Feedwater Treatment Chemicals

Benefits of treating boiler feedwater with oxygen scavengers

Treating your boiler feedwater with Veolia’s suite of oxygen scavengers goes a long way in preventing rapid failures of the feedwater system and costly downtime of steam generation equipment. The benefits of treating your boiler feedwater include:

• Controls dissolved oxygen pitting in boiler feedwater, boiler and steam condensate systems
• Extends equipment life and reliability
• Reduces maintenance costs associated with dissolved oxygen and equipment failures
• Minimizes feedwater and condensate iron and copper levels, reducing loading of scale-forming corrosion products to the boiler
• Reduces boiler system chemical treatment costs

What is a boiler feedwater treatment system?

A boiler feedwater treatment system is comprised of a mechanical deaeration step and a chemical deaeration step. Depending on its design, the mechanical deaeration can produce water with dissolved oxygen anywhere from 7 to 3000 ppb as O2. The chemical deaeration step is designed to neutralize the risk of this oxygen residual, reducing as close to zero as possible.

How does a boiler feedwater system (mechanical deaerator) work?

Mechanical deaeration relies on the tendency for gases to have reduced solubility in water at a higher temperature and for individual gases to seek equilibrium and distribute evenly in a given space. Thermal deaerators increase temperatures of the water to drive oxygen out of the water. Pressure deaerators inject steam to create a hot and oxygen-free environment, where the dissolved oxygen will want to transfer more readily. Vacuum deaerators rely only on the second principle of an oxygen-free space, without the help of higher temperatures. Each design has pros and cons and presents different levels of performance.

What are oxygen scavengers for boiler feedwater?

Oxygen scavengers are added to the boiler feedwater to remove trace oxygen, usually following a mechanical deaeration process. Various chemistries can be used as oxygen scavengers, and they will present different benefits. For low-pressure boilers (<900 psig or 62 barg), sulfite-based treatments are standard as they are fast-acting, convenient and economical. For high-pressure boilers (>900 psig or 62 barg), organic oxygen scavengers must be used to prevent sulfur contamination of the steam. In all cases, operating factors must be considered to ensure proper deoxygenation and system protection, such as pH, temperature and contact time.

What is the purpose of feeding oxygen scavengers to boiler systems?

Even following a high-performing mechanical deaeration process, trace oxygen can remain that will present a risk to the feedwater, boiler and condensate systems. Oxygen attack will most often be observed in the economizer section of the feedwater system, as oxygen corrosivity increases proportionally with temperature. An economizer leak can occur within hours of an oxygen contamination and lead to a complete shutdown of the boiler. Adequate treatment using an oxygen scavenger can prevent these costly incidents and offer peace of mind in the event of a deaerator upset.