What mechanism rotates and blows while extending and retracting to clear soot?

The correct answer is the long retractable soot blower. This mechanism is specifically designed for cleaning applications within a boiler or furnace where soot accumulation on heat exchanger surfaces can significantly reduce efficiency and increase fuel consumption.

A long retractable soot blower works by extending into the flue gas path and rotating to dislodge soot deposits from the walls of the boiler or heat exchanger. The action of extending, rotating, and then retracting allows it to effectively clear the accumulated soot without the need to shut down the system. This is crucial in maintaining operational efficiency and ensuring that the heat transfer surfaces remain clean to operate at optimal performance levels.

In contrast, the other options serve different functions and do not specifically address the need for soot removal in a boiler setting. A steam cleaner, for example, uses high-pressure steam for cleaning but is not designed for the specific operational conditions inside a boiler. A blower fan is generally used to move air or gases and does not have the machinery required for rotating and extending. The rotating brush could remove dirt and debris, but it lacks the necessary functionality to operate in the high-temperature environment found in boilers and does not incorporate the retractable mechanism needed for the application.

Therefore, the long retractable soot blower is the most relevant and effective