organic impurities and organic conditioning agents in … impurities and organic conditioning agents...

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Robert Svoboda Frank Gabrielli Herbert Hehs Hans-Günter Seipp Frank-Udo Leidich Bruce Roberts ABSTRACT Power plants are designed to run with pure water and steam. For simple cycles (no export steam) no other products should be necessary. If organic additives are used, the possible side effects have to be carefully addressed. Possible side effects include corrosive degradation products, interference with monitoring cation conduc- tivity, influence on boiling and on condensation, and fouling. Examples from boiler and turbine operation are given. Organic amines produce volatile acidic degradation products, but the amine provides cations for pH coun- terbalance. In contrast, organic oxygen scavengers, dispersants, chelants as well as organic impurities generally pro- duce volatile acidic degradation products, but with no cation for counterbalance. For this reason, such prod- ucts must be considered as potentially corrosive. From a power plant manufacturer's point of view, any organic matter in the steam/water cycle brings the risk of detrimental side effects. The general use of organic additives should thus be avoided and restricted to spe- cific needs and situations, as for example in certain process steam systems. BACKGROUND The steam/water cycle of a power plant operates with pure, conditioned water. Organic substances may be pres- ent either as an unwanted impurity, or as a functional addi- tive [1]. It is not within the scope of this paper to go into details of all these substances and to appraise the undisputed bene- fits of additives. Instead, a generalized overview and an assessment of possible side effects will be given. It is understood that individual products may differ and have to be fitted into the appropriate context. Boiler pressures also need individual consideration, as reactions and especially decomposition depend on temperature. ORGANIC IMPURITIES Organic impurities in the steam/water cycle originate mostly from the make-up water and, to a lesser degree, as residues from erection and maintenance, accidental intru- sions not considered. None of these impurities improve functionality in the steam/water cycle; what remains is just the possibility of detrimental effects. Degradation in the Steam/Water Cycle Once in the steam/water cycle, organic impurities are sub- ject to thermal degradation (decomposition and oxidation). Natural organic matter, like humic substances and poly- saccharides [1], will preferentially degrade to acetic acid and carbon dioxide, but also to other organic acids like formic, butyric, and propionic acid [2]. Oxalic acid has also been found in samples from steam/water cycles. If the organic impurity includes chlorine, then hydrochloric acid can be expected as a degradation product as well. Assessment of Degradation Products As a general rule, organic impurities produce volatile acidic degradation products with no cation for counterbalance. Therefore, they must be considered as potentially corro- sive. ORGANIC CONDITIONING AGENTS The most common basic conditioning agents in the steam/water cycle are NH 3 , N 2 H 4 , Na 3 PO 4 , NaOH and O 2 . In addition, there is a wide range of mostly organic addi- tives available to support individual needs. Most prominent are amines, to provide alkalization oxygen scavengers, to react with oxygen in the feedwa- ter or as a metal passivator dispersants and chelants to reduce deposits in the boiler Organic conditioning agents are usually applied in a con- centration range from 10 μg · kg –1 up to 10 mg · kg –1 . © 2006 by PowerPlantChemistry GmbH. All rights reserved. Organic Impurities and Organic Conditioning Agents in the Steam/Water Cycle: A Power Plant Manufacturer's Point of View Organic Impurities and Organic Conditioning Agents in the Steam/Water Cycle 502 PowerPlant Chemistry 2006, 8(8)

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Page 1: Organic Impurities and Organic Conditioning Agents in … Impurities and Organic Conditioning Agents in the Steam/Water Cycle PowerPlant Chemistry 2006, 8(8) 503 In addition to knowledge

Robert Svoboda

Frank Gabrielli

Herbert Hehs

Hans-Günter Seipp

Frank-Udo Leidich

Bruce Roberts

ABSTRACT

Power plants are designed to run with pure water andsteam. For simple cycles (no export steam) no otherproducts should be necessary. If organic additives areused, the possible side effects have to be carefullyaddressed.

Possible side effects include corrosive degradationproducts, interference with monitoring cation conduc-tivity, influence on boiling and on condensation, andfouling. Examples from boiler and turbine operation aregiven.

Organic amines produce volatile acidic degradationproducts, but the amine provides cations for pH coun-terbalance.

In contrast, organic oxygen scavengers, dispersants,chelants as well as organic impurities generally pro-duce volatile acidic degradation products, but with nocation for counterbalance. For this reason, such prod-ucts must be considered as potentially corrosive.

From a power plant manufacturer's point of view, anyorganic matter in the steam/water cycle brings the riskof detrimental side effects. The general use of organicadditives should thus be avoided and restricted to spe-cific needs and situations, as for example in certainprocess steam systems.

BACKGROUND

The steam/water cycle of a power plant operates withpure, conditioned water. Organic substances may be pres-ent either as an unwanted impurity, or as a functional addi-tive [1].

It is not within the scope of this paper to go into details ofall these substances and to appraise the undisputed bene-

fits of additives. Instead, a generalized overview and anassessment of possible side effects will be given. It isunderstood that individual products may differ and have tobe fitted into the appropriate context. Boiler pressures alsoneed individual consideration, as reactions and especiallydecomposition depend on temperature.

ORGANIC IMPURITIES

Organic impurities in the steam/water cycle originatemostly from the make-up water and, to a lesser degree, asresidues from erection and maintenance, accidental intru-sions not considered.

None of these impurities improve functionality in thesteam/water cycle; what remains is just the possibility ofdetrimental effects.

Degradation in the Steam/Water Cycle

Once in the steam/water cycle, organic impurities are sub-ject to thermal degradation (decomposition and oxidation).Natural organic matter, like humic substances and poly-saccharides [1], will preferentially degrade to acetic acidand carbon dioxide, but also to other organic acids likeformic, butyric, and propionic acid [2]. Oxalic acid has alsobeen found in samples from steam/water cycles.

If the organic impurity includes chlorine, then hydrochloricacid can be expected as a degradation product as well.

Assessment of Degradation Products

As a general rule, organic impurities produce volatile acidicdegradation products with no cation for counterbalance.Therefore, they must be considered as potentially corro-sive.

ORGANIC CONDITIONING AGENTS

The most common basic conditioning agents in thesteam/water cycle are NH3, N2H4, Na3PO4, NaOH and O2.In addition, there is a wide range of mostly organic addi-tives available to support individual needs. Most prominentare

– amines, to provide alkalization– oxygen scavengers, to react with oxygen in the feedwa-

ter or as a metal passivator– dispersants and chelants to reduce deposits in the

boiler

Organic conditioning agents are usually applied in a con-centration range from 10 µg · kg–1 up to M 10 mg · kg–1.© 2006 by PowerPlantChemistry GmbH. All rights reserved.

Organic Impurities and Organic Conditioning Agents in theSteam/Water Cycle: A Power Plant Manufacturer's Point of View

Organic Impurities and Organic Conditioning Agents in the Steam/Water Cycle

502 PowerPlant Chemistry 2006, 8(8)

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503PowerPlant Chemistry 2006, 8(8)

In addition to knowledge of the functionality of these prod-ucts, there is the question of possible side effects. Tailoredselection may help to address some of these concerns.

Degradation in the Steam/Water Cycle

Organic amines degrade to ammonia, carbon dioxide, andlow-chain carboxylic acids:

– Morpholine, as an example, produces acetic acid, andto a minor degree also formic, glycolic [3] and oxalicacid [4].

Organic oxygen scavengers degrade to carbon dioxideand organic acids:

– Carbohydrazide degrades to water, nitrogen, ammonia,and carbon dioxide;

– Ascorbic acid degrades over several steps, includingerythorbic acid, oxalic acid, acetic acid, formic acid andfinally carbon dioxide;

– Other organic scavengers, for example methylethylke-toxime (MEK), diethylhydroxylamine (DEHA) and hydro-quinone, degrade to terminally produce low-chain acidslike acetic, formic, and oxalic acid and carbon dioxide.

Organic dispersants and chelants degrade to organicacids:

– Dispersants and chelants are sometimes used in low-pressure boilers. Traditional dispersants are tannins,lignins and other natural organic derivates. Heat stablepolymers such as anionic carboxylates [5] and polyacry-late derivatives as well as chelants like ethylenediaminetetraacetic acid (EDTA) and nitrilotriacetic acid (NTA) arealso used. Degradation presumably also ends up involatile low-chain carboxylic acids.

Assessment of Degradation Products

Organic amines produce volatile acidic degradation prod-ucts, but the amine provides cations for counterbalance.

Generally, oxygen scavengers, dispersants and chelantsalso produce volatile acidic degradation products but withno cation for counterbalance. Thus, such products mustbe considered as potentially corrosive.

POSSIBLE SIDE EFFECTS IN THE STEAM/WATER CYCLE

When organic matter is entering the steam/water cycle,consideration has to be given to the possibility of detri-mental side effects.

Organic conditioning agents are applied in a controlledmanner and can address these side effects. Organic impu-rities are less predictable and harder to control.

Corrosive Degradation Products

Lowering of local pH Low pH conditions areknown to increase the risk of corrosion of most materials inthe cycle [6].

Volatile low-chain carboxylic acids, like acetic acid, canreach the whole steam/water cycle. At lower temperatures,they are less volatile, and will condense together withwater. The first condensate can have a high concentrationof such impurities [7]. Depending on the condensation ofthe conditioning agent, a high concentration of anionicimpurities may lead to low local pH. Only carbon dioxidehas a negligible influence on pH at temperatures of steamcondensation [8].

Depending on their distribution coefficient, acidic productsmay also stay to a certain degree in the boiler water andconcentrate at the site of evaporation. If the boiler waterdoes not have sufficient alkaline buffering, low pH condi-tions may also occur.

Figure 1 illustrates conditions at condensation. It is seenthat acetate concentrates with lower steam moisture, whileammonia partitions only to a minor degree into the con-densate and does not concentrate with lower moisture.With 2 µg · kg–1 acetate and 196 µg · kg–1 ammonia insteam, the early condensate at 1.1 % moisture has215 µg · kg–1 acetate but only 48 µg · kg–1 ammonia.

Specific Corrosion Mechanism Certain species,for example chloride and sulfate, are known to cause spe-cific corrosion effects other than the pH-effect. Some indi-cations have been found regarding acetate [9], but our ownresearch could not substantiate these concerns for turbinerotor steels [6].

Interference with Monitoring Cation Conductivity

Cation conductivity is the most important chemistry moni-toring parameter in the steam/water cycle. Low back-ground values permit sensitive detection of impurityingress, e.g., cooling water inleakage or polluted make-upwater. The natural background is the conductivity of purewater, 0.054 µS · cm–1 (at 25 °C). Most specifications setthe first action level at 0.20 µS · cm–1, for samples outsidethe boiler system. It is seen that there is only a small mar-gin permitted for any increase in background values.

Acidic degradation products, no matter if harmless or not,will show up by increased cation conductivity. Such anincrease in background impairs the value of the cationconductivity monitoring, increasing the risk of missingother chemistry incidents.

Influence of Boiling, Condensation

Certain species of organic matter, when in large concen-trations, can cause the boiler water to foam, leading tocarry-over of boiler water solids into the steam and in con-sequence to deposits in the superheater and in the turbine.

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Modification of the boiling process is possible when thesubstance influences surface tension. Generally, sucheffects interfere with proper boiler operation [10].

Modification of the condensation process on the otherhand can produce positive effects. In steam turbines, low-ering of surface tension at beginning condensation canimprove turbine efficiency by intensifying early nucleation[11]. Lower surface tension could also improve heat trans-fer on condenser tubes.

Fouling

A frequent problem with organic matter is fouling of ion-exchange resin, mostly in the make-up water treatmentplant, but also in condensate polishers.

Organic matter may also form precipitates, or togetherwith particles like iron oxides agglomerate to adhesivesludge. These can impair heat transfer, clog strainers andinstrument lines, and offer an environment for under-deposit corrosion.

ORGANIC MATTER AND DRUM-TYPE HRSGOPERATION

Chemistry-Related Operating Experience

The operating experience with heat recovery steam gener-ators (HRSGs) has in general been good to date with theexception of some units experiencing flow acceleratedcorrosion (FAC). FAC has been the subject of many articlesand presentations so for the purpose of this discussion itsuffices to briefly summarize the main influencing factors:

1. Water chemistry where all-volatile treatment (AVT) con-ditions result in a pH lower than 9 for extended periodsof time and/or reducing conditions due to an excessamount of oxygen scavengers.

2. Turbulence that allows the mass transport of ionicspecies by eddy diffusion.

3. The effect of temperature on metal loss parallels theeffect of temperature on solubility of iron oxide (mag-netite) in water. At low temperatures, the oxide that isformed is iron hydroxide; this shifts to magnetite at hightemperatures. These two materials have different solu-bility characteristics, accounting for a temperature peakaround 150–177 °C. Minimum and maximum tempera-ture limits for FAC have been reported for the most partin the range of 77 °C and 232 °C, respectively.

Regions within the HRSG that comprise these tempera-tures as well as higher mass transfer rates (or turbulence)and have experienced FAC are:

– Economizer tubes at high pressure (HP) and intermedi-ate pressure (IP) inlet headers

– low pressure (LP) evaporator surfaces at bends – LP drum internals– LP horizontal evaporative tube bends

Combined Cycle Chemistry Basics

AVT in combined cycles consists primarily of ammoniainjection to control pH. Chemicals such as hydrazine andother oxygen scavengers are restricted in combined cyclesif the feedwater oxygen concentration is maintained below10 µg · kg–1 by mechanical deaeration. Hydrazine orhydrazine substitutes are reducing agents that will lower

Figure 1: Concentration of acetate and ammonia in condensing steam. Measurements with an early condensate sampler[7]. Steam is condensed at different steam moistures, and the chemical composition of this early condensatemeasured. (For plant operating reasons, ammonia was not constant during this test; it can, however, beobserved that its relative distribution into the early condensate stayed constant for all moistures.)

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the oxidation reduction potential (ORP). Most of thehydrazine substitutes also have the potential to generateorganic acids. Either one of these factors can increaseFAC, but in combination, the potential is vastly increased.

AVT, or more specifically ammonia (and other amines), hastwo important characteristics that must be consideredwhen establishing the cycle chemistry program. Ammonia,which enters the LP boiler with the feedwater, controls theboiler water pH. Since some portion of the ammonia willvolatilize at the higher fluid temperature, the boiler waterpH will be slightly lower than that of the feedwater.

The other inherent characteristic of ammonia (and otheramines) is its lower ionic dissociation rate at higher tem-peratures. Consequently, the actual, local pH decreaseswith an increase in the fluid temperature as illustrated inFigure 2. This aspect of the ammonia pH/temperaturerelationship is generally masked in an operating plant sincethe pH is measured at ambient temperature conditions.These are the reasons that ammonia and similar aminesare not good buffers or considered effective neutralizingagents at higher temperatures. For example, strong alka-line buffers such sodium phosphate and sodium hydroxidedo not exhibit this relationship with temperature. The pHremains constant. Therefore, with AVT, relatively smallamounts of salts or other acid producing substances canhave a significant effect on pH in higher temperatureregions. This relationship is addressed when formulatingthe cycle water chemistry guidelines. However, operatorsand chemical service contractors must also realize thenature of AVT treatment, the behavior of treatment chemi-cals and their by-products, and that quick correctiveactions are required in the event of contamination ingress.

Corrosion by Organic Contaminants

Organic contaminants or organic-based treatment chemi-cals can thermally degrade at higher temperatures to formby-products or organic acids such as acetates or aceticacid. Figure 3 illustrates the effect of acetates on the hightemperature ammonia derived pH.

These by-products from feedwater and boiler waterorganic treatment chemicals can be found throughout thecycle (due to the volatilization and condensation process)regardless where these chemicals are injected. For exam-ple, organic dispersants that may be included with a phos-phate mixture (high buffering capacity) in the HP boilerwater can still be a source of organic by-products that canbe transported back to the LP system.

Many of the FAC incidences can be traced to theseorganic-based treatments. FAC attack of LP drum inter-nals and/or economizer inlet header tubes has occurred inseveral different combined cycle plants with the same typeof boiler water and feedwater organic chemical treatmentregime. The typical appearance of such an LP drum sepa-rator that has suffered FAC is shown in Figure 4. The HPand IP boiler water chemical treatment consisted of phos-phate compounds, caustic, and organic dispersants. Thefeedwater chemistry consisted of a mixture of organic-

based amines and anorganic-based oxygenscavenger. In theseHRSGs, the LP drumserves as a feedwatertank to the rest of the sys-tem. Therefore, the LPboiler water operates onAVT and receives no addi-tional treatment chemicalother than what is trans-ported with the feedwater.

Organic Impurities and Organic Conditioning Agents in the Steam/Water Cycle

505PowerPlant Chemistry 2006, 8(8)

Figure 2: Effect of temperature on pH, with 1.5 mg · kg–1

ammonium hydroxide, compared to pure water.

Figure 3: Effect of acetate contamination on pH (with1.5 mg · kg–1 ammonium hydroxide), comparedto pure water.

Figure 4:

FAC damage of boilerdrum internals.

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This type of boiler water/feedwater organic-based treat-ment has historically been limited to plants where indus-trial type boilers (single pressure – less than 68 bars) pro-vide steam for process applications. In these plants, theneutralizing amines are selected based on their volatility toprovide better pH control of condensing moisture inprocess piping systems in order to prevent acid attack(condensing gases such as CO2, H2S, etc.). Also, thereturn process condensate may have elevated concentra-tions of iron oxide and hence the use of dispersants in theboiler water to facilitate the blowdown of iron oxide/sus-pended matter. The saturation and superheated tempera-tures are low enough that thermal degradation of theorganic treatment chemicals is not problematic.

Conversely, in combined cycle plants, the steam isdirected to the steam turbine and nearly 100 % is con-densed and returned to the hotwell as feedwater. There isno process piping/equipment and only one feedwater pre-heater (it could be either carbon steel or stainless) associ-ated with this cycle. The amount of iron oxide generatedand transported by the feedwater is consequently very lowor certainly within the guidelines. Therefore, the basis forselecting an organic type treatment for these plants, wherethe pressure in the HP evaporator can be as high as140 bar and superheater/reheater outlet temperatures arearound 560 °C, is not clear. The outcome of applying ablend of amines (such as cyclohexylamine, morpholine,etc.), oxygen scavengers, and dispersants in the IP and HPboiler water is the generation and eventual transportationof organic acids and possibly organic chelants throughoutthe cycle. The portion that volatilizes from the boiler waterand chemicals directly transported by the attemperatorspray water can further breakdown in the superheater/reheater to produce additional organic derivatives, carbondioxide, low-chain carboxylic acids, ammonia, etc. In mostcases, carbon dioxide is not considered corrosive and inthe areas of interest, it does not appreciably affect the hightemperature pH (Figure 5). It will, however, increase the

cation conductivity, which can lead to other operationalcontrol issues. In these plants, for example, the feedwaterand LP boiler water pH – measured at 25 °C – would attimes be low (in the range of 8–9) because when therequired amount of amines for higher pH control was used,the generation of substantial amounts of CO2 would causethe cation conductivity in the steam to appreciably exceedits limit. The solution was to inject less amines, thus lowerpH, and so on.

ORGANIC MATTER AND STEAM TURBINEOPERATION

Organic Impurities

Corrosion Fatigue (CF) CF cracking was observedin the low-pressure turbine blade steeples of a 150 MWpower plant (steam data: HP: 14.9 MPa/538 °C, IP:3.3 MPa/538 °C, LP: 0.6 MPa/299 °C; drum boiler withlow-level phosphate treatment; feedwater ammonia/hydrazine for pH 9.0–9.6).

In order to clarify steam chemistry, special measurementswith an early condensate sampler (ECS) were made [12].The ECS is a device to simulate the liquid phase that formsat beginning condensation and therefore also the liquidfilm that covers the steam turbine at this location [7].Results are summarized in Table 1.

The results clearly show that acetate and formate concen-trate in the early condensate, while, due to its volatility,ammonia depletes. The result is an acidic pH condition,which is known to enhance corrosion.

Data from the period when the damage occurred show200 µg · kg–1 acetate and 50 µg · kg–1 formate in steam.Together with the concentration ratio for these species asdetermined with the ECS measurements, a pH in the earlycondensate of 4.0 was calculated.

The origin of this organic contamination was raw watercontaining relatively large amounts of organic matter(humic acids) that was poorly retained in the make-upwater plant and subsequently degraded in the boiler.

Flow Accelerated Corrosion (FAC) FAC wasobserved in several 60 MW steam turbines (steam data:5.7 MPa/525 °C, no reheat; drum boiler with low-levelphosphate treatment; feedwater ammonia/hydrazine forpH > 9.0).

One such plant has a brass-tubed condenser, with lowsalinity, high natural organics cooling water. With time, thecondenser developed cooling water leaks that were notimmediately detected due to the low salinity of the coolingwater. Considerable amounts of organic matter hadentered the steam/water cycle. At an inspection, the outletcasing of the IP turbine (carbon steel) showed severe

Figure 5: Comparison of pH for ammonia, carbondioxide and pure water.

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attack by FAC (Figure 6). This part of theturbine is at the point of beginning con-densation (0.1 MPa/98 °C). With such lowsteam moisture, such turbine casings donot show FAC under normal operatingconditions. It was concluded that organicdegradation products provided pH condi-tions that resulted in an FAC attack, whichwas not common among machines of thistype with good water chemistry.

FAC attacks that were reported from afew other plants of this type had the samecause. In these cases it was material lossup to 18 mm on the LP rotor inlet, near theblade attachment. Chemistry investiga-tions showed a cation conductivity ofcondensate of 0.2–0.7 µS · cm–1, and amix of organic acids, predominantly acetic acid, was iden-tified. Their source was degradation of organic mattercoming from the make-up water [2].

Stress Corrosion Cracking (SCC) SCC was expe-rienced on shrouds of stationary blades in a 290 MWnuclear steam turbine (steam data: HP: 6.3 MPa/380 °C,IP: 1.5 MPa/250 °C) [2].

Cracks and fracture occurred on the riveted shrouds of11 % Cr steel at IP stationary blade rows 7 to 10. In thiszone, the first condensation occurs (near 0.67 MPa/160 °C). Besides this cracking, FAC was also observed oncarbon or low-alloyed steels of the IP rotor and the LP cas-ing, as well as pitting in the related low-pressure feedwaterheater. Subsequent steam purity analysis identified a mix-ture of 97 % acetic acid, 2.2 % propionic acid, and 0.3 %butyric acid. Acetic acid concentration in steam wasmeasured to be 30 µg · kg–1, and with an early type of ECS[13] 290 µg · kg–1 in the early condensate.

Here also, the origin of this organic contamination was rawwater containing relatively large amounts of organic matter(humic acids) that was poorly retained in the make-upwater plant and subsequently degraded in the boiler.

Organic Conditioning Agents

Proprietary Amines and Organic Scavenger in a Com-bined Cycle Plant The steam/water cycle (HP6.1 MPa/485 °C, LP 2.1 MPa/168 °C) was conditioned withan undisclosed, proprietary mix of morpholine-basedamines and organic oxygen scavengers [14].

As a result, acetate concentrations of 40–80 µg · kg–1 insteam, and 400–800 µg · kg–1 in boiler water wereobserved, together with a cation conductivity in steam of0.5 µS · cm–1.

Although the plant did not experience any related dam-ages within the first operating years, this type of cyclechemistry does not permit a transparent chemistry moni-toring, and possible side effects remain at least partlyunaddressed.

Morpholine Conditioning in a PWR Power Plant Thisinteresting case study illustrates the interaction of amineconditioning and the side effect of its decomposition prod-ucts on local pH.

The original concept of water treatment in this plant waswith ammonia/hydrazine. As an additional requirement,boric acid had to be added to the steam generator water(for limited periods of time). In order to counteract theacidic effect of boric acid, morpholine was also added.However, morpholine decomposed and produced aceticacid.

Table 2 shows the measured input data as well as the cal-culated distribution into the liquid phase at beginning con-densation (blade rows 5/6, 120 °C) and at the LP turbineoutlet (37 °C). This considerable chemistry mix showed upwith a cation conductivity in condensate of only0.16 µS · cm–1 (at 25 °C).

The resulting pH values are summarized in Table 3. Item#1 represents the pH of neutral water at temperature (at25 °C, pH = 7), and item #2 standard hydrazine/ammoniachemistry. Items #3 and #4 indicate the effect of adding

Figure 6: FAC at the outlet of the IP turbine casing, nearthe zone of first condensation.

Species Unit Boiler Water Steam Early Condensate

Chloride 72 2 16

Sulfate 190 2 8

Phosphate 390 < 5 < 5

Acetate µg · kg–1 37 17 587

Formate 2 2 497

Carbonate 550 135 210

Ammonia – 1 330 317

pH (25 °C) – 9.4 5.7

pH (100 °C) – 8.1 5.7

Table 1: Results of ECS measurements. pH as calculated from analysis data.

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boric acid and morpholine. Item #5 represents the actualchemistry.

It is seen that morpholine clearly compensates the effectsof boric acid as well as of its decomposition productacetate (compare items #2 and #5).

Improvement of Turbine Efficiency We haveinvestigated the possibility of increasing steam turbine effi-ciency by adding long-chain polyamines in a large test tur-bine to enhance condensation [11]. This facility permits theexact and representative measurement of turbine effi-ciency. For practical reasons, we selected current prod-ucts from three different suppliers.

The tests showed that two of these products provided aslight significant increase in efficiency. This was, however,only under conditions of very high-end moistures and ofvery high product concentrations that are not feasible forpractical use.

This topic of course merits further consideration.

CONCLUSIONS

Power plants are designed to run with pure water andsteam. For simple cycles (no export steam) no other prod-ucts are necessary.

Combined cycle plants (no process steam applications)don't require any organic additives. If organic additives areused in plants with process steam applications, the possi-ble side effects have to be carefully addressed.

Organic amines produce volatile acidic degradation prod-ucts, but the amine provides cations for counterbalance.

Organic oxygen scavengers, dispersants, chelants as wellas organic impurities generally produce volatile acidicdegradation products but with no cation for counterbal-ance. For this reason, such products must be consideredas potentially corrosive.

From a power plant manufacturer's point of view anyorganic matter in the steam/water cycle brings the risk ofdetrimental side effects and should thus be avoided unlessnecessary, for example in certain process steam systems.

REFERENCES

[1] Organic Matter and Dissolved Carbon Dioxide in theSteam Water Circuit of Power Plant, 2002. VGBPowerTech Service GmbH, Essen, Germany, M 418Le.

[2] Bodmer, M., Combustion 1998 (March), 35.

[3] Dauvois, V., Lambert, I., Proc., BNES Conference onWater Chemistry for Nuclear Reactor Systems, 1986(Bournemouth, United Kingdom), 369.

[4] Desmoulins, D., Menet, O., CEGB Amine Workshop,1986 (Bristol, UK).

[5] The Nalco Water Handbook (Ed.: F. N. Kemmer),1988. McGraw-Hill Book Company, New York, NY,U.S.A., Second Edition.

[6] Svoboda, R., Denk, J., Maggi, C., PowerPlantChemistry 2003, 5(10), 581.

[7] Svoboda, R., Pflug, H.-D., Warnecke, T., Koebel, M.,VGB PowerTech 2004, 84(11), 74.

[8] Bursik, A., Jensen, P. J., PowerPlant Chemistry 1999,1(3), 28.

Parameter Unit Condensate LP blade LP turbine(input data) row 5/6 outlet

Ammonia 4 150 400 170

Hydrazine 40 400 380

Boric Acid (as B) µg · kg–1 230 4 600 2 300

Morpholine 4 530 2 900 12 200

Acetate 20 400 20

Table 2:

Cycle chemistry in a PWR cycle withammonia, hydrazine, boric acid,morpholine and its decompositionproduct acetate. Values measured incondensate. The values in the LPturbine are calculated, based oncondensate.

pH (at temperature) in Liquid Phase

Item # Chemistry LP blade row 5/6 LP turbine outlet (120 °C) (37 °C)

1 Pure water 5.99 6.81

2 plus ammonia, hydrazine 7.09 8.54

3 plus boric acid 6.99 7.91

4 plus morpholine 7.15 8.56

5 plus acetate 7.06 8.54

Table 3:

pH at beginning condensation(LP blade row 5/6) and at LP turbineoutlet, at temperature.

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[9] Denk, J., Svoboda, R., Proc., International Con-ference Interaction of Organics and Organic CycleTreatment Chemicals with Water, Steam, andMaterials, 2005 (Stuttgart, Germany), and PowerPlantChemistry 2006, 8(7), 401.

[10] Samuel, T., Revue Brown Boveri 1962, 49(11/12),519.

[11] Kreitmeier, F., Seipp, H.-G., Svoboda, R., ResearchProject 032 7060J, AG Turbo II/Phase 1, DE, FinalReport, 2003.

[12] Stodola, J., Svoboda, R., Proc., Steam Chemistry:Interaction of Chemical Species with Water, Steam,and Materials during Evaporation, Superheating andCondensation (Eds.: R. B. Dooley, A. Bursik), 1999(Freiburg, Germany). Electric Power ResearchInstitute, Palo Alto, CA, U.S.A., TR-114837.

[13] Svoboda, R., Bodmer, M., PowerPlant Chemistry2004, 6(11), 673.

[14] Sandmann, H., Svoboda, R., Seipp, H.-G., Hahn, F.,Proc., Conference on Organic Conditioning Agentsand Oxygen Scavengers, 1994 (Lahnstein, Germany).VGB Kraftwerkstechnik GmbH, Essen, Germany,VGB-TB 450.

Paper presented at the International ConferenceInteraction of Organics and Organic Cycle TreatmentChemicals with Water, Steam, and Materials, Stuttgart,Germany, October 4–6, 2005.

THE AUTHORS

Robert Svoboda (Ph.D., Physics, University of Vienna,Austria, postdoctoral studies on reactor metallurgy inSaclay, France) has been with the chemical laboratory ofAlstom Power, Baden, Switzerland since 1969 (formerlypart of Brown Boveri & Cie), where he headed the PowerPlant Chemistry Section, and in 1992 the Power PlantChemistry Department in Mannheim, Germany. He hassince returned to Switzerland as a technical advisor. Hiswork is concentrated on water chemistry, corrosion andradiation technology.

Frank Gabrielli (B.S. and M.S., Chemical Engineering,University of Connecticut, Storrs, CT, U.S.A.) is a technicalfellow, Corrosion and Chemical Technologies, Power PlantLaboratories, ALSTOM Power, Windsor, CT. Frank Gabrielliis responsible for corrosion and water/steam technologyfor the boiler group. He has been employed for 38 years byALSTOM Power (formerly Combustion Engineering/ABB)and has held various consulting and managerial positionsin the R&D department dealing with processes related tonuclear and fossil plants. He has published more than 30papers and was chairman of the ASME Research andTechnology Main Committee for Water and Steam inThermal Systems.

Herbert Hehs (Dipl.-Ing. (FH), Chemical Technology,Hochschule Mannheim – University of Applied Sciences,Mannheim, Germany) has been working at ALSTOMSwitzerland (formerly part of Brown Boveri & Cie) since1985, where he heads the Power Plant Chemistry Group atBaden in Switzerland. His work mainly involves chemistrysupport for the tendering, engineering and service depart-ments working on power plants. His special interests areaspects of electrochemical corrosion and chemical condi-tioning.

Hans-Günter Seipp (Dipl.-Ing. (FH), Chemical Technology)was with Alstom Power Support GmbH, Mannheim (for-merly part of Brown Boveri & Cie) from 1965 until his retire-ment in 2003, where he first headed the Water Chemistryand Corrosion Group. He has actively contributed to sev-eral working groups under VGB, DIN, etc. for more than 38years and has published more than 75 technical papers inpower plant chemistry. Since 2003, Hans-Günter Seipphas been active as a consultant in the field of power plantchemistry.

Frank-Udo Leidich (M.S., Chemical Engineering, Uni-versity of Dortmund, Dortmund, Ph.D., Technical Uni-versity Darmstadt, Darmstadt, both in Germany) has beenemployed by ALSTOM Power Generation AG (formerlyABB) since 1992. He worked from 1992 until 2002 in thepower plant chemistry department, and was responsiblefor chemical engineering of water/steam cycles and chem-ical commissioning of power plants. Frank-Udo Leidichhas been head of the power plant chemistry department ofALSTOM Power Generation AG since 2002.

Bruce Roberts (B.S. and Ph.D., Metallurgy, University ofWales, Cardiff, UK) joined the Westinghouse SteamTurbine Division, Lester, PA, U.S.A. in 1968, where hebecame the manager of the Materials Technology division.He joined the General Electric Company (GEC) UK in 1976at their Central Metallurgical Laboratories, then took a postwith Elliott Turbomachinery from 1979 to 1981 as a materi-als engineering manager. He again joined GEC in 1981,now ALSTOM. Bruce Roberts took early retirement in 2003when head of Engineering Metallurgy, and is now acting asa consultant for ALSTOM. His predominant interest overthe whole period has been the low temperature corrosionenhanced behavior of low and high alloy steels.

CONTACT

Robert SvobodaALSTOM (Schweiz) AGMaterials TGTMP.O. Box5401 BadenSwitzerland

E-mail: [email protected]