In a D-type boiler with an integral superheater, what protects the superheater from overheating during initial steam formation?

In a D-type boiler with an integral superheater, the superheater protection steam (SHPS) plays a critical role in protecting the superheater from overheating during the initial steam formation phase. As the boiler begins to heat up and generate steam, there is a risk that the superheater can be exposed to high temperatures without sufficient steam flow, which can lead to overheating and potential damage.

The SHPS provides a means of ensuring that steam flows through the superheater even before the boiler reaches operational pressure. This flow of steam helps maintain a safe temperature within the superheater by absorbing some of the heat that would otherwise raise its temperature excessively. By doing so, the SHPS prevents the superheater tubes from overheating, which is vital for maintaining the integrity and operational efficiency of the entire boiler system.

The other options may involve components related to steam generation or coolant flows, but they do not serve the specific function of protecting the superheater during the initial phase of steam generation as effectively as superheater protection steam does.