At what temperature does dissolved oxygen in the boiler coil water precipitate?

Under normal conditions, the dissolved oxygen in water gradually decreases as the temperature rises; at 104 degrees, it essentially escapes. As for pressure, it depends on the specific circumstances – it differs in coiled tubes and deaerators. In a deaerator, at 104 degrees, the dissolved oxygen level is roughly 0.1–0.2 kg. In coiled tubes, there is water pressure, and it’s difficult to establish a clear relationship between temperature and pressure.

According to the law of partial pressures, in theory, as long as the temperature of the water exceeds the saturation temperature corresponding to that pressure, the gases dissolved in the water will precipitate. Therefore, it depends on what the temperature of the water in the coil is, and this is generally difficult to determine. Generally, external deaeration methods are used, such as chemical deaeration, vacuum deaeration, stripping deaeration, and thermal deaeration (atmospheric type or pressure type). The appropriate deaeration method is chosen based on the boiler’s parameters and water quality requirements; the temperature of the deaerated water varies significantly in this regard. The 104°C mentioned refers to atmospheric thermal deaerators, which operate at a pressure of 0.02 MPa (gauge pressure), with a corresponding saturated temperature of 104°C. This method is commonly used in industrial steam boilers, while power station boilers generally use pressure deaeration, resulting in a much higher temperature for the deaerated water.

According to Henry’s law and Dalton’s law, oxygen and other non-condensable gases will precipitate at the saturation temperature corresponding to a given pressure; at 1 atmosphere of pressure and 104 degrees, oxygen will precipitate. However, boiler water is usually deoxygenated to keep the oxygen concentration below 7–15 ppb, in order to prevent oxygen-induced corrosion.