Question 58 CEL01 - Chief Engineer - Limited

The Correct Answer is C ### Explanation for why Option C (991 kg/m³) is correct: The effectiveness of centrifugation in separating water and solid contaminants from fuel oil relies heavily on the difference in density between the fuel oil and the water/impurities. Centrifugal separators are designed to separate liquids of differing specific gravities (densities). * **Maximum Density Limit:** For a standard centrifugal separator (like a purifier) to effectively separate water from the fuel, the density of the fuel oil must be significantly lower than the density of the water. Fresh water density is approximately $1000 \text{ kg/m}^3$ at $15^\circ\text{C}$. Seawater density is slightly higher (around $1025 \text{ kg/m}^3$). * **Operational Margin:** If the fuel density approaches or exceeds the density of the water, the water-in-fuel emulsion becomes too stable, or the separating bowl cannot effectively eject the water (because the water is denser than the fuel and thus moves to the outside edge, which must be clearly distinguishable from the fuel). * **Industry Standard Limit (ISO 8217):** The practical and safety limit for density at which standard marine centrifugal purifiers can operate effectively is typically set just below the density of water. The maximum allowed density for residual marine fuels (such as RMG 380 or similar grades) specified in the ISO 8217 standard is usually $991 \text{ kg/m}^3$ at $15^\circ\text{C}$. Fuels with densities above this limit cannot be adequately treated using conventional purifiers because the separation of water (which has a density close to $1000 \text{ kg/m}^3$) becomes impossible or highly inefficient. ### Explanation for why the other options are incorrect: * **A) 791 kg/m³:** This density is characteristic of very light distillate fuels, such as Marine Gas Oil (MGO). While these fuels are easily centrifuged, $791 \text{ kg/m}^3$ is far below the maximum density limit that standard residual fuel centrifuges can handle. * **B) 891 kg/m³:** This density is typical of Marine Diesel Oil (MDO) or some lighter intermediate fuels. Like option A, this density is well within the effective range of a purifier but does not represent the maximum allowed density for proper centrifugation, especially when dealing with heavier residual fuels. * **D) 1091 kg/m³:** A fuel density of $1091 \text{ kg/m}^3$ at $15^\circ\text{C}$ is significantly higher than the density of water ($1000 \text{ kg/m}^3$). If the fuel density is higher than the water density, the standard operation of the purifier fails. The water would effectively move toward the 'light' (clean oil) side of the separator disc stack instead of being effectively discharged as heavy sludge/contaminants. Such fuel cannot be treated by conventional centrifuges.