Question 41 MODE02 - Assistant MODU Engineer

The Correct Answer is C **Why Option C ("Water-tube natural-circulation steam boiler") is correct:** Soot blowers are devices designed to remove soot, ash, and slag deposits from the heat transfer surfaces (like boiler tubes) of a boiler while it is operating. These deposits significantly reduce the boiler's thermal efficiency and can lead to corrosion. Water-tube boilers, whether natural or forced circulation, are primarily used for generating large quantities of high-pressure, high-temperature steam. When used as auxiliary boilers (often meaning they are designed to burn heavy fuel oils, like Heavy Fuel Oil - HFO, or waste heat), the combustion of these fuels produces significant amounts of soot and ash, which adhere readily to the external surfaces of the water tubes (the gas-side). Therefore, water-tube boilers require regular cleaning via soot blowers (often steam or air-powered) to maintain efficiency and safety. **Why the other options are incorrect:** * **A) Electric steam boiler:** This boiler generates steam using electrical heating elements immersed in water. Since there is no combustion process, no flue gases are produced, and consequently, there is no soot or ash to accumulate on the heating surfaces. Soot blowers are unnecessary. * **B) Water-tube forced-circulation steam boiler:** While this type *is* a water-tube boiler and *does* produce soot when firing combustible fuels, it is generally **less common** as an auxiliary boiler on ships compared to the simpler and more robust natural-circulation design (often D-type or similar roof-fired designs). Both B and C require soot blowers, but C represents the typical, widely used auxiliary boiler configuration in the marine industry that necessitates this equipment. If a choice must be made among common configurations, C is the definitive example of an auxiliary boiler requiring soot blowing. (In an ideal scenario, a specific modern water-tube auxiliary boiler would definitely have them, but the classic natural-circulation boiler remains the most common type needing blowers.) * **D) Fire-tube steam boiler:** Fire-tube boilers (like Scotch or vertical composite boilers) pass the hot combustion gases *inside* the tubes, while the water surrounds them. Although these boilers do produce soot, their operating characteristics and construction (lower gas velocity, fewer tubes, simpler access for manual cleaning or less sophisticated automatic cleaning systems) often mean they utilize alternative methods or simpler devices than the sophisticated, permanently installed soot blowers typically seen on larger, higher-capacity water-tube boilers (C). While some larger fire-tube boilers may have them, soot blowers are most characteristic of the water-tube design used for high-capacity, high-soot-producing auxiliary service (C).