELECTRIC, 2000 pH vs. oxygen concentration defined by the Union of the Electricity Industry – EURELECTRIC in the year 2000 for the feed water for Cu-free and Cu-alloys circuits

17. Action Levels limit parameters for acid conductivity Ref: Chemical guidelines for water/steam cycle of fossil fired units, Union of the Electricity Industry - EURELECTRIC, 2000

18. Action levels for pH – boiler water Ref: Chemical guidelines for water/steam cycle of fossil fired units, Union of the Electricity Industry - EURELECTRIC, 2000 pH vs. solid alkaline concentration defined for Action Levels by the Union of the Electricity Industry – EURELECTRIC in the year 2000 for the boiler feed water and solid alkalizer

19. Assessment of water/steam chemistry by quality indices Ref: Chemical guidelines for water/steam cycle of fossil fired units, Union of the Electricity Industry - EURELECTRIC, 2000

20. Assessment of water/steam chemistry by quality indices The exponential function is normalized for action level limits defining: at P = L 1p I = 1 at P = L 2p I = 10 at P = L 3p I = 100 at P = 3xL 3p I = 1000 Index I p - related to the selected Action levels is defined: for L 1 < P ≤ L 2 for L 2 < P ≤L 3 for P > L 3 I p = index for parameter p, P = monitored value for parameter P, L 1 = threshold for AL1, L 2 = threshold for AL2, L 3 = threshold for AL3 Ref: Chemical guidelines for water/steam cycle of fossil fired units, Union of the Electricity Industry - EURELECTRIC, 2000

21. Example of lifetime evaluation A. Ideal purity, B. Good practice, C. Unattended control operation mode (1. base load, 2. cycling load, 3. peak load) Operation mode = 1. base load, 2. cycling load, 3. peak load Ref: Chemical guidelines for water/steam cycle of fossil fired units, Union of the Electricity Industry - EURELECTRIC, 2000