ISSN 0040-6015, Thermal Engineering, 2018, Vol. 65, No. 1, pp. 39–44. © Pleiades Publishing, Inc., 2018. Original Russian Text © B.M. Larin, 2018, published in Teploenergetika.
WATER TREATMENT AND WATER-CHEMISTRY
Water-Chemistry and Its Utility Systems in CCP Power Units (Review) B. M. Larin Ivanovo State Power University, Ivanovo, 153003 Russia e-mail:
[email protected] Received March 16, 2017; in final form, May 31, 2017
Abstract⎯Damageability of heat transfer surfaces of waste heat recovery steam generators (HRSG) of combined-cycle plants (CCP) can be reduced due to an increase in the quality of make-up and feed water, the use of phosphate-alkaline or amino compound water chemistry (WC), and improved chemical quality control of the heat carrier and make-up water preparation techniques. Temporary quality standards for the heat medium developed by the All-Russia Thermal Engineering institute (VTI) for CCP power units are presented in comparison with the IAPWS standards; preferences for the choice of a WC type for some power units commissioned in Russia in the first decade of this century are shown; and operational data on the quality of feed, boiler water, and steam for two large CCP-450 and CCP-425 power units are given. The state and prospects for the development of chemical-technological monitoring systems and CCP water treatment plants are noted. Estimability of some CCP diagnostic parameters by measuring specific electric conductivity and pH is shown. An extensive bibliography on this topic is given. Keywords: water chemistry, CCP power units, chemical control, specific electric conductivity, film-forming and neutralizing amines DOI: 10.1134/S0040601517120059
CCPs at foreign TPPs had become a frequent practice ten years earlier. To date, not only abroad but also in Russia, significant experience in the operation of CCP power units and their water chemistry has been accumulated and requires summarizing [4–10]. In the initial period of CCP power unit operation, it was established that the main operating costs related to damage of heat-recovery steam generators and a reduction in the efficiency of the CCP by 50–70% depend on the water-chemistry state [4, 5]. The choice of the WC is affected by features of heat-recovery steam generators due to their design. Such features include the following: (1) A smaller pipe wall thickness (3 mm) and a larger pipe surface area compared to conventional power steam generators. (2) An increase in the velocity of the two-phase medium (water-steam mixture) to 20 m/s in the upper evaporative part of the low-pressure circuit. (3) A large number of HRSG pipe bends and difficulty of their discharging during draining. (4) A possibility of boiler water flow-in into the superheater when the gas turbine is switched off. In addition, it should be noted that there is a much larger number of CCP power unit start-stops in comparison with the design operation mode, including power units in Europe and the United States.
Optimum water chemistry is supported by a set of measures ensuring the operation of heat and power equipment with a minimal corrosion rate of structural metals and minimal deposits of solid products on the heat exchange surfaces [1]. Under TPP operation conditions, the corrosion rate is estimated by direct measurement of metal (Fe, Cu) concentration in the feed and boiler water as well as by an analysis of the amount of deposits on the pipe cuttings involved in the heat exchange processes. A WC state is characterized by chemical parameters of the heat carrier quality and depends on the temperature, state, and velocity of the medium, and the type and state of the metal of the heat exchange surfaces. For domestic steam power heat-recovery steam generators and other cycle arrangement equipment, quality standards for feed water, boiler water, steam, and other heat carrier streams were developed and regularly revised. The main guideline was the Operational Regulation, the latest edition of which was published in 2003 [2]. Since then, the norms have not been revised, and the newly introduced TPP equipment is mostly represented by power units of binary combined-cycle plants, completed to a great extent with time-tested imported equipment [3, 4]. A main power unit CCP-450T of the Northwest TPP (St. Petersburg) was put into operation in late 2000, while binary 39
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Table 1. Feed water quality standards for CCP drum-type waste heat recovery steam generators [13] Water chemistry Benchmark pH Specific electrical conductivity, μS/cm: χН χ
AV
AC
9.2–9.6
8.9–9.2
Less than 0.2 4.0–11.0
Not more than 0.5 –
Concentration, μg/dm3, not more than:
C NH3
1000.0
–
C O2 (after deaerator)
10.0
10.0
C SiO 2 СFe СNa ТОС СCl
20.0
10.0
20.0 10.0 100.0 3.0
10.0 5.0 – 3.0
0.1
0.1
Сpp, mg/dm3
Sufficiently complete information about the CCP power unit water chemistry state appeared in the domestic print media about a decade ago and was primarily associated with an assessment of HRSG damageability [4, 5] and heat carrier quality standards [6, 7]. The experience of operation of the CCP-450 power unit at the Northwest TPP in St. Petersburg showed that a horizontal arrangement of the HRSG tube bank with sagging of the middle sections up to 18 mm leads to the accumulation of condensation water during the steam generator draining, which contributes to the development of stand still corrosion [4]. In the HRSG operation, corrosion pits developed as a result of multistage concentration of hydrocarbonates and chlorides under the deposit layer. The HRSG was halted 130 times for 6 years of operation, and more than ten halts were up to 2 weeks or more. It was shown in [6–8, 11, 12] that foreign TPPs with CCP power units impose high requirements to the heat carrier quality, including the indicators typical for the Russian power industry (specific electric conductivity χ, pH, oxygen concentration of C O2 , iron CFe, copper CCu, sodium CNa, silicic acid C SiO2 ) and new, in particular total organic carbon—TOC. There is a high demand for the organization of reliable chemical-engineering monitoring systems for the water chemistry of the main and auxiliary circuits of the CCP power units. Summary of the first experience of CPP power units' operation, with allowance for foreign studies, made it possible for VTI to develop temporary heat carrier quality standards [13], which include—in addition to the above indices—heat carrier χН cation conductivity, concentration of ammonia C NH3 , chloride СCl, free phosphates C PO 4 , petroleum products
Сpp, polyamines Cpa, and caustic soda СNaOH (with respect to СНaOH = 2.5 CCl). In this document, the following water chemistry is recommended for single-, two-, and three-pressure heat-recovery steam generators: (1) All-volatile (AV) and amino compound (AC) water treatment for the condensate-feed pipeline according to the standards presented in Table 1; (2) Phosphate (Ph), hydrate (H), amino compound (AC) for the evaporation loop according to the standards presented in Table 2. The feed water, boiler water (see Tables 1, 2) and steam quality standards correspond to foreign standards [6] with respect to the all-volatile WC if the condenser tubes are made of austenitic steel. In this case, the allvolatile WC of the feed water can be combined with phosphate, hydrate, or phosphate-alkaline treatment of the boiler water. The amino compound water chemistry involves the addition of organic amine mixtures for corrective treatment of the entire power unit steam-generating circuit. At the first stage of the CCP power unit implementation, there were two main types of water chemistry equally presented in Russia: AV and AC [4]. The International Association for the Properties of Water and Steam (IAPWS) clarified and published quality standards for feed water for the ammonia treatment and boiler water for the phosphate and hydrate treatments [8, 14, 15]. In almost all cases, it is recommended to equip steam turbine condensers with austenitic steel tubes and maintain the following feed water quality standards: pH = 9.2–9.8, χH no more than 0.3 μS/cm, СNa no more than 3 μg/kg. When NaOH is admixed to in the boiler water of the high-pressure circuit, the pH should not be more THERMAL ENGINEERING
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Table 2. Boiler water quality standards for CCP waste heat recovery steam generators [13] Water chemistry Benchmark pH Specific electrical conductivity, μS/cm: χ χH
Ph
H
AC
9.3–9.6
9.3–9.6
8.9–9.6
10.0–30.0 –
6–10 Not more than 30
Not more than 10 –
Concentration, μg/dm3:
C SiO 2
Not more than 200.0
Not more than 200.0
Not more than 200.0
C PO4
0.5–2.0
–
–
СCl
Not more than 1200.0
Not more than 1200.0
–
Not more than 30.0
Not more than 30.0
СFe Concentration, СNa
Not more than 30.0
mg/dm3: –
СNaOH*
0.5–1.5
–
Сpp
1.0–2.6
Not more than 0.1
Сpa
–
Not more than 0.1 –
– – Not more than 0.1 Not less than 2.0
* With respect for СNaOH = 2.5CCl.
than 9.6 [4, 13] to avoid caustic cracking of the pipelines and CNa in the superheated steam not more than 2 μg/kg when χH is not more than 0.2 μS/cm. Table 3 shows operational data for two CCP power units of high capacity with two- and three-pressure HRSGs operating under hydrate WC. As follows from Table 3, the water and steam quality indicators of these units slightly differ compared to each other and, to a large extent, meet the standards [8, 13]. The excess of the rated ammonia concentration in the feed water (more than 1000 μg/kg) is caused by high pH values (9.48– 9.52) and sodium concentration in the boiler water in the NaOH addition scenario. There are much more questions on the arrangement of the amino compound water chemistry for CCP power units. High damageability of the HRSG pipe bends of the first CCP power units, noted in [4, 5], initiated the expansion of amino compound water treatment using mixtures of organic amines with continuous addition, including for the purpose of equipment preservation [9, 16–19]. Typically, such complex reagents are a mixture of film-forming and neutralizing amines with admixtures of other organics. The former create a protective film on the tube surface, preventing the access of depolarizers, and the latter increase the pH of the medium like the action of ammonia [18–20]. Having a lower evaporation distribution factor in comparison with ammonia, these amines are able to support an alkaline medium reaction in the feed and boiler water, while the selection of the film-forming amine components ensures the THERMAL ENGINEERING
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evaporation of a significant part of them and passivation of the power unit steam circuit [21, 22]. The most widespread in Russia were imported reagents for the amine compound treatment of Helamin BRW-150N, Helamin-906 N, and Getamine V211 brands. VTI’s experts have developed a domestic complex reagent that passed an industrial test at the CCP-325 power unit of the Ivanovo CPP [18]. Having real advantages for CCP power units in comparison with the phosphate and hydrate WC, the amino compound water chemistry is not without some disadvantages. This is, first of all, a high cost and significant complex reagent consumption; in addition, the film-forming amines may adversely affect ion exchangers of the condensate purification plant (condensate demineralizer) and sensing elements of the automatic inspection devices for heat carrier chemical quality control. Along with this, careful input quality control of the reagent to be purchased is required. The distribution of the AC water treatment may be very limited without solving the above problems. It is also necessary to develop a regulatory framework for the amino compound treatment, since the heat carrier quality in this case does not fit into the standards of the ammonia treatment. VTI’s developments [13] give the main guidelines in this matter; however, the water and steam quality standards of CCP power units require further refinement. The arrangement of the optimal CCP power unit water chemistry is influenced by the state of a chemical process monitoring system (CPMS) and a makeup water treatment configuration. The scope and
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Table 3. Operational data on the feed and boiler water quality for CCP power units Power unit Benchmark CCP-450T
CCP-425
Feed water Specific electrical conductivity, μS/cm: χ
8.0
9.2
χН
0.19
0.3
9.48
9.52
СNa
5.0
1.3
C NH3
1250
1600
C O2
–
10
CFe
5
4
рН Concentration, μg/kg
High pressure boiler water Specific electrical conductivity, μS/cm: χ
10.8
χН
9.5
0.58
9.48
9.55
СNa
1210
1300
CFe
10
25
рН
12.5
Concentration, μg/kg
Superheated steam Specific electrical conductivity, μS/cm: χ
–
9.6
χН
0.3
0.2
рН
–
9.4
СNa, μg/kg
–
1.3
Table 4. Calculation results of the heat carrier quality parameters for the CCP-425 power unit Sampling location Benchmark DC
FW
BWHP
BWMP
BWLP
SSMP
SHSMP
C NH3
1550
1600
76.4
151
148
1927
1722
CCl
11.5
17.2
48.3
46
142
19.6
11.5
CNa
8.2
12.0
1322
2396
2107
14.5
8.28
p-alkalinity
–
–
41
81
80
–
–
total
33
34
68
100
86
38
35
Concentration, μg/kg
Alkalinity, μg-equiv/dm3
DC—desalted condensate; FW—feed water; BWHP, BWMP, BWLP—boiler water of high, medium, and low pressures; SSMP, SHSMP—saturated and superheated steam of medium pressure. THERMAL ENGINEERING
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WATER-CHEMISTRY AND ITS UTILITY SYSTEMS IN CCP POWER UNITS
Z, rub/m3 2 3
15
1 10 5
4 0
2
4
6 8 10 3 C SO2– + C – , mg-equiv/dm Cl 4
Fig. 1. Dependence of the cost price Z of desalted water in (1, 2) ion-exchange, (3) reverse osmosis, and (4) thermal processes on the total concentration of strong acid ions in the initial water [28].
essence of the control within CPMS are determined by quality standards of the heat carrier [6–8, 13] and are represented for the phosphate and hydrate WC by a well-known set of automatic analyzers. CCP power unit equipment is often completed with imported inspection devices; however, the domestic instrumentation is able to provide chemical control of the main rated and diagnostic parameters [7, 13]. It is of interest to expand CPMS in terms of diagnostic indicators on the basis of mathematical models of heat carrier ionic equilibrium and measurements of specific electric conductivity and pH [23, 24]. Thus, according to the measurements of these indicators for the CCP-425 power unit, calculated values represented in Table 4 were obtained. Automatic monitoring of electrical conductivity and pH measurements provides reliable control of the main ionogenic indicators of feed, boiler water, and steam quality, including ammonia, salinity and alkalinity. The make-up water treatment configuration for CCP power units is arranged in accordance with the requirements of standards [6–8, 13] with allowance for the quality of natural (source) water and the toolbox of technical facilities and apparatus. For the moment, imported reverse osmosis systems (ROS) and installations mainly prevail in the modern Russian market [25, 26]. They are often used without accounting for the quality of the source water, which leads to a longterm adjustment of the ROS, selection of the component composition, and operation mode for specific characteristics of the treated water, including the need for chemical membrane washings [26, 27]. In all cases of ROS operation, the quality of permeate does not meet the requirements for the make-up water for CCP power units [13], which complicates the water treatment system with water purification apparatus. Ionexchange filters are most reliable for this purpose, in particular mixed-bed ones. THERMAL ENGINEERING
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It cannot hurt to recall that the first reverse osmosis systems in Russia were developed by VNIIAM, manufactured by domestic enterprises, and put into operation at Zuevskaya GRES (Donetsk oblast) in 1989 and at Mosenergo TPP-23 in 1997. One of the main developers of these systems was E.B. Yurchevskii. As far back as the beginning of this century, he calculated performance indicators for three water treatment technologies: chemical, membrane, and thermal desalination [28]. The results of the calculated comparison of these technologies are represented in Fig. 1. They show that chemical desalination is preferred for lowmineralized water (the total concentration of strong acid ions does not exceed 3 mg-equiv/dm3). To date, the situation with regard to the information shown in Fig. 1 may have changed slightly in favor of membrane technologies; however, the use of ROS for the purification of natural waters in the central and northern area of Russia (low-mineralized with an elevated content of organoferric compounds) requires deep pretreatment and does not provide an economic and environmental gain [29]. CONCLUSIONS (1) A reduction of damageability of waste heat steam generator components is possible by replacing the material of pipe bends with austenitic steel and arranging the optimal water chemistry. (2) Water chemistry is realized under the conditions of strict requirements for the feed water quality, which is determined by the producers of waste heat steam generators and IAPWS and VTI guidelines. (3) Operational reliability of the water chemistry is impossible without high-quality chemical monitoring and make-up water treatment. There are best practices in these areas in the Russian power industry; however, their further development is necessary to improve the quality and reduce the cost of auxiliary systems. REFERENCES 1. V. N. Voronov, T. I. Petrova, Water Chemistries of TPPs and NPPs (Mosk. Energ. Inst., Moscow, 2009) [in Russian]. 2. Rules of Technical Operation of Power Plants and Grids of the Russian Federation (ORGRES, Moscow, 2003) [in Russian]. 3. A. Ya. Kopsov, “Specific features relating to implementation of investment projects in the Russian power industry,” Therm. Eng. 57, 641–645 (2010). 4. A. F. Bogachev, Yu. A. Radin, and O. B. Gerasimenko, Specific Features of Operation and Damageability of Waste-Heat Boilers of Binary Combined Cycle Units (Energoatomizdat, Moscow, 2008). 5. G. V. Tomarov, A. V. Mikhailov, E. V. Velichko, and V. A. Budanov, “Extending the erosion-corrosion service life of the tube system of heat-recovery boilers used as part of combined-cycle plants,” Therm. Eng. 57, 22–27 (2010).
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6. T. I. Petrova and A. Yu. Petrov, “Water chemistries of thermal power plants with steam-and-gas units (by foreign data),” Nov. Ross. Elektroenerg., No. 4, 44–56 (2007). 7. V. N. Voronov and T. I. Petrova, “Improvement of water chemistries and chemical monitoring at thermal power stations,” Therm. Eng. 57, 543–548 (2010). 8. T. I. Petrova, K. A. Orlov, and R. B. Dooley, “International water and steam quality standards on thermal power plants at all-volatile treatment,” Therm. Eng. 63, 896–902 (2016). doi 10.1134/S0040601516100086 9. S. Yu. Suslov, A. V. Kirilina, I. A. Sergeev, E. A. Sokolova, I. S. Suslov, and L. A. Borozdina, “Experience gained from conduction of water chemistry with the use of helamin in the PGU-39 power units at the sochi thermal power station,” Therm. Eng. 59, 502–508 (2012). 10. I. V. Krutitskii, A. V. Zverev, A. N. Sobolev, and M. B. Balashov, “Experience gained from mastering the operation of the Kirishi district power station unit 6 modernized using the combined-cycle technology,” Therm. Eng. 61, 12–21 (2014). doi 10.1134/ S0040601514010054 11. R. Svoboda, F. Gabrielly, E. Liebig, H. Hens, and H. Sandmann, “Combined cycle power plant chemistry — Concepts and field experience,” in Proc. 6h Int. EPRI Conf. on Cycle Chemistry in Fossil Plants, Columbus, OH, USA, June 27–29, 2000, pp. 34.1—34.20. 12. H. Takaku, V. Abe, M. Miyajima, “Essential of revised guideline: Water conditioning and boiler in Japan,” Presented at IAPWS Meeting (2007). https://www.iaps.org. 13. STO 70238424.27.100.013-2009. Water Treatment Systems and Water Chemistry of TPPs. Terms of Creation. Norms and Requirements (InVEL, Moscow, 2009). 14. Phosphate and NaOH Treatments for the Steam-Water Circuits of Drum Boilers of Fossil and Combined Cycle/HRSG Power Plants (Int. Assoc. for the Properties of Water and Steam, 2015). http://www.iaps.org. 15. Volatile Treatment for the Steam-Water Circuits of Fossis and Combined Cycle/HRSG Power Plants (Int. Assoc. for the Properties of Water and Steam, 2015). http://www.iaps.org. 16. G. A. Filippov, V. A. Mikhailov, E. V. Velichko, A. V. Mikhailov, A. V. Chugin, and A. I. Novozhilov, “Use of film-forming amines for corrosion protection of the steam-water duct of PGU-450 power unit,” Tyazh. Mashinostr., No. 4, 14–17 (2007). 17. S. Yu. Suslov and A. V. Kirilina, “On the choice of reagents during conduct of amine chemistries,” Energetik, No. 1, 39–44 (2011). 18. S. Yu. Suslov, A. V. Kirilina, I. A. Sergeev, T. V. Zezyulya, E. A. Sokolova, E. V. Eremina, and N. F. Timofeev,
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
“Complex amine-based reagents,” Therm. Eng. 64, 237–241 (2017). doi 10.1134/S0040601517030065 A. Bursik, “Polyamine/Amine treatment — A reasonable alternative for conditioning high pressure cycles with drum boilers,” PowerPlant Chem. 6, 545–549 (2004). R. Kluk, J. Torres, A. Antompierti, and J. Rivera, “Experiences using neutralizing amines to control pH and minimize FAC in a combined-cycle power plant,” PowerPlant Chem. 13, 5–20 (2011). R. Crovetto, A. M. Rossi, and E. Murtagh, “Research Evaluation of Polyamine Chemistry for Boiler Treatment: Corrosion Protection,” in Proc. NACE Corrosion Conf. and Expo 2011, Houston, TX, Mar. 13–17, 2011 (NACE Int., 2011), pp. 2224–2239, Paper No. 11391. T. I. Petrova, I. A. Burakov, A. A. Zonov, A. A. Kruglova, and D. K. Gadzhiev, “Influence of physicochemical parameters on transition of amines from boiling water into saturated steam,” Vestn. Mosk. Energ. Inst., No. 4, 36–41 (2013). B. M. Larin and A. B. Larin, “Improvement of chemical monitoring of water-chemistry conditions at thermal power stations based on electric conductivity and pH measurements,” Therm. Eng. 63, 374–378 (2016). doi 10.1134/S0040601516030058 A. B. Larin and A. V. Kolegov, “Monitoring of water chemistry conditions of power units of TPPs with combined cycle units,” Vestn. IGEU, No. 3. 14–18 (2013). A. A. Panteleev, A. V. Zhadan, S. L. Gromov, D. V. Tropina, and O. V. Arkhipova, “Starting the water treatment system of the 410-MW combinedcycle plant at the Krasnodar cogeneration station,” Therm. Eng. 59, 524–526 (2012). V. V. Bobinkin, S. Yu. Larionov, A. A. Panteleev, D. A. Shapovalov, and M. M. Shilov, “Optimization of membrane elements’ array in industrial reverse osmosis units,” Therm. Eng. 62, 735–740 (2015). doi 10.1134/ S0040601515100031 A. A. Panteleev, V. V. Bobinkin, S. Yu. Larionov, B. E. Ryabchikov, V. B. Smirnov, and D. A. Shapovalov, “The choice of the chemical purification technology for reverse osmosis units at industrial enterprises,” Nov. Ross. Elektroenerg., No. 4, 22–31 (2016). E. B. Yurchevskii and B. M. Larin, “Development, study, and introduction of water-treatment equipment with improved environmental characteristics,” Therm. Eng. 52, 532–538 (2005). B. M. Larin, E. N. Bushuev, A. B. Larin, E. A. Karpychev, and A. V. Zhadan, “Improvement of water treatment at thermal power plants,” Therm. Eng. 62, 286– 292 (2015). doi 10.1134/S0040601515020056
Translated by A. Kolemeisn
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