Which of the following can prevent scale formation in a boiler?

Regular blowdown is instrumental in preventing scale formation in a boiler because it helps to remove concentrated impurities and dissolved solids from the water. As water is heated in a boiler, minerals and other contaminants can precipitate and accumulate in the system, leading to scale buildup on heat transfer surfaces. By performing regular blowdowns, operators can maintain appropriate water chemistry, keeping the concentrations of these impurities in check. This process not only helps prevent scale but also enhances boiler efficiency and reliability.

In contrast, increasing water pH may not specifically address the control of scale, as scale formation can be influenced by multiple factors, including the concentration of hardness salts. Lowering water temperature can reduce the tendency of certain solids to precipitate, but it does not directly target the removal of existing impurities that can result in scale. Similarly, adding more make-up water can dilute certain concentrations but does not actively prevent or remove the scale-forming materials already present in the boiler system. Hence, regular blowdown stands out as the most effective measure for managing and preventing scale buildup within the boiler.