Question 60 OSE02 - Assistant Engineer - OSV

The Correct Answer is C ### Explanation of Why Option C ("3") is Correct Option 3 in Illustration MO-0197 represents a **forced-circulation boiler (La Mont type or similar)**. In a forced-circulation boiler, a pump (represented generally by the presence of a circulating system) is used to actively push or force the water/steam mixture through the tubes. This design allows for higher operating pressures, faster starting times, and typically smaller water drum sizes compared to natural circulation types (like those represented by figures 1 and 2, which rely primarily on density differences for flow). Forced circulation is characteristic of modern, high-pressure steam generators, commonly used in specialized applications like certain types of oil spill response vessels where high efficiency and rapid response are critical. ### Explanation of Why the Other Options are Incorrect * **Option A (1):** Figure 1 typically represents a **fire-tube boiler** (like a Scotch marine boiler). In this design, hot combustion gases pass through tubes surrounded by water. This is a natural circulation type and is distinct from the high-pressure forced-circulation water-tube design. * **Option B (2):** Figure 2 typically represents a **natural-circulation water-tube boiler** (like a conventional D-type or A-type marine boiler). In this type, water flows through tubes, and circulation is achieved naturally due to density differences between the heated water/steam mixture in the risers and the cooler water in the downcomers. It does not rely on a dedicated pump to force the flow. * **Option D (4):** Figure 4 typically represents a **once-through steam generator** (like a Benson or Sulzer monotube boiler). While this type is also forced-circulation, it completely lacks a steam drum or circulating pump (the entire feedwater flow is converted to superheated steam in one pass). Although it shares the "forced" characteristic, Figure 3 is the standard diagrammatic representation of a forced-circulation *boiler* (drum-type) where a dedicated pump actively moves water around the circuit, which is often the specific forced-circulation design referred to in comparative illustrations.