Question 74Steam Plants - Assistant Engineer

The correct answer is A) Superheater support tubes. Superheater support tubes can serve as downcomers at low firing rates and as generating tubes at high firing rates on some boilers. At low firing rates, the superheater support tubes help circulate the water from the steam drum to the furnace, acting as downcomers. At high firing rates, the superheater support tubes generate steam, functioning as generating tubes. The other options are incorrect because water screen tubes, water wall tubes, and riser tubes do not typically serve this dual function of downcomers and generating tubes based on firing rate. Their primary roles are different, such as protecting the furnace walls (water screen tubes) or transporting water/steam (water wall tubes and riser tubes).