The 2024 Electric Utility Chemistry Workshop: Providing valuable information for many industries
O&M

The 2024 Electric Utility Chemistry Workshop: Providing valuable information for many industries

By Brad Buecker, Buecker & Associates, LLC and EUCW Planning Committee member

The Electric Utility Chemistry Workshop was organized in the early 1980s as a conference to provide solid, practical information about steam generation chemistry, makeup water and cooling water treatment, air emissions control, environmental regulations and other topics to power plant personnel in the Great Lakes region.

Direct utility participation and abundant networking opportunities were key features of the EUCW. These benefits attracted personnel from other parts of the country, and now, as the workshop emerges from the disruption of the pandemic, we are seeing more national and international participation, including this year from Power Engineering’s/POWERGEN International’s Kevin Clark. A heretofore somewhat overlooked benefit of this conference is its potential value for those employed at cogeneration and large industrial plants, as water/steam treatment issues cut across many industries.

The following discussion highlights several important topics from this year’s event. The positive response to the diversity of topics has the committee considering a rename of the conference to the Electric Utility and Cogeneration Chemistry Workshop (EUC2W).

Cooling water

Virtually all large industrial plants have multiple cooling water systems. While some large heat exchangers such as power plant steam surface condensers may be on once-through cooling, many cooling systems are of the open-recirculating design that have a cooling tower as the core heat discharge process.

Figure 1. Flow schematic of a typical induced-draft cooling tower.1

A universal feature of cooling towers is that evaporation increases the dissolved and suspended solids concentration of the recirculating water, which requires a combination of blowdown and precise chemistry control to minimize scale formation and corrosion. (Sidestream filtration is a common, but not always employed method for suspended solids removal.1) Furthermore, cooling systems provide an excellent environment for microbiological fouling that can cause extreme problems.

Figure 2. Heavy microbiological fouling and silt accumulation in a heat exchanger.2

With the substantial aid of expert colleagues, this author has discussed cooling water treatment methods and program evolution numerous times during the last 15 years of the EUCW. Key points include:

• The very popular acid/chromate programs of the middle of the last century have disappeared due to concerns over the toxicity of hexavalent chromium (Cr6+).
• The primary replacement programs relied on inorganic and organic phosphates, with perhaps a small dosage of zinc, for scale and corrosion protection. However, calcium phosphate deposition became a major problem with these programs, requiring development of polymers to control this deposition. In recent years, concerns have dramatically grown about phosphate in cooling tower blowdown and its influence on receiving water bodies such as lakes and rivers. Phosphorus is a primary nutrient for algae growth in surface waters.
• The major water treatment companies have developed non-phosphorus (non-P) programs that rely on specialized organic compounds and additives to establish a direct barrier on metal surfaces to minimize corrosion. The formulations typically include advanced polymeric compounds for scale control.
• Microbiological fouling control continues to be of paramount importance. However, the higher pH (typically near or slightly above 8) of modern scale/corrosion control programs can reduce the efficacy of chlorine (usually fed as bleach) treatment. Alternative oxidizers such as chlorine dioxide and monochloramine may be more effective in these moderately alkaline environments. Periodic treatment with non-oxidizing biocides can also be beneficial. Careful evaluation is necessary for selection of the best treatment method. And, changes to a biocide feed program are not allowed without approval of the proper regulatory authorities.

Makeup water treatment

Makeup water treatment technology has evolved substantially in the last several decades. This section provides an overview of important developments, starting with a fundamental requirement for new projects and finishing with discussion directly related to co-generation and industrial applications.

Importance of comprehensive raw water analyses

One of this author’s important tasks for several years was review of proposed makeup water treatment configurations for new combined cycle power plants and other industrial facilities. Comprehensive, and ideally historical, raw water chemistry data is very important to correctly size and select treatment systems and treatment programs, but only on rare occasions did the design specs for new projects contain complete analyses. Even when a report offered comprehensive data, it was usually based on a single “snapshot” analysis. The chemistry of many supplies can change significantly over seasons and often after heavy precipitation, necessitating the need for more than a single analysis. Cases are known in which the original treatment system had to be replaced because it could not process the makeup water per improper design based on faulty or missing raw water quality data. Understandably, replacement costs were quite large.

Pretreatment system evolution

In the last century, clarification/sand filtration was a standard method for raw water suspended solids removal. Clarifiers were typically circular in shape and had a large footprint to allow the particles produced by coagulation and flocculation to settle into a sludge blanket within the outer clarifier zone. A common metric for clarifier operation is the rise rate, which is the ratio in gallons-per-minute of effluent divided by the surface area at the top of the clarifier. A reasonable rise rate for large circular clarifiers was around 1 gpm/ft2. Periodic sludge blowdown is important to maintain the blanket at a proper depth.

Detailed discussion of clarifier evolution is beyond the scope of this article, but a modern clarifier technology, which utilizes microsand ballast that is recycled to the process, is shown in Figure 3.

Figure 3. Reproduction of the Acti-Flo® process.1 Acti-Flo is a registered trademark of Veolia Water.

An immediate observation is the rectangular nature of the unit and the inclined plates (lamella style) to improve floc settling. A key feature is the use of microsand to enhance floc formation, with sand recovery and recycle in hydrocyclones. Rise rates of 25 gpm/ft2 or greater may be possible in such units, greatly reducing the footprint.

It should be noted that other similar systems have appeared. A prime example is Xylem’s CoMag® process with a ballast material of the iron oxide, magnetite (Fe3O4). This process has emerged as a treatment method for some industrial wastewaters containing heavy metals, where some metals co-precipitate with magnetite and are directly removed from solution.

Yet another twist to makeup water treatment is the increasing use of alternative sources, most notably municipal wastewater treatment plant effluent, for industrial plant makeup. These waters may require additional treatment equipment such as membrane bioreactors (MBR) or moving-bed bioreactors (MBBR) to reduce the concentrations of microbiological nutrients and food.1, 3

Advancements in high-purity water production for utility boilers

When this author began his career in the early 1980s, a very common method for high-purity makeup production for utility boilers was pretreatment by clarification/filtration followed by ion exchange (IX) for dissolved solids reduction to part-per-billion (ppb) concentrations. The typical but by no means exclusive IX arrangement was strong acid cation (SAC)-strong base anion (SBA)-mixed bed (MB). This process proved effective, but service runs were relatively short, especially with feed water having high dissolved solids concentrations. An outcome was frequent IX resin regenerations that consumed significant quantities of acid and caustic.

Within the last four decades, the membrane technology of reverse osmosis (RO) has evolved and become quite mature. RO membranes can remove 99% of dissolved solids, which made them ideal for retrofit at plants with IX units and excellent as the core demineralization process in new makeup systems. Also emerging during this time period was membrane-based micro- and ultrafiltration (MF and UF, respectively) pretreatment technology.

In many cases, these units can replace clarifiers/filters for suspended solids removal of RO feed water. (The author once initiated a project to replace an aging clarifier with MF at a former power plant, and the unit performed superbly.) Accordingly, a common makeup water configuration for modern combined cycle power plants is MF (or UF) / RO / MB polishing. Popular is an arrangement that includes mixed-bed portable units, aka “bottles,” that an outside vendor swaps out and regenerates at their facility.

Paradoxically, makeup water treatment for low pressure boilers (<600 psig) may be more troublesome than for high-pressure units, but the difficulties can be mindset- rather than technology-based. Because low-pressure boilers have reduced heat fluxes as compared to utility boilers, makeup quality requirements are more relaxed.4 Critical, however, is hardness removal to minimize the potential for scale formation. Ion exchange sodium softening, sometimes with downstream dealkalization, has been a popular technique for decades. Sodium softeners are straightforward to operate, and resin regeneration only requires simple brine solutions.

Unfortunately, way too many cases are known where plant management has focused on process chemistry and engineering to the neglect of water treatment support, both from an infrastructure and staffing perspective. Periodic softener upsets (and sometimes complete unit failure) allow hardness excursions. Figure 4 illustrates one outcome.

Figure 4. Bulges and blisters in a boiler tube from overheating due to internal deposits.1 Failure is the eventual result.

One of the first items a consultant often examines when called in to investigate boiler tube failures is softener operating history. Further information is available in references 3 and 5.

Cogeneration presents a wild card with condensate return

One other major issue exists when comparing cogeneration/industrial boiler operation to utility units. The water/steam path for fossil-fired power boilers is usually straightforward. Steam produced in the boiler and superheater/reheater drives a turbine to generate electricity. The turbine exhaust steam is condensed in a water-cooled (or perhaps air-cooled) condenser, with the condensate returning directly to the boiler. The condensate and steam typically remain pure unless a condenser cooling water leak, or, more rarely, a makeup water system upset, introduces contaminants. The situation is often quite different at co-generation and large industrial plants, where condensate may come from a variety of heat exchangers and processes. Impurities can potentially include inorganic ions, suspended solids, acids and alkalis, and organic compounds.

Figure 4. Generic flow diagram of a cogeneration water/steam network.1 The blowdown heat exchanger and feedwater heater may not be present in some configurations. Note the multiple condensate return lines, common for industrial plants.

Depending on the intermediate and final products that circulate through process heat exchangers and reaction vessels, a wide variety of compounds can potentially enter the condensate. These impurities include inorganic ions, acids and bases, suspended solids, and organics. The author once visited a chemical plant where organic contamination of the condensate return caused foaming in four, 550 psig package boilers, which in turn required frequent and costly superheater replacements.

Several possibilities may be available to minimize impurity transport from condensate to steam generators. The root cause solution is to repair heat exchanger leaks and eliminate problems at the source. This may be easier said than done given that large plants can have dozens if not hundreds of heat exchangers with complicated configurations.

Condensate polishing is a viable option in some cases. For example, ion exchange is a mature technology for removing inorganic ions from condensate (it is an absolute requirement for protecting supercritical power boilers). Activated carbon may perhaps be effective for some organic compounds, but molecular size, presence of active groups, and other factors can influence the reactivity of the organics towards carbon. Laboratory and pilot testing are often needed to determine the viability of activated carbon polishing.

Sometimes necessary (and as Figure 4 includes) are automatic dump valves that, as the name implies, dump the condensate to drain if on-line instrumentation detects contaminant ingress. Of course, condensate dumping requires increased makeup water production and it adds to the load on a plant’s wastewater treatment system.

A key takeaway from this section is that while several solutions may be available to protect boilers from condensate contamination, careful analysis and testing is necessary to determine the proper solution. But the investment can pay for itself many times over.

Conclusion

Many industries face water/steam treatment issues that are well known in the power industry. The EUCW is a place to hear presentations and participate in valuable discussions about these issues and modern technologies to address them. Because I am also actively involved with POWERGEN International, I hope to address several of these topics at PGI 2025 next January.

References

  1. Water Essentials Handbook (Tech. Ed.: B. Buecker). ChemTreat, Inc., Glen Allen, VA, 2023.  Currently being released in digital format at https://www.chemtreat.com/.
  2. R. Post, B. Buecker, and S. Shulder, “Power Plant Cooling Water Fundamentals”; pre-conference seminar for the 37th Annual Electric Utility Chemistry Workshop, June 6, 2017, Champaign, Ill.
  3. B. Buecker and E. Sylvester, “Foundational and Modern Concepts in Makeup Water Treatment”; pre-conference seminar for the 42nd Annual Electric Utility Chemistry Workshop, June 4, 2024, Champaign, Ill.
  4. Consensus on Operating Practices for the Control of Feedwater and Boiler Water Chemistry in Modern Industrial Boilers, The American Society of Mechanical Engineers, New York, NY, 2021.
  5. E. Sylvester, “Makeup Water Treatment Processes – Ignore at Your Peril”; presentation at the 42nd Annual Electric Utility Chemistry Workshop, June 4-6, 2024, Champaign, Ill.

About the Author: Brad Buecker is president of Buecker & Associates, LLC, consulting and technical writing/marketing. Most recently he served as a senior technical publicist with ChemTreat, Inc. He has many years of experience in or supporting the power industry, much of it in steam generation chemistry, water treatment, air quality control, and results engineering positions with City Water, Light & Power (Springfield, Ill.) and Kansas City Power & Light Company’s (now Evergy) La Cygne, Kan., station. His work has also included eleven years with two engineering firms, Burns & McDonnell and Kiewit, and he spent two years as acting water/wastewater supervisor at a chemical plant. Buecker has a B.S. in chemistry from Iowa State University with additional course work in fluid mechanics, energy and materials balances, and advanced inorganic chemistry. He has authored or co-authored over 250 articles for various technical trade magazines, and he has written three books on power plant chemistry and air pollution control. He is a member of the ACS, AIChE, AIST, ASME, AWT, CTI, the Electric Utility Chemistry Workshop planning committee, and he is active with the International Water Conference and POWERGEN International.