Question 15

The Correct Answer is B **Explanation for Option B (Generating tubes):** Item "F" in the illustrated D-type single furnace boiler (Illustration SG-0008, typically representing a standard industrial or marine boiler configuration) points to the main bank of tubes that line the furnace side of the boiler and connect the steam drum to the lower water drum (or header). These tubes are immersed in the boiler water and are directly exposed to the high heat flux from the furnace gases (radiant and convective heat transfer). Their primary function is to contain the water that is heated to saturation temperature and then converted into steam (a process known as generation). Therefore, these are correctly identified as **Generating tubes** (or Boiler/Evaporator tubes). **Explanation of Incorrect Options:** * **A) Superheater tubes:** Superheater tubes are positioned *after* the steam generation zone (or in a cooler gas pass) and receive saturated steam, not water. Their purpose is to raise the temperature of the steam above saturation temperature (superheat it). Item F is clearly located in the primary steam generation area, receiving water from the lower drum. * **C) Desuperheater tubes:** Desuperheaters are components used to reduce the temperature of superheated steam (usually by spraying water) and are not a type of tube bank forming the main heating surface of the boiler. * **D) Screening tubes:** Screening tubes are usually placed directly in front of the superheater tubes or across the furnace exit to protect the more vulnerable superheater tubes from excessive radiant heat, thereby "screening" them. While they generate steam, their specific structural designation and location (high heat flux zone defining the main bank) differ from the tubes labeled F, which represent the bulk **Generating tubes** of the boiler's convection pass.