Boiler water treatment for steam and hot water boilers: feedwater and makeup quality, deaeration, internal chemical treatment, condensate return, chemical cleaning, and the causes of boiler failure. The overview that follows, from the AWT Boiler Subcommittee, covers boiler types and the water problems they face.
The overview below, from the AWT Boiler Subcommittee, describes the types of boiler and the water problems each faces. The articles go on to cover the treatment programs, chemistry and equipment that deal with them.
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Boilers are critical industrial and commercial equipment that convert materials used for creating BTUs (oil, natural gas, coal, wood, wasteheat or flue gasses, etc. ) and imparting those BTU's through heat exchange into water or water based fluids to produce steam or hot water or other organic fluids to increase temperatures of these fluids for various applications used for heating, cooking, sterilzation, etc. As a water treatment concern, when water or water based fluids are utilized because of the properties of water and the minerals and dissolved gases in water various problems can occur. Scale, Corrosion, Deposition and Fouling are all water based problems that impact the boiler performance and heat transfer effciency. Thus boiler systems present unique challenges that require careful management of feedwater quality, internal water chemistry, and operational parameters to ensure equipment longevity, efficiency, and safety.
Boilers are most often metal (carbon steel) pressure vessels that burn fossil fuels to create heat and the water based fluids are utilized to take the heat from the metal so the metal does not deform or melt or damage the metal container and those BTU's can now be converted into steam or hot water. Boilers are essential in:
- Industrial manufacturing – powering processes in food production, chemicals, textiles, oil and gas refining, plastics manufacturing, paper manufacturing, primary metals manufacturing, pharmaceuticals and many others.
- Commercial facilities – providing steam or hot water for heating, domestic hot water systems, humdification, sterilization, cleaning in hospitals, hotels, laundries and many others.
- Energy generation – creating steam for turbines in power plants, pumps and renewable energy systems,
- Process applications – supporting specialized operations in breweries, milk and chesse products processing, distilleries, and many many others.
Boilers are generally classified by design type:
- Firetube boilers – The flame and hot gases flow through a series of tubes immersed in water; so the water volume is much greater than the flame area. (We call this system ( Fire in the tubes thus Firetube Boilers). These units can be compact and are less efficient but great for low-to-medium pressure steam or hot water applications. Firetube boilers can either be dry-back or wet-back and how many passes the hot gases go back and forth thru the boiler to recover the maximum amount of BTU's, which decribes the design of the firetube boilers.
- Watertube boilers – The flame is in the central part of the boiler called the burner chamber or fire box and water flows through a set pattern of tubes surrounded by the hot gases. Thus Water in the tubes is called Watertube boilers). The design can be "A", "O", "D" or have other designs. These units can also have superheaters for making higher-pressure and higher temperature steam.
Steam Generators - Utilize the basic concept of the watertube design to generate steam faster. However, these boilers have much less water in them and thus water quality issues are magnified.
- Electric boilers – use resistance heating or electrodes; ideal for clean steam applications, but are also used when fossil fuels are unavailable.
- Specialty designs – including coil-tube, copper tube, bent-tube, tubeless, and modular systems optimized for specific applications, The specifics of each design and metallurgy can cause their own individual problems.
Proper water treatment is fundamental to boiler reliability and efficiency. Untreated or poorly treated water leads to:
Scaling and Deposits
- Hardness minerals (calcium and magnesium) precipitate and form scale on heat transfer surfaces
- Scale reduces heat transfer efficiency and increases fuel consumption
- Thick scale can cause localized overheating and tube failure
Corrosion
- Dissolved oxygen causes iron corrosion, leading to pitting and equipment failure
- Low pH environments accelerate corrosion of steel components
- Corrosion byproducts (iron oxide) contaminate steam quality
- CO2 driven off with steam can cause acidic steam which will degrade steam and condensate piping.
Carryover
- Dissolved minerals are carried into the steam with excessive foaming or high water levels
- Contaminants deposit on turbine blades and downstream equipment
- Reduces steam quality and damages sensitive processes such as sterilzation or other high quality steam requirements such as that required in direct steam injection applications.
Priming and Foaming
- High dissolved solids concentration or surfactants cause foam formation
- Foam can cause water to be carried over into the steam line
- Results in poor steam separation and operational instability
Water treatment for boiler systems typically involves:
-
Pretreatment of Feedwater
- Softening (ion exchange) to remove hardness
- Reverse osmosis (RO) for demineralized water in high-pressure systems
- Filtration to remove suspended solids and organic matter
- Deaeration to remove dissolved oxygen
-
Internal Chemical Treatment
- Phosphate treatment for hardness precipitation
- Alkalinity control to maintain pH in the 10-11 range
- Oxygen scavengers to protect against corrosion
- Silica control in high-pressure systems
- Chelating agents for advanced deposit prevention
-
Operational Control
- Blowdown management to control Total Dissolved Solids (TDS)
- Water level maintenance to prevent foaming and carryover
- Monitoring and testing of boiler water chemistry
- Regular equipment inspection and cleaning
Most boiler manufacturers specify target ranges for boiler feedwater and boiler water:
| Parameter |
Typical Feedwater Spec |
Typical Boiler Water Spec |
| pH |
7.5-8.5 |
10-11 |
| Total Hardness |
<1 ppm |
<5 ppm (often 0) |
| Oxygen |
<0.007 ppm |
<0.007 ppm |
| Total Alkalinity |
Variable |
200-700 ppm |
| Chlorides |
<50-200 ppm |
<200 ppm |
| Silica |
<5 ppm |
<5 ppm (high-pressure) |
| Total Dissolved Solids |
<500 ppm |
< 3,000-8,500 ppm |
| Suspended Solids |
<5 ppm |
<300 ppm |
Note: Specifications vary significantly by boiler type and operating pressure. Always consult manufacturer guidelines.
- Low-pressure systems (<15 psig) are more forgiving of water quality variations
- High-pressure systems (>300 psig) require strict water quality control to prevent scaling and stress corrosion cracking
- Ultra-high-pressure systems may require reverse osmosis or demineralized water
- Gas-fired boilers are sensitive to silica and alkalinity
- Oil-fired boilers may require additional corrosion inhibition
- Electric boilers often need very pure water to prevent deposits on heating elements
- Watertube boilers with smaller tubes are more prone to scale and require stricter pretreatment
- Tubeless designs may require treatment strategies that avoid certain deposit-forming chemicals
- Rapid circulation systems need careful blowdown management to prevent concentrating minerals
- Some boiler materials are incompatible with certain treatment chemicals
- Phosphate-based treatments work well in most systems but not in some specialty designs
- Chelant-based treatments offer superior deposit prevention but cost more
- Always verify chemical compatibility with your specific boiler model
- Process steam for food, pharmaceutical, or semiconductor applications requires very high purity
- Clean steam generators may be required for sensitive applications
- Standard boilers produce steam quality that may not meet specialized industry standards
- Know your boiler specifications – obtain and follow the manufacturer's water treatment guidelines
- Test regularly – implement a testing schedule (daily to weekly depending on system size)
- Maintain dosing accuracy – use automated chemical feed systems when possible
- Monitor TDS – perform blowdown to manage Total Dissolved Solids concentration
- Document everything – keep records of water tests, chemical additions, and maintenance
- Work with a water professional – consider partnering with a water treatment specialist for complex systems
- Plan for turnover – ensure staff understand the importance of boiler water treatment
- Boiler Manufacturer Directory – Review specifications and treatment requirements for specific boiler models
- Industrial Water Chemistry – Understanding hardness, alkalinity, pH, and other key parameters
- Chemical Treatment Systems – Overview of softeners, reverse osmosis, and other treatment equipment
- Steam Generation Quality – Best practices for producing clean steam for sensitive applications
Explore the boiler section of the AWT Knowledge Hub to learn more about specific manufacturers, treatment technologies, and operational guidance.
Source
- Credit: AWT Boiler Subcommittee