21. The auxiliary steam boiler on your oil platform supply vessel is equipped with soot blowers for maintaining heat transfer efficiency. On which of the following auxiliary boiler types would soot blowers most likely be fitted?

Soot blowers are primarily used on fuel-fired water-tube natural-circulation boilers to maintain heat transfer efficiency by removing soot deposits from tube banks; other boiler types, particularly electric boilers, lack the necessary combustion byproducts for soot formation and are therefore not equipped with soot blowers.