Explain the function of a de-aerator.

The function of a de-aerator is to remove oxygen and other dissolved gases from feedwater to prevent corrosion within the boiler and the entire steam system. When water contains dissolved oxygen and carbon dioxide, it can lead to significant issues such as pitting and other forms of corrosion in boiler tubes and other system components. By using a de-aerator, the feedwater is heated, which decreases the solubility of these gases, allowing them to escape. This process not only protects the integrity of the system but also enhances overall efficiency and longevity by minimizing potential damage caused by corrosion.

While the other choices address functions that may seem relevant to boiler operation, they do not accurately describe the primary role of a de-aerator. Adding chemicals relates to water treatment, cooling steam pertains to turbine operations, and increasing water temperature generally refers to the operation of a feedwater heater, but none directly align with the de-aerator's key function of removing harmful gases.