Boiler Water Treatment Technology
Boiler water is treated to control corrosion, prevent scale, and reduce deposition throughout the boiler system. ProChemTech has developed a proven line of chemical products, many USDA approved, and equipment for economically addressing these traditional concerns while reducing water and chemical use, minimizing environmental impact, and providing a safer working environment. The following is a summary of these products and equipment; please contact us for additional information.
External Scale Control
The first line of defense in a boiler system is to soften the makeup water to a residual total hardness of less than 5 mg/l. ProChemTech has developed and manufactures water softeners to provide softened makeup water for both commercial and industrial use. Standard units range in capacity from 9 gpm single resin tank units to 750 gpm dual resin tank units with custom design units up to 1,000 gpm.
Internal Chemical Treatments for Scale Control
Even with good quality softened makeup water, chemical treatment of the boiler water is required to prevent scale formation from hardness leakage through the softener and products of boiler system corrosion. ProChemTech currently provides products based on the following chemistries for preventing boiler scale.
Carbonate Cycle: Chemical precipitation of scale forming elements, mainly calcium and magnesium, in the bulk boiler water by addition of carbonate and hydroxide ion to the boiler water prevents scale formation on boiler heat transfer surfaces. A dispersant polymer is required to control deposition of the precipitated materials on heat transfer surfaces. This chemistry is recommended only for low pressure, light load boilers; units with no condensate return; and boiler systems operating with hard makeup water.
Phosphate Cycle: Again, chemical precipitation of scale forming elements in the bulk boiler water by addition of phosphate to the boiler water is utilized to prevent scale formation on boiler heat transfer surfaces. Phosphate precipitation has been found to provide much better control of scale formation than the carbonate cycle in higher pressure, high load boilers. A dispersant polymer is required to control deposition of the precipitated materials on heat transfer surfaces.
Chelant Cycle: Chelants, such as EDTA and NTA, prevent scale formation by chemically combining with the scale formers to make completely soluble compounds. The major downsides of this chemistry are that chelants are expensive, must be fed in proportion to the amount of hardness present in the makeup water, and can corrode the boiler if fed in excess.
Sequestrant Cycle: ProChemTech developed use of sequestrant chemistry as an improvement on discussed older technologies. In this chemistry phosphonates prevent scale formation by sequestering the hardness crystals as they develop in the bulk boiler water, preventing any growth beyond micron size, while a dispersant polymer prevents deposition of the micron sized precipitated materials on heat transfer surfaces. Two major advantages of sequestrant chemistry are that it is non-stoichiometric; the phosphonate needed is not proportional to the makeup hardness, unlike all other boiler scale control chemistries, and the micron size of the precipitates permit easy removal in the blowdown. All ProChemTech sequestrant products are traced with molybdate for easy and accurate product dose control.
Corrosion Control
Corrosion control in a boiler system begins with removal of as much oxygen from the makeup water as possible via preheating in a feedwater tank or deaerator. Residual oxygen is then chemically removed from the boiler water by feed of one, or more, oxygen scavengers into the boiler. ProChemTech provides oxygen scavengers based on the following chemistries.
sulfite – traditionally the lowest cost, most utilized oxygen scavenger
erythorbic acid – a higher cost product that is used when dissolved solids in the boiler water must be minimized
DEHA amine – a higher cost product that is also used when dissolved solids in the boiler water must be minimized and for prevention of oxygen corrosion in the condensate system
In addition to removing corrosion causing oxygen from the boiler water, the pH of the boiler water is also maintained between 9.0 and 11.5.
Keeping the boiler water pH within this alkaline range, along with a minimum OH alkalinity of 100 mg/l, minimizes ferrous metal corrosion. Both pH and OH alkalinity levels are maintained by either cycling the alkalinity present in the makeup water or by addition of hydroxide ion.
Steam condensate is an additional corrosion concern as carbon dioxide produced by decomposition of bicarbonate ion in the boiler condenses with the steam to produce carbonic acid, which is corrosive to ferrous and copper alloys. Two types of products are provided to address this problem, various volatile neutralizing amines, single amines and mixtures, are fed into the boiler to increase pH of condensate to 8.0 to 8.5. As noted, DEHA is also utilized as a volatile oxygen scavenger in systems where oxygen entry into the condensate system results in corrosion.
If the bicarbonate level of the makeup water is very high, use of a filming amine, which protects the condensate piping by forming a water repellant film on the metal, may be much more economical than neutralizing amines. An external treatment may also prove of interest, anion exchange replacement of the bicarbonate ion with chloride ion, in a process very similar to cation exchange water softening. ProChemTech custom designs and builds such units as needed.
Program Control
Control of boiler water cycles of concentration via automatic conductivity based blowdown and feed of the various chemical products proportional to makeup water use is very important to obtaining adequate control of scale, corrosion, and deposition in the boiler system. ProChemTech provides assembled, easy to install boiler chemistry control panels which incorporate the latest developments in instrumentation and WEB based remote monitoring and control.
Treatment Program Design
Each boiler system is unique as to its equipment, use, and makeup water; to obtain the most effective, economical treatment program each boiler system should have a program designed by a skilled professional specific to that installation. ProChemTech water treatment specialists have the experience and training to design such programs utilizing our comprehensive chemical and equipment lines.
Routine on Site Service
Once an appropriate boiler water treatment program has been designed and any needed external and chemistry control equipment is installed, we provide routine on-site service and support. This can range from a simple review of operator logs to a “hands off” full service program where our trained technicians handle all the treatment chemicals; maintain external, feed, and control equipment; and undertake all routine control testing and adjustments. This service is designed for each specific boiler installation in partnership with the customer to meet their objectives.
Corporate Support
Our account managers and service technicians are supported by an experienced corporate group that includes a Certified Water Technologist, state licensed operators, engineers, and electronic technicians. Our equipment manufacturing facility and two chemical manufacturing plants stand ready to fill any needs for standard or custom design equipment and chemical product needs.
In addition to our two field support, product development, and treatability laboratories; our business operations are fully supported by our central water and scale analysis laboratory. This laboratory is equipped with the most modern analytical equipment such as atomic absorption spectrophotometer, IR spectrometer, VIS/UV spectrophotometer, conductivity bride, pH meters, and full wet and biological laboratory capability.
Environmental
Due to increasing concerns about the substantial brine discharge from cation exchange water softeners, ProChemTech has developed chemical water softeners based upon our proven inclined plate clarifiers. These units chemically precipitate hardness ions from the makeup water and have no brine discharge.