What is the primary purpose of a preheater?

The primary purpose of a preheater is to recover heat from combustion products. This process improves the overall efficiency of a heating system by utilizing waste heat that would otherwise be lost to the environment. In many industrial applications, preheaters are used to warm incoming air or fluid before it enters the combustion area, ensuring that less fuel is needed to reach the desired temperatures. This heat recovery not only enhances energy efficiency but can also lead to reduced operational costs and lower emissions, as it maximizes the use of energy generated during combustion.

Considering the other options, cooling down steam is contrary to the preheater's function, as it is designed to facilitate heating rather than cooling. Increasing boiler pressure is related to the operational parameters of the boiler itself and is not a direct function of a preheater. Filtering impurities in water pertains to water treatment processes, not directly to heating or preheating functions. Each of these aspects contrasts with the heat recovery goal of a preheater, reinforcing why recovering heat from combustion products is indeed its primary purpose.