Preventive vs. Reactive Maintenance:  Don’t Neglect Makeup Water and Condensate Return Treatment – Part 2

Brad Buecker, President, Buecker & Associates, LLC

Posted 3/26/2024


Part 1 of this series examined a common makeup water treatment method, sodium softening, for industrial steam generators.  A primary takeaway from that installment is that poor design, operation, and/or maintenance of sodium softeners can allow hardness carryover to boilers, which in turn can lead to scale formation in boiler tubes.  The article also briefly mentioned that more modern technologies, e.g., reverse osmosis (RO), can produce reliable and pure boiler water makeup.  (We will explore RO technology in greater detail in a subsequent article.)  However, even very pure makeup production can be negated by impurities in condensate return streams.  This article examines several of the most important issues in this regard.  

Condensate Return – A Potential Witches Brew of Impurities

The water/steam cycle for fossil-fired power boilers is usually straightforward.  Steam produced in the boiler 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 to the boiler.  The condensate and steam in this network typically remains very pure unless a condenser cooling water leak, or perhaps a makeup water system upset, introduces contaminants.  The situation is often quite different at co-generation and large industrial plants, where condensate is returned to the boilers from perhaps a variety of chemical processes.

Return-Condensate system
Figure 1.  Generic flow diagram of a co-generation water/steam path.  The blowdown heat exchanger and feedwater heater may not be present in some configurations.  Note the multiple condensate return lines. (1)

As a precursor to the main text below, the following case history provides a clear example of problems that can be caused by return-condensate contamination.

Case History 

A number of years ago, this author and a colleague visited an organic chemicals plant that had four 550-psig package boilers with superheaters.  The steam provided energy to multiple plant heat exchangers, with recovery of most of the condensate.  Each of the boiler superheaters failed, on average, every 1.5–2 years from internal deposition and subsequent overheating of the tubes.  Inspection of an extracted superheater tube bundle revealed deposits of approximately ⅛–¼ inches in depth.  Additional inspection revealed foam issuing from the saturated steam sample line of every boiler.  The cause of the foam formation became quickly apparent, as water/steam chemistry analyses performed by an outside vendor included data showing total organic carbon (TOC) concentrations of up to 200 mg/L in the condensate return.  Contrast that with the <0.5 mg/L feedwater TOC recommendation from Figure 1 in Part 1 of this series. (2)  No treatment processes or condensate polishing systems were in place to remove these organics (five phenol derivatives) upstream of the boilers.  Based on the TOC data alone, it became quite understandable why foam was issuing from the steam sample lines, and why the superheaters rapidly accumulated deposits and then failed from overheating.  

The frequent superheater replacements represented a reactive, not preventive, approach. Admittedly, proactive solutions would probably have been expensive.  Condensate dumping would have required installation of a much larger makeup water production system and possibly an upgrade to the plant wastewater treatment system.  Retrofit of activated carbon filters for polishing may or may not have been viable, per issues related to molecular characteristics of the impurities and reaction kinetics, but laboratory and perhaps pilot testing were definitely warranted.  Activated carbon is produced from several raw materials, including coal, coconut shells, and others.  An evaluation and perhaps even pilot testing of different activated carbons may have identified a possible polishing solution.  However, it became clear to us that management was looking for a “magic pixie dust” approach to solve the issue at very low cost.  Unfortunately, in the real world such solutions are rare.

Other Return-Condensate Impurities

While the condensate-return impurities in the above case history were all within the same chemical family, a much larger variety may exist at other facilities such as refineries and petrochemical plants.  The figure below outlines, in schematic format, typical refinery unit operations.

Figure 2.  Schematic of common refinery processes. (3)

Steam provides the energy to many of these processes; and with the wide variety of raw, intermediate and final products, the possibilities for contaminant leakage into condensate return are substantial.  Some impurities may be so nasty that the condensate cannot be reclaimed, but others can be recovered with straightforward techniques including activated carbon. (4)  

Another common condensate return difficulty comes from carbonic acid corrosion of carbon steel piping.

Return-Condensate Carbonic acid grooving of a condensate return line.
Figure 3. Carbonic acid grooving of a condensate return line. (1)

A frequent source of CO2 in condensate is carryover from the makeup system.  If only sodium softening is utilized for treatment, bicarbonate alkalinity (HCO3) will enter the boiler, where it in large measure converts to CO2 via the following reactions:

2HCO3 + heat ® CO32- + CO2­ + H2O                                           Eq. 1

CO32- + heat ® CO2­ + OH                                                              Eq. 2

The conversion of CO2 from the combined reactions may reach 90%.  CO2 flashes off with steam, and when the CO2re-dissolves in the condensate it influences the acidity of condensate return.  

CO2 + H2O ⇌ H2CO3 ⇌ H+ + HCO3                                              Eq. 3

Long-term carbon-steel corrosion as shown in Figure 3 is a frequent result.     

Compounding the problem of direct corrosion is that the corrosion products will transport to the steam generators and form porous deposits on boiler tubes and other internals.  These can cause overheating and failures.

Preventive Condensate Chemistry Control Measures

Of course, for many condensate-return contamination issues, the ideal approach is to address the root cause of the problem.  However, finding and repairing process heat exchanger leaks may be difficult due to tight or intricate configurations that make access and maintenance problematic.  The next best alternative may be condensate “polishing” of one form or another, as we noted above when discussing activated carbon.  For power industry and some co-generation applications (4), where condensate impurities are typically inorganic ions, ion exchange condensate polishing can be very beneficial.  (In fact, IX polishing is an absolute must for supercritical power units.)  Mixed-bed ion exchange, which utilizes blended cation and anion resins, will reduce to trace concentrations the various species that may be in condensate, including hardness, sodium, chloride, and sulfate.

Mechanical or chemical treatment methods may be possible for carbonic acid corrosion control.  On the makeup water treatment side, with sodium softening as the core process, common is a downstream step to remove bicarbonate alkalinity.  Figure 4 offers an illustration of one method, the forced-draft decarbonator.  

Figure 4.  Basic schematic of a forced-draft decarbonator. (1)

Possibly with the aid of a small acid feed upstream of the tower, most of the alkalinity will convert to CO2, which escapes in the tower vent with the aid of a forced-draft fan.  Caustic feed to the decarbonator effluent readjusts the pH.  This fundamental arrangement can reduce alkalinity to low part-per-million (ppm) levels.  An alternative to the forced-draft decarbonator shown above is a dealkalizer softening arrangement, where a strong base anion (SBA) unit would follow the softeners.  SBA resin, when regenerated with brine, puts the resin in the chloride cycle where it can then remove alkalinity.

As mentioned in Part 1, sodium softening (and alkalinity removal) does nothing to remove other ions including chloride, sulfate, and silica.  It may be beneficial to remove these impurities from the makeup stream, particularly if condensate return to the steam generators is of good quality.  In that respect, basic two-stage, single-pass RO is becoming more common as a softener replacement.  RO will remove 99% or greater of the total dissolved ions.  This allows the boiler cycles of concentration to be raised, resulting in reduced blowdown.  Occasionally, this author sees references that call demineralized water “hungry water,” with the seeming implication that it is equivalent to acid and will be very aggressive towards metals, and particularly carbon steel.  As has been demonstrated in the power industry, proper chemical treatment of high-purity water can make it quite stable with regard to reactivity towards metals.Within the condensate system, a well-known technique to neutralize carbonic acid is injection of an alkalizing amine or amines at strategic points within the network.  Figure 5 shows the most common alkalizing amines. 

Figure 5.  List of common alkalizing amines.

Careful evaluation of steam-generating and condensate return system design and operation is necessary to select the most appropriate amine or amine blend.  One important consideration is the presence of copper alloys in the network.  Such alloys have long been a common choice for heat exchanger tubes due to copper’s excellent heat transfer properties, but the presence of ammonia and oxygen can cause serious copper corrosion.

Steam traps are another item that often receive reactive rather than preventive maintenance.  Steam trap monitoring can be a daunting task at co-gen and industrial facilities, as a large system may contain hundreds of traps.  But without regular monitoring and repair, malfunctioning traps can reduce process efficiency, induce mechanical damage in piping systems, and potentially cause condensate contamination. (5)   


Many impurities may transport to boilers via contaminated condensate return.  Boiler tube and steam system failures are usually much more costly than preventive installation of treatment equipment and chemistry programs.  This article touched upon only some of the important condensate return issues, but will hopefully galvanize readers to focus on these critical topics. 


  1. Water Essentials Handbook (Tech. Ed.: B. Buecker). ChemTreat, Inc., Glen Allen, VA, 2023.  Currently being released in digital format at
  2. B. Buecker, “Preventative vs. Reactive Maintenance:  Don’t Neglect Makeup Water and Condensate Return Treatment – Part 1”; Maintenance World, January 2024.
  3. “Detailed Study of the Petroleum Refining Category – 2019 Report”; EPA 821-R-19-008, U.S. Environmental Protection Agency, Washington, D.C., September 2019.
  4. Buecker, B., Koom-Dadzie, A., Barbot, E., and F. Murphy, “Makeup Water Treatment and Condensate Return:  Major Influences on Chemistry Control in Co-Gen and Industrial Steam Generators”; from the 41st Annual Electric Utility Chemistry Workshop, June 6-8, 2013, Champaign, Illinois.
  5. J. LaPree, “Digital Tools Help Optimize Steam Systems”; Chemical Engineering, February 2023.


Brad Buecker

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, IL, USA) and Kansas City Power & Light Company's (now Evergy) La Cygne, KS, USA, 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 has written three books on power plant chemistry and air pollution control. He is a member of the ACS, AIChE, AIST, ASME, AWT, the Electric Utility Chemistry Workshop planning committee, and he is active with the International Water Conference and Power-Gen International.

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