Oxygen scavengers

Introduction

Oxygen scavengers, also known as oxygen absorbers, anti-oxygen agents, or oxygen scavengers, are used to remove oxygen in various industries. These agents react with dissolved oxygen and prevent the reduction of oxygen to hydroxide ions, thus acting as corrosion inhibitors.
The removal of dissolved oxygen from water, known as deaeration, is carried out through conventional mechanical, thermal, and chemical methods. The most common types of chemical oxygen scavengers include hydrazine, sodium sulfite, etc. When selecting a chemical anti-oxygen substance for water, factors such as pH, reaction rate, pressure, temperature, residence time, and so on are important.
Oxygen scavengers are chemical compounds used to remove oxygen from water to prevent corrosion in boilers. This corrosion occurs more rapidly, especially at high temperatures, in iron and steel. Oxygen scavengers prevent dissolved oxygen from reaching the metal surface by forming a protective layer on it. As a result, the rate of corrosion is reduced. In fact, if oxygen is not removed from the environment, the oxygen in the solution combines with iron, causing rapid oxidation, which leads to corrosion.

To prevent corrosion, oxygen removal is done in two ways:

1. Physical removal method using equipment such as a deaerator
2. Chemical removal method

Physical Removal Method:
For removing large amounts of oxygen, the physical method is usually preferred because it is more cost-effective. Although a deaerator can reduce the amount of oxygen to less than 0.5 - 1 mg/L, this amount of oxygen can still cause serious issues in steam boilers.

Chemical Removal Method:
To completely remove the remaining oxygen in the water after physical removal, the chemical removal method is used.

Classification of Oxygen Scavengers:

• Organic
• Inorganic

Types of Chemical Oxygen Scavengers:

• Sodium sulfite
• Erythorbate
• Diethylhydroxylamine (DEHA)
• Hydroquinone
• Hydrazine
• Carbohydrazide
• Methyl ethyl ketoxime (MEKO)

Sulfite compounds are inorganic antioxidants, while DEHA (diethylhydroxylamine) and carbohydrazides are organic antioxidants. The figure below shows the reaction between oxygen and three examples of oxygen scavengers, leading to their removal from the system.

Sulfite is the cheapest and most active O2 scavenger for medium and lower pressure boilers (up to 600 psig (42 bar abs)). Sodium sulfite reacts with O2 to form sodium sulfate, which causes solid formation in the boiler system. Therefore, sulfite is not suitable for high-pressure or supercritical boilers. In high-pressure boilers, diethylhydroxylamine is more commonly used.
Hydrazine does not produce corrosive gases at high pressures and temperatures.
Due to the harmful effects of hydrazine on human health and the environment, its use is not recommended.
The unique properties of DEHA, such as its volatility, dispersibility, and very low toxicity, make it a suitable oxygen scavenger.

Conclusion
Oxygen scavengers are reducing agents that effectively react with even very low levels of residual oxygen in water due to weathering. They are usually added to the storage section of the deaerator to allow time for reaction before the feed water reaches the boiler.
Low-pressure boilers sometimes do not include mechanical deaerators. In such systems, the deaerators must perform the entire task of removing dissolved oxygen. Obviously, much higher doses are required in this case.
Deaerators are divided into several categories. Deoxygenating compounds include sulfites and ascorbates (non-volatile) and hydrazines, hydroquinones, hydroxyamines, and ketoximes (volatile).

Abrizan Company proudly announces that it has been and continues to be active in the production of various types of deoxygenating agents. The company's quality products are used in the oil and gas industries as well as in the water industry.
In the oil and gas sector, deoxygenating agents for desalination units are produced.
In the water sector, the following deoxygenating agents are produced by Abrizan

Company:

• Carbohydrazide-based deoxygenating agents
• DEHA-based deoxygenating agents
• Sodium sulfite-based deoxygenating agents