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Polyamine/Amine Treatment ­ A Reasonable Alternative

Polyamine/Amine Treatment ­ A Reasonable Alternative for Conditioning High Pressure Cycles with Drum Boilers

Albert Bursik

both water and steam), underdeposit corrosion (still relatively common in utility boilers and heat recovery steam generators), and stress corrosion cracking of turbine blades or discs all seem to be no trouble at all. None of the problems mentioned count in comparison to the industry problem with organics [1]. Organic treatment chemicals have been suspect for many decades. Operators using them have been derided; the additives themselves have been deprecatingly called "snake oils." It is not clear who was the first to adopt this designation, typically used for additives to lubricants or fuels, for non-traditional and non-conventional additives to plants and soils, for additives used in the cosmetic industry (e.g., in skin- and hair-care products), in alternative medicine, and in many other areas. With the term "snake oils," the organic cycle additives were put on the same level with gimcrack [2]. Probably for this reason, the application of organic fossil plant cycle treatment chemicals ­ organics ­ is considered very negative and is not covered in any internationally acknowledged cycle chemistry guideline. Dooley's continuum of treatments (Figure 1 [3]) does not include the application of organic treatment chemicals either.

ABSTRACT

The polyamine/amine treatment is applied in hundreds and hundreds of fossil plant cycles, particularly in the industry. Over the last decade, the extent of its application in utilities has been increasing. This paper focuses on the polyamine/amine regime in cycles with drum boilers, although one case study is presented which reports on application of this treatment in units with once-through steam generators. The major hindrance with respect to the use of this treatment in utilities is the fact that the cation conductivity of steam increases slightly when this treatment is applied. Operation experience in industrial power and steam generation and in utilities demonstrates that a slight cation conductivity increase in the steam does not cause any turbine-related problems, assuming that the pH is correctly set by low-molecular volatile amines being a part of the polyamine/amine formulation. Steam cation conductivity-related studies for establishing the actual interaction of slightly contaminated steam and turbine materials in the presence of an adequate alkalizing agent (a low-molecular amine with a favorable distribution behavior), i.e., when the early condensate is adequately alkaline, are suggested.

Current Situation The current situation is very interesting. Despite the fact that the use of organic cycle treatment chemicals is not advised in any major international cycle chemistry guideline, many variations of the amine treatment have been used for decades in industrial steam and power generation. The extent of amine treatment use in fossil power plants is also increasing [2].

AN ALTERNATIVE PLANT CYCLE CHEMISTRY TREATMENT

The Problem with Organics In recent years, many publications in the cycle chemistryrelated literature have dealt with a very attractive topic, namely with organics. A complete listing of all the relevant references would make use of more space than is at the author's disposal. One gets the strong impression that this topic is the only important plant cycle chemistry issue. The most frequent causes of component failures in plant cycles seem to fall into oblivion or at least become negligible: flow-accelerated corrosion (a corrosion mechanism that represents a major potential danger to cycle equipment and staff), corrosion fatigue (not rare with components or component parts which come into contact with

Polyamine/Amine Treatment in Industrial und Utility Power Generation In an application report, theoretical discussions of pros and cons of amine use for conditioning a fossil plant cycle are inappropriate. Nevertheless, some of the most important reasons for an operator to decide in favor of feedwater alkalizing with amines for his or her particular cycle(s) are: ­ reduction of corrosion generation and corrosion product transport into the boiler, ­ improvement in the feedwater purity, which results in decreased blowdown losses,

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­ faster startups (lower corrosion product transport during startup).

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Polyamine/Amine Treatment ­ A Reasonable Alternative

Figure 1: Continuum of treatments [3].

All the abovementioned advantages are the result of an increased pH in the condensing steam (due to a more favorable distribution behavior of amines in comparison to ammonia), even in the presence of decomposition products of the amines themselves. The combination of polyamines with low-volatile amines dealt with in this paper reveals further benefits: ­ as a rule, an additional boiler water treatment is not required, ­ the steam generator is self-cleaning (polyamines in combination with dispersants), ­ there is an increase in turbine efficiency, and ­ there is less corrosion during idle periods. These additional benefits are predominantly the result of polyamine film forming on all surfaces in the cycle. Adsorption of surface-active polyamines on metal surfaces, e.g., in waterwalls, creates a local high-pH environment and inhibits corrosion even in the presence of certain contaminants or when the pH in the bulk is lower than expected. All operators applying polyamines report on extremely clean turbine blades. It is easy to understand that doing without phosphates when conditioning boiler water results in less mechanical carryover of phosphates and, for this reason, less turbine blade deposit buildup. In addition, the presence of surface-active polyamines in the steam helps in the removal of older turbine blade deposits and prevents the formation of new deposits even if the concentration of contaminants in steam is relatively high. To be honest, amine application also has some disadvantages. In most cases, the cation conductivity of steam (and condensate and ­ in units without condensate polishers ­ of feedwater) in units on amine treatment is slightly in-

creased. For this reason, the monitoring of the plant cycle chemistry may become somewhat complicated. However, a multiplicity of operators, particularly in industrial steam and power generation, has decided to capitalize on the advantages of this treatment and to master the possible disadvantages. In the following, the use of a non-traditional polyamine/ amine treatment is demonstrated in some case studies. In 1 all cases reported, Helamin® , a proprietary product containing both polyamines and volatile amines, was used as the plant cycle treatment chemical. The pressure range covered in the examples is very wide, as is the range of main steam temperatures.

APPLICATION EXAMPLES

Case Study 1 A large European refinery operates steam generators (conventional drum boilers, heat recovery steam generators, and refinery-typical steam-generating systems) with a to­1 tal steaming capacity of about 2 050 t · h . The two high ­1 pressure boilers (steaming capacity 700 t · h each) supply superheated steam with the following parameters: pressure 9 MPa (1 305 psi) and temperature 520 °C (968 °F). The steam generated in the high pressure and other boilers is used at different pressure levels in the range between 0.4 MPa (58 psi) and 8.9 MPa (1 291 psi). The total length of the steam pipelines is more than 70 000 m (more than 43.5 miles); the condensate lines are of a corresponding length.

1

Helamin® is a registered trademark of Filtro, SA, Geneva, Switzerland

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Polyamine/Amine Treatment ­ A Reasonable Alternative

The use of the polyamine/amine treatment started in 1993 in the old power plant and later this treatment was used in all types of boilers (conventional and heat recovery) and in all other steam-generating refinery systems. There were several reasons for the conversion from a typical phosphate/ammonia/hydrazine treatment to the polyamine/ amine treatment: heavy corrosion and corrosion product transport in the steam/condensate systems, deposition of corrosion products in the boilers, and deposits on the turbine blades. It is probably worth mentioning that an equivalent polyamine/polyacrylate proprietary mixture was also used for preoperational boil-out of the high pressure boilers. After the application of the new treatment, the corrosion product transport in the whole system was significantly reduced, the subsequent boiler and turbine inspections revealing clean surfaces in both the boilers and the turbines. Figure 2 shows the boiler drum of one of the steam generators. The photograph was taken during a major boiler overhaul. A slight increase in cation conductivity in the cycles is a typical attendant circumstance of the polyamine/amine application. The operator reports on cation conductivity in ­1 the range of 0.15 to 0.35 µS · cm during prolonged operating periods. Due to problems with raw water organics passing the makeup system during a few months of the ­1 year, the cation conductivity peaks up to 0.5 µS · cm . Even in such situations, the corrosion product generation and transport is successfully controlled. The use of the polyamine/amine treatment in a complex multipressure steam-generating system demonstrates an important treatment advantage: the same chemical is used in the same concentration in boilers regardless of the particular individual system pressure. In comparison to phosFigure 2: Boiler drum ­ unit on polyamine/amine treatment. phate treatment, this fact markedly simplifies both the boiler water chemistry (pressure-dependent phosphate concentrations vs. uniform conditions) and its surveillance.

Case Study 2 On a large chemical industry site in Europe (in a nitric acid production unit), polyamine/amine cycle chemistry treatment was introduced, replacing the classic European phosphate treatment. Both the boiler (drum pressure 8 MPa (1 160 psi)) and the turbine were supplied by wellknown European original equipment manufacturers. The major reason for converting the unit from phosphate treatment to polyamine/amine treatment was trouble with turbine fouling. The turbine had to be frequently cleaned (washed) to recover the turbine performance. After introducing the new chemical treatment, the turbine washes were no longer required. Figure 3 depicts the performance improvement. During the application of the phosphate

Figure 3: Turbine performance ­ phosphate treatment vs. polyamine/amine treatment.

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treatment, the mean turbine output was approximately 22.7 MW. After 9 months operation on polyamine/amine treatment, the plate rating of 25 MW was achieved (without any turbine wash). Improvement in the boiler and turbine operation and the efficiency increase realized result in non-negligible savings. The reader may transfer the improvement achieved (22.7 MW 25 MW) and thereby the savings realized to his or her own unit or utility operated on phosphate treatment.

treated with the polyamine/amine treatment chemical since 1996. The units are equipped with condensate polishers. Another unit was recently commissioned and is treated with the same chemical. The reason for the plant cycle treatment selection was long holds during startups due to a high concentration of iron oxides in the feedwater when applying the all-volatile treatment (AVT) in units being subject to frequent shutdowns/startups and load variations. During the conversion from the AVT to polyamine/amine treatment, two parameters have controlled the treatment chemical dosage: the pH (pH target value > 9) and the ­1 cation conductivity ( 0.2 µS · cm ) in the cycle. The operation practice shows that after the startup, the cation ­1 conductivity reaches values about 0.5 µS · cm and falls ­1 down to 0.2 µS · cm in continuous operation. In 2001/2002, early condensate measurements were carried out, revealing that the early condensate pH is higher than the bulk steam/condensate pH even in the presence of low-molecular acids [5]. The early condensate pHs depicted in Figure 4 are measured (not calculated) values.

Case Study 3 Inadequate thermal stability of organic cycle treatment chemicals is often cited as evidence against their use in fossil plant cycles. It is assumed that these chemicals are completely decomposed, the final decomposition products being low-molecular organic acids and carbon dioxide. In arguing thus, the main residence time of organics in water-touched and steam-touched boiler parts is completely disregarded. Considering a particular 14 MPa (2 030 psi) drum boiler unit as an example, Tavast estimates that the period during which the chemical remains in the drum system is in the order of one hour (the precise time depends on the percentage of blowdown), and in the superheater only in the order of a few tens of seconds [4]. In cycles with once-through boilers, the residence time is markedly shorter. This case study demonstrates that ­ for this reason ­ a successful use of polyamine/amine treatment is possible even in cycles with once-through boilers with high pressures and temperatures. In one European combined heat and power generating plant, two cycles with subcritical once-through steam generators (main steam pressure/temperature 200 bar/ 540 °C, reheat steam temperature 540 °C) have been

Case Study 4 In a large paper mill, polyamine/amine treatment is applied in a unit with a drum-type boiler with a steaming capacity ­1 ­1 of 125 t · h (276 000 lb · h ). The main steam parameters are: pressure 9.5 MPa (1 378 psi) and temperature 525 °C (977 °F). After commissioning, the treatment used was ammonia/hydrazine AVT combined with phosphate dosing into the boiler water. As is typical in paper mills, long steam and condensate lines between the boiler house and the individual paper machines and frequent air ingress into the low pressure and high pressure condensates resulted in heavy corrosion in the boiler peripheral paper mill equip-

Figure 4: pH of the early condensate samples ­ a unit with a once-through steam generator on polyamine/amine treatment.

Figure 5: Paper mill ­ parts taken from the equipment vs. a part from the spare part stock.

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ment. The unit suffered from heavy corrosion product transport into the boiler and fast buildup of boiler tube deposits. A boiler tube hot side deposit weight of ­2 760 g · m was determined. The boiler had to be chemically cleaned. After the chemical clean, the unit cycle treatment was converted to polyamine/amine treatment. As a result of the cycle treatment conversion, the iron content of the condensates ­ after a short period with higher iron levels (cleaning of surfaces in paper mill equipment, outside of the boiler system) ­ has dramatically decreased to levels customary in non-industrial power stations ­1 ­1 (<< 20 µg · kg , mostly < 10 µg · kg ). Figure 5 is a comparison of the condition of two parts of a drum drier, dismantled from an operating paper machine (two upper parts), and a part from the spare part stock.

Figure 6: Boiler drum internals after polyamine/ polyacrylate application [7].

Some Further Examples Polyamine/amine treatment has a long history in plant cycle treatment, mostly in industrial applications. The operation conditions in industrial steam-generating systems are typically more difficult than those in utility units. If a plant cycle treatment can cope with hard industrial conditions, why shouldn't this treatment be able to cope with the more favorable situations in utilities? Concerns with respect to corrosion caused by breakdown products of organic cycle treatment chemicals, particularly in areas of beginning steam condensation (e.g., in a low pressure part of a condensing turbine), have resulted in a prejudiced rejection of this treatment. However, the positive experience in industrial power and steam generation is attracting the attention of utilities experiencing cycle chemistry problems. Some examples are mentioned below. As reported by Galt [7], feedback on the application of polyamine treatment for on-line boiler cleaning has peaked the interest of a world-famous South African utility. The Belgian experience [8] suggests that even in this utility, some possible application candidates are present. Even though the trial at a 200 MW unit with drum-type boilers operating at 12 MPa (1 740 psi) with a main steam temperature of 535 °C (995 °F) had to be prematurely concluded, a reduction of the average waterwall oxide thickness from around 540 µm to 159­285 µm could be reached in four months of polyamine/polyacrylate use. Figure 6 shows the boiler drum internals after polyamine/ polyacrylate application [7]. In many countries all over the world, polyamine/amine treatment is successfully being applied. For example, in the Middle East, in tens of power plants generating power and steam for desalination installations and in refineries, this treatment is applied. The steaming capacity of the in­1 dividual steam generators ranges from 300 t · h ­1 ­1 ­1 (661 000 lb · h ) to 620 t · h (1 367 000 lb · h ), the main steam pressure from 6.5 MPa (943 psi) to 12.7 MPa (1 842 psi), and the main steam temperature from 480 °C (896 °F) to 540 °C (1 004 °F). Despite the frequent load variations induced by alteration between pure power production and power production and steam sendout to desalination units, the cation conductivity in the cycles is ­1 maintained at a low level ( 0.3 µS · cm ). The major reason for the polyamine/amine treatment application was corrosion product generation and transport when operating on traditional plant cycle treatments. Only the application of the new treatment has led to iron levels in the order ­1 of < 10 µg · kg , even in brine heater condensates of the desalination plants. In the countries of the former Soviet Union, the use of the polyamine/amine treatment is also increasing. The pressure of the units treated ranges between 4 MPa (580 psi) and 14.0 MPa (2 030 psi) and the main steam temperature between 440 °C (824 °F) and 560 °C (1 040 °F). The treatment is applied in the majority of cases in older units without condensate polishers which are experiencing problems with condenser tightness, heavy corrosion product generation and transport, boiler tube deposit buildup and fouling of turbines. The operation results so far confirm that the polyamine/amine treatment application may help in establishing reasonable cycle chemistry conditions even in such complicated cases.

THE EXASPERATING CATION CONDUCTIVITY

The major problem hindering the frequent use of polyamine/amine treatment in utilities is the cation conductivity problem. The major turbine manufacturers de­1 mand cation conductivity of steam < 0.2 µS · cm ; the philosophy of the major industry guidelines is identical. The fact is neglected that cation conductivity is neither a chemical nor a physical property of the media. It is actually a hypothetical matter: it is the conductivity of a sam+ ple in which no other cations except the cation H are present. This indicates that a value measured does not have any meaningfulness with respect to the actual properties of the media. The original media (upstream of the

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cation exchanger) may have a high or a low pH; i.e., it may be non-corrosive or strongly corrosive with respect to ironbased materials [9]. Industry experience proves that even at increased cation conductivity, failure- and damage-free operation of the cycle in the presence of organic alkalizing agents is possible. This is a result of favorable distribution coefficients of low-molecular volatile amines. For this reason, in the phase transition zone of a low pressure turbine, amines are capable not only of coping with their own decomposition products (e.g., acetates and formates), but also with certain levels of inorganic contaminants possibly present in the steam. The experience in the industrial steam generation proves ­1 that cation conductivities in the range of 0.5 µS · cm do not cause any turbine-related problems, assuming that pH is correctly set by low-molecular volatile amines. A serious and deep study of this topic is desirable. The major turbine manufacturers should carefully investigate whether the materials and the design of low pressure turbines are actually so inadequate that the turbines cannot accept steam with a cation conductivity somewhat higher than ­1 the ominous 0.2 µS · cm , even though the pH of the early condensate is markedly higher than 9 and the specific conductivity of the early condensate is, e.g., ­1 < 10 µS · cm . Such evaluations should only focus on technical issues and not be prejudged by possible warranty aspects. The long-term experience with the polyamine/amine treatment demonstrates that a slightly increased cation conductivity does not endanger low pressure parts of condensing turbines. Bursik et al. have ­ in a somewhat provocative manner ­ suggested that polyamine/amine treatment should be in-

corporated into Dooley's continuum of treatments [2]. The more operation experience that is gained with this treatment, the more justifiable this opinion becomes [Figure 7].

REFERENCES

[1] [2] Bursik, A., Staudt, U. W., PowerPlant Chemistry 2001, 3(3), 136. a) Bursik, A., Bezzoli, P., Graf, A., The Seventh International Conference on Cycle Chemistry in Fossil Plants (Houston, TX, U.S.A.), 2003. Electric Power Research Institute, Palo Alto, CA, U.S.A. b) Bursik, A., Bezzoli, P., Graf, A., PowerPlant Chemistry 2003, 5(6), 373. a) Dooley, B., Shields, K., The Seventh International Conference on Cycle Chemistry in Fossil Plants (Houston, TX, U.S.A.), 2003. Electric Power Research Institute, Palo Alto, CA, U.S.A. b) Dooley, B., Shields, K., PowerPlant Chemistry 2004, 6(3), 153. Tavast, J., PowerPlant Chemistry Seminar "Combined Cycles and Heat Recovery Steam Generators ­ Development, Boiler Tube Failures, Chemistry, and Monitoring", 2002, Contribution to the discussion. PowerPlant Chemistry GmbH, Neulussheim, Germany. Bursik, L., PowerPlant Chemistry 2002, 4(2), 81. Grabli, A., Massalha, L., VGB Symposium Industrieund Heizkraftwerke, BHKW 2004 (Bochum, Germany), 2004. VGB PowerTech, Essen, Germany.

[3]

[4]

[5] [6]

Figure 7: Continuum of treatments including polyamine/amine treatment [2].

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[7]

Galt, K. J., Proc. (on CD), ESAA Power Station Chemistry 2004 Conference (Pokolbin, NSW, Australia), 2004 . Energy Supply Association of Australia, Melbourne, VIC, Australia. Roofthooft, R., Eyckmans, M., Verheyden, K., de Pourcq, D., VGB PowerTech 2001, 81(3), 83. Bursik, A., PowerPlant Chemistry 2002, 4(10), 597.

CONTACT

Albert Bursik PowerPlant Chemistry GmbH P.O. Box 1269 68806 Neulussheim Germany E-mail: [email protected]

[8] [9]

THE AUTHOR

Albert Bursik (Ph.D., Chemical Engineering, Institute of Chemistry and Chemical Technology in Prague, Czech Republic, Mechanical Engineering, University of Stuttgart, Germany) has worked for over 35 years as a chemist in several utilities. Albert Bursik is an Honorary Fellow of the International Association for the Properties of Water and Steam and has published more than 200 scientific and technical publications. He is a professor at the University of Stuttgart and works as the editor of the PowerPlant Chemistry® journal.

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