Power plant analysisQuality control in power plants (process water,turbine oils, fuels, and operating materials)
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Metrohm – customized analysis for water, turbine oil,fuels, and operating materials in power plantsEnergy and power plantsEnergy supply has become a major issue of modern times. As a leading manufacturer of equipment for chemical 03The importance of energy even plays a role in Greek my analysis, we are well aware of the challenges. We offerthology. Zeus withheld fire from humanity, thus re mov ing state-of-the-art instruments and systems for analysis soall prospects of civilization. But the humans had Prome lu tions in your power plant, both in the laboratory andtheus on their side: he stole fire from the gods and gave in-process.it back to mankind. Unfortunately, Prometheus is nolon here to help us. Humankind has had to fend for ger You can rely on our expertiseitself by developing power plants to convert kinetic (wind, Metrohm offers not only the most modern equipment,water) and thermal energy (nuclear energy, che cal mi but also complete solutions for specific analytical requireener into electrical power. gy) ments. Your contact partners at Metrohm are specialists who will develop applications tailored to your needs andIncreasing energy consumption provide competent support for all analytical issues inThe rapid increase in the Earth’s population, which is power plants.grow by about 80 million every year, has also led to ingrising energy consumption. Calculations by the Inter a n tional Energy Agency (IEA) predict that the global energydemand will increase by about 65% by 2035. A majorfraction of the required energy will continue to be provided by fossil fuel-fired and nuclear power plants.Relevance of analysis in power plantsWith its high-performance laboratory and process analysis instruments, Metrohm contributes to a reliable andsustainable operation of power plants and helps to minimize costly downtimes. This includes analysis of the proc ess water circulating in the various cooling circuits, theoils and lubricants used in turbines, as well as fuels andoperating materials.
Power plant analysis04 I. Process water Water circuits in thermal power plants Thermal power plants use the heat generated by com EPPSA (European Power Plant Suppliers’ Assoia c tion), bustion or nuclear fission to produce steam, which is fed IAPWS (International Association for the Properties of into a turbine driving a generator that converts the me Water and Steam), and EPRI (Electric Power Research chanical energy into electrical energy. Downstream of Institute). Furthermore, there are also the safety stan the turbine, the steam is condensed to water in a con dards of the International Atomic Energy Agency (IAEA) denser. This water is fed into a feed tank from where it is that apply exclusively to nuclear power generation. pumped back into the steam boiler. Cooling water flows through the condenser in a separate circuit and removes The water chemistry depends on the type of power plant, the heat of condensation released by the steam via a the cooling circuit design, and the construction materi heat exchanger. Nuclear power plants with pressurized als. Every cooling circuit has a unique design and its own water reactors have an additional water circuit known as analytical requirements. If this brochure does not include the primary circuit. your power plant application, please contact your Metrohm representative. An optimized water chemistry is essential All thermal power plants use water as a central (operat Process and laboratory parameters ing) medium. As a liquid, it is used for cooling and as a With respect to instrumentation, there are two analytical gas, it drives the turbines. In nuclear power plants, it also objectives: determination of process parameters and la moderates the fission neutrons and thus controls nuclear boatory parameters. The former are key criteria that are r fission. A well-devised water chemistry ensures safe and usually measured online and are used to continuously efficient power plant operation. control the operating conditions. In contrast, laboratory parameters are determined offline and generally at de Guidelines of VGB, EPRI, EPPSA, IAPWS, and the fined intervals. They provide additional diagnostic infor IAEA safety standards mation and supplement the online measurements; how Nearly 50% of the unplanned downtimes in power plants ever, they are not used for primary control of the operat are caused by contaminants or problems with the chem ing conditions. istry of the water-steam circuit, with corrosion being the primary factor. Various guidelines define permissible ope The following two flow charts show key parameters of rating ranges, and they are used by power plant opera the water chemistry that are determined in power plants tors as a fundamental means of orientation. These in with two, respectively, three circuits. The numbers in clude guidelines from the VGB (Vereinigung der Gross brackets refer to the page(s) on which the application is kesselbesitzer e.V., Association of Large Boiler Ope ators), r described.
Water-steam circuitpH value (pp. 6–7) Amines (p. 17)Conductivity (p. 7) Iron (pp. 16, 20–21)Total hardness (pp. 10–11) Copper (pp. 16, 20–21, 22)Sodium (pp. 14, 17) Zinc (pp. 16, 20, 22)Silica (p. 14) Cobalt (pp. 16, 20)Phosphate (p. 14)Hydrazine (p. 15) Nickel (pp. 16, 20, 22) Corrosive anions (pp. 17–19, 23) 05 Cooling water circuit pH value (pp. 6–7) Conductivity (p. 7) Total hardness (pp. 10–11) Chloride (p. 11) Corrosion inhibitors (p. 12) Heavy metals (p. 12)Analytical parameters monitored in a power plant with two water circuitsPrimary circuit Water-steam circuitpH value (p. 6–7) (parameters mentioned above)Conductivity (p. 7)Boric acid (pp. 24–25)Lithium (p. 26)Nickel, zinc (p. 27)Calcium, magnesium (p. 27)Corrosive anions (p. 28) Cooling water circuit (parameters mentioned above)Analytical parameters monitored in a pressurized water reactor with three water circuitsII. Turbine and lubricating oils III. Fuels and operating materialsTurbine and lubricating oils are exposed to extreme con Pages 36 to 37 describe the use of combustion ion chroditions in power plants. Numerous international stan matography to determine the amounts of halogens anddards define the requirements and test procedures for sulfur in all combustible samples, both solid and liquid,in-service maintenance of the turbines. Pages 32 to 35 of such as coal, refuse, in consumer goods such as latexthis brochure describe two test procedures defined in gloves, or to investigate ion-exchange resins used to conASTM D 4378: potentiometric determination of the acid d ition process water.and base numbers and determination of the water content using Karl Fischer titration.
I. Process water in power plants06 pH value and conductivity All thermal power plants convert energy generated by combustion processes or nuclear fission into heat that is then used to vaporize water as an operating fluid. High- pressure superheated steam is fed to the blades of a high-pressure turbine causing it to rotate, thus producing electricity via a coupled generator. The steam is expand ed in the low-pressure zone of the turbine and then condensed to water in a cooled condenser. This conden sate is purified, preheated, and pumped as feed water to the evaporator. The primary cooling water flowing through kilometers of piping in the condenser dissipates the heat of condensation. High-purity steam is essential if the steam turbine is to operate efficiently and trouble free. pH value The corrosion properties of metals are primarily deter mined by the oxygen content and the pH value of the water. Higher pH values (i.e., less acidic) lower the driving force of the corrosion. The strongest corrosion occurs at pH values below 8; whereas passivation reactions usually dominate at higher values. The pH value is a key param eter to control the amount of lithium hydroxide that has to be added to the primary circuit of a pressurized water reactor; in water steam circuits, the pH value controls the amount of added amines. The pH value can be determined with the 867 pH Mo dule – equipped with software or touch control – or with the 780 pH Meter. The recommended sensor is the Aqua trode Plus, which guarantees the highest accuracy for pH measurements in process waters with a low ionic strength. Aquatrode Plus: the fixed ground-joint diaphragm is insensitive to contamination and guarantees a low-noise measuring signal in water matrices with a low ionic strength.
ConductivityThe conductivity indicates the amount of dissolved min pH value and conductivity – process parameters The pH value and the conductivity have to be determined 07erals. It is a measure of the water purity and is one of the quasi-continuously at numerous locations within the coolmost important parameters for any chemical control i ng circuit. This can be achieved with the Process Ana zer lyprogram in a power plant. It is determined at numerous ADI 2045TI from Metrohm Applikon. It combines thesesampling points in the power plant, for example, in the direct measurements with various analytical methodscooling water circuit, in feed and makeup water, at the and is designed for simultaneous analysis of multipleoutlet of the condensate pump, and in the primary circuit sample streams and parameters. Measurements are carof a pressurized water reactor. In high-purity process ried out on unpressurized sample streams in the high-water, it reflects the amount of added additives such as temperature water circuits that have been cooled toammonium or amines. A sudden increase in the conduc room temperature and in which the online sensors aretivity often indicates a leakage because carbon dioxide located.from the air has dissolved in the water.An important parameter is the cationic or acid conductivity, which is measured at the outlet of the cation ex changer and reveals the presence of corrosive acid residues.The conductivity of the acid anions is greatly increasedbecause the counterions – ammonium or sodium – havebeen repla by the hydronium ions, which have a cedsignificantly higher conductivity. Mea surement of theconductivity downstream of the cation exchanger is animportant parameter for detecting leakages. The conductivity of ultrapure water in water-steam circuits isgenerally about 0.15 µS/cm. If this value is ex ceededwithout previous addition of additives, this is of an tenindication that contaminants from the cooling water circuit have infiltrated.Determining the conductivity of ultrapure water is challenging. One solution is the 856 Conductivity Module,either software- or touch-controlled, in combination witha stainless steel conductivity measuring cell. The 856 Conductivity Module (center) with 900 Touch Control and 801 Stirrer
Corrosion08 Corrosion of metals in power plants is a commonly oc cur ring phenomenon due to the continuous contact of Electrochemical analysis methods are becoming increas ingly common for quantifying the corrosion rates. These the metal with a corroding environment. According to are far superior to traditional methods, such as determi the definition in DIN EN ISO 8044, corrosion is a physico- nation of the weight loss, because they provide more chemical interaction between a metal and its surround detailed information about corrosion phenomena with ings and which results in a measurable change in the less effort and time. The capabilities of the electrochemi material that can have a negative impact on the function cal methods are reflected in numerous international of the metal or even the entire system. These interactions standards. are usually of an electrochemical nature. The objective is to use suitable treatment and conditioning of the water to minimize the corrosion rate and the transport of cor rosion products within the circuits. Selection of important standards relating to corrosion measurement Standard Brief description ASTM G 102, Standard practice for calculation of corrosion rates and related information from electrochemical measurements DIN 50918 Corrosion of metals; electrochemical corrosion tests ASTM G 106, Standard practice for electrochemical impedance measurements DIN EN ISO 16773 ASTM G 5, Standard reference test method for making potentiostatic and potentiodynamic anodic polarization measurements DIN EN ISO 17475 Corrosion of metals and alloys – electrochemical test methods – Guidelines for conducting potentiostatic and potentiodynamic polarization measurements ASTM G 199 Standard guide for electrochemical noise measurements Standard practice for evaluation of hydrogen uptake, permeation, and transport ASTM G 148 in metals by electrochemical technique Standard test method for electrochemical critical pitting temperature testing of ASTM G 150 stainless steels DIN 50919 Corrosion of metal; investigations of galvanic corrosion in electrolytic solutions The most important electrochemical methods for corro test solution un defined conditions shows the first der sion testing are linear polarization (LP), electrochemical signs of corrosive attack in the form of deep pits. CPT is noise measurement (ECN), and electrochemical imped determined at a constant polarization potential and is ance spectroscopy (EIS). revealed by a sharp rise in the anodic current density. The more resistant the material is to pitting corrosion, the The critical pitting temperature in accordance higher is its CPT. The CPT can be determined with the with ASTM G 150 Autolab PGSTAT 302N or 128N with an optional pX1000 The critical pitting temperature (CPT) indicates the corro module. The temperature of the measuring cell is con sion resistance of a material at high temperatures. It is trolled by an external thermostat connected to a corro the temperature at which a me surface exposed to a tal sion cell.
Hydrogen permeation in accordance withASTM G 148 09Electrochemically generated hydrogen, absorbed by that are separated by a membrane made from the metalsome metallic surfaces, can permeate the material chang being investigated. Hydrogen is generated electrochemiing its mechanical properties. Determination of hydrogen cally at the cathode, whereas the hydrogen that has difpermeation in metals is thus an important pa meter in ra fused through the metal membrane is oxidized at acorrosion research. Electrochemically control hydrogen led constant potential at the anode. The oxidation current ispermeation is measured using a Devanathan-Stachurski directly proportional to the amount of hydrogen diffus(double) cell. It comprises two separate electrolytic cells ing through the metal membrane. 1.2E-5 Sample #2, transient #2 1E-5 Sample #2, transient #1 WE(1). Current (A) 8E-6 6E-6 4E-6 2E-6 0 -2E-6 0 10000 20000 30000 40000 50000 60000 70000 Time (s)Schematic diagram of the Devanathan-Stachurski cell for electro Hydrogen permeation measurements on two samples of carbonchemically controlled hydrogen permeation measurements steel with differing thicknessesMetrohm Autolab offers a complete range of electro mo dules (FRA32M for electrochemical impedance andchemical instruments for measuring corrosion: be it the ECN for electrochemical noise measurements) or furthercompact (PGSTAT101) or modular (PGSTAT302N, 128N, accessoies (electrochemical cells, corrosion cells, elec r100N, 302F) models, be it in combination with optional trodes). Autolab PGSTAT128N with FRA32M module www.metrohm-autolab.com
Cooling water10 Cooling water is used to condense the exhaust steam from the turbine to water, which is then sent back to the A control parameter for the feed water is the total hardness, which corresponds to the sum of the water-steam circuit as feed water. The heat of condensa alkaline earth metal cations. In practice, it ap tion from the steam is transferred to this cooling water as pro ximates to the sum of the calcium and it flows through the kilometers of piping – usually made magnesium hardness. This is determined by of titanium – in the condenser. The cooling water is cool complexometric titration with the titrant ed either by once-through cooling, in which the water is Na2EDTA and a Ca2+-selective electrode (as taken from a river and returned at a slightly higher tem per ISO 6095). perature, or in a circuit in a cooling tower. In a wet cool ing tower, this heat is dissipated into the atmosphere: as the warmed-up cooling water falls from a great height in the tower, the heat is transferred to the rising air stream. Con tinuous circulation of the cooling water in creases the concentration of contaminants. This necessitates water analyses to control corrosion and deposition processes tak place in the cooling water circuit. How ing ever, the purity requirements of cooling water are much lower com pared to those of the boiler feed water. Some of the parameters are discussed below. Determination of the water hardness using an ion-selective electrode (ISE) Alkaline earth salts dissolved in cooling water can deposit po in the kilometers of piping in the condenser. These de sits form an insulating layer that hinders heat transfer and lowers the condenser’s operating efficiency. The same app to an even greater degree to the steam generator lies in the water-steam circuit. Combined polymer membrane electrode for determining calcium and magnesium The MATi1 comprises the 815 Robotic USB Sample Processor XL, several 800 Dosinos, the 856 Conductivity Module, and the 905 Titrando. It is particularly suitable for fully automated analyses of process waters in power plants.
Colorimetric determination of the water hardness– process parameters 11In addition to determination with an ISE, described onpage 10, the water hardness can also be determined bycolorimetry. After adding the indicator hydroxynaphtholblue, a red complex forms at pH values above 7. AddingEDTA solution changes the color back to blue. The colorchange is proportional to the concentration of alkalineearth metal ions. Determinations in the sub-µg/L rangecan be conveniently carried out in only 10 minutes usingan Alert Analyzer from Metrohm Applikon. For highercal cium and magnesium concentrations, ADI Analyzerscan also be used.ChlorideBecause chloride ions promote metal corrosion, theirconcentration in cooling water should not exceed certainlimits. Chloride ions are determined by potentiometrictitration with the titrant AgNO3 after pH adjustment withnitric acid. A combined Ag-ring electrode, the Ag-Titrode,is used as the sensor. This electrode is maintenance-freebecause a pH glass membrane is used as reference electrode. In this way, it is no longer necessary to replenishelectrolyte. The Ag-Titrode for chloride determination
12 Corrosion inhibitors 2-mercaptobenzothiazole 15 Steel corrosion can be inhibited by adding zinc ions, 14 13 phos phates, or phosphonates. These form thin films on 12 tolyltriazole the metal that protect it against corrosion. Corrosion of 11 benzotriazole 10 copper and its alloys can be inhibited by adding triazoles Intensity [mAU] 9 8 such as tolyltriazole, benzotriazole, and 2-mercaptoben 7 zothiazole in the mg/L range. They form sparingly soluble 6 5 compounds on the surface of the metal. Because the 4 3 copper compounds of the triazoles are not resistant to 2 oxidation and also react with added microbiocides, the 1 0 triazoles have to be replenished, which necessitates regu 0 2 4 6 8 10 12 14 16 18 20 22 Time [min] lar determinations. This can be carried out by ion chro a m t ography with spectrophotometric detection. Sample of cooling water spiked with 1 mg/L of each corrosion in hibitor; column: Prontosil 120-3-C18-AQ 150/4.0; eluent: 0.5% phosphoric acid and 25% acetonitrile, 0.8 mL/min; column tem Heavy metals perature 40 °C; wavelength: 214 nm (only the 2-mercaptoben Heavy metals such as Cu, Fe, Zn, and Pb mainly enter the zothiazole is detected at 320 nm); sample volume: 20 µL cooling water via corrosion. In the branched piping sys tem inside the condenser, they lead to incrustations with These heavy metals can be determined with the 797 VA a very high resistance to thermal conduction that hamper Computrace. This all-round measuring stand allows exact heat transfer. They also act as catalysts for further con and sensitive determination of trace metals in cooling tamination. water. Sample preparation in the process water is not necessary.
Water-steam circuit – boiler feed waterBoiler feed water is the operating medium in the water-steam circuit of a thermal power plant and consists of ge rator lead to corrosion and deposits that severely re ne duce the efficiency of the power plant. This can be 13recycled condensate from the water-steam circuit and com bated with an optimized feed water chemistry. Onconditioned makeup water. As it flows through the pip the one hand, the water must be ultrapure and on theing of the steam generator, it is heated and converted other, the addition of conditioning agents (phosphates,into high-purity steam that drives the turbines, thus gen oxygen scavengers) must be continuously monitored. Theerating electricity via the coupled generators. After the re quire ments for the water circulating in the water-steamexhaust steam exits the turbine, it is condensed in a circuit are very stringent and are defined, for ex ample, indownstream condenser at the lowest possible tempera the standards EN 12952 (water-tube boilers and auxiliarytures and then recirculated back into the steam genera installations) and EN 12953 (shell boilers).tor as feed water. The very high temperatures in the steamEN 12953: Requirements for the feed water of steam boilers and hot-water boilers Parameter Feed water Makeup water Operating pressure [bar] > 0.5 to 20 > 20 entire range pH value at 25 °C > 9.2 > 9.2 > 7.0 Conductivity at 25 °C [µS/cm] < 6000 < 3000 < 1500 Total hardness (Ca + Mg) [mmol/L] < 0.01 < 0.01 < 0.05 Iron [mg/L] < 0.3 < 0.1 < 0.2 Copper [mg/L] < 0.05 < 0.03 < 0.1 Silica [mg/L] pressure-dependent Oxygen [mg/L] < 0.05 < 0.02 – Oil/grease [mg/L] < 1 < 1 <1 Organic substances* – * Organic substances can be degraded to products that increase acid conductivity, corrosion, and deposits. Furthermore, they can lead to foaming and/or the formation of deposits. Their concentration in boiler feed water should thus be kept as low as possible.The methods described below apply to measuring limit Steam for heating purposes and process steamvalues at different locations in the water-steam circuit Steam is not only used to drive turbines, but also for heaand include the analyses of steam, condensate, boiler t ing purposes or as process steam in the chemical indusfeed water, and makeup water. These methods are also try. Many of the applications described in this brochureused to control the water chemistry in the cooling system also apply to these applications; however, they are notof a boiling water reactor or a pressurized water reactor discussed here.and in the cooling circuit.
Sodium determination using ion-selective electrodes – process parameters Sodium ions are nearly always present in water. The ma Silica is determined colorimetrically after treatment with joity originates from the sodium hydroxide and trisodium r ammonium molybdate and subsequent reduction of the phosphate additives for conditioning boiler water. Eleva resulting yellow silicomolybdic acid with ascorbic acid to14 ted sodium concentrations in the water-steam circuit also blue silicomolybdous acid. Interference by phosphate, indicate leakages in the condenser where sodium-eni r which is also determined by adding ammonium molyb ched cooling water infiltrates the high-purity pro cess date, is avoided by adding oxalic acid. Analysis is carried wa Sodium ions corrode metals and produce harmful ter. out with an Alert Analyzer; the detection limits are in the deposits in the process water system and on tur bine blades. lower µg/L range. Sodium concentrations in power plant waters are usually Phosphate determination – process parameters less than 50 µg/L. The easiest way to measure the con Phosphates are one of the most commonly used agents centration is using ion-selective electrodes (ISE) and an for conditioning cooling and boiler feed water. They form ammonium or diisopropylamine buffer. In contrast, the corrosion-resistant protective films on metal surfaces; ion-selective electrodes with polymer membranes used in cracks and defects are phosphatized in their presence. the Alert Analyzers do not need a buffer. Their mode of Boiler feed water is treated with trisodium phosphate operation is simple: the polymer membrane contains a (TNP), which reduces the residual hardness, phosphatiz molecule (ionophore) that binds only sodium ions. When es, and alkalizes the water. Excessive TNP concentrations sodium ions penetrate this membrane, they change its lead to undesirable foaming. Phosphate is usually added electrochemical properties and thus alter the potential. quasi-continuously. Detection limits are in the sub-µg/L range. In-process determinations are carried out colorimetrically Sodium can also be determined by ion chromatography. using the phosphomolybdenum blue method at 875 nm. Indeed, this is the method of choice if other cations have Ammonium molybdate reacts under acidic conditions to be determined as well (page 17). with orthophosphate to the yellow dodecamolybdophos horic acid (H3[P(Mo3O10)4]), which is reduced to phos p Silica – process parameters phomolybdenum blue by strong reducing agents such as An excessive silica concentration in the boiler feed water ascorbic acid. The detection limits lie in the mg/L range. or makeup water of power plants must be avoided. Silica Measurements are carried out with an Alert Ana lyzer, (SiO2) is a very weakly dissociated acid. During the treat ADI 2019 or ADI 2045. ment of makeup water colloidal silica is not retained by the ion exchangers and is hydrolyzed into soluble silica in the boiler. Owing to its volatility, it can enter the steam circuit at elevated pressures and then deposit on turbine blades, particularly in the presence of alkaline earth metals.
Oxygen scavenger (hydrazine) – process parametersDissolved oxygen is one of the main causes of corrosion Furthermore, hydrazine increases the pH value and is alsoin water circuits, which is why water is always thermally a good corrosion inhibitor. It forms a passivating layer ofdegassed before use. The residual oxygen is removed magnetite in steel boilers and a protective oxide layer on mically – usually by adding reducing agents such asche copper alloys.hydrazine or sulfite. Sulfite salts have the drawback that 15they are oxidized to corrosive sulfate and thus increase Hydrazine is determined colorimetrically with p-dimethylthe salt content in the water-steam circuit. Although hy aminobenzaldehyde at 440 nm and is detected withd zine is classified as carcinogenic, its efficiency in water ra Alert Analyzers. The analysis takes 10 minutes; the deteccircuits is hard to beat. It is an excellent oxygen scaven tion limit is in the lower µg/L range. Increasing use isger, and its oxidation and decomposition products are being made of diethylhydroxylamine (DEHA) as an oxysalt free because they consist of only nitrogen, water, gen scavenger. It can also be detected colorimetricallyand ammonia. with the Alert Analyzer. DEHA reduces added Fe(III) to Fe(II), which is then determined colorimetrically.N2H4 + O2 → N2 + 2 H2OOverview of colorimetric determinations in power plant chemistry – process parameters Concentration range Method Analyte Analyzer [mg/L] (color reagent) Water hardness (Ca, Mg) 0.005–5 Hydroxynaphthol blue (HNB) Alert, ADI 2019, ADI 2045 Iron (Fe2+) 0.005–1 Triazine Alert, ADI 2019, ADI 2045 Copper (Cu2+) 0.02–5 2,2-Bicinchoninic acid Alert, ADI 2019, ADI 2045 Nickel (Ni2+) 0.02–3 Dimethylglyoxime Alert, ADI 2019, ADI 2045 Zinc (Zn2+) 0.02–2 Zincon Alert, ADI 2019, ADI 2045 Phosphate 0.01–7 Phosphomolybdenum blue Alert, ADI 2019, ADI 2045 Silica 0.005–5 Molybdenum blue Alert, ADI 2019, ADI 2045 Hydrazine 0.005–0.5 p-Dimethylaminobenzaldehyde Alert, ADI 2019, ADI 2045 Diethylhydroxylamine 0.005–0.5 Fe3+ Alert, ADI 2019, ADI 2045 (DEHA)Ion selective Colorimetric• Ammonium • Aluminium• Calcium • Ammonium• Chloride • Chromium• Fluoride • Copper• Nitrate • Hydrazine• Potassium • Iron• Sodium • Nickel • Nitrate • Nitrite • Phosphate • Silica • Zinc«Plug and analyze» – the two variants of the operator-friendly Alert Analyzers: the Alert ADI 2003 for measuring with ion-selectiveelectrodes (left) and the Alert ADI 2004 for colorimetric measurements. www.metrohm-applikon.com
16 Transition metals Metal surfaces in the power plant are in continuous con flushes them in the form of their negatively charged an tact with water and/or steam and corrosion occurs every io complexes onto the anion-exchange column, where nic where. Ions of the metals iron, copper, and nickel are they are separated. In the post-column reaction, the important corrosion indicators. They are entrained by the me react with the chelating agent PAR to spectro tals steam and deposit on the turbine blades, thus greatly chemically active complexes that are determined by decreasing the efficiency. UV/VIS detection. This method can differentiate between iron(II) and iron(III). As demonstrated by the cation deter Transition metals are determined by ion chromatography mination in the water-steam circuit of a boiling water with UV/VIS detection. Samples are prepared using Inline reactor on page 22, these can also be determined di Preconcentration of the metal cations. The eluent re rectly using conductivity detection. moves the me from the preconcentration column and tals Inline Preconcentration of samples in the sub-µg/L range: The sample is withdrawn via the injection valve into a buffer volume. After the valve has been switched over, a sample volume, which depends on the preconcentration volume (0.1 to 10 mL), is applied to the preconcentration column. From here, the metals elute onto the separation column and then react with PAR in the post-column reactor to produce UV/VIS-active complexes that can be determined by the UV/VIS detector. The PAR reagent is supplied by a low maintenance, easily cleaned, and precise dosing unit. 60 Simulated sample from a water-steam circuit, spiked with 55 2 µg/L each of iron(III), copper, nickel, zinc, and cobalt; column: 50 Metro A Supp 10 - 75/4.0 (6.1020.070); eluent: 7 mmol/L sep 45 40 dipicolinic acid, 5.6 mol/L Na2SO4, 66 mmol/L NaOH, 74 mmol/L 35 formic acid, 1 mL/min; column temperature: 45 °C; precon Intensity [mAU] 30 centration volume: 4000 µL; post-column reaction (PCR) with 25 0.11 g/L 4-(2-pyridylazo)resorcinol (PAR); flow rate: 0.2 mL/min; iron(III) 20 cobalt 15 UV/VIS detection at 510 nm. Alternatively, microbore columns copper nickel 10 can be used; they consume less eluent and sample. zinc 5 0 -5 -10 -15 0 1 2 3 4 5 6 7 8 9 10 Time [min]
Amines and cationsExcessively low pH values increase the corrosion poten ume is transferred with microliter precision to the condi 17tial, whereas excessively high pH values destroy the pro tioned preconcentration column. The column is thentective layer on the metals. Adjustment of the pH value rinsed with ultrapure water to remove the unwantedis challenging because the requirement for minimum matrix. This protects the chromatography column andcor rosion and maximum protective layer leaves very little improves the separation efficiency. Anions can be de terflexibility. pH values are usually adjusted with Lewis bases mi ed in a concentration range from 0.01 to 10 000 µg/L. nsuch as amines. Ion chromatography with conductivitydetection provides an effective means to control amine 24addition. Alkali metals and alkaline earth metals can also ammonium 22 20be determined in the same analysis run. This enables 18immediate detection of leakages by infiltrating cooling Conductivity [µS/cm] 16water. Preconcentration volumes of 4 mL are sufficient to 14 dimethlylamine (DMA) 3-methoxypropylamine 12determine sodium concentrations down to 0.05 µg/L. sodium 10 magnesium ethanolamine potassium 8 morpholine calciumCorrosive anions at trace levels 6 nickel zinc 4Chloride causes pitting corrosion on turbine blades and 2rotors. In combination with sulfate, it also leads to corro 0 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30sion fatigue and stress corrosion cracking (SCC). Volatile Time [min]ammonium compounds enhance these effects. Con sequently, even trace levels of corrosive anions must be Simulated sample from a water-steam circuit treated with 1 mg/L of each amine and cation. All cations have a linear measurng idetermined. Trace analysis of anions in the water-steam range. Column: Metrosep C 4 - 250/4.0 (6.1050.430); eluent:circuit is based on a combination of Inline Preconcentra- 2.5 mmol/L HNO3 and 0.5 mmol/L oxalic acid, 0.9 mL/min;tion and Matrix Elimination (MiPCT-ME). The target vol column temperature: 32 °C; sample volume: 100 µL
18 Schematic diagram of combined Inline Preconcentration with Matrix Elimination (MiPCT-ME) for samples in the µg/L range: The 800 Dosino aspirates the required sample volume through the injection valve (1) into the buffer volume (2). After the valve has been switched over, this volume is applied to the preconcentration column (3) from where the ions elute to the chroma tography column (4) after the valve has been switched over again. 1.24 Concentration* Detection limit RSD Recovery rate [µg/L] [µg/L] [%] [%] 1.20 Fluoride 0.496 0.010 0.6 99.1 Chloride 0.496 0.010 0.6 99.2 fluoride 1.16 Nitrite 0.494 0.040 2.6 98.8 Bromide 0.487 0.009 0.7 97.4 Nitrate 0.512 0.007 0.5 102.4 1.12 Phosphate 0.473 0.072 4.8 94.6 Conductivity [µS/cm] Sulfate 0.505 0.028 1.9 101.0 1.08 * Mean of six determinations chloride 1.04 1.00 nitrite bromide phosphate nitrate sulfate 0.96 0.92 0.88 0.84 0 2 4 6 8 10 12 14 16 18 20 Time [min] Simulated sample from a water-steam circuit treated with 0.5 µg/L of each anion; MiPCT-ME guarantees recovery rates and precision in the sub-µg/L range that are otherwise only achieved in the mg/L range. Preconcentration volume: 4000 µL; column: Metrosep A Supp 5 - 150/4.0 (6.1006.520); eluent: 3.2 mmol/L Na2CO3, 1.0 mmol/L NaHCO3, 0.7 mL/min; column temperature: 35 °C Automatic calibration Both techniques, Metrohm intelligent Preconcentration with Matrix Elimination (MiPCT-ME) and Metrohm intelligent Partial Loop Injection Technique (MiPT) are ideally suited for routine analysis in power plants. With a single standard, a multipoint ca ration is prepared and concentration ranges from the ng/L to the mg/L range are covered. lib
Chloride and sulfate in supercritical water-steamcircuits 19The higher the temperature and pressure of the steam per ritical boiler technologies have the highest require cdriving the turbine blades is, the greater is the efficiency ments for boiler materials because these conditions proof the thermodynamic cycles. Power plants that use mote corrosion and the formation of deposits. Metrohm’swater above the critical point in the water-steam circuit high-performance ion chromatography system provides(374 °C and 221 bar) thus produce significantly more fast, flexible, and extremely sensitive monitoring of theelectricity for a given amount of fuel. However, such su anion concentration in supercritical water-steam circuits.The online monitoring system can analyze up to five freely selectable sample streams in alternation. If necessary, the samples passthrough an ultrafiltration cell before being analyzed. Two further ports of the 10-port selector valve are used for the calibration andcheck standards. 2.4 2.2 2.0 1.8 Conductivity [µS/cm] 1.6 1.4 phosphate 1.2 chloride 1.0 0.8 sulfate 0.6 0.4 0.2 0.0 0 2 4 6 8 10 12 14 16 18 Time [min] Simulated sample from the water-steam circuit of a super- crii ally operated reactor treated with 1 µg/L anions; column: tc Metrosep A Supp 10 - 100/2.0 (6.1020.210); eluent: 5 mmol/L Na2CO3, 5 mmol/L NaHCO3, 0.25 mL/min; column temperature: 45 °C; preconcentration volume: 4000 µL
20 Iron At high temperatures, steam reacts with the iron in the -200 Fe carbon steel of steam boilers. This leads to the formation of a thin layer of magnetite, an iron(II,III) oxide, which -150 passivates the steel surface protecting it against further corrosion (Schikorr reaction). Under unfavorable condi I [nA] -100 tions, the inhibiting magnetite layer can flake off, which leads to elevated iron concentrations in the water-steam -50 circuit. A regular iron determination enables monitoring of not only corrosion processes but also the formation 0 and destruction of the protective magnetite layer. -0.2 -0.4 -0.6 -0.8 -1.0 -1.2 Adsorptive stripping voltammetry (AdSV) provides fast U [V] and sensitive detection of iron in process waters of the Voltammetric determination of iron water-steam circuit (boiler feed water, makeup water, condensate) in power plants. This is achieved by adding Copper and other heavy metals (iron, zinc, suitable complexing agents to convert the iron into ad cadmium, lead, nickel, cobalt) sor bable complexes that are reduced on the electrode Copper alloys are now used almost exclusively in con surface after a defined preconcentration time. Detection densers of the water-steam circuit. The drawback is the limits in the lower µg/L range can be achieved using susceptibility of copper and its alloys to corrosion by am 2,3-dihydroxynaphthalene (DHN) as the complexing monia. The resulting corrosion products initiate further agent. Direct calibration by standard addition to the corrosive attack. Copper compounds already precipitate sample enables matrix-independent determination. from steam in the high-pressure regions of steam tur bines and deposit on the blades. They are determined voltammetrically according to DIN 38406-16. Sample pre paration is not necessary. 797 VA Computrace: A user-friendly all-round measuring stand for sensitive determination of trace metals in process waters of power plants
21Trace analysis of heavy metals – processparametersThe online determination of heavy metals at trace levels Adding 2,4,6-tripyridyl-s-triazine to iron(II) produces ais performed with the ADI 2045VA Analyzer from violet complex that can be determined colorimetrically atMetrohm Applikon. The central unit of the ADI 2045VA 590 nm in the lower µg/L range. The iron(III) content isis the 797 VA Computrace. This analyzer can be used to determined after it has been reduced to iron(II).monitor the various water circuits in power plants usingonline voltammetry of up to four sample streams. Copper usually enters the water-steam circuit from one of its alloys. It is detected as the copper(I) ion by addingIron and copper – process parameters the sodium salt of 2,2-bicinchoninic acid. The resultingQuasi-continuous analysis of the iron concentrations in violet complex is detected at 550 nm down to the lowerthe condensate can be used for early detection of corro µg/L range. The copper(II) content is determined after itsion processes in turbines, pumps, or heat exchangers has been reduced to copper(I).(water-steam circuit). Quasi-continuous analyses alsogu rantee that no dissolved iron reaches the condensate a Similar to the other colorimetric determinations, iron andstream and thus the turbine blades where it would cause copper are analyzed with an Alert Analyzer. Alternatively,damage. a ADI 2019 or ADI 2045 Analyzer from Metrohm Applikon can be used. www.metrohm-applikon.com
Water-steam circuit in a boiling water reactor (BWR)22 In a boiling water reactor (BWR), the energy generated by nuclear fission is used to evaporate water. The result As already described on pages 10 to 11, at elevated tem eratures, salts of the alkaline earth metals deposit on p ing steam is fed directly to the turbine driving the gene the heat transfer surfaces as an insulating layer of boiler rators. Contaminants, such as corrosion products from scale that reduces heat transfer. Ion chromatography the pipeline and tank materials, enter the water-steam with conductivity detection provides sensitive determina circuit and thus reach the fuel assemblies. This also app tion of Cu, Zn, Ni, alkali metals, alkaline earth metals, and lies to leakages in the condenser that allow constituents ammonium. from the less pure cooling water to enter the water- steam circuit so that they can reach the fuel assemblies 2.9 where they adversely affect the operating conditions. 2.5 ammonium The water chemistry in the BWR varies according to ma sodium Conductivity [µS/cm] 2.1 nu facturer and plant engineering. Nobel metals are often 1.7 copper magnesium potassium added because they form a thin protective layer on the 1.3 system surfaces. calcium nickel zinc 0.9 0.5 Cations as well as copper, zinc, and nickel Corrosion of steel and brass alloys liberates corrosive ions 0.1 0 2 4 6 8 10 12 14 16 18 20 22 of the metals nickel, copper, and zinc. These are readily Time [min] entrained by the steam and then deposit on turbine blades, thus considerably reducing the efficiency. In addi Simulated sample from a water-steam circuit, spiked with 0.5 µg/L of the standard cations as well as copper, nickel, and tion, the metals released by corrosion undergo nuclear zinc; column: Metrosep C 4 - 250/2.0 (6.1050.230); eluent: reactions and thus increase radiation in the power plant. 2.5 mmol/L HNO3, 0.5 mmol/L oxalic acid, 0.4 mL/min; col To limit corrosion of the materials and to prevent the umn temperature: 32 °C; preconcentration volume of sample: formation of radioactive 60Co (produced by neutron cap 9800 µL ture by the stable 59Co isotope present in the steel alloys), the cooling water in the BWR is often treated with de pleted zinc oxide (contains < 1% of the stable main iso The transition metals can also be determined spectropho tope 64Zn). tometrically, as described on page 16.
23Corrosive anions 0.20The combination of Metrohm Inline Preconcentration 0.18(MiPCT) and automatic calibration enables detection of 0.16corrosive anions in the lower µg/L range. This method is Conductivity [µS/cm] 0.14suitable for water-steam circuits in nuclear and fossil fuel- 0.12fired reactors. Chromate can also be analyzed at the 0.10 chloride 0.08same time to a detection limit of 50 ng/L. The detection fluoride chromate sulfate nitrate oxalate 0.06limits can be lowered even further by increasing the pre 0.04concentration volume. 0.02 0.00 0 2 4 6 8 10 12 14 16 Time [min] Simulated sample from a water-steam circuit of a boiling water reactor treated with 50 ng/L of each of the standard anions and chromate; column: Metrosep A Supp 5 - 150/4.0 (6.1006.520); eluent: 4.8 mmol/L Na2CO3, 1.5 mmol/L NaHCO3, 0.8 mL/min; column temperature: 30 °C; preconcentration volume: 2000 µL
Primary circuit in a pressurized water reactor (PWR)24 The most common types of nuclear reactors are the boil ing water reactor (BWR) and the pressurized water reac Boric acid A simple and quick determination of the boric acid con tor (PWR). The PWR has three circuits, whereas the BWR centration is important to control the reactivity in the PWR. has only two. The primary circuit of the PWR circulates Boric acid has an acidity constant Ka1 of 5.75⋅10-10 water under a high pressure (up to 160 bar) through the (pKa = 9.24), which means it is a weak acid that is difficult reactor core. It absorbs the heat released by nuclear fis to titrate. The addition of polyalcohols, for example, sion. In the steam generator, the water – now at a tem mannitol, leads to the formation of complexes with a perature of approx. 325 °C – transfers its heat to the greater acidic strength that behave like a monovalent se condary circuit, which is a conventional water-steam acid which can be easily titrated with sodium hydroxide circuit with steam generator, turbine, and cooled con solution. The equilibrium of the complexation reaction denser. The additional circuit in the PWR ensures that the lies on the right-hand side of the following equation: radioactive materials remain in the primary circuit. R1 OH OH R1 O O R1 2 + B- + 3 H 2O + H+ B HO OH O O R2 OH R2 R2 The pressurized water reactor is controlled by the control rods in the core and by the boric acid dissolved in the In the manual determination method, the sample is primary circuit. The 10B isotope, in particular, acts as a pipetted into a titration cell, diluted with distilled water, mo derator and captures the fission neutrons that keep and treated with a defined (excess) volume of a saturated the nuclear chain reaction going and which are respon mannitol solution. After stirring, the mixture is titrated sible for the reactivity of the reactor. Determination of with 0.1 molar sodium hydroxide solution to a pH value the constituents in the primary circuit is extremely impor of 8.5. Accurate pipetting and determination of the tant with regard to reactor safety and its efficiency. blank value of mannitol are essential for precise determi nation of boric acid. This method can also be used to determine the boric acid content in the spent fuel pool. Titrimetric determination of the boric acid content in a simulated sample from the primary circuit of a PWR: red line: titration with out added mannitol; blue line: after addition of mannitol.
25The Robotic Boric Acid AnalyzerMetrohm offers a fully automated system for the analysisof boric acid. It includes not only complete traceability,but also a high sample throughput during 365/24/7 operations.Boric acid – process parametersPressurized water reactors, which use light water, do notallow the fuel assemblies to be exchanged during operation so that a fuel reserve has to be in place at the startof an operating cycle. The associated excess activity inthe reactor is controlled by a higher boric acid concentration. As the fuels burn up, the boric acid concentrationhas to be lowered to keep the reactor running at maximum output. This is achieved by replacing water containing boric acid with ultrapure water: the boric acid concentration between two fuel reloadings varies between2000 mg/L and almost zero.Quasi-continuous control of the constantly changingamounts of boric acid in the primary circuit is extremelyimportant for efficient and reliable operation. Continuousdetermination of the boric acid in the process is thusessential. Both the ADI 2016 and the ADI 2045TI Ana lyzers from Metrohm Applikon provide fast and reliabledetermination via potentiometric titration. As alreadydescribed on page 24, the acidic boric acid esters resulting from the addition of mannitol are titrated. ADI 2045TI – a flexible analyzer for online applications in power plant chemistry
26 Lithium An optimum pH value of the water in the primary circuit 40 36 prevents attack of the metallic materials and destruction lithium 32 of the protective layers adhering to them. The addition of Conductivity [µS/cm] 28 boric acid to the primary circuit of the PWR lowers the 24 pH value and thus increases the corrosion potential. This 20 16 is prevented by adding an alkalizing agent to the primary 12 circuit. Monoisotopic lithium hydroxide 7Li (approx. 2 mg/L) 8 is used in most pressurized water reactors. On the one 4 hand, 7Li does not undergo any undesirable nuclear re ac 0 0 1 2 3 4 5 6 7 8 9 10 t ions, and on the other hand, it is already present in the Time [min] reactor because it is formed by a neutron capture reac tion of the boron: 10B(n,α)7Li. Simulated sample from the primary circuit of a PWR containing 1 g/L boric acid, treated with 1.7 mg/L lithium hydroxide; col umn: Metrosep C 4 - 250/2.0 (6.1050.230); eluent: 2.5 mmol/L Lithium cations can be determined with the intelligent HNO3, 0.5 mmol/L oxalic acid, 0.4 mL/min; column temperature: partial loop injection technique (MiPT). Based on the ac 32 °C; sample volume: 20 µL tual sample concentration, the system calculates and in jects the required volume (2–200 µL) of undiluted sample. This method is fast, precise, and can be combi ed with n ultrafiltration.
Further cationsThe same ion chromatograph as that used to analyze tions can be used. The only difference is the required 27lithium can also be used to determine nickel, zinc, calci preconcentration volumes.um, and magnesium. Even the same separating condiCombined Inline Preconcentration and Matrix Elimination for the determination of metals in the µg/L range. The samples from theprimary circuit are withdrawn through the injection valve into a buffer volume. After switching to the fill position, the accuratelydispensed volume is transferred to the preconcentration column.Nickel, zinc, calcium, and magnesium 2.0 a ammoniumNickel is an important alloying metal that increases the 1.9 lithiumcorrosion resistance of steel. However, if nickel ions enter 1.7the primary circuit, they promote corrosion. Therefore, 1.5 Conductivity [µS/cm] 1.3their concentration must be checked at regular intervals. magnesium 1.1Depleted zinc (containing < 1% of the stable main iso 0.9tope 64Zn) is often added to the primary circuit. This not calcium 0.7 zinc nickelonly reduces the radioactivity on the component surfac 0.5 sodiumes, but it also lowers corrosion of the metal surfaces in 0.3 0.1contact with the water. 0 2 4 6 8 10 12 14 16 18 20 Time [min]In the primary circuit, which contains boric acid and lithi umhydroxide, combined Inline Preconcentration and Matrix Simulated sample from the primary circuit of a pressurized water reactor containing 2 g/L boric acid and 3.3 mg/L lithium hydroxElimination can be used to determine the metal concen ide, treated with 2 µg/L each of nickel, zinc, calcium, and magtrations down to the sub-µg/L range. nesium; column: Metrosep C 4 - 250/2.0 (6.1050.230); eluent: 2.5 mmol/L HNO3, 0.5 mmol/L oxalic acid, 0.4 mL/min; column temperature: 32 °C; preconcentration volume: 1000 µL
28 Corrosive anions Anions corrode metals and their concentration must be 1.05 0.95 fluoride checked at regular intervals. The analytical challenge is to 0.85 detect anions in the µg/L range alongside gram quan- 0.75 Conductivity [µS/cm] 0.65 tities of boric acid and lithium hydroxide. The analysis is nitrite 0.55 carried out fully automatically using a combination of formate chloride 0.45 Inline Matrix Elimination (for the borate) and Inline Neu 0.35 nitrate bromide sulfate phosphate tralization (for the LiOH). Successful trace analysis de 0.25 pends on the implemented preconcentration technique. 0.15 glycolate Detection is also successful if boric acid is neutralized 0.05 acetate with ammonium instead of LiOH. A further advantage is 0 4 8 12 16 20 24 28 32 Time [min] automatic calibration. It guarantees excellent detection limits, a high reproducibility, and excellent re covery rates. Water sample from the primary circuit of a pressurized water re actor containing 2 g/L boric acid and 3.3 mg/L lithium hydroxide spiked with 2 µg/L anions; column: Metrosep A Supp 7 - 250/4.0 In addition to the standard anions – fluoride, chloride, (6.1006.630); eluent: 3.6 mmol/L Na2CO3, 0.8 mL/min; column ni trate, and sulfate – important organic degradation pro temperature: 45 °C; preconcentration volume: 2000 µL d ucts such as glycolate, formate and acetate are deter mined with high precision. Their presence usually indi cates defective ion exchangers that are used to condition the boiler feed water.
29WastewaterRecycling of process water in the cooling circuits is be regulated, and compliance with limit values necessitatescoming increasingly common in modern power plants. precise analysis. Metrohm brochures on water and enviWhen the water is finally discharged into the environ r n en al analysis discuss numerous analytical wastewa o m tment, it must comply with the limit values for a large ter app cations. This document describes an exemplary linumber of compounds. Most constituents originate from de mi ation of heavy metals and process analysis in ter nchemicals added to the water during conditioning. These flue gas cleaning plants.include corrosion inhibitors, oxygen scavengers, alkalis,and acids. There is also radioactive and boric acid-con Heavy metals in wastewatertaining wastewater from the circuits of boiling water and In the water circuits of power plants, water is in permapressurized water reactors. The stringent mandatory re nent contact with metals and metal alloys. Heavy metalsquirements entail comprehensive wastewater analysis. enter the water circuits due to corrosion and must therePara meters such as the pH value, conductivity, chemical fore also be taken into account. Zinc, cadmium, lead,oxygen demand (COD) as well as the concentration of and copper can be determined with high sensitivity byheavy metals, hydrazine, chloride, and sulfate are strictly voltammetry in accordance with DIN 38406 Part 16.
30 Wastewater from flue gas cleaning – process parameters The combustion of fossil fuels – including incineration of This is the application field of the online or atline analyz domestic refuse – produces atmospheric pollutants such ers of Metrohm Applikon, regardless of whether it is for as carbon dioxide, nitrogen oxides, and sulfur oxides as a single sample stream or for complex multiple sample well as dust. These all have to be removed from the flue streams. The analyzers are based on wet chemical meth gas. In the first step, the nitrogen oxides are catalytically ods such as titration, colorimetry, or measurements with reduced to nitrogen. Electric filters then remove the dust ion-selective electrodes. before the scrubbing towers in the flue gas desulfuriza tion plant convert sulfur dioxide into sulfate using a lime stone slurry and oxygen, turning it into gypsum. The resulting wastewater is contaminated and must be subjected to complex chemical and physical treatments before it can be discharged into the environment. The analytical parameters that need controlling require mea surement of the pH value, analysis of sulfur species, and determination of heavy metals.