Question 54 3AE02 - Third Assistant Engineer (Alt)

The Correct Answer is D **Explanation of Option D (Correct):** The device shown in Illustration MO-0110 is typically a Flash-Type Distiller (Fresh Water Generator). This device uses evaporation to separate pure water (distillate) from seawater. The demister (sometimes called a mist eliminator) is a crucial component located after the evaporator stage. Its function is to intercept and remove fine droplets of brine (concentrated seawater) entrained in the steam/vapor before the vapor is condensed. These brine droplets contain high concentrations of dissolved salts, primarily chlorides. If the demister is improperly installed, it cannot effectively remove these brine droplets. As a result, the brine droplets will carry over with the steam into the condenser and mix with the distilled water (the product). This contamination will cause an increase in the salinity (chloride content) of the distillate, which is measured by the salinity cell located near the distillate pump. Therefore, an increase of chlorides measured at the distillate pump salinity cell will occur. **Explanation of Incorrect Options:** * **A) The temperature of the device will decrease.** Improper demister installation primarily affects product purity, not the overall thermal dynamics or operating temperature of the stages. Temperature is primarily controlled by steam input, vacuum, and seawater flow. * **B) The vacuum of the device will increase.** Vacuum is primarily maintained by the air ejector system. While excessive non-condensable gas buildup could slightly affect vacuum, demister installation issues do not typically cause the vacuum level to increase (meaning pressure would decrease). If anything, major carryover could potentially lead to operational instability, but it is not the primary consequence and doesn't directly cause a vacuum increase. * **C) Interstage leakage will cause a decrease in output.** Interstage leakage refers to brine or vapor leaking between different pressure stages of a multi-stage distiller, which indeed can decrease efficiency and output. However, demister installation problems are defined as vapor/brine carryover (which reduces purity), not structural leakage between stages.