By Brad Buecker, Buecker & Associates, LLC
Even though the large coal plants constructed in the last century continue to be decommissioned, many thousands of other steam-generating units provide the energy for electricity generation and process heating at combined cycle power plants, co-generation and combined heat and power (CHP) facilities, and heavy industrial plants.
Maintaining proper chemistry across a broad spectrum, from cooling water to steam generation to condensate return is extremely critical for plant reliability. Important and cutting-edge developments in this regard were the focus of discussion at the recent 41st Annual Electric Utility Chemistry Workshop (EUCW), hosted by the University of Illinois Urbana-Champaign. This article highlights some, but certainly not all, of the topics presented at this year’s event. Interested readers need to pencil in June 7-9, 2024 for the next event.
Since 2007, the workshop has offered a four-hour, pre-conference seminar that has rotated between steam generation chemistry, cooling water treatment, makeup water production and wastewater treatment. Your author has been thrilled to be a part of every one of these seminars (usually with support from expert colleagues), and was the presenter of this year’s event, which rotated back to cooling water. Many of the discussion points reflected information offered in a recent Power Engineering series (1), but several important items are worthy of review here.
- For the many plants that have cooling towers for one or more process applications, conscientious monitoring and control are critical for reliability. Often, towers sit in remote locations and may be somewhat forgotten. Chemistry upsets, and especially microbiological fouling, can occur very rapidly and cause severe problems. Cases are well known of partial cooling tower collapse due to excessive fouling and weight gain in cooling tower fill. Of course, prior to such a catastrophe, tower heat transfer would have been greatly impacted, which most likely would have already caused a significant loss in process efficiency. Numerous oxidizing and non-oxidizing biocides are available for microbiological control, and programs can often be tailored for specific plant needs.
- Corrosion and scale control programs continue to improve with chemistry that directly protects metal surfaces. These programs have also allowed many plants to reduce or eliminate phosphorus (as inorganic and organic phosphates) in cooling tower discharge, which has important environmental benefits.
- Sophisticated computer software programs are available to calculate chemical feed dosages, chemical inventories, alarm conditions, and other parameters. The systems can be configured to provide data to any location within the plant and also to outside experts for evaluation and prompt response.
Steam generation chemistry
Apart from renewables, many of the retired coal-fired power plants in the country have been replaced with combined cycle units. In general, these plants produce about 2/3 of their power from the combustion turbines and 1/3 from steam turbines supplied by heat recovery steam generators (HRSGs).
Because virtually no HRSG has copper alloys in the feedwater system, the recommended feedwater chemistry program is all-volatile treatment oxidizing (AVT(O)), with no oxygen scavenger feed. (2) This is a concept that too many combined cycle plant personnel still do not understand.
At the EUCW, a colleague from one of the most well-known utilities in the country outlined how the chemistry staff is installing supplemental feedwater and economizer oxygen injection systems to reduce flow-accelerated corrosion (FAC) in existing HRSGs. FAC is an extremely serious phenomenon that since 1986 has been responsible for a number of accidents, several with fatalities, at power plants around the country. The many tight-radius elbows in the low-pressure sections of HRSGs can be particularly susceptible to this attack.
Another excellent paper highlighted the fundamental metallurgical aspects of important HRSG corrosion mechanisms, including FAC, thermal fatigue, and water-side deposit-related failures. Most power units now cycle up and down in load regularly because they follow renewable energy load swings. Load fluctuations and on/off operation induce thermal and mechanical cycling stresses in steam generator components. Also, cycling can generate iron oxide corrosion products that transport to and from deposits in the HRSG evaporators, i.e., boilers. These build-ups then serve as potential sites for under-deposit corrosion (UDC).
A well-known mechanism that afflicts many HRSGs is hydrogen damage. Operation outside of recommended chemistry limits allows impurities to enter the HRSG and concentrate under deposits, causing the corrosion. Hydrogen damage is very insidious and difficult to detect. Tubes may continue to fail causing frequent outages.
A topic of several papers at this year’s workshop is the continued growth of film-forming products (FFP) for protection of steam generator internals. These products, both film-forming amines (FFA) and non-amines, have been promoted for well over a decade, with stories circulating of both successful and unsuccessful applications.
Successful applications were the theme of these papers, with data showing reduction of carbon steel corrosion during both normal operation and unit outages. A key issue is that even if a FFP trial indicates a product is effective, that is no excuse to abandon other recommended treatment methods such as maintaining an alkaline pH in feedwater and boiler water, and so forth. A previous difficulty with FFP use has been direct measurement of product residuals, but the workshop included a paper that described a new procedure for analyzing FFA concentrations.
High-purity makeup water production
In the last two to three decades of the 20th century and continuing onwards, the core technology of ion exchange (IX) for high-purity water production was mostly replaced with reverse osmosis (RO) for bulk demineralization with mixed-bed IX or continuous electrodeionization (CEDI) for RO permeate polishing. Furthermore, the membrane technologies of micro- and ultrafiltration have become common as RO pretreatment methods to remove suspended solids.
While membrane technologies are mature, lessons are still being learned to enhance performance and reliability. A technical specialist from a co-generation facility outlined steps that he and colleagues had taken to optimize performance of a RO-CEDI treatment system installed at their facility five years ago.
These steps included specifying the correct analytical instrumentation to monitor system performance, conducting tests to optimize performance of upstream media filters, ensuring that chemical feed systems operated properly from day one and establishing steady state conditions as much as possible to cushion the system from mechanical stresses. Water hammer can be very damaging to high-purity makeup equipment.
As the discussion above suggests, the EUCW offers valuable information (and networking) for not only power plant personnel but also co-gen and industrial steam generation plant employees. In that regard, the author had the good fortune of preparing a paper with co-authors from the refinery and co-generation industries that discussed dealing with condensate return and the many potential impurities that may be in those streams.
A more detailed discussion of these issues will soon appear in Power Engineering. Beyond the pre-workshop seminar on cooling water, a paper in the main session examined raw makeup water manganese removal, as this element can cause serious corrosion in steam condensers.
For the first time in several years, a paper was offered that addressed the nuclear power industry, in this case a new makeup water ion exchange resin that will also de-oxygenate water. The appearance of this paper undoubtedly was spurred by increasing interest in small modular reactors (SMRs) as a technology to reduce the carbon imprint from power production.
The next EUCW will be held June 7-9, 2024 in Champaign. Later this year, interested readers will be able to find more information at https://conferences.illinois.edu/eucw. Or, please feel free to contact me for additional details.
- B. Buecker, “Advanced cooling water treatment concepts, Parts 1-6”; Power Engineering, November 2022-February 2023.
- B. Buecker, “HRSG Steam Generation Issues: Reemphasizing the Importance of FAC Corrosion Control, Parts 1-4”; Power Engineering, September-October 2022. The series includes references for more detailed information on the subject.
Brad Buecker is president of Buecker & Associates, LLC, consulting and technical writing/marketing. Most recently he served as Senior Technical Publicist with ChemTreat, Inc. He has over four decades of experience in or supporting the power and industrial water treatment industries, much of it in steam generation chemistry, water treatment, air quality control, and results engineering positions with City Water, Light & Power (Springfield, Illinois) and Kansas City Power & Light Company’s (now Evergy) La Cygne, Kansas station. His work also included 11 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 has written three books on power plant chemistry and air pollution control. He is on the Electric Utility Chemistry Workshop planning committee. He may be reached at firstname.lastname@example.org.
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