Between periodic boiler cleaning the gas surfaces of the boiler tubes should be kept as clean as practicable. To facilitate this, soot blowers, steam or air operated, are often fitted. They enable the tube surfaces to be cleaned of loose sooty deposits rapidly without shut down of the boiler.
Figure above shows a typical soot blower arrangement fitted to a Scotch type boiler.
With steam supplied to the blower and the steam supply line thoroughly drained. Rotation of the blower hand wheel causes the supply tube and nozzle to move towards the combustion chamber. Nozzle and tube are rotated as they move inwards by means of a scroll cut in the nut and a stationary pin 'A' in the body assembly that runs in the scroll. Ports in the tube communicate the steam supply line with the nozzle.
The arrangement enables rotating, fine, high pressure jets of steam to be discharged to the tube plate over a considerable area.
When not in use, the retractable nozzle of the blower is well within the housing tube and is therefore protected from overheating, which could cause burning and distortion of the nozzle.
Too frequent use of the blower should be avoided as this could cause wastage of the tube plate. It is advisable to operate the blower regularly even if the boiler tubes are clean (in this case without steam supply to the blower) to ensure the blower unit is free and in operable order.
"REED'S GENERAL ENGINEERING KNOWLEDGE FOR MARINE ENGINEERS", by Leslie Jackson and Thomas D. Morton