Priming and Foaming in Steam Boilers | Causes, Effects, and Prevention

Priming:

As the steam boiler generates steam rapidly, some water particles are carried along with the steam. The process of formation of wet steam is known as priming. Due to the carryover of water droplets in the steam, the energy efficiency of the steam is reduced. It leads to salt crystals deposition on the superheaters and turbines. Improper construction of steam boilers, sudden fluctuation in steam demand, and excessive ratings are some of the primary causes of priming. 

Minute drops entrainment is unavoidable in steam boilers. If the boiler water carryover is excessive, it results in steam-carried solids producing turbine blade deposits. The composition of the deposits is similar to the dissolved solids in the boiler water. Since priming is a major cause of the high level of boiler water carryover, it consequently leads to the failure of superheaters. Priming takes place due to the viscosity of water and its possibility of foaming. These properties depend on the alkalinity, presence of organic substances, and total dissolved solids or TDS. The level of priming is related to the design of the steam boiler and the steaming rate.

Priming leads to the deposit formation in the valves that causes overheating and corrosion in superheaters. It affects the heat transfer that results in low quality of processed product, higher level of steam consumption, and lowers the overall lifecycle of the steam boiler system. 

Causes of Priming:

• Large amount of dissolved solids like alkali sulfates and chlorides present
• Sudden boiling operation
• Inadequate amount of steam space
• Improper design of steam boiler
•  Sudden acceleration in steam-production rate

Effects of Priming:

• Reduction in boiler efficiency
• Increase in maintenance costs
• Lowers the lifespan of the machinery parts

Prevention for priming:

• Improved steam boiler design
• Introducing mechanical steam purifiers in boiler systems
• Maintaining low water levels in the boiler
• Utilization of soft water
• Reducing the amount of dissolved salts in the feedwater Ensuring chemical presence in the boiler water does not exceed the required amount
• 
  

Foaming:

Foaming is the unrelenting formation of bubbles or foam in the steam boiler that does not cease easily. It is caused due to the oily substances in water that reduce the surface tension in the boiler water. The contamination of the steam with solids in boiler water causes water carryover. The froth or bubbles formed at the surface of the boiler passes out with the steam. The phenomenon, known as foaming, is caused by a high concentration of solids present in the boiler water. It has been found that particular substances such as alkalis, fats, oils, grease, and specific types of organic matter are specifically instrumental in foaming.

In addition, the suspended solids accumulated in the surface film that surrounds the steam bubble result in a persistent deposition. It leads to resistance in the bursting of a steam bubble that builds up foam. It has been observed that finer suspended particles accumulate on a higher level in the bubble. 

Causes of Foaming:

•  High level of dissolved solids in boiler water
• Increase in water level
• Higher impurities
•  High presence of chemicals

Effects of Foaming:

• The actual height of the water column cannot be accurately estimated, which makes the maintenance of the pressure part challenging.
• The dissolved salts in the water passed by the wet steam damages the turbine blades and superheaters, resultantly reducing their efficiency
• The dissolved salts in the water may impact the other machinery parts that decrease the overall lifespan of the steam boiler.

Prevention of Foaming:

Introducing anti-foaming agents such as castor oil, tannic acid, gallic acid, etc.

 Administrating compounds like sodium aluminate for eliminating oil from the boiler water

Since 1983, Rakhoh Boilers has emerged as a trusted boiler manufacturer in Pune, delivering efficient and reliable industrial steam boilers in over 26 countries globally. We manufacture superior quality products like steam boilers, waste heat recovery boilers, thermic fluid heaters, and boiler accessories. We are renowned for our excellent after-sales services like energy audit, boiler automation, steam trap assessment, annual boiler maintenance, etc., to ensure the hassle-free efficiency and productivity of the steam boilers.

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