In order to maintain optimum heat transfer rates in the convection section, the outside surface of the tubes and fins (or studs) should be free of soot, ash and other deposits. On line cleaning of the outside of the convection tubes is called soot blowing.
Soot blowing equipment can use either steam or air as the blowing medium. Steam is the most common. Retractable, motor driven soot blowers are more expensive but more effective than stationary, rotary soot blowers. They last longer and require less maintenance than stationary, rotary soot blowers because the lance is removed from the flue gas stream when not in use.