Vacuum Oxygen Remover

Vacuum Oxygen Remover Overview and Applications:

In power plants, the feedwater for boilers and various industrial boilers, after being softened or desalinated, removes the hardness ions Ca2+ and Mg2+, but the dissolved oxygen in the water is not removed. The water without oxygen removal entering the boiler can cause severe oxygen corrosion in the boiler equipment (mainly the economizer) and the steam turbine passages, shortening the lifespan of the equipment. The oxygen corrosion in the economizer increases the iron content in the water, and the rate of oxidation iron scale formation on the water-cooled wall tubes is proportional to the iron content in the feedwater. The oxidation iron scale not only has poor thermal conductivity, causing the water-cooled wall tubes to overheat and fail due to inadequate cooling, but it also leads to under-deposit corrosion beneath the scale, accelerating the damage to the water-cooled wall tubes. This reduces the reliability of the boiler's safe operation, increases the frequency of shutdowns, and thus, it is necessary to remove oxygen from the boiler feedwater.

In the water treatment process for boiler feedwater, deoxygenation is a crucial step. Oxygen is a primary corrosive agent in both the feedwater system and the boiler. Oxygen in the feedwater must be removed quickly, as it can corrode the boiler feedwater system and components. The corrosion product, ferric oxide, can enter the boiler, settle or adhere to the boiler tube walls and heat surfaces, forming insoluble iron scale that hinders heat transfer. Moreover, corrosion can cause pitting on the inner walls of pipes, increasing the resistance coefficient. Severe pipe corrosion can even lead to pipe explosion accidents. It is stipulated by the state that steam boilers with an evaporation rate of 2 tons per hour or more and hot water boilers with a water temperature of 95℃ or higher must undergo deoxygenation. For many years, many boiler feedwater treatment professionals have been seeking an efficient and economic deoxygenation method, and vacuum deoxygenation is one of the very good options.

Vacuum Oxygen Remover Operating Principle

The principle of vacuum deoxygenation utilizes Henry's Law and Dalton's Law. According to Henry's Law, in a closed container, any gas present at the water surface has a solubility proportional to its partial pressure, and this solubility is solely dependent on the gas's own partial pressure. At a given pressure, as water temperature increases, the partial pressure of water vapor rises, while the partial pressures of air and oxygen decrease. At 100℃, the partial pressure of oxygen drops to zero, and the dissolved oxygen in the water also reaches zero. When the pressure above the water surface is less than atmospheric pressure, the solubility of oxygen can reach zero at lower water temperatures. This allows the oxygen molecules in the space above the water surface to be expelled or converted into other gases, resulting in zero oxygen partial pressure. Consequently, oxygen in the water continuously escapes, achieving the deoxygenation effect.

This deoxygenation method is typically conducted at temperatures ranging from 30℃ to 60℃. It can achieve deoxygenation at low water surface temperatures (at 60℃ or room temperature), and is suitable for steam boilers with high thermal load fluctuations and poor thermal deoxygenation effects, such as thermal boilers. Compared to thermal deoxygenation technology, it requires lower heating conditions, reduces the steam consumption in the boiler room, and can be installed at a lower level. However, this also demands a certain height difference and higher operational management requirements for key equipment like jet pumps and pressure pumps than thermal deoxygenation.